Power feedback control method suitable for matching control of low-frequency oscillation suppression

Abstract

The invention belongs to the technical field of matching control of a network construction type system, and particularly discloses a power feedback control method suitable for matching control low-frequency oscillation suppression, which comprises the following steps: establishing a power-frequency transfer relation of a multi-matching control parallel system, analyzing the torque of the multi-matching control parallel system based on a damping torque method, and calculating the power-frequency transfer relation of the multi-matching control parallel system; determining an introduction factor of a negative damping torque component in the multi-matching control parallel system and a stability condition in the multi-matching control parallel system; and then additional damping control based on power feedback is designed through a lead-lag compensator, a negative damping torque part in the multi-matching control parallel system is compensated, and power feedback control is completed. According to the method, the problems that the dynamic response of the whole system becomes extremely complex due to the dynamic interaction among the converters when a plurality of matched control network-forming converters exist in the network-forming system, and the oscillation suppression effect under the multi-machine system is difficult to guarantee by the existing suppression strategy are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of matching control of a networked system, and in particular relates to a power feedback control method suitable for matching control of low-frequency oscillation suppression. Background Art

[0002] Grid-forming (GFM) converters, by simulating the external characteristics of synchronous generators, can provide inertia support and actively regulate the grid. In recent years, they have garnered widespread attention from both academia and industry. Key control methods include droop control, virtual synchronous generator control, virtual oscillators, and matching control. Both droop control and virtual synchronous generator control are implemented by simulating the external characteristics of synchronous generators. Previous studies have shown that droop control and virtual synchronous generator control are approximately equivalent. While these two control methods provide stable grid support, they typically require a constant DC voltage and power source on the DC side. Therefore, when using these two types of grid-forming control in photovoltaic systems, they require significant power reserves and must operate below their maximum power operating point, resulting in resource waste. Virtual oscillators, based on the limit cycle principle of nonlinear systems, are rarely used in large power grids due to their complex implementation and lack of intuitiveness. In contrast, matching control provides inertia and frequency support to the system based on the energy stored in the DC side capacitors. It does not require high power reserves from the grid-side power supply, and its synchronization mechanism is similar to that of a synchronous machine. It has strong interpretability and has good application prospects in power-limited new energy sources such as photovoltaics and wind power.

[0003] However, establishing a synchronization mechanism between DC voltage and AC frequency also provides an additional channel for disturbances to propagate between the AC and DC sides, potentially leading to severe low-frequency oscillations in the system. Existing research has conducted targeted analyses and demonstrated that low-frequency oscillation modes in matching control pose a risk of system instability. However, the mechanism of negative damping in matching control has not been fully explored, making it difficult to provide specific guidance for the design of low-frequency oscillation suppression strategies.

[0004] Currently, scholars at home and abroad have proposed several effective suppression strategies. One approach simulates the switching losses of the converter by connecting a resistor in parallel with the DC capacitor to enhance the system's damping capacity. However, the presence of the actual resistor results in unnecessary power loss, reducing energy transfer efficiency. Another oscillation suppression strategy based on a notch filter enhances the damping capacity of low-frequency oscillations by reshaping the gain of the power feedback loop. However, the damping ratio of the notch filter affects both the synchronous oscillation and the low-frequency oscillation control, resulting in a trade-off in parameter design. A method that suppresses low-frequency oscillations caused by matching control by feeding the q-axis voltage back into the frequency link has shown good suppression effectiveness for power oscillations caused by the constant power dynamic characteristics of the DC side. However, these control strategies are designed for grid-type systems with a single matching control. When a system contains multiple grid-type converters with matching control, the dynamic interactions between these converters will complicate the dynamic response of the entire system. These suppression strategies are difficult to guarantee effective oscillation suppression in multi-machine systems. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that when there are multiple matching-controlled grid-type converters in a grid-type system, the dynamic interaction between the converters causes the dynamic response of the entire system to become extremely complex, and the existing suppression strategy is difficult to ensure the oscillation suppression effect in a multi-machine system. A power feedback control method suitable for matching-controlled low-frequency oscillation suppression is proposed.

[0006] The technical solution of the present invention is: a power feedback control method suitable for matching and controlling low-frequency oscillation suppression, comprising the following steps: The power-frequency transfer relationship of the multi-matching control parallel system is established, and the torque of the multi-matching control parallel system is analyzed based on the damping torque method; Based on the results of damping torque analysis, the factors that introduce negative damping torque components in the multi-matching control parallel system and the stability conditions in the multi-matching control parallel system are determined; Based on the introduction of negative damping torque component and stability conditions, additional damping control based on power feedback is designed through lead-lag compensator to compensate the negative damping torque part in the multi-matching control parallel system and complete power feedback control.

[0007] Preferably, the process of establishing the power-frequency transfer relationship of the multi-matching control parallel system is as follows: When the grid-type converters are connected in parallel, The grid-type converter is regarded as a separate subsystem, and the rest of the grid-type converters are regarded as another subsystem. When power disturbance occurs on the grid side When , the power balance at the grid connection point is expressed as:

[0008] in, Indicates the magnitude of the power disturbance occurring on the grid side, Indicates the i The active power output by each grid-connected converter is Indicates the The power-frequency transfer relationship of a grid-connected converter at the grid connection point is: Indicates the The power-frequency transfer relationship of a grid-connected converter at the grid connection point is: Represents the frequency disturbance component of the grid connection point; Then the power-frequency transfer relationship at the grid connection point is obtained, that is, the power-frequency transfer relationship of the multi-matching control parallel system is:

[0009] Among them, the power-frequency transfer relationship at the grid connection point is regarded as the closed-loop transfer function of the negative feedback system. represents the feedforward gain, represents the open-loop transfer function of the system.

[0010] Preferably, the torque of the multi-matching control parallel system is analyzed based on the damping torque method, specifically: According to the power-frequency transfer relationship of the multi-matching controlled parallel system, the power angle dynamics of the multi-matching controlled parallel system is obtained; According to the Phillips model, the power angle dynamics of the synchronous generator are obtained; Comparing the power angle dynamics of the multi-matching control parallel system and the synchronous generator, the key control parameters that determine the low-frequency oscillation damping capacity of the grid-type system are obtained as follows: , when the frequency is The low-frequency oscillation formula is:

[0011] in, represents the damping torque coefficient of the multi-matching control parallel system, represents the power synchronization coefficient of the grid-type converter, Represents the proportional parameter of the active power control loop, Represents the damping torque introduced by the active control loop, represents the integral coefficient of the DC voltage control loop, represents the power injected into the grid-connected converter, represents the steady-state value of the DC voltage, It represents the equivalent damping torque introduced by the DC voltage loop; Formed Provide positive damping torque for multi-matching control parallel system, Introducing negative damping torque, the integral coefficient of the DC voltage control loop is The increase of the proportional parameter of the active power control loop The reduction of leads to severe oscillation of the multi-matching control parallel system.

[0012] As a preferred embodiment, the negative damping torque is introduced in the multi-matching control parallel system because: in the multi-matching control parallel system, when the output power is fed back to the frequency dynamics, a phase lag of -180° is brought about through two integral links, resulting in a DC voltage control loop parameter of Introduce a negative damping torque component.

[0013] Preferably, the stability condition in the multi-matching control parallel system is that the damping torque of the grid-type converter under each matching control is greater than zero, that is, the phase margin of the multi-matching control parallel system is positive.

[0014] Preferably, when the phase margin of the multi-matching control parallel system is positive, the power-frequency transfer relationship at the grid connection point satisfies the following conditions:

[0015]

[0016] in, Indicates existence, represents the total number of grid-connected converters in parallel, represents the frequency of the grid-type photovoltaic low-frequency oscillation, represents the phase of the transfer function, Represents and Denotes the transfer function and exist s = jω r The value of represents the Laplace operator, , represents the real part of the transfer function.

[0017] Preferably, the transfer function of the lead-lag compensator is for:

[0018] in, represents the Laplace operator, and Represented as two time constants of the lead-lag compensator.

[0019] As a preference, adjust the two time constants of the lead-lag compensator and ,satisfy When the lead-lag compensator transfer function is The phase of is greater than zero, and the additional damping control introduced is used to compensate for the negative damping torque in the multi-matching control parallel system.

[0020] The beneficial effects of the present invention are: The power feedback control method for suppressing low-frequency oscillations of matching control proposed in the present invention can effectively suppress the low-frequency oscillation problem of a grid-connected system composed of a single matching control or multiple matching controls. The present invention establishes the power-frequency transfer relationship of a grid-type system under matching control, and analyzes the contribution of each control parameter to the synchronous torque and the damping torque based on the damping torque method; then, based on the damping torque, the stability condition in the multi-machine system is obtained, which is that the damping torque of the converter under each matching control is greater than zero, thereby proposing an additional damping control based on power feedback based on the lead-lag compensator to compensate for the negative damping torque part in the grid-type system. The control principle of the method proposed in the present invention is simple and easy to implement. It can effectively improve the system stability in both single-mechanism grid-type systems and multi-mechanism grid-type systems, and avoid system low-frequency oscillation instability. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The figure shows a flow chart of a power feedback control method for matching and controlling low-frequency oscillation suppression provided in embodiment 1 of the present invention.

[0022] Figure 2 The figure shows a schematic diagram of a grid-connected photovoltaic system based on matching control provided in Example 1 of the present invention.

[0023] Figure 3 The figure shows a power frequency transfer function block diagram of a grid-connected photovoltaic system based on matching control provided in Example 1 of the present invention.

[0024] Figure 4 Shown is a schematic diagram of torque in the grid-type photovoltaic system provided in Example 1 of the present invention.

[0025] Figure 5 Shown is a schematic diagram of a multi-machine parallel system provided in Example 1 of the present invention.

[0026] Figure 6 The figure shows an equivalent system of the power-frequency relationship of the grid connection point provided in Example 1 of the present invention.

[0027] Figure 7 Shown is a schematic diagram of the damping enhancement strategy provided in Example 1 of the present invention.

[0028] Figure 8 Shown is the embodiment 2 of the present invention provided k i Schematic diagram of power waveforms under different control strategies when the parameter is 20p.u.

[0029] Figure 9 Shown is the embodiment 2 of the present invention provided k i Schematic diagram of power waveforms under different control strategies when the parameter is 30p.u.

[0030] Figure 10 The figure shows the power response of the conventional matching control proposed in the present invention when two grid-type converters provided in the second embodiment of the present invention are operated in parallel.

[0031] Figure 11 The figure shows the power response of the damping enhancement strategy proposed in the present invention when two grid-type converters provided in Example 2 of the present invention are operated in parallel. DETAILED DESCRIPTION

[0032] The exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the accompanying drawings are merely exemplary and are intended to illustrate the principles and spirit of the present invention, rather than to limit the scope of the present invention.

[0033] Example 1: like Figure 1 As shown, a power feedback control method suitable for matching and controlling low-frequency oscillation suppression includes the following steps: S1. Establish the power-frequency transfer relationship of the multi-matching control parallel system and analyze the torque of the multi-matching control parallel system based on the damping torque method; S2. Based on the damping torque analysis results, determine the factors that introduce the negative damping torque component in the multi-matching control parallel system and the stability conditions in the multi-matching control parallel system; S3. Based on the introduction of the negative damping torque component and the stability conditions, an additional damping control based on power feedback is designed through a lead-lag compensator to compensate for the negative damping torque part in the multi-matching control parallel system and complete the power feedback control.

[0034] In this embodiment, Figure 2 The topology and control block diagram of the grid-connected photovoltaic system based on matching control (hereinafter referred to as the grid-connected photovoltaic system). is the power output by the photovoltaic array, is the power injected into the converter. is the DC side capacitor. and They are filter inductance and equivalent resistance respectively; It is the filter capacitor; and are the grid impedance and equivalent resistance respectively. is the converter terminal current, and are the output current and voltage of the inverter respectively. The converter adopts matching control, which mainly includes DC voltage control loop, active power control loop, reactive power control loop and voltage and current double closed loop control. is the reference voltage on the DC side; 、 is the reference output power of the converter; and are the rated output voltage and frequency respectively. and are the active power and reactive power output by the converter respectively; and are the angular frequency and voltage phase angle of the converter output respectively.

[0035] According to the power relationship on the DC side, the dynamic equation of DC voltage can be obtained as follows:

[0036] in, Indicates the voltage on the DC side, represents the differential symbol, Indicates time; Expressing the variables in the dynamic equation of DC voltage as the sum of their steady-state values ​​and disturbance values ​​yields:

[0037] in, and denote the steady-state components of DC voltage and power, respectively, and denote the disturbance components of DC voltage and power respectively; Eliminating the steady-state component and high-order disturbance component, the relationship between DC voltage and DC output power can be obtained as follows:

[0038] in, represents the Laplace operator; When the power loss on the converter is neglected, the relationship between DC voltage and DC output power can be expressed as Replaced with the output power of the converter In networks with higher voltage levels, the grid impedance is mainly inductive, and the active and reactive powers are decoupled. In this case, the active power can be obtained from the power flow formula as follows:

[0039] in, Indicates the inductive reactance of the grid impedance, represents the sine function, δ is the difference between the phase angle of the converter output voltage and the phase angle of the grid voltage. Therefore, after linearizing the above equation, we can get:

[0040] in, represents the disturbance component of the grid-type converter output power angle, is the power synchronization coefficient of the grid-type converter, which represents the power transmission limit of the grid-type photovoltaic system. The DC voltage control loop in the matching control uses a PI controller to maintain the DC voltage constant. Its control equation is:

[0041] in, represents the output of the DC voltage control loop, represents the proportional coefficient of the DC voltage control loop, Represents the integral coefficient of the DC voltage control loop, which serves as the reference input of the active power control loop. The active power control loop uses a proportional link to adjust the active power output of the converter and establish the converter frequency. Its control equation is:

[0042] in, Represents the proportional parameter of the active power control loop. Therefore, the power frequency transfer function block diagram of the grid-type photovoltaic system can be obtained as follows: Figure 3 shown.

[0043] When the reference value does not change, according to Figure 3 The power angle dynamics of the grid-type photovoltaic system can be obtained as follows:

[0044] Multiplying both sides by the Laplace operator gives:

[0045] in, and They represent the damping torque and synchronization torque of the network system under matching control respectively; According to the Phillips model, the power angle dynamics in a synchronous generator can be described as:

[0046] in, represents the damping of the synchronous generator, represents the inertia of the synchronous generator, Indicates the power synchronization coefficient of the synchronous generator. Frequency-dependent D / M It is the damping torque that affects the low-frequency oscillation of the system. Its physical meaning is clear: the force (torque) that is proportional to the speed (angular velocity) is the braking force (torque) of the motion displacement (angular displacement) and plays a damping role. It is the synchronous torque that determines the synchronous capability of the unit, and it affects the oscillation frequency of the output power. Therefore, by comparing the above two equations, we can find that It is the key to determine the low-frequency oscillation damping capacity of the grid-type photovoltaic system. When the low-frequency oscillation mode is , It can be expressed as:

[0047] like Figure 4 is a torque diagram of a grid-type photovoltaic system, where T DVC is the equivalent torque generated by the DC voltage loop. It can be seen that Formed Provides a positive damping torque to the system, and k i Parameters involved A negative damping torque is introduced into the system. When the damping of the system is greater than 0, k i The increase of parameters and As the value of decreases, the damping of the low-frequency oscillation mode of the system will gradually decrease, causing the system oscillation to become more serious. On the other hand, in the formula middle, It mainly affects the oscillation frequency of the grid-type photovoltaic system. and The increase, Increasing will result in an increase in the frequency of oscillation.

[0048] like Figure 5 Shown n Schematic diagram of parallel operation of grid-connected photovoltaics, where the output power of GFM_i ( i = 1,2,…, n )use The power-frequency transfer relationship of each grid-connected photovoltaic system at the point of common coupling (PCC) is:

[0049] in, Indicates the The power-frequency transfer relationship of a grid-connected converter at the grid connection point is: Indicates the frequency disturbance at the grid connection point; For simplicity, the analysis starts from n = 2. When power disturbance occurs on the grid side When , the power balance at PCC can be expressed as:

[0050] in, Indicates the magnitude of the power disturbance occurring on the grid side, Indicates the active power output by the first grid-connected converter, Indicates the active power output by the second grid-connected converter, represents the power-frequency transfer relationship of the first grid-connected converter at the grid connection point, It represents the power-frequency transfer relationship of the second grid-connected converter at the grid connection point; Therefore, the power-frequency transfer relationship at the PCC can be derived as:

[0051] The power-frequency transfer relationship at the PCC can be understood as the closed-loop transfer function of the negative feedback system, such as Figure 6 As shown, the feedforward gain is , the feedback gain is .therefore, represents the open-loop transfer function of the grid-connected photovoltaic system. According to the Nyquist stability criterion, as long as the following conditions are met:

[0052] It can be guaranteed Figure 6 The phase margin of the system shown is positive, that is, the grid-connected photovoltaic system remains stable. A sufficient condition for the above equation to be true is:

[0053] in, Indicates existence, represents the total number of grid-connected converters in parallel, represents the frequency of the grid-type photovoltaic low-frequency oscillation, represents the phase of the transfer function, Represents and Denotes the transfer function and exist s = jω r The value of represents the Laplace operator, represents pi, represents the real part of the transfer function; It can be deduced The expression is:

[0054] Therefore, when the formula is satisfied: When Establishment, description Figure 6 The system shown is stable.

[0055] By comparing the formula and It can be seen that when both GFM converters have positive damping torque, the parallel system remains stable. Subsequently, this analysis is extended to the case where multiple converter units operate in parallel. The first converter is considered as a separate subsystem, and the remaining converters are considered as another subsystem. Figure 5 The power balance relationship at the PCC shown in the figure can be obtained:

[0056] Similarly, the power-frequency relationship at PCC can be expressed as:

[0057] The above formula can also be regarded as the closed-loop transfer function of the negative feedback system. According to the previous analysis, when the damping torque contributed by each GFM converter is positive, the formula is satisfied. Therefore, applying the addition rules for complex numbers, we get:

[0058] because G j ( jω r ) is also positive, so we can conclude that:

[0059] The above formula shows that the formula The equivalent negative feedback system described by always maintains a positive phase margin. Therefore, when n When multiple GFM converter units are operated in parallel, the system can remain stable as long as each GFM converter provides positive damping torque.

[0060] Therefore, whether it is a single converter or a system composed of multiple converters, the stability of the system fundamentally depends on ensuring that the damping torque of each grid-type converter is positive. However, the integral gain of the DC voltage control loop is Introducing negative damping torque into the system may lead to system instability. Therefore, an additional damping control strategy is needed to improve the stability of the system.

[0061] according to Figure 3 It can be seen that The negative damping torque introduced by the parameters to the system is due to the two integral links from the output power feedback to the frequency dynamics, which brings a -180° phase lag. Therefore, this paper considers introducing additional damping torque to the system through power feedback based on the lead-lag compensator to compensate for the negative damping torque generated by the DC voltage control loop, such as Figure 7 As shown. The transfer function of the lead-lag compensator is for:

[0062] when T 1> T 2 o'clock, The phase of is greater than zero, so an additional torque is introduced into the system through power feedback. This additional torque has a positive damping torque, which compensates for the DC voltage control loop. k i Negative damping torque introduced by the parameter.

[0063] The present invention proposes a power feedback control strategy suitable for suppressing low-frequency oscillations of matching control, which can effectively suppress the low-frequency oscillation problem of a grid-connected system composed of a single matching control or multiple matching controls. This method establishes the power-frequency transfer relationship of the system under matching control, and analyzes the contribution of each control parameter to the synchronous torque and damping torque based on the damping torque method; then, based on the damping torque, it is obtained that the stability condition in the multi-machine system is that the damping torque of the converter under each matching control is greater than zero, thereby proposing an additional damping control based on power feedback based on the lead-lag compensator to compensate for the negative damping torque part in the system. The present invention derives the control mechanism of this method in detail, and the control principle of this method is simple and easy to implement. It can effectively improve the system stability in both single-machine and multi-machine systems and avoid system low-frequency oscillation instability.

[0064] Example 2: Based on Example 1, a simulation model of a grid-connected photovoltaic system based on matching control was built in MATLAB / Simulink in the embodiment of the present invention to verify the control effect of the power feedback control method for matching control low-frequency oscillation suppression proposed in the present invention.

[0065] When a load fluctuation of 0.4MW occurs in 8s, the traditional matching control and Figure 6 The improved control strategy is shown in Table 1 to compare the power output of the system.

[0066] Table 1 System parameters

[0067] exist Figure 8 In, when When the parameter is 20p.u, the system oscillation is more obvious and lasts for a long time, and it takes about 10.5s to reach a steady state. However, after adopting the damping improvement strategy proposed in this invention, the power output of the converter recovers to a steady state after a short oscillation in about 8.6s. When the parameter is large, such as Figure 9 middle =30p.u., when load fluctuation occurs, the converter may experience low-frequency oscillation instability. From the previous analysis, we know that this is due to The parameter is too large, which causes the negative damping part of the system to exceed the positive damping part. After adopting the damping improvement strategy proposed in the present invention, the power oscillation of the converter can be quickly attenuated and restored to a steady state. It can be seen that the damping improvement strategy proposed in the present invention can effectively compensate for The negative damping torque introduced by the parameter into the system improves the stability of the system.

[0068] Figure 10 The power waveforms of two grid-connected photovoltaic systems under matching control are shown. The value is 40p.u, GFM_2 The value is 20p.u. Figure 8 and Figure 9 As shown in , when only GFM_2 is connected to the grid, the system remains stable. Figure 10 As shown in the figure, when the proposed damping enhancement strategy is not adopted, after GFM_1 and GFM_2 are connected in parallel, the power output of the two units begins to oscillate and gradually diverge. The negative damping torque generated by the value is too large, causing the total system damping to be less than zero, thus causing the system to be unstable. Therefore, even if GFM_2 itself provides a positive damping torque, it still becomes unstable due to the gradual divergence of electrical quantities such as system power and frequency. On the contrary, if Figure 11 As shown in Figure 3, when the proposed damping enhancement strategy is applied to two units, the output power of each unit reaches a steady state in about 9 seconds after experiencing a brief oscillation. This shows that the proposed strategy is also effective in suppressing oscillations in multi-machine systems.

[0069] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and it should be understood that the scope of protection of the present invention is not limited to such specific descriptions and embodiments. Those skilled in the art can make various other specific variations and combinations based on the technical teachings disclosed in the present invention without departing from the essence of the present invention, and such variations and combinations are still within the scope of protection of the present invention.

Claims

1. A power feedback control method suitable for matching and controlling low-frequency oscillation suppression, characterized in that: The following steps are involved: The power-frequency transfer relationship of the multi-matching control parallel system is established, and the torque of the multi-matching control parallel system is analyzed based on the damping torque method; Based on the results of damping torque analysis, the factors that introduce negative damping torque components in the multi-matching control parallel system and the stability conditions in the multi-matching control parallel system are determined; Based on the introduction of negative damping torque component and stability conditions, additional damping control based on power feedback is designed through lead-lag compensator to compensate the negative damping torque part in the multi-matching control parallel system and complete power feedback control.

2. The power feedback control method for matching control of low-frequency oscillation suppression according to claim 1, characterized in that: The process of establishing the power-frequency transfer relationship of the multi-matching control parallel system is as follows: When the grid-type converters are connected in parallel, The grid-type converter is regarded as a separate subsystem, and the rest of the grid-type converters are regarded as another subsystem. When power disturbance occurs on the grid side When , the power balance at the grid connection point is expressed as: in, Indicates the magnitude of the power disturbance occurring on the grid side, Indicates the i The active power output by each grid-connected converter is Indicates the The power-frequency transfer relationship of a grid-connected converter at the grid connection point is: Indicates the The power-frequency transfer relationship of a grid-connected converter at the grid connection point is: Represents the frequency disturbance component of the grid connection point; Then the power-frequency transfer relationship at the grid connection point is obtained, that is, the power-frequency transfer relationship of the multi-matching control parallel system is: Among them, the power-frequency transfer relationship at the grid connection point is regarded as the closed-loop transfer function of the negative feedback system. represents the feedforward gain, represents the open-loop transfer function of the system.

3. The power feedback control method for matching control of low-frequency oscillation suppression according to claim 1, characterized in that: The torque analysis of the multi-matching control parallel system based on the damping torque method is as follows: According to the power-frequency transfer relationship of the multi-matching controlled parallel system, the power angle dynamics of the multi-matching controlled parallel system is obtained; According to the Phillips model, the power angle dynamics of the synchronous generator are obtained; Comparing the power angle dynamics of the multi-matching control parallel system and the synchronous generator, the key control parameters that determine the low-frequency oscillation damping capacity of the grid-type system are obtained as follows: , when the frequency is The low-frequency oscillation formula is: in, represents the damping torque coefficient of the multi-matching control parallel system, represents the power synchronization coefficient of the grid-type converter, Represents the proportional parameter of the active power control loop, Represents the damping torque introduced by the active control loop, represents the integral coefficient of the DC voltage control loop, represents the power injected into the grid-connected converter, represents the steady-state value of the DC voltage, It represents the equivalent damping torque introduced by the DC voltage loop; Formed Provide positive damping torque for multi-matching control parallel system, Introducing negative damping torque, the integral coefficient of the DC voltage control loop is The increase of the proportional parameter of the active power control loop The reduction of leads to severe oscillation of the multi-matching control parallel system.

4. The power feedback control method for matching control of low-frequency oscillation suppression according to claim 3, characterized in that: The reason for the introduction of negative damping torque in the multi-matching control parallel system is that in the multi-matching control parallel system, when the output power is fed back to the frequency dynamics, a phase lag of -180° is introduced through two integral links, resulting in a DC voltage control loop parameter of Introduce a negative damping torque component.

5. The power feedback control method for matching control of low-frequency oscillation suppression according to claim 2, characterized in that: The stability condition of the multi-matching control parallel system is that the damping torque of the grid-type converter under each matching control is greater than zero, that is, the phase margin of the multi-matching control parallel system is positive.

6. The power feedback control method for matching control of low-frequency oscillation suppression according to claim 5, characterized in that: When the phase margin of the multi-matching control parallel system is positive, the power-frequency transfer relationship at the grid connection point satisfies the following conditions: in, Indicates existence, represents the total number of grid-connected converters in parallel, represents the frequency of the grid-type photovoltaic low-frequency oscillation, represents the phase of the transfer function, Represents and Denotes the transfer function and exist s = jω r The value of represents the Laplace operator, , represents the real part of the transfer function.

7. The power feedback control method for matching control of low frequency oscillation suppression according to claim 1, characterized in that: The transfer function of the lead-lag compensator for: in, represents the Laplace operator, and Represented as two time constants of the lead-lag compensator.

8. The power feedback control method for matching control of low-frequency oscillation suppression according to claim 7, characterized in that: Adjust the two time constants of the lead-lag compensator and ,satisfy When the lead-lag compensator transfer function is The phase of is greater than zero, and the additional damping control introduced is used to compensate for the negative damping torque in the multi-matching control parallel system.

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