Vector power synchronization control method without phase-locked loop

Abstract

According to the vector power synchronization control method without the phase-locked loop, self-synchronization with a power grid is achieved through power synchronization control, and active and reactive decoupling and conjugate pole elimination are achieved through a cross decoupling control structure controlled by vector current; in an adopted vector power synchronous controller, an open-loop control part is used for keeping the stability of a system and tracking a reference signal, and a closed-loop control part is used for eliminating the influence of small signal disturbance in the open-loop control part.

Description

Technical Field

[0001] The present invention belongs to the technical fields of vector current control, power synchronization control, etc., and in particular relates to a vector power synchronization control method without a phase-locked loop. Background Art

[0002] With the transformation of the global energy structure, the rapid development of renewable energy and large-scale access to the grid have posed new challenges to the stability of the power system. In traditional power systems, the synchronization of generators and grids is usually achieved through vector current control (VCC). VCC relies on a phase-locked loop (PLL) to track the phase information of the grid to achieve precise control of active power and reactive power. This method performs well in terms of stability and control performance and is widely used in power system control, especially under strong AC system conditions. However, with the widespread application of distributed energy, the proportion of weak grids in power systems has increased, which has put higher requirements on the performance of VCC. PLL is sensitive to fluctuations in grid frequency and phase. In weak grids, changes in grid impedance and harmonic interference can cause PLL to be unable to track accurately, thereby causing system oscillation or even instability. In addition, the traditional VCC architecture has limited flexibility and robustness when dealing with complex grid conditions, especially in scenarios with weak grids and high proportions of renewable energy access.

[0003] To overcome these challenges, power synchronization control (PSC) has gradually attracted the attention of academia and industry as a new grid-connected control strategy that does not rely on PLL. PSC avoids dependence on PLL by directly utilizing the natural synchronization mechanism of the power grid, thereby improving the system's anti-disturbance capability and stability. However, PSC has two outstanding problems: 1) There is an obvious coupling between active power and reactive power control in PSC, which increases the complexity of controller design and debugging and may reduce system performance under certain operating conditions. 2) The PSC control loop contains two conjugate poles at the fundamental frequency, which makes the system face stability challenges when operating under strong AC grid conditions, especially in the case of large external disturbances, which may cause the system's dynamic response to be less than ideal or even oscillation. Summary of the invention

[0004] In order to solve the problems existing in the above-mentioned prior art, the present invention proposes a control method without a phase-locked loop - a vector power synchronization control method (VPSC). The present invention utilizes the power synchronization concept of PSC to achieve self-synchronization with the power grid. And the cross-decoupling control structure of VCC is used to achieve active and reactive decoupling and the elimination of conjugate poles, thereby improving the stability and dynamic response performance of the system in a strong AC power grid. The vector power synchronization controller design proposed in the present invention consists of two parts: 1) open-loop control; 2) closed-loop control. Open-loop control can effectively maintain the stability of the system and track the reference signal; closed-loop control can effectively eliminate the influence of small signal disturbances. The cooperation between the two makes the controller design scheme proposed in the present invention not only meet the requirements of the grid-forming (GFM) controller, but also has excellent dynamic performance and robustness, providing a new solution for the stable operation of future power systems.

[0005] The present invention specifically adopts the following technical solutions:

[0006] A phase-locked loop-free vector power synchronization control method realizes self-synchronization with a power grid through power synchronization control, and utilizes a cross-decoupling control structure of vector current control to realize active and reactive power decoupling and elimination of conjugate poles; in the adopted vector power synchronization controller, the open-loop control part is used to maintain the stability of the system and track the reference signal, and the closed-loop control part is used to eliminate the influence of small signal disturbances in the open-loop control part.

[0007] Furthermore, by introducing the decoupling matrix C into the control system dec-vcc , to eliminate the cross-coupling terms between active power and reactive power, so that active power and reactive power can be controlled independently; in the power control loop, ensure that the active control loop only affects the active power, and the reactive control loop only affects the reactive power.

[0008] Furthermore, the open-loop control part adopts a grid control structure, and obtains the voltage amplitude V of the converter through the power angle equation. c0 and phase θ vc0 :

[0009]

[0010] Among them, q ref and p ref are active power and reactive power references respectively, is the grid voltage V g The initial phase angle, V c and V g The phase difference, Vc is the voltage of the voltage source converter; ω1 is the fundamental angular frequency, V g0 is the grid voltage amplitude, L is the converter inductance, and t represents time.

[0011] Furthermore, the control characteristics of the closed-loop control part are as follows:

[0012]

[0013] in The controlled object of network control;

[0014] C p-vcc and C dec-vcc denote the control matrix and decoupling matrix of the vector power synchronous controller respectively; and are the reference values ​​of the phase disturbance and amplitude disturbance of the voltage of the voltage source converter respectively;

[0015] The loop gain is:

[0016]

[0017] Among them, H s (s) = k ps +k is / s is PI regulator; and are the loop gains for active and reactive control respectively; the PI regulator parameters are designed according to the cutoff frequency and phase margin of the closed-loop gain:

[0018]

[0019] where ω sb and PM s are the cutoff frequency and phase margin of VPSC respectively.

[0020] Furthermore, active power-frequency droop control and grid voltage amplitude control are achieved through the following slow outer loop control:

[0021] set up and are the inherent reference values ​​of active power and reactive power respectively, and are the additional reference values ​​generated by the outer loop respectively; and New reference value for the vector power controller

[0022] The active power control loop consists of a frequency detection part and an active power-frequency droop control part; the droop coefficient k fd The size of depends on the dynamic characteristics of the power grid; the reactive power control loop consists of an amplitude detection part implemented by Clark transform and a voltage droop control part implemented by a PI controller.

[0023] Furthermore, the loop gain of the adopted voltage amplitude controller is:

[0024]

[0025] Where L g is the equivalent grid inductance, Vg0 is the rated grid voltage; δ g is the power angle of the grid inductance;

[0026] Voltage Amplitude Regulator H v The parameters of (s) are determined by the following rules:

[0027]

[0028] where ω vb and PM v are the cut-off frequency and phase margin of voltage amplitude control respectively; the active power and reactive power reference values ​​should satisfy the apparent power constraint:

[0029]

[0030] Among them, S vpsc is the rated apparent power of the vector power synchronous control method.

[0031] And, a vector power synchronous control device without a phase-locked loop, based on the above control method, whose control system module is a vector power synchronous controller, wherein the open-loop control part is used to maintain the stability of the system and track the reference signal, and the closed-loop control part is used to eliminate the influence of small signal disturbances in the open-loop control part to control the voltage source converter.

[0032] Furthermore, a converter module, a signal acquisition module, a data processing module and a control system module; the converter module receives a signal from the control system module to control the switch of the power electronic device and control the amplitude v of the output voltage cmag and Phase Adjust the output of active and reactive power of the converter; the signal acquisition module monitors the electrical quantity signals including voltage and current in real time, and collects the amplitude v of the grid voltage gmag and Phase The collected signal data is transmitted to the data processing module to calculate the signals including power and frequency, and the data is converted through Clark transformation and Park transformation; the data processing module transmits the calculated control target reference signal to the control system module; the control system module receives the control target reference signal from the data processing module, and the reference signal is processed by the controller to generate a corresponding switching signal and transmit it to the converter module.

[0033] An electronic device comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the above-mentioned vector power synchronization control method without a phase-locked loop are implemented.

[0034] A non-transitory computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of a vector power synchronization control method without a phase-locked loop as described above.

[0035] Compared with the prior art, the present invention and its preferred embodiments have at least the following outstanding advantages:

[0036] (1) Eliminate the cross-coupling terms between active power and reactive power to achieve independent power control

[0037] In traditional power control, active power and reactive power usually have cross coupling. This coupling will lead to the following problems: when controlling active power, reactive power may also be affected; coupling makes control complicated, especially in the dynamic response process, it is difficult to accurately control power output. The vector power synchronous control method proposed in this invention introduces a decoupling matrix C in the control system. dec-vcc , eliminating the cross-coupling terms between active power and reactive power, so that the two can be controlled independently. In the power control loop, ensure that the active control loop only affects the active power, and the reactive control loop only affects the reactive power. Eliminate the uncertainty caused by the coupling between the two in the traditional method, improve the control accuracy and response speed of the system, especially in the complex power grid environment The stability of the system.

[0038] (2) Eliminate the conjugate pole at the fundamental frequency to improve the robustness of the system

[0039] In the traditional VSC control strategy, the conjugate poles at the fundamental frequency are prone to cause resonance and instability of the system. The vector power synchronous control method proposed in the present invention can eliminate the conjugate poles, reduce the oscillation of the system, avoid the system instability caused by it, and enhance the stability of the system under various operating conditions. In addition, the present invention can improve the dynamic response capability of the system and improve the robustness of the system, so that it can still maintain a good working state when facing dynamic loads or power grid fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0041] Figure 1 is a circuit topology diagram of a voltage source converter;

[0042] Figure 2 It is the GFM control structure;

[0043] Figure 3 The vector power synchronization control structure of the embodiment of the present invention;

[0044] Figure 4 An equivalent vector power synchronization control loop according to an embodiment of the present invention;

[0045] Figure 5 Active power-frequency droop control and grid voltage amplitude control according to an embodiment of the present invention;

[0046] Figure 6 A structural diagram of a preferred embodiment of a device provided for implementing the method of the present invention. DETAILED DESCRIPTION

[0047] Hereinafter, the specific embodiments of the present application will be described in detail with reference to the accompanying drawings. According to these detailed descriptions, those skilled in the art can clearly understand the present application and can implement the present application. Without violating the principles of the present application, the features in the various embodiments can be combined to obtain new implementations, or certain features in certain embodiments can be replaced to obtain other preferred implementations.

[0048] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail with the accompanying drawings as follows:

[0049] The purpose of this invention is to solve two significant problems in the application of power synchronization control in networking technology: 1) the coupling problem between active power and reactive power; 2) the conjugate pole problem in the control system. In order to solve these problems, the proposed VPSC combines the advantages of vector current control and power synchronization control, and provides a new GFM control scheme. The control scheme and controller parameter design principles of the proposed vector power synchronization control method are as follows:

[0050] The present invention first analyzes the voltage source converter (VSC) topology, which consists of two parts: the physical system and the control system. Figure 1 As shown, the VSC is connected to the AC grid through an inductor L and changes the voltage v c The GFM (Grid Forming Control) control associated with the present invention does not rely on the PLL-based grid voltage phase detection. The typical GFM control structure consists of a power calculation module and a power controller module, such as Figure 2 As shown. The power calculation module outputs power by measuring the voltage and current signals, which contain both the amplitude and phase information of the grid voltage. Therefore, the output power of the VSC can also be expressed by the power angle equation of the inductor:

[0051]

[0052] Where ω1 is the fundamental angular frequency, V g0 is the grid voltage amplitude, v cmag and Respectively represent the initial amplitude and phase of the VSC voltage. According to the above formula, by adjusting v cmag and The output power of the VSC can be directly controlled.

[0053] Secondly, by comparing the controlled object of GFM control and the controlled object of vector current control, in order to ensure that the network control can have similar dynamic characteristics as the vector current control, the present invention proposes a new control scheme, such as Figure 3 As shown, it consists of two parts: 1) open-loop control and 2) closed-loop control.

[0054] Among them, the designed open-loop controller is a typical grid controller structure, and the voltage amplitude V of the converter is directly obtained through the power angle equation. c0 and phase θ vc0 :

[0055]

[0056] Among them, q ref and p ref are active power and reactive power references respectively, is the grid voltage V g The initial phase angle, V c and V g The phase difference is approximately equal to 0.

[0057] For infinite AC systems, open-loop control can effectively maintain system stability and track the reference signal. However, the actual power system is not ideal, and its dynamic characteristics depend on the operating conditions. This means that the amplitude and phase of the grid voltage are not fixed, and they may change. In addition, there may be errors between the actual value and the theoretical value of the converter inductance L, which may cause the output power of the VSC in open-loop control to deviate from the reference value. Generally speaking, these errors are within 10% and can be regarded as small signal disturbances. Therefore, only a small signal closed-loop controller is needed to compensate for these differences.

[0058] In order to make up for the shortcomings of open-loop control, the present invention proposes a method such as Figure 3 The closed-loop control vector power synchronous controller shown has the following control characteristics:

[0059]

[0060] in It is the controlled object of GFM.

[0061] C p-vcc and C dec-vcc They represent the control matrix and decoupling matrix of the vector power synchronous controller respectively. and are the reference values ​​of the phase disturbance and amplitude disturbance of the VSC voltage respectively. From the above formula, the equivalent vector power synchronization control loop can be obtained as Figure 4 As shown, it can be seen that the active and reactive power control loops are decoupled, from which the loop gain can be deduced as:

[0062]

[0063] Among them, H s (s) = k ps +k is / s is PI regulator. and is the loop gain of active and reactive control. Then, the PI regulator parameters are designed according to the cutoff frequency and phase margin of the closed-loop gain:

[0064]

[0065] where ω sb and PM s are the cutoff frequency and phase margin of VPSC respectively.

[0066] In addition to fast active / reactive power control, active power-frequency droop control and grid voltage amplitude control are also required in some special cases. In order to achieve the above requirements, a slower outer loop control can be implemented, such as Figure 5 shown.

[0067] and is the inherent reference value of active power and reactive power, and An additional reference value generated for the outer loop. and Then it is the new reference value of the vector power controller (such as Figure 3 ).

[0068] The active power control loop consists of a frequency detection part and an active power-frequency droop control part. fdThe size depends on the dynamic characteristics of the power grid. Similarly, the reactive power control loop consists of an amplitude detection part and a voltage droop control part. The former can be achieved through Clark transformation, and the latter through a PI controller. In order to ensure that the outer loop controller has good dynamic characteristics, the voltage amplitude control bandwidth should be designed to be much lower than the inner loop control (generally 5% to 10% of the inner loop). Then, the actual reactive power will be very close to its reference value q within its outer loop bandwidth. ref . Therefore, the loop gain of the voltage amplitude controller can be properly estimated:

[0069]

[0070] Where L g is the equivalent grid inductance, Vg0 is the rated grid voltage. g is the power angle of the grid inductance, which is generally close to 0 and can be ignored to simplify the design of the voltage amplitude controller. Then, the voltage amplitude regulator H v The parameters of (s) can be determined by the following rules:

[0071]

[0072] where ω vb and PM v are the cutoff frequency and phase margin of voltage amplitude control respectively. vb Can be designed to be 0.05~0.1ω sb , PM v It can be set to about π / 4. In addition, the active power and reactive power reference values ​​should satisfy the apparent power constraint:

[0073]

[0074] Where S vpsc is the rated apparent power of VPSC.

[0075] The following provides a preferred device design for implementing the above scheme:

[0076] The device structure diagram of the control method proposed in this embodiment is as follows Figure 6 As shown in the figure, it mainly consists of four parts: converter module, signal acquisition module, data processing module and control system module. The converter module receives signals from the control system to control the switch of the power electronic device to control the amplitude of the output voltage v cmag and Phase Adjust the output of active and reactive power of the converter. The signal acquisition module monitors the voltage and current and other electrical quantity signals in real time, and collects the amplitude of the grid voltage v gmag and Phase The collected signal data is transmitted to the data processing module, the power, frequency and other signals are calculated, and the data is converted through Clark transformation and Park transformation. The data processing module transmits the calculated control target reference signal to the control system module. The control system module receives the control target reference signal from the data processing module. After the reference signal is processed by the controller, the corresponding switching signal is generated and transmitted to the converter module to achieve precise control of the power conversion process, thereby realizing closed-loop control of the entire system. The following is a detailed introduction to each part.

[0077] (1) Voltage source converter module: The main function of the converter module is to realize the conversion of DC power and AC power. It usually uses power electronic devices (IGBT, etc.) to perform efficient power conversion. This module is the core component of the entire device and is directly responsible for the conversion and transmission of power.

[0078] (2) Signal acquisition module: The signal acquisition module is used to monitor the output signal of the voltage source converter module in real time, including parameters such as voltage and current.

[0079] (3) Data processing module: The main task of the data processing module is to analyze and process the raw signal data from the signal acquisition module, including filtering, signal transformation, parameter calculation and other operations. The processed data will be used to generate the reference signal of the control system.

[0080] (4) Control system module: The control system module is the "brain" of the entire device and is responsible for generating control signals to ensure that the voltage source converter module operates as expected. It consists of two parts: open-loop control and closed-loop control. The open-loop control can effectively maintain the stability of the system and track the reference signal; the closed-loop control can effectively eliminate the influence of small signal disturbances.

[0081] The modules work together to achieve efficient conversion and control of electrical energy.

[0082] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present invention should be understood by people with ordinary skills in the field to which the present invention belongs. The "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0083] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

[0084] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of a vector power synchronization control method without a phase-locked loop under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A vector power synchronization control method without a phase-locked loop, characterized in that: Self-synchronization with the power grid is achieved through power synchronization control, and active and reactive power decoupling and elimination of conjugate poles are achieved using the cross-decoupling control structure of vector current control; in the adopted vector power synchronization controller, the open-loop control part is used to maintain the stability of the system and track the reference signal, and the closed-loop control part is used to eliminate the influence of small signal disturbances in the open-loop control part.

2. The method for vector power synchronization control without a phase-locked loop according to claim 1, characterized in that: By introducing the decoupling matrix C in the control system dec-vcc , to eliminate the cross-coupling terms between active power and reactive power, so that active power and reactive power can be controlled independently; in the power control loop, ensure that the active control loop only affects the active power, and the reactive control loop only affects the reactive power.

3. The method for vector power synchronization control without a phase-locked loop according to claim 1, characterized in that: The open-loop control part adopts a grid control structure, and the voltage amplitude V of the converter is obtained through the power angle equation. c0 and phase θ vc0 : Among them, q ref and p ref are active power and reactive power references respectively, is the grid voltage V g The initial phase angle, V c and V g The phase difference, Vc is the voltage of the voltage source converter; ω1 is the fundamental angular frequency, V g0 is the grid voltage amplitude, L is the converter inductance, and t represents time.

4. The method for vector power synchronization control without a phase-locked loop according to claim 3, characterized in that: The control characteristics of the closed-loop control part are as follows: in The controlled object of network control; C p-vcc and C dec-vcc denote the control matrix and decoupling matrix of the vector power synchronous controller respectively; and are the reference values ​​of the phase disturbance and amplitude disturbance of the voltage of the voltage source converter respectively; The loop gain is: Among them, H s (s) = k ps +k is / s is PI regulator; and are the loop gains for active and reactive control respectively; the PI regulator parameters are designed according to the cutoff frequency and phase margin of the closed-loop gain: where ω sb and PM s are the cutoff frequency and phase margin of VPSC respectively.

5. The method for vector power synchronization control without a phase-locked loop according to claim 4, characterized in that: Active power-frequency droop control and grid voltage amplitude control are achieved through the following slow outer loop control: set up and are the inherent reference values ​​of active power and reactive power respectively, and are the additional reference values ​​generated by the outer loop respectively; and New reference value for the vector power controller The active power control loop consists of a frequency detection part and an active power-frequency droop control part; the droop coefficient k fd The size of depends on the dynamic characteristics of the power grid; the reactive power control loop consists of an amplitude detection part implemented by Clark transform and a voltage droop control part implemented by a PI controller.

6. A phase-locked loop-free vector power synchronization control method according to claim 5, characterized in that: The loop gain of the voltage amplitude controller used is: Where L g is the equivalent grid inductance, Vg0 is the rated grid voltage; δ g is the power angle of the grid inductance; Voltage Amplitude Regulator H v The parameters of (s) are determined by the following rules: where ω vb and PM v are the cut-off frequency and phase margin of voltage amplitude control respectively; the active power and reactive power reference values ​​should satisfy the apparent power constraint: Among them, S vpsc is the rated apparent power of the vector power synchronous control method.

7. A vector power synchronization control device without a phase-locked loop, characterized in that: Based on the control method described in any one of claims 1-6, the control system module is a vector power synchronous controller, wherein the open-loop control part is used to maintain the stability of the system and track the reference signal, and the closed-loop control part is used to eliminate the influence of small signal disturbances in the open-loop control part to control the voltage source converter.

8. A phase-locked loop-free vector power synchronous control device according to claim 7, characterized in that: include: A converter module, a signal acquisition module, a data processing module and a control system module; the converter module receives a signal from the control system module to control the switch of the power electronic device and control the amplitude of the output voltage v cmag and Phase Adjust the output of active and reactive power of the converter; the signal acquisition module monitors the electrical quantity signals including voltage and current in real time, and collects the amplitude v of the grid voltage gmag and Phase The collected signal data is transmitted to the data processing module to calculate the signals including power and frequency, and the data is converted through Clark transformation and Park transformation; the data processing module transmits the calculated control target reference signal to the control system module; the control system module receives the control target reference signal from the data processing module, and the reference signal is processed by the controller to generate a corresponding switching signal and transmit it to the converter module.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of a vector power synchronization control method without a phase-locked loop are implemented as described in any one of claims 1-6.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of a phase-locked loop-free vector power synchronization control method as described in any one of claims 1 to 6 are implemented.

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