1. Instantaneous reactive power-based i_p-i_qThe harmonic current detection method is characterized in that a frequency self-adaptive filter based on the SOGI principle is embedded into a control system of the SOGI-FLL in advance to form ESOGI-FLL; converting three-phase current into two-phase current i through coordinates_p、i_qTo i, pair_p、i_qFiltering through a low-pass filter series average value to obtain a direct current component; and then replacing a phase-locked loop with an ESOGI-FLL frequency-locked loop, replacing the phase-locked loop with a frequency-locked loop, and outputting a rotating signal with the same frequency as the power grid voltage signal by a sine-cosine generator.

2. Instantaneous reactive power based i according to claim 1_p-i_qThe harmonic current detection method is characterized in that the low-pass filter adopts a second-order Butterworth filter.

3. Instantaneous reactive power based i according to claim 1_p-i_qThe harmonic current detection method is characterized in that the harmonic current detection method is applied to i_p、i_qThe specific content of the direct current component obtained by filtering the low-pass filter series average value is as follows:

the method comprises the steps of serially connecting a Low Pass Filter (LPF) with a current average filtering module to form an improved filter, using an integral delay and gain link to proxy the LPF, filtering instantaneous active current and reactive current through the current average filtering module, taking a period T as a node, and taking T/6 periods of a delay module in a current average method in the period, namely obtaining a direct current component with an alternating current component of zero and only a fundamental wave positive sequence current corresponding to the alternating current component after the T/6 periods.

4. Instantaneous reactive power based i of claim 3_p-i_qThe harmonic current detection method is characterized in that the expression of the direct current component is as follows:

in the formula I₁、Respectively, the current and the corresponding phase of the fundamental positive sequence component.

5. Instantaneous reactive power based i according to claim 1_p-i_qThe harmonic current detection method is characterized in that the phase closed-loop transfer functions of the single-phase ESOGI-FLL are respectively as follows:

in the formula, ω₀、U_gAnd theta₀Frequency, amplitude and phase, K, respectively, of the network voltage_p4Is the proportionality coefficient of the preceding stage SOGI, K_p3And K_i3Proportional and integral coefficients, ω, of the subsequent SOGI-FLL stage_gIs the input signal of the SOGI.

Background

A large number of power electronic devices are connected into a power grid, so that the problem of harmonic pollution needs to be considered, and electrical equipment is damaged or even serious economic loss can be caused due to overhigh harmonic content. Harmonic detection is a premise of harmonic suppression, effective harmonic suppression can be performed according to detected harmonics only if the harmonics are accurately detected, and when the detected harmonic voltages deviate, accurate harmonic suppression cannot be performed on a system, so that safe and stable operation of the system can be influenced. Therefore, how to select a proper harmonic detection method is very important.

At present, common harmonic detection methods include fourier transform method, wavelet transform method, neural network method and harmonic detection method based on instantaneous reactive power. The fourier transform method is classified into a discrete fourier transform method and a fast fourier transform method, and can detect stationary signals. The wavelet transform method can detect fluctuating and non-stationary harmonic signals, is suitable for time domain and frequency domain, and has higher resolution. Neural networks are currently signal processing methods that compare leading edges, and currently apply adaptive harmonic detection and multi-layer feed-forward methods. The first three harmonic detection methods have various problems and limited application scenarios. The Fourier transform method is suitable for detecting stationary signals, non-stationary signals cannot be detected, meanwhile, the calculation amount of the Fourier transform method is large, a large amount of detection time is consumed, and the application range is small. The wavelet transform method needs to determine an optimal wavelet basis selection value in the harmonic detection process, and the selection process is complex, long in required time and difficult to realize. The neural network is a signal processing method at the leading edge of the current comparison, and the main development bottleneck is that the construction aspect of the neural network has no unified standard, and the neural network has strong randomness, large calculated amount and poor real-time performance, so the neural network is not widely applied.

The harmonic detection method based on instantaneous reactive power is mainly applied when non-stationary signals are detected and when the grid voltage is distorted. The harmonic detection method based on the instantaneous reactive power theory is divided into a p-q detection method based on the instantaneous reactive power and an i detection method based on the instantaneous reactive power_p-i_qAnd (4) detecting. However, the p-q detection method based on instantaneous reactive power is susceptible to voltage distortion when the grid voltage is distorted, and the accuracy is low.

Disclosure of Invention

The present invention is directed to overcoming the above-mentioned drawbacks of the prior art and providing an instantaneous reactive power based i_p-i_qA harmonic current detection method.

The purpose of the invention can be realized by the following technical scheme:

instantaneous reactive power-based i_p-i_qHarmonic current detectorThe method comprises the steps of embedding a frequency self-adaptive filter based on the SOGI principle into a control system of the SOGI-FLL to form ESOGI-FLL in advance; converting three-phase current into two-phase current i through coordinates_p、i_qTo i, pair_p、i_qFiltering through a low-pass filter series average value to obtain a direct current component; and then replacing a phase-locked loop with an ESOGI-FLL frequency-locked loop, replacing the phase-locked loop with a frequency-locked loop, and outputting a rotating signal with the same frequency as the power grid voltage signal by a sine-cosine generator.

To i_p、i_qThe specific content of the direct current component obtained by filtering the low-pass filter series average value is as follows:

the method comprises the steps of serially connecting a Low Pass Filter (LPF) with a current average filtering module to form an improved filter, using an integral delay and gain link to proxy the LPF, filtering instantaneous active current and reactive current through the current average filtering module, taking a period T as a node, and taking T/6 periods of a delay module in a current average method in the period, namely obtaining a direct current component with an alternating current component of zero and only a fundamental wave positive sequence current corresponding to the alternating current component after the T/6 periods.

The expression of the direct current component is as follows:

in the formula I₁、Respectively, the current and the corresponding phase of the fundamental positive sequence component.

The phase closed-loop transfer functions of the single-phase ESOGI-FLL are respectively as follows:

in the formula, ω₀、U_gAnd theta₀Frequency, amplitude and phase, K, respectively, of the network voltage_p4Is the proportionality coefficient of the preceding stage SOGI, K_p3And K_i3Proportional and integral coefficients, ω, of the subsequent SOGI-FLL stage_gIs the input signal of the SOGI.

Further, the low-pass filter adopts a second-order Butterworth filter.

The invention provides i based on instantaneous reactive power_p-i_qCompared with the prior art, the harmonic current detection method at least has the following beneficial effects:

1) according to the invention, the active and reactive currents ip and iq of the three-phase load are filtered through the series average value of the low-pass filters to obtain the direct-current component, so that the detection precision of the traditional filter is maintained, and the dynamic response speed is shortened; and meanwhile, the frequency locking ring is easy to realize, stable and reliable, the harmonic suppression efficiency of a subsequent active power filter is improved, and the power grid voltage harmonic and direct current component disturbance capability is improved.

2) The ESOGI-FLL frequency-locked loop is adopted to replace a phase-locked loop, so that the response speed is increased, the precision is improved, and compared with the SOGI-FLL frequency-locked loop, the ESOGI-FLL frequency-locked loop is obviously superior to the SOGI-FLL frequency-locked loop in the aspect of restraining direct-current component disturbance and inter-harmonic component disturbance in the voltage of a power grid; meanwhile, by adopting the method of connecting the Butterworth low-pass filter and the current average filter in series, the fundamental positive sequence active current can be accurately obtained under the conditions of asymmetric and distorted three-phase voltage, and the initial phase is zero and is consistent with the positive sequence voltage.

3) By adopting the second-order Butterworth filter, the fundamental positive sequence current contains higher harmonics, and the harmonic detection result generates errors. Therefore, average filtering is added in the design of the improved low-pass filter, the detection delay of the harmonic current is reduced, and the fundamental wave positive sequence active current is accurately obtained under the condition of asymmetric and distorted voltage.

4) The method is different from the problem that the phase precision of the phase-locked loop is poor under the condition that the power grid voltage is distorted, the frequency-locked loop is easy to realize, stable and reliable, and the robustness and reliability of the whole harmonic detection system are improved; integration, delay and gain links are added, the algorithm is easy to realize, the harmonic current detection delay is reduced to T/6, and the average filtering algorithm has higher dynamic response speed; simulation analysis shows that the harmonic distortion rate of the fundamental positive sequence current can be effectively reduced in a three-phase unbalanced system by the method; the active power filter is an effective way for inhibiting harmonic pollution, accurately and quickly detects harmonic generated by a system, and has important significance for inhibiting the harmonic.

5) The added average filtering equipment circuit is easy to realize, ESOGI-FLL is easy to realize, stable and reliable compared with a frequency locking ring, and the robustness and reliability of a harmonic detection system are improved; the harmonic detection method and the harmonic detection device can effectively detect the harmonic problem generated by a large amount of power electronic equipment accessed into a power system, prevent the low harmonic treatment efficiency caused by the deviation of the harmonic detection, accurately and quickly improve the effectiveness of the harmonic detection capability and increase the economy of the harmonic detection capability at the same time.

Drawings

FIG. 1 is a schematic diagram of the apparatus of the present invention;

FIG. 2 is a schematic block diagram of a current averaging method for obtaining a DC component in an embodiment;

FIG. 3 is a schematic diagram of a filter optimized by the method of the present invention in an embodiment;

FIG. 4 is a phase small signal model of the single-phase SOGI-FLL in the embodiment;

FIG. 5 is a phase small signal model of the single-phase ESOGI-FLL in the embodiment;

FIG. 6 shows an example of the instantaneous reactive power-based i_p-i_qThe principle of the harmonic current detection method is shown schematically.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.

Examples

The invention provides an i based on instantaneous reactive power_p-i_qHarmonic current detection method aiming at the traditional i_p-i_qThe harmonic current detection method is improved in two aspects. On one hand, a frequency self-adaptive filter based on a second-order generalized integrator (SOGI) principle is embedded into a control system of a second-order generalized integrator-frequency locked loop (SOGI-FLL) to form an embedded second-order generalized integrator-frequency locked loop (ESOGI-FLL) to replace a traditional Phase Locked Loop (PLL) and output a rotating signal with the same frequency as a voltage phase.

On the other hand, the low-pass filter is improved in a mode that the average filter and the Butterworth filter are connected in series. Different from the mutual contradiction between the time delay and the filtering effect of the traditional low-pass filter, the invention replaces the low-pass filter with the integration, time delay and gain links, reduces the detection time delay of harmonic current, and obtains accurate fundamental wave active current under the condition of asymmetric and distorted three-phase voltage.

FIG. 1 shows a conventional i_p-i_qA harmonic current detection method schematic diagram. I.e. the active current i of the three-phase load current to be detected is first detected_pAnd a reactive current i_qObtaining direct current components of active power current and reactive power current through a low-pass filter; then obtaining current i through matrix conversion_a，i_b，i_cFundamental component i of_af，i_bd，i_cd(ii) a Finally, the current i is converted into_a，i_b，i_cWith fundamental wave content i_af，i_bd，i_cdObtaining harmonic current i by subtracting_ah，i_bh，i_ch. The distortion of a voltage waveform is eliminated by a PLL and grid voltage in-phase sine and cosine signal generating circuit, and a transformation matrix C is as follows:

after being filtered by an LPF low-pass filter, i can be obtained_pAnd i_qDirect current component of (a):

finally, the current i of the three-phase load_a，i_b，i_cAnd the fundamental component i_af，i_bd，i_cdThe harmonic current i of the load current can be obtained by subtracting_ah，i_bh，i_ch：

According to the invention, a frequency self-adaptive filter based on the principle of an SOGI (second-order generalized integrator) is embedded into a control system of the SOGI-FLL to form an ESOGI-FLL, and an ESOGI-FLL frequency-locking loop is adopted to replace a phase-locked loop to output a rotating signal with the same phase and frequency as a voltage. The ESOGI-FLL is formed by embedding a frequency adaptive filter based on the SOGI principle into a control loop of the SOGI-FLL, an input signal omega g of the SOGI is directly given by a later stage SOGI-FLL, and a phase small signal model of the single-phase ESOGI-FLL is obtained, as shown in FIG. 5. K in FIG. 4_p、K_iProportional and integral parameters of the proportional-integral regulator of the SOGI-FLL, respectively. Omega₀、U_gAnd theta₀Respectively, the frequency, amplitude and phase of the grid voltage. K in FIG. 5_p4Is the proportionality coefficient of the preceding stage SOGI, K_p3And K_i3Respectively, the proportional coefficient and the integral coefficient of the subsequent stage SOGI-FLL. Similarly, the ESOGI-FLL is formed by embedding a frequency adaptive filter based on the SOGI principle into a control loop of the SOGI-FLL, and the input signal omega of the SOGI_gGiven directly by the latter stage SOGI-FLL, a phase small signal model of the single-phase ESOGI-FLL shown in fig. 4 can be obtained.

Phase closed loop transfer function G of single-phase SOGI-FLL_p1(s) is:

the phase closed-loop transfer functions of the single-phase ESOGI-FLL are respectively as follows:

ESOGI-FLL is obviously superior to SOGI-FLL in the aspect of restraining the direct current component disturbance in the power grid voltage, namely the SOGI-FLL is susceptible to the influence of the direct current component, and the evaluated frequency differential signal of the SOGI-FLL contains a large pulsation component; the interference of the direct current component can be eliminated, and the frequency differential signal can be accurately evaluated.

FIG. 6 shows the instantaneous reactive power-based i of the present invention_p-i_qThe principle of the harmonic current detection method is shown schematically. That is, the frequency-locked loop FLL is used to replace the phase-locked loop to output a rotation signal having the same frequency as the voltage phase, wherein the transformation matrix C' can be written as follows:

at the same time, three-phase currents i_a，i_b，i_cInstantaneous active and reactive currents are obtained after Clarke and Park conversion, odd harmonics in the instantaneous active and reactive currents are filtered by an LPF, and filtering time is reduced to T/6 through average filtering. And subtracting the obtained fundamental component to obtain the harmonic current.

Specifically, three-phase current is converted into two phases through abc- α β coordinates, the fundamental current becomes a direct current amount, the harmonic currents of 5 th and 7 th become 6 th, and the harmonic currents of 11 th and 13 th become 12 th, that is, after the harmonics of (6n +1) th and (6n +5) th are converted, the numbers of times become 6n and (6n +6) th, respectively, which are multiples of 6. Therefore, for i_p、i_qAfter 1/6 fundamental wave period, the obtained non-zero average value component is the dc value corresponding to the fundamental wave component, and the specific principle is as shown in fig. 2 and 3: the low-pass filter is improved by connecting an average filter and a Butterworth LPF filter in series, namely two-phase current i_p、i_qInput to a Butterworth filter by using a second-order ButtThe error filter can cause the fundamental positive sequence current to contain higher harmonics, and can cause the harmonic detection result to generate errors. Therefore, average value filtering is added in the design of the improved low-pass filter, the detection delay of harmonic current is reduced, and the fundamental wave positive sequence active current is accurately obtained under the condition of asymmetric and distorted voltage. I.e. a two-phase current i_p、i_qAfter being input into a Butterworth filter, the integral is carried out, and then two-phase current i is used_p、i_qAnd respectively subtracting the obtained corresponding average values to obtain the harmonic wave and the reactive current component to be detected.

The average filtering in FIG. 2 is a calculated current i_p、i_qThe block of averages replaces the LPF in the conventional algorithm. In a three-phase bridge rectifier circuit composed of diode rectification load with resistance inductance, the current mainly contains subharmonics (6k +/-1) of 5 th, 7 th, 11 th, 13 th, 17 th, and the like. Instantaneous active and reactive currents i_p、i_qIf the delay module in the current average value method takes T/6 cycles, namely the T/6 cycles, the alternating current component is 0 and only the direct current component corresponding to the fundamental wave positive sequence current remains, thus compared with the case that the delay cycle takes T, the dynamic response speed of detection is greatly improved. According to the principle of the current average method, the current average is calculated as follows:

after instantaneous active current and reactive current are filtered by a current average value module, a period time T is taken as a node, the alternating current component values of harmonic components in the period are all 0, the direct current component of a fundamental wave positive sequence component is not influenced, the direct current component still exists and is transmitted to the next link, and the result is taken into the following formula:

in the formula I₁、Respectively, the current and the corresponding phase of the fundamental positive sequence component.

When the three-phase circuit is asymmetric in fig. 3, the average filtering detection performance is poor. The low pass filter LPF is connected with the current average value module in series, wherein the LPF connected in series plays a role in attenuating odd harmonic components, and the current average value module plays a role in filtering low-frequency harmonics. The alternating current component corresponding to the harmonic current of the improved filter is almost filtered out, and only the direct current component corresponding to the fundamental positive sequence current is left.

The technological improvement point of this patent has two main aspects. The first is to filter the series average value of the conventional low-pass filter LPF to form a modified filter. The LPF is replaced by the integration delay and gain links, the algorithm is easy to realize, if the delay module in the current average value method takes T/6 periods, the harmonic current detection delay is reduced, and meanwhile, the filtering algorithm has higher dynamic response speed. The second is to replace the phase-locked loop with a frequency-locked loop. The three-phase SOGI-FLL can eliminate the frequency multiplication component of 2 contained in the input signal of the integral regulator, namely, the input signal of the integral regulator can directly evaluate the frequency differential signal and can avoid the problem of harmonic amplification caused by frequency differential operation. The SOGI-FLL has a limited ability to suppress grid voltage disturbances. ESOGI-FLL is obviously superior to SOGI-FLL in the aspect of restraining the direct current component disturbance in the power grid voltage, namely the SOGI-FLL is susceptible to the influence of the direct current component, and the evaluated frequency differential signal of the SOGI-FLL contains a large pulsation component; the interference of the direct current component can be eliminated, and the frequency differential signal can be accurately evaluated.

And performing simulation verification on the improved harmonic current detection algorithm by using MATLAB. Simulation results show that the improved harmonic detection method is more traditional i_p-i_qThe harmonic detection method has improved accuracy in both response speed and final detection of harmonics.

The invention firstly carries active and reactive current i to the three-phase load_p、i_qThe direct current component is obtained by filtering the low-pass filter series average value, so that the traditional filtering is reservedThe dynamic response speed is shortened while the detection precision of the device is improved. And then, a frequency-locked loop is adopted to replace a phase-locked loop, and a sine-cosine generator outputs a rotating signal with the same frequency as the power grid voltage signal, so that the problem of poor phase precision of the phase-locked loop under the condition of power grid voltage distortion is solved, and meanwhile, the frequency-locked loop is easy to realize, stable and reliable, so that the harmonic suppression efficiency of a subsequent active power filter is improved.

While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and those skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.