Asymmetric damping voltage controller for grid-forming converter and control method of asymmetric damping voltage controller

Abstract

The invention belongs to the technical field of new energy network construction type converters, and particularly relates to an asymmetric damping voltage controller for a network construction type converter and a control method thereof, and the method comprises the following steps: 1, obtaining the inductive current and capacitor voltage of a filter in a current system; 2, a power calculation module calculates active power and reactive power; 3, the active control loop and the reactive control loop obtain active power and reactive power; calculating a phase angle generated by active loop control and a reference value of an inverter output voltage amplitude; 4, the asymmetric damping voltage controller obtains the reference values of the phase angle and the output voltage amplitude of the inverter and the capacitor voltage; an asymmetric damping voltage controller is adopted to suppress power oscillation, and an output current reference value is generated; and a modulation voltage signal is generated through the current controller. According to the invention, an effective technical means is provided for improving the stability and dynamic performance of the power electronic equipment in a high-permeability new energy scene.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy grid-forming converters, and particularly relates to an asymmetric damping voltage controller for a grid-forming converter and a control method thereof. Background Art

[0002] With the continuous increase in the penetration rate of new energy, the power system is gradually evolving from a traditional synchronous machine-dominated architecture to a structure centered on power electronic converters. In the scenario of high-proportion new energy access, power electronic devices have become the key support for power grid operation. However, since converters inherently lack rotational inertia, it is difficult for them to provide effective frequency and voltage support during grid disturbances, resulting in a significant decline in the stability of the power grid after being disturbed. Therefore, as a new generation of power electronic devices, grid-forming converters have become an important technology in high-proportion new energy power grids due to their voltage source characteristics and self-synchronization ability.

[0003] Currently, the inner-loop control of grid-forming converters usually adopts a voltage-current double-loop control structure, where the outer-loop voltage controller is responsible for tracking the reference voltage generated by the active power loop and the reactive power loop, and the inner-loop current controller is used to track the current command. However, existing voltage controllers mostly adopt a symmetric structure, with limited damping ability. In addition, traditional voltage controllers are prone to introducing resonance peaks in the low-frequency band, increasing the risk of low-frequency oscillation of grid-forming converters and reducing the system stability margin.

[0004] In view of the above problems, the present invention proposes an asymmetric damping voltage controller for a grid-forming converter and a control method thereof. Summary of the Invention

[0005] The purpose of the present invention is to provide an asymmetric damping voltage controller for a grid-forming converter and a control method thereof, which can effectively suppress low-frequency power oscillation, improve the stability and robustness of the system. At the same time, aiming at the problem that traditional voltage controllers are prone to cause oscillations under strong grid conditions, the present invention introduces an asymmetric damping loop to improve the dynamic response performance of the system. In addition, without significantly increasing the control complexity, the present invention enhances the adaptability of the converter in a complex grid environment, ensuring the stability and reliability of the grid-forming converter during operation in a high-penetration new energy scenario.

[0006] The technical solutions adopted by the present invention are specifically as follows:

[0007] An asymmetric damping voltage controller for a grid-forming converter, comprising:

[0008] A power calculation module: used to calculate the active power and reactive power by acquiring the inductor current and capacitor voltage of the filter in the current system;

[0009] Active power control loop (APC) and reactive power control loop (RPC): used to calculate the reference values of the phase angle and the amplitude of the inverter output voltage;

[0010] Asymmetric damping voltage controller: used to generate the reference value of the output current;

[0011] Current controller: generates a modulation voltage signal.

[0012] An asymmetric damping voltage control method for a network-forming converter, which uses an asymmetric damping voltage controller. The asymmetric damping voltage control method includes the following steps:

[0013] Step 1: Obtain the inductor current i of the filter and the capacitor voltage v in the current system; Ldq and the capacitor voltage v; Cdq ;

[0014] Step 2: The power calculation module obtains the inductor current i and the capacitor voltage v; and calculates the active power P and the reactive power Q. In step 2, using the power calculation module specifically includes the following steps: Ldq and the capacitor voltage v; Cdq ; and calculates the active power P; e and the reactive power Q; e ; In step 2, using the power calculation module specifically includes the following steps:

[0015] Step 201: Transform the abc coordinate system to the dq coordinate system by Park and Clark transforms for the capacitor voltage and inductor current collected in step 1;

[0016] Step 202: Calculate the active and reactive powers of the system through the instantaneous power theory.

[0017]

[0018] where v Cdq , i Ldq respectively represent the components of the capacitor voltage and inductor current corresponding to the dq axes.

[0019] Step 3: The active power control loop (APC) and reactive power control loop (RPC) obtain the active power P and the reactive power Q; calculate the phase angle θ generated by the active loop control and the reference value E of the amplitude of the inverter output voltage. In step 3, through the active power control loop (APC) and reactive power control loop (RPC), calculating the reference values of the phase angle and the amplitude of the inverter output voltage specifically includes the following steps; e and the reactive power Q; e ; calculate the phase angle θ generated by the active loop control and the reference value E of the amplitude of the inverter output voltage; m ; In step 3, through the active power control loop (APC) and reactive power control loop (RPC), calculating the reference values of the phase angle and the amplitude of the inverter output voltage specifically includes the following steps;

[0020] Step 301: Use the active power control loop to generate the phase angle. The control principle is based on formula 2. This control loop adjusts the phase angle according to the active power information in the system to synchronize with the power grid;

[0021]

[0022] Among them, the active power reference value P set is specified by the superior dispatching; ω n and ω respectively represent the rated angular frequency and the actual angular frequency of the power grid, J and Dp respectively represent the moment of inertia and the damping coefficient of the system, and θ is the phase angle generated by the active loop control;

[0023] Step 302: Use the reactive power control loop to generate the reference signal of the inverter output voltage amplitude. The control principle is based on Formula 3. This loop adjusts the output voltage amplitude of the inverter according to the change of reactive power to ensure the voltage stability of the system;

[0024]

[0025] Among them, the reactive power reference value Q set is given by the superior dispatching; V n and V o respectively represent the rated phase voltage amplitude of the power grid and the actual output phase voltage amplitude of the inverter, and K and Dq are respectively the reactive loop integral coefficient and the reactive droop coefficient.

[0026] Step 4: The asymmetric damping voltage controller obtains the phase angle θ generated by the active loop control and the reference value E of the inverter output voltage amplitude m ; at the same time, it obtains the capacitor voltage v Cdq ; and uses the asymmetric damping voltage controller to suppress the power oscillation, generate the reference value i of the output current Lrefdq ; and generates the modulation voltage signal v Lrefdq through the current controller. In the said Step 4, the step of using the asymmetric damping voltage controller to suppress the power oscillation and generate the reference value of the output current specifically includes the following steps:

[0027] Step 401: Introduce the q-axis voltage error into the d-axis integral controller through low-pass filtering (LPF) and the proportional coefficient k q , where the low-pass filtering can be expressed as:

[0028]

[0029] where ω c is the cut-off frequency and s is the Laplace operator;

[0030] Step 402: The d-axis reference current i Lrefd generated by the d-axis voltage control in the improved asymmetric damping control is composed of the output of the PI controller through (4.1) and the d-axis voltage error. Thus, the d-axis reference current component i Ldref can be expressed as

[0031]

[0032] where k p and k i respectively represent the proportional gain and integral gain of the voltage loop;

[0033] Step 403: Obtain the q-axis current reference value i Lrefq through the PI controller for the voltage error of the q-axis, which can be expressed as

[0034]

[0035] Step 404: Respectively pass the d-axis reference current i Lrefd and the q-axis reference current i Lrefq obtained in Step 402 and Step 403 through the current proportional-integral controller to obtain the modulation voltage v Lrefdq .

[0036] The technical effects achieved by the present invention are as follows:

[0037] The present invention proposes an asymmetric damping voltage controller for a network-forming converter and its control method. Based on the traditional voltage loop, the proposed asymmetric damping voltage controller effectively solves the problem of insufficient damping ability of the existing voltage controller. By introducing an asymmetric damping loop and applying additional loop damping to the voltage error signal, it can effectively suppress power oscillation in the low-frequency range. Asymmetric damping can effectively weaken low-frequency oscillation, significantly improve the stability and dynamic response speed of the system, and prevent instability caused by grid disturbances.

[0038] The present invention can effectively suppress low-frequency power oscillation and improve the stability and robustness of the system. At the same time, aiming at the problem that the traditional voltage controller is prone to oscillation under strong grid conditions, the present invention improves the dynamic response performance of the system by introducing an asymmetric damping loop. In addition, the control structure of the present invention does not significantly increase the complexity, but significantly improves the adaptability and dynamic performance of the network-forming converter in a complex grid environment, ensuring the stability and reliability of the network-forming converter in a high-penetration new energy scenario; this technology can improve the stability of power electronic devices in a high-proportion new energy access scenario.

[0039] The present invention can be widely applied to new energy grid-connected systems, microgrids, and energy storage systems, providing an effective technical means to improve the stability and dynamic performance of power electronic devices in a high-penetration new energy scenario, and contributing to the green and low-carbon development of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic diagram of the topology and control of the network-forming converter in the present invention;

[0041] Figure 2 It is a schematic diagram of the improved asymmetric damping voltage controller in the present invention;

[0042] Figure 3 It is a schematic diagram of the control results before and after improvement when the active power is stepped by 0.5 p.u. under the condition that the grid strength SCR = 8 in the present invention; In the figure: Figure 3 (a) is a schematic diagram of the control result before improvement; Figure 3 (b) is a schematic diagram of the control result after improvement;

[0043] Figure 4 It is a schematic diagram of the control results before and after improvement when the active power is stepped by 0.5 p.u. under the condition that the grid strength SCR = 10 in the present invention; In the figure: Figure 4 (a) is a schematic diagram of the control result before improvement; Figure 4 (b) is a schematic diagram of the control result after improvement;

[0044] Figure 5 It is a flowchart of an asymmetric damping voltage control method for a grid-forming converter in the present invention. Specific embodiments

[0045] In order to make the purpose and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with embodiments. It should be understood that the following text only describes one or several specific implementation manners of the present invention, and does not strictly limit the scope of protection specifically claimed by the present invention.

[0046] As Figure 1 shown, an asymmetric damping voltage controller for a grid-forming converter includes:

[0047] A power calculation module: used to calculate the active power and reactive power by obtaining the inductor current and capacitor voltage of the filter in the current system;

[0048] An active power control loop (APC) and a reactive power control loop (RPC): used to calculate the reference values of the phase angle and the inverter output voltage amplitude;

[0049] An asymmetric damping voltage controller: used to generate the reference value of the output current;

[0050] A current controller: generates a modulation voltage signal.

[0051] As Figures 1 - 5 shown, an asymmetric damping voltage control method for a grid-forming converter uses an asymmetric damping voltage controller, and the asymmetric damping voltage control method includes the following steps:

[0052] Step 1: Obtain the inductor current i of the filter in the current system Ldqand the capacitor voltage v Cdq ;

[0053] Step 2: The power calculation module obtains the inductor current i Ldq and the capacitor voltage v Cdq ; and calculates the active power P e and the reactive power Q e ; In step 2, using the power calculation module, it specifically includes the following steps:

[0054] Step 201: Transform the capacitor voltage and inductor current collected in step 1 from the abc coordinate system to the dq coordinate system through Park and Clark transforms;

[0055] Step 202: Calculate the active and reactive powers of the system through the instantaneous power theory

[0056]

[0057] where v Cdq , i Ldq respectively represent the components of the capacitor voltage and inductor current corresponding to the dq axes.

[0058] Step 3: The active power control loop (APC) and the reactive power control loop (RPC) obtain the active power P e and the reactive power Q e ; Calculate the phase angle θ generated by the active loop control and the reference value E of the inverter output voltage amplitude m ; In step 3, through the active power control loop (APC) and the reactive power control loop (RPC), calculate the reference values of the phase angle and the inverter output voltage amplitude, specifically including the following steps;

[0059] Step 301: Use the active power control loop to generate the phase angle. The control principle is based on formula 2. This control loop adjusts the phase angle according to the active power information in the system to synchronize with the power grid;

[0060]

[0061] where the active power reference value P set is specified by the superior dispatching; ω n and ω respectively represent the rated angular frequency and the actual angular frequency of the power grid, J and Dp respectively represent the moment of inertia and damping coefficient of the system, and θ is the phase angle generated by the active loop control;

[0062] Step 302: Use the reactive power control loop to generate the reference signal of the inverter output voltage amplitude. The control principle is based on formula 3. This loop adjusts the output voltage amplitude of the inverter according to the change of the reactive power to ensure the voltage stability of the system;

[0063]

[0064] Among them, the reactive power reference value Q set is given by the superior dispatching; V n and V o respectively represent the rated phase voltage amplitude of the power grid and the actual output phase voltage amplitude of the inverter, and K and Dq are the integral coefficient of the reactive power loop and the reactive power droop coefficient respectively.

[0065] Step 4: The asymmetric damping voltage controller obtains the phase angle θ generated by the active loop control and the reference value E of the inverter output voltage amplitude m ; at the same time, it obtains the capacitor voltage v Cdq ; and uses the asymmetric damping voltage controller to suppress the power oscillation, generating the output current reference value i Lrefdq ; and generates the modulation voltage signal v Lrefdq . In step 4, using the asymmetric damping voltage controller to suppress the power oscillation and generate the output current reference value specifically includes the following steps:

[0066] Step 401: Introduce the q-axis voltage error into the d-axis integral controller through low-pass filtering (LPF) and the proportional coefficient k q , where the low-pass filtering can be expressed as:

[0067]

[0068] where ω c is the cut-off frequency and s is the Laplace operator;

[0069] Step 402: The d-axis reference current i Lrefd generated by the d-axis voltage control in the improved asymmetric damping control consists of the output of the PI controller and the d-axis voltage error. Thus, the d-axis reference current component i Ldref can be expressed as

[0070]

[0071] where k p and k i respectively represent the proportional gain and integral gain of the voltage loop;

[0072] Step 403: Obtain the q-axis current reference value i Lrefq by passing the q-axis voltage error through the PI controller, which can be expressed as

[0073]

[0074] Step 404: The d-axis reference current i Lrefd and the q-axis reference current i obtained in steps 402 and 403 respectivelyLrefq Through a current proportional-integral controller respectively, the modulation voltage v is obtained Lrefdq .

[0075] Specifically, Figure 1 The topology and its control of the grid-forming converter are presented. The inverter is connected to the power grid (the equivalent resistance Rg and inductance Lg of the power grid) through an LC filter (filter inductance L f and filter capacitor C f ) via the point of common coupling (PCC). The obtained capacitor voltage v C(abc) and inductor current i L(abc) are subjected to dq transformation, and the active power P e and reactive power Q e are calculated using the instantaneous power theory. Through the active power control loop (APC) and the reactive power control loop (RPC), the voltage amplitude E m and the phase angle reference value θ are generated. Further, an improved asymmetric voltage damping controller is used to generate the current reference value i Lrefdq , and finally the voltage reference is generated using current control.

[0076] Figure 2 For the improved asymmetric damping voltage controller, the q-axis voltage error is introduced into the d-axis integral controller through low-pass filtering (LPF) and the proportional coefficient k q , where k p and k i represent the proportional gain and integral gain of the voltage loop respectively.

[0077] Please refer to Figure 3 As shown, when the grid strength SCR = 8, the active power is stepped by 0.5 p.u. The control result before improvement is as shown in Figure 3 (a). The overshoot M p of the active power is 26.3%, and the adjustment time t s is 489.7 ms. The overshoot of the system is large and the adjustment time is too long. By adding the asymmetric damping voltage control proposed in the present invention for improvement, the experimental result is as shown in Figure 3 (b). It can be observed that the overshoot of the active power is significantly suppressed, dropping from 26.3% before improvement to 16.3%. In addition, the adjustment time t s is reduced from 489.7 ms to 135.5 ms, proving that the present invention can effectively suppress power oscillation in the low-frequency range and significantly improve the system stability and dynamic response speed.

[0078] Please refer to Figure 4 As shown, when the grid strength SCR = 10, the active power is stepped by 0.5 p.u. The control result before improvement is as shown in Figure 4(a), it can be observed that the system oscillates and becomes unstable. By adding the asymmetric damping voltage control proposed in the present invention for improvement, the result is as shown in Figure 4 (b). The system can operate stably and normally. It is proved that the method of the present invention significantly improves the adaptability and dynamic performance of the grid-forming converter in a complex power grid environment. This technology can improve the stability of power electronic devices in scenarios with a high proportion of new energy access.

[0079] The present invention proposes an asymmetric damping voltage controller for a grid-forming converter and its control method. Based on the traditional voltage loop, the asymmetric damping voltage controller proposed in the present invention effectively solves the problem of insufficient damping capacity of the existing voltage controller. By introducing an asymmetric damping loop and applying additional loop damping to the voltage error signal, it can effectively suppress power oscillation in the low-frequency range. Asymmetric damping can effectively weaken low-frequency oscillation, significantly improve the stability and dynamic response speed of the system, and prevent instability caused by power grid disturbances.

[0080] The present invention can effectively suppress low-frequency power oscillation and improve the stability and robustness of the system. At the same time, aiming at the problem that the traditional voltage controller is prone to oscillation under strong grid conditions, the present invention improves the dynamic response performance of the system by introducing an asymmetric damping loop. In addition, the control structure of the present invention does not significantly increase the complexity, but significantly improves the adaptability and dynamic performance of the grid-forming converter in a complex power grid environment, ensuring the stability and reliability of the grid-forming converter in scenarios with a high penetration rate of new energy; this technology can improve the stability of power electronic devices in scenarios with a high proportion of new energy access.

[0081] The present invention can be widely applied to new energy grid-connected systems, microgrids and energy storage systems, providing an effective technical means to improve the stability and dynamic performance of power electronic devices in scenarios with a high penetration rate of new energy, and contributing to the green and low-carbon development of the power system.

[0082] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention. The structures, devices and operation methods not specifically described and explained in the present invention are implemented according to the conventional means in the art without special description and limitation.

Claims

1. An asymmetric damping voltage controller for a network-forming converter, characterized in that: Including: Power calculation module: used to calculate the active power and reactive power of the inductor current and capacitor voltage of the filter in the current system; Active power control loop (APC) and reactive power control loop (RPC): used to calculate the reference values of the phase angle and the amplitude of the inverter output voltage; Asymmetric damping voltage controller: used to generate the reference value of the output current; Current controller: generates a modulation voltage signal.

2. An asymmetric damping voltage control method for a network-forming converter, characterized in that: The asymmetric damping voltage control method uses the asymmetric damping voltage controller in claim 1, and the asymmetric damping voltage control method includes the following steps: Step 1: Obtain the inductor current i of the filter in the current system Ldq and the capacitor voltage v Cdq ; Step 2: The power calculation module obtains the inductor current i Ldq and the capacitor voltage v Cdq ; and calculates the active power P e and the reactive power Q e ; Step 3: The active power control loop (APC) and the reactive power control loop (RPC) obtain the active power P e and the reactive power Q e ; calculate the phase angle θ generated by the active loop control and the reference value E of the inverter output voltage amplitude m ; Step 4: The asymmetric damping voltage controller obtains the phase angle θ generated by the active loop control and the reference value E of the inverter output voltage amplitude m ; At the same time, it obtains the capacitor voltage v Cdq ; And uses the asymmetric damping voltage controller to suppress power oscillation and generate the output current reference value i Lrefdq ; And generates the modulation voltage signal v through the current controller Lrefdq .

3. The asymmetric damping voltage control method for a network-forming converter according to claim 2, characterized in that: In step 2, using the power calculation module, specifically includes the following steps: Step 201: Transform the abc coordinate system to the dq coordinate system by Park and Clark transforms of the capacitor voltage and inductor current collected in step 1; Step 202: Calculate the active and reactive powers of the system through the instantaneous power theory where v Cdq , i Ldq represent the components of the capacitor voltage and inductor current corresponding to the dq axes respectively.

4. The asymmetric damping voltage control method for a network-forming converter according to claim 3, wherein: In step 3, through the active power control loop (APC) and the reactive power control loop (RPC), calculate the reference values of the phase angle and the amplitude of the inverter output voltage, specifically including the following steps; Step 301: Use the active power control loop to generate the phase angle, and the control principle is based on formula 2. This control loop adjusts the phase angle according to the active power information in the system to synchronize with the power grid; Among them, the reference value of active power P set is specified by the superior dispatching; ω n and ω respectively represent the rated angular frequency and the actual angular frequency of the power grid, J and Dp respectively represent the moment of inertia and the damping coefficient of the system, and θ is the phase angle generated by the active loop control; Step 302: Use the reactive power control loop to generate the reference signal of the amplitude of the inverter output voltage, and the control principle is based on formula 3. This loop adjusts the amplitude of the inverter output voltage according to the change of the reactive power to ensure the voltage stability of the system; Among them, the reactive power reference value Q set is given by the superior dispatching; V n and V o respectively represent the rated phase voltage amplitude of the power grid and the actual output phase voltage amplitude of the inverter, and K and Dq are the integral coefficient of the reactive power loop and the reactive power droop coefficient respectively.

5. The asymmetric damping voltage control method for a network-forming converter according to claim 4, wherein: In step 4, the asymmetric damping voltage controller is used to suppress power oscillation and generate the reference value of the output current, specifically including the following steps: Step 401: Introduce the q-axis voltage error into the d-axis integral controller through low-pass filtering (LPF) and a proportional coefficient k q where the low-pass filtering can be expressed as: where ω c is the cut-off frequency, and s is the Laplace operator; Step 402: The d-axis reference current i generated by the d-axis voltage control in the improved asymmetric damping control Lrefd is composed of the output of the PI controller through the d-axis voltage error. Thus, the d-axis reference current component i Ldref can be expressed as where k p and k i represent the proportional gain and integral gain of the voltage loop, respectively; Step 403: Obtain the q-axis current reference value \(i\) by passing the q-axis voltage error through a PI controller Lrefq , which can be expressed as Step 404: Pass the d-axis reference current i Lrefd and the q-axis reference current i Lrefq obtained in Step 402 and Step 403 respectively through a current proportional-integral controller to obtain a modulation voltage v Lrefdq .

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