Measurement and correction method for frequency-coupled sequence admittance of grid-forming converter system

Abstract

Disclosed in the present invention is a measurement and correction method for the frequency-coupled sequence admittance of a grid-forming converter system. The method comprises: injecting several three-phase voltage perturbations having different frequency values into a grid-forming converter system, and acquiring outputted voltage and current response data; on the basis of the voltage and current response data, acquiring a frequency-coupled sequence admittance measurement result; acquiring a compensation factor for phase correction; and using the compensation factor to perform phase correction, so as to obtain an optimized sequence admittance result. In the technical solution provided by the present invention, the impedance measurement of a grid-connected system is realized by means of injecting perturbation signals at a point of common coupling, and grid impedance is estimated by means of collected impedance data; and phase correction is performed on coupled components of measured frequency-coupled sequence admittance by means of taking into account the effect of the grid impedance, thereby improving the measurement accuracy of the frequency-coupled sequence admittance of a grid-connected grid-forming converter system, facilitating accurate analysis of the stability of the grid-connected grid-forming converter system, and thus optimizing system scheduling and operation strategies.

Description

A method for measuring and correcting the frequency coupling sequence admittance of a grid converter system Technical Field

[0001] This invention relates to the field of frequency coupled sequence admittance measurement, and more particularly to a method for measuring and correcting the frequency coupled sequence admittance of a grid-type converter system. Background Technology

[0002] In the context of the current global energy transition, new energy power generation equipment, such as wind and solar power, is increasingly becoming an important component of achieving sustainable development. Because these power electronic devices employ asymmetrical control structures, they often face frequency coupling problems during grid-connected operation, which can lead to decreased system stability and reduced power quality. Frequency coupling 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 grid-connected new energy power generation equipment, the modeling, measurement, and analysis of frequency coupling sequence admittance are of great significance for ensuring the stable operation of the power grid.

[0003] Traditional measurement methods often neglect the influence of grid impedance on the phase of the coupled sequence admittance component current in weak grid environments, thus affecting measurement accuracy. Grid-connected renewable energy power generation equipment, due to its unique structure and operating characteristics, is even more sensitive to frequency coupling, further impacting the overall safety and reliability of the power system. Since the grid impedance cannot be ignored in power systems connected to grid-connected converters, a new measurement and correction method is needed for frequency coupled sequence admittance in grid-connected converter systems to meet the required measurement accuracy. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the current technology, the present invention provides a method for measuring and correcting the frequency coupling sequence admittance of a grid-connected converter system. By using the frequency coupling sequence admittance component phase correction method, the method realizes the accurate measurement of the frequency coupling sequence admittance of the grid-connected converter, which is beneficial to the accurate analysis of the stability of the grid-connected converter system.

[0005] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0006] Inject three-phase voltage disturbances of different frequencies into the grid-type converter system several times and obtain the output voltage and current response data;

[0007] Based on the voltage and current response data, obtain the frequency-coupled sequence admittance measurement results;

[0008] Based on the characteristics of the grid-type converter system and voltage and current response data, the compensation factor for phase correction is obtained;

[0009] The ordered admittance measurement results are phase-corrected using a compensation factor to obtain optimized ordered admittance results.

[0010] According to one aspect of the present invention, the method of injecting three-phase voltage disturbances of different frequencies into a grid-type converter system several times and obtaining output voltage and current response data includes:

[0011] Set the fundamental frequency f1 and a frequency table containing several frequency points;

[0012] The frequency points in the frequency table are traversed, and a three-phase voltage disturbance of a certain frequency value is injected into the grid-type converter system according to the frequency point value and the fundamental frequency to obtain the output voltage and current response data.

[0013] According to one aspect of the present invention, the setting of the fundamental frequency f1 and the frequency table containing a plurality of frequency points further includes:

[0014] The frequency values ​​in the frequency table are set sequentially from smallest to largest.

[0015] According to one aspect of the present invention, the method of injecting three-phase voltage disturbances of different frequencies into the grid-type converter system several times and obtaining the output voltage and current response data further includes:

[0016] Preset cutoff frequency;

[0017] When traversing the frequency points in the frequency table, the measurement ends when the frequency point is greater than or equal to the sweep cutoff frequency.

[0018] According to one aspect of the present invention, the step of injecting a three-phase voltage disturbance of a certain frequency value into the grid-type converter system based on the frequency point value and the fundamental frequency, and obtaining the output voltage and current response data, includes:

[0019] When the frequency point value fp < 2f1, a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, and C1, and phases of 10, 240, and 120 is first injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained.

[0020] Then, positive-sequence voltage disturbances with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10°, 24°, and 12° are injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained.

[0021] According to one aspect of the present invention, the step of injecting a three-phase voltage disturbance of a certain frequency value into the grid-type converter system based on the frequency point value, and obtaining the output voltage and current response data includes:

[0022] When the frequency point value fp≥2f1, first inject a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, C1, and phases of 0, 240, and 120 into the grid-type converter system. After the system stabilizes, obtain the output voltage and current response data.

[0023] 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 degrees is injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained.

[0024] According to one aspect of the invention, the fundamental frequency f1 is set to 50 Hz.

[0025] According to one aspect of the present invention, obtaining the phase correction compensation factor based on the characteristics of the grid-type converter system and voltage and current response data includes:

[0026] Estimate the grid impedance based on voltage and current response data;

[0027] Based on the grid impedance, an adjustment coefficient is introduced, and the compensation factor for phase correction is calculated.

[0028] 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 .

[0029] According to one aspect of the present invention, the method for measuring and correcting the frequency coupling sequence admittance of the grid-type converter system further includes:

[0030] The sequence admittance measurement results and the optimized sequence admittance results are plotted as curves to compare the effects before and after phase correction.

[0031] Advantages of implementing this invention:

[0032] This invention provides a method for measuring and correcting the frequency coupling sequence admittance of a grid-connected converter system. It employs a grid connection point disturbance signal injection method to measure the impedance of the grid-connected system, and estimates the grid impedance using the collected impedance data. Considering the influence of grid impedance, the method performs phase correction on the coupled component of the measured frequency coupling sequence admittance, thereby improving the measurement accuracy of the frequency coupling sequence admittance of the grid-connected converter system. This facilitates accurate analysis of the stability of the grid-connected converter system, thereby optimizing system scheduling and operation strategies and improving the accessibility of renewable energy. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 is a flowchart of a method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system according to the present invention;

[0035] Figure 2 shows a new energy converter grid connection system according to the present invention;

[0036] Figure 3 shows a grid-type converter control loop according to the present invention;

[0037] Figure 4 is an equivalent schematic diagram of frequency coupling in the new energy grid-connected system described in this invention;

[0038] Figure 5 shows the frequency coupling sequence admittance curve without phase correction as described in this invention;

[0039] Figure 6 shows the frequency coupling sequence admittance curve with phase correction as described in this invention. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Example 1

[0042] As shown in Figure 1, a method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system includes the following steps:

[0043] S1: Inject three-phase voltage disturbances of different frequencies into the grid-type converter system several times and obtain the output voltage and current response data.

[0044] In practical applications, frequency-coupled sequence admittance sweep programs can be developed using MATLAB, Simulink, or Python to measure and analyze the frequency response characteristics of grid-connected power generation equipment for new energy sources.

[0045] Specifically, the frequency scanning procedure mainly includes the following steps:

[0046] (1) Based on the power grid system architecture, build a grid-type converter system model, including a sequence impedance model that considers frequency coupling.

[0047] (2) Inject small perturbation signals: Inject small perturbation signals into the model. Generally, a sine signal is used as the perturbation signal, and the frequency varies within a certain range to ensure that the required frequency response range can be covered.

[0048] (3) Frequency sweep simulation: Sweep the frequency of the disturbance signal and record the system current and voltage response data at each frequency.

[0049] (4) Data processing and plotting: Using the frequency sweep results, plot the Bode plot of the sequence impedance considering frequency coupling, where the horizontal axis is the frequency and the vertical axis is the magnitude and phase of the sequence impedance.

[0050] Figure 2 shows a grid-connected renewable energy converter system provided by this method, where PCC is the common coupling point between the renewable energy converter and the power grid, and V dc L is the DC side voltage. f For the filter inductor, R d For the filter resistor, i abc The three-phase currents A, B, and C sampled by the PCC, v abc The PCC samples the three-phase voltages A, B, and C. f For the filter capacitor, i gabc L is the grid-side current. g R is the grid-side inductance. g This refers to the grid-side resistance. Specifically, L can be... g Set to 20mH, R g Set to 0.2Ω.

[0051] Figure 3 shows the control loop of the grid-type converter used in this method, where P ref Active power setpoint, Q ref P is the given value for the reactive power loop. e Q is the instantaneous value of active power. e This is the instantaneous value of reactive power. D p Where is the active power damping coefficient, J is the inertia coefficient, K is the reactive power droop coefficient, and V is the reactive power droop coefficient. ref V is the setpoint for the reactive power loop voltage amplitude. m D is the given value for the single-phase voltage amplitude of the power grid. q For the reactive power loop virtual coefficient, θ GFM E is the output phase angle of the active power loop. m Given the output voltage amplitude of the reactive power loop, the synchronous modulation waves ma, mb, and mc can be expressed as:

[0052]

[0053] In the formula, K f =2 / V dc .

[0054] Specifically, step S1 includes:

[0055] S11: Set the fundamental frequency f1 and a frequency table containing several frequency points.

[0056] In practical applications, the frequency sweep program can be initialized by setting the fundamental frequency f1 to 50Hz; the frequency table contains 35 frequency points, which are set as [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].

[0057] In addition, the frequency sweeping program also needs to set parameters such as communication port and measurement storage address.

[0058] S12: Traverse the frequency points in the frequency table, and inject a three-phase voltage disturbance of a certain frequency value into the grid-type converter system according to the frequency point value and the fundamental frequency, and obtain the output voltage and current response data.

[0059] Specifically, the frequency sweep measurement process is divided into two cases:

[0060] 1. When the frequency value fp < 2f1, i.e., fp < 100Hz:

[0061] (1) First, inject a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, and C1, and phases of 10°, 24°, and 12° into the grid-type converter system. After the system stabilizes, obtain the output voltage and current response data:

[0062]

[0063]

[0064]

[0065]

[0066] (2) Then, positive sequence voltage disturbances with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10°, 24°, and 12° are injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained:

[0067]

[0068]

[0069]

[0070]

[0071] Where t0' and t0" represent the times of the first and second sampling, respectively; V is voltage, I is current, and φ is phase angle.

[0072] 2. When the frequency value fp ≥ 2f1, that is, when fp ≥ 100Hz:

[0073] (1) First, inject a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, and C1, and phases of 0, 240, and 120 degrees respectively into the grid-type converter system. After the system stabilizes, obtain the output voltage and current response data:

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] (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 degrees is injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained:

[0080]

[0081]

[0082]

[0083]

[0084] S2: Obtain the frequency-coupled sequence admittance measurement results based on the voltage and current response data.

[0085] Admittance is a general term for conductance and susceptance, used to describe the ease with which alternating current flows through a circuit or system. Admittance is the reciprocal of impedance, denoted by Y, and its unit is Siemens (S). Admittance is a complex number consisting of a real part (conductance) and an imaginary part (susceptance).

[0086] When calculating the sequence admittance of frequency coupling in a grid-type converter system, the sequence admittance measurement results include: the sequence admittance component Y. 11 Y 12 Y 21 Y 22 The calculation formula is as follows:

[0087]

[0088] S3: Obtain the phase correction compensation factor based on the characteristics of the grid-type converter system and the voltage and current response data.

[0089] Step S3 includes:

[0090] (1) Estimate the grid impedance based on the voltage and current response data.

[0091] Assuming a total of n frequency disturbances are injected, i.e., n sequence admittance measurements are performed, the estimated grid impedance Zg can be expressed as:

[0092]

[0093] In the formula, V pi ' and I gpi ' These are the positive sequence voltage and positive sequence current measured after the i-th injection of perturbation in step S2, respectively, f pi Let be the frequency of the disturbance source injected for the i-th time.

[0094] (2) Based on the grid impedance, an adjustment coefficient is introduced to calculate the compensation factor for phase correction.

[0095] Figure 4 is an equivalent schematic diagram of frequency coupling in a new energy grid-connected system, with the system injected with disturbance source V. p (f p After that, two types of response excitation e'(f) will be generated through the converter control loop. p ) and e'(f p -2f1), under the action of two response excitations, respectively generate coupled excitation e"(f p -2f1) and e"(f pTherefore, the disturbance frequencies collected in the actual process are the current components at frequency fp and fp-2f1, which include both the current components generated by the response excitation on the converter impedance and grid impedance, and the current components under the coupled response excitation. In this process, the influence of 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. Engineering experience shows that the converter impedance at high frequencies is much greater than the grid impedance; therefore, the grid's influence on the converter is mainly reflected in the low-frequency range. Using the voltage component as a reference, this method reduces the influence of the coupled components to the phase of the coupled current components and introduces a compensation factor λ to achieve phase correction of the sequence admittance in frequency coupling measurements.

[0096] The formula for calculating the compensation factor λ is:

[0097]

[0098] In the formula, Z GFM (f p ) = / α is an adjustment coefficient, with a value ranging from 0.6 to 1; is the power grid impedance angle; angle() represents the phase of the vector within the brackets; || represents the magnitude of the vector.

[0099] S4: Use a compensation factor to perform phase correction on the ordered admittance measurement results to obtain optimized ordered admittance results.

[0100] Specifically, the result after phase correction of the sequential admittance is expressed as follows:

[0101]

[0102] Preferably, the method further includes:

[0103] S5: Plot the sequence admittance measurement results and the optimized sequence admittance results as curves to compare the effects before and after phase correction.

[0104] The method described above was used to measure the grid-connected system of the grid-type new energy converter. The obtained frequency coupling sequence admittance results were plotted as curves. The curve without phase correction is shown in Figure 5, and the curve with phase correction is shown in Figure 6.

[0105] In Figures 5 and 6, the solid line represents the frequency coupling sequence admittance curve of the grid-type new energy converter derived theoretically. The formula for the curve in the complex frequency domain is as follows:

[0106]

[0107] In the formula, N, M, T, W, Nl M l T l W l The expression is as follows:

[0108]

[0109] In the formula, V1=V1 * =V1 / 2;I1=(I1 / 2)e ±jφi1 ;I1 * =(I1 / 2)e ∓jφi1 V1=V ref I1=P ref / (1.5*V ref );φ i1 The phase of the fundamental current is s1, whose value is obtained from simulation measurements; s1 = 2πf p s2=2πf p -4πf1, s0=2πf p -2πf1; 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 the complex number; D q It is the reactive power ring damping coefficient.

[0110] In Figures 5 and 6, the "*" marks represent the sequence admittance values ​​at the perturbation frequencies fp and fp-2f1 measured using a frequency sweep procedure. Figure 5 shows the coupling component Y of the mesh-type frequency-coupled sequence admittance without phase correction. 12 and Y 21 The measured phase values ​​and the theoretical curve values ​​show significant errors when the frequency f < 100Hz. However, under the same simulation conditions, the measured values ​​of the mesh-type frequency coupling sequence admittance after phase correction, as shown in Figure 6, are in high agreement with the theoretical values, verifying the effectiveness of this method.

[0111] The beneficial effects of this embodiment are as follows:

[0112] This method takes into account that grid-connected new energy converters need to be connected to a relatively weak power grid to achieve stable operation, and the grid impedance cannot be ignored, thus its impact on frequency coupling components cannot be ignored.

[0113] This method uses grid-connected point disturbance signal injection to measure the impedance of the grid-connected system, and estimates the grid impedance using the collected impedance data. Considering the influence of grid impedance, the measured frequency coupling sequence admittance coupling component is phase-corrected, thereby improving the measurement accuracy of the frequency coupling sequence admittance of the grid-connected system of the grid-connected converter. This is beneficial for the accurate analysis of the stability of the grid-connected system of the grid-connected converter, thereby optimizing system scheduling and operation strategies, improving the access capability of renewable energy, and promoting the further development of new energy power generation technology.

[0114] Example 2

[0115] As shown in Figure 1, a method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system includes the following steps:

[0116] S1: Inject three-phase voltage disturbances of different frequencies into the grid-type converter system several times and obtain the output voltage and current response data.

[0117] In practical applications, frequency-coupled sequence admittance sweep programs can be developed using MATLAB, Simulink, or Python to measure and analyze the frequency response characteristics of grid-connected power generation equipment for new energy sources.

[0118] Specifically, the frequency scanning procedure mainly includes the following steps:

[0119] (1) Based on the power grid system architecture, build a grid-type converter system model, including a sequence impedance model that considers frequency coupling.

[0120] (2) Inject small perturbation signals: Inject small perturbation signals into the model. Generally, a sine signal is used as the perturbation signal, and the frequency varies within a certain range to ensure that the required frequency response range can be covered.

[0121] (3) Frequency sweep simulation: Sweep the frequency of the disturbance signal and record the system current and voltage response data at each frequency.

[0122] (4) Data processing and plotting: Using the frequency sweep results, plot the Bode plot of the sequence impedance considering frequency coupling, where the horizontal axis is the frequency and the vertical axis is the magnitude and phase of the sequence impedance.

[0123] Figure 2 shows a grid-connected renewable energy converter system provided by this method, where PCC is the common coupling point between the renewable energy converter and the power grid, and V dc L is the DC side voltage. f For the filter inductor, R d For the filter resistor, i abc The three-phase currents A, B, and C sampled by the PCC, v abc The PCC samples the three-phase voltages A, B, and C. fFor the filter capacitor, i gabc L is the grid-side current. g R is the grid-side inductance. g This refers to the grid-side resistance. Specifically, L can be... g Set to 20mH, R g Set to 0.2Ω.

[0124] Figure 3 shows the control loop of the grid-type converter used in this method, where P ref Active power setpoint, Q ref P is the given value for the reactive power loop. e Q is the instantaneous value of active power. e This is the instantaneous value of reactive power. D p Where is the active power damping coefficient, J is the inertia coefficient, K is the reactive power droop coefficient, and V is the reactive power droop coefficient. ref V is the setpoint for the reactive power loop voltage amplitude. m D is the given value for the single-phase voltage amplitude of the power grid. q For the reactive power loop virtual coefficient, θ GFM E is the output phase angle of the active power loop. m Given the output voltage amplitude of the reactive power loop, the synchronous modulation waves ma, mb, and mc can be expressed as:

[0125]

[0126] In the formula, K f =2 / V dc .

[0127] Specifically, step S1 includes:

[0128] S11: Set the fundamental frequency f1 and a frequency table containing several frequency points.

[0129] In practical applications, the frequency sweep program can be initialized by setting the fundamental frequency f1 to 50Hz; the frequency table contains 35 frequency points, which are set as [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].

[0130] In addition, the frequency sweeping program also needs to set parameters such as communication port and measurement storage address.

[0131] When constructing a frequency sweep program, the sweep cutoff frequency, i.e., the upper limit frequency of the sweep, can be set according to the actual power grid characteristics. When the frequency sweep program is executed, if a frequency point greater than or equal to the sweep cutoff frequency is encountered, the frequency sweep program does not need to be executed again.

[0132] When initializing the frequency sweep program, the frequency sweep cutoff frequency is preset.

[0133] When setting up the frequency table, set the frequency points in the table from smallest to largest in sequence.

[0134] When traversing the frequency points in the frequency table, the frequency points are processed in ascending order. 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.

[0135] S12: Traverse the frequency points in the frequency table, and inject a three-phase voltage disturbance of a certain frequency value into the grid-type converter system according to the frequency point value and the fundamental frequency, and obtain the output voltage and current response data.

[0136] Specifically, the frequency sweep measurement process is divided into two cases:

[0137] 1. When the frequency value fp < 2f1, i.e., fp < 100Hz:

[0138] (1) First, inject a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, and C1, and phases of 10°, 24°, and 12° into the grid-type converter system. After the system stabilizes, obtain the output voltage and current response data:

[0139]

[0140]

[0141]

[0142]

[0143] (2) Then, positive sequence voltage disturbances with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10°, 24°, and 12° are injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained:

[0144]

[0145]

[0146]

[0147]

[0148] Where t0' and t0" represent the times of the first and second sampling, respectively; V is voltage, I is current, and φ is phase angle.

[0149] 2. When the frequency value fp ≥ 2f1, that is, when fp ≥ 100Hz:

[0150] (1) First, inject a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, and C1, and phases of 0, 240, and 120 degrees respectively into the grid-type converter system. After the system stabilizes, obtain the output voltage and current response data:

[0151]

[0152]

[0153]

[0154]

[0155]

[0156] (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 degrees is injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained:

[0157]

[0158]

[0159]

[0160]

[0161] S2: Obtain the frequency-coupled sequence admittance measurement results based on the voltage and current response data.

[0162] Admittance is a general term for conductance and susceptance, used to describe the ease with which alternating current flows through a circuit or system. Admittance is the reciprocal of impedance, denoted by Y, and its unit is Siemens (S). Admittance is a complex number consisting of a real part (conductance) and an imaginary part (susceptance).

[0163] When calculating the sequence admittance of frequency coupling in a grid-type converter system, the sequence admittance measurement results include: the sequence admittance component Y. 11 Y 12 Y 21Y 22 The calculation formula is as follows:

[0164]

[0165] S3: Obtain the phase correction compensation factor based on the characteristics of the grid-type converter system and the voltage and current response data.

[0166] Step S3 includes:

[0167] (1) Estimate the grid impedance based on the voltage and current response data.

[0168] Assuming a total of n frequency disturbances are injected, i.e., n sequence admittance measurements are performed, the estimated grid impedance Zg can be expressed as:

[0169]

[0170] In the formula, V pi ' and I gpi ' These are the positive sequence voltage and positive sequence current measured after the i-th injection of perturbation in step S2, respectively, f pi Let be the frequency of the disturbance source injected for the i-th time.

[0171] (2) Based on the grid impedance, an adjustment coefficient is introduced to calculate the compensation factor for phase correction.

[0172] Figure 4 is an equivalent schematic diagram of frequency coupling in a new energy grid-connected system, with the system injected with disturbance source V. p (f p After that, two types of response excitation e'(f) will be generated through the converter control loop. p ) and e'(f p -2f1), under the action of two response excitations, respectively generate coupled excitation e"(f p -2f1) and e"(f p Therefore, the disturbance frequencies collected in the actual process are the current components at frequency fp and fp-2f1, which include both the current components generated by the response excitation on the converter impedance and grid impedance, and the current components under the coupled response excitation. In this process, the influence of 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. Engineering experience shows that the converter impedance at high frequencies is much greater than the grid impedance; therefore, the grid's influence on the converter is mainly reflected in the low-frequency range. Using the voltage component as a reference, this method reduces the influence of the coupled components to the phase of the coupled current components and introduces a compensation factor λ to achieve phase correction of the sequence admittance in frequency coupling measurements.

[0173] The formula for calculating the compensation factor λ is:

[0174]

[0175] In the formula, Z GFM (f p ) = / α is an adjustment coefficient, with a value ranging from 0.6 to 1; is the power grid impedance angle; angle() represents the phase of the vector within the brackets; || represents the magnitude of the vector.

[0176] S4: Use a compensation factor to perform phase correction on the ordered admittance measurement results to obtain optimized ordered admittance results.

[0177] Specifically, the result after phase correction of the sequential admittance is expressed as follows:

[0178]

[0179] Preferably, the method further includes:

[0180] S5: Plot the sequence admittance measurement results and the optimized sequence admittance results as curves to compare the effects before and after phase correction.

[0181] The method described above was used to measure the grid-connected system of the grid-type new energy converter. The obtained frequency coupling sequence admittance results were plotted as curves. The curve without phase correction is shown in Figure 5, and the curve with phase correction is shown in Figure 6.

[0182] In Figures 5 and 6, the solid line represents the frequency coupling sequence admittance curve of the grid-type new energy converter derived theoretically. The formula for the curve in the complex frequency domain is as follows:

[0183]

[0184] In the formula, N, M, T, W, N l M l T l W l The expression is as follows:

[0185]

[0186] In the formula, V1=V1 * =V1 / 2;I1=(I1 / 2)e ±jφi1 ;I1 * =(I1 / 2)e ∓jφi1 V1=V ref I1=P ref / (1.5*V ref );φ i1The phase of the fundamental current is s1, whose value is obtained from simulation measurements; s1 = 2πf p s2=2πf p -4πf1, s0=2πf p -2πf1; 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 the complex number; D q It is the reactive power ring damping coefficient.

[0187] In Figures 5 and 6, the "*" marks represent the sequence admittance values ​​at the perturbation frequencies fp and fp-2f1 measured using a frequency sweep procedure. Figure 5 shows the coupling component Y of the mesh-type frequency-coupled sequence admittance without phase correction. 12 and Y 21 The measured phase values ​​and the theoretical curve values ​​show significant errors when the frequency f < 100Hz. However, under the same simulation conditions, the measured values ​​of the mesh-type frequency coupling sequence admittance after phase correction, as shown in Figure 6, are in high agreement with the theoretical values, verifying the effectiveness of this method.

[0188] The beneficial effects of this embodiment are as follows: This method also presets the sweep cutoff frequency, sets the frequency point values ​​in the frequency table from small to large in sequence, and processes the frequency points from small to large in sequence when traversing the frequency points in the frequency table. When the frequency point is greater than or equal to the sweep cutoff frequency, the sweep program can be terminated directly, thereby reducing the amount of calculation.

[0189] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system, characterized in that, Includes the following steps: Inject three-phase voltage disturbances of different frequencies into the grid-type converter system several times and obtain the output voltage and current response data; Based on the voltage and current response data, obtain the frequency-coupled sequence admittance measurement results; Based on the characteristics of the grid-type converter system and voltage and current response data, the compensation factor for phase correction is obtained; The ordered admittance measurement results are phase-corrected using a compensation factor to obtain optimized ordered admittance results.

2. The method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system according to claim 1, characterized in that, The process of injecting three-phase voltage disturbances of different frequencies into the grid-type converter system and obtaining the 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 a three-phase voltage disturbance of a certain frequency value is injected into the grid-type converter system according to the frequency point value and the fundamental frequency to obtain the output voltage and current response data.

3. The method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system according to claim 2, characterized in that, The setting of the fundamental frequency f1 and the frequency table containing several frequency points also includes: The frequency values ​​in the frequency table are set sequentially from smallest to largest.

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

5. The method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system according to claim 2, characterized in that, The process of injecting a three-phase voltage disturbance of a certain frequency value into the grid-type converter system based on the frequency point value and the fundamental frequency, and obtaining the output voltage and current response data includes: When the frequency point value fp < 2f1, a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, and C1, and phases of 10, 240, and 120 is first injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained. Then, positive-sequence voltage disturbances with a frequency of 2f1-fp, three-phase amplitudes of A2, B2, and C2, and phases of 10°, 24°, and 12° are injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained.

6. The method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system according to claim 2, characterized in that, The process of injecting a three-phase voltage disturbance of a certain frequency value into the grid-type converter system based on the frequency point value, and obtaining the output voltage and current response data includes: When the frequency point value fp≥2f1, first inject a positive sequence voltage disturbance with frequency fp, three-phase amplitudes A1, B1, C1, and phases of 0, 240, and 120 into the grid-type converter system. After the system stabilizes, 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 degrees is injected into the grid-type converter system. After the system stabilizes, the output voltage and current response data are obtained.

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

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

9. The method for measuring and correcting the frequency coupling sequence admittance of a grid-type converter system according to claim 1, characterized in that, The sequence admittance measurement results include: sequence admittance component Y. 11 Y 12 Y 21 Y 22 .

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

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