A control method and control device for a converter

Abstract

This invention discloses a control method and device for a converter. The converter is electrically connected to a controller, which includes a first regulating control unit and a second regulating control unit. The method includes: acquiring the three-phase voltage and three-phase current values ​​on the AC side of the converter; inputting the three-phase voltage and three-phase current values ​​as feedback signals to the first regulating control unit to control the output of a three-phase main modulation wave signal; inputting the three-phase current value as a feedback signal to the second regulating control unit to control the output of a three-phase modulation wave fine-tuning signal; adding the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal respectively to obtain the three-phase modulation wave signal of the converter; and using the modulation wave signal to control the output of a pulse signal through a pulse width modulation control unit to drive the converter to operate. The technical solution provided by this invention improves the stability and safety of converter operation, thereby reducing the harm to the safe operation of the power grid and improving power quality.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, and in particular to a converter control method and control device. Background Technology

[0002] Different converters based on converter topologies include various types. Among them, flexible DC transmission technology based on modular multilevel converters (MMCs) has advantages such as flexible control, low harmonic content, ability to supply power to passive systems, and no commutation failure issues. It is widely used in long-distance power transmission, offshore wind power DC transmission, new energy grid connection, asynchronous grid interconnection, and power supply to isolated drilling platforms. Flexible DC converters are nonlinear power electronic devices, which are prone to generating harmonics on the DC side during normal operation. The main reasons for the generation of DC side harmonics in flexible DC converters are: firstly, when there are background harmonics in the AC grid voltage, the AC side of the converter will generate harmonic currents of the same order, which are transmitted to the DC side through the converter to generate harmonics of different frequencies; secondly, since MMCs usually use nearest-level approximation modulation, the modulation process may generate characteristic harmonic components on both the AC and DC sides, which are more pronounced at lower levels.

[0003] Due to the combined effects of transmission lines, DC reactors, and flexible DC converters, the DC network itself has an inherent resonant point. When the DC-side harmonic frequency coincides with the inherent resonant frequency, resonance is easily triggered, jeopardizing the safe and stable operation of the power system. Simultaneously, due to the interaction between the AC and DC sides of the flexible DC converter, DC-side harmonics can be transmitted back to the AC side, further deteriorating the power quality of AC-side harmonic currents. Therefore, it is necessary to suppress DC-side harmonics in flexible DC converters. Summary of the Invention

[0004] This invention provides a control method and control device for a converter to improve the stability and safety of converter operation, thereby reducing the harm to the safe operation of the power grid and improving power quality.

[0005] In a first aspect, embodiments of the present invention provide a control method for a converter, wherein the converter is electrically connected to a controller, the controller being used to control the operation of the converter, the controller including a first regulating control unit and a second regulating control unit, the method comprising:

[0006] Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter;

[0007] The three-phase voltage values ​​and the three-phase current values ​​are input as feedback signals to the first regulation and control unit to control the output of the three-phase main modulation wave signal;

[0008] The three-phase current values ​​are input as feedback signals to the second adjustment and control unit to control the output of the three-phase modulation wave fine-tuning signal.

[0009] The three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added together to obtain the three-phase modulation wave signal of the converter.

[0010] The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0011] Secondly, embodiments of the present invention also provide a control device for a converter, including the converter and a controller electrically connected to the converter. The controller is used to control the operation of the converter. The controller includes a sampling module, a control module, and a drive module. The control module includes a first adjustment control unit and a second adjustment control unit.

[0012] The sampling module is used to collect the three-phase voltage and three-phase current values ​​on the AC side of the converter;

[0013] The control module is used to input the three-phase voltage value and the three-phase current value as feedback signals to the first adjustment control unit and control the output of the three-phase main modulation wave signal, and to input the three-phase current value as feedback signals to the second adjustment control unit and control the output of the three-phase modulation wave fine adjustment signal. Then, the three-phase main modulation wave signal and the three-phase modulation wave fine adjustment signal are added respectively to obtain the three-phase modulation wave signal of the converter.

[0014] The drive module is used to control the output pulse signal through the pulse width modulation control unit using the modulated wave signal, so as to drive the converter to work.

[0015] The technical solution of this invention collects the three-phase voltage and three-phase current values ​​on the AC side of the converter. These values ​​are then input as feedback signals to a first regulating control unit, which controls the output of a three-phase main modulation wave signal. Simultaneously, the three-phase current values ​​are input as feedback signals to a second regulating control unit, which controls the output of a three-phase modulation wave fine-tuning signal. This fine-tuning signal compensates for further stabilization of the converter and improvement of power quality. The three-phase main modulation wave signal and the fine-tuning signal are then added correspondingly to obtain the converter's three-phase modulation wave signal. This signal is then used to control the output of a pulse width modulation control unit to drive the converter. This results in lower harmonic content in the converter's grid-connected current, higher quality, and ensures stable operation of the converter, while simultaneously improving the power quality and security of the power grid system.

[0016] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0018] Figure 1 This is a schematic diagram of the control structure of a converter provided in an embodiment of the present invention;

[0019] Figure 2 A flowchart of a converter control method provided in an embodiment of the present invention;

[0020] Figure 3 A flowchart of another converter control method provided in an embodiment of the present invention;

[0021] Figure 4 This is a schematic diagram of another converter control structure provided in an embodiment of the present invention;

[0022] Figure 5 A flowchart of another converter control method provided in an embodiment of the present invention;

[0023] Figure 6 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention;

[0024] Figure 7 A flowchart of another converter control method provided in an embodiment of the present invention;

[0025] Figure 8 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention;

[0026] Figure 9 A flowchart of another converter control method provided in an embodiment of the present invention;

[0027] Figure 10 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention;

[0028] Figure 11 A flowchart of another converter control method provided in an embodiment of the present invention;

[0029] Figure 12This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention;

[0030] Figure 13 A flowchart of another converter control method provided in an embodiment of the present invention;

[0031] Figure 14 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention;

[0032] Figure 15 A flowchart of another converter control method provided in an embodiment of the present invention;

[0033] Figure 16 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention;

[0034] Figure 17 This is a schematic diagram of the structure of a converter control device provided in an embodiment of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 should fall within the scope of protection of the present invention.

[0036] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0037] Figure 1 This is a schematic diagram of the control structure of a converter provided in an embodiment of the present invention. Figure 2 A flowchart of a converter control method provided in an embodiment of the present invention, combined with... Figure 1 and Figure 2As shown, the converter is electrically connected to the controller 100, which controls the operation of the converter. The controller 100 includes a first regulation control unit 11 and a second regulation control unit 12. The control method includes:

[0038] S101: Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0039] S102. Input the three-phase voltage and three-phase current values ​​as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal.

[0040] The first regulating control unit can use conventional control strategies for converters to control the output three-phase main modulation wave signal, such as a control strategy consisting of a power outer loop and a current inner loop. This embodiment of the invention does not limit this.

[0041] S103. Input the three-phase current value as a feedback signal to the second regulation and control unit to control the output of the three-phase modulation wave fine-tuning signal.

[0042] The second regulation and control unit is used to perform harmonic suppression control based on the three-phase current value and generate a three-phase modulation wave fine-tuning signal to suppress the harmonics generated on the DC side of the converter due to the background harmonics of the grid voltage.

[0043] S104. Add the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal respectively to obtain the three-phase modulation wave signal of the converter.

[0044] S105. The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0045] Understandably, converters include those based on modular multilevel converters (MMC), see reference. Figure 1 As shown, Figure 1 An exemplary circuit diagram of an MMC converter is shown. At least one single-power module (SM) is connected in series on each arm of the converter. The Larm is the filter inductor on the AC side, and the three-phase voltages on the AC side are u... a u b and u c (For ease of description, three-phase voltage can be represented by u) abc (represented), the three-phase currents are i a i b and i c (For ease of description, three-phase current can be represented by i) abc (Indicated), the MMC converter is electrically connected to the AC power grid via transformer T, and electrically connected to the converter via controller 10, which collects the three-phase voltage u on the AC side of the converter.abc and three-phase current i abc Closed-loop control is performed, and pulse signals are output to the switching transistors in the single-power module of the converter to achieve stable operation of the converter.

[0046] The controller 100 may be a controller that runs control algorithms based on digital signal processing (DSP) or other control chips, but this embodiment of the invention does not limit this.

[0047] Specifically, the three-phase voltage value u on the AC side of the converter is acquired through a voltage sensor. abc And the current sensor collects the three-phase current value i on the AC side of the converter. abc Then the three-phase voltage value u abc and three-phase current value i abc The input is sent to the first regulating control unit 11 for control processing, and the three-phase main modulation wave u can be obtained. m1abc Understandably, the first regulating control unit 11 can be controlled using a traditional dual closed-loop control strategy (i.e., a power outer loop and a current inner loop control strategy), and then output a three-phase main modulation wave u. m1abc If only the three-phase main modulation wave u is used m1abc The pulse width modulation control unit 13 controls the output of pulse signals that can turn the switching transistors inside the converter on or off, thereby driving the converter to operate. If odd-order background harmonics exist in the AC power grid, even-order harmonics will be generated on the DC side of the converter. Furthermore, due to the interaction of multiple converters on their DC sides within the power grid system, these DC-side harmonics will be transmitted back to the AC side, further deteriorating the AC power quality, affecting the stable operation of the converter, and even threatening the safe operation of the power grid system. Further, the collected three-phase current i... abc Simultaneously, the signal is input to the second regulation and control unit 12 for harmonic suppression control, and a three-phase modulation wave fine-tuning signal u is output. m2abc And the three-phase main modulation wave u m1abc and the three-phase modulated wave fine-tuning signal u m2abc Adding them together yields the three-phase modulated wave signal u. mabc Then the three-phase modulated wave signal u mabc The pulse width modulation control unit 13 performs modulation processing and outputs pulse signals to drive the operation of the converter, thereby suppressing harmonics on the DC side of the converter, ensuring that the grid-connected current of the converter has high quality and low harmonic content, and improving the power quality and safety of the power grid system.

[0048] It is understood that the control processing through the first adjustment control unit 11 and the second adjustment control unit 12 includes signal processing methods such as coordinate transformation that are well known to those skilled in the art. The embodiments of the present invention do not impose special limitations on this, and the specific method of coordinate transformation can be selected according to different actual control strategies.

[0049] It should be noted that the present invention does not specifically limit the specific pulse width modulation strategy adopted by the pulse width modulation control unit 13, such as adopting a carrier modulation strategy or a space vector modulation strategy.

[0050] In this embodiment of the invention, the three-phase voltage and three-phase current values ​​of the AC side of the converter are collected and input as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal. At the same time, the three-phase current value is input as a feedback signal to the second regulating control unit to control the output of the three-phase modulation wave fine-tuning signal. The three-phase modulation wave fine-tuning signal can compensate for further stabilization of the converter and improvement of power quality. Then, the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added respectively to obtain the three-phase modulation wave signal of the converter. The modulation wave signal is then used to control the output of the pulse width modulation control unit to drive the converter to work, so that the grid-connected current of the converter has a low harmonic content and high quality, ensuring the stable operation of the converter, while improving the power quality and safety of the power grid system.

[0051] Optional, Figure 3 A flowchart of another converter control method provided in an embodiment of the present invention. Figure 4 This is a schematic diagram of another converter control structure provided in an embodiment of the present invention, combined with... Figure 3 and Figure 4 As shown, the second adjustment and control unit 12 includes a circulating current suppression unit 121 and a harmonic suppression unit 122; the three-phase current is input as a feedback signal to the second adjustment and control unit to control the output of a three-phase modulation wave fine-tuning signal, including: performing a first coordinate transformation on the three-phase current values ​​to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, wherein the angle of the first coordinate transformation is θ, θ=2θ PLL θ PLL The phase angle of the positive sequence voltage in the three-phase voltage values ​​is defined. The direct-axis and quadrature-axis currents are input to the circulating current suppression unit, controlling the output of the direct-axis and quadrature-axis voltage signals. The zero-sequence circulating current signal is obtained by summing the currents of each phase in the three-phase current values ​​and inputting it to the harmonic suppression unit, controlling the output of the zero-sequence voltage signal. The direct-axis, quadrature-axis, and zero-sequence voltage signals are then transformed using a second coordinate system to obtain the three-phase modulation wave fine-tuning signal in the three-phase coordinate system, where the angle of the second coordinate transformation is θ, where θ = 2θ. PLL θ PLLLet be the phase angle of the positive sequence voltage in the three-phase voltage values. Therefore, the control method includes:

[0052] S201. Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0053] S202. The three-phase voltage and three-phase current values ​​are input as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal.

[0054] S203. Perform a first coordinate transformation on the three-phase current values ​​to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, where the angle of the first coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0055] Specifically, according to the first coordinate transformation formula (i.e., the abc-dq coordinate transformation formula), the three-phase current value i in the three-phase coordinate system can be directly transformed. abc Converted to direct-axis current i in a two-phase rotating coordinate system d and cross-axis current i q When performing coordinate transformation, the corresponding transformation angle θ is twice the phase angle of the positive sequence voltage in the grid voltage value, that is, θ = 2θ. PLL Among them, the phase angle θ of the positive sequence voltage in the three-phase voltage values. PLL The phase angle of the positive sequence voltage in the three-phase power grid voltage value can be extracted by a conventional phase-locked loop. This embodiment of the invention does not limit the specific type of phase-locked loop.

[0056] S204. Input the direct-axis current and quadrature-axis current to the circulating current suppression unit to control the output of the direct-axis voltage signal and quadrature-axis voltage signal.

[0057] The circulating current suppression unit 121 may include a proportional-integral-derivative adjustment control unit or a proportional-integral adjustment control unit for follow control processing, and the present invention does not limit this.

[0058] Specifically, the circulating current suppression unit determines the direction of the current based on the obtained direct-axis current i. d and cross-axis current i q Further control processing is performed to obtain the direct-axis voltage signal u. d and quadrature axis voltage signal u q .

[0059] S205. The zero-sequence circulating current signal is obtained by summing the current of each phase in the three-phase current values. The zero-sequence circulating current signal is input to the harmonic suppression unit to control the output of the zero-sequence voltage signal.

[0060] Understandably, ideally, the three-phase current value i abcThe zero-sequence circulating current signal i0 corresponding to the sum of the currents of each phase should be zero, that is, i0 = i a +i b +i c =0.

[0061] The harmonic suppression unit 122 may include a proportional resonance adjustment control unit for follow control processing, etc., but the embodiments of the present invention do not limit this.

[0062] Specifically, after acquiring the zero-sequence circulating current signal i0, the harmonic suppression unit 122 performs further control processing and outputs the zero-sequence voltage signal u0.

[0063] S206. The direct-axis voltage signal, quadrature-axis voltage signal, and zero-sequence voltage signal are transformed into a three-phase modulation wave fine-tuning signal in a three-phase coordinate system through a second coordinate transformation, wherein the angle of the second coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0064] Specifically, according to the second coordinate transformation formula (dq0-abc coordinate transformation formula), the direct-axis voltage signal u can be transformed. d quadrature axis voltage signal u q The zero-sequence voltage signal u0 is converted into a three-phase voltage signal in a three-phase coordinate system, i.e., a three-phase modulation wave fine-tuning signal u. m2abc .

[0065] S207. Add the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal respectively to obtain the three-phase modulation wave signal of the converter.

[0066] S208. The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0067] In this embodiment, the second regulating control unit 12 is used to adjust the three-phase current value i abc When performing control processing, the direct-axis current i can be first... d and cross-axis current i q The input is sent to the circulating current suppression unit 121 for control processing to obtain the direct-axis voltage signal u. d and quadrature axis voltage signal u q .

[0068] The zero-sequence circulating current signal is obtained by summing the currents of each phase in the three-phase current values. This zero-sequence circulating current signal is then input to the harmonic suppression unit 122 for control processing to obtain the zero-sequence voltage signal u0. Finally, the direct-axis voltage signal u0 is... d quadrature axis voltage signal u qThe zero-sequence voltage signal u0 is further calculated using the second coordinate transformation formula to obtain the three-phase modulation wave fine-tuning signal u in the three-phase coordinate system. m2abc Then, it is made to match the three-phase main modulation wave u m1abc The summation yields the three-phase modulated wave signal u. mabc Then the three-phase modulated wave signal u mabc The pulse width modulation control unit 13 modulates and outputs pulse signals to drive the converter, thereby suppressing harmonics on the DC side of the converter, ensuring that the grid-connected current of the converter has high quality and low harmonic content, and improving the power quality and safety of the power grid system.

[0069] It should be noted that the formulas for the first coordinate transformation and the second transformation are commonly used calculation formulas by those skilled in the art, and will not be described in detail here.

[0070] Optional, Figure 5 A flowchart illustrating another converter control method provided in this embodiment of the invention. Figure 6 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention, combined with... Figure 5 and Figure 6 As shown, the harmonic suppression unit 122 includes a bandpass filter unit 1221 and a proportional resonant control unit 1222. The method involves summing the currents of each phase in the three-phase current values ​​to obtain a zero-sequence circulating current signal, inputting the zero-sequence circulating current signal to the harmonic suppression unit, and controlling the output of a zero-sequence voltage signal. This includes: summing the currents of each phase in the three-phase current values ​​to obtain a zero-sequence circulating current signal; inputting the zero-sequence circulating current signal to the bandpass filter unit to control the output of a harmonic signal; subtracting the harmonic signal from a first reference signal to obtain a first difference value; and inputting the first difference value to the proportional resonant control unit to control the output of a zero-sequence voltage signal. Therefore, this control method includes:

[0071] S301: Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0072] S302. The three-phase voltage and three-phase current values ​​are input as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal.

[0073] S303. Perform a first coordinate transformation on the three-phase current values ​​to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, where the angle of the first coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0074] S304. Input the direct-axis current and quadrature-axis current to the circulating current suppression unit to control the output of the direct-axis voltage signal and quadrature-axis voltage signal.

[0075] S305. The zero-sequence circulating current signal is obtained by summing the current of each phase in the three-phase current values. The zero-sequence circulating current signal is input into the bandpass filter unit to control the output harmonic signal.

[0076] The transfer function of the bandpass filter unit 1221 can be expressed as:

[0077]

[0078] Among them, A vp For bandpass gain, Q quality factor (1 / Q damping coefficient), ω n The characteristic angular frequency is denoted as ω.

[0079] Specifically, the embodiments of the present invention address A. vp The values ​​of ω and Q are not specifically limited and can be selectively set according to the design requirements of the control algorithm. n To determine the characteristic angular frequency of the pass-through filter unit, based on ω n Depending on the specific frequency setting, the bandpass filter unit 1221 can filter ω-free filters. n Signals of other angular frequencies are attenuated, meaning only signals with an angular frequency of ω can be output. n Harmonic signals.

[0080] S306. The first difference is obtained by subtracting the harmonic signal from the first reference signal. The first difference is input to the proportional resonant control unit to control the output of the zero-sequence voltage signal.

[0081] The transfer function of the proportional resonant control unit 1222 can be expressed as:

[0082]

[0083] Where, k p k is the proportionality coefficient. r ω is the resonance coefficient. n The characteristic angular frequency is denoted as ω.

[0084] Specifically, the first reference signal can be zero. The control input signal of the proportional resonant control unit 1222, i.e. the first difference, is obtained by subtracting the first reference signal from the harmonic signal. Then, the proportional resonant control unit performs further control processing on the first difference to obtain the zero-sequence voltage signal u0.

[0085] S307. The direct-axis voltage signal, quadrature-axis voltage signal, and zero-sequence voltage signal are transformed into a three-phase modulation wave fine-tuning signal in a three-phase coordinate system through a second coordinate transformation, wherein the angle of the second coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0086] S308. The three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added to each other respectively to obtain the three-phase modulation wave signal of the converter.

[0087] S309. The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0088] In this embodiment of the invention, when using the harmonic suppression unit 122 to control and process the zero-sequence circulating current signal, it is necessary to first reduce the three-phase current value i abc The zero-sequence circulating current signal i0 is obtained by summing the currents of each phase in the converter. This zero-sequence circulating current signal is then input to the bandpass filter unit 1221 to further obtain the harmonic signal with the characteristic angular frequency. The harmonic signal is then subtracted from the first reference signal (i.e., 0) to obtain the error control signal, which is then adjusted and controlled by the proportional resonant control unit 1222 to make the harmonic signal follow the first reference signal. The zero-sequence voltage signal u0 is then output for subsequent control processing, thereby suppressing the harmonics on the DC side of the converter and improving the stability and safety of the converter operation.

[0089] Optionally, the resonant frequencies in the bandpass filter unit 1221 and the proportional resonant control unit 1222 are the same, meaning the parameter settings corresponding to the characteristic angular frequencies in the bandpass filter unit 1221 and the proportional resonant control unit 1222 are identical. This ensures the stability of the entire control system.

[0090] Optional, Figure 7 A flowchart illustrating another converter control method provided in this embodiment of the invention. Figure 8 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention, combined with... Figure 7 and Figure 8 As shown, the harmonic suppression unit 122 further includes a limiting unit 1223; after obtaining a first difference value by subtracting the harmonic signal from the first reference signal, and inputting the first difference value to the proportional resonant control unit to control the output zero-sequence voltage signal, the method includes: comparing the zero-sequence voltage signal with the limiting range formed by the lower limit value to the upper limit value within the limiting unit, and determining whether the zero-sequence voltage signal exceeds the limiting range; if the zero-sequence voltage signal does not exceed the limiting range, the output zero-sequence voltage signal remains unchanged; if the zero-sequence voltage signal exceeds the limiting range, the output zero-sequence voltage signal is the upper limit value or the lower limit value. Therefore, this control method includes:

[0091] S401: Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0092] S402. The three-phase voltage and three-phase current values ​​are input as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal.

[0093] S403. Perform a first coordinate transformation on the three-phase current values ​​to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, where the angle of the first coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0094] S404: Input the direct-axis current and quadrature-axis current to the circulating current suppression unit, and control the output of the direct-axis voltage signal and quadrature-axis voltage signal.

[0095] S405. The zero-sequence circulating current signal is obtained by summing the current values ​​of each phase in the three-phase current. The zero-sequence circulating current signal is input into the bandpass filter unit to control the output harmonic signal.

[0096] S406. The first difference is obtained by subtracting the harmonic signal from the first reference signal. The first difference is input to the proportional resonant control unit to control the output of the zero-sequence voltage signal.

[0097] S407. Compare the zero-sequence voltage signal with the limiting range consisting of the lower limit value to the upper limit value within the limiting unit, and determine whether the zero-sequence voltage signal exceeds the limiting range. If the zero-sequence voltage signal does not exceed the limiting range, the output zero-sequence voltage signal remains unchanged. If the zero-sequence voltage signal exceeds the limiting range, the output zero-sequence voltage signal is the upper limit value or the lower limit value.

[0098] The lower limit and upper limit values ​​in the limiting unit 1223 can be selectively set according to actual control requirements, and this embodiment of the invention does not limit them.

[0099] Specifically, to reduce the impact of the second regulating control unit 12 on system stability, the zero-sequence voltage signal output by the proportional resonant control unit 1222 is limited. This prevents disturbances in the grid voltage from affecting the output of the proportional resonant control unit 1222, causing the zero-sequence voltage signal u0 to exceed the normal controllable range. Consequently, the three-phase modulation wave fine-tuning signal ultimately obtained by the second regulating control unit 12 exceeds the maximum modulation index of the modulation wave (usually 1, which is understood to be a per-unit value), thus affecting the operation of the converter. For example, the absolute values ​​of the lower and upper limits in the limiting unit 1223 should not exceed 0.1.

[0100] S408. The direct-axis voltage signal, quadrature-axis voltage signal, and zero-sequence voltage signal are transformed using a second coordinate system to obtain a three-phase modulation wave fine-tuning signal in a three-phase coordinate system, wherein the angle of the second coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0101] S409. Add the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal respectively to obtain the three-phase modulation wave signal of the converter.

[0102] S410: The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0103] Optional, Figure 9 A flowchart illustrating another converter control method provided in this embodiment of the invention. Figure 10 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention, combined with... Figure 9 and Figure 10 As shown, the second regulating control unit 12 further includes a harmonic detection unit 123; after summing the currents of each phase in the three-phase current values ​​to obtain the zero-sequence circulating current signal, it further includes: performing harmonic detection on the zero-sequence circulating current signal, determining the harmonic frequency of the zero-sequence circulating current signal, and inputting the harmonic frequency to the harmonic suppression unit. Therefore, this control method includes:

[0104] S501: Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0105] S502: Input the three-phase voltage and three-phase current values ​​as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal.

[0106] S503. Perform a first coordinate transformation on the three-phase current values ​​to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, where the angle of the first coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0107] S504: Input the direct-axis current and quadrature-axis current to the circulating current suppression unit, and control the output of the direct-axis voltage signal and quadrature-axis voltage signal.

[0108] S505. The zero-sequence circulating current signal is obtained by summing the current values ​​of each phase in the three-phase current.

[0109] S506. Perform harmonic detection on the zero-sequence circulating current signal, determine the harmonic frequency of the zero-sequence circulating current signal, and input the harmonic frequency to the harmonic suppression unit.

[0110] refer to Figure 8 and Figure 10 When the harmonic suppression unit 122 uses the zero-sequence circulating current signal i0 for control processing, it needs to obtain the frequency value of the harmonic component in the zero-sequence circulating current signal i0 and then convert it into the characteristic angular frequency value. Therefore, the harmonic detection unit 123 can perform harmonic detection on the zero-sequence circulating current signal i0 to obtain the frequency value of the harmonic component in the zero-sequence circulating current signal i0.

[0111] It should be noted that the embodiments of the present invention do not limit the specific detection method of the harmonic detection unit 123, such as using Fourier analysis to detect harmonic frequencies.

[0112] S507: Input the zero-sequence circulating current signal to the harmonic suppression unit and control the output of the zero-sequence voltage signal.

[0113] S508. The direct-axis voltage signal, quadrature-axis voltage signal, and zero-sequence voltage signal are transformed by a second coordinate system to obtain a three-phase modulation wave fine-tuning signal in a three-phase coordinate system, wherein the angle of the second coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0114] S509. The three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added to each other respectively to obtain the three-phase modulation wave signal of the converter.

[0115] S510: The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0116] Optional, Figure 11 A flowchart illustrating another converter control method provided in this embodiment of the invention. Figure 12 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention, combined with... Figure 11 and Figure 12 As shown, the circulating current suppression unit 121 includes a first proportional-integral (PI) control unit 1211 and a second PI control unit 1212. Inputting direct-axis current and quadrature-axis current into the circulating current suppression unit and controlling the output of direct-axis voltage signals and quadrature-axis voltage signals includes: inputting the direct-axis current into the first PI control unit to control the output of the direct-axis voltage signal; and inputting the quadrature-axis current into the second PI control unit to control the output of the quadrature-axis voltage signal. Therefore, this control method includes:

[0117] S601: Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0118] S602. The three-phase voltage and three-phase current values ​​are input as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal.

[0119] S603. Perform a first coordinate transformation on the three-phase current values ​​to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, where the angle of the first coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0120] S604. Input the direct-axis current to the first proportional-integral adjustment control unit to control the output of the direct-axis voltage signal, and input the quadrature-axis current to the second proportional-integral adjustment control unit to control the output of the quadrature-axis voltage signal.

[0121] The transfer function of a proportional-integral control unit can be expressed as:

[0122]

[0123] Where, k pi k is the proportionality coefficient. i is the integral coefficient.

[0124] The specific values ​​of the proportional coefficient and integral coefficient in the first proportional-integral control unit 1211 and the second proportional-integral control unit 1212 can be selectively set according to actual conditions, and the embodiments of the present invention do not limit this.

[0125] Furthermore, the proportional coefficient or integral coefficient in the first proportional-integral control unit and the second proportional-integral control unit may be the same or different, and the embodiments of the present invention do not limit this.

[0126] S605: Add the current of each phase in the three-phase current values ​​to obtain the zero-sequence circulating current signal, input the zero-sequence circulating current signal to the harmonic suppression unit, and control the output of the zero-sequence voltage signal.

[0127] S606. The direct-axis voltage signal, quadrature-axis voltage signal, and zero-sequence voltage signal are transformed into a three-phase modulation wave fine-tuning signal in a three-phase coordinate system through a second coordinate transformation, wherein the angle of the second coordinate transformation is θ, θ = 2θ. PLL θ PLL It represents the phase angle of the positive sequence voltage in the three-phase voltage values.

[0128] S607. The three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added to each other respectively to obtain the three-phase modulation wave signal of the converter.

[0129] S608: The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0130] Optional, Figure 13 A flowchart illustrating another converter control method provided in this embodiment of the invention. Figure 14 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention, combined with... Figure 13 and Figure 14As shown, the first regulating control unit 11 includes a power control unit 111 and a current control unit 112. The method of inputting three-phase voltage and three-phase current values ​​as feedback signals to the first regulating control unit to control the output of a three-phase main modulation wave signal includes: inputting the three-phase voltage and three-phase current values ​​to the power control unit to control the output of a current reference value; and inputting the current reference value and the three-phase current values ​​to the current control unit to control the output of a three-phase main modulation wave signal. Therefore, this control method includes:

[0131] S701: Collects the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0132] S702: Input the three-phase voltage and three-phase current values ​​to the power control unit to control the output current reference value.

[0133] The power control unit 111 can include reactive power control and active power control on the grid side of the converter. While ensuring the maximum active power output of the converter, it can also provide reactive power, specifically inductive reactive power or capacitive reactive power, to maintain the stability of the grid voltage.

[0134] Specifically, the power control unit 111 can adjust the three-phase voltage value u. abc and three-phase current value i abc Perform active and reactive power control, and control the output current reference value i. ref This serves as a reference value for controlling the current in the current control unit 112. It is understood that the output current reference value i varies depending on the coordinate system upon which the power control unit 111 operates during the control process. ref They will also differ; for example, the power control unit 111 is based on the three-phase voltage value u abc and three-phase current value i abc When the control is switched to a two-phase rotating coordinate system, the reference value of the output current controlled by the power control unit 111 is i. ref_dq This is the DC current reference value i. ref_d and cross-axis current reference value i ref_q The feedback current signal in the corresponding current control unit 112 also needs to be the current in a two-phase rotating coordinate system, that is, the three-phase current value i needs to be... abc The current in the two-phase rotating coordinate system is obtained by performing a coordinate transformation.

[0135] The specific control strategy of the power control unit 111 will not be described in detail in this embodiment of the invention, and conventional power control strategies can be used for control.

[0136] S703: Input the current reference value and the three-phase current value to the current control unit to control the output of the three-phase main modulation wave signal.

[0137] Specifically, the current control unit 112 can be based on the positive and negative sequence decoupling control of the three-phase current values, i.e., the DC current reference value i ref_d and cross-axis current reference value i ref_q The closed-loop control reference value for the positive-sequence current is zero, while the closed-loop control reference value for the negative-sequence current is zero. Simultaneously, the positive and negative-sequence current components, calculated using a conventional positive-negative-sequence decoupling unit, are subtracted from their corresponding reference values. These differences are then tracked and controlled by a regulating control unit (e.g., a proportional-integral control unit) to obtain voltage signals. Coordinate transformation is then performed to obtain the three-phase main modulation wave signals. It is understandable that the current control unit 112 employs a positive-negative-sequence decoupling control algorithm for the three-phase current values, which can further suppress the negative-sequence component in the three-phase current, thereby utilizing the balance of the three-phase current and improving the quality of the grid-connected current.

[0138] The specific algorithm for the positive and negative order decoupling unit in this embodiment of the invention will not be described in detail, as it is well known to those skilled in the art.

[0139] It should be noted that the current control unit 112 includes, but is not limited to, the methods described above, and may also employ other conventional control methods. This embodiment of the invention does not limit these methods.

[0140] S704: Input the three-phase current value as a feedback signal to the second regulation and control unit, and control the output of the three-phase modulation wave fine-tuning signal.

[0141] S705. Add the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal respectively to obtain the three-phase modulation wave signal of the converter.

[0142] S706: The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0143] Optional, Figure 15 A flowchart illustrating another converter control method provided in this embodiment of the invention. Figure 16 This is a schematic diagram of the control structure of another converter provided in an embodiment of the present invention, combined with... Figure 15 and Figure 16 As shown, the controller 100 also includes a phase-locked control unit 14; after acquiring the three-phase voltage and three-phase current values ​​on the AC side of the converter, it further includes: inputting the three-phase voltage values ​​to the phase-locked control unit, controlling the phase angle of the positive-sequence voltage in the output three-phase voltage values; and inputting the phase angle of the positive-sequence voltage in the three-phase voltage values ​​to the first regulating control unit and the second regulating control unit. Therefore, this control method includes:

[0144] S801: Collects the three-phase voltage and three-phase current values ​​on the AC side of the converter.

[0145] S802. Input the three-phase voltage values ​​to the phase-locked control unit, control the phase angle of the positive sequence voltage in the three-phase voltage values, and input the phase angle of the positive sequence voltage in the three-phase voltage values ​​to the first adjustment control unit and the second adjustment control unit.

[0146] The phase-locked control unit 14 includes, but is not limited to, a phase-locked loop (SOGI-PLL) based on a second-order generalized integrator for phase angle detection. Using SOGI-PLL for phase angle detection can quickly and accurately detect the phase angle θ of the positive sequence voltage in the three-phase voltage values. PLL Then it is transmitted to the first adjustment control unit 11 and the second adjustment control unit 12 as the rotation angle of the coordinate transformation in the first adjustment control unit 11 and the second adjustment control unit 12.

[0147] S803: Input the three-phase voltage and three-phase current values ​​as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal.

[0148] S804: Input the three-phase current value as a feedback signal to the second regulation and control unit, and control the output of the three-phase modulation wave fine-tuning signal.

[0149] S805. Add the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal respectively to obtain the three-phase modulation wave signal of the converter.

[0150] S806: The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work.

[0151] Based on the same inventive concept, embodiments of the present invention also provide a control device for a converter. Figure 17This is a schematic diagram of a control device for a converter according to an embodiment of the present invention. The control device includes a converter 200 and a controller 100 electrically connected to the converter 200. The controller 100 is used to control the operation of the converter 200. The controller 100 includes a sampling module 20, a control module 10, and a drive module 30. The control module 10 includes a first adjustment control unit 11 and a second adjustment control unit 12. The sampling module 20 is used to collect the three-phase voltage and three-phase current values ​​on the AC side of the converter. The control module 10 is used to input the three-phase voltage and three-phase current values ​​as feedback signals to the first adjustment control unit 11 to control the output of a three-phase main modulation wave signal, and to input the three-phase current values ​​as feedback signals to the second adjustment control unit 12 to control the output of a three-phase modulation wave fine-tuning signal. Then, the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added respectively to obtain the three-phase modulation wave signal of the converter, and the modulation wave signal is used to control the output of a pulse signal through a pulse width modulation control unit. The drive module 30 is used to drive the converter to work according to the output pulse signal.

[0152] The sampling module 20 includes a voltage sensor and a current sensor. The voltage sensor is used to collect the three-phase voltage values ​​on the AC side of the converter, and the current sensor is used to collect the three-phase current values ​​on the AC side of the converter. This embodiment of the invention does not limit the specific types of voltage and current sensors; they can be selectively set according to actual conditions. Furthermore, the sampling module 20 may also include signal processing units such as filters to filter out noise and other signals, ensuring the stability of the entire control system.

[0153] Specifically, the control module 10 includes, but is not limited to, a DSP or other control chip. It inputs the three-phase voltage and three-phase current values ​​as feedback signals to the first regulating control unit 11 to control the output of the three-phase main modulation wave signal. It also inputs the three-phase current values ​​as feedback signals to the second regulating control unit 12 to control the output of the three-phase modulation wave fine-tuning signal. Then, the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added to each other to obtain the three-phase modulation wave signal of the converter. The modulation wave signal is used to control the output of the pulse signal through the pulse width modulation control unit. Then, the drive module 30 outputs the pulse signal to each switch of the current transformer to drive the converter to work, ensuring that the grid-connected current of the converter has high quality and low harmonic content, thereby improving the power quality and safety of the power grid system.

[0154] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A control method for a converter, characterized in that, The converter is electrically connected to a controller, the controller being used to control the operation of the converter, the controller including a first regulation control unit and a second regulation control unit, the method including: Collect the three-phase voltage and three-phase current values ​​on the AC side of the converter; The three-phase voltage values ​​and the three-phase current values ​​are input as feedback signals to the first regulation and control unit to control the output of the three-phase main modulation wave signal; The three-phase current values ​​are input as feedback signals to the second adjustment and control unit to control the output of the three-phase modulation wave fine-tuning signal. The three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added together to obtain the three-phase modulation wave signal of the converter. The modulated wave signal is used to control the output pulse signal through the pulse width modulation control unit to drive the converter to work; The second adjustment and control unit includes a circulating current suppression unit and a harmonic suppression unit; The three-phase current values ​​are input as feedback signals to the second adjustment and control unit to control the output of a three-phase modulated wave fine-tuning signal, including: The three-phase current values ​​are subjected to a first coordinate transformation to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, wherein the angle of the first coordinate transformation is . , , The phase angle of the positive sequence voltage in the three-phase voltage values; The direct-axis current and the quadrature-axis current are input to the circulating current suppression unit to control the output of the direct-axis voltage signal and the quadrature-axis voltage signal; The zero-sequence circulating current signal is obtained by summing the currents of each phase in the three-phase current values. The zero-sequence circulating current signal is then input to the harmonic suppression unit to control the output of the zero-sequence voltage signal. The direct-axis voltage signal, quadrature-axis voltage signal, and zero-sequence voltage signal are transformed using a second coordinate system to obtain the three-phase modulation wave fine-tuning signal in a three-phase coordinate system, wherein the angle of the second coordinate transformation is . , , The phase angle of the positive sequence voltage in the three-phase voltage values; The harmonic suppression unit includes a proportional resonant adjustment control unit for follow-up control processing.

2. The control method for the converter according to claim 1, characterized in that, The harmonic suppression unit includes a bandpass filter unit and a proportional resonant control unit; The zero-sequence circulating current signal is obtained by summing the currents of each phase in the three-phase current values. This zero-sequence circulating current signal is then input to the harmonic suppression unit to control the output of the zero-sequence voltage signal, including: The zero-sequence circulating current signal is obtained by summing the currents of each phase in the three-phase current values. The zero-sequence circulating current signal is then input into the bandpass filter unit to control the output harmonic signal. The first difference is obtained by subtracting the harmonic signal from the first reference signal, and the first difference is input to the proportional resonant control unit to control the output of the zero-sequence voltage signal.

3. The control method for the converter according to claim 2, characterized in that, The bandpass filter unit and the proportional resonant control unit have the same resonant frequency.

4. The control method for the converter according to claim 2, characterized in that, The harmonic suppression unit also includes an amplitude limiting unit; After obtaining a first difference by subtracting the harmonic signal from the first reference signal, and inputting the first difference to the proportional resonant control unit to control the output of the zero-sequence voltage signal, the process includes: The zero-sequence voltage signal is compared with the limiting range consisting of the lower limit value to the upper limit value within the limiting unit to determine whether the zero-sequence voltage signal exceeds the limiting range. If the zero-sequence voltage signal does not exceed the limiting range, the output zero-sequence voltage signal remains unchanged. If the zero-sequence voltage signal exceeds the limiting range, the output zero-sequence voltage signal is the upper limit value or the lower limit value.

5. The control method for the converter according to claim 1, characterized in that, The second adjustment and control unit also includes a harmonic detection unit; After summing the phase currents of the three-phase current values ​​to obtain the zero-sequence circulating current signal, the method further includes: Harmonic detection is performed on the zero-sequence circulating current signal to determine the harmonic frequency of the zero-sequence circulating current signal, and the harmonic frequency is input to the harmonic suppression unit.

6. The control method for the converter according to claim 1, characterized in that, The circulating flow suppression unit includes a first proportional-integral adjustment control unit and a second proportional-integral adjustment control unit; The direct-axis current and the quadrature-axis current are input to the circulating current suppression unit to control the output of direct-axis voltage signals and quadrature-axis voltage signals, including: The direct-axis current is input to the first proportional-integral adjustment control unit to control the output of the direct-axis voltage signal; The quadrature-axis current is input to the second proportional-integral control unit to control the output quadrature-axis voltage signal.

7. The control method for the converter according to claim 1, characterized in that, The first regulation and control unit includes a power control unit and a current control unit; The three-phase voltage values ​​and the three-phase current values ​​are input as feedback signals to the first regulating control unit to control the output of the three-phase main modulation wave signal, including: The three-phase voltage values ​​and the three-phase current values ​​are input to the power control unit to control the output current reference value; The current reference value and the three-phase current value are input to the current control unit to control the output of the three-phase main modulation wave signal.

8. The control method for the converter according to claim 1, characterized in that, The controller also includes a phase-locked control unit; After acquiring the three-phase voltage and three-phase current values ​​on the AC side of the converter, the process also includes: The three-phase voltage values ​​are input to the phase-locked control unit, which controls the phase angle of the positive sequence voltage in the three-phase voltage values ​​to be output. The phase angle of the positive sequence voltage in the three-phase voltage values ​​is input to the first adjustment control unit and the second adjustment control unit.

9. A control device for a converter, characterized in that, The device includes the converter and a controller electrically connected to the converter. The controller is used to control the operation of the converter. The controller includes a sampling module, a control module, and a drive module. The control module includes a first regulation control unit and a second regulation control unit. The sampling module is used to collect the three-phase voltage and three-phase current values ​​on the AC side of the converter; The control module is used to input the three-phase voltage value and the three-phase current value as feedback signals to the first adjustment control unit to control the output of the three-phase main modulation wave signal, and to input the three-phase current value as feedback signals to the second adjustment control unit to control the output of the three-phase modulation wave fine-tuning signal. Then, the three-phase main modulation wave signal and the three-phase modulation wave fine-tuning signal are added respectively to obtain the three-phase modulation wave signal of the converter, and the modulation wave signal is used to control the output of the pulse signal through the pulse width modulation control unit. The drive module is used to drive the converter to work according to the pulse signal; The second adjustment and control unit includes a circulating current suppression unit and a harmonic suppression unit; The control module is also used for: The three-phase current values ​​are subjected to a first coordinate transformation to obtain the direct-axis current and quadrature-axis current in a two-phase rotating coordinate system, wherein the angle of the first coordinate transformation is . , , The phase angle of the positive sequence voltage in the three-phase voltage values; The direct-axis current and the quadrature-axis current are input to the circulating current suppression unit to control the output of the direct-axis voltage signal and the quadrature-axis voltage signal; The zero-sequence circulating current signal is obtained by summing the currents of each phase in the three-phase current values. The zero-sequence circulating current signal is then input to the harmonic suppression unit to control the output of the zero-sequence voltage signal. The direct-axis voltage signal, quadrature-axis voltage signal, and zero-sequence voltage signal are transformed using a second coordinate system to obtain the three-phase modulation wave fine-tuning signal in a three-phase coordinate system, wherein the angle of the second coordinate transformation is . , , The phase angle of the positive sequence voltage in the three-phase voltage values; The harmonic suppression unit includes a proportional resonant adjustment control unit for follow-up control processing.

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