Low-cost power distribution network PMU and working method thereof
1. The utility model provides a low-cost distribution network PMU which characterized in that: the system comprises an active Venturi bridge filter circuit, a Schmitt trigger circuit, an active single-phase full-wave rectification circuit, an RC filter circuit with a reverse check diode, a synchronous time pulse interface circuit, a serial analog-to-digital converter, a microprocessor and a communication interface circuit;
the active Venturi bridge filter circuit comprises an operational amplifier U1Diode D1、D2Input port series resistor R1Capacitor C1And the output port is connected with a resistor R in parallel2Capacitor C2DC power sources VCC, VSS, and a resistor R1One end of which is connected to the input signal uiThe other end of the diode D1Cathode of (2), diode D2Anode and capacitor C1Are connected together at one end, a diode D1Anode of (2) is connected to a positive power supply VCC, and a diode D2The cathode of the capacitor is connected with a negative power supply VSS and a capacitor C1Another terminal of (1), a capacitor C2And a resistor R2One end of is connected with an operational amplifier U1Of the inverting input terminal of the operational amplifier U1The positive phase input end of the power supply is connected to a power supply reference 0V; capacitor C2Another terminal of (1) and a resistor R2And the other end of the operational amplifier U1The output ends of the two are connected together; the voltage signal filtered by the active Venturi bridge filter circuit is uo；
The Schmitt trigger circuit comprises a comparator U2Diode D3Comparator input end resistor R3Pull-up resistor R4Balance resistance R5A feedback resistor R6Output port parallel resistor R7、R8DC power sources VCC, VSS, and a resistor R3Is connected to the filtered input signal usThe other end is connected with a comparator U2Input port low level node of (1), comparator U2The positive power supply input node and the negative power supply input node are respectively connected with the positive pole of a direct current power supply VCC and the negative pole of a direct current power supply VSS, and a resistor R4One end of the resistor R is connected with the anode of a direct current power supply VCC, and the resistor R4Another end of the resistor R is connected with a resistor R6And a diode D3Anode of (2), resistanceR6Another end of the resistor R is connected with a resistor R5And a comparator U2Input port high level node of (2), diode D3Cathode connection resistance R7、R8One terminal of (1), resistance R5、R7、R8Is connected to a reference ground, the shaped measurement signal uspSlave diode D3Resistance R7、R8The common terminal of (1);
the active single-phase full-wave rectification circuit and the RC filter circuit with the reverse check diode comprise an operational amplifier U3Diode D4、D5、D6、D7、D8Input end resistor R of circuit9And the input and output end resistor R of the operational amplifier10、R11、R12、R13The output end of the circuit is connected with a filter resistor R in parallel14Filter capacitor C3DC voltage sources VCC, VSS, and resistor R9Is connected to the filtered input signal usAnd the other end is respectively connected with a diode D4Cathode and diode D5Anode of (2), diode D4Respectively connected with an operational amplifier U3Input port low level node of (1), resistance R10One terminal of (1), diode D6Anode and diode D7Cathode of (2), diode D5Respectively connected with an operational amplifier U3Input port high level node and resistor R11One terminal of (1), an operational amplifier U3The positive power supply input node and the negative power supply input node are respectively connected with the positive pole of a direct current power supply VCC and the negative pole of a direct current power supply VSS, and a resistor R10、R11Is commonly connected to a reference ground, diode D6、D7Is connected with the resistor R at the other end12One terminal of (1), resistance R12The other ends of the two are respectively connected with an operational amplifier U3Output node and resistor R13One terminal of (1), resistance R13Another end of the diode D8Anode of (2), diode D8Cathode of (2) is connected with a capacitor C3And a resistor R14One terminal of (C), a capacitor3And a resistance R14Is connected with a reference ground, full-wave rectified measuring signal uoSlave diode D8Capacitor C3Resistance R14The common terminal of (1);
the synchronous time pulse interface circuit comprises a diode D9Optical coupler isolation element OC1Circuit input end resistor R15And a circuit output end resistor R16A DC voltage source VDD, a resistor R15One end of the time synchronizer is connected with the pulse signal output end of the time synchronizer, and the other end of the time synchronizer is connected with the diode D9Cathode and optical coupling isolator OC1Input port high level node of (2), diode D9Anode and optical coupling isolator OC1The input port low level node is connected with a reference ground and an optical coupling isolation device OC1The output port high level node is connected with the anode of a direct current voltage source VDD, and the optical coupling isolation device OC1Output port low level node connecting resistance R16One terminal of (1), resistance R16The other end of the output voltage is connected with the negative electrode of a direct current power supply VDD to output pulse voltage uoSlave optical coupling isolator OC1And a resistance R16The common terminal of (1);
the microprocessor calculates the frequency and the phase of the three-phase alternating voltage and the three-phase alternating current to be measured by adopting a signal zero-crossing detection method, wherein a square wave voltage signal containing the frequency and the phase information of the three-phase alternating voltage and the three-phase alternating current to be measured and a synchronous time signal are connected to 8 different signal capture input ends of TIM2 and TIM3 of the microprocessor STM32F 103;
the serial analog-to-digital converter carries out fixed sampling period T on 6 paths of direct-current voltage signals containing ripples and containing amplitude information of three-phase alternating-current voltage and three-phase alternating-current signals to be measuredSSampling;
the communication interface circuit converts TTL levels containing three-phase alternating-current voltage and amplitude, frequency and phase information of three-phase alternating-current signals sent by the microprocessor STM32F103 into RS485 serial port levels;
and a universal asynchronous serial transceiver is arranged in the microprocessor and is used as a universal data bus for transmitting the amplitude, frequency and phase of the measured voltage and current signals calculated by the microprocessor to a communication interface circuit.
2. The PMU for a low-cost power distribution network of claim 1, wherein: the microprocessor is of the model STM32F 103.
3. The PMU for a low-cost power distribution network of claim 1, wherein: the serial analog-to-digital converter is MAX 1300.
4. The PMU for a low-cost power distribution network of claim 1, wherein: the communication interface circuit model is MAX 1480.
5. A method for operating PMUs on a low cost power distribution network as defined in claim 1, the method comprising the steps of:
(1) filtering voltage signals output by the secondary side of a voltage transformer arranged in a power distribution network PMU and voltage signals obtained after I/V conversion of current signals output by the secondary side of a current transformer arranged in the power distribution network PMU by adopting an active Venturi bridge filter circuit, attenuating direct current components and high frequency components existing in the measured voltage signals, and reserving amplitude, frequency and phase information of fundamental frequency components in the measured voltage signals;
(2) shaping the voltage signal filtered by the active Venturi bridge filter circuit by adopting a Schmitt trigger circuit to obtain a square wave voltage signal containing the frequency and phase information of the voltage signal to be measured and the current signal;
(3) a single-phase active full-wave rectification circuit is adopted to carry out full-wave rectification on the voltage signal filtered by the active Venturi bridge filter circuit; filtering the full-wave rectified voltage signal by using an RC filter circuit with a reverse check diode to obtain a direct current voltage signal containing ripples and amplitude information of the measured voltage signal and the current signal;
(4) a synchronous time pulse interface circuit comprising a single photoelectric coupler is adopted to realize the input of a synchronous time pulse signal from a time synchronization device;
(5) connecting 6 paths of square wave voltage signals and synchronous time pulse signals containing three-phase alternating current voltage signals to be detected and frequency and phase information of the three-phase alternating current signals to a signal capturing input end of a microprocessor; the microprocessor adopts a signal edge time difference detection method to synchronously calculate the frequency and the phase of the three-phase alternating current voltage signal and the three-phase alternating current signal to be detected;
(6) sampling period fixing T is carried out on 6 paths of direct current voltage signals containing ripples and containing three-phase alternating current voltage signals to be detected and amplitude information of the three-phase alternating current signals by adopting an 8-channel and 16-bit serial analog-to-digital converter (ADC)SContinuous sampling of (2); the microprocessor calculates the average value of N sampling values of the DC voltage signal containing ripples obtained in 1 time window with the length equal to the period T of the AC signal to be measured, and the average value is calculated according to the condition that T cannot be measured by TSCorrecting the average value of the obtained N sampling values under the condition of integer division to obtain a corrected average value, and solving the amplitude of the measured alternating current signal by establishing a mathematical model of the relation between the amplitude of the measured alternating current signal and the corrected average value;
(7) and a universal asynchronous serial transceiver UART of the microprocessor and a communication interface circuit are used as a communication interface of the power distribution network PMU for carrying out data exchange with external equipment.
Background
With the massive access of distributed power sources, distributed energy storage devices And electric vehicles, the structure And dynamic characteristics of a power distribution network are deeply changed And become more complex, And effective monitoring is difficult to implement by using a conventional power distribution network SCADA (Supervisory Control And Data Acquisition).
In recent years, researchers at home and abroad and the power industry have paid high attention to PMU of a power distribution network and have conducted deep research on related technologies. However, the PMU cost of the power distribution network which is developed successfully at home and abroad is higher. Therefore, in order to meet the economic requirement of large-scale application of the PMU of the power distribution network on the medium and low voltage level of the power distribution network, research on a new low-cost PMU of the power distribution network has practical significance.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides the low-cost power distribution network PMU which is suitable for large-scale application in medium and low voltage levels of the power distribution network. The PMU of the power distribution network adopts a non-discrete Fourier transform method to realize high-precision measurement of the amplitude, the frequency and the phase of the alternating voltage signal and the alternating current signal of the power distribution network.
The object of the invention is achieved by the following technical measures.
A low-cost power distribution network PMU comprises an active Venturi bridge filter circuit, a Schmitt trigger circuit, an active single-phase full-wave rectification circuit, an RC filter circuit with a reverse check diode, a synchronous time pulse interface circuit, a serial analog-to-digital converter, a microprocessor and a communication interface circuit.
The active Venturi bridge filter circuit comprises an operational amplifier U1Diode D1、D2Input port series resistor R1Capacitor C1And the output port is connected with a resistor R in parallel2Capacitor C2DC power sources VCC, VSS, and a resistor R1One end of which is connected to the input signal uiThe other end of the diode D1Cathode of (2), diode D2Anode and capacitor C1Are connected together at one end, a diode D1Anode of (2) is connected to a positive power supply VCC, and a diode D2The cathode of the capacitor is connected with a negative power supply VSS and a capacitor C1Another terminal of (1), a capacitor C2And a resistor R2One end of is connected with an operational amplifier U1Of the inverting input terminal of the operational amplifier U1The positive phase input end of the power supply is connected to a power supply reference 0V; capacitor C2Another terminal of (1) and a resistor R2And the other end of the operational amplifier U1The output ends of the two are connected together; the voltage signal filtered by the active Venturi bridge filter circuit is uo。
The transfer function of the active Venturi bridge filter circuit is shown as the formula (1):
where ω -2 π f is the angular frequency of the voltage signal being filtered, and where f is the frequency of the voltage signal being filtered. Selection of R2＝2R1，C1＝2C2，ω0R1C1When 1, the transfer function H (j ω) of formula (1)0) 1, i.e. representing the output u of the active venturi bridge filter circuit0＝-uiThe output voltage signal is exactly in anti-phase with the input voltage signal, and f corresponds to0＝ω0The/2 pi is called the central frequency of the active Venturi bridge filter circuit. The PMU of the power distribution network selects the center frequency of the active Venturi bridge filter circuit as the rated frequency of the power distribution network, and corresponds to omega of the power distribution network with the rated frequency of 50Hz0100 pi and corresponds to a distribution network omega with a nominal frequency of 60Hz0120 pi. Since the frequency of the distribution network is not necessarily exactly equal to the nominal frequency during actual operation, when the frequency of the distribution network during actual operation deviates from the nominal frequency, the transfer function represented by equation (1) has amplitude attenuation and phase deviation of 180 °. The PMU of the power distribution network adopts a common correction method with the lowest cost, namely: when the active Venturi bridge filter circuit is designed, firstly, the center frequency is equal to the rated frequency and omega0R1C1Circuit parameter R is calculated on the premise of 11And C1(ii) a Then, within a range of +/-10% of the rated frequency, the amplitude attenuation coefficient and the offset of the phase deviation of 180 degrees of the active Venturi bridge filter circuit are calculated every time the frequency is increased or decreased by 1Hz, and the two groups of obtained parameters are stored in a nonvolatile memory of a PMU (phasor measurement Unit) of the power distribution network of the invention to be quoted by a software correction algorithm. When the frequency of the voltage signal output by the secondary side of the voltage transformer and the current transformer (the current signal output by the secondary side of the current transformer is subjected to I/V conversion) which are arranged in the synchronous phasor measurement unit is 50HZ, the amplitude and the input of the voltage signal are outputThe voltage signals have equal amplitude and 180-degree phase difference, and are further subjected to software compensation through a microprocessor, namely, the phase shift electrical angle is compensatedThereby obtaining the actual phasor of the measured voltage. The active Venturi bridge filter circuit filters out various harmonic components and direct-current components in the voltage signal to be measured, and the voltage signal input to the Schmitt trigger circuit and the active single-phase full-wave rectification circuit only contains fundamental frequency components.
The Schmitt trigger circuit comprises a comparator U2Diode D3Comparator input end resistor R3Pull-up resistor R4Balance resistance R5A feedback resistor R6Output port parallel resistor R7、R8DC power sources VCC, VSS, and a resistor R3Is connected to the filtered input signal usThe other end is connected with a comparator U2Input port low level node of (1), comparator U2The positive power supply input node and the negative power supply input node are respectively connected with the positive pole of a direct current power supply VCC and the negative pole of a direct current power supply VSS, and a resistor R4One end of the resistor R is connected with the anode of a direct current power supply VCC, and the resistor R4Another end of the resistor R is connected with a resistor R6And a diode D3Anode of (2), resistance R6Another end of the resistor R is connected with a resistor R5And a comparator U2Input port high level node of (2), diode D3Cathode connection resistance R7、R8One terminal of (1), resistance R5、R7、R8Is connected to a reference ground, the shaped measurement signal uspSlave diode D3Resistance R7、R8To the common terminal of (a).
The Schmitt trigger circuit works on the principle that when an input voltage signal u is inputsGreater than a positive threshold voltage u+Time-of-flight operational amplifier output uskFrom uskmaxJump to uskmin(ii) a When u issLess than a negative threshold voltage u-Time-of-flight operational amplifier output uskFrom uskminJump to uskm aWherein the positive threshold voltage is u+＝β·uskmax＝R5/(R5+R6)·uskmaxNegative threshold voltage of u-＝β·uskmin＝R5/(R5+R6)·uskmin. In addition, u is led through a diodeskIs intercepted when u is negativeskAt a positive level, uspAt a positive level, when uskAt negative voltage level, uspIs pulled down to a zero level, thereby forming a positive polarity square wave voltage signal having only a positive level and a zero level.
The active single-phase full-wave rectification circuit and the RC filter circuit with the reverse check diode comprise an operational amplifier U3Diode D4、D5、D6、D7、D8Input end resistor R of circuit9And the input and output end resistor R of the operational amplifier10、R11、R12、R13The output end of the circuit is connected with a filter resistor R in parallel14Filter capacitor C3DC voltage sources VCC, VSS, and resistor R9Is connected to the filtered input signal usAnd the other end is respectively connected with a diode D4Cathode and diode D5Anode of (2), diode D4Respectively connected with an operational amplifier U3Input port low level node of (1), resistance R10One terminal of (1), diode D6Anode and diode D7Cathode of (2), diode D5Respectively connected with an operational amplifier U3Input port high level node and resistor R11One terminal of (1), an operational amplifier U3The positive power supply input node and the negative power supply input node are respectively connected with the positive pole of a direct current power supply VCC and the negative pole of a direct current power supply VSS, and a resistor R10、R11Is commonly connected to a reference ground, diode D6、D7Is connected with the resistor R at the other end12One terminal of (1), resistance R12The other ends of the two are respectively connected with an operational amplifier U3Output node and resistor R13One terminal of (1), resistance R13Another end of the diode D8Anode of (2), diode D8Cathode of (2) is connected with a capacitor C3And a resistor R14One terminal of (C), a capacitor3And a resistance R14Is connected with a reference ground, full-wave rectified measuring signal uoSlave diode D8Capacitor C3Resistance R14To the common terminal of (a).
The working principle of the active single-phase full-wave rectification circuit and the RC filter circuit with the reverse check diode is that an alternating voltage signal u is inputsPositive half-wave signal pass through resistor R9Diode D5Resistance R11Forming a loop with the reference, the operational amplifier U being based on the virtual short-circuit characteristic of the operational amplifier3The high level node and the low level node of the input port are equal in voltage, and when the circuit meets R9＝R10＝R11＝R12An output voltage signal u passing through an active single-phase full-wave rectification circuitsqThrough a resistance R12Diode D7And a resistance R10Loop formed with reference ground and input AC voltage signal usPositive half-wave signal pass through resistor R9Diode D5Resistance R11Is fully equivalent to a loop formed by reference ground, and outputs a voltage signal usqWith input AC voltage signal usThe positive half-wave signals of the two-way signal are completely equal; when inputting an AC voltage signal usWhen the signal is negative half-wave signal, the diode D5Cut-off, operational amplifier U3The high level node of the input port of (1) is a reference ground potential. Based on the virtual short-circuit characteristic of the operational amplifier, U3The low level node of the input port is also the ground reference potential when the circuit meets R9＝R12While inputting an AC voltage signal usThrough a resistance R9Diode D4Diode D7Resistance R12And an output voltage signal usqThe loop formed is completely symmetrical, so that the output voltage signal u is now presentsqFor inputting an AC voltage signal usThe inverted positive half-wave signal. Diode D in active single-phase full-wave rectification circuit6As a dry-out-resistance for circuitsA parasitic diode in the diode D7When the circuit is cut off and interference signals appear in the circuit, the voltage signal u is outputsqIn the absence of D7Cut-off and the presence of a much amplified interference signal, diode D6Can ensure that the interference signal is opposite to the output voltage signal usqThe influence of (c) is minimized.
As can be seen from the above description, the input AC voltage signal usRectified into a unidirectional full-wave rectified voltage signal u by an active single-phase full-wave rectification circuitsq，usqI.e. will usThe positive half cycle of (2) is kept unchanged, and the negative half cycle is inverted to positive to obtain a full-wave voltage signal with single direction and large pulsation. If the load is only a resistive load R, the voltage signal u is outputoAlso a full-wave DC voltage signal with large pulsation, and a unidirectional full-wave rectified voltage signal usqAfter passing through the RC filter circuit with the reverse check diode, the original full-wave DC voltage waveform with large pulsation becomes smooth, the pulsation component is reduced, and the output voltage uoThe average value of (c) is improved. Diode D8Play the role of reverse non-return, so that the filter capacitor C3Only with R14A discharge loop is formed, and the condition of reverse inversion cannot occur.
The synchronous time pulse interface circuit comprises a diode D9Optical coupler isolation element OC1Circuit input end resistor R15And a circuit output end resistor R16A DC voltage source VDD, a resistor R15One end of the time synchronizer is connected with the pulse signal output end of the time synchronizer, and the other end of the time synchronizer is connected with the diode D9Cathode and optical coupling isolator OC1Input port high level node of (2), diode D9Anode and optical coupling isolator OC1The input port low level node is connected with a reference ground and an optical coupling isolation device OC1The output port high level node is connected with the anode of a direct current voltage source VDD, and the optical coupling isolation device OC1Output port low level node connecting resistance R16One terminal of (1), resistance R16The other end of the output voltage is connected with the negative electrode of a direct current power supply VDD to output pulse voltage uoSlave optical coupling isolator OC1And a resistance R16To the common terminal of (a).
The working principle of the synchronous pulse interface circuit is that the time synchronizer sends out a synchronous time signal, and the output positive level enables the optical coupling isolation device OC1The light emitting diode at the input port emits light by current, and the optical coupling isolator OC1The phototriode at the output port generates current after being illuminated, and the collector-emitter branch is conducted, so that R is16To generate a corresponding output pulse voltage uo。
The microprocessor is of the STM32F103 model, and the frequency and the phase of the three-phase alternating voltage and the three-phase alternating current to be measured are calculated by adopting a signal zero-crossing detection method. The working principle is as follows: the method comprises the steps that 6 paths of square wave voltage signals and synchronous time signals containing frequency and phase information of three-phase alternating current voltage and three-phase alternating current signals to be detected are connected to signal capture input ends of a microprocessor, each capture input end continuously detects whether a capture input signal jumps or not, when the corresponding capture input signal jumps (rising edge or falling edge), the count value of a timer corresponding to the jump moment can be automatically written into a capture register group, and the written count value can be stored according to the time sequence. The capturing modules do not need CPU intervention, and the working process is completed through corresponding sequential circuits. When the capture input end captures the signal jump, the capture module sends an interrupt request signal to the CPU, after the CPU receives the request signal, if the capture interrupt is enabled, the count value in the capture register is read through interrupt response, and if the capture interrupt is not enabled, the count value in the register is read through inquiring the request signal. At the accurate acquisition of the synchronization time signal (…, t)m-1,tm…) and square wave voltage signal (…, t)n-2,tn-1,tn,tn+1…) are then obtained, and the measured voltage, the frequency of the current signal and t are obtainedmThe phase at the moment is:
in the formula, f (t)n) Frequency of voltage, current signal to be measured, Tsp(tn) For the period of the square-wave voltage signal, θ (t)m) For the measured voltage and current signals at tmThe phase of the time of day. From the above formula, it can be seen that t is the required time difference as long as t can be accurately obtainedm-tnAnd tn-tn-1Then the frequency and phase of the measured signal can be calculated.
The serial analog-to-digital converter is MAX1300 in model, and the working principle is as follows: the method comprises the step of carrying out fixed sampling period T on 6 paths of direct-current voltage signals containing ripples and amplitude information of three-phase alternating-current voltage and three-phase alternating-current signals to be measuredSAnd (6) sampling.
The working principle of the microprocessor for solving the amplitude of the measured alternating current signal is that the microprocessor firstly carries out averaging calculation on N sampling values of a direct current voltage signal containing ripples obtained in a time window with a long period T of the measured alternating current signal, and the average value is calculated according to the condition that T can not be frequently solved by TSThe actual situation of the integer division is corrected by a correction method to the obtained average value. Specifically, the number of sampling points of a measured alternating voltage and current signal in a period T is calculated as follows:
in the formula, N is NTM is NTThe fractional part of (a). When the sampling values of the N +1 sampling points are f (0), f (1), f (2),. ·, f (N-2), f (N-1), f (N), respectively, the sampling average value U of the dc voltage signal is obtainedoavComprises the following steps:
to obtain direct currentSampled average value U of voltage signaloavThen, considering that diodes exist in an active single-phase full-wave rectification and RC filter circuit with reverse check diodes, the uncertainty of the conduction voltage drop of the diodes causes the amplitude U of the measured voltage and current signalsmWith the sampled average value U of the DC voltage signaloavNo longer conform to the theoretical expression. Therefore, the invention builds an active single-phase full-wave rectification circuit and an RC filter circuit with a reverse check diode through software to simulate, and changes an input sine wave signal usAmplitude of UmTo obtain different output DC voltage signals uoAverage value of UoavBy mean value UoavAs an argument, the input signal amplitude UmAs a dependent variable, a plot can be made about UmAnd UoavThe scatter diagram of (1) is plotted, observed and fitted with UmAnd UoavThe relationship between them yields the following expression:
Um＝1.117×Uoav+0.4686
according to the above formula, the sampling average value U of the DC voltage signal is substitutedoavThe amplitude U of the measured voltage and current signals can be calculatedm。
The microprocessor is internally provided with a universal asynchronous serial transceiver, and the working principle is that the universal asynchronous serial transceiver is used as a universal data bus to transmit the amplitude, the frequency and the phase of a measured voltage signal and a measured current signal which are calculated by the microprocessor to a communication interface circuit.
The communication interface circuit is of a MAX1480 model, and the working principle is that TTL levels containing amplitude, frequency and phase information of measured voltage and current signals sent by a microprocessor are converted into corresponding serial port communication protocol levels, so that the distance, the speed and the anti-interference capability of data transmission are increased.
The invention also provides a working method of the low-cost power distribution network PMU, which comprises the following steps:
(1) an active Venturi bridge filter circuit is adopted to filter voltage signals obtained by I/V conversion of voltage signals output by the secondary side of a built-in voltage transformer of a power distribution network PMU and current signals output by the secondary side of the built-in current transformer, so that direct current components and high frequency components possibly existing in the measured voltage signals are attenuated, and amplitude, frequency and phase information of fundamental frequency components in the measured voltage signals are kept as far as possible;
(2) shaping the voltage signal filtered by the active Venturi bridge filter circuit by adopting a Schmitt trigger circuit to obtain a square wave voltage signal containing the frequency and phase information of the voltage signal to be measured and the current signal;
(3) a single-phase active full-wave rectification circuit is adopted to carry out full-wave rectification on the voltage signal filtered by the active Venturi bridge filter circuit; filtering the full-wave rectified voltage signal by using an RC filter circuit with a reverse check diode to obtain a direct current voltage signal containing ripples and amplitude information of the measured voltage signal and the current signal;
(4) a synchronous time pulse interface circuit comprising a single photoelectric coupler is adopted to realize the input of a synchronous time pulse signal from a time synchronization device;
(5) connecting 6 paths of square wave voltage signals and synchronous time pulse signals containing three-phase alternating current voltage signals to be detected and frequency and phase information of the three-phase alternating current signals to a signal capturing input end of a microprocessor; the microprocessor adopts a signal edge time difference detection method to synchronously calculate the frequency and the phase of the three-phase alternating current voltage signal and the three-phase alternating current signal to be detected;
(6) sampling period and fixing T of 6 paths of direct current voltage signals containing ripples and containing three-phase alternating current voltage signals to be detected and amplitude information of the three-phase alternating current signals by adopting an 8-channel and 16-bit serial Analog-to-Digital Converter (ADC)SContinuous sampling of (2); the microprocessor calculates the average value of N sampling values of the DC voltage signal containing ripples obtained in 1 time window with the length equal to the period T of the AC signal to be measured, and the average value is calculated according to the condition that T cannot be measured by TSCorrecting the average value of the obtained N sampling values under the condition of integer division to obtain a corrected average value, and solving the amplitude of the measured alternating current signal by establishing a mathematical model of the relation between the amplitude of the measured alternating current signal and the corrected average value;
(7) a Universal Asynchronous Receiver/Transmitter (UART) of a microprocessor and a communication interface circuit are used as a communication interface of a power distribution network PMU for data exchange with external equipment.
By adopting the steps (1) to (7), the PMU of the power distribution network can realize high-precision synchronous measurement of three-phase alternating voltage signals and amplitudes, frequencies and phases of the three-phase alternating voltage signals of the power distribution network without adopting expensive ADC and microprocessor chips, has low manufacturing cost, and is suitable for large-scale application on the medium-voltage and low-voltage power distribution network layers.
Compared with the prior art, the invention has the following beneficial effects:
1. the synchronous phasor measurement unit can realize high-precision synchronous measurement of the amplitude, the frequency and the phase of the three-phase alternating voltage and the three-phase alternating current of the power distribution network without adopting expensive ADC and microprocessor chips, has low manufacturing cost and is suitable for large-scale deployment in the power distribution network.
2. The synchronous phasor measurement unit extracts the frequency and the phase of the phasor by using a signal zero-crossing detection method, and can still meet the requirement of high-precision measurement under the condition of frequency offset.
Drawings
Fig. 1 is a schematic diagram of the operation of a synchrophasor measurement unit according to an embodiment of the present invention.
Fig. 2 is a schematic circuit diagram of an active venturi bridge filter circuit according to an embodiment of the present invention.
Fig. 3 is an amplitude-frequency characteristic curve of the active venturi bridge filter circuit according to the embodiment of the present invention.
Fig. 4 is a phase-frequency characteristic curve of the active venturi bridge filter circuit according to the embodiment of the present invention.
Fig. 5 is a schematic circuit diagram of a schmitt trigger circuit according to an embodiment of the present invention.
Fig. 6 is a schematic circuit diagram of an active single-phase full-wave rectifier circuit and an RC filter circuit with a reverse check diode according to an embodiment of the present invention.
Fig. 7 is a circuit schematic diagram of a synchronous time pulse interface circuit according to an embodiment of the present invention.
Fig. 8 is a working schematic diagram for calculating the measured three-phase voltage, current signal frequency and phase by using a signal zero-crossing detection method according to an embodiment of the present invention.
FIG. 9 shows an input signal u of an active single-phase full-wave rectification circuit and an RC filter simulation circuit with a reverse check diode according to an embodiment of the present inventionsFull wave rectified signal uspOutput signal uoThe simulated waveform of (2).
FIG. 10 shows an active single-phase full-wave rectification and RC filter simulation circuit with reverse check diodes according to an embodiment of the present invention for different input sine wave signals usNext, a sine wave signal u is inputsAmplitude of UmAnd output a DC voltage uoAverage value of UoavThe scatter plot of (a).
FIG. 11 shows an active single-phase full-wave rectification and RC filter simulation circuit with reverse check diodes according to an embodiment of the present invention for different input sine wave signals usNext, a sine wave signal u is inputsAmplitude of UmAnd an output voltage uoAverage value of UoavFitting the graph by the least squares method.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Fig. 1 shows an operation schematic diagram of a synchronized phasor measurement unit according to an embodiment of the present invention, which is provided in an embodiment of the present invention, and aims to meet a requirement of development of a power distribution network on large-scale PMU deployment. The synchronous phasor measurement unit adopts a non-discrete Fourier transform method to realize the phasor of alternating voltage and alternating current of a power distribution network in order to achieve the aim of low costHigh precision measurement of amplitude, frequency and phase. Wherein: three-phase voltage signal u to be measuredA、uB、uCHas a common terminal of uNFrom the secondary side of a bus voltage transformer of the distribution network, u if the operating voltage of the corresponding bus is equal to the nominal voltage of the primary winding of the voltage transformerA、uB、uC、uNThe effective value of line voltage between is 100V, and the effective value of phase voltage isThree-phase measured current signal iA、iB、iCHas a common terminal of iNThey come from the secondary side of the distribution network branch current transformer, if the corresponding branch operating current is equal to the rated current of the current transformer primary winding, iA、iB、iCHas an effective value of 5A.
Firstly, an active Venturi bridge filter circuit is adopted to carry out filtering processing on a voltage signal output by the secondary side of a voltage transformer built in a power distribution network PMU and a voltage signal obtained after I/V conversion of a current signal output by the secondary side of a built-in current transformer.
Secondly, a Schmitt trigger circuit is adopted to shape the voltage signal filtered by the active Venturi bridge filter circuit so as to obtain a square wave voltage signal containing the frequency and phase information of the voltage signal to be measured and the current signal.
Thirdly, a single-phase active full-wave rectification circuit is adopted to carry out full-wave rectification on the voltage signal filtered by the active Venturi bridge filter circuit; and an RC filter circuit with a reverse check diode is adopted to filter the voltage signal after full-wave rectification so as to obtain a direct-current voltage signal containing ripples and amplitude information of the voltage signal and the current signal to be measured.
Fourthly, a synchronous time pulse interface circuit comprising a single photoelectric coupler is adopted to realize the input of the synchronous time pulse signal from the time synchronizer.
Fifthly, connecting 6 paths of square wave voltage signals and synchronous time pulse signals containing the three-phase alternating current voltage signals to be detected, the frequency and the phase information of the three-phase alternating current signals to a signal capturing input end of a microprocessor; software in the microprocessor adopts a signal edge time difference detection method to synchronously calculate the frequency and the phase of the three-phase alternating current voltage signal and the three-phase alternating current signal to be measured.
Sixthly, an 8-channel and 16-bit serial Analog-to-Digital Converter (ADC) is adopted to carry out sampling period fixing on 6 direct current voltage signals containing the three-phase alternating current voltage signal to be detected and amplitude information of the three-phase alternating current signal and containing ripples and to be TSContinuous sampling of (2); software in the microprocessor calculates the average value of N sampling values of the DC voltage signal containing ripples obtained in 1 time window with the length equal to the period T of the AC signal to be measured, and the average value is calculated according to the condition that T cannot be measured by T frequentlySIn the actual situation of the integer division, a correction method is adopted to correct the average value of the obtained N sampling values so as to obtain a corrected average value; and further solving the amplitude of the measured alternating current signal by establishing a mathematical model of the relation between the amplitude of the measured alternating current signal and the corrected average value.
And seventhly, a Universal Asynchronous Receiver/Transmitter (UART) of the microprocessor and a communication interface circuit are used as a communication interface for exchanging data with external equipment of the PMU of the power distribution network.
By adopting the technical means, the synchronous phasor measurement unit provided by the embodiment of the invention can realize high-precision synchronous measurement of the amplitude, frequency and phase of three-phase alternating current voltage and three-phase alternating current of the power distribution network without adopting expensive ADC and microprocessor chips, has low manufacturing cost and is suitable for large-scale deployment in the power distribution network.
The synchronous phasor measurement unit comprises an active Venturi bridge filter circuit, a Schmitt trigger circuit, an active single-phase full-wave rectification circuit, an RC filter circuit with a reverse check diode, a synchronous time pulse interface circuit, a serial analog-to-digital converter, a microprocessor and a communication interface circuit.
The embodiment of the invention provides a source of an active Venturi bridge filter circuitThe schematic diagram is shown in fig. 2. The working power supply of the active Venturi bridge filter circuit adopts a three-terminal direct-current power supply with symmetrical positive and negative voltages, wherein the positive power supply is VCC, the power supply reference ground is 0V, and the negative power supply is VSS. The active Venturi bridge filter circuit is characterized in that the types of components used are respectively an operational amplifier U1Is OP07, diode D1、D21N4148, the input port is connected in series with a resistor R1Has a resistance value of 31k omega and a capacitance C1The capacitance value of (1) is 0.1uf, and the output port is connected with a resistor R in parallel2Has a resistance value of 62k omega and a capacitance C2The capacitance of (1) is 0.05uf, and the direct current power supplies VCC and VSS are +12V and-12V, respectively. The connection mode of the components of the active Venturi bridge filter circuit is as follows: resistance R1One end of which is connected to the input signal uiThe other end of the diode D1Cathode of (2), diode D2Anode and capacitor C1Are connected together at one end; diode D1Anode of (2) is connected to a positive power supply VCC, and a diode D2The cathode of the anode is connected with a negative power supply VSS; capacitor C1Another terminal of (1), a capacitor C2And a resistor R2One end of is connected with an operational amplifier U1Of the inverting input terminal of the operational amplifier U1The positive phase input end of the power supply is connected to a power supply reference 0V; capacitor C2Another terminal of (1) and a resistor R2And the other end of the operational amplifier U1The output ends of the two are connected together; the voltage signal filtered by the active Venturi bridge filter circuit is uo。
The transfer function of the active Venturi bridge filter circuit is shown as follows:
according to actual parameters provided by the embodiment of the invention, the PMU of the power distribution network selects the central frequency of the active Venturi bridge filter circuit to correspond to omega of the power distribution network with the rated frequency of 50Hz0100 pi, since the frequency of the distribution network does not necessarily exactly equal the nominal frequency during actual operation, the transfer function of the above characterization is used when the frequency of the actual operation of the distribution network deviates from the nominal frequencyThere is an amplitude decay in the number, while the phase also deviates by 180 °. The PMU of the power distribution network of the embodiment of the invention adopts a common correction method with the lowest cost, and the specific embodiment is that the amplitude-frequency characteristic and the phase-frequency characteristic of an active Venturi bridge filter circuit near 50Hz can be obtained according to a transfer function, as shown in tables 1 and 2.
TABLE 1 f050Hz, active Venturi bridge filter circuit at f0Nearby amplitude-frequency characteristic
Frequency (Hz)
45.0
45.5
46.0
46.5
47.0
47.5
48.0
Gain of
0.9945
0.9956
0.9965
0.9974
0.9981
0.9987
0.9992
Frequency (Hz)
48.5
49.0
49.5
50.0
50.5
51.0
51.5
Gain of
0.9995
0.9998
0.9999
1.0000
0.9999
0.9998
0.9996
Frequency (Hz)
52.0
52.5
53.0
53.5
54.0
54.5
55.0
Gain of
0.9992
0.9988
0.9983
0.9977
0.9970
0.9963
0.9955
Active Venturi bridge filter circuit at f0The amplitude-frequency characteristic curve in the vicinity is shown in fig. 3. TABLE 2 band pass filter at f0Nearby phase frequency characteristics.
TABLE 2f050Hz, active Venturi bridge filter circuit at f0Nearby phase frequency characteristic
Active Venturi bridge filter circuit at f0The phase frequency characteristic in the vicinity is shown in fig. 4. As can be seen from tables 1 and 2 and the amplitude-frequency and phase-frequency characteristic curves, at f0In the nearby range, the gain change of the filter is always within 0.5%, the gain is nearly 1, the amplitude can not be considered for compensation, but the phase change amplitude is large, the phase shift of 45Hz and 50Hz has a difference of 6.026 degrees, the phase compensation is carried out according to the corresponding frequency, and the phase can be subjected to software compensation by adopting an interpolation method or a table look-up method, so that the high-precision measurement of the phase is ensured.
Suppose that the actual voltage phasors of the A phase, the B phase and the C phase are respectively UA∠θA、UB∠θB、UC∠θCThat is, the voltage phasors of the A phase, B phase and C phase calculated by the microprocessor are U'A∠θ'A、U'B∠θ'B、U'C∠θ'CI.e. the output signal after passing through the filter, the phase shift caused by the filter is at an electrical angle ofAnd the amplitude error is small and negligible, so the following relationship is satisfied:
UA＝U'A,UB＝U'B,UC＝U'C
it can be seen that the phase θ 'of the obtained A, B, C three-phase voltage phasor'A,θ'B,θ'CPerforming software compensation, i.e. subtracting the phase-shifted electrical angles, respectivelyThe actual phase theta of A, B, C three-phase voltage can be obtainedA,θB,θCSo as to obtain the actual A, B, C three-phase voltage phasor UA∠θA、UB∠θB、UC∠θC。
A schematic diagram of a schmitt trigger circuit provided by an embodiment of the present invention is shown in fig. 5. The Schmitt trigger circuit comprises a comparator U with the components of different types2Is LM339, diode D3Is 1N4148, the resistances of the input end resistor, the pull-up resistor, the balance resistor and the feedback resistor of the comparator are respectively R3Is 1k omega, R4Is 5.1 k.OMEGA.R5Is 1k omega, R6Is 102k omega, and the resistance values of the output port parallel resistors are respectively R7Is 5.1 k.OMEGA.R86.8k omega, and the DC power supplies VCC and VSS are + -12V, respectively. The Schmitt trigger circuit is connected in such a way that a resistor R3Is connected to the filtered input signal usThe other end is connected with a comparator U2Input port low level node of (1), comparator U2The positive power supply input node and the negative power supply input node are respectively connected with the positive pole of a direct current power supply VCC and the negative pole of a direct current power supply VSS, and a resistor R4One end of the resistor R is connected with the anode of a direct current power supply VCC, and the resistor R4Another end of the resistor R is connected with a resistor R6And a diode D3Anode of (2), resistance R6Another end of the resistor R is connected with a resistor R5And a comparator U2Input port high level node of (2), diode D3Cathode connection resistance R7、R8One terminal of (1), resistance R5、R7、R8Is connected to a reference ground, the shaped measurement signal uspSlave diode D3Resistance R7、R8To the common terminal of (a).
The Schmitt trigger circuit works on the principle that when an input voltage signal u is inputsGreater than a positive threshold voltage u+Time-of-flight operational amplifier output uskFrom uskmaxJump to uskmin(ii) a When u issLess than a negative threshold voltage u-Time-of-flight operational amplifier output uskFrom uskminJump to uskmaWherein the positive threshold voltage is u+＝β·uskmax＝R5/(R5+R6)·uskmaxThe negative threshold voltage is u- ═ beta.uskmin＝R5/(R5+R6)·uskmin. In addition, u is led through a diodeskIs intercepted when u is negativeskAt a positive level, uspAt a positive level, when uskAt negative voltage level, uspIs pulled down to a zero level, thereby forming a positive polarity square wave voltage signal having only a positive level and a zero level.
A schematic diagram of an active single-phase full-wave rectification circuit and an RC filter circuit with a reverse check diode according to an embodiment of the present invention is shown in fig. 6. The active single-phase full-wave rectification circuit and the RC filter circuit with the reverse check diode respectively have the components and the models of an operational amplifier U3Is OP07, diode D4、D5、D6、D7、D8Is 1N4007, and has a circuit input terminal resistance R9The resistance value of (1) is 10k omega, and the resistance values of the input and output end resistors of the operational amplifier are respectively R10、R11、R12Is 10k omega, R13Is 100 omega, the output end of the circuit is connected with a filter resistor R in parallel14Has a resistance value of 10k omega and a filter capacitor C3The capacitance of the capacitor is 4.7uf, and the DC voltage sources VCC and VSS are respectively +/-12V. The active single-phase full-wave rectification circuit and the RC filter circuit with the reverse check diode are connected in a way that a resistor R9Is connected to the filtered input signal usAnd the other end is respectively connected with a diode D4Cathode and diode D5Anode of (2), diode D4Respectively connected with an operational amplifier U3Input port low level node of (1), resistance R10One terminal of (1), diode D6Anode and diode D7Cathode of (2), diode D5Respectively connected with an operational amplifier U3Input port high level node and resistor R11One terminal of (1), an operational amplifier U3The positive power supply input node and the negative power supply input node are respectively connected with the positive pole of a direct current power supply VCC and the negative pole of a direct current power supply VSS, and a resistor R10、R11Is commonly connected to a reference ground, diode D6、D7Is connected with the resistor R at the other end12One terminal of (1), resistance R12The other ends of the two are respectively connected with an operational amplifier U3Output node and resistor R13One terminal of (1), resistance R13Another end of the diode D8Anode of (2), diode D8Cathode of (2) is connected with a capacitor C3And a resistor R14One terminal of (C), a capacitor3And a resistance R14Is connected with a reference ground, full-wave rectified measuring signal uoSlave diode D8Capacitor C3Resistance R14To the common terminal of (a).
The working principle of the active single-phase full-wave rectification circuit and the RC filter circuit with the reverse check diode is that an alternating voltage signal u is inputsPositive half-wave signal pass through resistor R9Diode D5Resistance R11Forming a loop with the reference, the operational amplifier U being based on the virtual short-circuit characteristic of the operational amplifier3The high level node and the low level node of the input port are equal in voltage, and when the circuit meets R9＝R10＝R11＝R12An output voltage signal u passing through an active single-phase full-wave rectification circuitsqThrough a resistance R12Diode D7And a resistance R10Loop formed with reference ground and input AC voltage signal usPositive half-wave signal pass through resistor R9Diode D5Resistance R11Is fully equivalent to a loop formed by reference ground, and outputs a voltage signal usqWith input AC voltage signal usThe positive half-wave signals of the two-way signal are completely equal; when inputting an AC voltage signal usWhen the signal is negative half-wave signal, the diode D5Cut-off, operational amplifier U3The high level node of the input port of (1) is a reference ground potential. Based on the virtual short-circuit characteristic of the operational amplifier, U3The low level node of the input port is also the ground reference potential when the circuit meets R9＝R12While inputting an AC voltage signal usThrough a resistance R9Diode D4Diode D7Resistance R12And an output voltage signal usqThe loop formed is completely symmetrical, so that the output voltage signal u is now presentsqFor inputting an AC voltage signal usThe inverted positive half-wave signal. Diode D in active single-phase full-wave rectification circuit6As circuit antijamming diode in diode D7When the circuit is cut off and interference signals appear in the circuit, the voltage signal u is outputsqIn the absence of D7Cut-off and the presence of a much amplified interference signal, diode D6Can ensure that the interference signal is opposite to the output voltage signal usqThe influence of (c) is minimized.
As can be seen from the above description, the input AC voltage signal usRectified into a unidirectional full-wave rectified voltage signal u by an active single-phase full-wave rectification circuitsq，usqI.e. will usThe positive half cycle of (2) is kept unchanged, and the negative half cycle is inverted to positive to obtain a full-wave voltage signal with single direction and large pulsation. If the load is only a resistive load R, the voltage signal u is outputoAlso a full-wave DC voltage signal with large pulsation, and a unidirectional full-wave rectified voltage signal usqAfter passing through the RC filter circuit with the reverse check diode, the original full-wave DC voltage waveform with large pulsation becomes smooth, the pulsation component is reduced, and the output voltage uoThe average value of (c) is improved. Diode D8Play the role of reverse non-return, so that the filter capacitor C3Only with R14A discharge loop is formed, and the condition of reverse inversion cannot occur.
A schematic diagram of a synchronous time pulse interface circuit provided by an embodiment of the present invention is shown in fig. 7. The synchronous time pulse interface is electrically connectedThe type of the used component is diode D9Is 1N4148, optical coupling isolation element OC1Model of TLP521-1, circuit input end resistor R15The resistance value of (3) is 510 omega, and the resistance R of the output end of the circuit16Has a resistance value of 10k omega and a dc voltage source VDD of + 5V. The synchronous pulse interface circuit is connected in a manner that a resistor R15One end of the time synchronizer is connected with the pulse signal output end of the time synchronizer, and the other end of the time synchronizer is connected with the diode D9Cathode and optical coupling isolator OC1Input port high level node of (2), diode D9Anode and optical coupling isolator OC1The input port low level node is connected with a reference ground and an optical coupling isolation device OC1The output port high level node is connected with the anode of a direct current voltage source VDD, and the optical coupling isolation device OC1Output port low level node connecting resistance R16One terminal of (1), resistance R16The other end of the output voltage is connected with the negative electrode of a direct current power supply VDD to output pulse voltage uoSlave optical coupling isolator OC1And a resistance R16To the common terminal of (a).
The working principle of the synchronous time pulse interface circuit is that the time synchronizer sends out a synchronous time signal, and the output positive level enables the optical coupling isolation device OC1The light emitting diode at the input port emits light by current, and the optical coupling isolator OC1The phototriode at the output port generates current after being illuminated, and the collector-emitter branch is conducted, so that R is16To generate a corresponding output pulse voltage uo。
The model of the component used by the microprocessor provided by the embodiment of the invention is STM32F103, and a working principle diagram for calculating the frequency and the phase of the three-phase alternating current voltage and the three-phase alternating current by using a signal zero-crossing detection method adopted by microprocessor STM32F103 software of the synchronous phasor measurement unit provided by the embodiment of the invention is shown in FIG. 8, wherein a square wave voltage signal containing information of the three-phase voltage, the frequency and the phase of the current signal to be measured and a synchronous time signal are connected into 8 different TIM2 and TIM3 signal capture input ends of the microprocessor STM32F103, and each capture input end continuously detects whether a capture input signal occurs or notAnd jumping, when the corresponding capture input signal jumps on the rising edge, the count value of the TIM timer corresponding to the jumping time can be automatically written into the capture register group, and the written count value is stored according to the time sequence. The capturing modules do not need CPU intervention, and the working process is completed through corresponding sequential circuits. When the capture input end captures the signal jump, the capture module sends an interrupt request signal to the CPU, after the CPU receives the request signal, if the capture interrupt is enabled, the count value in the capture register is read through interrupt response, and if the capture interrupt is not enabled, the count value in the register is read through inquiring the request signal. At the accurate acquisition of the synchronization time signal (…, t)m-1,tm…) and square wave voltage signal (…, t)n-2,tn-1,tn,tn+1…) are obtained, and further, the measured voltage, the frequency of the current signal and t can be obtainedmThe phase at the moment is:
in the formula, f (t)n) Frequency of voltage, current signal to be measured, Tsp(tn) For the period of the square-wave voltage signal, θ (t)m) For the measured voltage and current signals at tmThe phase of the time of day. From the above formula, it can be seen that t is the required time difference as long as t can be accurately obtainedm-tnAnd tn-tn-1Then the frequency and phase of the measured signal can be calculated.
The 8-channel and 16-bit serial analog-to-digital converter provided by the embodiment of the invention has the component model MAX1300, and the working principle of the serial analog-to-digital converter MAX1300 is that 6 paths of direct current voltage signals containing ripples and amplitude information of three-phase alternating current signals to be measured are subjected to a fixed sampling period TSAnd (6) sampling.
The working principle of the microprocessor for solving the amplitude of the measured alternating current signal by software is that the microprocessor STM32F103 firstly carries out averaging calculation on N sampling values of a direct current voltage signal containing ripples obtained in a time window with a period T of the measured alternating current signal, and the average value is calculated according to the condition that T cannot be frequently solved by TSThe actual situation of the integer division is corrected by a correction method to the obtained average value. Specifically, the number of sampling points of a measured alternating voltage and current signal in a period T is calculated as follows:
in the formula, N is NTM is NTThe fractional part of (a). When the sampling values of the N +1 sampling points are f (0), f (1), f (2),. ·, f (N-2), f (N-1), f (N), respectively, the sampling average value U of the dc voltage signal is obtainedoavComprises the following steps:
obtaining the sampling average value U of the DC voltage signaloavThen, considering that diodes exist in an active single-phase full-wave rectification and RC filter circuit with reverse check diodes, the uncertainty of the conduction voltage drop of the diodes causes the amplitude U of the measured voltage and current signalsmWith the sampled average value U of the DC voltage signaloavNo longer conform to the theoretical expression. Therefore, the invention utilizes the simulation software multisim14.0 of the board-level analog/digital circuit board to build a simulation example corresponding to the graph 6 for simulation, in the simulation example, when a sine wave signal with the amplitude of 4.5V and the frequency of power frequency is input, a sine wave signal u is inputsFull wave rectified signal uspOutput signal uoThe simulated waveform of (2) is shown in fig. 9, and is substantially consistent with theoretical analysis. Further, by varying the input sine wave signal usAmplitude of UmTo obtain different output DC voltage signals uoAverage value of UoavBy mean value UoavAs an argument, the input signal amplitude UmAs a dependent variable, the dependent variable can be plotted against U by MatlabmAnd UoavThe amplitude U is obtained by observing the scattergram (see FIG. 10)mAnd the mean value UoavThe relationship between the two is linear. Finally, the amplitude U is corrected by using a least square methodmAnd the mean value UoavThe relationship between them is fitted, and the result of the least square fitting is shown in fig. 11, which yields the following expression:
Um＝1.117×Uoav+0.4686
according to the above formula, the sampling average value U of the DC voltage signal is substitutedoavThe amplitude U of the measured voltage and current signals can be calculatedm。
The microprocessor STM32F103 provided by the embodiment of the invention is internally provided with a universal asynchronous serial transceiver, and the working principle is that the microprocessor STM32F103 is used as an internal universal data bus for transmitting the amplitude, the frequency and the phase of three-phase alternating current voltage and three-phase alternating current signals obtained by calculation to a communication interface circuit.
The communication interface circuit provided by the embodiment of the invention has the advantages that the model of the used components is that the communication interface chip is MAX1480, and the working principle of the communication interface circuit is that the communication interface chip MAX1480 converts TTL level containing three-phase alternating-current voltage, amplitude, frequency and phase information of a three-phase alternating-current signal sent by a microprocessor STM32F103 into RS485 serial level, so that the distance, the speed and the anti-interference capability of data transmission are increased.
Details not described in the present specification belong to the prior art known to those skilled in the art.
It will be understood by those skilled in the art that the foregoing is merely a preferred embodiment of the present invention, and is not intended to limit the invention, such that any modification, equivalent replacement or improvement made within the spirit and principle of the present invention shall be included within the scope of the present invention.
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