Applicable to the refined evaluation of converter overload capacity and PQ operation domain correction method

Abstract

The present invention relates to a method suitable for fine evaluation of overload capacity of a converter and PQ The operating domain correction method belongs to the technical field of AC / DC converter overload capacity calculation optimization. The invention introduces the influence of PWM pulse signal on the current flowing through the switching device IGBT to make a refined evaluation of the converter current overload capacity; and based on the refined i IGBT ( t )right PQ The present invention can more accurately calculate the current flowing through the IGBT switching device, thereby providing a more refined evaluation of the overload capacity of the converter. At the same time, taking into account the influence of the switching signal, it can improve the overload capacity of the converter obtained by the traditional method. PQ The operating domain is corrected to ensure the stable operation of the converter and improve the stability and safety of the power system operation.

Description

Technical Field

[0001] The present invention relates to a method suitable for fine evaluation of overload capacity of a converter and PQ The invention discloses an operation domain correction method, belonging to the technical field of AC / DC converter overload capacity calculation optimization. Background Art

[0002] An AC / DC Converter is a power electronic device used to achieve conversion between alternating current (AC) and direct current (DC). This device plays an important role in many fields such as power conversion in power systems, high-voltage direct current transmission (HVDC), and renewable energy grid connection. Therefore, studying the problem of converter overload is crucial to ensure the stability and reliability of power systems. Through in-depth analysis and refined evaluation of the overload capacity of converters under various working conditions, problems caused by equipment overload can be prevented and reduced, the reliability of converters can be improved, the design and operation strategies of power equipment can be optimized, and the flexibility and adaptability of the power grid can be enhanced.

[0003] For the overload problem of the converter, the overload current flowing through the converter switch device is usually regarded as a criterion for measuring whether it is overloaded. However, the existing overload current collection and calculation has certain defects. Usually, the phase current flowing through the converter outlet is used as the criterion, but the influence of the pulse signal on the overload current is ignored, resulting in PQ The operating domain is too conservative, and the overload capacity potential of the switching device is wasted. Therefore, taking into account the influence of the pulse signal and making a detailed evaluation of the current flowing through the converter switching device can better analyze and solve the problem.

[0004] In addition, the converter overload problem is related to PQ The operating domain is closely related. PQ Calculation of the operating domain includes active power P and reactive power Q The active power P is closely related to the amplitude of the overload current. PQ In the figure, the active power P is usually proportional to the overload current flowing through the switch device, that is, when the output active power P When the reactive power increases, the overload current flowing through the switching device will also increase. Q It is related to the phase angle of the overload current. When the inverter provides reactive power, it usually adjusts the phase of the current to cause a certain offset from the voltage phase. This offset will affect the overload current waveform flowing through the switching device, thereby affecting the operating efficiency and heat loss of the inverter.

[0005] Precise calculation PQIn practice, the operating domain can help engineers determine the rated power and reactive power of the inverter, thereby designing a suitable inverter topology and control strategy. It can also be used to optimize the grid-connected operation of the inverter to ensure stable output of active and reactive power under different load conditions. PQ The range of the operating domain is not conducive to the measurement and improvement of the converter overload capacity. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a method for finely evaluating the overload capacity of a converter and PQ The operating domain correction method can more accurately calculate the current flowing through the IGBT switching device, thereby providing a more refined assessment of the overload capacity of the converter. At the same time, taking into account the influence of the switching signal, it can improve the previous traditional method. PQ The operating domain is corrected to ensure the stable operation of the converter and improve the stability and safety of the power system operation.

[0007] The technical solution of the present invention is as follows:

[0008] A method for fine evaluation and optimization of converter overload capacity PQ The domain correction method is run, comprising the following steps:

[0009] By introducing the influence of PWM pulse signal on the current flowing through the switching device IGBT, the current overload capacity of the converter is refined and evaluated. The formula is as follows:

[0010] (1);

[0011] in, Represents the current flowing through the IGBT switching device after refined evaluation, i a ( t ) is the phase current flowing through the converter outlet, s a ( t ) is the switching signal of the lower bridge arm affected by the pulse signal;

[0012] Based on the refined right PQ Run the domain to make corrections.

[0013] Preferably, during the refined evaluation of the current overload capacity of the converter, i a ( t ), s a ( t ) are calculated by the following formulas:

[0014] (2);

[0015] (3);

[0016] in, I s Indicates the amplitude of phase A current, which is defined as: , ; ω represents the angular frequency, t Indicates time, S It represents the amplitude of the three-phase apparent power, U pcc Indicates the voltage amplitude at PCC point, Indicates the initial phase of phase A current;

[0017] S m is the amplitude of the fundamental frequency component decomposed after FFT analysis, θ sm is the initial phase of the fundamental frequency component after FFT analysis and decomposition, , U c Indicates the voltage amplitude at the converter outlet side, U dc Indicates the DC side voltage. Indicates the initial phase angle of the converter output voltage.

[0018] Preferably, the present invention further includes verifying the current flowing through the IGBT switch device after the refined evaluation, and the verification process is:

[0019] From formulas (1) to (3), we can get:

[0020] (4);

[0021] Calculate the effective value of the current flowing through the IGBT switch device I IGBT_rms :

[0022] (5);

[0023] The measured value of the current flowing through the IGBT switching device is obtained by formula (6): I ca_rms , which is the actual value:

[0024] (6);

[0025] in, i ca ( t) is the instantaneous value of the phase current flowing through the converter outlet. By setting the given PQ After the power is measured, the current waveform at the converter outlet is obtained through an oscilloscope, and then FFT analysis is performed to obtain the components of each frequency by superimposing them;

[0026] Compare effective values I IGBT_rms With measured value I ca_rms , when the two are equal, the verification passes.

[0027] Preferably, the influence of overmodulation and PWM pulse signal on the current flowing through the switching device IGBT is not considered. PQ The operation domain is shown in formula (10). The center of the operation domain is , the radius of the operating domain is :

[0028] (10);

[0029] Using SPWM control, the AC fundamental voltage amplitude output by the voltage source converter is U c With DC side voltage U d The relationship of formula (11) is:

[0030] (11);

[0031] in, M Represents the modulation degree of SPWM (0≤ M ≤1), that is, the ratio of the peak value of the sinusoidal modulation to the amplitude of the triangular carrier;

[0032] Substituting formula (11) into formula (10) yields the power characteristic equation limited by the DC side voltage under the influence of overmodulation, as shown in formula (12):

[0033] (12);

[0034] Then consider the influence of PWM pulse signal. After verification, the effective value of the current flowing through the upper and lower IGBT switch tubes is equal. Therefore, the upper switch tube is selected for calculation, and a maximum effective value of the current flowing through the IGBT switch device is set, which is recorded as I rms_max , then the effective value flowing through the upper tube of the IGBT switch device I IGBT_rms and I rms_max The existence relationship is shown in formula (13):

[0035] (13);

[0036] in, i IGBT_up ( t ) is obtained from formula (14):

[0037] (14);

[0038] pass , , for formula (14) I s , θ ia Written as containing unknown quantity S and The expression of S m and θ sm According to formula (15), it can be written as S and Expression of

[0039] (15);

[0040] in, R S Represents the line resistance, L S Indicates line inductance;

[0041] Here, the derivation process of formula (15) is:

[0042] because Represents the phasor value of the voltage at the converter outlet side, U c Indicates the voltage amplitude at the outlet side of the meter converter. The expression is as follows:

[0043] (16);

[0044] in, j represents the imaginary unit, From formula (17), we get:

[0045] (17);

[0046] Add the square of the real part and the square of the imaginary part of formula (16) and take the square root, then multiply , we can get the amplitude U c ,Will U c Divide by Udc , we can get the value in formula (15) S m , divide the imaginary part in equation (16) by the real part and then use the inverse tangent function to obtain θ sm .

[0047] Formula (12) establishes PQ The range is the operating domain A. There are two unknown quantities in formula (13): S and ,exist Each value in the range [0, 2π] , the corresponding apparent power can be obtained by numerical solution method S , each corresponding S The value points are determined in polar coordinates, and several S The values ​​are connected to get the operation domain B. The operation domain B is intersected with the operation domain A to get the final corrected PQ Run the domain.

[0048] It should be noted that in the process of fine evaluation of the current overload capacity of the converter, due to a specific working condition, S and are all known numbers. PQ When running a domain, S and Is an unknown quantity.

[0049] For any details not provided in the present invention, please refer to the prior art.

[0050] The beneficial effects of the present invention are:

[0051] The present invention proposes a method suitable for fine evaluation of converter overload capacity and P Q operating domain correction method, which can more accurately calculate the current flowing through the IGBT switching device, thereby providing a more refined assessment of the overload capacity of the converter. At the same time, taking into account the influence of the switching signal, it can improve the previous traditional solution. PQ The difference between this method and the prior art is that the PWM pulse switching signal is introduced to participate in the analysis of the converter overload capacity. In the implementation process, based on the three-phase converter model, this method not only considers the impact of the overmodulation problem, but also analyzes the impact of the phase angle offset generated by the PWM pulse signal on the existing PQ Limitations brought by the operating domain. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings in the specification, which constitute a part of the present application, are used to provide further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0053] Figure 1 A schematic diagram of the relationship for calculating the current flowing through the IGBT switching device;

[0054] Figure 2 A schematic diagram of the refined evaluation process and verification flow for the current overload capability of the converter;

[0055] Figure 3 It is the equivalent schematic diagram of three-phase converter;

[0056] Figure 4 The waveform diagram of the upper bridge arm PWM pulse signal is analyzed by FFT;

[0057] Figure 5 is the operating range of the converter under ideal conditions;

[0058] Figure 6 The modified converter takes into account the influence of pulse signal PQ Operational domain;

[0059] Figure 7 For flow through I IGBT Switching device current diagram and partial enlarged diagram, where (a) is the current flowing through I IGBT Switching device current diagram, (b) is a partial enlarged view of (a);

[0060] Figure 8 1 is a comparison diagram of the current flowing through the IGBT switching device inside and outside the corrected operating domain, where (a) is the current flowing through the IGBT switching device inside the corrected operating domain, and (b) is the current flowing through the IGBT switching device outside the corrected operating domain. DETAILED DESCRIPTION

[0061] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the drawings in the implementation of this specification, but are not limited to this. Anything not fully described in the present invention shall be based on the conventional technology in the art.

[0062] The actual overload current is collected in the converter as follows: Figure 1 As shown, it consists of the phase current flowing through the converter outlet i a ( t ) and the pulse signal of this phase.

[0063] The topology of the three-phase converter is Figure 1As shown in the figure, the components from left to right are the DC side voltage, the converter main circuit composed of IGBT and the power grid. The DC side is converted into AC value by the converter and then connected to the AC side power grid after passing through the filter. Figure 1 In this example, we take the upper arm of the A-phase IGBT as an example: n The dot represents the zero potential reference point; a , b , c They represent the lead-out points at the A-phase, B-phase and C-phase outlets of the converter, respectively, and are connected to the power grid; U sa , U sb , U sc Respectively represent the voltage amplitude of each phase A, B, and C on the grid side; PWMA_U, PWMB_U, PWMC_U, PWMA_D, PWMB_D, and PWMC_D represent the pulse signals of each IGBT switch device respectively; U dc Represents the bus voltage on the DC side; Definition s a ( t ) is the switching signal of the bridge arm, namely PWMA_U; i a ( t ) is the current flowing through the converter outlet, It is the actual current flowing through the IGBT device, that is, the current flowing through the IGBT switching device after refined evaluation.

[0064] Usually, when evaluating the overload capacity of the converter, i a ( t ) is regarded as the current flowing through the switching device IGBT, and s a ( t ) has an impact on IGBT devices. Therefore, if Figure 1 As shown, in order to more precisely measure the overload capacity of the converter, the defined As a new calculation standard. By integrating the current in one cycle, we can obtain i a ( t )and After comparing the difference, we can get the effective value of The effective value obtained by integration is compared with i a ( t) is often smaller than the effective value obtained by integrating. After considering the influence of overmodulation, the present invention finds that the switching signal will have an influence on the phase of the voltage phasor at the output of the converter, thus affecting the active power. P、 Reactive power Q Finally, the present invention concludes that PQ The operating domain is no longer a circle, but follows the switch signal s a ( t )’s intervention.

[0065] Example 1

[0066] A method for fine evaluation and optimization of converter overload capacity PQ Run domain correction methods, such as Figure 1 As shown, the following steps are included:

[0067] By introducing the influence of PWM pulse signal on the current flowing through the switching device IGBT, the current overload capacity of the converter is refined and evaluated. The formula is as follows:

[0068] (1);

[0069] in, Represents the current flowing through the IGBT switching device after refined evaluation;

[0070] like Figure 3 As shown, the equivalent schematic diagram of the three-phase converter is established. First, the calculation formula for the effective value of the current flowing through the converter in a unit cycle without considering the influence of the PWM pulse signal is given. i a ( t ) is the phase current flowing through the converter outlet;

[0071] s a ( t ) is the switching signal of the lower bridge arm affected by the pulse signal;

[0072] Based on the refined right PQ Run the domain to make corrections.

[0073] like Figure 2 As shown in the figure, during the process of fine evaluation of the current overload capacity of the converter, i a ( t ), s a ( t ) are calculated by the following formulas:

[0074] (2);

[0075] (3);

[0076] in, I s Indicates the amplitude of phase A current, which is defined as: , ; ω represents the angular frequency, t Indicates time, S It represents the amplitude of the three-phase apparent power, U pcc Indicates the voltage amplitude at PCC point, Indicates the initial phase of phase A current;

[0077] The pulse signal of the bridge arm is sampled and Fourier (FFT) analysis is performed to facilitate subsequent calculations, such as Figure 4 As shown in the figure, after FFT analysis, it is concluded that the square wave pulse signal component is mainly composed of DC component and base frequency component (ignoring the effect of high frequency component). Therefore, the instantaneous value of the IGBT pulse signal of the upper and lower bridge arms is s a ( t ) can be written as formula (3), where S m is the amplitude of the fundamental frequency component decomposed after FFT analysis, θ sm is the initial phase of the fundamental frequency component after FFT analysis and decomposition, , U c Indicates the voltage amplitude at the converter outlet side, U dc Indicates the DC side voltage. Indicates the initial phase angle of the converter output voltage.

[0078] This embodiment also includes verifying the current flowing through the IGBT switch device after the refined evaluation, and the verification process is:

[0079] After taking into account the influence of PWM pulse, the instantaneous value of the current flowing through the upper and lower bridge arms is It can be obtained from formulas (1) to (3):

[0080] (4);

[0081] Calculate the effective value of the current flowing through the IGBT switch device I IGBT_rms :

[0082] (5);

[0083] The measured value of the current flowing through the IGBT switching device is obtained by formula (6): I ca_rms , which is the actual value:

[0084] (6);

[0085] in, i ca ( t ) is the instantaneous value of the phase current flowing through the converter outlet. By setting the given PQ After the power is measured, the current waveform at the converter outlet is obtained through an oscilloscope, and then FFT analysis is performed to obtain the components of each frequency by superimposing them;

[0086] Compare effective values I IGBT_rms With measured value I ca_rms , when the two are equal, the verification passes.

[0087] Furthermore, when the resistance of the connecting transformer and phase reactor is ignored, the amplitude of the fundamental frequency component of the converter AC bus voltage is U s The amplitude of the fundamental frequency component of the AC output voltage U c Acting together on the equivalent reactance X , which determines the active power exchanged between the converter and the AC system P and reactive power Q , as shown in formula (7) and formula (8), respectively, where Represents the phase voltage phasor at the converter output Relative to the grid side phase voltage phasor The phase shift angle.

[0088] (7);

[0089] (8);

[0090] (9);

[0091] Rewriting formula (8) into formula (9) and then squaring formula (7) before and after the equal sign and adding them together, we can get formula (10), that is, without considering the influence of overmodulation and PWM pulse signal on the current flowing through the switching device IGBT, the ideal state of the converter station is PQ The operation domain is shown in formula (10). The center of the operation domain is , the radius of the operating domain is ,like Figure 5 As shown;

[0092] (10);

[0093] On the basis of the above, considering the over-modulation effect and PWM pulse signal limitation, Figure 5 First, consider the influence of overmodulation. Assuming that a certain transmission system adopts SPWM control, the AC fundamental voltage amplitude output by the voltage source converter is U c With DC side voltage U d The relationship of equation (11) is:

[0094] (11);

[0095] in, M Represents the modulation degree of SPWM (0≤ M ≤1), that is, the ratio of the peak value of the sinusoidal modulation to the amplitude of the triangular carrier;

[0096] Substituting formula (11) into formula (10) yields the power characteristic equation limited by the DC side voltage under the influence of overmodulation, as shown in formula (12):

[0097] (12);

[0098] Then consider the influence of PWM pulse signal. After verification, the effective value of the current flowing through the upper and lower IGBT switch tubes is equal. Therefore, the upper switch tube is selected for calculation, and a maximum effective value of the current flowing through the IGBT switch device is set, which is recorded as I rms_max , then the effective value flowing through the upper tube of the IGBT switch device I IGBT_rms and I rms_max The existence relationship is shown in formula (13):

[0099] (13);

[0100] in, i IGBT_up ( t ) is obtained from formula (14):

[0101] (14);

[0102] Formula (4) represents the upper and lower tubes, while formula (14) represents only the upper tube, with a minus sign difference;

[0103] pass , , for formula (14) Is , θ ia Written as containing unknown quantity S and The expression of S m and θ sm According to formula (15), it can be written as S and Expression of

[0104] (15);

[0105] in, R S Represents the line resistance, L S Indicates line inductance;

[0106] Here, the derivation process of formula (15) is:

[0107] because Represents the phasor value of the voltage at the converter outlet side, U c Indicates the voltage amplitude at the output side of the meter converter. The expression is as follows:

[0108] (16);

[0109] in, j represents the imaginary unit, From formula (17), we get:

[0110] (17);

[0111] Add the square of the real part and the square of the imaginary part of formula (16) and take the square root, then multiply , you can get the amplitude U c ,Will U c Divide by U dc , we can get the value in formula (15) S m , divide the imaginary part in equation (16) by the real part and then use the inverse tangent function to obtain θ sm .

[0112] Formula (12) establishes PQ The range is the operating domain A. There are two unknown quantities in formula (13): S and ,exist Each radian in the value range of [0, 2π] can be numerically solved to obtain the corresponding apparent power. S , you can use the fsolve function in MATLAB, which essentially uses the least squares method to make the constructed equation " I IGBT_rms - I rms_max The right side of the equation is approximately equal to 0, and then gradually approaches the solution of the nonlinear equation. The fsolve function can be used to solve a S Value. S The value points are determined in polar coordinates, and several S The values ​​are connected to get the operation domain B. The operation domain B is intersected with the operation domain A to get the final corrected PQ Run the domain.

[0113] It should be noted that in the process of fine evaluation of the current overload capacity of the converter, due to a specific working condition, S and are all known numbers. PQ When running a domain, S and Is an unknown quantity.

[0114] In order to verify the proposed method for fine evaluation of converter overload capacity and PQ The effectiveness of the operating domain correction method is verified by building a model in Matlab / Simulink for simulation, and the operating domain calculation of given parameters is performed.

[0115] Based on formula (12), formula (13) and Table 1, the following calculation is performed under this condition: PQ Operation domain. Because the modulation degree of SPWM M The value range is 0≤ M ≤1, take M Substituting the maximum value 1 into the data calculation, formula (12) can be written as shown in formula (18), and defined as the operating domain A. I rms_max When 30A is taken, the operation domain B can be obtained by the optimization solution method. The operation domain B and the operation domain A are intersected to obtain the operation domain under this working condition, as shown in Figure 6 shown.

[0116] (18);

[0117] In order to verify the proposed method for fine evaluation of converter overload capacity, the following examples are combined to illustrate the above-mentioned method for fine calculation of converter switch device current taking into account pulse signals and PQ The operation domain correction method is verified. The main circuit parameters of the three-phase converter are shown in Table 1 below.

[0118] Table 1 Main circuit parameters of three-phase converter

[0119]

[0120] Four types of converters that can ensure stable operation were randomly selected. PQ Given the working conditions, as shown in Table 2. The following is an explanation of each case in Table 2. The traditional calculation scheme for the effective value of the current flowing through the switching device is shown in formula (19):

[0121] (19);

[0122] I k represents the effective value of the current flowing through the switch device obtained by the traditional calculation scheme (i.e., the value corresponding to the traditional scheme in Table 2). The proposed scheme is a new method for calculating the effective value of the current flowing through the converter proposed by the present invention, which can be calculated by formula (12) (i.e., the value corresponding to the proposed scheme in Table 2). The current flowing through the A-phase upper bridge arm switch device IGBT is collected by an oscilloscope, i.e. Figure 7 of i ca ( t )(A), for I ca The instantaneous value of Figure 7 As shown. By performing FFT analysis on the current, we can get Figure 6 The amplitude and phase angle of each frequency component of the current in the medium are obtained, and then the measured value of the current under various working conditions is obtained in MATLAB / Simulink. I ca_rms (i.e., the actual value in Table 2). Error 1 represents the ratio of the difference between the traditional solution and the actual value to the actual value, and Error 2 represents the ratio of the difference between the solution proposed in the present invention and the actual value to the actual value.

[0123] Table 2 Current comparison table under given working conditions

[0124]

[0125] It can be found from Table 2 that: no matter what the working condition is, it can be seen from the data of error 1 that there is a big gap between the current value obtained by the traditional solution and the actual value. It can be seen from the data of error 2 that the current value calculated by the solution proposed in the present invention is not much different from the actual value, and is always slightly lower than the actual value. This is because the solution proposed in the present invention ignores some high-frequency components during the FFT analysis of the PWM pulse signal. Therefore, this current refinement calculation method has been verified.

[0126] Secondly PQ Run the domain correction method to verify. First, Figure 5 As shown, find any one in the unmodified running domain M Find any one in the corrected running domain N Points (as long as one is within the final corrected operating domain and the other is outside the operating domain), compare the current waveforms of these two power points, the waveform comparison diagram is as follows Figure 8 As shown. It can be seen from the current waveform M The current waveform flowing through the converter IGBT at point 1 is not ideal, and the waveform is intermittent. N The current at the point is relatively ideal, the waveform is not discontinuous, and the pulse area is surrounded by the sine wave as the envelope, which is in line with expectations, indicating the correctness of the operating domain correction scheme proposed by the present invention. I rms_max When the value is determined (here 30A), select the boundary point of the operating domain in this case k 1 , k 2 , k 3 Verify. k 1 , k 2 , k 3 The point data conditions are brought back to the simulation model, and the traditional scheme, the proposed scheme, the actual value, and the set value are compared. I rms_max The current values ​​are compared as shown in Table 3. In Table 3, the set value is the maximum current that the set IGBT switch device can withstand. I rms_max , which is 30 A. Error 3 is the ratio of the difference between the proposed solution and the set value.

[0127] Table 3 I rms_max Comparison table of current values ​​flowing through IGBT devices under various boundary conditions when set to 30A

[0128]

[0129] Use the method in formula (13) to calculate the current value in this case. If I rms_maxAs can be seen from Table 3, the current value calculated by the calculation scheme proposed by the present invention is close to the set value. Due to the influence of high-order harmonics, it is slightly smaller than the actual value, while the current value obtained by the traditional scheme is very different from the set value. Since the error between the current value calculated by the calculation scheme proposed by the present invention and the set value is very small, the correction method is verified.

[0130] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A PQ operation domain correction method based on refined evaluation of converter overload capacity, characterized in that: The steps include: By introducing the influence of PWM pulse signal on the current flowing through the switching device IGBT, the current overload capacity of the converter is refined and evaluated. The formula is as follows: i IGBT (t)=i a (t)×s a (t)(1); Among them, i IGBT (t) represents the current flowing through the IGBT switching device after refined evaluation, i a (t) is the phase current flowing through the converter outlet, s a (t) is the switching signal of the lower bridge arm affected by the pulse signal; Based on the refined i IGBT (t) Modify the PQ operation domain; During the refined evaluation of the converter current overload capacity, i a (t), s a (t) are calculated by the following formula: i a (t)=I s cos(ωt+θ ia )(2); s a (t)=0.5±S m cos(ωt+θ sm )(3); Among them, I s Indicates the amplitude of phase A current, which is defined as: ω represents the angular frequency, t represents the time, S represents the amplitude of the three-phase apparent power, U pcc Indicates the voltage amplitude at PCC point, Indicates the initial phase of phase A current; S m is the amplitude of the fundamental frequency component decomposed after FFT analysis, θ sm is the initial phase of the fundamental frequency component after FFT analysis and decomposition, U c Indicates the voltage amplitude at the converter outlet, U dc Indicates the DC side voltage. Indicates the initial phase angle of the converter output voltage; The current flowing through the IGBT switching device after refined evaluation is verified. The verification process is as follows: From formulas (1) to (3), we can get: i IGBT (t)=i a (t)×s a (t)=I s cos(ωt+θ ia )×[0.5±S m cos(ωt+θ sm )](4) Calculate the effective value I flowing through the IGBT switch device IGBT_rms : The measured value of the current flowing through the IGBT switching device is obtained by formula (6): ca_rms , which is the actual value: Among them, i ca (t) is the current flowing through the switching device IGBT. After setting the given PQ power in the Simulink model, the current of the switching device IGBT is obtained through an oscilloscope, and then FFT analysis is performed to obtain the current by superimposing the components of each frequency. Comparison of effective value I IGBT_rms With the measured value I ca_rms , when the two are equal, the verification passes; Without considering the influence of overmodulation and PWM pulse signal on the current flowing through the switching device IGBT, the PQ operation domain of the converter station under ideal conditions is as shown in formula (10), and the center of the operation domain is The radius of the operating domain is U s U c / X: Using SPWM control, the AC fundamental voltage amplitude U output by the voltage source converter c With DC link voltage U d The relationship of formula (11) is: Where M represents the modulation degree of SPWM, that is, the ratio of the sinusoidal modulation peak value to the triangular carrier amplitude; Substituting formula (11) into formula (10) yields the power characteristic equation limited by the DC side voltage under the influence of overmodulation, as shown in formula (12): Then consider the influence of PWM pulse signal. After verification, the effective value of the current flowing through the upper and lower IGBT switch tubes is equal. Therefore, the upper switch tube is selected for calculation, and a maximum effective value of the current flowing through the IGBT switch device is set, which is recorded as I rms_max , then the effective value I flowing through the upper tube of the IGBT switch device IGBT_rms with I rms_max The existence relationship is shown in formula (13): Among them, i IGBT_up (t) is obtained from formula (14): i IGBT_up (t)=i a (t)×s a (t)=I s cos(ωt+θ ia )×[0.5+S m cos(ωt+θ sm )](14) For I in formula (14), s ,θ ia Written as containing unknown quantity S and The expression of S m and θ sm According to formula (15), it can be written as Expression of Among them, R S Indicates line resistance, L S Indicates line inductance; The PQ range established by formula (12) is the operating domain A. There are two unknown quantities S and exist Each value in the range [0, 2π] The corresponding apparent power S can be obtained by numerical solution method. The corresponding S value point is determined in the polar coordinate system. When several S values ​​are connected, the operating domain B is obtained. The intersection of the operating domain B and the operating domain A is taken to obtain the final corrected PQ operating domain.

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