Multi-voltage feed-forward control method and system of power grid support type inverter and storage medium

Abstract

The invention discloses a multi-voltage feed-forward control method and system for a power grid support type inverter and a storage medium, and aims to introduce multi-voltage feed-forward control to solve the problem that oscillation and instability are easily generated between a following grid type power grid support type inverter and an inductive power grid, and perform error calculation and control of a power outer loop and a current inner loop according to a feed-forward value. According to the multi-voltage feed-forward control strategy provided by the invention, the problem of instability caused by an outer loop control link and a current inner loop control link can be solved at the same time, and the stability of the grid-following type voltage support type inverter can be greatly improved.

Description

Technical Field

[0001] The present invention relates to power electronic control technology, and in particular to a multi-voltage feedforward control method, system and storage medium for a grid-supported inverter. Background Art

[0002] Traditional grid-connected inverters operating under constant current or constant power control are unable to effectively support the grid. Grid-connected inverters that actively support the grid's frequency and voltage are the future development trend. These inverters are called grid-support inverters. Grid-support inverters are currently divided into grid-building and grid-following inverters. The grid support provided by grid-building inverters has been extensively researched. However, most existing grid-connected inverters are grid-following inverters based on phase-locked loops (PLLs). These inverters can also provide grid voltage and frequency support with minimal control improvements. However, grid-following inverters are prone to interaction with inductive grids, especially with the addition of active and reactive power support control. This interaction is exacerbated, leading to poorer stability. Control of grid-support inverters that incorporate active and reactive power support is complex, and existing control strategies are not applicable to these inverters. Therefore, there is an urgent need for stability optimization control of grid-support inverters to improve their stability.

[0003] Existing control schemes are only aimed at optimizing the inner loop or outer loop of the grid-locked converter. For example, reference [1] (Z. Xie, Y. Chen, W. Wu, W. Gong, and JM Guerrero, “Stability Enhancing Voltage Feed-Forward Inverter Control Method to Reduce the Effects of Phase-Locked Loop and Grid Impedance,” IEEE J. Emerg. Sel. Top. Power Electron. ,vol. 9, no. 3, pp. 3000–3009, Jun. 2021.) only proposed a multi-voltage feedforward control strategy to address the instability problem caused by the current inner loop and the phase-locked loop, while the literature [2] (X. Lin, H. Wen, J. Yu, J. Zhang, andJ. C.-H. Peng, “Role Determination of Impedance Coupling in GCC With DC-Link Virtual Inertia Control,” IEEE Trans. Ind. Electron., vol. 71, no. 3, pp.2533–2544, Mar. 2024.) An optimization control is proposed for the active power control loop alone. These controls can only solve the stability problem caused by a certain loop. However, the grid-supported inverter with a grid-following structure may cause system instability in both the outer loop and the inner loop. Therefore, the existing control strategies are not applicable to this type of inverter. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a multi-voltage feedforward control method, system and storage medium for a grid-supported inverter in view of the shortcomings of the existing technology, so as to greatly improve the stability of the grid-following voltage-supported inverter.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a multi-voltage feedforward control method for a grid-supported inverter, comprising the following steps:

[0006] S1, sampling the three-phase voltage v at the common coupling point a 、v b 、v c and the three-phase inductor current i La 、i Lb 、i Lc , for the three-phase voltage v a 、v b 、v c and the three-phase inductor current i La 、i Lb 、i Lc Perform dq coordinate transformation to obtain the dq axis voltage signal v d , v q and dq axis current signal i d ,i q ; S2. Use the following formula to obtain the multi-voltage feedforward value i dref1 with i qref1 : ; Among them, G PI (s) is the transfer function of the PI controller in the phase-locked loop, s is a complex variable in the frequency domain, i qref is the reactive current command value, i dref is the active current command value; S3. Use the following formula to calculate the output c of the current inner loop on the dq axis. d 、c q : ; Among them, i der with i qer are the input d-axis and q-axis errors, i der =i dref -i d+i dref1 ,i qer =i qref -i q -i qref1 , G i (s) is the PI controller of the inner loop of the dq axis current, K L is the decoupling coefficient of the inner current loop, K f is the voltage feed-forward coefficient; S4, the output c of the inner current loop on the dq axis d 、c q Performing dq inverse transformation to obtain a three-phase modulation signal, performing SPWM modulation on the three-phase modulation signal to obtain a switching signal of a three-phase H-bridge of a grid-supported inverter.

[0007] The present invention outputs i dref1 with i qref1 To improve the stability of the current inner loop, the stability of the grid-supported inverter can be improved.

[0008] Active current command value i dref The expression is: Among them, P ref is the final active power command value, P ref = P set + P add , where P set is the active power given value, P add The present invention can quickly make the active power value reach the command value P ref , and P can be changed separately set To change the stable output power, or change the active support control parameters separately to change the output value P of active support control add .

[0009] ;ω n is the natural rotation angular frequency of the grid voltage, ω g is the grid angular frequency obtained by the phase-locked loop, ω1 is the output of the multi-voltage feedforward control, , H f (s) is a high-pass filter, J is the differential coefficient of active support control, D p is the proportional coefficient of active support control, K fi It is a first-order low-pass filter. The active support control of the present invention can be achieved by changing the proportional coefficient D p To reduce the frequency deviation value of the power system, the frequency change rate of the power system can also be reduced by changing the differential coefficient J. p The range of is usually selected between 1 and 10, and the range of J is usually selected between 0.01 and 0.1.

[0010] H f The expression of (s) is: ;τ1=K P_PLL / K I_PLL ,τ2=1 / ω hpf , K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, ω hpf is the cutoff frequency of the high-pass filter.

[0011] Reactive current command value i qref The expression is: Among them, Q ref is the final reactive power command value, Q ref = Q set + Q add – Q1, Q set is the reactive power given value, Q add is the output value of reactive support control, Q1 is the output of multi-feedforward control, , H v (s) is a first-order high-pass filter. The present invention can quickly make the reactive power value reach the command value Q ref , and Q can be changed independently set To change the stable output power, or change the reactive support control parameters separately to change the output value Q of the reactive support control add .

[0012] ;in, is the given value of the voltage at the point of common coupling, D v The reactive support control of the present invention can be achieved by changing the proportional coefficient D v To reduce the voltage deviation value of the power system, it is easy to implement. v The range is usually chosen to be between 100 and 500.

[0013] H v The expression of (s) is: Among them, D v is the proportional coefficient of reactive support control, τ3=1 / ω hpv ,ω hpv is the cutoff frequency of the first-order high-pass filter.

[0014] Three-phase modulated signal c a , c b , c c The expression is: ; where θ PLL is the output phase angle of the phase-locked loop, ,ω g is the grid angular frequency obtained by the phase-locked loop, , K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, ω n is the natural rotation angular frequency of the grid voltage.

[0015] As an inventive concept, the present invention also provides a multi-voltage feedforward control system for a grid-supported inverter, comprising a memory, a processor, and a computer program stored in the memory; the processor executes the computer program to implement the steps of the above method.

[0016] As an inventive concept, the present invention also provides a computer-readable storage medium having a computer program / instruction stored thereon; the computer program / instruction implements the steps of the above method when executed by a processor.

[0017] Compared with the prior art, the present invention has the following advantages: the present invention solves the instability caused by the power support outer loop and the current inner loop at the same time through the multi-voltage feedforward method. Specifically, the stability of the power outer loop is improved by outputting ω1 and Q1, and the stability of the power outer loop is improved by outputting i dref1 with i qref1 To improve the stability of the inner current loop, it can solve the instability problems caused by the outer loop control link and the inner current loop control link at the same time, and greatly improve the stability of the grid-following voltage support inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The control block diagram of the grid-supported inverter and the structure diagram of the grid-connected system; Figure 2 Graph showing three-phase voltage and current waveforms of a grid-supported inverter when grid impedance changes when the multi-feedforward control in an embodiment of the present invention is not adopted; Figure 3 1 is a diagram showing three-phase voltage and current waveforms of a grid-supported inverter when grid impedance changes after adopting the multi-feedforward control in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0020] Example 1

[0021] This embodiment addresses the problem that a grid-supported inverter that follows the grid is prone to oscillation and instability with the inductive grid, and proposes a multi-voltage feedforward control method that can significantly improve the stability of the grid-supported inverter. Embodiment 1 of the present invention includes the following steps: S1, sampling the three-phase voltage v at the common coupling point (PCC) abc and the three-phase inductor current i Labc , for the three-phase voltage v abc and the three-phase inductor current i Labc Perform dq coordinate transformation to obtain dq axis voltage signal v d , v q and dq axis current signal i d ,i q .

[0022] The dq coordinate transformation formula is: ; Where: θ PLL is the output phase angle of the phase-locked loop. The vector symbol in the above formula is 、 、 Can refer to the three-phase voltage v a 、v b 、v c and the three-phase inductor current i La 、i Lb 、i Lc .

[0023] S2, v q After control, the grid phase θ is obtained PLL The expression of the phase-locked loop is: ; ω g is the grid angular frequency obtained by the phase-locked loop, ω g The expression is: ; Where: v q is the q-axis voltage signal, K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, and s is a complex variable in the frequency domain. n is the natural rotation angular frequency of the grid voltage, in the embodiment of the present invention, ω n = 2πf, f is the voltage frequency of the power grid, and in the embodiment of the present invention, f = 50.

[0024] S3, using multi-voltage feedforward control to obtain feedforward values ​​ω1, Q1, idref1 with i qref1 , where ω1 is fed forward to active power support control, Q1 is fed forward to reactive power control, i dref1 with i qref1 Feedforward to the error calculation of the current inner loop.

[0025] Among them, the expression formula of ω1 is: ; Among them, v q is the q-axis voltage signal, G PI (s) is the transfer function of the PI controller in the phase-locked loop, H f (s) is a high-pass filter, H f The expression of (s) is: , where τ1=K P_PLL / K I_PLL ,τ2=1 / ω hpf , K P_PLL With K I_PLL They are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop. hpf is the cutoff frequency of the high-pass filter in this feedforward branch. s is a complex variable in the frequency domain. The advantage of this feedforward control loop is that the value of τ1 is determined by the PI parameters of the phase-locked loop, so no further design is required. Only the parameters related to τ2 need to be designed.

[0026] Among them, the expression formula of Q1 is: ; Among them, v d is the d-axis voltage signal, H v (s) is a first-order high-pass filter, H v The expression of (s) is: , where D v is the proportional coefficient in reactive support control, τ3=1 / ω hpv ,ω hpv is the cutoff frequency of the first-order high-pass filter. s is a complex variable in the frequency domain. The advantage of this feedforward control loop is its simplicity; only the parameters related to τ3 need to be designed.

[0027] Among them, i dref1 The expression formula is: ; Among them, v q is the q-axis voltage signal, G PI (s) is the transfer function of the PI controller in the phase-locked loop, i qref is the reactive current command value output by the reactive power control loop. s is a complex variable in the frequency domain. The advantage of this feedforward control loop is that the G PI (s) is the PI controller of the phase-locked loop, so no additional parameter design is required.

[0028] Among them, i qref1 The expression formula is: ; Among them, v q is the q-axis voltage signal, G PI (s) is the transfer function of the PI controller in the phase-locked loop, i dref is the active current command value output by the active power control loop. s is a complex variable in the frequency domain. The advantage of this feedforward control loop is that the G PI (s) is the PI parameter of the phase-locked loop, so no additional parameter design is required.

[0029] Although the entire multi-feedforward control is designed to 4 feedforward loops, only the relevant parameters ω of τ2 and τ3 need to be designed. hpf With ω hpv It is relatively simple to use and easy to implement in actual controllers.

[0030] S4, respectively through active power support control and reactive power support control to obtain P add With Q add .

[0031] Among them, P add The expression formula is: ; Among them, ω n is the natural rotation angular frequency of the grid voltage, ω g is the grid angular frequency obtained by the phase-locked loop, ω1 is the output of the multi-voltage feedforward control, J is the differential coefficient of the active support control, D p is the proportional coefficient of active support control, K fi It is a first-order low-pass filter when performing differentiation, K fi The expression is , τ fi =1 / ω fi ,ω fi is the cutoff frequency of the first-order low-pass filter; Q add The expression formula is: ;in, is the given value of the voltage at the point of common coupling, v d is the d-axis voltage signal of the three-phase voltage at PCC, D v is the proportional coefficient of reactive support control;

[0032] S5, through power control, obtain active current command value i dref and reactive current command value i qref , where power control includes active power control and reactive power control.

[0033] The expression of active power control is: ; where v d is the d-axis voltage signal of the three-phase voltage at PCC; P ref is the final active power command value, P ref =P set + P add , where P set is the active power given value, P add It is the output value of active power support control.

[0034] The expression of reactive power control is: ; Among them, v d is the d-axis voltage signal of the three-phase voltage at PCC; Q ref is the final reactive power command value, Q ref =Q set + Q add – Q1, where Q set is the reactive power given value, Q add is the output value of reactive support control, and Q1 is the output of multi-feedforward control.

[0035] S6. Calculate and control the error of the current inner loop based on the feedforward value.

[0036] The expression of the current inner loop control is: ; Among them, c d 、c q They are the output of the inner current loop on the dq axis, i der with i qer are the input d-axis and q-axis errors respectively. der The expression is i der =i dref -i d + i dref1 ,i dref is the output of the active power control loop, i d is the d-axis signal of the three-phase inductor current, i dref1 is the output of the multi-feedforward control. qer The expression is i qer = i qref -i q -i qref1 ,i qref is the output of the reactive power control loop, i q is the q-axis signal of the three-phase inductor current, i qref1 is the output of the multi-feedforward control.

[0037] G i (s) = K pi +K ii / s is the PI controller of the inner loop of the dq axis current, K pi With K ii K is the proportional coefficient and integral coefficient of the current inner loop PI controller. L = ω n L f / (V dc / 2) is the decoupling coefficient of the inner current loop, ω n is the natural rotation angular frequency of the grid voltage, L f is the filter inductor, K f = 2 / V dc is the voltage feedforward coefficient, V dc is the DC side voltage.

[0038] S7, according to the output value c of the current inner loop d 、c q Perform dq inverse transformation and then perform SPWM modulation to obtain the switching signals S1-S6 of the three-phase H-bridge.

[0039] The formula for the inverse dq coordinate transformation is: ; Where: θ PLL is the output phase angle of the phase-locked loop, c d 、c q is the output value of the inner loop of the dq axis current, c a , c b , c c is the three-phase modulated signal obtained after dq inverse transformation. a , c b , c c After SPWM modulation, the switching signals S1-S6 of the three-phase H-bridge are obtained.

[0040] Under the system parameters and control parameters shown in Table 1, a comparative simulation of grid impedance changes of the grid-supported inverter with and without multi-voltage feedforward control is carried out. The simulation waveforms are shown in Figure 1. Figures 2 and 3 As shown;

[0041] 1. When the grid-supported inverter does not adopt the multi-voltage feedforward control method of the present invention, Figure 2 Given the grid inductance L g The three-phase voltage waveform and three-phase inductor current waveform of PCC point when it changes from 2.3mH to 15.3mH. As can be seen from the figure, when L g=2.3mH, the grid-supported inverter has lost stability, and there are a lot of harmonics in the voltage and current waveforms; when L g When the voltage increases to 15.3mH, the stability of the grid-supported inverter deteriorates further and the waveform quality becomes worse. This shows that the grid-supported inverter has poor adaptability to grid impedance and is very prone to instability.

[0042] 2. When the grid-supported inverter adopts the multi-voltage feedforward control method proposed in this invention, Figure 3 Given the grid inductance L g The three-phase voltage waveform and three-phase inductor current waveform of PCC point when the impedance changes from 2.3mH to 15.3mH. As can be seen from the figure, when the grid impedance L g When the grid impedance L is 2.3mH, the grid-supported inverter system remains stable and the waveform is a standard sine wave. g After increasing to 15.3mH, the grid-supported inverter continued to maintain system stability after approximately 0.2s of adjustment, and the voltage and current waveforms remained good. This demonstrates that the multi-voltage feedforward control proposed in this embodiment of the present invention can significantly improve the grid-supported inverter's adaptability to grid impedance and overall system stability.

[0043] Example 2

[0044] Embodiment 2 of the present invention provides a control system corresponding to the above-mentioned embodiment 1, including a memory, a processor, and a computer program stored in the memory; the processor executes the computer program in the memory to implement the steps of the method of the above-mentioned embodiment 1.

[0045] In some implementations, the memory may be a high-speed random access memory (RAM), and may also include a non-volatile memory, such as at least one disk storage.

[0046] In other implementations, the processor may be a central processing unit (CPU), a digital signal processor (DSP), or other general-purpose processors, which are not limited herein.

[0047] Example 3

[0048] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to the above-mentioned embodiment 1, on which a computer program / instruction is stored. When the computer program / instruction is executed by a processor, the steps of the method of the above-mentioned embodiment 1 are implemented.

[0049] Computer readable storage media can be tangible devices that hold and store instructions used by instruction execution devices. Computer readable storage media can be, for example, but not limited to, electronic storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any combination thereof.

[0050] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of a fully hardware embodiment, a fully software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present application may be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0051] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0052] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0053] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0054] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A multi-voltage feedforward control method for a grid-supported inverter, characterized in that: The following steps are involved: S1, sampling the three-phase voltage v at the common coupling point a 、v b 、v c and the three-phase inductor current i La 、i Lb 、i Lc , for the three-phase voltage v a 、v b 、v c and the three-phase inductor current i La 、i Lb 、i Lc Perform dq coordinate transformation to obtain the dq axis voltage signal v d , v q and dq axis current signal i d ,i q ; S2. Use the following formula to obtain the multi-voltage feedforward value i dref1 with i qref1 : ； ； Among them, G PI (s) is the transfer function of the PI controller in the phase-locked loop, s is a complex variable in the frequency domain, i qref is the reactive current command value, i dref is the active current command value; S3. Use the following formula to calculate the output c of the current inner loop on the dq axis. d 、c q : ； Among them, i der with i qer are the input d-axis and q-axis errors, i der =i dref -i d + i dref1 ,i qer = i qref -i q -i qref1 , G i (s) is the PI controller of the inner loop of the dq axis current, K L is the decoupling coefficient of the inner current loop, K f is the voltage feed-forward coefficient; S4, the output c of the inner current loop on the dq axis d 、c q Performing dq inverse transformation to obtain a three-phase modulation signal, performing SPWM modulation on the three-phase modulation signal to obtain a switching signal of a three-phase H-bridge of a grid-supported inverter.

2. The multi-voltage feedforward control method for a grid-supported inverter according to claim 1, wherein: Active current command value i dref The expression is: Among them, P ref is the final active power command value, P ref = P set + P add , where P set is the active power given value, P add It is the output value of active power support control.

3. The multi-voltage feedforward control method for a grid-supported inverter according to claim 2, wherein: ;ω n is the natural rotation angular frequency of the grid voltage, ω g is the grid angular frequency obtained by the phase-locked loop, ω1 is the output of the multi-voltage feedforward control, , H f (s) is a high-pass filter, J is the differential coefficient of active support control, D p is the proportional coefficient of active support control, K fi It is a first-order low-pass filter.

4. The multi-voltage feedforward control method for a grid-supported inverter according to claim 3, wherein: H f The expression of (s) is: ;τ1=K P_PLL / K I_PLL ,τ2=1 / ω hpf , K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, ω hpf is the cutoff frequency of the high-pass filter.

5. The multi-voltage feedforward control method for a grid-supported inverter according to claim 1, wherein: Reactive current command value i qref The expression is: Among them, Q ref is the final reactive power command value, Q ref =Q set + Q add – Q1, Q set is the reactive power given value, Q add is the output value of reactive support control, Q1 is the output of multi-feedforward control, , H v (s) is a first-order high-pass filter.

6. The multi-voltage feedforward control method for a grid-supported inverter according to claim 5, characterized in that: ;in, is the given value of the voltage at the point of common coupling, D v is the proportional coefficient of reactive support control.

7. The multi-voltage feedforward control method for a grid-supported inverter according to claim 5, characterized in that: H v The expression of (s) is: Among them, D v is the proportional coefficient of reactive support control, τ3=1 / ω hpv ,ω hpv is the cutoff frequency of the first-order high-pass filter.

8. The multi-voltage feedforward control method for a grid-supported inverter according to claim 1, characterized in that: Three-phase modulated signal c a , c b , c c The expression is: ; where θ PLL is the output phase angle of the phase-locked loop, ,ω g is the grid angular frequency obtained by the phase-locked loop, , K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, ω n is the natural rotation angular frequency of the grid voltage.

9. A multi-voltage feedforward control system for a grid-supported inverter, comprising a memory, a processor, and a computer program stored in the memory; characterized in that: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 8.

10. A computer-readable storage medium having a computer program / instruction stored thereon; characterized in that: When the computer program / instructions are executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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