Methods for measuring converter impedance to overcome nonlinear effects

Abstract

This invention provides a converter impedance measurement method that overcomes the influence of nonlinearity. By injecting voltage disturbance signals of different frequencies and amplitudes multiple times, the impedance is determined based on the voltage and current responses of the voltage disturbance signals. The method also takes into account the voltage and current responses caused by circuit disturbances, which can effectively avoid the influence of nonlinear behavior in the process of determining the impedance group of the converter under test, ensure the final measurement accuracy, and provide accurate data reference for subsequent impedance stability analysis and the formulation of impedance stabilization strategies.

Description

Technical Field

[0001] This invention relates to a method for measuring the impedance of power equipment, and more particularly to a method for measuring the impedance of a converter that overcomes the effects of nonlinearity. Background Technology

[0002] Converters are widely used in new energy grid connection scenarios. When new energy converters from different manufacturers operate together, instability may occur, manifesting as non-characteristic subharmonics in the voltage and current waveforms of the converter output. In severe cases, this can lead to the shutdown of new energy units and the shutdown of new energy power plants.

[0003] Impedance stability analysis can be used to analyze such unstable phenomena and guide the determination of stable control strategies. However, the prerequisite for impedance stability analysis is obtaining the impedance of the converter equipment. In the existing technology, the converter impedance can be obtained through two methods: impedance measurement and mathematical modeling. Since mathematical modeling requires a complete understanding of the internal control structure and control parameters of the converter, and manufacturers do not disclose such information due to trade secret considerations, the accuracy of mathematical modeling is extremely low and difficult to apply in practice. Impedance measurement requires injecting a disturbance signal into the converter under test, obtaining the corresponding voltage and current responses, and then determining the impedance of the converter under test by the ratio of voltage and current. However, this method is prone to inducing nonlinear behavior of the converter under test when injecting disturbance signals, resulting in a large deviation between the actual impedance of the converter under test and the measured impedance, low accuracy, and poor effectiveness of the final impedance analysis results and control strategies.

[0004] Therefore, in order to solve the above-mentioned technical problems, it is urgent to propose a new technical approach. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a converter impedance measurement method that overcomes the influence of nonlinearity. By injecting voltage disturbance signals of different frequencies and amplitudes multiple times, the impedance is determined based on the voltage and current responses of the voltage disturbance signals. The method also takes into account the voltage and current responses caused by circuit disturbances, which can effectively avoid the influence of nonlinear behavior in the process of determining the impedance group of the converter under test, ensure the final measurement accuracy, and provide accurate data reference for subsequent impedance stability analysis and the formulation of impedance stability strategies.

[0006] This invention provides a converter impedance measurement method that overcomes the effects of nonlinearity, comprising the following steps:

[0007] S1. Inject a voltage disturbance signal V into the converter under test. pert1 (f), the voltage disturbance signal V pert1 (f) has a frequency of f and a voltage disturbance signal V pert1The amplitude of (f) is 10% of the rated voltage amplitude of the converter under test; where f = (f1, f2, ..., f n );

[0008] S2. Obtain the response voltage V of the converter under test. P1 (f) and response current I P1 (f);

[0009] S3. Response voltage V based on the converter under test P1 (f) and response current I P1 (f) Determine the impedance array Z1(f) of the converter under test: Z1(f) = (|Z1(f)|, ∠Z1(f)), where: |Z1(f)| represents the impedance magnitude of the converter under test, and ∠Z1(f) represents the phase of the converter under test;

[0010] S4. Inject a voltage disturbance signal V into the converter under test. pert2 (f), the voltage disturbance signal V pert2 (f) has a frequency of f and a voltage disturbance signal V pert2 (f) has an amplitude of 5% of the rated voltage amplitude of the converter under test;

[0011] S5. Obtain the response voltage V of the converter under test. P2 (f) and response current I P2 (f) and determine the impedance array Z2(f) of the converter under test: Z2(f) = (|Z2(f)|, ∠Z2(f));

[0012] S6. Determine whether the impedance array Z1(f) and impedance array Z2(f) meet the set conditions. If they do, the impedance amplitude of the converter under test is |Z1(f)|. If they do not meet the conditions, proceed to step S7.

[0013] S7. Inject a current disturbance signal I into the converter under test. pert1 (f) The current disturbance signal I pert1 (f) has a frequency of f and a current disturbance signal I pert1 (f) The amplitude is 5% of the rated current amplitude of the converter under test;

[0014] S8. Obtain the current disturbance signal I of the converter under test. pert1 (f) Response voltage V P3 (f) and response current I P3 (f), and determine the impedance array Z3(f) of the converter under test: Z3(f) = (|Z3(f)|, ∠Z3(f));

[0015] S9. When the impedance arrays Z1(f) and Z3(f) meet the set conditions, the impedance amplitude |Z1(f)| in the impedance array Z1(f) that meets the conditions is selected as the impedance of the converter under test.

[0016] Furthermore, the response voltage V of the converter under test is obtained. P1 (f) and response current I P1 (f) Specifically includes:

[0017] ;

[0018] ;

[0019] in: , and These are the three-phase voltages of the converter under test. , and These are the three-phase currents of the converter under test; e represents the natural constant, and π represents pi.

[0020] Where: response voltage V P2 (f) and response current I P2 (f) and current disturbance signal I pert1 (f) Response voltage V P3 (f) and response current I P3 The calculation formula for (f) and the response voltage V P1 (f) and response current I P1 The calculation formula for (f) is the same.

[0021] Furthermore, the impedance array Z1(f) of the converter under test is determined by the following method:

[0022] ,

[0023] ;

[0024] Where: Re() represents the real part of the converter impedance, and Im() represents the imaginary part of the converter impedance;

[0025] The calculation formulas for impedance arrays Z2(f) and Z3(f) are the same as those for impedance array Z1(f).

[0026] Furthermore, the conditions for setting the impedance arrays Z1(f) and Z2(f) are as follows:

[0027] ||Z1 (f)|-|Z2 (f)||<α and |∠Z1 (f)-∠Z2 (f)|<β;

[0028] The conditions for setting the impedance arrays Z1(f) and Z3(f) are as follows:

[0029] ||Z1 (f)|-|Z3 (f)||<α and |∠Z1 (f)-∠Z3 (f)|<β;

[0030] Where α and β represent the set threshold values.

[0031] Furthermore, in steps S6 and S9: when only frequency f i The impedance array Z1(f) corresponding to the disturbance signal below i ) and Z2(f i ) or Z1(f i ) and Z3(f i If the set conditions are met, then |Z1(f) i | As the impedance of the converter under test;

[0032] When the impedance arrays Z1(f) and Z2(f) or Z1(f) and Z3(f) corresponding to disturbance signals at multiple frequencies meet the set conditions, the average value of |Z1(f)| corresponding to the current multiple frequencies is taken as the impedance of the converter under test.

[0033] The beneficial effects of this invention are as follows: By injecting voltage disturbance signals of different frequencies and amplitudes multiple times, and then determining the impedance based on the voltage and current responses of the voltage disturbance signals, this invention also takes into account the voltage and current responses caused by circuit disturbances. This effectively avoids the influence of nonlinear behavior in the process of determining the impedance group of the converter under test, ensures the final measurement accuracy, and provides accurate data reference for subsequent impedance stability analysis and the formulation of impedance stability strategies. Attached Figure Description

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0035] Figure 1 This is a schematic diagram of the process of the present invention.

[0036] Figure 2 A comparison diagram of the modulation waveforms of voltage disturbance injection and switching current disturbance injection in this invention.

[0037] Figure 3 The results are from existing methods.

[0038] Figure 4 The measurement results are those obtained using the method of this invention. Detailed Implementation

[0039] The present invention will be further described in detail below:

[0040] This invention provides a converter impedance measurement method that overcomes the effects of nonlinearity, comprising the following steps:

[0041] S1. Inject a voltage disturbance signal V into the converter under test. pert1 (f), the voltage disturbance signal V pert1 (f) has a frequency of f and a voltage disturbance signal V pert1 The amplitude of (f) is 10% of the rated voltage amplitude of the converter under test; where f = (f1, f2, ..., f n In other words, there are multiple voltage disturbance signals, namely V pert1 (f1), V pert1 (f2), ...V pert1 (f n Each voltage disturbance signal has the same amplitude, but different frequencies.

[0042] S2. Obtain the response voltage V of the converter under test. P1 (f) and response current I P1 (f);

[0043] S3. Response voltage V based on the converter under test P1 (f) and response current I P1 (f) Determine the impedance array Z1(f) of the converter under test: Z1(f) = (|Z1(f)|, ∠Z1(f)), where |Z1(f)| represents the impedance magnitude of the converter under test, and ∠Z1(f) represents the phase of the converter under test; based on the above, the impedance array Z1(f) also has n elements, namely Z1(f1), Z1(f2), ... Z1(f n );

[0044] S4. Inject a voltage disturbance signal V into the converter under test. pert2 (f), the voltage disturbance signal V pert2 (f) has a frequency of f and a voltage disturbance signal V pert2 (f) has an amplitude of 5% of the rated voltage amplitude of the converter under test; similarly, the voltage disturbance signal V pert2 (f) also has n values, each with an amplitude of 5% of the rated voltage amplitude of the converter under test, but with different frequencies, and V pert1 (f1) and V pert2 The frequencies of (f1) are the same;

[0045] S5. Obtain the response voltage V of the converter under test. P2 (f) and response current I P2 (f) and determine the impedance array Z2(f) of the converter under test: Z2(f) = (|Z2(f)|, ∠Z2(f));

[0046] S6. Determine whether the impedance arrays Z1(f) and Z2(f) meet the set conditions. If they do, the impedance amplitude of the converter under test is |Z1(f)|. If not, proceed to step S7. The set conditions are:

[0047] ||Z1(f)|-|Z2(f)||<α and |∠Z1(f)-∠Z2(f)|<β; α and β represent the set thresholds. Generally, α is 2 and β is 5; when only frequency f is present... i The impedance array Z1(f) corresponding to the disturbance signal below i ) and Z2(f i If the set conditions are met, then |Z1(f) i |Z1(f3)| is used as the impedance of the converter under test. For example, if only Z1(f3) and Z2(f3) meet the set conditions, then |Z1(f3)| is the impedance value of the converter under test. When the impedance arrays Z1(f) and Z2(f) corresponding to disturbance signals at multiple frequencies meet the set conditions, then the average value of |Z1(f)| corresponding to the current multiple frequencies is used as the impedance of the converter under test. For example, if Z1(f1) and Z2(f1), Z1(f3) and Z2(f3), and Z1(f7) and Z2(f7) corresponding to f1, f3, and f7 all meet the set conditions in n frequencies, then the impedance value of the converter under test is (|Z1(f1)|+|Z1(f3)|+|Z1(f7)|) / 3.

[0048] S7. Inject a current disturbance signal I into the converter under test. pert1 (f) The current disturbance signal I pert1 (f) has a frequency of f and a current disturbance signal I pert1 (f) The amplitude is 5% of the rated current amplitude of the converter under test;

[0049] S8. Obtain the current disturbance signal I of the converter under test. pert1 (f) Response voltage V P3 (f) and response current I P3 (f), and determine the impedance array Z3(f) of the converter under test: Z3(f) = (|Z3(f)|, ∠Z3(f)); Although the injected disturbance signal is a current signal at this time, it still has corresponding response voltage and response current in each phase of the converter under test, thereby determining the response impedance array.

[0050] S9. When the impedance arrays Z1(f) and Z3(f) satisfy the set conditions, the impedance amplitude |Z1(f)| in the impedance array Z1(f) that meets the conditions is selected as the impedance of the converter under test. Wherein: the set conditions are ||Z1(f)|-|Z3(f)||<α and |∠Z1(f)-∠Z3(f)|<β; where: α and β represent the set thresholds. Generally, α is 2 and β is 5; when only frequency f... i The impedance array Z1(f) corresponding to the disturbance signal below i ) and Z3(f i If the set conditions are met, then |Z1(f) i |Z1(f4)| is used as the impedance of the converter under test. For example, if only Z1(f4) and Z3(f4) meet the set conditions, then |Z1(f4)| is the impedance value of the converter under test. When the impedance arrays Z1(f) and Z3(f) corresponding to disturbance signals at multiple frequencies meet the set conditions, then the average value of |Z1(f)| corresponding to the current multiple frequencies is used as the impedance of the converter under test. For example, in n frequencies, if Z1(f2) and Z3(f2), Z1(f4) and Z3(f4), and Z1(f4) and Z3(f8) corresponding to f2, f4, and f8 all meet the set conditions, then |Z1(f4)| is used as the impedance value of the converter under test. Given the given conditions, the impedance value of the converter under test is (|Z1(f2)|+|Z1(f4)|+|Z1(f8)|) / 3. This invention, by repeatedly injecting voltage disturbance signals of different frequencies and amplitudes, and then determining the impedance based on the voltage and current responses of the disturbance signals, while also considering the voltage and current responses caused by circuit disturbances, effectively avoids the influence of nonlinear behavior during the determination of the converter's impedance group, ensuring the final measurement accuracy and providing accurate data reference for subsequent impedance stability analysis and the formulation of impedance stabilization strategies.

[0051] In this embodiment, the response voltage V of the converter under test is obtained. P1 (f) and response current I P1 (f) Specifically includes:

[0052] ;

[0053] ;

[0054] in: , and These are the three-phase voltages of the converter under test. , and These are the three-phase currents of the converter under test; e represents the natural constant, and π represents pi.

[0055] Where: response voltage V P2 (f) and response current I P2 (f) and current disturbance signal I pert1 (f) Response voltage V P3 (f) and response current I P3 The calculation formula for (f) and the response voltage V P1 (f) and response current I P1 The calculation formula for (f) is the same, that is: response voltage V P2 (f) and response current I P2 (f) and current disturbance signal I pert1 (f) Response voltage V P3 (f) and response current I P3 The structure of the calculation formula for (f) and the response voltage V P1 (f) and response current I P1 (f) is the same, except that the corresponding three-phase voltage and three-phase current values ​​in the formula are replaced accordingly.

[0056] The impedance array Z1(f) of the converter under test is determined by the following method:

[0057] ,

[0058] ;

[0059] Where: Re() represents the real part of the converter impedance, and Im() represents the imaginary part of the converter impedance;

[0060] The calculation formulas for impedance arrays Z2(f) and Z3(f) are the same as those for impedance array Z1(f). Similarly, the structural form of the calculation formulas for impedance arrays Z2(f) and Z3(f) is the same as that for impedance array Z1(f). The only difference is that when calculating impedance arrays Z2(f) and Z3(f), the parameters are replaced with the corresponding parameters of Z2(f) and Z3(f).

[0061] The following specific examples further illustrate this point:

[0062] like Figure 2 The figure shows a comparison of the modulation waveforms of voltage perturbation injection and switched current perturbation injection. As can be seen from the figure, when the voltage-to-current perturbation injection method of this invention is used, no nonlinearity is observed in the modulator waveform.

[0063] Figure 3 This is the Bode plot result for the existing measurement method. The solid line represents the analytical values ​​of the mathematical model, and the asterisks represent the measurement results of the existing method. The plot shows that deviations occur in the measurement results at certain frequencies. Figure 4 This is a Bode plot showing the measurement results of this invention. The solid line represents the analytical values ​​of the mathematical model, and the asterisks represent the measurement results of the proposed measurement method. The measurement results agree well with the analytical values, proving the effectiveness of the method.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for measuring converter impedance to overcome nonlinear effects, characterized in that: Includes the following steps: S1. Inject a voltage disturbance signal V into the converter under test. pert1 (f), the voltage disturbance signal V pert1 (f) has a frequency of f and a voltage disturbance signal V pert1 The amplitude of (f) is 10% of the rated voltage amplitude of the converter under test; where f = (f1, f2, ..., f n ); S2. Obtain the response voltage V of the converter under test. P1 (f) and response current I P1 (f); S3. Response voltage V based on the converter under test P1 (f) and response current I P1 (f) Determine the impedance array Z1(f) of the converter under test: Z1(f) = (|Z1(f)|, ∠Z1(f)), where: |Z1(f)| represents the impedance magnitude of the converter under test, and ∠Z1(f) represents the phase of the converter under test; S4. Inject a voltage disturbance signal V into the converter under test. pert2 (f), the voltage disturbance signal V pert2 (f) has a frequency of f and a voltage disturbance signal V pert2 (f) has an amplitude of 5% of the rated voltage amplitude of the converter under test; S5. Obtain the response voltage V of the converter under test. P2 (f) and response current I P2 (f) and determine the impedance array Z2(f) of the converter under test: Z2(f) = (|Z2(f)|, ∠Z2(f)); S6. Determine whether the impedance array Z1(f) and impedance array Z2(f) meet the set conditions. If they do, the impedance amplitude of the converter under test is |Z1(f)|. If they do not meet the conditions, proceed to step S7. S7. Inject a current disturbance signal I into the converter under test. pert1 (f) The current disturbance signal I pert1 (f) has a frequency of f and a current disturbance signal I pert1 (f) The amplitude is 5% of the rated current amplitude of the converter under test; S8. Obtain the current disturbance signal I of the converter under test. pert1 (f) Response voltage V P3 (f) and response current I P3 (f), and determine the impedance array Z3(f) of the converter under test: Z3(f) = (|Z3(f)|, ∠Z3(f)); S9. When the impedance arrays Z1(f) and Z3(f) meet the set conditions, the impedance amplitude |Z1(f)| in the impedance array Z1(f) that meets the conditions is selected as the impedance of the converter under test.

2. The converter impedance measurement method for overcoming nonlinear effects according to claim 1, characterized in that: Obtain the response voltage V of the converter under test P1 (f) and response current I P1 (f) Specifically includes: ； ； in: , and These are the three-phase voltages of the converter under test. , and These are the three-phase currents of the converter under test; e represents the natural constant, and π represents pi. Where: response voltage V P2 (f) and response current I P2 (f) and current disturbance signal I pert1 (f) Response voltage V P3 (f) and response current I P3 The calculation formula for (f) and the response voltage V P1 (f) and response current I P1 The calculation formula for (f) is the same.

3. The converter impedance measurement method for overcoming nonlinear effects according to claim 2, characterized in that: The impedance array Z1(f) of the converter under test is determined by the following method: ， ； Where: Re() represents the real part of the converter impedance, and Im() represents the imaginary part of the converter impedance; The calculation formulas for impedance arrays Z2(f) and Z3(f) are the same as those for impedance array Z1(f).

4. The converter impedance measurement method for overcoming nonlinear effects according to claim 1, characterized in that: The conditions for setting the impedance arrays Z1(f) and Z2(f) are as follows: ||Z1 (f)|-|Z2 (f)||<α and |∠Z1 (f)-∠Z2 (f)|<β; The conditions for setting the impedance arrays Z1(f) and Z3(f) are as follows: ||Z1 (f)|-|Z3 (f)||<α and |∠Z1 (f)-∠Z3 (f)|<β; Where α and β represent the set threshold values.

5. The converter impedance measurement method for overcoming nonlinear effects according to claim 1, characterized in that: In steps S6 and S9: when only frequency f i The impedance array Z1(f) corresponding to the disturbance signal below i ) and Z2(f i ) or Z1(f i ) and Z3(f i If the set conditions are met, then |Z1(f) i | As the impedance of the converter under test; When the impedance arrays Z1(f) and Z2(f) or Z1(f) and Z3(f) corresponding to disturbance signals at multiple frequencies meet the set conditions, the average value of |Z1(f)| corresponding to the current multiple frequencies is taken as the impedance of the converter under test.

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