An asymmetric damping voltage controller for grid-forming converters and a control method thereof

Abstract

The present application belongs to the technical field of new energy network construction type converter, and particularly relates to an asymmetric damping voltage controller for a network construction type converter and a control method thereof, comprising the following steps: step 1: obtaining the inductance current of a filter and the capacitance voltage in the current system; step 2: a power calculation module calculates active power and reactive power; step 3: an active control loop and a reactive control loop obtain the active power and the reactive power; the phase angle generated by the active loop control and the reference value of the inverter output voltage amplitude are calculated; step 4: the asymmetric damping voltage controller obtains the phase angle, the reference value of the inverter output voltage amplitude and the capacitance voltage; and the asymmetric damping voltage controller is used to suppress power oscillation to generate an output current reference value; and a current controller is used to generate a modulation voltage signal. The present application provides an effective technical means for improving the stability and dynamic performance of power electronic equipment in a high penetration rate new energy scene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of new energy network construction type converter, and particularly relates to an asymmetric damping voltage controller for a network construction type converter and a control method thereof. BACKGROUND

[0002] With the continuous rise of new energy penetration rate, the power system is gradually evolving from the traditional synchronous machine dominated architecture to the structure taking power electronic converters as the core. In the scenario of high proportion of new energy access, power electronic devices have become the key support for power grid operation. However, due to the lack of rotational inertia in essence, the converter is difficult to provide effective frequency and voltage support when the power grid is disturbed, resulting in a significant decrease in the stability of the power grid after being disturbed. Therefore, as a new generation of power electronic device, the network construction type converter, which has voltage source characteristics and self-synchronization capability, becomes an important technology in high proportion of new energy power grid.

[0003] At present, the inner loop control of the network construction type converter usually adopts a voltage and current double loop control structure, in which the outer loop voltage controller is responsible for tracking the reference voltage generated by the active ring and the reactive ring, and the inner loop current controller is used to track the current instruction. However, the existing voltage controller mostly adopts a symmetric structure, and the damping capacity is limited. In addition, the traditional voltage controller is easy to introduce a resonance peak in the low frequency band, which aggravates the risk of low frequency oscillation of the network construction type converter and reduces the stability margin of the system.

[0004] In view of the above problems, the application provides an asymmetric damping voltage controller for a network construction type converter and a control method thereof. SUMMARY

[0005] The purpose of the application is to provide an asymmetric damping voltage controller for a network construction type converter and a control method thereof, which can effectively suppress low frequency power oscillation and improve the stability and robustness of the system. At the same time, in view of the problem that the traditional voltage controller is easy to cause oscillation under strong grid conditions, the application improves the dynamic response performance of the system by introducing an asymmetric damping loop. In addition, the application enhances the adaptability of the converter in complex grid environment without significantly increasing the control complexity, and ensures the stability and reliability of the network construction type converter in the scenario of high penetration rate of new energy.

[0006] The technical scheme adopted by the application is as follows:

[0007] An asymmetric damping voltage controller for a network construction type converter, comprising:

[0008] a power calculation module for calculating the active power and the reactive power of the inductance current and the capacitance voltage of the filter in the current system;

[0009] Active power control loop (APC) and reactive power control loop (RPC): for calculating the reference value of phase angle and inverter output voltage amplitude;

[0010] Asymmetrical damping voltage controller: for generating output current reference value;

[0011] Current controller: generating modulation voltage signal.

[0012] An asymmetrical damping voltage control method for grid-forming converter, using an asymmetrical damping voltage controller, the asymmetrical damping voltage control method comprising the following steps:

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

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

[0015] Step 201: changing the abc coordinate system to dq coordinate system through Park and Clark transformation by using the capacitor voltage and inductor current collected in the step 1;

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

[0017]

[0018] Wherein v Cdq and i Ldq respectively represent the dq-axis component of capacitor voltage and inductor current.

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

[0020] Step 301: generating phase angle by using active power control loop, the control principle is according to formula 2, and the control loop adjusts the phase angle according to the active power information in the system to realize synchronization with the power grid;

[0021]

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

[0023] Step 302: generating the inverter output voltage amplitude reference signal using the reactive control loop, the control principle of which is according to formula 3, which adjusts the output voltage amplitude of the inverter according to the change of the reactive power to ensure the voltage stability of the system;

[0024]

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

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

[0027] Step 401: introducing the q-axis voltage error through low-pass filtering (LPF) and a proportional coefficient k q into the d-axis integral controller, wherein the low-pass filtering can be represented 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 (4.1) and the output of the PI controller of the d-axis voltage error, and thus, the d-axis reference current component i Ldref can be represented as

[0031]

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

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

[0034]

[0035] Step 404: obtaining the d-axis reference current i Lrefd and the q-axis reference current i Lrefq through current proportional integral controllers respectively, to obtain the modulation voltage v Lrefdq .

[0036] The technical effects achieved by the present application are:

[0037] The present application provides an asymmetric damping voltage controller for grid-connected converters and a control method thereof. Based on the conventional voltage loop, the asymmetric damping voltage controller proposed in the present application effectively solves the problem of insufficient damping capability of the existing voltage controller, introduces an asymmetric damping loop, and through the application of additional loop damping to the voltage error signal, can effectively suppress power oscillation in the low frequency range. The asymmetric damping can effectively weaken the low-frequency oscillation, significantly improve the stability and dynamic response speed of the system, and prevent instability phenomenon caused by power grid disturbance.

[0038] The present application can effectively suppress low-frequency power oscillation and improve the stability and robustness of the system. At the same time, in view of the problem that the conventional voltage controller is prone to oscillation under strong power grid conditions, the present application introduces an asymmetric damping loop to improve the dynamic response performance of the system. In addition, the present application does not significantly increase the complexity of the control structure, but significantly improves the adaptability and dynamic performance of the grid-connected converter in complex power grid environment, ensuring the stability and reliability of the grid-connected converter in high penetration rate new energy scenarios. The technology can improve the stability of power electronic equipment in high proportion of new energy access scenarios.

[0039] The present application can be widely applied in new energy grid-connected systems, microgrids and energy storage systems, providing an effective technical means for improving the stability and dynamic performance of power electronic equipment in high penetration rate new energy scenarios, and helping to promote the green and low-carbon development of power systems. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is the grid-connected converter topology and control schematic diagram in the present application;

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

[0042] Figure 3 is a schematic diagram of control results before and after improvement in the present application when the grid strength SCR=8 and the active power step is 0.5 p.u.; in the figure: Figure 3 (a) is a schematic diagram of control results before improvement; Figure 3 (b) is a schematic diagram of control results after improvement;

[0043] Figure 4 is a schematic diagram of control results before and after improvement in the present application when the grid strength SCR=10 and the active power step is 0.5 p.u.; in the figure: Figure 4 (a) is a schematic diagram of control results before improvement; Figure 4 (b) is a schematic diagram of control results after improvement;

[0044] Figure 5 is a flowchart of an asymmetric damping voltage control method for grid-forming converters in the present application. DETAILED DESCRIPTION

[0045] In order to make the objects and advantages of the present application clearer, the present application will be specifically described below in combination with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present application, and does not strictly limit the specific protection scope requested by the present application.

[0046] As shown in Figure 1 , an asymmetric damping voltage controller for grid-forming converters comprises:

[0047] a power calculation module for calculating active power and reactive power by obtaining the inductor current and capacitor voltage of the filter in the current system;

[0048] an active control loop (APC) and a reactive control loop (RPC) for calculating the reference values of the phase angle and the inverter output voltage amplitude;

[0049] an asymmetric damping voltage controller for generating an output current reference value;

[0050] a current controller for generating a modulated voltage signal.

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

[0052] Step 1: obtaining the inductor current i Ldqand capacitor voltage v Cdq ;

[0053] Step 2: the power calculation module acquires inductance current i Ldq and capacitor voltage v Cdq ; and calculates active power P e and reactive power Q e ; in step 2, the power calculation module specifically includes the following steps:

[0054] Step 201: the capacitor voltage and inductance current collected in step 1 are changed from abc coordinate system to dq coordinate system through Park and Clark transformation;

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

[0056]

[0057] where v Cdq and i Ldq respectively represent the dq-axis components corresponding to the capacitor voltage and inductance current.

[0058] Step 3: the active control loop (APC) and the reactive control loop (RPC) acquire active power P e and 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, the phase angle and the reference value of the inverter output voltage amplitude are calculated through the active control loop (APC) and the reactive control loop (RPC), specifically including the following steps:

[0059] Step 301: the active control loop generates the phase angle, and the control principle is according to formula 2. This control loop adjusts the phase angle according to the active power information in the system to realize synchronization with the power grid;

[0060]

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

[0062] Step 302: the reactive control loop generates the reference signal of the inverter output voltage amplitude, and the control principle is according to 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] where Q set is given by the superior dispatch; V n and V o represent the rated phase voltage amplitude of the power grid and the actual output phase voltage amplitude of the inverter, respectively, and K and Dq are the integral coefficient of the reactive power loop and the droop coefficient of the reactive power, 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 m of the inverter output voltage amplitude, and simultaneously obtains the capacitor voltage v Cdq , and generates the output current reference value i Lrefdq by using the asymmetric damping voltage controller to suppress power oscillation, and generates the modulation voltage signal v Lrefdq by using the current controller. In step 4, the asymmetric damping voltage controller is used to suppress power oscillation to generate the output current reference value, which specifically includes the following steps:

[0066] Step 401: the q-axis voltage error is introduced into the d-axis integral controller by low-pass filtering (LPF) and a proportional coefficient k q , and the low-pass filtering can be represented as:

[0067]

[0068] where ω c is the cutoff 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 is composed of (4.1) and the output quantity of the PI controller of the d-axis voltage error, and thus the d-axis reference current component i Ldref can be represented as

[0070]

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

[0072] Step 403: the q-axis voltage error is subjected to the PI controller to obtain the q-axis current reference value i Lrefq , which can be represented as

[0073]

[0074] Step 404: the d-axis reference current i Lrefd and the q-axis reference current iLrefq The modulation voltage v is obtained by passing the current proportional-integral controller. Lrefdq .

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

[0076] Figure 2 To improve the asymmetric damped voltage controller, the q-axis voltage error is filtered by a low-pass filter (LPF) and a proportional coefficient k. q Introduced into the d-axis integral controller, where k p and k i These represent the proportional gain and integral gain of the voltage loop, respectively.

[0077] Please see Figure 3 As shown, with grid strength SCR=8, the active power will increase by 0.5 pu. The control results before the improvement are as follows: Figure 3 As shown in (a), the active power overshoot M p It is 26.3%, and the settling time is t. s The overshoot was 489.7 ms, indicating a large system overshoot and excessively long settling time. An improvement was made by incorporating the asymmetric damped voltage control proposed in this invention. Experimental results are as follows: Figure 3 As shown in (b), the active power overshoot was significantly suppressed, decreasing from 26.3% to 16.3%. Furthermore, the settling time t... s The reduction from 489.7ms to 135.5ms demonstrates that the present invention can effectively suppress power oscillations in the low-frequency range and significantly improve system stability and dynamic response speed.

[0078] Please see Figure 4 As shown, with grid strength SCR=10, the active power will increase by 0.5 pu. The control results before the improvement are as follows: Figure 4(a) shown, the system can be observed to oscillate instability. By adding the asymmetric damping voltage control proposed in the present application, the results are as shown in Figure 4 (b) shown, the system can work stably. It is proved that the method of the present application significantly improves the adaptability and dynamic performance of the grid-forming converter in the complex power grid environment. The technology can improve the stability of power electronic equipment in the high proportion of new energy access scene.

[0079] The present application proposes an asymmetric damping voltage controller for grid-forming converter and a control method thereof. Based on the traditional voltage loop, the asymmetric damping voltage controller proposed in the present application effectively solves the problem of insufficient damping capacity of the existing voltage controller, introduces an asymmetric damping loop, and by 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 phenomenon caused by power grid disturbance.

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

[0081] The present application can be widely used in new energy grid-connected system, microgrid and energy storage system, providing an effective technical means for improving the stability and dynamic performance of power electronic equipment in the high penetration rate of new energy scene, and helping to promote the green and low-carbon development of power system.

[0082] The above is only the preferred embodiment of the present application, it should be pointed out that for the ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, these improvements and refinements should also be considered as the protection scope of the present application. The structures, devices and operation methods not specifically described and explained in the present application, such as no special description and limitation, are implemented according to the conventional means in the art.

Claims

1. An asymmetric damping voltage control method for a meshed type converter, characterized by: The method comprises the following steps: Step 1: Get the inductor current of the filter in the current system i Ldq and the capacitor voltage v Cdq ; Step 2: Power calculation module gets inductor current i Ldq and capacitor voltage v Cdq ; and calculates active power P e and reactive power Q e ; Step 3: Active power control loop (APC) and reactive power control loop (RPC) acquire active power P e and reactive power Q e ; calculate the reference value of phase angle generated by active loop control θ and inverter output voltage amplitude E m ; Step 4: Asymmetric damping voltage controller obtains phase angle generated by active loop control θ and reference value of inverter output voltage amplitude E m ; simultaneously obtains capacitor voltage v Cdq ; and uses asymmetric damping voltage controller to suppress power oscillation to generate output current reference value i Lrefdq ; and generates modulation voltage signal through current controller v Lrefdq ; In the step 4, the asymmetric damping voltage controller is used to suppress power oscillation and generate an output current reference value, and the step specifically comprises the following steps: Step 401 : applying q The axis voltage error is passed through a low pass filter (LPF) and a proportional coefficient k q is introduced to d the axis integral controller, where the low pass filter can be represented as: wherein ω c is the cut-off frequency, s is the Laplacian operator; Step 402: in the improved asymmetric damping control d The shaft voltage control generates d The shaft reference current i Lrefd From (4.1) and d The shaft voltage error is composed of the output quantity of the PI controller, so, d The shaft reference current component i Ldref Can be expressed as Where k p And k i The proportional gain and integral gain of the voltage loop are represented by Kp and Ki, respectively; Step 403: obtaining q The voltage error of the shaft is obtained through a PI controller q The current reference value of the shaft i Lrefq which can be expressed as ; Step 404: obtaining the modulation voltage d Shaft reference current i Lrefd And q Shaft reference current i Lrefq respectively through current proportional-integral controllers v Lrefdq .

2. The asymmetric damping voltage control method for a grid forming converter according to claim 1, wherein: In the step 2, the power calculation module is used, and the step specifically comprises the following steps: Step 201: Transform the capacitor voltage and inductor current collected in Step 1 from the stationary reference frame to the rotating reference frame using Park and Clark transformations abc coordinate system to dq coordinate system; Step 202: Calculate the system active and reactive power by transient power theory where v Cdq , i Ldq Vcand ILrepresent the capacitor voltage and inductor current corresponding dq axis subcomponent, respectively.

3. The method of claim 2, wherein the asymmetric damping voltage control method for a grid forming converter is characterized by: In the step 3, the reference value of the phase angle and the inverter output voltage amplitude is calculated through an active power control loop (APC) and a reactive power control loop (RPC), and the step specifically comprises the following steps. Step 301: the phase angle is generated by using the active power control loop, the control principle is according to formula 2, the control loop adjusts the phase angle according to the active power information in the system, and synchronization with the power grid is realized. wherein the active power reference value P set is specified by a superior dispatch; ω n and ω represent the nominal and actual angular frequency of the power grid, respectively, J and Dp represent the moment of inertia and the damping coefficient of the system, respectively, θ is the phase angle generated by the active loop control; Step 302: the inverter output voltage amplitude reference signal is generated by using the reactive power control loop, the control principle is according to formula 3, the loop adjusts the inverter output voltage amplitude according to the change of the reactive power, and the voltage stability of the system is ensured. wherein the reactive power reference value Q set is given by the superior dispatch; V n and V o denote the rated phase voltage amplitude of the power grid and the actual output phase voltage amplitude of the inverter, respectively, K and Dq are the reactive ring integral coefficient and the reactive droop coefficient, respectively.

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