Double-feedforward optimization control method and system of energy storage converter and storage medium

Abstract

The invention discloses a double-feed-forward optimization control method and system of an energy storage converter and a storage medium, and a double-voltage feed-forward control link is newly added in an instruction of a current loop in an original control strategy. An original control strategy comprises a phase-locked loop based on a synchronous rotating coordinate system, dq conversion of three-phase voltage and three-phase current, an outer loop power control loop and current inner loop control, and the outer loop power control comprises active power control and reactive power control. Wherein the active power instruction Pset and the reactive power instruction Qset are transmitted to the energy storage converter through calculating the power of the load by the upper layer controller. According to the method, the instability problem caused by reactive current is reduced, and the stability of the energy storage converter in a weak power grid is improved.

Description

Technical Field

[0001] The present invention relates to power electronic control technology, and in particular to a dual feedforward optimization control method, system and storage medium for an energy storage converter. Background Art

[0002] Phase-locked loop-based current source converters (PSLs) are prone to interaction with inductive weak grids, ultimately leading to oscillation and instability. Because current source converters have a fast response to power commands, energy storage converters are often designed as such. Power systems are often equipped with energy storage converters to supply local loads, which often include a large number of resistive and inductive loads. Resistive loads consume active power, while inductive loads consume reactive power. Therefore, energy storage converters often need to output both active and reactive power simultaneously to ensure power balance. Current source converters that simultaneously output both active and reactive power are prone to interaction with weak grids, ultimately leading to system instability. Therefore, stable control strategies for energy storage converters in weak grids are urgently needed.

[0003] Most of the existing stability control schemes are aimed at studying the stability control of renewable energy converters under weak power grids. Since renewable energy converters often output fixed active current or active power, existing studies such as the literature [1] (F. Chen, L. Zhao, L. Harnefors, X. Wang, J. Kukkola, and M. Routimo, “Enhanced Q -Axis Voltage-Integral Damping Control for Fast PLL-SynchronizedInverters in Weak Grids," IEEE Trans. Power Electron. , vol. 39, no. 1, pp.424–435, Jan. 2024.), is aimed at single voltage feedforward control of renewable energy converters with only active current output, while the literature [2] (Z. Xie, Y. Chen, W. Wu, W. Gong, and JM Guerrero, “StabilityEnhancing Voltage Feed-Forward Inverter Control Method to Reduce the Effectsof Phase-Locked Loop and Grid Impedance,” IEEE J. Emerg. Sel. Top. Power Electron., vol. 9, no. 3, pp. 3000–3009, Jun. 2021.) proposed a dual feedforward control, but the coefficients in the feedforward are all fixed values, which is only applicable to grid-connected converters with fixed output current, but not to energy storage converters whose output current varies with load.

[0004] For energy storage converters that need to output active power and reactive power simultaneously, voltage feedforward control that only considers active power or active current cannot meet stability requirements, and the load power size is not fixed, which will cause the fixed feedforward coefficient to be unable to meet the requirements. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a dual feedforward optimization control method, system and storage medium for an energy storage converter in response to the shortcomings of the existing technology, so as to improve the stability of the energy storage converter under weak power grids and maintain the stability of the system even if a large reactive current is output.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is: a dual feedforward optimization control method for an energy storage converter, comprising the following steps: 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, using v d Calculate the active current command value i dref1 and reactive current command value i qref1 , and then calculate the d-axis active current command value i according to the dual voltage feedforward control dref2 and the q-axis reactive current command value i qref2 ; S3. Perform current inner loop control based on the corrected current loop command value: ;in, , , G i(s) is the PI controller of the inner loop of the d and q axis currents, K L is the decoupling coefficient of the inner current loop, K f is the voltage feedforward coefficient, c d 、c q are the outputs of the inner current loop on the d and q axes respectively; S4, the output c of the current inner loop on the d and q axes d 、c q Perform dq coordinate inverse transformation to obtain a three-phase modulation signal, and perform SPWM modulation on the three-phase modulation signal to obtain a switching signal of a three-phase H-bridge.

[0007] The present invention proposes a dual voltage feedforward control, which considers the feedforward decoupling of active current and reactive current, and the coefficient in the feedforward is not a fixed value, but is based on the i output of the outer loop power control. dref1 with i qref1 This multiplication method ensures the flexibility and reliability of decoupling control and is easy to implement in the control of energy storage converters. The present invention adds a dual-voltage feedforward control link to the current loop instructions, thereby reducing the instability caused by reactive current and improving the stability of the energy storage converter in weak grid conditions.

[0008] In step S2, ; Among them, P set With Q set They are respectively the command value of active power and the command value of reactive power. Through this control, the output power can quickly reach the given value P set With Q set , and the control form is simple.

[0009] In step S2, ; Among them, G PI (s) is the transfer function of the PI controller in the phase-locked loop, and s is a complex variable in the frequency domain. PI The control parameters of (s) depend on the PI control parameters of the phase-locked loop, and no additional parameter design is required, which makes it easier to implement in practice.

[0010] G of the PI controller of the inner loop of the dq axis current i (s) is expressed as: G i (s)=K pi +K ii / s;K pi With K ii are the proportional coefficient and integral coefficient of the current inner loop PI controller.

[0011] K L =ω0L f / (V dc / 2), V dc is the DC side voltage. ω0 is the natural rotation angular frequency of the power grid, L f For the filter inductor.

[0012] K f = 2 / V dc , V dc is the DC side voltage. Voltage feedforward can improve the response speed of the energy storage converter to the grid voltage.

[0013] The output c of the inner current loop on the d and q axes d 、c q The calculation formula for the inverse dq coordinate transformation is: ; where θ PLL is the output phase angle of the phase-locked loop, c a , c b , c c is the three-phase modulated signal obtained after dq inverse transformation.

[0014] ;K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop (PLL), and ω0 is the inherent rotational angular frequency of the power grid. The PLL can quickly track the phase of the power grid.

[0015] As an inventive concept, the present invention also provides a dual feedforward optimization control system for an energy storage converter, 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 beneficial effects: the present invention adds a new dual voltage feedforward control link in the current loop instruction, thereby reducing the instability problem caused by reactive current and improving the stability of the energy storage converter under weak power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The hardware structure and control block diagram of the entire energy storage converter system; Figure 2 The three-phase voltage waveform and three-phase inductor current waveform of the energy storage converter under traditional control after the reactive load changes from 5kVar to 10kVar; Figure 3The three-phase voltage waveform and three-phase inductor current waveform of the energy storage converter under single voltage feedforward control proposed in reference [1] after the reactive load changes from 5kVar to 10kVar; Figure 4 The three-phase voltage waveforms and three-phase inductor current waveforms of the energy storage converter under dual voltage feedforward control proposed in an embodiment of the present invention after the reactive load changes from 5kVar to 10kVar. 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] Embodiment 1 of the present invention provides a dual feedforward optimization control method for an energy storage converter, comprising the following steps:

[0022] 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 .

[0023] The dq coordinate transformation is as follows: ; Where: θ PLL is the output phase angle of the phase-locked loop. The vector symbol in the above 、 、 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 .

[0024] S2, v q After PI control, the grid phase θ is obtained PLL The expression of the phase-locked loop is: ; Among them: K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, ω0 is the natural rotation angular frequency of the power grid. In the embodiment of the present invention, ω0 = 2πf, and f is the voltage frequency of the power grid. In the embodiment of the present invention, f = 50.

[0025] S3, obtain the active current command value i through outer loop power control dref1 and reactive current command value i qref1 , where the outer loop power control includes active power control and reactive power control.

[0026] The expression of active power control is: ; The expression of reactive power control is: ; Among them, v d is the d-axis voltage signal of the three-phase voltage at PCC; P set With Q set They are the command values ​​of active power and reactive power respectively. Their values ​​are obtained through communication with the upper controller (such as 485 communication, CAN communication, etc.). The upper controller samples the three-phase voltage v at PCC point. abc The current i of the three-phase resistive and inductive load ldabc To calculate the load power, the inductive load in this embodiment includes a load resistor R load and load inductance L load The power calculation method of the upper controller can be referred to the following literature: Hou Shiying, Pan Chong, Lü Houyu, et al. Comparative study of instantaneous power theory of three-phase four-wire system [J]. High Voltage Technology, 2007, (05): 114-117.

[0027] S4. Use dual feedforward control to correct the current loop command value.

[0028] Among them, the correction formula of the d-axis current loop is: ; Among them, i dref1 is the active current command value obtained by the active power control loop, i dref2 is the output value on the d-axis in the dual voltage feedforward.

[0029] i dref2 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 qref1 It is the reactive current command value output by the reactive power control loop.

[0030] The correction formula for the q-axis current loop is: ; Among them, i qref1 is the reactive current command value obtained by the reactive power control loop, i qref2 is the output value on the q axis in the dual voltage feedforward.

[0031] i qref2 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 dref1 It is the active current command value output by the active power control loop.

[0032] S5. Perform current inner loop control according to the corrected current loop command value.

[0033] 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, 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 =ω0L f / (V dc / 2) is the decoupling coefficient of the inner current loop, K f = 2 / V dc is the voltage feedforward coefficient, V dc is the DC side voltage.

[0034] S6, 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.

[0035] The formula for the inverse dq coordinate transformation is: ; Where: θ PLLis 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.

[0036] Under the weak grid system parameters and control parameters shown in Table 1, the load conversion simulation of the energy storage converter under different control strategies is carried out. The simulation waveform is as follows: Figure 2-Figure 4 As shown:

[0037] When feedforward control is not used, Figure 2 The three-phase voltage and inductor current waveforms at the PCC point of the energy storage converter under conventional control are shown as the reactive output power increases from 5kVar to 10kVar. It can be seen that when the active power is 5kW and the reactive power is 5kVar, the energy storage converter remains stable in a weak grid, with the output waveforms being sinusoidal. However, when the active output power remains constant and the reactive output power increases to 10kVar, the energy storage converter in a weak grid begins to become unstable, with a large number of harmonics appearing in the output waveform.

[0038] When the single voltage feedforward control shown in reference [1] is adopted, Figure 3 The three-phase voltage and three-phase inductor current waveforms at the PCC point of the energy storage converter are shown as the reactive output power increases from 5kVar to 10kVar. It can be seen that when the active power is 5kW and the reactive power is 5kVar, the energy storage converter remains stable in a weak grid, with the output waveforms being sinusoidal. However, when the active output power remains constant and the reactive output power increases to 10kVar, the energy storage converter in a weak grid begins to become unstable, with a large number of harmonics appearing in the output waveform.

[0039] When the dual voltage feedforward control proposed in the embodiment of the present invention is adopted, Figure 4The waveforms of the three-phase voltage and three-phase inductor current at the PCC point of the energy storage converter are shown when the reactive output power increases from 5kVar to 10kVar. It can be seen that when the active power is 5kW and the reactive power is 5kVar, the energy storage converter under the weak grid can remain stable, and the output waveforms are all sinusoidal; but when the active output power remains unchanged and the reactive output power increases to 10kVar, the energy storage converter under the weak grid can still remain stable, and the output waveform is still a sine wave. This shows that the dual voltage feedforward control strategy proposed in the embodiment of the present invention can improve the stability of the energy storage converter under the weak grid.

[0040] Example 2

[0041] 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.

[0042] 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.

[0043] 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.

[0044] Example 3

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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 dual feedforward optimization control method for an energy storage converter, 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, using v d Calculate the active current command value i dref1 and reactive current command value i qref1 , and then calculate the d-axis active current command value i dref2 and the q-axis reactive current command value i qref2 ; S3. Perform current inner loop control based on the corrected current loop command value: ;in, , , G i (s) is the PI controller of the inner loop of the d and q axis currents, K L is the decoupling coefficient of the inner current loop, K f is the voltage feedforward coefficient, c d 、c q are the outputs of the inner current loop on the d and q axes respectively; S4, the output c of the current inner loop on the d and q axes d 、c q Perform dq coordinate inverse transformation to obtain a three-phase modulation signal, and perform SPWM modulation on the three-phase modulation signal to obtain a switching signal of a three-phase H-bridge.

2. The dual feedforward optimization control method for the energy storage converter according to claim 1, characterized in that: In step S2, ; Among them, P set With Q set They are the command value of active power and the command value of reactive power respectively.

3. The dual feedforward optimization control method for the energy storage converter according to claim 2, characterized in that: In step S2, ; Among them, G PI (s) is the transfer function of the PI controller in the phase-locked loop, and s is a complex variable in the frequency domain.

4. The dual feedforward optimization control method for the energy storage converter according to claim 1, characterized in that: G of the PI controller of the inner loop of the dq axis current i (s) is expressed as: G i (s)=K pi +K ii / s;K pi With K ii are the proportional coefficient and integral coefficient of the current inner loop PI controller.

5. The dual feedforward optimization control method for the energy storage converter according to claim 1, characterized in that: K L =ω0L f / (V dc / 2), V dc is the DC side voltage, ω0 is the natural rotation angular frequency of the power grid, L f For the filter inductor.

6. The dual feedforward optimization control method for the energy storage converter according to claim 1, characterized in that: K f = 2 / V dc , V dc is the DC side voltage.

7. The dual feedforward optimization control method for the energy storage converter according to claim 1, characterized in that: The output c of the inner current loop on the d and q axes d 、c q The calculation formula for the inverse dq coordinate transformation is: ； Among them, θ PLL is the output phase angle of the phase-locked loop, c a , c b , c c is the three-phase modulated signal obtained after dq inverse transformation.

8. The dual feedforward optimization control method for the energy storage converter according to claim 7, characterized in that: ;K P_PLL With K I_PLL are the proportional coefficient and integral coefficient of the PI controller in the phase-locked loop, and ω0 is the natural rotation angular frequency of the power grid.

9. A dual feedforward optimization control system for an energy storage converter, 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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