Dual feedforward optimization control method, system and storage medium for energy storage converter

Abstract

This invention discloses a dual-feedforward optimized control method, system, and storage medium for an energy storage converter. In the original control strategy, a dual-voltage feedforward control loop is added to the current loop command. The original control strategy includes a phase-locked loop based on a synchronous rotating coordinate system, dq transformation of three-phase voltage and three-phase current, an outer power control loop, and an inner current control loop. The outer power control includes active power control and reactive power control, wherein the active power command P... set With reactive power command Q set The upper-level controller calculates the load power and transmits it to the energy storage converter. This invention reduces the instability caused by reactive current and improves the stability of the energy storage converter under weak power grid conditions.

Description

Technical Field

[0001] This 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 Technology

[0002] Current-source converters based on phase-locked loops (PLLs) are prone to interaction with inductive weak power grids, ultimately leading to oscillations and instability. Because current-source converters have a fast response to power commands, energy storage converters are often designed as current-source converters. Power systems are often equipped with energy storage converters to supply local loads, which typically 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 energy storage converters that simultaneously output active and reactive power are prone to interaction with weak power grids, ultimately leading to system instability. Therefore, stable control strategies for energy storage converters in weak power grids urgently need to be studied.

[0003] Most existing stability control schemes are designed for the stability control of new energy converters under weak power grid conditions. Since new energy converters often output fixed active current or active power, existing research, such as reference [1] (F. Chen, L. Zhao, L. Harnefors, X. Wang, J. Kukkola, and M. Routimo, "Enhanced"), focuses on the stability control of new energy converters under weak power grid conditions. 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 for single voltage feedforward control of new energy converters with only active current output, while reference [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.Although a dual feedforward control method is proposed in (vol. 9, no. 3, pp. 3000–3009, Jun. 2021.), the coefficients in the feedforward are all fixed values. This method is only applicable to grid-connected converters with fixed output current, and not to energy storage converters where the output current changes with the load.

[0004] For energy storage converters that need to output both active and reactive power simultaneously, voltage feedforward control that only considers active power or active current cannot meet stability requirements. Furthermore, since the load power is not fixed, a fixed feedforward coefficient cannot 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 energy storage converters to address the shortcomings of the existing technology, thereby improving the stability of energy storage converters under weak power grid conditions and maintaining system stability even when outputting large reactive currents.

[0006] To solve the above-mentioned 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:

[0007] S1, the three-phase voltage v at the sampling common coupling point a v b v c With the three-phase inductor current i La i Lb i Lc For three-phase voltage v a v b v c With the three-phase inductor current i La i Lb i Lc Perform a dq coordinate transformation to obtain the dq-axis voltage signal v. d v q With dq axis current signal i d i q ;

[0008] S2, using v d Calculate the active current command value i dref1 With reactive current command value i qref1 Then, based on the dual-voltage feedforward control, the d-axis active current command value i is calculated. dref2 With q-axis reactive current command value i qref2 ;

[0009] S3. Perform inner current loop control based on the corrected current loop command value: ;in, , G i (s) is a PI controller for the inner loop of the d-axis and q-axis currents, K L K is the decoupling coefficient of the inner current loop. f c is the voltage feedforward coefficient. d c q These are the outputs of the inner current loop on the d and q axes, respectively.

[0010] S4. Output c of the inner current loop on the d and q axes d c q Perform inverse dq coordinate transformation to obtain a three-phase modulation signal, and perform SPWM modulation on the three-phase modulation signal to obtain the switching signal of the three-phase H-bridge.

[0011] This invention proposes a dual-voltage feedforward control that simultaneously considers feedforward decoupling of active and reactive currents. Furthermore, the coefficients in the feedforward are not fixed values, but are adjusted based on the output i of the outer-loop power control. dref1 with i qref1 The multiplicative approach ensures the flexibility and reliability of decoupled control and facilitates its implementation in the control of energy storage converters. This invention adds a dual-voltage feedforward control loop to the current loop command, thereby reducing instability caused by reactive current and improving the stability of the energy storage converter under weak grid conditions.

[0012] In step S2, ; Among them, P set With Q set These are the command values ​​for active power and reactive power, respectively. This control allows the output power to quickly reach the given value P. set With Q set Moreover, the control method is simple.

[0013] In step S2, ; Among them, G PI (s) is the transfer function of the PI controller in the phase-locked loop, where s is a complex variable in the frequency domain. In this feedforward control, G... PI The control parameters of (s) depend on the PI control parameters of the phase-locked loop, and no additional parameter design is required, making it relatively easy to implement in practice.

[0014] G of the PI controller in the inner loop of the dq-axis current i The expression for (s) is: G i (s)=K pi +K ii / s;K pi With K ii These are the proportional and integral coefficients of the current inner-loop PI controller.

[0015] K L =ω0L f / (V dc / 2), V dc This represents the DC-side voltage. ω0 is the natural rotational angular frequency of the power grid, and L... f This is a filter inductor.

[0016] K f = 2 / V dc V dc This is the DC-side voltage. Voltage feedforward can improve the response speed of the energy storage converter to the grid voltage.

[0017] The output c of the inner current loop on the d and q axes d c q The formula for calculating the inverse dq coordinate transformation is: ; where θ PLL c is the output phase angle of the phase-locked loop. a c b c c This is the three-phase modulated signal obtained after the inverse dq transformation.

[0018] ;K P_PLL With K I_PLL These represent the proportional and integral coefficients of the PI controller in the phase-locked loop (PLL), respectively, and ω0 is the natural rotational angular frequency of the power grid. The PLL can quickly track the phase of the power grid.

[0019] As an inventive concept, the present invention also provides a dual feedforward optimization control system for an energy storage converter, including 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.

[0020] As an inventive concept, the present invention also provides a computer-readable storage medium having a computer program / instructions stored thereon; when the computer program / instructions are executed by a processor, they implement the steps of the above-described method.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adds a dual voltage feedforward control loop to the current loop command, thereby reducing the instability problem caused by reactive current and improving the stability of the energy storage converter under weak grid conditions. Attached Figure Description

[0022] Figure 1 The hardware structure and control block diagram of the entire energy storage converter system;

[0023] Figure 2The three-phase voltage waveform and three-phase inductor current waveform of the energy storage converter under conventional control after the reactive load changes from 5kVar to 10kVar.

[0024] Figure 3 The 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.

[0025] Figure 4 The three-phase voltage waveform and three-phase inductor current waveform of the energy storage converter under dual voltage feedforward control proposed in the embodiment of the present invention after the reactive load changes from 5kVar to 10kVar. Detailed Implementation

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

[0027] Example 1

[0028] Embodiment 1 of the present invention provides a dual feedforward optimization control method for an energy storage converter, comprising the following steps:

[0029] S1, sampling the three-phase voltage v at the point of common coupling (PCC) abc With the three-phase inductor current i Labc For three-phase voltage v abc With the three-phase inductor current i Labc Perform dq coordinate transformation to obtain the dq axis voltage signal v d v q With dq axis current signal i d i q .

[0030] The formula for the dq coordinate transformation is as follows:

[0031] ;

[0032] Where: θ PLL This represents the output phase angle of the phase-locked loop. The vector symbols mentioned above... , , It can refer to the three-phase voltage V a v b v c and three-phase inductor current i La iLb i Lc .

[0033] S2, for v q After performing PI control, the grid phase θ is obtained. PLL The expression for the phase-locked loop is:

[0034] ;

[0035] Where: K P_PLL With K I_PLL These are the proportional and integral coefficients of the PI controller in the phase-locked loop, respectively. ω0 is the inherent rotational angular frequency of the power grid. In this embodiment, ω0 = 2πf, and f is the voltage frequency of the power grid. In this embodiment, f = 50.

[0036] S3. Obtain the active current command value i through outer loop power control. dref1 With reactive current command value i qref1 The outer loop power control includes active power control and reactive power control.

[0037] The expression for active power control is:

[0038] ;

[0039] The expression for reactive power control is:

[0040] ;

[0041] Among them, v d This is the d-axis voltage signal of the three-phase voltage at PCC; P set With Q set These are the command values ​​for active power and reactive power, respectively. These values ​​are obtained from the upper-level controller via communication (such as RS-485 or CAN communication). The upper-level controller obtains these values ​​by sampling the three-phase voltage V at the PCC point. abc The current i of the three-phase resistive-inductive load ldabc To calculate the load power, the resistive-inductive load in this embodiment includes the load resistance R. load With load inductance L load For the power calculation method of the upper-level controller, please refer to the following: Hou Shiying, Pan Chong, Lü Houyu, et al. Comparative study on instantaneous power theory of three-phase four-wire system [J]. High Voltage Engineering, 2007, (05): 114-117.

[0042] S4. Use dual feedforward control to correct the current loop command value.

[0043] The correction formula for the d-axis current loop is as follows:

[0044] ;

[0045] Among them, i dref1 i is the active current command value obtained from the active power control loop. dref2 This represents the output value on the d-axis in a dual-voltage feedforward configuration.

[0046] i dref2 The formula for expressing it is:

[0047] ;

[0048] Among them, v q It 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.

[0049] The correction formula for the q-axis current loop is:

[0050] ;

[0051] Among them, i qref1 i is the reactive current command value obtained from the reactive power control loop. qref2 This is the output value on the q-axis in a dual voltage feedforward configuration.

[0052] i qref2 The formula for expressing it is:

[0053] ;

[0054] Among them, v q It 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.

[0055] S5. Perform inner current loop control based on the corrected current loop command value.

[0056] The expression for the current inner loop control is:

[0057] ;

[0058] Among them, c d c q These are the outputs of the inner current loop on the dq axis, G. i (s)=K pi +K ii / s is the PI controller for the inner loop of the dq-axis current, K pi With K ii K represents the proportional and integral coefficients 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 V is the voltage feedforward coefficient. dc This is the DC side voltage.

[0059] S6. Based on the output value c of the inner current 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.

[0060] The inverse dq coordinate transformation is given by the following formula:

[0061] ;

[0062] Where: θ PLL c is the output phase angle of the phase-locked loop. d c q c is the output value of the inner loop of the dq-axis current. a c b c c This is the three-phase modulated signal obtained after inverse dq transformation. Let c... a c b c c After SPWM modulation, the switching signals S1-S6 of the three-phase H-bridge are obtained.

[0063] Under the weak grid system parameters and control parameters shown in Table 1, load transformation simulations were performed on the energy storage converter under different control strategies. The simulation waveforms are shown below. Figures 2-4 As shown:

[0064]

[0065] When feedforward control is not used Figure 2 The waveforms of the three-phase voltage and three-phase inductor current at the PCC point of the energy storage converter under conventional control are shown when the reactive power output 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 a weak grid can remain stable, and the output waveform is sinusoidal. However, when the active power output remains constant and the reactive power output increases to 10kVar, the energy storage converter under a weak grid begins to become unstable, and the output waveform contains a large number of harmonics.

[0066] When using the single-voltage feedforward control shown in reference [1], Figure 3The 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 power output 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 a weak power grid can remain stable, and the output waveform is sinusoidal. However, when the active power output remains constant and the reactive power output increases to 10kVar, the energy storage converter under a weak power grid begins to become unstable, and the output waveform contains a large number of harmonics.

[0067] When the dual-voltage feedforward control proposed in the embodiments of the present invention is adopted, Figure 4 The diagram illustrates the three-phase voltage and three-phase inductor current waveforms at the PCC point of the energy storage converter as the reactive power output increases from 5 kVar to 10 kVar. It can be seen that when the active power is 5 kW and the reactive power is 5 kVar, the energy storage converter under a weak grid can remain stable, with both output waveforms being sinusoidal. However, when the active power output remains constant and the reactive power output increases to 10 kVar, the energy storage converter under a weak grid can still remain stable, and the output waveform remains sinusoidal. This demonstrates that the dual-voltage feedforward control strategy proposed in this embodiment can improve the stability of the energy storage converter under weak grid conditions.

[0068] Example 2

[0069] Embodiment 2 of the present invention provides a control system corresponding to Embodiment 1 above, 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 Embodiment 1 above.

[0070] In some implementations, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0071] In other implementations, the processor can be any type of general-purpose processor, such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation here.

[0072] Example 3

[0073] Embodiment 3 of the present invention provides a computer-readable storage medium corresponding to Embodiment 1 above, on which a computer program / instructions are stored. When the computer program / instructions are executed by a processor, they implement the steps of the method of Embodiment 1 above.

[0074] A computer-readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0075] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can 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 this application can be implemented in various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0076] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0077] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0078] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0079] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A dual-feedforward optimization control method for an energy storage converter, characterized in that, Includes the following steps: S1, the three-phase voltage v at the sampling common coupling point a v b v c With the three-phase inductor current i La i Lb i Lc For three-phase voltage v a v b v c With the three-phase inductor current i La i Lb i Lc Perform a dq coordinate transformation to obtain the dq-axis voltage signal v. d v q With dq axis current signal i d i q ; S2, using v d Calculate the active current command value i dref1 With reactive current command value i qref1 Then, the d-axis active current command value i is calculated. dref2 With q-axis reactive current command value i qref2 ; S3. Perform inner current loop control based on the corrected current loop command value: ;in, , G i (s) is a PI controller for the inner loop of the d-axis and q-axis currents, K L K is the decoupling coefficient of the inner current loop. f c is the voltage feedforward coefficient. d c q These are the outputs of the inner current loop on the d and q axes, respectively. S4. Output c of the inner current loop on the d and q axes d c q Perform inverse dq coordinate transformation to obtain a three-phase modulation signal, and perform SPWM modulation on the three-phase modulation signal to obtain the switching signal of the three-phase H-bridge; In step S2, ; Among them, P set With Q set These are the command values ​​for active power and reactive power, respectively. In step S2, ; Among them, G PI (s) is the transfer function of the PI controller in the phase-locked loop, where s is a complex variable in the frequency domain.

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

3. 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 Where ω is the DC side voltage, ω0 is the natural rotational angular frequency of the power grid, and L f This is a filter inductor.

4. 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 This is the DC side voltage.

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

6. The dual-feedforward optimization control method for the energy storage converter according to claim 5, characterized in that, ;K P_PLL With K I_PLL These are the proportional and integral coefficients of the PI controller in the phase-locked loop, respectively, and ω0 is the natural rotational angular frequency of the power grid.

7. 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 6.

8. A computer-readable storage medium having a computer program / instructions stored thereon; characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method described in any one of claims 1 to 6.

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