A damping optimization control method based on a virtual synchronous generator

Abstract

This invention discloses a damping optimization control method based on a virtual synchronous generator, comprising the following steps: S1, determining the first active power and reactive power by collecting the output voltage and current of the VSG; S2, determining the second active power and PSS compensation power; S3, determining the frequency of the VSG output based on the result of S2; S4, outputting the internal reference voltage of the converter through the reactive-excitation control equation of the virtual synchronous generator, and combining the three-phase voltage of the converter internal voltage with the phase output of the virtual synchronous generator; S5, modifying the internal reference voltage of the converter using the three-phase voltage and the phase of the virtual synchronous generator by Parker variation output; avoiding the droop effect caused by the damping term in the rotor swing equation of the virtual synchronous generator, eliminating the active power deviation caused by the introduction of the damping coefficient for droop control, strengthening the effectiveness of droop control while improving the damping capability of the system, and enhancing the system's ability to suppress dynamic oscillations of active power.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, and in particular to a control method based on damping optimization of a virtual synchronous generator. Background Technology

[0002] Driven by both energy transition and technological advancements, the power system is exhibiting a "dual-high" development trend: a high proportion of renewable energy and a high proportion of power electronic equipment. However, in recent years, the scale of new energy generation connected to weak power grids has been expanding, posing challenges to the stability of the power system. Power electronic converters, acting as a bridge between distributed power sources and the grid, require optimized control strategies, which are crucial for the stable and safe operation of the power system. The electrification of the power grid and the integration of distributed power sources can lead to a loss of system inertia, threatening the safe operation of the power grid.

[0003] Virtual synchronous machines (VSGs) have become a focus of research in microgrid inverter control because they can simulate traditional synchronous generators to provide inertia and damping capabilities to power systems, thereby improving system frequency and voltage stability. However, for traditional VSG control strategies, the introduction of damping can affect the droop control of microgrids, causing deviations. Furthermore, a large damping coefficient can lead to poor droop effects; for example, when the grid frequency drops and the VSG recovers to steady state, its active power will differ from the original steady state, and this difference will further increase with the increase of the damping coefficient.

[0004] For example, a Chinese patent document, "Optimal Virtual Inertial Control Method Based on UNI Synchronous Generator", with publication number CN105006834A, discloses a method that organically combines the three control degrees of freedom in the virtual synchronous generator: droop coefficient m, virtual inertia J, and virtual damping D. However, it does not optimize the droop control. Summary of the Invention

[0005] To address the issue of deviation in droop control in existing technologies, this invention provides a damping optimization control method based on a synchronous generator. This method resolves the impact of the damping term introduced by the virtual synchronous generator control strategy on the droop control effect, eliminates active power deviation caused by frequency fluctuations, and further enhances the system's damping capability and improves system stability through the dynamic damping term.

[0006] A further objective of this invention is to compensate for damping power by feeding the active power deviation forward to the active power control loop of the VSG via the PSS compensator to form additional damping control.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A damping optimization control method based on a virtual synchronous generator, characterized by comprising the following steps:

[0009] S1. Determine the first active power by collecting the output voltage and current of the VSG. and reactive power ;

[0010] S2. Determine the second active power. The PSS compensation power is determined based on the results of S1. ;

[0011] S3. Determine the output frequency of VSG based on the result of S2. ;

[0012] S4. Output the internal reference voltage of the converter through the reactive power-excitation control equation of the virtual synchronous machine, combined with the phase of the virtual synchronous machine. The three-phase voltage of the output converter's internal voltage;

[0013] S5. Utilizing three-phase voltage and virtual synchronizer phase The internal reference voltage of the converter is modified using Parker variable output. Through active power control, reactive power control, and PSS damped power control, the impact of the damping term introduced by the virtual synchronous generation control strategy on the droop control effect is addressed, eliminating active power deviation caused by frequency fluctuations. Additional damping control is formed by feeding the active power deviation forward to the VSG active power control loop via the PSS compensator to compensate for the damping power.

[0014] Preferably, S1 includes S11, which calculates the virtual synchronizer phase using the angular frequency of the Parker variation. ;

[0015] S12, Utilizing the phase of a virtual synchronizer Together with the sampled voltage and current signals, the Parker converter outputs the internal voltage and current of the converter. The coordinate components are used to obtain the first active power output of the VSG. and reactive power This avoids the drooping effect caused by the damping term in the rotor rocking equation of a virtual synchronous machine simulation.

[0016] Preferably, S2 includes S21, which uses a virtual synchronous machine to simulate the rotor rocking equation to output the angular frequency of the Parker transform. ;

[0017] S22, Utilizing angular frequency The second active power is obtained by using the droop control equation, given the system's rated angular frequency and the given active power. ;

[0018] S23, Utilizing the second active power and first active power The difference is used as the input of the power system stabilizer to obtain the PSS compensation power through the signal of the PI controller. This eliminates the active power deviation caused by the introduction of the damping coefficient in droop control, thus enhancing the effectiveness of droop control.

[0019] Preferably, the angular frequency of the Parker transform is generated by simulating the following rotor rocking equation.

[0020] ;

[0021] in, P is the second active power, J is the first active power, D is the virtual inertia, and D is the damping coefficient. ω is the rated angular frequency; δ is the VSG power angle. The electrical angular frequency of the synchronous virtual machine can be obtained.

[0022] Preferably, the second active power is obtained from the given system rated angular frequency and the given active power. The following droop control equation is derived.

[0023] ;

[0024] in, Where is the active power-frequency droop factor, E is the internal electromotive force, U is the peak grid-side voltage, and X is the synchronization reactance. This is the active power setpoint. The electromagnetic power for droop control can be obtained.

[0025] Preferably, the first active power P and reactive power Q are obtained from the internal voltage and current of the converter and calculated using the following equations.

[0026] ;

[0027] The internal electromotive force of the VSG is represented by E; U N X is the rated voltage of the power grid; X is the synchronous reactance. The actual active power can be obtained.

[0028] Preferably, the power controlled by PSS It is obtained by passing the power difference through a high-pass filter and a gain module consisting of phase angle compensation and compensation gain K. Then, a PI controller is used to... Follow the accurate value As input to the PSS controller, it generates PSS compensation power to compensate for the damping power caused by the damping coefficient. It can reduce the active power deviation caused by the introduction of damping coefficient and damping feedback channel.

[0029] The present invention has the following advantages:

[0030] This approach avoids the droop effect caused by the damping term in the rotor swing equation of the virtual synchronous machine simulation, eliminates the active power deviation caused by the introduction of the damping coefficient in droop control, enhances the effectiveness of droop control, improves the system's damping capability, improves dynamic performance, optimizes the system's dynamic characteristics, enhances the system's ability to suppress dynamic oscillations of active power, and improves the system's stability. Attached Figure Description

[0031] The accompanying drawings described below are merely exemplary. Those skilled in the art can derive other embodiments based on the provided drawings without any inventive effort.

[0032] Figure 1 This is a schematic diagram of the control principle of the virtual synchronous generator in the second embodiment of the present invention.

[0033] Figure 2 This is the main circuit structure for VSG control in the second embodiment of the present invention.

[0034] Figure 3 This is a schematic diagram of the VSG controlled by PSS in the second embodiment of the present invention.

[0035] Figure 4 This is a diagram of the damping torque structure in the second embodiment of the present invention.

[0036] Figure 5 This is a vector diagram of the electromagnetic torque increment in the second embodiment of the present invention.

[0037] Figure 6 This refers to the active power output of the VSG when the frequency changes in the second embodiment of the present invention.

[0038] Figure 7 This refers to the reactive power output of the VSG in the second embodiment of the present invention.

[0039] Figure 8 This refers to the active power output of the VSG before and after the short-circuit fault is cleared in the second embodiment of the present invention.

[0040] Figure 9 This is a flowchart illustrating the method steps of the first embodiment of the present invention. Detailed Implementation

[0041] The following specific embodiments illustrate the implementation of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] like Figure 9 As shown, in the first embodiment, the present invention discloses a damping optimization control method based on a virtual synchronous generator, including: S1, determining the first active power by collecting the output voltage and current of the VSG. and reactive power S11. Calculate the phase of the virtual synchronizer using the angular frequency of the Parker variation. ;

[0043] The angular frequency of the Parker transform is generated by simulating the following rotor rocking equation.

[0044] ;

[0045] in, P is the second active power, J is the first active power, D is the virtual inertia, and D is the damping coefficient. ω is the rated angular frequency; δ is the VSG power angle.

[0046] S12, Utilizing the phase of a virtual synchronizer Together with the sampled voltage and current signals, the Parker converter outputs the internal voltage and current of the converter. The coordinate components are used to obtain the first active power output of the VSG. and reactive power The first active power P and reactive power Q are obtained from the internal voltage and current of the converter and are calculated using the following equations.

[0047] ;

[0048] The internal electromotive force of the VSG is represented by E; U N X is the rated voltage of the power grid; X is the synchronous reactance.

[0049] S2. Determine the second active power. The PSS compensation power is determined based on the results of S1. S21. The angular frequency of the Parker transform is output by simulating the rotor rocking equation using a virtual synchronous machine. ;

[0050] S22, Utilizing angular frequency The second active power is obtained by using the droop control equation, given the system's rated angular frequency and the given active power. The second active power is obtained from the given system rated angular frequency and the given active power. The following droop control equation is derived.

[0051] ;

[0052] in, Where is the active power-frequency droop factor, E is the internal electromotive force, U is the peak grid-side voltage, and X is the synchronization reactance. This is the given value for active power. Second active power. It is a given value obtained from the droop control equation.

[0053] S23, Utilizing the second active power and first active power The difference is used as the input of the power system stabilizer to obtain the PSS compensation power through the signal of the PI controller. PSS-controlled power It is obtained by passing the power difference through a high-pass filter and a gain module consisting of phase angle compensation and compensation gain K. This is achieved through a PI controller. Follow the accurate value As input to the PSS controller, it generates PSS compensation power to compensate for the damping power caused by the damping coefficient. .

[0054] S3. Determine the output frequency of VSG based on the result of S2. .

[0055] S4. Output the internal reference voltage of the converter through the reactive power-excitation control equation of the virtual synchronous machine, combined with the phase of the virtual synchronous machine. The three-phase voltage of the output converter's internal voltage.

[0056] S5. Utilizing three-phase voltage and virtual synchronizer phase The internal reference voltage of the converter is modified using the Parker variable output.

[0057] In use, the active power deviation is fed forward to the active power control loop of the VSG through the PSS compensator to form an additional damping control, thereby compensating for the damping power.

[0058] In the second embodiment, the principle of the present invention is as follows:

[0059] The three-phase grid-connected virtual synchronous machine control structure mainly consists of three parts: active power-frequency control, reactive power control, and PSS damped power control. By acquiring the VSG output voltage and current, and calculating the output active power P and output reactive power Q through a power calculation stage, the angular frequency ω and internal electromotive force E are obtained through active power-frequency control and reactive power-voltage control stages, respectively. These two are then combined to obtain the VSG internal electromotive force vector E. The voltage reference value is obtained by subtracting the voltage drop across the synchronization impedance from the vector E in the electromagnetic equation control stage. Furthermore, under the control of the dual closed-loop system, the output voltage u in steady state is guaranteed to be consistent with its reference value. The values ​​are equal, satisfying the VSG control requirements. A typical control structure is as follows: Figure 1 As shown.

[0060] Figure 2 A schematic diagram of a three-phase virtual synchronous generator being connected to the grid is provided. It can be seen that the three-phase virtual synchronous generator is connected to the power grid via a filter and then through a line. Among these... Indicates the DC bus voltage. This indicates the three-phase output current of the inverter. This represents the voltage at point PCC. Indicates the filter inductance. Indicates the filter resistor. Indicates the filter capacitor. and Indicates the circuit resistance. (By...) The voltage at the midpoint of the inverter bridge arm is represented. The current in the filter inductor is represented.

[0061] Figure 3 The control structure diagram of the VSG controlled by the PSS is given. Figure 4 Therefore, the power consists of three parts, namely the damping power generated by the damping circuit. Power controlled by PSS and the second active power under droop control .in The main reason for the deviation in active power is the feedback signal generated by the damping coefficient feedback channel. This deviation is due to the fact that the power controlled by the PSS... It is obtained by passing the power difference through a high-pass filter and a gain module consisting of phase angle compensation and compensation gain K. This is achieved through a PI controller. Follow the accurate value As input to the PSS controller, it generates PSS compensation power to compensate for the damping power caused by the damping coefficient. Among them, the second active power It is a given value obtained from the droop control equation.

[0062] Figure 4 The damping torque structure diagram of PSS optimized control is given, showing the mechanical torque generated by droop control. Electromagnetic torque generated by the voltage regulation stage Additional torque generated by PSS composition.

[0063] Figure 5 An electromagnetic torque vector diagram is given. The additional torque generated by the voltage regulator, the damping torque generated under traditional VSG control is The resultant torque is PSS will generate additional damping torque. Decomposed into The positive damping torque of the shaft is Generate new damping torque The resultant torque is It can be seen that the system's damping torque increases, and its damping capacity is improved.

[0064] As the above analysis shows, the control method proposed in this invention can effectively eliminate the deviation caused by the introduction of damping in the active power-frequency droop control of the virtual synchronous machine. It utilizes dynamic damping to enhance the system's damping capability, thereby improving system stability. The mechanism by which this damping effect is provided can be understood through… Figure 6 As can be seen from the electromagnetic torque vector diagram, when the PSS-optimized damping control method proposed in this invention is used, a positive damping torque can be decomposed, thereby improving the damping capability of the system and achieving the goal of stabilizing the system.

[0065] In use, this invention employs a single virtual synchronous machine integrated into an infinite system, such as... Figure 2 For example, a simulation of grid connection of a DC power supply with an inverter controlled by a virtual synchronous machine is performed. The inverter adopts the control method proposed in this invention. The relevant parameters of the virtual synchronous machine are shown in Table 1.

[0066] Table 1 Parameters of Virtual Synchronous Generator Examples

[0067]

[0068] Figure 6 The active power output of the VSG after stabilization of frequency fluctuations is presented under both the traditional control strategy and the control method proposed in this invention. It can be seen that as the system frequency changes, the active power output of the VSG also changes. Based on the droop control principle, .pass Figure 6(a) It can be seen that the output power under the traditional control strategy is 231,000 W, which deviates from the theoretical value, while the output power under the improved control strategy is 234,000 W. This indicates that the traditional control strategy produced a large deviation, which was eliminated after optimization. Furthermore, according to Figures (b) and (c), increasing the frequency by 0.1 Hz and 0.15 Hz respectively, the theoretical output power analysis values ​​should be 230,900 W and 227,800 W, which are consistent with the improved VSG output values. Under the traditional control strategy, the deviation increases with the increase of the frequency change value, indicating that the effectiveness of droop control gradually decreases. Simultaneously, it can be seen that with the increase of the frequency deviation, the oscillation time increases under the traditional control strategy, while the oscillation time decreases significantly under the improved control strategy, indicating that the system damping increases and the system stability improves.

[0069] Figure 7 The reactive power output of the VSG in the simulation example of this invention is given. A reactive power jump is set at 0.5 s, and it can be seen that the reactive power output of the VSG... Always follow the given value The VSG dynamic process is excessively smooth, and the degree of dynamic coupling is not aggravated. This indicates that the optimization will not affect the reactive power-voltage regulation link, but only the droop control, and will not affect the overall normal operation of the system.

[0070] To verify the stability of the system, Figure 8 The dynamic characteristics of the active power output of the VSG before and after the large load is disconnected in the system of the embodiment are given. When a single VSG operates with a load, the VSG output power follows the given value of 237 kW. At 0.5 s, the system is connected to a large load, the system frequency drops, and the system becomes unstable; at 0.9 s, the load is disconnected, and the system frequency returns to its rated value. Figure 9 It can be seen that when a heavy load is removed, the system cannot maintain normal operation under the traditional control strategy. However, under the improved control strategy, the system can quickly recover to normal operation. The control method proposed in this invention can improve the system's damping and significantly enhance its static stability.

[0071] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A control method based on damping optimization of a virtual synchronous generator, characterized in that, Includes the following steps: S1. Determine the first active power by collecting the output voltage and current of the VSG. and reactive power ; The second active power is obtained from the given system rated angular frequency and the given active power. ; S2. Determine the second active power. The PSS compensation power is determined based on the results of S1. ; PSS-controlled power It is obtained by passing the power difference through a high-pass filter and a gain module consisting of phase angle compensation and compensation gain K; S3. Determine the output frequency of VSG based on the result of S2. ; S4. Output the internal reference voltage of the converter through the reactive power-excitation control equation of the virtual synchronous machine, combined with the phase of the virtual synchronous machine. The three-phase voltage of the output converter's internal voltage; S5. Utilizing three-phase voltage and virtual synchronizer phase The internal reference voltage of the converter is modified using the Parker variable output.

2. The control method based on damping optimization of a virtual synchronous generator according to claim 1, characterized in that, S1 includes S11, which calculates the virtual synchronizer phase using the angular frequency of the Parker variation. ; S12, Utilizing the phase of a virtual synchronizer Together with the sampled voltage and current signals, the Parker converter outputs the internal voltage and current of the converter. The coordinate components are used to obtain the first active power output of the VSG. and reactive power .

3. A control method based on damping optimization of a virtual synchronous generator according to claim 1 or 2, characterized in that, S2 includes S21, which uses a virtual synchronous machine to simulate the rotor rocking equation to output the angular frequency of the Parker transform. ; S22, Utilizing angular frequency The second active power is obtained by using the droop control equation, given the system's rated angular frequency and the given active power. ; S23, Utilizing the second active power and first active power The difference is used as the input of the power system stabilizer to obtain the PSS compensation power through the signal of the PI controller. .

4. The control method based on damping optimization of a virtual synchronous generator according to claim 3, characterized in that, The angular frequency of the Parker transform is generated by simulating the following rotor rocking equation. ； in, Where P is the electromagnetic power, J is the actual active power, and D is the virtual inertia. ω is the rated angular frequency, δ is the electrical angular frequency, and δ is the VSG power angle.

5. The control method based on damping optimization of a virtual synchronous generator according to claim 4, characterized in that, The second active power is obtained from the given system rated angular frequency and the given active power. The following droop control equation is derived. ； in, Where is the active power-frequency droop factor, E is the internal electromotive force, U is the peak grid-side voltage, and X is the synchronization reactance. This is the given value for active power.

6. The control method based on damping optimization of a virtual synchronous generator according to claim 4, characterized in that, The first active power P and reactive power Q are obtained from the internal voltage and current of the converter and are calculated using the following equations. ； The internal electromotive force of the VSG is represented by E; U N X is the rated voltage of the power grid; X is the synchronous reactance.

7. The control method based on damping optimization of a virtual synchronous generator according to claim 5, characterized in that, Through the PI controller Follow the accurate value As input to the PSS controller, it generates PSS compensation power to compensate for the damping power caused by the damping coefficient. .

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