Improved oscillation suppression method of virtual synchronous machine

Abstract

The invention discloses an improved oscillation suppression method of a virtual synchronous machine. The method comprises the following steps: constructing a virtual synchronous motor, and obtaining characteristic parameters and variables including frequency and amplitude of the virtual synchronous motor; constructing an active-reactive power coupling feedback item based on low-pass filtering, and coupling the active-reactive power coupling feedback item with the obtained virtual synchronous motor; and establishing an output power-frequency / voltage dynamic response model of the virtual synchronous generator by adopting a single-machine grid-connected system, and analyzing and verifying the improved control of the virtual synchronous generator. The improved oscillation suppression method provided by the invention is based on an active-reactive power coupling feedback item of low-pass filtering, and through dual mechanisms of frequency selective filtering and power decoupling, while medium-frequency power oscillation is effectively suppressed, the stability of the system is remarkably improved, and further, the system stability is improved. The method has the advantages of high real-time performance and no need of additional hardware, and can meet the technical requirements in the fields of new energy grid connection, micro-grid control and the like.

Description

Technical Field

[0001] This invention relates to a virtual synchronous machine oscillation suppression method, specifically an improved oscillation suppression method for virtual synchronous machines, belonging to the field of microgrid control technology. Background Technology

[0002] Microgrids are small-scale, decentralized, and independent systems capable of self-control, protection, and management. They can operate in islanded mode or connected to the main power grid. Microgrids help reduce the impact of wind and solar power, which have intermittent, fluctuating, and anti-peak-shaving characteristics, on the main power grid, effectively increasing wind and solar power penetration, reducing grid vulnerability, and making the power system more reliable, cleaner, more economical, and safer. This is of great significance for promoting the sustainable development of the power industry. To overcome the problem of insufficient inertia in islanded microgrids, Virtual Synchronous Generators (VSGs) have been proposed. VSGs introduce the oscillation equations of synchronous generators into their control algorithms, enabling the inverter to simulate both the steady-state and transient characteristics of synchronous generators, providing sufficient inertial support. While maintaining the existing power system architecture, VSGs are becoming the most effective control scheme for enhancing system inertia and improving frequency stability. In recent years, considering the dynamics of line inductance, it has been found that when the line inductance is large and the resistance is small, strong power coupling exists between the active and reactive power in the mid-frequency range (10Hz~100Hz), which easily induces mid-frequency oscillations, also known as synchronous frequency resonance, potentially leading to system instability. Connecting a real resistor in series with the converter can suppress mid-frequency oscillations, but this incurs additional losses. Some studies have proposed classical virtual resistance control strategies to suppress oscillations caused by high line impedance inductance; however, the virtual resistance control method for suppressing mid-frequency power oscillations has limited control freedom. Therefore, there is an urgent need to study a multi-control variable suppression strategy for mid-frequency power oscillations based on a virtual synchronous machine. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides an improved oscillation suppression method for virtual synchronous machines. This improved oscillation suppression method is based on a low-pass filtered coupled active and reactive power feedback term. Through a dual mechanism of frequency-selective filtering and power decoupling, it effectively suppresses medium-frequency power oscillations while significantly improving system stability. Furthermore, this method has the advantages of strong real-time performance and requires no additional hardware, meeting the technical requirements of fields such as renewable energy grid connection and microgrid control.

[0004] To achieve the above-mentioned technical effects, the present invention provides an improved oscillation suppression method for virtual synchronizers, comprising:

[0005] Step S1: Construct a virtual synchronous motor and obtain its characteristic parameters and variables, including frequency and amplitude;

[0006] Step S2: Construct a low-pass filter active-reactive power coupling feedback term and improve the virtual synchronous motor phase obtained in step S1;

[0007] Step S3: Establish the output power-frequency / voltage dynamic response model of the virtual synchronous generator using a single-machine grid-connected system, and analyze and verify the improved virtual synchronous motor in step S2.

[0008] The technical solution provided by this invention can specifically suppress the synchronous frequency resonance of the virtual synchronous motor by adjusting the active-reactive power coupling feedback term, especially for medium frequency oscillations between 50 and 100 Hz. In addition, the directional adjustment of the above feedback term can also increase the damping ratio and significantly improve the system stability.

[0009] As a preferred embodiment, the characteristic parameters and variables include: angular frequency, phase angle, active reference power, active output power, inertia coefficient, damping coefficient, reactive reference power, reactive output power, and reactive droop coefficient.

[0010] As a preferred embodiment, the virtual synchronous motor's characteristic parameters and variable expressions, including frequency and amplitude, are as follows:

[0011] Formula 1: ;

[0012] In Equation 1: J i ω is the coefficient of inertia. i Let ω* represent the angular frequency of the i-th virtual synchronizer, and P represent the nominal angular frequency. * and P i D represents the active reference power and output power of the i-th inverter, respectively. i V is the damping coefficient; i Q represents the intermediate variable that produces the voltage amplitude. * and Q i D represents the reactive reference power and output power of the i-th inverter, respectively. qi E represents the reactive power droop factor. i E represents the voltage amplitude of the i-th virtual synchronous machine. * This represents the amplitude reference, and K represents the voltage amplitude integral coefficient.

[0013] As a preferred embodiment, the coupled active-reactive power feedback term of the low-pass filter includes:

[0014] Formula 3: ;and

[0015] Formula 4: ;

[0016] The expression for the improved virtual synchronous motor phase is:

[0017] Formula 5: ;

[0018] In equations 3-5: δ i Let b represent the phase angle of the i-th virtual synchronizer. i The low-pass filter phase angle-active loop coupling feedback coefficient, r i denoted as the low-pass filter voltage-reactive power control loop coupling feedback coefficient, and s represents the Laplace operator.

[0019] As a preferred embodiment, the process for establishing the output power-frequency / voltage dynamic response model of the virtual synchronous generator is as follows:

[0020] Step S3-1: Construct a small-signal model of the inverter output power through the line impedance. The process is as follows:

[0021] Formula 6: ;

[0022] Formula 7: ;

[0023] Step S3-2: Given that the control bandwidth of the power loop is much smaller than the control bandwidth of the dual closed-loop system, the output power-frequency / voltage dynamic response model of the virtual synchronous generator can be expressed as:

[0024] Formula 8: ;

[0025] Formula 9: ;

[0026] Formula 10: ;

[0027] In equations 6-9: , , , ;ω p V represents the angular frequency of the power grid. p P represents the voltage amplitude of the power grid. gi and Q gi C represents the active power and reactive power output to the power grid, respectively. ai (s), D ai (s), C i (s), D i (s) is a 2×2 transfer function matrix, C ai (s), D ai (s), C i (s), Di (s) is a 2×2 transfer function matrix.

[0028] As a preferred embodiment, the process of analyzing and verifying the coupled virtual synchronous motor is as follows: Step S3-3, based on the output power-frequency / voltage dynamic response model of the virtual synchronous generator, the correlation between the inverter output power and the grid-connected power is obtained, and the calculation process is as follows:

[0029] Formula 11: ;

[0030] Formula 12: ;

[0031] Formula 13: ;

[0032] In equations 11-13: I represents a 2×2 identity matrix. and This is the process function matrix.

[0033] As a preferred embodiment, the correlation between the inverter output power and the grid-connected power is expressed as follows:

[0034] Formula 14: ;

[0035] Formula 15: ;

[0036] In equations 14 and 15: and This is the analysis function matrix for grid-connected power.

[0037] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are as follows:

[0038] 1) The improved oscillation suppression method provided by this invention is based on a low-pass filter coupled active-reactive power feedback term. Through a dual mechanism of frequency-selective filtering and power decoupling, this method effectively suppresses medium-frequency power oscillations while significantly improving system stability. Furthermore, this method has the advantages of strong real-time performance and requires no additional hardware, meeting the technical requirements of fields such as new energy grid connection and microgrid control.

[0039] 2) In the technical solution provided by the present invention, by adjusting the active-reactive power coupling feedback term, the synchronous frequency resonance of the virtual synchronous motor can be specifically suppressed, especially for medium frequency oscillations between 50 and 100 Hz. In addition, the directional adjustment of the above feedback term can also increase the damping ratio and significantly improve the system stability. Attached Figure Description

[0040] Figure 1 This is the Bode plot of the inverter output active power response transfer function under reactive power reference disturbance in Embodiment 1 of the present invention.

[0041] in, Figure 1 (a) Different low-pass filter phase angles - reactive power feedback coefficients (b) i Bode plot of transfer function, Figure 1 (b) represents the active power feedback coefficient r for different low-pass filter voltages. i Bode plot of transfer function;

[0042] Figure 2 In Embodiment 1 of this invention, the low-pass filter phase angle-reactive power feedback coefficient b i Root locus diagram of the system as the value increases;

[0043] Figure 3 The low-pass filter voltage-active power feedback coefficient r in Embodiment 1 of this invention i Root locus diagram of the system as the value increases;

[0044] Figure 4 This is a reactive power reference disturbance waveform diagram under the VSG control method in the prior art of Comparative Example 1 of the present invention;

[0045] in, Figure 4 (a) is the waveform of the output active power. Figure 4 (b) is the waveform diagram of the output reactive power;

[0046] Figure 5 This is a reactive power reference disturbance waveform diagram of the improved oscillation suppression method in Embodiment 1 of the present invention;

[0047] in, Figure 5 (a) is the waveform diagram of the output active power. Figure 5 (b) is the waveform diagram of the output reactive power. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention more apparent, exemplary embodiments according to the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are merely a part of the embodiments of the present invention, and not all of the embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein. Based on the embodiments of the present invention described herein, all other embodiments obtained by those skilled in the art without inventive effort should fall within the protection scope of the present invention.

[0049] Example 1

[0050] This embodiment provides an improved oscillation suppression method for virtual synchronizers, specifically:

[0051] Step S1: Construct a virtual synchronous motor and obtain its characteristic parameters and variables, including frequency and amplitude;

[0052] The characteristic parameters and variables include: angular frequency, phase angle, active reference power, active output power, inertia coefficient, damping coefficient, reactive reference power, reactive output power, and reactive droop coefficient.

[0053] The virtual synchronous motor is expressed as follows regarding its characteristic parameters and variables, including frequency and amplitude:

[0054] Formula 1: ;

[0055] In Equation 1: J i ω is the coefficient of inertia. i Let ω* represent the angular frequency of the i-th virtual synchronizer, and P represent the nominal angular frequency. * and P i D represents the active reference power and output power of the i-th inverter, respectively. i V is the damping coefficient; i Q represents the intermediate variable that produces the voltage amplitude. * and Q i D represents the reactive reference power and output power of the i-th inverter, respectively. qi E represents the reactive power droop factor. i E represents the voltage amplitude of the i-th virtual synchronous machine. * This represents the amplitude reference, and K represents the voltage amplitude integral coefficient.

[0056] Step S2: Construct a low-pass filtered coupled active-reactive power feedback term and couple it with the virtual synchronous motor obtained in step S1;

[0057] The low-pass filter's coupled active-reactive power feedback term includes:

[0058] Formula 3: ;and

[0059] Formula 4: ;

[0060] The expression for the coupled virtual synchronous motor is:

[0061] Formula 5: ;

[0062] In equations 3-5: δ i Let b represent the phase angle of the i-th virtual synchronizer. i The low-pass filter phase angle-active loop coupling feedback coefficient, r irepresents the low-pass filter voltage-reactive power control loop coupling feedback coefficient, and s represents the Laplace operator;

[0063] Step S3: Establish the output power-frequency / voltage dynamic response model of the virtual synchronous generator using a single-machine grid-connected system, and analyze and verify the coupled virtual synchronous motor from step S2 to obtain the result.

[0064] The process of establishing the output power-frequency / voltage dynamic response model of the virtual synchronous generator is as follows:

[0065] Step S3-1: Construct a small-signal model of the inverter output power through the line impedance. The process is as follows:

[0066] Formula 6: ;

[0067] Formula 7: ;

[0068] Step S3-2: Given that the control bandwidth of the power loop is much smaller than the control bandwidth of the dual closed-loop system, the output power-frequency / voltage dynamic response model of the virtual synchronous generator can be expressed as:

[0069] Formula 8: ;

[0070] Formula 9: ;

[0071] Formula 10: ;

[0072] In equations 6-9: , , , ;ω p V represents the angular frequency of the power grid. p P represents the voltage amplitude of the power grid. gi and Q gi C represents the active power and reactive power output to the power grid, respectively. ai (s), D ai (s), C i (s), D i (s) is a 2×2 transfer function matrix, C ai (s), D ai (s), C i (s), D i (s) is a 2×2 transfer function matrix.

[0073] The process of analyzing and verifying the coupled virtual synchronous motor is as follows: Step S3-3, based on the output power-frequency / voltage dynamic response model of the virtual synchronous generator, the correlation between the inverter output power and the grid-connected power is obtained. The calculation process is as follows:

[0074] Formula 11: ;

[0075] Formula 12: ;

[0076] Formula 13: ;

[0077] In equations 11-13: I represents a 2×2 identity matrix. and This is the process function matrix.

[0078] In the correlation between the inverter output power and the grid-connected power, the grid-connected power is expressed as:

[0079] Formula 14: ;

[0080] Formula 15: ;

[0081] In equations 14 and 15: and This is the analysis function matrix for grid-connected power.

[0082] Comparative Example 1

[0083] This comparative example represents the VSG control method in the prior art.

[0084] The present invention performed a transfer function Bode test on the improved oscillation suppression method provided in Example 1, and the results are as follows: Figure 1 As shown. (Through) Figure 1 (a) It can be seen that, There are two main resonant peaks. The low-frequency resonant peak is mainly around 3Hz, and this peak is primarily related to the inertia coefficient and damping coefficient of the active-frequency control loop, which has been fully demonstrated and analyzed in existing studies. In addition, the Bode plot also exhibits a resonant peak with an oscillation frequency between 50Hz and 100Hz (hereinafter referred to as the medium frequency). Increasing the low-pass filter phase angle-reactive power feedback coefficient b... i The mid-frequency resonant peak was significantly reduced, indicating that increasing the low-pass filter phase angle-reactive power feedback coefficient can effectively suppress mid-frequency oscillations; furthermore, similarly, from Figure 1 (b) The Bode plot shows that increasing the low-pass filter voltage-active feedback coefficient r i This also significantly reduced the mid-frequency resonant peak value, and, along with adjusting the phase angle-reactive feedback coefficient b...i The difference lies in adjusting the low-pass filter voltage - active feedback coefficient r. i It has less impact on oscillations below 10Hz (low frequency) and more effectively suppresses mid-frequency resonance peaks. The Bode plot analysis above verifies the effectiveness of the proposed improved synchronous frequency resonance suppression control.

[0085] also, Figure 2 and Figure 3 These represent the low-pass filter phase angle and the reactive power feedback coefficient b, respectively. i When the system root locus and low-pass filter voltage-active power feedback coefficient r are increased i The system root locus increases. Figure 2 Display low-pass filter phase angle - reactive power feedback coefficient b i When the value is increased, the characteristic roots of the system in the 50Hz-100Hz range (medium frequency) shift to the left half-plane. When the oscillations at the medium frequency are severe or even cause system instability, the low-pass filter phase angle-reactive power feedback coefficient b can be increased. i This helps the eigenvalue cross from the right half-plane to the left half-plane, improving system stability. Figure 3 Display low-pass filter voltage - active power feedback coefficient r i When the value is increased, the mid-frequency characteristic root of the system shifts to the left half-plane. Similarly, increasing the low-pass filter voltage-active feedback coefficient r... i This helps the eigenvalue cross from the right half-plane to the left half-plane, improving system stability and significantly increasing the damping ratio. The analysis results show that increasing the coefficient b... i and r i Both can effectively improve system stability, but increasing the coefficient r i The effect is better than b i .

[0086] Furthermore, to verify the effectiveness of the method provided in Example 1 in suppressing medium-frequency oscillations, this invention also conducted simulation verification on Example 1 and Comparative Example 1 based on a single-machine grid-connected system, and the results are as follows: Figure 4 and Figure 5 As shown. Figure 4 (a) and Figure 4 (b) Represents the output active and reactive power waveforms of a single-machine grid-connected system based on traditional virtual synchronous machine control under reactive power reference disturbance. Figure 4 When displaying reactive power reference disturbance, the method provided in Comparative Example 1 exhibits severe medium-frequency oscillations, which are measured to be Hz by FFT analysis. Figure 5 (a) and Figure 5 (b) respectively represent the output active and reactive power waveforms of the method provided in Example 1 when the reactive power reference disturbance of a single-machine grid-connected system is applied. Figure 5When the reactive power reference disturbance is displayed, the medium-frequency oscillation of the system is effectively suppressed under the traditional virtual synchronous machine control. Simulation verifies the effectiveness of the proposed improved control strategy, which is consistent with the above theoretical analysis results.

Claims

1. An improved oscillation suppression method for a virtual synchronous machine, characterized in that, The application relates to a method for establishing a virtual synchronous generator, comprising the following steps: S1, constructing a virtual synchronous motor and obtaining characteristic parameters and variables of the virtual synchronous motor, including frequency and amplitude; S2, constructing a low-pass filtered active-reactive power coupling feedback item and improving the virtual synchronous motor obtained in step S1; S3, establishing an output power-frequency / voltage dynamic response model of the virtual synchronous generator by using a single-machine grid-connected system, and analyzing and verifying the improved virtual synchronous motor in step S2.

2. The improved oscillation suppression method of a virtual synchronous machine according to claim 1, characterized in that: The characteristic parameters and variables include angular frequency, phase angle, active reference power, active output power, inertia coefficient, damping coefficient, reactive reference power, reactive output power and reactive droop coefficient.

3. The improved oscillation suppression method of a virtual synchronous machine according to claim 2, characterized in that: The expression of the virtual synchronous motor about the characteristic parameters and variables, including frequency and amplitude, is as follows: Formula 1: ; In formula 1: J i is the inertia coefficient, ω i denotes the angular frequency of the i-th virtual synchronous machine, ω* denotes the nominal angular frequency, P * and P i denote the active reference power and the output power of the i-th inverter, respectively, D i is the damping coefficient; Q * and Q i denote the reactive reference power and the output power of the i-th inverter, respectively, D qi denotes the reactive droop coefficient, E i denotes the voltage amplitude of the i-th virtual synchronous machine, E * denotes the amplitude reference, K denotes the voltage amplitude integral coefficient.

4. The improved oscillation suppression method of a virtual synchronous machine according to claim 3, characterized in that: The low-pass filtered active-reactive power coupling feedback item comprises: Formula 3: ; and Formula 4: ; The expression of the improved virtual synchronous motor is as follows: Formula 5: ; In formulas 3-5: V i denotes an intermediate variable for the voltage amplitude, δ i denotes the phase angle of the i-th virtual synchronous machine, b i denotes the low-pass filtered phase angle-active power loop coupling feedback coefficient, r i denotes the low-pass filtered voltage-reactive power control loop coupling feedback coefficient, s denotes the Laplace operator.

5. The improved oscillation suppression method of a virtual synchronous machine according to claim 4, characterized in that: The establishment process of the output power-frequency / voltage dynamic response model of the virtual synchronous generator is as follows: S3-1, constructing a small-signal model of inverter output power through line impedance, and the process is as follows: Formula 6: ; Formula 7: ; S3-2, on the premise that the control bandwidth of the power loop is much smaller than the double-closed-loop control bandwidth, the output power-frequency / voltage dynamic response model of the virtual synchronous generator can be expressed as: Formula 8: ; Formula 9: ; Formula 10: ; in formulas 6-9: , , , ; ω p denotes the angular frequency of the power grid, V p denotes the voltage amplitude of the power grid, P gi and Q gi denote the active and reactive power output to the power grid, respectively, C ai (s), D ai (s), C i (s), D i (s) are 2x2 transfer function matrices. C ai (s), D ai (s), C i (s), D i (s) are 2x2 transfer function matrices.

6. The improved oscillation suppression method of a virtual synchronous machine according to claim 5, characterized in that: The process of analyzing and verifying the coupled virtual synchronous motor is as follows: S3-3, according to the output power-frequency / voltage dynamic response model of the virtual synchronous generator, the correlation between the inverter output power and the grid-connected power is obtained, and the calculation process is as follows: Formula 11: ; Formula 12: ; Formula 13: ; In formulas 11-13: I represents a 2x2 unit matrix, and is a process function matrix.

7. The improved oscillation suppression method of a virtual synchronous machine according to claim 6, characterized in that: In the correlation between the inverter output power and the grid-connected power, the grid-connected power is expressed as: Formula 14: ; Formula 15: ; In formulas 14 and 15: and is the analytical transfer function matrix for the grid-connected power.

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