1. A frequency detection method suitable for power electronic equipment networking control, the method comprising:

carrying out d/q axis voltage calculation on the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on a virtual coordinate system with preset fixed frequency;

performing outer product calculation on the calculated d/q axis voltage and the voltage subjected to the frequency selection characteristic of the first-order generalized integrator to obtain the sine of the difference value of the virtual phase angle and the detected phase angle;

and performing integral accumulation on the sine of the difference value until the sine of the difference value is zero, adding a preset fixed frequency and the deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

2. The method of claim 1, wherein the detecting an actual grid frequency by integrating and accumulating the sine of the difference until the sine of the difference is zero and adding a preset fixed frequency and a deviation of the actual grid frequency from the preset fixed frequency comprises:

step 1: inputting the phase angle difference value into an integrator or a quasi-integrator, and performing integral accumulation to obtain the deviation between the actual power grid frequency and the preset fixed frequency;

step 2: calculating the deviation of the actual power grid angular frequency and the preset fixed angular frequency by using an angular velocity formula based on the deviation of the actual power grid frequency and the preset fixed frequency;

and step 3: based on the frequency selection characteristic of the first-order generalized integrator, performing low-pass filtering on d/q-axis voltages of corresponding three-phase voltage instantaneous values by using the deviation between the actual grid angular frequency and the preset fixed angular frequency to obtain d/q-axis voltages of the three-phase voltage instantaneous values after the frequency selection characteristic;

and 4, step 4: calculating the sine of the difference value between the virtual phase angle and the detected phase angle based on the d/q axis voltage of the three-phase voltage instantaneous value after the frequency selection characteristic and the corresponding d/q axis voltage of the three-phase voltage instantaneous value;

and 5: and if the sine of the difference value is not zero, returning to the step 1, otherwise, adding the deviation between the preset fixed frequency and the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

3. The method of claim 2, wherein the first order generalized integrator is expressed as follows:

wherein G(s) is a first-order generalized integrator, s is the Laplace operator, ω_c1The cutoff frequency of the first-order generalized integrator, j is the complex factor of the complex vector, and Δ ω is the estimated value of the difference between the virtual angular frequency and the actual angular frequency.

4. The method of claim 1, wherein the virtual phase angle and the sine of the detected phase angle difference are calculated as follows:

wherein sin delta theta is the sine of the difference between the virtual phase angle and the detected phase angle, u_sdFor d-axis voltage, u, of instantaneous values of three-phase voltage in a virtual coordinate system of a predetermined fixed frequency_sqQ-axis voltage, u 'of three-phase voltage instantaneous value under virtual coordinate system of preset fixed frequency'_sdThe d-axis voltage of the instantaneous value of the three-phase voltage is the voltage value u 'after the frequency selection characteristic of the first-order generalized integrator'_sqThe q-axis voltage of the three-phase voltage instantaneous value is a voltage value after passing through the frequency selection characteristic of a first-order generalized integrator.

5. The method according to claim 1, wherein the d/q axis voltage calculation of the collected instantaneous values of the three-phase voltage of the power electronic grid-connected equipment terminal based on the virtual coordinate system with the preset fixed frequency comprises:

and performing Parker transformation on the acquired results of Clarke transformation on the three-phase voltage instantaneous values of the power electronic grid-connected equipment end in a virtual coordinate system with preset fixed frequency to obtain d/q-axis voltages of the three-phase voltage instantaneous values.

6. The method of claim 5, wherein the d-axis voltage after the frequency-selective characteristic of the first-order generalized integrator is calculated as follows:

wherein u'_sdThe d-axis voltage of the three-phase voltage instantaneous value is the voltage value after the frequency selection characteristic of a first-order generalized integrator, s is a Laplace operator, omega_c1Is the cut-off frequency of the first-order generalized integrator, j is the complex factor of the complex vector, Δ ω is the difference between the virtual angular frequency and the actual angular frequency, u_sdAnd d-axis voltage of the three-phase voltage instantaneous value under a virtual coordinate system with preset fixed frequency is obtained.

7. The method of claim 5, wherein the q-axis voltage after the frequency-selective characteristic of the first-order generalized integrator is calculated as follows:

wherein u'_sqThe q-axis voltage of the three-phase voltage instantaneous value is the voltage value u after the frequency selection characteristic of a first-order generalized integrator_sqThe q-axis voltage of the three-phase voltage instantaneous value under a virtual coordinate system with preset fixed frequency is represented by a Laplace operator, omega_c1The cutoff frequency of the first-order generalized integrator, j is the complex factor of the complex vector, and Δ ω is the difference between the virtual angular frequency and the actual angular frequency.

8. The method of claim 1, wherein the integrator is expressed as follows:

wherein H₁(s) is an integrator, and s is a Laplace operator.

9. The method of claim 1, wherein the quasi-integrator is expressed as follows:

wherein H₂(s) is a quasi-integrator, s is the Laplace operator, ω_c2The cut-off frequency of the quasi-integrator.

10. A frequency detection apparatus suitable for networking control of power electronic equipment, the apparatus comprising:

the first calculation module is used for calculating d/q axis voltage of the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on a virtual coordinate system with preset fixed frequency;

the second calculation module is used for performing outer product calculation on the calculated d/q axis voltage and the voltage subjected to the frequency selection characteristic of the first-order generalized integrator to obtain the sine of the difference value between the virtual phase angle and the detected phase angle;

and the accumulation and detection module is used for accumulating the sine of the difference value through integration until the sine of the difference value is zero, adding a preset fixed frequency and the deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

Background

The grid frequency is an important parameter for measuring the running state of the power system and is one of a plurality of basic parameters required by the grid-connected inverter for realizing voltage following and power control. With the integration of power electronic control new energy power generation such as wind power and photovoltaic into a power grid, the penetration power of the new energy of a power system is gradually improved, and the frequency supporting capacity of a corresponding traditional synchronous generator is greatly reduced. In order to solve the problem of frequency stability caused by the reduction of the frequency modulation capability of an electric power system with large-scale new energy access, the participation of electric power electronic grid-connected equipment such as a distributed power supply and new energy power generation in system frequency modulation has become a necessary requirement of new energy grid connection.

At present, a power grid synchronous signal detection method has more researches and obtains some achievements. The phase-locked loop is a common method for detecting power grid frequency information, but theoretical research and engineering examples show that the phase-locked loop has instability risk in a weak power grid environment. The influence of a phase-locked loop on the stability of a grid-connected inverter system is analyzed in part of researches, the fact that the instability of the system under the weak grid environment is caused by the overhigh bandwidth of the phase-locked loop is considered, however, a design method of phase-locked loop parameters is not provided, and some researches consider the influence of the phase-locked loop and the interaction between the phase-locked loop and the system on the stability of the system, and a design method of the phase-locked loop parameters is provided, but the design is complex. It is proposed in the literature that a phase-locked loop algorithm based on synchronous rotating coordinates has an inherent low-frequency oscillation characteristic, and this characteristic will cause a low-frequency power oscillation phenomenon and possibly cause system instability. The research shows that the phase-locked loop cannot accurately output the frequency information of the power grid under the weak power grid environment, and the problem can be obviously solved by eliminating the closed-loop adjusting process, so that the related research provides an open-loop detection method of the power grid frequency.

The zero-crossing detection method is a typical open-loop phase measurement method, but the method is only suitable for occasions with constant voltage phase and frequency of the power grid. The filter is designed by utilizing a least square estimation method, so that the rapid open-loop phase locking can be realized, the performance is better when the detected frequency is close to the normal working frequency, but the performance is poorer when the frequency is deviated. Other open-loop methods design the filter for specific conditions. In addition, the frequency information of the power grid is acquired based on the open-loop detection method, so that first-order difference operation needs to be carried out on the detected phase information, and the frequency detection precision is relatively low under the condition of low sampling rate; increasing the sampling rate can improve the accuracy of the measurement, but can amplify high frequency random noise. Research proposes a rapid open-loop detection method for a power grid synchronous phase, which realizes rapid and accurate acquisition of the power grid synchronous phase in a severe environment, but the research does not relate to a detection method for power grid frequency, and limits the application range of the method. Obviously, the open-loop methods cannot realize accurate detection of the power grid frequency.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a frequency detection method suitable for networking control of power electronic equipment, which comprises the following steps:

carrying out d/q axis voltage calculation on the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on a virtual coordinate system with preset fixed frequency;

performing outer product calculation on the calculated d/q axis voltage and the voltage subjected to the frequency selection characteristic of the first-order generalized integrator to obtain the sine of the difference value of the virtual phase angle and the detected phase angle;

and performing integral accumulation on the sine of the difference value until the sine of the difference value is zero, adding a preset fixed frequency and the deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

Preferably, the integrating and accumulating the sine of the difference value until the sine of the difference value is zero, adding a preset fixed frequency and a deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency includes:

step 1: inputting the phase angle difference value into an integrator or a quasi-integrator, and performing integral accumulation to obtain the deviation between the actual power grid frequency and the preset fixed frequency;

step 2: calculating the deviation of the actual power grid angular frequency and the preset fixed angular frequency by using an angular velocity formula based on the deviation of the actual power grid frequency and the preset fixed frequency;

and step 3: based on the frequency selection characteristic of the first-order generalized integrator, performing low-pass filtering on d/q-axis voltages of corresponding three-phase voltage instantaneous values by using the deviation between the actual grid angular frequency and the preset fixed angular frequency to obtain d/q-axis voltages of the three-phase voltage instantaneous values after the frequency selection characteristic;

and 4, step 4: calculating the sine of the difference value between the virtual phase angle and the detected phase angle based on the d/q axis voltage of the three-phase voltage instantaneous value after the frequency selection characteristic and the corresponding d/q axis voltage of the three-phase voltage instantaneous value;

and 5: and if the sine of the difference value is not zero, returning to the step 1, otherwise, adding the deviation between the preset fixed frequency and the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

Further, the expression of the first-order generalized integrator is as follows:

wherein G(s) is a first-order generalized integrator, s is the Laplace operator, ω_c1The cutoff frequency of the first-order generalized integrator, j is the complex factor of the complex vector, and Δ ω is the estimated value of the difference between the virtual angular frequency and the actual angular frequency.

Preferably, the calculation of the sine of the virtual phase angle and the detected phase angle difference is as follows:

wherein sin delta theta is the sine of the difference between the virtual phase angle and the detected phase angle, u_sdFor d-axis voltage, u, of instantaneous values of three-phase voltage in a virtual coordinate system of a predetermined fixed frequency_sqQ-axis voltage, u 'of three-phase voltage instantaneous value under virtual coordinate system of preset fixed frequency'_sdThe d-axis voltage of the instantaneous value of the three-phase voltage is the voltage value u 'after the frequency selection characteristic of the first-order generalized integrator'_sqFrequency selection device for q-axis voltage of three-phase voltage instantaneous value through first-order generalized integratorThe voltage value after sex.

Preferably, the d/q axis voltage calculation of the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on the virtual coordinate system with the preset fixed frequency includes:

and performing Parker transformation on the acquired results of Clarke transformation on the three-phase voltage instantaneous values of the power electronic grid-connected equipment end in a virtual coordinate system with preset fixed frequency to obtain d/q-axis voltages of the three-phase voltage instantaneous values.

Further, the d-axis voltage after passing through the frequency selection characteristic of the first-order generalized integrator is calculated as follows:

wherein u'_sdThe d-axis voltage of the three-phase voltage instantaneous value is the voltage value after the frequency selection characteristic of a first-order generalized integrator, s is a Laplace operator, omega_c1Is the cut-off frequency of the first-order generalized integrator, j is the complex factor of the complex vector, Δ ω is the difference between the virtual angular frequency and the actual angular frequency, u_sdAnd d-axis voltage of the three-phase voltage instantaneous value under a virtual coordinate system with preset fixed frequency is obtained.

Further, the q-axis voltage after the frequency selection characteristic of the first-order generalized integrator is calculated as follows:

wherein u'_sqThe q-axis voltage of the three-phase voltage instantaneous value is the voltage value u after the frequency selection characteristic of a first-order generalized integrator_sqThe q-axis voltage of the three-phase voltage instantaneous value under a virtual coordinate system with preset fixed frequency is represented by a Laplace operator, omega_c1The cutoff frequency of the first-order generalized integrator, j is the complex factor of the complex vector, and Δ ω is the difference between the virtual angular frequency and the actual angular frequency.

Preferably, the expression of the integrator is as follows:

wherein H₁(s) is an integrator, and s is a Laplace operator.

Preferably, the expression of the quasi-integrator is as follows:

wherein H₂(s) is a quasi-integrator, s is the Laplace operator, ω_c2The cut-off frequency of the quasi-integrator.

Based on the same inventive concept, the invention also provides a frequency detection device suitable for networking control of power electronic equipment, which comprises:

the first calculation module is used for calculating d/q axis voltage of the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on a virtual coordinate system with preset fixed frequency;

the second calculation module is used for performing outer product calculation on the calculated d/q axis voltage and the voltage subjected to the frequency selection characteristic of the first-order generalized integrator to obtain the sine of the difference value between the virtual phase angle and the detected phase angle;

and the accumulation and detection module is used for accumulating the sine of the difference value through integration until the sine of the difference value is zero, adding a preset fixed frequency and the deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

Compared with the closest prior art, the invention has the following beneficial effects:

the invention provides a frequency detection method and a frequency detection device suitable for networking control of power electronic equipment, wherein the frequency detection method comprises the following steps: carrying out d/q axis voltage calculation on the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on a virtual coordinate system with preset fixed frequency; performing outer product calculation on the calculated d/q axis voltage and the voltage subjected to the frequency selection characteristic of the first-order generalized integrator to obtain the sine of the difference value of the virtual phase angle and the detected phase angle; integrating and accumulating the sine of the difference value until the sine of the difference value is zero, adding a preset fixed frequency and the deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency; the technical scheme provided by the invention can still keep the accurate tracking of the detection frequency to the actual frequency under the condition of the change of the power grid frequency, has short dynamic response time, realizes the quick and accurate detection of the power grid frequency and has strong anti-interference capability.

Drawings

Fig. 1 is a flowchart of a frequency detection method suitable for networking control of power electronic equipment according to the present invention;

FIG. 2 is a main circuit diagram of a frequency detection method suitable for power electronic equipment networking control according to the present invention;

FIG. 3 is a simulation result diagram of actual frequency and detection frequency of a frequency detection method suitable for networking control of power electronic equipment according to the present invention;

fig. 4 is a structural diagram of a frequency detection device suitable for networking control of power electronic equipment according to the present invention.

Detailed Description

The following describes embodiments of the present invention in further detail with reference to the accompanying drawings.

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

The invention provides a frequency detection method suitable for networking control of power electronic equipment, which comprises the following steps of:

step 101: carrying out d/q axis voltage calculation on the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on a virtual coordinate system with preset fixed frequency;

step 102: performing outer product calculation on the calculated d/q axis voltage and the voltage subjected to the frequency selection characteristic of the first-order generalized integrator to obtain the sine of the difference value of the virtual phase angle and the detected phase angle;

step 103: and performing integral accumulation on the sine of the difference value until the sine of the difference value is zero, adding a preset fixed frequency and the deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

Step 101, specifically comprising:

the method comprises the steps of collecting three-phase voltage instantaneous values u of a power electronic grid-connected equipment end through a sensor_sa、u_sb、u_scRespectively representing the instantaneous values of the three-phase voltages acquired.

Using Clarke transformation to convert three-phase voltage u_sa、u_sb、u_scClarke conversion is carried out to obtain the alpha-axis component u of the three-phase voltage_sαAnd a beta axis component u_sβ；

The expression for the Clarke transform is as follows:

by using Parker transformation, a fixed frequency of 50Hz is used as a virtual reference frequency, namely, phase angles theta generated by sawtooth waves with a period of 20ms and an amplitude of 2 pi are respectively corresponding to u_sα～u_sβParker transformation is carried out to obtain a virtual coordinate system (rotation angular frequency omega) at fixed frequency₁100 pi rad/s) d-axis component u of three-phase voltage_sdAnd q-axis component u_sq；

The expression of the Parker transform is as follows:

the phase angle θ is a sawtooth-like phase angle signal having a period of 20ms and an amplitude of 2 π.

Step 102, specifically comprising:

the obtained u_sdAnd u_sqAfter passing through two first-order generalized integrators (also called reduced-order generalized integrators) with the same parameters, respectively, a d-axis voltage and a q-axis voltage u 'at the detected frequency can be obtained'_sdAnd u'_sqThe expression in the frequency domain is,

in the equation, Δ ω ═ 2 pi · Δ f denotes a resonance frequency, Δ ω denotes a rotation angle frequency deviation (difference between a virtual angular frequency and an actual angular frequency), and Δ f denotes a frequency deviation (difference between a virtual frequency and an actual frequency), as shown in fig. 1. u'_sdVoltage amplitude u 'corresponding to d-axis component of three-phase voltage instantaneous value of power electronic grid-connected equipment end at detected frequency'_sqCorresponding to the q-axis component of the three-phase voltage instantaneous value of the power electronic grid-connected equipment end, the voltage amplitude at the detected frequency is G(s), the first-order generalized integrator is G(s), the s is a Laplace operator, and omega_c1For the cut-off frequency, it is typically set between 5-25rad/s, j being the complex factor of the complex vector.

To make a frequency estimation using the phase angle difference Δ θ between the virtual phase angle and the detected phase angle, a vector outer product may be introduced, taking into account that Δ θ varies around zero degrees. Constructing the voltage vector at the virtual phase angle as:

U_sdq＝u_sd+j·u_sq

the voltage vector after passing through the first-order generalized integrator is:

U′_sdq＝u′_sd+j·u′_sq

U′_sdq＝G(s)·U_sdq

in the formula, u_sd、u_sqIs d and q axis components, u 'of voltage at virtual phase angle at fixed frequency'_sd、u′_sqIn order to detect the d and q axis components of the voltage after passing through the first-order generalized integrator under the frequency, the complex factor of the j complex vector is detected.

Phase angle (U) between them_sdqPhase angle minus U'_sdqPhase angle) can be expressed as,

in which sin delta theta is the sine of the difference between the virtual phase angle and the detected phase angle,is the square value of the d-axis component of the instantaneous values of the three-phase voltages,is the square value of the q-axis component of the three-phase voltage instantaneous value,the squared value of the voltage amplitude at the detected frequency corresponding to the d-axis component of the three-phase voltage instantaneous value passing through the first-order integrator,the square value of the voltage amplitude at the detected frequency is corresponding to the q-axis component of the three-phase voltage instantaneous value passing through the first-order integrator.

Step 103, specifically comprising:

the sine of the difference between the virtual phase angle and the detected phase angle is taken into an integrator or quasi-integrator, which outputs an estimated value of the deviation between the detected frequency and the actual grid frequency, and the detected frequency and the actual grid frequency are combinedThe estimated value of the deviation of the frequency is brought into a first-order generalized integrator for integral accumulation, and the value output by the first-order generalized integrator is compared with the d-axis voltage and the q-axis voltage u 'at the detected frequency'_sdAnd u'_sqCalculating the sine of the difference value between the new virtual phase angle and the detected phase angle, then substituting the sine of the difference value between the new virtual phase angle and the detected phase angle into an integrator or a quasi-integrator, performing iteration until the sine of the difference value between the virtual phase angle and the detected phase angle is zero to obtain the deviation of the detected frequency and the actual power grid frequency, and finally adding the deviation of the detected frequency and the actual power grid frequency with the fixed frequency to obtain the actual power grid frequency.

Under the steady state condition, if the detected frequency is equal to the actual power grid frequency, the frequency deviation is zero, and the phase angle of G(s) at the resonant frequency is zero degree; when the frequency disturbance causes the actual grid frequency to be reduced, the frequency deviation is a positive number, the phase angle of G(s) at the resonant frequency is a negative value, the detection frequency is gradually reduced and approaches to the actual frequency through integral accumulation, and when the detection frequency is equal to the actual grid frequency, the phase angle of G(s) is zero, and the new steady state is entered; when the frequency disturbance causes the actual power grid frequency to rise, the frequency deviation is a negative number, the phase angle of G(s) at the resonant frequency is a positive value, the detection frequency gradually rises and approaches to the actual frequency through integral accumulation, and when the detection frequency is equal to the actual power grid frequency, the phase angle of G(s) is zero, and the new steady state is entered.

At actual grid frequency of 49-51H_ZWhen the frequency fluctuates in the interval, because the deviation angle of the power grid frequency is relatively small, the frequency can be approximately considered,

sinΔθ≈Δθ

this also reflects the grid frequency f_gWhen the resonant frequency converges to the difference between the actual grid frequency and the virtual reference frequency, U_sdqAnd U'_sdqOuter product (U)_sdq×U′_sdq) Is zero. Introducing an integrator or quasi-integrator (expression is as follows), and adding U_sdqAnd U'_sdqOuter product (U)_sdq×U′_sdq) As error input for frequency estimation, and forms a frequency estimation closed loop with a reduced-order generalized integratorAnd controlling to obtain the static error-free estimation of the voltage frequency of the power grid.

An integrator:

a quasi-integrator:

in the formula, H₁(s) is an integrator, H₂(s) is a quasi-integrator, s is the Laplace operator, ω_c2The cut-off frequency of the quasi-integrator.

Meanwhile, the integral node (quasi-integral regulator) can play a certain filtering role in the estimation of the voltage frequency of the power grid, and meanwhile, the resonance frequency of the degradation generalized integrator adopted by the invention is near the fundamental frequency and is the same as the frequency deviation amount, so that the negative sequence and harmonic voltage disturbance can be attenuated to a certain extent, and the anti-interference performance of the frequency estimation method is enhanced.

Example 2

In order to verify the correctness of the theory of the frequency detection method suitable for grid-connected control of the power electronic equipment, a power grid frequency estimation control simulation model with a main circuit diagram as shown in fig. 2 is built in MATLAB/Simulink simulation software. In the simulation, the actual frequency of the power grid fluctuates at 1.0 s. At this time, the frequency detection value obtained according to the control strategy is compared with the actual frequency, and the simulation result can be obtained as shown in fig. 3.

According to simulation results, the frequency detection method provided by the patent can still keep accurate tracking of the detection frequency to the actual frequency under the condition of power grid frequency change, has short dynamic response time, can play a certain filtering role on the estimation value in the power grid electrical frequency, and has strong anti-interference capability.

Example 3

The invention provides a frequency detection device suitable for networking control of power electronic equipment, as shown in fig. 4, the device comprises:

the first calculation module is used for calculating d/q axis voltage of the collected three-phase voltage instantaneous value of the power electronic grid-connected equipment terminal based on a virtual coordinate system with preset fixed frequency;

the second calculation module is used for performing outer product calculation on the calculated d/q axis voltage and the voltage subjected to the frequency selection characteristic of the first-order generalized integrator to obtain the sine of the difference value between the virtual phase angle and the detected phase angle;

and the accumulation and detection module is used for accumulating the sine of the difference value through integration until the sine of the difference value is zero, adding a preset fixed frequency and the deviation between the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency.

Preferably, the first calculating module is specifically configured to:

performing Parker transformation on the acquired results of Clarke transformation on the three-phase voltage instantaneous values of the power electronic grid-connected equipment end in a virtual coordinate system with preset fixed frequency to obtain d/q-axis voltages of the three-phase voltage instantaneous values;

the calculation formula of the d-axis voltage after the frequency selection characteristic of the first-order generalized integrator is as follows:

wherein u'_sdThe d-axis voltage of the three-phase voltage instantaneous value is the voltage value after the frequency selection characteristic of a first-order generalized integrator, s is a Laplace operator, omega_c1Is the cut-off frequency of the first-order generalized integrator, j is the complex factor of the complex vector, Δ ω is the difference between the virtual angular frequency and the actual angular frequency, u_sdAnd d-axis voltage of the three-phase voltage instantaneous value under a virtual coordinate system with preset fixed frequency is obtained.

The q-axis voltage after the frequency selection characteristic of the first-order generalized integrator is calculated as follows:

wherein u'_sqFirst-order generalized integrator for q-axis voltage passing through three-phase voltage instantaneous valueVoltage value u after frequency-selective characteristic_sqThe q-axis voltage of the three-phase voltage instantaneous value under a virtual coordinate system with preset fixed frequency is represented by a Laplace operator, omega_c1The cutoff frequency of the first-order generalized integrator, j is the complex factor of the complex vector, and Δ ω is the difference between the virtual angular frequency and the actual angular frequency.

Preferably, the second calculating module is specifically configured to:

the calculation of the sine of the virtual phase angle and the detected phase angle difference is as follows:

wherein sin delta theta is the sine of the difference between the virtual phase angle and the detected phase angle, u_sdFor d-axis voltage, u, of instantaneous values of three-phase voltage in a virtual coordinate system of a predetermined fixed frequency_sqQ-axis voltage, u 'of three-phase voltage instantaneous value under virtual coordinate system of preset fixed frequency'_sdThe d-axis voltage of the instantaneous value of the three-phase voltage is the voltage value u 'after the frequency selection characteristic of the first-order generalized integrator'_sqThe q-axis voltage of the three-phase voltage instantaneous value is a voltage value after passing through the frequency selection characteristic of a first-order generalized integrator.

Preferably, the accumulation and detection module is specifically configured to:

step 1: inputting the phase angle difference value into an integrator or a quasi-integrator, and performing integral accumulation to obtain the deviation between the actual power grid frequency and the preset fixed frequency;

step 2: multiplying the deviations of the actual power grid frequency and the preset fixed frequency by 2 pi respectively to obtain the deviations of the actual power grid angular frequency and the preset fixed angular frequency;

and step 3: based on the frequency selection characteristic of the first-order generalized integrator, performing low-pass filtering on d/q-axis voltages of corresponding three-phase voltage instantaneous values by using the deviation between the actual grid angular frequency and the preset fixed angular frequency to obtain d/q-axis voltages of the three-phase voltage instantaneous values after the frequency selection characteristic;

and 4, step 4: calculating the sine of the difference value between the virtual phase angle and the detected phase angle based on the d/q axis voltage of the three-phase voltage instantaneous value after the frequency selection characteristic and the corresponding d/q axis voltage of the three-phase voltage instantaneous value;

and 5: if the sine of the difference value is not zero, returning to the step 1, otherwise, adding a preset fixed frequency and the deviation of the actual power grid frequency and the preset fixed frequency, and detecting the actual power grid frequency;

the expression of the first order generalized integrator is as follows:

wherein G(s) is a first-order generalized integrator, s is the Laplace operator, ω_c1The frequency is the cut-off frequency of a first-order generalized integrator, j is a complex factor of a complex vector, and delta omega is an estimated value of the difference value of the virtual angular frequency and the actual angular frequency;

the expression of the integrator is as follows:

wherein H₁(s) is an integrator, and s is a Laplace operator.

The expression of the quasi-integrator is as follows:

wherein H₂(s) is a quasi-integrator, s is the Laplace operator, ω_c2The cut-off frequency of the quasi-integrator.

As will be appreciated by one skilled in the art, embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.