Three-phase four-wire inverter control method, controller and inversion control system

Abstract

The invention belongs to the technical field of power electronics of power supply or power distribution, and provides a control method of a three-phase four-wire inverter, a controller and an inversion control system. A first control component is generated by using a phase angle, an inversion side three-phase current sampling value and a proportional integral compensator; a second control component and a third control component are generated by using a power grid voltage angular frequency, a neutral line current sampling value, a repetitive controller and a proportional resonance controller, the three control components are combined to control an inverter power switch tube, a proportional integral compensator is still adopted, the algorithm is simple, parameters are easy to design, and the reliability is high. And meanwhile, a repetitive-proportional resonance (RC-PR) composite controller is utilized to realize suppression of neutral line fundamental wave and harmonic current, and the method has faster dynamic response to load abrupt change, so that optimization of dynamic performance and steady-state performance is realized.

Description

Technical Field

[0001] This application relates to the field of power electronics technology for power supply or distribution, and in particular to a control method, controller and inverter control system for a three-phase four-wire inverter. Background Technology

[0002] Grid-connected inverters are the core component for distributed energy access to the power grid, and their performance directly determines the quality of the grid-connected current. Three-phase four-wire inverters can achieve higher power output and better power quality, and have a wide range of applications. However, in three-phase four-wire power supply systems, factors such as unbalanced grid voltage, nonlinear loads in the grid, and limitations of the inverter's own DC bus capacitor capacity result in the inverter's neutral line containing fundamental and harmonic current components, which affects the quality of the inverter's output power and may even fail to meet grid connection requirements. For example, when equipment (such as energy storage converters) undergoes power adjustment or unbalanced fault ride-through, a transient fundamental current will appear on the neutral line. Existing control methods for inverters, which use the inverter output current or grid current as feedback signals and employ proportional-integral methods to adjust the error signal and control the inverter's operation, suffer from insufficient suppression of steady-state errors and harmonics in the output current when applied to three-phase four-wire grid-connected inverters, making them susceptible to grid voltage distortion and harmonic interference. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide a control method, controller and inverter control system for a three-phase four-wire inverter.

[0004] In a first aspect, embodiments of this application provide a three-phase four-wire inverter control method, comprising the following steps: acquiring three-phase voltage sampling values ​​from the grid side, and inputting the three-phase voltage sampling values ​​from the grid side into a phase-locked loop module to obtain a phase angle and a grid voltage angular frequency; acquiring three-phase current sampling values ​​from the inverter side, and using the phase angle, the three-phase current sampling values ​​from the inverter side, and a first control circuit including a proportional-integral compensator connected between the three-phase current sampling circuit from the inverter side and a PWM generation module to generate a first control component; acquiring neutral current sampling values, and using the grid voltage angular frequency, the neutral current sampling values, and a second control circuit including a repetitive controller and a proportional-resonant controller connected between the neutral current sampling circuit from the neutral side and the PWM generation module to generate a second control component and a third control component; and inputting the first control component, the second control component, and the third control component into the PWM generation module to generate control signals for the inverter power switching transistors.

[0005] In some embodiments, generating a first control component using the phase angle, the inverter-side three-phase current sampled values, and a first control circuit connected between the inverter-side three-phase current sampling circuit and the PWM generation module, which includes a proportional-integral compensator, includes the following steps: obtaining a first-axis current component and a second-axis current component from the inverter-side three-phase current sampled values ​​and the phase angle input coordinate transformation module; inputting a first difference between the first-axis current component and the corresponding first-axis current reference value, and a second difference between the second-axis current component and the corresponding second-axis current reference value, respectively, into the proportional-integral compensator to obtain a first-axis control component and a second-axis control component; and obtaining a first control component in a three-phase coordinate system from the first-axis control component, the second-axis control component, and the phase angle input coordinate inverse transformation module.

[0006] In some embodiments, the step of generating a second control component and a third control component using the grid voltage angular frequency, the neutral current sample value, and a second control circuit connected between the neutral current sampling circuit and the PWM generation module, which includes a repetitive controller and a proportional resonant controller, includes the following steps: subtracting the neutral current reference value from the neutral current sample value after passing it through a low-pass filter module to obtain a neutral current difference; inputting the neutral current difference and the grid voltage angular frequency into the repetitive controller to obtain the second control component; and passing the neutral current difference and the grid voltage angular frequency through the proportional resonant controller to obtain the third control component.

[0007] In some embodiments, the transfer function of the proportional-integral compensator The expression is: In the expression, z is a discrete-domain operator. This is the proportional gain coefficient. The integral gain coefficient; the transfer function of the repetitive controller. The expression is: In the expression, N is the number of samples in one period, and C(z) is the compensator. , For the adjustable gain of the repetitive controller, For phase lead compensation, It is a low-pass filter. The coefficients of the internal mode filter; the transfer function of the proportional resonant controller. The expression is: In the expression, s is a continuous operator. ω is the fundamental angular frequency.

[0008] In some embodiments, Q(z) is a constant ranging from [0.9, 0.95], and K... r =0.5, k=6; S1(z)=1, or S1(z) is a low-pass filter.

[0009] In some embodiments, the transfer function of the proportional resonant controller The expression is: In the expression, s is a continuous operator. This is the proportional gain coefficient. The integral gain coefficient, The fundamental angular frequency, For bandwidth.

[0010] In a second aspect, this application provides a three-phase four-wire inverter control circuit, comprising: a grid-side three-phase voltage sampling circuit for acquiring grid-side three-phase voltage sampling values; an inverter-side three-phase current sampling circuit for acquiring inverter-side three-phase current sampling values; a neutral current sampling circuit for acquiring neutral current sampling values; a phase-locked loop module connected to the grid-side three-phase voltage sampling circuit, a first control circuit, and a second control circuit, for receiving the input grid-side three-phase voltage sampling values, obtaining a phase angle and a grid voltage angular frequency, and inputting the phase angle to the first control circuit and the grid voltage angular frequency to the second control circuit; the first control circuit includes a PWM generation module connected from the inverter-side three-phase current sampling circuit. The circuit includes a first control circuit comprising a proportional-integral compensator; the first control circuit is used to generate a first control component using the phase angle, the sampled value of the three-phase current on the inverter side, and the proportional-integral compensator; the second control circuit includes a circuit connecting the neutral current sampling circuit to the PWM generation module, the second control circuit including a repetitive controller and a proportional-resonant controller; the second control circuit is used to generate a second control component and a third control component using the grid voltage angular frequency, the sampled value of the neutral current, the repetitive controller, and the proportional-resonant controller; the PWM generation module is used to receive the input first control component, second control component, and third control component to generate control signals for the inverter power switching transistors.

[0011] In some embodiments, the first control circuit includes a coordinate transformation module, an error generation circuit, a proportional-integral compensator, and a coordinate inverse transformation module connected in sequence. The coordinate transformation module is used to receive the sampled values ​​of the three-phase current on the inverter side and the phase angle to obtain a first-axis current component and a second-axis current component. The error generation circuit is used to obtain a first difference based on the first-axis current component and the corresponding first-axis current reference value, and to obtain a second difference based on the second-axis current component and the corresponding second-axis current reference value. The proportional-integral compensator is used to receive the first difference and the second difference, and to obtain a first-axis control component and a second-axis control component based on the first difference and the second difference. The coordinate inverse transformation module is used to receive the input first-axis control component, the second-axis control component, and the phase angle to obtain a first control component in a three-phase coordinate system.

[0012] In some embodiments, the second control circuit includes a low-pass filter module, a neutral current error generation module, and a repetitive proportional resonant composite control module connected in sequence; the low-pass filter module is used to perform low-pass filtering on the collected neutral current sample value; the neutral current error generation module is used to obtain a neutral current difference based on the neutral current sample value after passing through the low-pass filter module and the neutral current reference value; in the repetitive proportional resonant composite control module, the repetitive controller and the proportional resonant controller are connected in parallel, the repetitive controller is used to obtain a second control component based on the neutral current difference and the grid voltage angular frequency, and the proportional resonant controller is used to obtain a third control component based on the neutral current difference and the grid voltage angular frequency.

[0013] Thirdly, this application provides an inverter control system for grid connection of an energy storage converter, including the three-phase four-wire inverter control circuit described in any of the above embodiments.

[0014] The beneficial effects that this application can achieve.

[0015] This application provides a three-phase four-wire inverter control method, controller, and inverter control system. It acquires the phase angle and grid voltage angular frequency, and uses the phase angle, the sampled values ​​of the inverter-side three-phase current, and a first control circuit containing a proportional-integral compensator to generate a first control component for the control signal used to generate the inverter power switch. It uses the grid voltage angular frequency, the sampled value of the neutral current, and a repetitive controller and a proportional-resonant controller to generate a second and third control component for the control signal used to generate the inverter power switch. The first, second, and third control components jointly control the inverter power switch. The proportional-integral compensator is still used to adjust the error signal of the inverter-side three-phase current on the dq axis and the reference current, and to control the inverter operation. The algorithm is simple, and the parameters are easy to design. Simultaneously, the repetitive-proportional resonant (RC-PR) composite controller is used to suppress the neutral fundamental and harmonic currents, and it has a faster dynamic response to load changes, achieving optimization of dynamic and steady-state performance. In addition, by inputting the grid voltage angular frequency ω output by the phase-locked loop into the control circuit, the frequency adaptability of the repetitive-proportional resonance (RC-PR) composite controller can be realized. This can effectively improve the ability to suppress transient fundamental currents that may appear on the neutral line when the equipment load power is adjusted or when an unbalanced fault occurs, resulting in higher system stability.

[0016] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of the three-phase four-wire inverter control circuit and inverter control system in an embodiment of this application is shown; Figure 2 A flowchart illustrating the three-phase four-wire inverter control method in an embodiment of this application is shown. Figure 3 A flowchart illustrating the generation of the first control component in the three-phase four-wire inverter control method of this application embodiment is shown. Figure 4 A schematic diagram of the process for generating the second control component and the third control component in the phase four-wire inverter control method of this application embodiment is shown. Figure 5A schematic diagram of an improved repeating controller according to an embodiment of this application is shown; Figure 6 The amplitude-frequency curves of the repetitive control discretization form in the embodiment of this application are shown.

[0019] Among them, 1-Grid-side three-phase voltage sampling circuit, 2-Phase-locked loop module, 3-First control circuit, 4-Second control circuit, 5-First proportional-integral compensator, 6-Second proportional-integral compensator, 7-Repetitive controller, 8-Proportional resonant controller, 9-PWM generation module, 10-Inverter-side three-phase current sampling circuit, 11-Neutral current sampling circuit, 12-Coordinate transformation module, 13-First axis error generation circuit, 14-Second axis error generation circuit, 15-Inverse coordinate transformation module, 16-Low-pass filter module, 17-Neutral current error generation module, 18-Repetitive proportional-resonant composite control module, 19-Proportional-integral compensator, 20-Error generation circuit, 21-Inverter bridge, 22-LCL filter, 23-AC EMI filter unit, 24-AC surge protector, 100-Inverter control system. Detailed Implementation

[0020] The term "comprising" in the specification, claims, and accompanying drawings of this application is synonymous with "including," "containing," or "characterized in," and is inclusive of endpoints or open-ended, and does not exclude additional unstated elements or method steps. "Comprising" is a technical term used in the language of the claims, meaning that the stated element is present, but other elements may be added and still form a construction or method within the scope of the claims.

[0021] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance. In this application, the term "about" means including minute variations (at most + / - 10%) of the stated value.

[0022] This application has found that existing inverter current control methods applied to three-phase four-wire grid-connected inverters have insufficient ability to suppress output current steady-state errors and harmonics, and are susceptible to grid voltage distortion and harmonic interference. To solve this problem, a proportional-integral compensator is used to adjust and control the inverter operation by adjusting the error signals of the three-phase current components on the dq axis and the reference current. At the same time, considering that the gain of the proportional resonance (PR) controller tends to infinity at the fundamental frequency, it can realize zero steady-state error tracking of sinusoidal quantities. On the basis of repetitive control, PR control is superimposed on the fundamental frequency to form a repetitive-proportional resonance (RC-PR) composite controller to suppress the neutral fundamental frequency and harmonic currents.

[0023] One embodiment of this application provides a three-phase four-wire inverter control method, comprising the following steps: acquiring three-phase voltage sampling values ​​from the grid side, and inputting the three-phase voltage sampling values ​​from the grid side into a phase-locked loop module to obtain a phase angle and a grid voltage angular frequency; acquiring three-phase current sampling values ​​from the inverter side, and using the phase angle, the three-phase current sampling values ​​from the inverter side, and a first control circuit including a proportional-integral compensator connected between the three-phase current sampling circuit from the inverter side and a PWM generation module to generate a first control component; acquiring neutral current sampling values, and using the grid voltage angular frequency, the neutral current sampling values, and a second control circuit including a repetitive controller and a proportional-resonant controller connected between the neutral current sampling circuit from the neutral side and the PWM generation module to generate a second control component and a third control component; and inputting the first control component, the second control component, and the third control component into the PWM generation module to generate control signals for the inverter power switching transistors.

[0024] In another embodiment of this application, a three-phase four-wire inverter control circuit is provided, comprising: a grid-side three-phase voltage sampling circuit for acquiring grid-side three-phase voltage sampling values; an inverter-side three-phase current sampling circuit for acquiring inverter-side three-phase current sampling values; a neutral current sampling circuit for acquiring neutral current sampling values; a phase-locked loop module connected to the grid-side three-phase voltage sampling circuit, a first control circuit, and a second control circuit, for receiving the input grid-side three-phase voltage sampling values, obtaining a phase angle and a grid voltage angular frequency, and inputting the phase angle to the first control circuit and the grid voltage angular frequency to the second control circuit; the first control circuit includes a circuit connected from the inverter-side three-phase current sampling circuit to a PWM generation module. The circuit includes a first control circuit comprising a proportional-integral compensator; the first control circuit is used to generate a first control component using the phase angle, the sampled value of the three-phase current on the inverter side, and the proportional-integral compensator; the second control circuit includes a circuit connecting the neutral current sampling circuit to the PWM generation module, the second control circuit including a repetitive controller and a proportional-resonant controller; the second control circuit is used to generate a second control component and a third control component using the grid voltage angular frequency, the sampled value of the neutral current, the repetitive controller, and the proportional-resonant controller, respectively; the PWM generation module is used to receive the input first control component, second control component, and third control component to generate control signals for the inverter power switching transistors.

[0025] The three-phase four-wire inverter control circuit and the three-phase four-wire inverter control method provided in this application use phase angle, three-phase current sampling values ​​on the inverter side and a first control circuit including a proportional-integral compensator to generate a first control component. The grid voltage angular frequency, neutral current sampling values ​​and a second control circuit including a repetitive controller and a proportional-resonant controller are used to generate a second control component and a third control component. The three control components jointly control the inverter power switching transistors. The proportional-integral compensator is still used. The algorithm is simple and the parameters are easy to design. At the same time, the repetitive-proportional resonant (RC-PR) composite controller is used to suppress the neutral fundamental current and harmonic current. It also has a faster dynamic response to load changes and achieves optimization of dynamic and steady-state performance.

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0028] Three-level converters have significant advantages over traditional two-level converters, leading to their widespread application. Neutral-point-clamped (NPC) three-level converters are the most widely used multilevel converters, offering the following advantages: (1) each power transistor withstands half the voltage of the DC side; (2) at the same switching frequency, the harmonic content of the output waveform is significantly reduced; and (3) power transistor switching losses are reduced. NPC three-level converters are widely used in three-phase three-wire (3P3W) systems, which contain split DC capacitors. The midpoint of the DC capacitors is directly connected to the AC power ground to form a three-phase four-wire (3P4W) system. However, in three-phase four-wire power supply systems, factors such as unbalanced grid voltage, nonlinear loads in the grid, and limitations of the inverter's own DC bus capacitor capacity result in the inverter's neutral line containing fundamental and harmonic current components. This affects the inverter's output power quality (due to the fundamental and zero-sequence components in the neutral current, the network neutral current becomes excessive, causing, for example, overload of the distribution transformer and distortion of the line current), and may even fail to meet grid connection requirements. For example, when equipment (such as power conversion systems, PCS) undergoes load power adjustment or unbalanced fault ride-through, a transient fundamental current will appear on the neutral line. Therefore, research on algorithms for suppressing the fundamental and harmonic currents in the neutral line of three-phase four-wire grid-connected inverters is an important topic.

[0029] Most existing current control methods for grid-connected inverter systems use the inverter-side inductor current (i.e., inverter output current) of the LCL low-pass filter or the grid-side inductor current (grid current) as feedback signals, employing proportional-integral (PI) or similar methods to adjust the error signal and control the inverter's operation. Because the LCL filter makes the controlled object a third-order system, a large gain spike exists near the filter's corner frequency. To ensure system stability, the gain of the PI regulator is limited, resulting in a small value. This leads to a small open-loop gain in the low-frequency range, limiting the system's ability to suppress output current steady-state error (the difference between the desired and actual steady-state output) and harmonics. Furthermore, since the PI regulator's gain at the grid fundamental frequency is finite, it generates steady-state error and harmonic interference when tracking sinusoidal signals, and is also susceptible to grid voltage distortion and harmonic interference. Therefore, existing current control methods for grid-connected inverter systems cannot be directly applied to the control of three-phase four-wire grid-connected inverters.

[0030] While existing repetitive control (RC) based on the internal model principle can effectively suppress harmonic pollution, it suffers from poor dynamic performance and ineffective suppression of aperiodic disturbances. Combining proportional-integral (PI) control with repetitive control in inverter control significantly improves control accuracy and dynamic performance, but the harmonic suppression capability of this composite control strategy is easily affected by the PI parameters, resulting in a complex controller design.

[0031] This application has found that existing inverter current control methods applied to three-phase four-wire grid-connected inverters have insufficient ability to suppress output current steady-state errors and harmonics, and are susceptible to grid voltage distortion and harmonic interference. To solve this problem, a proportional-integral compensator is used to adjust and control the inverter operation by adjusting the error signals of the three-phase current components on the dq axis and the reference current. At the same time, considering that the gain of the proportional resonance (PR) controller tends to infinity at the fundamental frequency, it can realize zero steady-state error tracking of sinusoidal quantities. On the basis of repetitive control, PR control is superimposed on the fundamental frequency to form a repetitive-proportional resonance (RC-PR) composite controller to suppress the neutral fundamental frequency and harmonic currents.

[0032] This application provides a three-phase four-wire inverter control circuit, such as... Figure 1As shown in the diagram. The three-phase four-wire inverter control circuit includes a grid-side three-phase voltage sampling circuit 1 (e.g., an AC voltage transformer), connected to the U-phase, V-phase, and W-phase lines on the grid side, used to acquire grid-side three-phase voltage sampling values ​​Vu, Vv, and Vw. The three-phase four-wire inverter control circuit also includes an inverter-side three-phase current sampling circuit 10 (e.g., a current transformer), used to acquire inverter-side three-phase current sampling values ​​Iu, Iv, and Iw. The three-phase four-wire inverter control circuit also includes a neutral current sampling circuit 11 (e.g., a current transformer), used to acquire the neutral current sampling value In. The three-phase four-wire inverter control circuit also includes a phase-locked loop (PLL) module 2. The PLL module 2 is connected to the grid-side three-phase voltage sampling circuit 1, the first control circuit 3, and the second control circuit 4. It receives the input grid-side three-phase voltage sampling values ​​Vu, Vv, and Vw, obtains the phase angle θ and the grid voltage angular frequency ω through its internal PLL circuit, and inputs the phase angle θ to the first control circuit 3 and the grid voltage angular frequency ω to the second control circuit 4. The three-phase four-wire inverter control circuit also includes the first control circuit 3, which includes circuitry connecting the inverter-side three-phase current sampling circuit 10 to the PWM generation module 9. The first control circuit 3 includes a proportional-integral (PI) compensator 19. The first control circuit 3 uses the phase angle θ, the grid-side three-phase voltage sampling values ​​Vu, Vv, and Vw, and the PI compensator 19 to generate a first control component for generating control signals for the inverter power switching transistors. In some embodiments of this application, the proportional-integral compensator 19 includes a first proportional-integral compensator 5 and a second proportional-integral compensator 6, which respectively compensate for the d-axis error component and the q-axis error component. The three-phase four-wire inverter control circuit also includes a second control circuit 4, which includes circuitry connecting the neutral current sampling circuit 11 to the PWM generation module 9. The second control circuit 4 includes a repetitive controller 7 and a proportional resonant controller 8. The second control circuit 4 is used to generate a second control component and a third control component for generating control signals for the inverter power switches using the grid voltage angular frequency ω, the neutral current sampling value In, and the repetitive controller 7 and the proportional resonant controller 8. The three-phase four-wire inverter control circuit also includes a PWM generation module 9, which receives the input first control component, second control component, and third control component to generate control signals for the inverter power switches.

[0033] Combination Figure 1As shown, the first control circuit 3 includes a coordinate transformation module 12, an error generation circuit 20, a proportional-integral compensator 19, and a coordinate inverse transformation module 15 connected in sequence. The coordinate transformation module 12 receives the input three-phase current sampling values ​​Iu, Iv, and Iw from the inverter side and the phase angle θ to obtain the first-axis current component IQ and the second-axis current component ID. The coordinate transformation module 12 converts the electrical quantities of the three-phase stationary coordinate system into a two-phase coordinate system, for example, using Clark / Park transformation or 3S / 2R transformation. The error generation circuit 20 obtains a first difference EIQ based on the first-axis current component IQ and the corresponding first-axis current reference value IQref, and a second difference EID based on the second-axis current component ID and the corresponding second-axis current reference value IDref. In this embodiment, the error generation circuit 20 includes a first error generation circuit 13 and a second error generation circuit 14. The first error generation circuit 13 obtains the first difference EIQ based on the first-axis current component IQ and the corresponding first-axis current reference value IQref. The second error generation circuit 14 is used to obtain a second difference EID based on the second axis current component ID and the corresponding second axis current reference value IDref. The proportional-integral compensator 19 is used to receive the first difference EIQ and the second difference EID, and obtain a first axis control component Uq and a second axis control component Ud based on the first difference EIQ and the second difference EID. In this embodiment, the proportional-integral compensator 19 includes a first proportional-integral compensator 5 and a second proportional-integral compensator 6. The first proportional-integral compensator 5 obtains the first axis control component Uq based on the first difference EIQ, and the second proportional-integral compensator 6 obtains the second axis control component Ud based on the second difference EID. The inverse coordinate transformation module 15 is used to receive the input first axis control component Uq, the second axis control component Ud, and the phase angle θ to obtain the first control component in a three-phase coordinate system. The inverse coordinate transformation module 15 converts the components of the two-phase coordinate system into electrical quantities in a three-phase stationary coordinate system, for example, using Clark inverse transformation / Park inverse transformation or 2r / 3s transformation.

[0034] Combination Figure 1As shown, the second control circuit 4 includes a low-pass filter module 16, a neutral current error generation module 17, and a repetitive proportional resonant composite control module 18 connected in sequence. The low-pass filter module 16 is used to low-pass filter the acquired neutral current sample value In. The neutral current error generation module 17 is used to obtain the neutral current difference Inerr based on the value inlp obtained from the neutral current sample value after the low-pass filter module and the neutral current reference value Inref. In some embodiments of this application, the neutral current reference value Inref is set to 0. The repetitive controller 7 and the proportional resonant controller 8 in the repetitive proportional resonant composite control module 18 are connected in parallel. The repetitive controller 7 is used to obtain a second control component based on the neutral current difference Inerr and the grid voltage angular frequency ω. The proportional resonant controller 8 is used to obtain a third control component based on the neutral current difference Inerr and the grid voltage angular frequency ω.

[0035] This application provides a three-phase four-wire inverter control circuit that still uses a proportional-integral compensator to adjust and control the inverter operation by modifying the error signals of the three-phase current components on the dq axis and the reference current. The algorithm is simple and the parameters are easy to design. Simultaneously, a repetitive-proportional resonant (RC-PR) composite controller is used to suppress the fundamental and harmonic currents of the neutral line, effectively suppressing harmonics and both aperiodic and periodic disturbances. It also exhibits a faster dynamic response to load surges, achieving optimal dynamic and steady-state performance. The feasibility of the scheme in this application has been verified on a 125kW three-phase four-wire NPC inverter. Under conditions such as unbalanced grid voltage, the fundamental and harmonic currents of the neutral line are significantly suppressed. In addition, considering the frequency sensitivity of the above-mentioned repetitive proportional resonant (RC-PR) composite controller, the grid voltage angular frequency ω output by the phase-locked loop is input to the control circuit to realize the frequency adaptability of the repetitive proportional resonant (RC-PR) composite controller. It has a wide frequency adaptation range, and the frequency adaptability of the controller is realized by adjusting the grid frequency in real time. The controller can effectively improve the ability to suppress transient fundamental current that will appear on the neutral line when the PCS load power is adjusted or when an unbalanced fault crosses, and has higher system stability.

[0036] Accordingly, an embodiment of this application provides a three-phase four-wire inverter control method, see [link to relevant documentation]. Figure 2 The steps shown are as follows: Step S01: Obtain the sampled values ​​of the three-phase voltage on the grid side, and input the sampled values ​​of the three-phase voltage on the grid side into the phase-locked loop module to obtain the phase angle and the angular frequency of the grid voltage; Step S02: Obtain the three-phase current sampling value on the inverter side, and use the phase angle, the three-phase current sampling value on the inverter side, and the first control circuit connected between the three-phase current sampling circuit on the inverter side and the PWM generation module, which includes a proportional-integral compensator, to generate a first control component; Step S03: Obtain the neutral current sampling value, and use the grid voltage angular frequency, the neutral current sampling value, and a second control circuit connected between the neutral current sampling circuit and the PWM generation module, which includes a repetitive controller and a proportional resonant controller, to generate a second control component and a third control component. Step S04: Input the first control component, the second control component, and the third control component into the PWM generation module to generate control signals for the inverter power switching transistors.

[0037] It should be noted that although step numbers S01, S02, S03, S04, etc., are used in the embodiments of this application, these step numbers do not constitute a limitation on the order of the steps. In some embodiments of this application, some steps can be performed simultaneously, or the order of the steps can be interchanged. For example, the control step of obtaining the first control component in step S02 and the step of obtaining the second and third control components in step S03 can be performed simultaneously, or the order can be interchanged, that is, step S03 can be run first to obtain the second and third control components, and then step S02 can be run to obtain the first control component. Similarly, the step numbers S0201, S0202, S0203 and step numbers S0301, S0302, S0303, etc., in the method below of this application do not constitute a limitation on the order of the steps.

[0038] In step S01, the three-phase voltage sample values ​​on the grid side can be obtained using an AC voltage transformer (i.e., a three-phase voltage sampling circuit on the grid side) installed on the grid side. A phase-locked loop (PLL) is a negative feedback system capable of automatically tracking the phase and frequency of an input signal. It is a widely used circuit structure and will not be described in detail here. The PLL module can output the phase angle and the grid voltage angular frequency based on the three-phase voltage sample values.

[0039] Combination Figure 3 As shown, the step of obtaining the first control component in step S02 further includes the following steps: Step S0201: Obtain the first axis current component and the second axis current component by combining the sampled values ​​of the three-phase current on the inverter side and the phase angle input coordinate transformation module; Step S0202: Input the first difference between the first axis current component and the corresponding first axis current reference value, and the second difference between the second axis current component and the corresponding second axis current reference value into the proportional-integral compensator to obtain the first axis control component and the second axis control component; Step S0203: The first control component in the three-phase coordinate system is obtained by the inverse transformation module of the first axis control component, the second axis control component and the phase angle input coordinate.

[0040] In step S0201, the inverter-side three-phase current sampling circuit acquires the sampled values ​​of the inverter-side three-phase current. The coordinate transformation module can be Clark transformation / Park transformation or 3S / 2R transformation. For example, Clark transformation can be used to convert the three-phase AC system into two-phase stationary coordinates, which facilitates system analysis.

[0041] In step S0202, the first axis current reference value and the second current reference value can be reference values ​​set based on experience. In some embodiments, the above reference values ​​can also be obtained by sampling the three-phase voltage on the grid side and then performing coordinate transformation and relational calculation.

[0042] The transfer function of the proportional-integral compensator in this application The expression is: In the expression, z is a discrete-domain operator. This is the proportional gain coefficient. This is the integral gain coefficient.

[0043] In step S0203, the coordinate inverse transformation module, such as Clark inverse transformation / Park inverse transformation or 2r / 3s transformation, converts the two-phase coordinates into three-phase AC coordinates.

[0044] Combination Figure 4 As shown, the step of obtaining the second control component and the third control component in step S03 further includes the following steps: S0301: Subtract the neutral current reference value from the sampled neutral current value after passing it through a low-pass filter module to obtain the neutral current difference; S0302: Input the neutral current difference and the grid voltage angular frequency into the repetitive controller to obtain the second control component; S0303: The difference in the neutral current and the angular frequency of the grid voltage are used to obtain the third control component through a proportional resonant controller.

[0045] The neutral current sampling circuit in step S0301 can acquire the sampled value of the neutral current. For example, a current transformer can be used for this circuit. The low-pass filter module is a conventional low-pass filter that filters out high-frequency components in the neutral current. The neutral current reference value can be a value set empirically, for example, it can be set to 0.

[0046] In step S0302, the repetitive controller is as follows: Figure 5 As shown, the controlled object is P(z), which is the transfer function of the system, and the transfer function of the repetitive controller. The expression is: , In the expression, N represents the number of samples in one cycle, i.e., one control cycle. N = system sampling frequency / fundamental frequency. For example, if the system sampling frequency is 16kHz and the fundamental frequency is 50Hz, then the number of samples in one cycle is: 16kHz / 50Hz = 320. In the control method of this application, the output grid voltage angular frequency of the phase-locked loop module is given to the repetitive controller. When the grid frequency changes, the real-time frequency of the grid is obtained through the phase-locked loop, and the period of the grid fundamental frequency is calculated, thereby calculating the control cycle in real time.

[0047] C(z) is a compensator. . Kr is the adjustable gain of the repetitive controller. The larger the gain, the faster the error convergence speed, but the lower the stability margin of the controller. The smaller the gain, the slower the error convergence speed, but the higher the stability margin of the repetitive controller. It is usually taken as a constant between 0 and 1. For phase advance compensation, the error of the current cycle is applied in advance in the next cycle to achieve phase advance compensation. This is a low-pass filter, configured to correct the low-to-mid frequencies of the controlled object to 1. For example, in some embodiments, after parameter calculation and trial and error, it is set as a first-order low-pass filter S1(z) = 5000 / s + 5000. As another example, in some embodiments... No signal correction is required. In other embodiments, Set as a second-order Butterworth low-pass filter. , This is the angular frequency corresponding to the filter cutoff frequency. The damping coefficient is... .

[0048] Let Q(z) be the coefficients of the internal model filter. Without Q(z), the control system would have N open-loop poles on the unit circle, causing it to exhibit critical oscillations. In this state, any change in the controlled object could easily lead to instability in the closed-loop system. Therefore, considering the stability and robustness of the control system, Q(z) is often added. Q(z) can be designed as a low-pass filter. The advantage of designing it as a low-pass filter is that it provides attenuation in the high-frequency range while maintaining constant gain in the mid-to-low-frequency range. The disadvantage is the unavoidable introduction of phase shift. As a trade-off, replacing Q(z) with a number close to 1 transforms the control system from a zero-error system into a flawed system.

[0049] Furthermore, in some embodiments of this application, Q(z) is a constant ranging from [0.9, 0.95], and K... r =0.5, k=6; S1(z)=1, or S1(z) is a low-pass filter, the repetitive controller in this application has good performance. For example, when Q(z)=0.9, 0.93 or 0.95, K r Good results can be achieved when k=0.5 and k=6. Figure 6 As shown in the amplitude-frequency curve of the repetitive control, its gain is relatively large at the DC component. During program processing, the DC component can be removed by the moving average method, so that the repetitive controller only acts on the fundamental and harmonic frequencies of the midpoint current, thus avoiding conflict with the DC bus midpoint voltage controller.

[0050] The transfer function of the proportional resonant controller in step S0303 of this application The expression is: In the expression, s is a continuous operator. This is the fundamental angular frequency. It can be seen that the proportional resonance (PR) controller... As the value approaches infinity, zero steady-state error control of AC signals can be achieved.

[0051] In practical systems, due to device saturation and hardware circuit limitations, it is difficult to achieve infinite gain at a specific frequency, and the mains frequency is not always constant. This makes it difficult for an ideal proportional resonant controller to achieve the desired effect in both implementation and use. In some embodiments of this application, using a quasi-PR controller to form a closed-loop control can effectively solve these problems. Although the quasi-PR controller cannot produce infinite gain at a specific frequency to achieve zero steady-state error control, the gain obtained by the quasi-PR controller at a specific frequency is still quite high, and the steady-state error is very small. In some embodiments of this application, the transfer function of the proportional resonant controller... The expression is: , In the expression, s is a continuous operator. This is the proportional gain coefficient. The integral gain coefficient, The fundamental angular frequency, For bandwidth. In some embodiments, ,in This refers to the frequency fluctuation range.

[0052] The three-phase four-wire inverter control method provided in this application still uses a proportional-integral compensator to adjust and compensate for the error signal of the three-phase current on the dq axis and the reference current on the inverter side, and generates a first control component for generating the control signal for the inverter power switch. The algorithm is simple and the parameters are easy to design. At the same time, a repetitive-proportional resonant (RC-PR) composite controller is used to generate a second and a third control component for generating the control signal for the inverter power switch. The first, second, and third control components are all input to the PWM generation module to generate the control signal for the inverter power switch. This can achieve suppression of the neutral fundamental current and harmonic currents, effectively suppressing harmonics and non-periodic and periodic disturbances. At the same time, it has a faster dynamic response to load changes, achieving optimization of dynamic and steady-state performance. The feasibility of the scheme in this application has been verified on a 125kW three-phase four-wire NPC inverter. Under conditions such as unbalanced grid voltage, the fundamental current and all harmonic currents of the neutral current are significantly suppressed. In addition, considering the frequency sensitivity of the above-mentioned repetitive proportional resonant (RC-PR) composite controller, the grid voltage angular frequency ω output by the phase-locked loop is input to the control circuit to realize the frequency adaptability of the repetitive proportional resonant (RC-PR) composite controller. It has a wide frequency adaptation range, and the frequency adaptability of the controller is realized by adjusting the grid frequency in real time. The controller can effectively improve the ability to suppress transient fundamental current that will appear on the neutral line when the equipment load power is adjusted or when an unbalanced fault crosses, and has higher system stability.

[0053] A Power Conversion System (PCS) is the core component of an energy storage system, responsible for bidirectional conversion of electrical energy. Unlike ordinary inverters, PCS can achieve bidirectional conversion between AC / DC and DC / AC, enabling bidirectional flow of electrical energy between the grid and the battery. Its core function is to act as a bridge between the battery energy storage unit and the grid (or load), achieving efficient and safe bidirectional energy flow. The PCS system mainly consists of power conversion units (including switching devices such as IGBTs), a control system, and a communication interface, and is a key component determining the performance of the entire energy storage system.

[0054] See Figure 1As shown in the illustration, an inverter control system 100 for PCS grid connection is also provided in the embodiments of this application, including an inverter bridge 21, an LCL filter 22, an AC EMI filter unit 23 (EMI, or electromagnetic interference), an AC surge protector 24, and a three-phase four-wire inverter control circuit as described in any of the above embodiments, connected in sequence. For the three-phase four-wire inverter control circuit, please refer to the description above; it will not be repeated here. The inverter bridge 21 includes a series of power switching transistors, the switching of which is controlled by a signal generated by a PWM generation module. The output of the inverter bridge 21 is connected to the LCL filter 22, the output of the LCL filter 22 is connected to the AC EMI filter unit 23, and the output of the AC EMI filter unit 23 is connected to the power grid. The AC surge protector 24 is disposed between the AC EMI filter unit 23 and the power grid side. The LCL filter 22 includes an inverter-side inductor Li, a filter capacitor Cf, and a grid-side inductor Lg. An electromagnetic interference filter (EMI filter) is an electronic device that reduces internal and external electromagnetic interference by suppressing conducted interference and improving electromagnetic compatibility. It is a conventional device and will not be described in detail here. AC surge protector 24 is a non-linear voltage limiting device installed in the converter station for overvoltage protection of various electrical equipment. It belongs to the category of metal oxide surge arresters and is also a conventional device, so it will not be described in detail here.

[0055] The inverter control system for PCS grid connection provided in this application embodiment adopts the three-phase four-wire inverter control circuit in the above embodiment. On the one hand, the parameters are easy to design, and on the other hand, it can suppress the neutral fundamental current and harmonic current. It can effectively improve the ability to suppress transient fundamental current that will appear on the neutral line when the PCS load power is adjusted or an unbalanced fault occurs. At the same time, it has a faster dynamic response to load changes, and achieves the optimization of dynamic performance and steady-state performance.

[0056] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A control method for a three-phase four-wire inverter, characterized in that, Includes the following steps: The three-phase voltage sampling values ​​on the grid side are obtained, and the three-phase voltage sampling values ​​on the grid side are input into the phase-locked loop module to obtain the phase angle and the grid voltage angular frequency; The inverter-side three-phase current sampling value is obtained, and a first control component is generated using the phase angle, the inverter-side three-phase current sampling value, and a first control circuit connected between the inverter-side three-phase current sampling circuit and the PWM generation module, which includes a proportional-integral compensator. The neutral current sampling value is obtained, and a second control component and a third control component are generated using the grid voltage angular frequency, the neutral current sampling value, and a second control circuit connected between the neutral current sampling circuit and the PWM generation module, which includes a repetitive controller and a proportional resonant controller. The first control component, the second control component, and the third control component are all input into the PWM generation module to generate control signals for the inverter power switching transistors.

2. The three-phase four-wire inverter control method according to claim 1, characterized in that, The step of generating a first control component using the phase angle, the inverter-side three-phase current sampling value, and a first control circuit connected between the inverter-side three-phase current sampling circuit and the PWM generation module, which includes a proportional-integral compensator, includes the following steps: The sampled values ​​of the three-phase current on the inverter side and the phase angle are both input into the coordinate transformation module to obtain the first-axis current component and the second-axis current component. The first difference between the first axis current component and the corresponding first axis current reference value, and the second difference between the second axis current component and the corresponding second axis current reference value are respectively input into the proportional-integral compensator to obtain the first axis control component and the second axis control component; The first control component in the three-phase coordinate system is obtained by the inverse transformation module of the first axis control component, the second axis control component and the phase angle input coordinate.

3. The three-phase four-wire inverter control method according to claim 1, characterized in that, The process of generating a second control component and a third control component using the grid voltage angular frequency, the neutral current sample value, and a second control circuit connected between the neutral current sampling circuit and the PWM generation module, which includes a repetitive controller and a proportional resonant controller, includes the following steps: The sampled value of the neutral current is passed through a low-pass filter module and then subtracted from the reference value of the neutral current to obtain the difference in the neutral current. The neutral current difference and the grid voltage angular frequency are input into the repetitive controller to obtain the second control component; The difference in the neutral current and the angular frequency of the grid voltage are used to obtain a third control component through a proportional resonant controller.

4. The three-phase four-wire inverter control method according to claim 1, characterized in that, The transfer function of the proportional-integral compensator The expression is: ， In the expression, z is a discrete-domain operator. This is the proportional gain coefficient. This is the integral gain coefficient; The transfer function of the repetitive controller The expression is: ， In the expression, N is the number of samples in one period, and C(z) is the compensator. , For the adjustable gain of the repetitive controller, For phase lead compensation, It is a low-pass filter. These are the coefficients of the internal model filter; The transfer function of the proportional resonant controller The expression is: ， In the expression, s is a continuous operator. ω is the fundamental angular frequency.

5. A three-phase four-wire inverter control method according to claim 4, characterized in that, Q(z) is a constant, ranging from [0.9, 0.95], and K... r =0.5, k=6; S1(z)=1, or S1(z) is a low-pass filter.

6. The three-phase four-wire inverter control method according to claim 1, characterized in that, The transfer function of the proportional resonant controller The expression is: ， In the expression, s is a continuous operator. This is the proportional gain coefficient. The integral gain coefficient, The fundamental angular frequency, For bandwidth.

7. A three-phase four-wire inverter control circuit, characterized in that, include: A three-phase voltage sampling circuit on the grid side is used to obtain sampled values ​​of the three-phase voltage on the grid side. The inverter-side three-phase current sampling circuit is used to obtain the sampled values ​​of the inverter-side three-phase current. Neutral current sampling circuit, used to obtain neutral current sampling value; The phase-locked loop module is connected to the three-phase voltage sampling circuit on the grid side, the first control circuit, and the second control circuit. It is used to receive the input three-phase voltage sampling values ​​on the grid side, obtain the phase angle and the grid voltage angular frequency, and input the phase angle into the first control circuit and the grid voltage angular frequency into the second control circuit. A first control circuit includes circuitry connecting a three-phase current sampling circuit on the inverter side to a PWM generation module. The first control circuit includes a proportional-integral compensator. The first control circuit is used to generate a first control component using the phase angle, the three-phase current sampling value on the inverter side, and the proportional-integral compensator. The second control circuit includes a circuit connecting the neutral current sampling circuit to the PWM generation module, and the second control circuit includes a repetitive controller and a proportional resonant controller. The second control circuit is used to generate a second control component and a third control component using the grid voltage angular frequency, the neutral current sampling value, the repetitive controller, and the proportional resonant controller, respectively. The PWM generation module is used to receive the first, second, and third control components and generate control signals for the inverter power switching transistors.

8. A three-phase four-wire inverter control circuit according to claim 7, characterized in that, The first control circuit includes a coordinate transformation module, an error generation circuit, a proportional-integral compensator, and an inverse coordinate transformation module connected in sequence. The coordinate transformation module is used to receive the sampled values ​​of the three-phase current on the inverter side and the phase angle to obtain the first axis current component and the second axis current component. The error generation circuit is used to obtain a first difference based on the first axis current component and the corresponding first axis current reference value, and to obtain a second difference based on the second axis current component and the corresponding second axis current reference value. The proportional-integral compensator is used to receive the first difference and the second difference, and to obtain the first axis control component and the second axis control component based on the first difference and the second difference. The coordinate inverse transformation module is used to receive the input first axis control component, the second axis control component and the phase angle to obtain the first control component in the three-phase coordinate system.

9. A three-phase four-wire inverter control circuit according to claim 7, characterized in that, The second control circuit includes a low-pass filter module, a neutral current error generation module, and a repetitive proportional resonance composite control module connected in sequence. The low-pass filter module is used to perform low-pass filtering on the collected neutral current sample value; The neutral current error generation module is used to obtain the neutral current difference based on the neutral current sample value and the neutral current reference value obtained through the low-pass filter module. In the repetitive proportional resonant composite control module, the repetitive controller and the proportional resonant controller are connected in parallel. The repetitive controller is used to obtain a second control component based on the neutral current difference and the grid voltage angular frequency, and the proportional resonant controller is used to obtain a third control component based on the neutral current difference and the grid voltage angular frequency.

10. An inverter control system for grid connection of an energy storage converter, characterized in that, Includes the three-phase four-wire inverter control circuit as described in any one of claims 7-9.

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