Measurement and correction method for frequency coupling sequence admittance of network construction type converter system

Abstract

The invention discloses a measurement and correction method for frequency coupling sequence admittance of a network-forming converter system, and the method comprises the steps: injecting three-phase voltage disturbances with different frequency values into the network-forming converter system for a plurality of times, and obtaining output voltage and current response data; according to the voltage and current response data, obtaining a frequency-coupled sequence admittance measurement result; obtaining a compensation factor of phase correction; and performing phase correction by using the compensation factor to obtain an optimized sequence admittance result. According to the technical scheme provided by the invention, the impedance measurement of the grid-connected system is realized by adopting a grid-connected point disturbance signal injection mode, and the power grid impedance is estimated through the collected impedance data; and phase correction is carried out on the measured frequency coupling sequence admittance coupling component by considering the influence of the power grid impedance, so that the measurement precision of the frequency coupling sequence admittance of the grid-connected system of the network construction type converter is improved, the accurate analysis of the stability of the grid-connected system of the network construction type converter is facilitated, and the scheduling and operation strategies of the system are optimized.

Description

Technical Field

[0001] The invention relates to the field of frequency-coupled sequence admittance measurement, and in particular to a measurement and correction method for the frequency-coupled sequence admittance of a grid-type converter system. Background Art

[0002] In the context of the current global energy transition, renewable energy power generation equipment, such as wind and solar power generation, is increasingly becoming an important component of achieving sustainable development. Since these power electronic devices use asymmetric control structures, they often face frequency coupling problems during grid-connected operation, which may lead to reduced system stability and power quality. Frequency-coupled sequence admittance refers to the admittance characteristics of a circuit or system to signals of different frequencies in the presence of frequency coupling effects. In renewable energy grid-connected power generation equipment, the modeling, measurement, and analysis of frequency-coupled sequence admittance are of great significance to ensure the stable operation of the power grid.

[0003] To address this problem, traditional measurement methods often ignore the influence of large grid impedance on the current phase of coupled sequence admittance component under weak power grid, thus affecting the measurement accuracy. Due to its unique structure and operating characteristics, grid-connected new energy power generation equipment is more sensitive to frequency coupling, which in turn affects the safety and reliability of the overall power system. Since the grid-connected converter is connected to the power system, the influence of grid impedance cannot be ignored. Therefore, in the face of the grid-connected converter grid-connected system, a new measurement correction method is needed for frequency coupled sequence admittance to meet its measurement accuracy requirements. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the current technology, the present invention provides a measurement and correction method for the frequency-coupled sequence admittance of a grid-connected converter system. By adopting a method of phase correction of the frequency-coupled sequence admittance component, accurate measurement of the frequency-coupled sequence admittance of a grid-connected converter is achieved, which is beneficial to accurate analysis of the stability of the grid-connected system of the grid-connected converter.

[0005] To achieve the above object, the embodiments of the present invention adopt the following technical solutions: Injecting three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system several times to obtain output voltage and current response data; Obtain frequency-coupled sequence admittance measurement results based on voltage and current response data; Obtain the compensation factor of phase correction according to the system characteristics of the grid-type converter and the voltage and current response data; The compensation factor is used to perform phase correction on the sequence admittance measurement results to obtain the optimized sequence admittance results.

[0006] According to one aspect of the present invention, injecting a plurality of three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system to obtain output voltage and current response data comprises: Set the fundamental frequency f1 and a frequency table containing several frequency points; The frequency points in the frequency table are traversed, and according to the frequency point values ​​and the fundamental frequency, a three-phase voltage disturbance with a certain frequency value is injected into the grid-type converter system to obtain the output voltage and current response data.

[0007] According to one aspect of the present invention, the step of setting the fundamental frequency f1 and the frequency table containing a plurality of frequency points further comprises: The frequency point values ​​in the frequency table are set from small to large.

[0008] According to one aspect of the present invention, injecting a plurality of three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system to obtain output voltage and current response data further comprises: Preset cutoff frequency; When traversing the frequency points in the frequency table, when the frequency point is greater than or equal to the sweep cutoff frequency, the measurement ends.

[0009] According to one aspect of the present invention, injecting a three-phase voltage disturbance of a certain frequency value into the grid-connected converter system according to the frequency point value and the fundamental frequency to obtain the output voltage and current response data includes: When the frequency point value fp<2f1, first inject a positive sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, C1, and phases of 10, 240, and 120 into the grid-type converter system. After the system is stable, obtain the output voltage and current response data. Then, a positive-sequence voltage disturbance with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10, 240, and 120 respectively, is injected into the grid-connected converter system. After the system is stable, the output voltage and current response data are obtained.

[0010] According to one aspect of the present invention, injecting a three-phase voltage disturbance of a certain frequency value into the grid-connected converter system according to the frequency point value to obtain output voltage and current response data includes: When the frequency point value fp≥2f1, first inject a positive sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, C1, and phases of 0, 240, and 120 into the grid-connected converter system. After the system is stable, obtain the output voltage and current response data. Then, a negative-sequence voltage disturbance with a frequency of fp-2f1, three-phase amplitudes of A2, B2, and C2, and phases of 0, 240, and 120 are injected into the grid-connected converter system. After the system is stable, the output voltage and current response data are obtained.

[0011] According to one aspect of the present invention, the fundamental frequency f1 is set to 50 Hz.

[0012] According to one aspect of the present invention, obtaining a compensation factor for phase correction according to the grid-connected converter system characteristics and voltage and current response data includes: Estimate grid impedance based on voltage and current response data; According to the grid impedance, the adjustment coefficient is introduced and the compensation factor of phase correction is calculated.

[0013] According to one aspect of the present invention, the sequence admittance measurement result includes: sequence admittance component Y 11 , Y 12 , Y 21 , Y 22 .

[0014] According to one aspect of the present invention, the method for measuring and correcting the frequency-coupled sequence admittance of the grid-type converter system further comprises: The sequence admittance measurement results and the optimized sequence admittance results are plotted into curves to compare the effects before and after phase correction.

[0015] Advantages of the present invention: The present invention provides a measurement and correction method for the frequency-coupled sequence admittance of a grid-connected converter system. The method adopts a grid-connected point disturbance signal injection method to realize impedance measurement of the grid-connected system, and estimates the grid impedance through the collected impedance data. The phase correction is performed on the coupled component of the measured frequency-coupled sequence admittance considering the influence of the grid impedance, thereby improving the measurement accuracy of the frequency-coupled sequence admittance of the grid-connected converter system, being beneficial to the accurate analysis of the stability of the grid-connected converter system, thereby optimizing the system scheduling and operation strategy, and improving the access capacity of renewable energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 It is a flow chart of a method for measuring and correcting frequency-coupled sequence admittance of a grid-type converter system according to the present invention; Figure 2A new energy converter grid-connected system according to the present invention; Figure 3 A grid-type converter control loop according to the present invention; Figure 4 It is an equivalent schematic diagram of the frequency coupling of the new energy grid-connected system according to the present invention; Figure 5 The frequency-coupled sequence admittance curve without adding phase correction described in the present invention; Figure 6 This is the frequency-coupled sequence admittance curve with phase correction added as described in the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] Embodiment 1

[0020] like Figure 1 As shown, a method for measuring and correcting frequency-coupled sequence admittance of a grid-type converter system comprises the following steps: S1: Inject three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system several times to obtain output voltage and current response data.

[0021] In practical applications, MATLAB, Simulink or Python can be used to develop a frequency-coupled sequence admittance sweep program to measure and analyze the frequency response characteristics of renewable energy grid-connected power generation equipment.

[0022] Specifically, the frequency sweep procedure mainly includes the following steps: (1) According to the grid system architecture, a grid-connected converter system model is constructed, including a sequence impedance model considering frequency coupling.

[0023] (2) Injecting small disturbance signals: Inject small disturbance signals into the model. Generally, a sinusoidal signal is used as the disturbance signal, and the frequency varies within a certain range to ensure that the required frequency response range can be covered.

[0024] (3) Frequency sweep simulation: Sweep the frequency of the disturbance signal and record the system current and voltage response data at each frequency.

[0025] (4) Data processing and drawing: Using the frequency sweep results, draw the Bode diagram of the sequence impedance considering frequency coupling, where the horizontal axis is the frequency and the vertical axis is the amplitude and phase of the sequence impedance.

[0026] Figure 2 A grid-connected new energy converter system is provided by the method, wherein the PCC is a common coupling point between the new energy converter and the power grid. V dc is the DC side voltage, L f is the filter inductor, R d is the filter resistor, i abc are the three-phase currents A, B, and C sampled by PCC, v abc The PCC samples the three-phase voltages A, B, and C. C f is the filter capacitor, i gabc is the grid side current, L g is the grid side inductance, R g is the grid side resistance. Specifically, L g Set to 20mH, R g Set to 0.2Ω.

[0027] Figure 3 This is the grid-type converter control loop used in this method, where P ref Active power setpoint, Q ref is the reactive loop given value, P e is the instantaneous value of active power, Q e is the instantaneous value of reactive power, , D p is the active damping coefficient, J is the inertia coefficient, K is the reactive loop droop coefficient, V ref is the given value of the reactive loop voltage amplitude, V m is the given value of the single-phase voltage amplitude of the power grid, D q is the virtual coefficient of the reactive loop, θ GFM is the active loop output phase angle, E m is the output voltage amplitude of the reactive loop, and the synchronous modulation waves ma, mb, and mc can be expressed as:

[0028] In the formula, Kf =2 / V dc .

[0029] Specifically, step S1 includes: S11: Setting the fundamental frequency f1 and a frequency table containing several frequency points.

[0030] In practical applications, the frequency sweep program can be initialized and the fundamental frequency f1 can be set to 50 Hz; the frequency table contains 35 frequency points, which are set to [10, 12, 15, 18, 22, 27, 33, 40, 60, 72, 88, 107, 130, 158, 193, 235, 287, 349, 425, 518, 631, 769, 936, 1141, 1389, 1693, 2062, 2512, 3060, 3728, 4541, 5532, 6739, 8209, 10000].

[0031] In addition, the frequency sweep program also needs to set parameters such as communication port and measurement storage address.

[0032] S12: traverse the frequency points in the frequency table, and inject a three-phase voltage disturbance of a certain frequency value into the grid-connected converter system according to the frequency point value and the fundamental frequency, and obtain output voltage and current response data.

[0033] Specifically, there are two situations when the frequency sweep program is measured: 1. When the frequency point value fp<2f1, that is, fp<100Hz: (1) First, a positive-sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, and C1, and phases of 10, 240, and 120 are injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: (2) Then, a positive-sequence voltage disturbance with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10, 240, and 120, is injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: in, t0' and t 0" represent the first sampling moment and the second sampling moment respectively; V is voltage, I is current; φ is phase angle.

[0034] 2. When the frequency point value fp ≥ 2f1, that is, fp ≥ 100Hz: (1) First, a positive sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, and C1, and phases of 0, 240, and 120 are injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: (2) Then, a negative sequence voltage disturbance with a frequency of fp-2f1, three-phase amplitudes of A2, B2, and C2, and phases of 0, 240, and 120 are injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: S2: Obtain the frequency-coupled sequence admittance measurement results based on the voltage and current response data.

[0035] Admittance is a general term for conductance and susceptance, and is used to describe the ease with which alternating current passes through a circuit or system. Admittance is the reciprocal of impedance, with the symbol Y and the unit being Siemens (S). Admittance is a complex number consisting of a real part (conductance) and an imaginary part (susceptance).

[0036] When calculating the sequence admittance results of the frequency coupling of the grid-type converter system, the sequence admittance measurement results include: sequence admittance component Y 11 , Y 12 , Y 21 , Y 22 , the calculation formula is as follows: S3: Obtain the compensation factor of phase correction according to the system characteristics of the grid-connected converter and the voltage and current response data.

[0037] Step S3 includes: (1) Estimate the grid impedance based on the voltage and current response data.

[0038] Assuming that n frequency disturbances are injected, that is, n-order admittance measurements are performed, the estimated grid impedance Zg can be expressed as: In the formula, V pi ' and I gpi ' are respectively the positive sequence voltage and positive sequence current measured after the i-th disturbance injection in step S2, f pi is the frequency of the disturbance source injected for the i-th time.

[0039] (2) According to the grid impedance, the adjustment coefficient is introduced and the compensation factor of phase correction is calculated.

[0040] Figure 4 This is an equivalent schematic diagram of the frequency coupling of the renewable energy grid-connected system. The system injects a disturbance source V p ( f p ) after the converter control loop generates two response excitations e '( f p )and e '( f p -2 f 1) Under the action of two response excitations, coupled excitations are generated respectively e "( f p -2 f 1) and e "( f p ). Therefore, the current components with disturbance frequencies of fp and fp-2f1 collected in the actual process include not only the current components generated by the response excitation on the converter impedance and the grid impedance, but also the current components under the coupling response excitation. In this process, the influence of the grid impedance on the phase of the coupled components, especially the current components, cannot be ignored. The coupled current components include the corresponding grid impedance influence. From engineering experience, it can be obtained that the impedance of the converter in the high frequency band is much larger than the grid impedance. Therefore, the influence of the grid on the converter is mainly reflected in the low frequency band. Taking the voltage component as the reference quantity, this method converts the influence of the coupled component into the phase of the coupled current component, and introduces the compensation factor λ to realize the phase correction of the frequency coupling measurement sequence admittance.

[0041] The calculation formula of the compensation factor λ is: In the formula, ZGFM ( f p ) = ; α is the adjustment coefficient, and its value range is 0.6~1; is the grid impedance angle; angle ( ) represents the phase of the vector in brackets; | | represents the magnitude of the vector modulus.

[0042] S4: Use the compensation factor to perform phase correction on the sequence admittance measurement result to obtain the optimized sequence admittance result.

[0043] Specifically, the result after sequence admittance phase correction is expressed as follows: Preferably, the method further comprises: S5: Plot the sequence admittance measurement results and the optimized sequence admittance results into a curve to compare the effects before and after phase correction.

[0044] The method is used to measure the grid-connected system of the grid-connected new energy converter mentioned above, and the obtained frequency coupling sequence admittance results are plotted into a curve. The curve without adding phase correction is shown as follows: Figure 5 As shown in the figure, the curve after adding phase correction is as follows Figure 6 shown.

[0045] Figure 5 and Figure 6 In the figure, the solid line represents the frequency-coupled sequence admittance curve of the grid-connected new energy converter derived theoretically. The formula of the complex frequency domain of the curve is as follows: In the formula, N, M, T, W, N l 、M l 、T l , W l The expression is as follows: Where V1=V1 * = V 1 / 2; I1=( I 1 / 2)e ±jφi1 ;I1 * =( I 1 / 2)e ∓jφi1 ; V 1= V ref ; I 1= P ref / (1.5* V ref ); φi1 is the phase of the fundamental current, and its value is obtained by simulation measurement; s 1=2π f p , s 2=2π f p -4π f 1, s 0=2π f p -2π f 1; PWM modulation coefficient K pwm =0.5; T ( s )=1 / s*( J * s + D p ); Delay function G del ( s )=e -1.5Tss , T s is the sampling time step; s is the Laplace operator; j is the imaginary unit of a complex number; D q is the damping coefficient of the reactive loop.

[0046] Figure 5 and Figure 6 In the figure, the “*” part indicates the order admittance value at the disturbance frequency fp and fp-2f1 measured by the frequency sweep procedure. Figure 5 It can be seen that the coupling component Y of the mesh-type frequency coupling order admittance without phase correction is 12 and Y 21 The phase measurement value and the value of the theoretical curve have a large error when the frequency f<100Hz. Under the same simulation conditions, the measured value of the network-type frequency coupling sequence admittance after adding phase correction is as follows: Figure 6 As shown in Figure 3, the measured values ​​are highly consistent with the theoretical values, which verifies the effectiveness of this method.

[0047] The beneficial effects of this embodiment are: This method takes into account that the grid-connected new energy converter needs to be connected to a weaker power grid to achieve stable operation, and the grid impedance cannot be ignored, and thus its impact on the frequency coupling component cannot be ignored.

[0048] This method uses a grid-connected point disturbance signal injection method to achieve impedance measurement of the grid-connected system, and estimates the grid impedance through the collected impedance data; considering the influence of the grid impedance, the measured frequency-coupled sequence admittance coupling component is phase-corrected, thereby improving the measurement accuracy of the frequency-coupled sequence admittance of the grid-connected system of the grid-connected converter, which is beneficial to the accurate analysis of the stability of the grid-connected system of the grid-connected converter, thereby optimizing the system scheduling and operation strategy, improving the access capacity of renewable energy, and promoting the further development of new energy power generation technology.

[0049] Embodiment 2 like Figure 1 As shown, a method for measuring and correcting frequency-coupled sequence admittance of a grid-type converter system comprises the following steps: S1: Inject three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system several times to obtain output voltage and current response data.

[0050] In practical applications, MATLAB, Simulink or Python can be used to develop a frequency-coupled sequence admittance sweep program to measure and analyze the frequency response characteristics of renewable energy grid-connected power generation equipment.

[0051] Specifically, the frequency sweep procedure mainly includes the following steps: (1) According to the grid system architecture, a grid-connected converter system model is constructed, including a sequence impedance model considering frequency coupling.

[0052] (2) Injecting small disturbance signals: Inject small disturbance signals into the model. Generally, a sinusoidal signal is used as the disturbance signal, and the frequency varies within a certain range to ensure that the required frequency response range can be covered.

[0053] (3) Frequency sweep simulation: Sweep the frequency of the disturbance signal and record the system current and voltage response data at each frequency.

[0054] (4) Data processing and drawing: Using the frequency sweep results, draw the Bode diagram of the sequence impedance considering frequency coupling, where the horizontal axis is the frequency and the vertical axis is the amplitude and phase of the sequence impedance.

[0055] Figure 2 A grid-connected new energy converter system is provided by the method, wherein the PCC is a common coupling point between the new energy converter and the power grid. V dc is the DC side voltage, L f is the filter inductor, R d is the filter resistor, i abc are the three-phase currents A, B, and C sampled by PCC, vabc The PCC samples the three-phase voltages A, B, and C. C f is the filter capacitor, i gabc is the grid side current, L g is the grid side inductance, R g is the grid side resistance. Specifically, L g Set to 20mH, R g Set to 0.2Ω.

[0056] Figure 3 This is the grid-type converter control loop used in this method, where P ref Active power setpoint, Q ref is the reactive loop given value, P e is the instantaneous value of active power, Q e is the instantaneous value of reactive power, , D p is the active damping coefficient, J is the inertia coefficient, K is the reactive loop droop coefficient, V ref is the given value of the reactive loop voltage amplitude, V m is the given value of the single-phase voltage amplitude of the power grid, D q is the virtual coefficient of the reactive loop, θ GFM is the active loop output phase angle, E m is the output voltage amplitude of the reactive loop, and the synchronous modulation waves ma, mb, and mc can be expressed as: In the formula, K f =2 / V dc .

[0057] Specifically, step S1 includes: S11: Setting the fundamental frequency f1 and a frequency table containing several frequency points.

[0058] In practical applications, the frequency sweep program can be initialized and the fundamental frequency f1 can be set to 50 Hz; the frequency table contains 35 frequency points, which are set to [10, 12, 15, 18, 22, 27, 33, 40, 60, 72, 88, 107, 130, 158, 193, 235, 287, 349, 425, 518, 631, 769, 936, 1141, 1389, 1693, 2062, 2512, 3060, 3728, 4541, 5532, 6739, 8209, 10000].

[0059] In addition, the frequency sweep program also needs to set parameters such as communication port and measurement storage address.

[0060] When constructing a frequency sweep program, the frequency sweep cutoff frequency, i.e., the upper frequency limit of the frequency sweep, can also be set according to the actual grid characteristics. When executing the frequency sweep program, if a frequency point greater than or equal to the frequency sweep cutoff frequency is encountered, the frequency sweep program does not need to be executed.

[0061] When initializing the frequency sweep program, the frequency sweep cutoff frequency is preset.

[0062] When setting the frequency table, set the frequency point values ​​in the frequency table from small to large.

[0063] When traversing the frequency points in the frequency table, the frequency points are processed in order from small to large. When the frequency point is greater than or equal to the sweep cutoff frequency, the sweep measurement can be ended directly to reduce the amount of calculation.

[0064] S12: traverse the frequency points in the frequency table, and inject a three-phase voltage disturbance of a certain frequency value into the grid-connected converter system according to the frequency point value and the fundamental frequency, and obtain output voltage and current response data.

[0065] Specifically, there are two situations when the frequency sweep program is measured: 1. When the frequency point value fp<2f1, that is, fp<100Hz: (1) First, a positive-sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, and C1, and phases of 10, 240, and 120 are injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: (2) Then, a positive-sequence voltage disturbance with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10, 240, and 120, is injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: in, t 0' and t 0" represent the first sampling moment and the second sampling moment respectively; V is voltage, I is current; φ is phase angle.

[0066] 2. When the frequency point value fp ≥ 2f1, that is, fp ≥ 100Hz: (1) First, a positive sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, and C1, and phases of 0, 240, and 120 are injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: (2) Then, a negative sequence voltage disturbance with a frequency of fp-2f1, three-phase amplitudes of A2, B2, and C2, and phases of 0, 240, and 120 are injected into the grid-connected converter system. After the system stabilizes, the output voltage and current response data are obtained: S2: Obtain the frequency-coupled sequence admittance measurement results based on the voltage and current response data.

[0067] Admittance is a general term for conductance and susceptance, and is used to describe the ease with which alternating current passes through a circuit or system. Admittance is the reciprocal of impedance, with the symbol Y and the unit being Siemens (S). Admittance is a complex number consisting of a real part (conductance) and an imaginary part (susceptance).

[0068] When calculating the sequence admittance results of the frequency coupling of the grid-type converter system, the sequence admittance measurement results include: sequence admittance component Y11 , Y 12 , Y 21 , Y 22 , the calculation formula is as follows: S3: Obtain the compensation factor of phase correction according to the system characteristics of the grid-connected converter and the voltage and current response data.

[0069] Step S3 includes: (1) Estimate the grid impedance based on the voltage and current response data.

[0070] Assuming that n frequency disturbances are injected, that is, n-order admittance measurements are performed, the estimated grid impedance Zg can be expressed as: In the formula, V pi ' and I gpi ' are respectively the positive sequence voltage and positive sequence current measured after the i-th disturbance injection in step S2, f pi is the frequency of the disturbance source injected for the i-th time.

[0071] (2) According to the grid impedance, the adjustment coefficient is introduced and the compensation factor of phase correction is calculated.

[0072] Figure 4 This is an equivalent schematic diagram of the frequency coupling of the renewable energy grid-connected system. The system injects a disturbance source V p ( f p ) after the converter control loop generates two response excitations e '( f p )and e '( f p -2 f 1) Under the action of two response excitations, coupled excitations are generated respectively e "( f p -2 f 1) and e "( f p). Therefore, the current components with disturbance frequencies of fp and fp-2f1 collected in the actual process include not only the current components generated by the response excitation on the converter impedance and the grid impedance, but also the current components under the coupling response excitation. In this process, the influence of the grid impedance on the phase of the coupled components, especially the current components, cannot be ignored. The coupled current components include the corresponding grid impedance influence. From engineering experience, it can be obtained that the impedance of the converter in the high frequency band is much larger than the grid impedance. Therefore, the influence of the grid on the converter is mainly reflected in the low frequency band. Taking the voltage component as the reference quantity, this method converts the influence of the coupled component into the phase of the coupled current component, and introduces the compensation factor λ to realize the phase correction of the frequency coupling measurement sequence admittance.

[0073] The calculation formula of the compensation factor λ is: In the formula, Z GFM ( f p ) = ; α is the adjustment coefficient, and its value range is 0.6~1; is the grid impedance angle; angle ( ) represents the phase of the vector in brackets; | | represents the magnitude of the vector modulus.

[0074] S4: Use the compensation factor to perform phase correction on the sequence admittance measurement result to obtain the optimized sequence admittance result.

[0075] Specifically, the result after sequence admittance phase correction is expressed as follows: Preferably, the method further comprises: S5: Plot the sequence admittance measurement results and the optimized sequence admittance results into a curve to compare the effects before and after phase correction.

[0076] The method is used to measure the grid-connected system of the grid-connected new energy converter mentioned above, and the obtained frequency coupling sequence admittance results are plotted into a curve. The curve without adding phase correction is shown as follows: Figure 5 As shown in the figure, the curve after adding phase correction is as follows Figure 6 shown.

[0077] Figure 5 and Figure 6 In the figure, the solid line represents the frequency-coupled sequence admittance curve of the grid-connected new energy converter derived theoretically. The formula of the complex frequency domain of the curve is as follows: In the formula, N, M, T, W, N l 、Ml 、T l , W l The expression is as follows: Where V1=V1 * = V 1 / 2; I1=( I 1 / 2)e ±jφi1 ;I1 * =( I 1 / 2)e ∓jφi1 ; V 1= V ref ; I 1= P ref / (1.5* V ref ); φ i1 is the phase of the fundamental current, and its value is obtained by simulation measurement; s 1=2π f p , s 2=2π f p -4π f 1, s 0=2π f p -2π f 1; PWM modulation coefficient K pwm =0.5; T ( s )=1 / s*( J * s + D p ); Delay function G del ( s )=e -1.5Tss , T s is the sampling time step; s is the Laplace operator; j is the imaginary unit of a complex number; D q is the damping coefficient of the reactive loop.

[0078] Figure 5 and Figure 6 In the figure, the “*” part indicates the order admittance value at the disturbance frequency fp and fp-2f1 measured by the frequency sweep procedure. Figure 5 It can be seen that the coupling component Y of the mesh-type frequency coupling order admittance without phase correction is 12 and Y21 The phase measurement value and the value of the theoretical curve have a large error when the frequency f<100Hz. Under the same simulation conditions, the measured value of the network-type frequency coupling sequence admittance after adding phase correction is as follows: Figure 6 As shown in Figure 3, the measured values ​​are highly consistent with the theoretical values, which verifies the effectiveness of this method.

[0079] The beneficial effect of this embodiment is that: this method also presets the sweep cutoff frequency, sets the frequency point values ​​in the frequency table in sequence from small to large, and when traversing the frequency points in the frequency table, processes the frequency points in sequence from small to large. When the frequency point is greater than or equal to the sweep cutoff frequency, the sweep program can be directly ended, thereby reducing the amount of calculation.

[0080] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the art within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for measuring and correcting frequency-coupled sequence admittance of a grid-type converter system, characterized in that: The following steps are involved: Injecting three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system several times to obtain output voltage and current response data; Obtain frequency-coupled sequence admittance measurement results based on voltage and current response data; Obtain the compensation factor of phase correction according to the system characteristics of the grid-type converter and the voltage and current response data; The compensation factor is used to perform phase correction on the sequence admittance measurement results to obtain the optimized sequence admittance results.

2. The method for measuring and correcting the frequency-coupled sequence admittance of a grid-connected converter system according to claim 1, characterized in that: The step of injecting a plurality of three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system to obtain output voltage and current response data includes: Set the fundamental frequency f1 and a frequency table containing several frequency points; The frequency points in the frequency table are traversed, and according to the frequency point values ​​and the fundamental frequency, a three-phase voltage disturbance with a certain frequency value is injected into the grid-type converter system to obtain the output voltage and current response data.

3. The method for measuring and correcting the frequency-coupled sequence admittance of a grid-connected converter system according to claim 2, characterized in that: The setting of the fundamental frequency f1 and the frequency table containing a plurality of frequency points also includes: The frequency point values ​​in the frequency table are set from small to large.

4. The method for measuring and correcting the frequency-coupled sequence admittance of a grid-connected converter system according to claim 3, characterized in that: The step of injecting a plurality of three-phase voltage disturbances of different frequency values ​​into the grid-connected converter system to obtain output voltage and current response data further includes: Preset cutoff frequency; When traversing the frequency points in the frequency table, when the frequency point is greater than or equal to the sweep cutoff frequency, the measurement ends.

5. The method for measuring and correcting the frequency-coupled sequence admittance of a grid-type converter system according to claim 2, characterized in that: The step of injecting a three-phase voltage disturbance of a certain frequency value into the grid-connected converter system according to the frequency point value and the fundamental frequency to obtain the output voltage and current response data includes: When the frequency point value fp<2f1, first inject a positive sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, C1, and phases of 10, 240, and 120 into the grid-type converter system. After the system is stable, obtain the output voltage and current response data. Then, a positive-sequence voltage disturbance with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10, 240, and 120 respectively, is injected into the grid-connected converter system. After the system is stable, the output voltage and current response data are obtained.

6. The method for measuring and correcting the frequency-coupled sequence admittance of a grid-connected converter system according to claim 2, characterized in that: The step of injecting a three-phase voltage disturbance of a certain frequency value into the grid-type converter system according to the frequency point value and obtaining the output voltage and current response data comprises: When the frequency point value fp≥2f1, first inject a positive sequence voltage disturbance with a frequency of fp, three-phase amplitudes of A1, B1, C1, and phases of 0, 240, and 120 into the grid-connected converter system. After the system is stable, obtain the output voltage and current response data. Then, a negative-sequence voltage disturbance with a frequency of fp-2f1, three-phase amplitudes of A2, B2, and C2, and phases of 0, 240, and 120 are injected into the grid-connected converter system. After the system is stable, the output voltage and current response data are obtained.

7. The method for measuring and correcting frequency-coupled sequence admittance of a grid-connected converter system according to claim 2, characterized in that: The fundamental frequency f1 is set to 50 Hz.

8. The method for measuring and correcting frequency-coupled sequence admittance of a grid-connected converter system according to claim 1, characterized in that: The method of obtaining the compensation factor for phase correction according to the grid-type converter system characteristics and voltage and current response data includes: Estimate grid impedance based on voltage and current response data; According to the grid impedance, the adjustment coefficient is introduced and the compensation factor of phase correction is calculated.

9. The method for measuring and correcting frequency-coupled sequence admittance of a grid-connected converter system according to claim 1, characterized in that: The sequence admittance measurement result includes: sequence admittance component Y 11 , Y 12 , Y 21 , Y 22 .

10. The method for measuring and correcting frequency-coupled sequence admittance of a grid-connected converter system according to claim 1, characterized in that: The method for measuring and correcting the frequency-coupled sequence admittance of the grid-type converter system also includes: The sequence admittance measurement results and the optimized sequence admittance results are plotted into curves to compare the effects before and after phase correction.

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