Transient damping control method based on virtual synchronous generator

Abstract

The invention discloses a transient damping control method based on a virtual synchronous generator, and belongs to the field of new energy converter technology control. The method comprises the following steps: firstly, sampling output voltage and current of a converter, and calculating instantaneous active power and reactive power output by a virtual synchronous generator through the sampled voltage and current; then, an output phase instruction value and a voltage control instruction value are obtained through an active outer loop algorithm and a reactive outer loop control algorithm of the virtual synchronous generator with angular frequency feedforward compensation; and finally, a PWM modulation signal is obtained through voltage and current double-closed-loop control, so that the control of the virtual synchronous generator is realized. According to the invention, the angular frequency is set to feed forward after passing through the transient link and the gain link, the overall damping of the system is transiently compensated, the overshoot and oscillation of the system are suppressed on the premise of not losing the steady-state characteristic of the system, and the stability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy converter control, and in particular to a transient damping control method for a virtual synchronous generator. Background Art

[0002] With the rapid development of renewable energy, traditional power systems are gradually shifting towards distributed generation and smart grids. However, with the increase in the penetration rate of new energy generation, the proportion of synchronous generators in the power system has decreased, and the stable operation of the system is facing challenges. In order to enhance the dynamic characteristics and stability of the power grid, domestic and foreign experts have proposed a variety of control strategies based on virtual synchronous generators. These control strategies aim to improve the damping of the system, thereby reducing oscillations and achieving stable operation of the system. When the virtual synchronous generator is connected to the grid, increasing the fixed damping coefficient of the system will suppress the active overshoot and oscillation of the system. However, due to the coupling of the fixed damping coefficient of the system and the droop coefficient of the system, both of which are proportional coefficients of power deviation and frequency deviation, they will jointly affect the steady-state deviation of power in a linear superposition manner. If the fixed damping coefficient of the system is set too large and the system operating frequency deviates from the rated frequency, the steady-state deviation of the steady-state power output of the virtual synchronous generator will increase.

[0003] At present, in order to solve the problem of setting the damping coefficient of virtual synchronous generator, many papers and patents have proposed adaptive damping or damping decoupling solutions, which can obtain suitable parameters through adaptive algorithms or decouple the dynamic characteristics and steady-state characteristics of the system to eliminate the influence of fixed damping coefficient on steady-state characteristics. For example:

[0004] In the "An Improved Parameter Adaptive Method for VSG for Single-Phase Photovoltaic Energy Storage" published on July 25, 2023 in Chinese patent document CN116488211A, the patent selects the virtual moment of inertia and damping coefficient in steady state, and according to the transfer function of the improved parameter adaptive strategy, sets the damping ratio of the VSG system, selects the amplitude margin and phase margin of the VSG system, and obtains the boundary conditions of the damping coefficient. Through the adaptive algorithm, the actual frequency and active power of the VSG system are sampled and calculated, and substituted into the improved parameter adaptive strategy and boundary conditions for judgment to obtain the damping coefficient after adaptation. The problem with this method is that the parameter requirements of the system are relatively complex and the parameter adaptive adjustment range is difficult to define.

[0005] The article entitled "Control Strategy of Virtual Synchronous Generator Based on Bandpass Damped Power Feedback" by Li Mingxuan, Wang Yue, Xu Ningyi, Niu Ruigen, and Lei Wanjun, Transactions of the Chinese Society of Electrotechnical Engineering, Issue 10, 2018, pp. 2176-2185, introduced a high-pass filter in the damping feedback loop to achieve decoupling control between the angular dynamic characteristics and steady-state characteristics of the virtual synchronous generator. However, this method introduces many parameter variables, which increases the difficulty of VSG power-frequency stability analysis. Summary of the invention

[0006] The technical problem to be solved by the present invention is that obvious overshoot and oscillation will occur during the dynamic process of the system, resulting in insufficient system stability. Specifically, the present invention proposes a method for improving system stability based on transient damping control, setting the angular frequency to feed forward after the transient link and the gain link, and the damping of the entire transient compensation system, so as to suppress the overshoot and oscillation of the system without losing the steady-state characteristics, thereby improving the system stability.

[0007] To achieve the above object, the present invention proposes a transient damping control method based on a virtual synchronous generator, comprising the following steps:

[0008] Step 1: Sample the three-phase voltage u at the output side of the virtual synchronous generator converter a ,u b ,u c and three-phase current i a ,i b ,i c , and through coordinate transformation, we can get the voltage dq axis component U d ,U q and the current dq axis component I d ,I q ;

[0009] Step 2: Obtain the voltage control command value E through the reactive power control algorithm ref , the expression of the reactive power control algorithm is:

[0010] E ref =E0+m(Qref-Q)

[0011] Where E0 is the rated output phase voltage amplitude of the virtual synchronous generator, m is the reactive power droop coefficient, Q ref is the reactive power command value, Q is the actual output reactive power of the virtual synchronous generator;

[0012] Step 3: Obtain the output angular frequency instruction ω through the active power control algorithm ref , and then calculate the output phase command value δ ref , δ ref =∫ω ref ;

[0013] Step 4: Get the voltage control command E according to step 2 ref And the output phase command value δ obtained in step 3 ref , perform voltage and current double closed-loop control to generate PWM modulation signal;

[0014] Step 5: Perform triangular carrier modulation on the inverter according to the PWM modulation signal obtained in step 4, and output a converter power switch drive signal.

[0015] Preferably, in step 3, the output angular frequency instruction ω is obtained by the active power control algorithm. ref The process is as follows:

[0016] First, the input power P of the virtual inertia link of the synchronous virtual generator is obtained through the primary frequency modulation formula m , the primary frequency modulation formula is:

[0017] P m =P ref +K f Δω″

[0018] Among them, P ref is the active power command value of the virtual synchronous generator, K f is the primary frequency modulation coefficient, Δω″ is the angular frequency difference of the previous control cycle, Δω″=ω-ω0, ω is the actual output angular frequency of the virtual synchronous generator in the previous control cycle, and ω0 is the rated angular frequency of the virtual synchronous generator;

[0019] Secondly, calculate the instantaneous active power P generated by the virtual synchronous generator e , and its calculation formula is:

[0020] Then, the input power P is obtained through the virtual inertia link of the synchronous virtual generator. m The instantaneous active power P generated by the virtual synchronous generator e Calculate the angular frequency difference Δω of the current control cycle, and the calculation formula is:

[0021]

[0022] Among them, D w is the damping coefficient, J w is the virtual inertia, s is the Laplace operator;

[0023] Finally, the angular frequency difference Δω of the current control cycle is compensated by the lag link and the proportional link to obtain the angular frequency difference Δω′ after transient compensation, thereby obtaining the output angular frequency command ω ref , and their calculation formulas are:

[0024]

[0025] ω ref =Δω′+ω0

[0026] Among them, K c is the compensation coefficient, Tc is the time coefficient of the first-order lag link.

[0027] The transient damping control method based on a virtual synchronous generator disclosed in the present invention has the following beneficial effects compared with the control method based on an adaptive algorithm and the control method based on decoupling of dynamic characteristics and steady-state characteristics:

[0028] 1. This control method realizes the compensation of transient damping by using the transient compensation coefficient of the feedforward angular frequency and the transient time coefficient on the basis of the constant damping voltage controlled virtual synchronous generator. The introduced parameters are relatively few and the response speed is relatively fast.

[0029] 2. When this control method establishes a small signal model, the system can be reduced to a second-order system for analysis through the order reduction method. When designing parameters, the parameter design is simple and the stability margin is large, which has a good ability to improve system stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a control block diagram of the virtual synchronous generator converter of the present invention.

[0031] Figure 2 This is a block diagram of active power optimization of the virtual synchronous generator of the present invention.

[0032] Figure 3 The figure shows the comparison of the actual active power generated by the virtual synchronous generator under the working conditions before and after the optimization of the present invention. DETAILED DESCRIPTION

[0033] The embodiments of the present invention and the prior art are described in detail below with reference to the accompanying drawings.

[0034] Figure 1 The control block diagram of the virtual synchronous generator converter of the present invention is as follows: Figure 1 It can be seen that the DC side of the converter is connected to a new energy DC power source (PV DC) provided by photovoltaic or wind power or energy storage, and the AC side is connected in series with a filter inductor L, a line impedance Z L Then it is connected to the three-phase grid (Gird). Another filter capacitor C is connected to the filter inductor L and the line impedance Z L The other end is grounded.

[0035] Figure 2 This is a flowchart of the virtual synchronous generator active power optimization program of the present invention. Figure 1 and Figure 2 It can be seen that the transient damping control method based on the virtual synchronous generator provided by the present invention comprises the following steps:

[0036] Step 1: Sample the three-phase voltage u at the output side of the virtual synchronous generator converter a ,ub ,u c and three-phase current i a ,i b ,i c , and through coordinate transformation, we can get the voltage dq axis component U d ,U q and the current dq axis component I d ,I q .

[0037] Step 2: Obtain the voltage control command value E through the reactive power control algorithm ref , the expression of the reactive power control algorithm is:

[0038] E ref =E0+m(Qref-Q)

[0039] Where E0 is the rated output phase voltage amplitude of the virtual synchronous generator, m is the reactive power droop coefficient, Q ref is the reactive power command value, and Q is the actual output reactive power of the virtual synchronous generator.

[0040] In this embodiment, E0 = 220V, Q ref =0.

[0041] Step 3: Obtain the output angular frequency instruction ω through the active power control algorithm ref , and then calculate the output phase command value δ ref , δ ref =∫ω ref .

[0042] The output angular frequency instruction ω is obtained by the active power control algorithm ref The process is as follows:

[0043] First, the input power P of the virtual inertia link of the synchronous virtual generator is obtained through the primary frequency modulation formula m , the primary frequency modulation formula is:

[0044] P m =P ref +K f Δω″

[0045] Among them, P ref is the active power command value of the virtual synchronous generator, K f is the primary frequency modulation coefficient, Δω″ is the angular frequency difference of the previous control cycle, Δω″=ω-ω0, ω is the actual output angular frequency of the virtual synchronous generator in the previous control cycle, and ω0 is the rated angular frequency of the virtual synchronous generator;

[0046] Secondly, calculate the instantaneous active power P generated by the virtual synchronous generator e, and its calculation formula is:

[0047] Then, the input power P is obtained through the virtual inertia link of the synchronous virtual generator. m The instantaneous active power P generated by the virtual synchronous generator e Calculate the angular frequency difference Δω of the current control cycle, and the calculation formula is:

[0048]

[0049] Among them, D w is the damping coefficient, J w is the virtual inertia, s is the Laplace operator;

[0050] Finally, the angular frequency difference Δω of the current control cycle is compensated by the lag link and the proportional link to obtain the angular frequency difference Δω′ after transient compensation, thereby obtaining the output angular frequency command ω ref , and their calculation formulas are:

[0051]

[0052] ω ref =Δω′+ω0

[0053] Among them, K c is the compensation coefficient, T c is the time coefficient of the first-order lag link.

[0054] In this embodiment, P ref =20KW, K f =12.7,ω0=314.15,D w =19.1,

[0055] J w =1, K c =800, T c =0.005,ω0=314.15.

[0056] Step 4: Get the voltage control command E according to step 2 ref And the output phase command value δ obtained in step 3 ref , perform voltage and current dual closed-loop control to generate PWM modulation signal.

[0057] Step 5: Perform triangular carrier modulation on the inverter according to the PWM modulation signal obtained in step 4, and output a converter power switch drive signal.

[0058] In order to verify the accuracy of the experiment, a simulation was carried out. Figure 3 Given the active power command value P refAt time t=0, the active power P generated by the virtual synchronous generator increases from 0KW to 20KW. e Changes before and after optimization, all parameters remain constant during simulation. It can be seen that after subtracting from the first-order lag link and compensating with the compensation coefficient, the transient gain of the system is improved and the transient characteristics of the system are enhanced. Since the addition of the optimization link does not affect the constant damping of the system, it will not affect the steady-state error of the system, solving the problem that the system cannot take into account both dynamic characteristics and stability characteristics. As can be seen from the figure, the addition of the transient link significantly improves the damping characteristics of the system and suppresses the overshoot of active power. There is no loss of the steady state of the system, which means that the generation of transient damping will only temporarily increase the damping of the system and will not affect the final steady state, which greatly enhances the dynamic characteristics and stability of the system.

Claims

1. A transient damping control method based on a virtual synchronous generator, characterized in that: The steps include: Step 1: Sample the three-phase voltage u at the output side of the virtual synchronous generator converter a ,u b ,u c and three-phase current i a ,i b ,i c , and the voltage dq axis components U are obtained by coordinate transformation d ,U q and the current dq axis component I d ,I q ; Step 2: Obtain the voltage control command value E through the reactive power control algorithm ref , the expression of the reactive power control algorithm is: E ref =E0+m(Q ref -Q) Where E0 is the rated output phase voltage amplitude of the virtual synchronous generator, m is the reactive power droop coefficient, Q ref is the reactive power command value, Q is the actual output reactive power of the virtual synchronous generator; Step 3: Obtain the output angular frequency instruction ω through the active power control algorithm ref , and then calculate the output phase command value δ ref , δ ref =∫ω ref ; Step 4: Get the voltage control command E according to step 2 ref And the output phase command value δ obtained in step 3 ref , perform voltage and current double closed-loop control to generate PWM modulation signal; Step 5: Perform triangular carrier modulation on the inverter according to the PWM modulation signal obtained in step 4, and output a converter power switch drive signal.

2. The transient damping control method of a virtual synchronous generator according to claim 1, characterized in that: Step 3: The output angular frequency command ω is obtained by the active power control algorithm. ref The process is as follows: First, the input power P of the virtual inertia link of the synchronous virtual generator is obtained through the primary frequency modulation formula m , the primary frequency modulation formula is: P m =P ref +K f Give me Among them, P ref is the active power command value of the virtual synchronous generator, K f is the primary frequency modulation coefficient, Δω″ is the angular frequency difference of the previous control cycle, Δω″=ω-ω0, ω is the actual output angular frequency of the virtual synchronous generator in the previous control cycle, and ω0 is the rated angular frequency of the virtual synchronous generator; Secondly, calculate the instantaneous active power P generated by the virtual synchronous generator e , and its calculation formula is: Then, the input power P is obtained through the virtual inertia link of the synchronous virtual generator. m The instantaneous active power P generated by the virtual synchronous generator e Calculate the angular frequency difference Δω of the current control cycle, and the calculation formula is: Among them, D w is the damping coefficient, J w is the virtual inertia, s is the Laplace operator; Finally, the angular frequency difference Δω of the current control cycle is compensated by the lag link and the proportional link to obtain the angular frequency difference Δω′ after transient compensation, thereby obtaining the output angular frequency command ω ref , and their calculation formulas are: oh ref =Dω′+ω0 Among them, K c is the compensation coefficient, T c is the time coefficient of the first-order lag link.

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