Self-synchronizing voltage source control method based on damping and droop coefficient independent adjustment

Abstract

The invention discloses a self-synchronizing voltage source control method based on damping and droop coefficient independent adjustment, and belongs to the field of new energy power generation. The control method comprises the steps that an active-frequency droop coefficient m and a virtual damping coefficient D are designed, so that the steady-state active power is only determined by m, and independent adjustment of m and D is achieved; and generating a terminal voltage amplitude instruction through the reactive power-voltage droop coefficient n, the reactive power deviation delta Q and the output voltage zero-sequence component u0 to realize reactive power-voltage droop control. And the reactive power-voltage droop coefficient n independently adjusts the dynamic response of the reactive power and the voltage amplitude, and does not influence the steady-state characteristic of active power-frequency droop control. Compared with the prior art, only the network side voltage needs to be sampled, the hardware cost is saved, and grid-connected pre-synchronization can be achieved without obtaining the total impedance on the line.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy power generation, in particular to a self-synchronous voltage source control method based on independent adjustment of damping and droop coefficients. BACKGROUND

[0002] Synchronous generators provide inertia for traditional power systems, and the supporting role of inertia is necessary to ensure the safe and stable operation of power systems. The inertia of traditional power systems is the sum of the inertia of all synchronous generators in the system. With the high penetration of distributed power sources with power electronic inverters as interfaces into the grid, the total inertia of the grid system is significantly reduced, making it difficult to ensure stable frequency regulation of the grid when it is subjected to large power fluctuations, and even causing more serious consequences. Various methods have been proposed to solve this problem.

[0003] In recent years, with the increasing penetration of new energy power generation units in power systems, and at the same time, the gradual reduction of traditional centralized primary energy, the rotational inertia of the system is gradually reduced, the frequency fluctuation is larger, and the intermittent nature of primary energy exacerbates the frequency fluctuation of the grid, making the frequency stability problem of the system increasingly serious. And with the increase of the penetration of distributed power grid, its role in the grid will change, and distributed power will no longer just provide power to the grid, but also need to have certain voltage and frequency support capability to stabilize the grid operation. However, the current distributed power based on current source grid-connected control mode does not have voltage support capability, and its stability and dynamic stability performance have great differences when connected to different grid structures, and the grid adaptability is poor.

[0004] (1) Constant power (P / Q) control method can ensure the constant active and reactive power output of the power system, effectively track the reference value and achieve power decoupling. In grid-connected mode, it has strong control response capability and can dynamically adjust the frequency and voltage to make the grid more stable. However, in off-grid mode, it cannot achieve stable output of system voltage and frequency.

[0005] (2) Constant voltage and frequency (V / F) control can keep the frequency and voltage output of the grid-connected inverter stable. When V / F control is used for grid-connected inverter, voltage and current double-loop control technology is mainly used to achieve stable tracking of output voltage. When operating in off-grid mode, it can control the dynamic output of frequency and voltage to achieve grid stability, but when operating in grid-connected mode, it is difficult to achieve effective and safe control of current.

[0006] (3)Droop control simulates the primary frequency and voltage regulation characteristics of synchronous generators, and the working principle is that the inverter power supply detects the size of its own output power, and decouples the active power and reactive power control. According to the droop characteristic, the output frequency and voltage amplitude reference value are obtained, so as to reasonably allocate the active and reactive power of the system. The inverter power supply can realize the adjustment function of voltage amplitude and frequency through droop control, but it lacks inertia and damping, and cannot guarantee the stable output of the grid-connected system frequency and voltage.

[0007] Domestic and foreign scholars have put forward various improvement schemes for the above problems, but the core defects have not been fundamentally solved:

[0008] The invention patent titled "A virtual synchronous machine control parameter optimization method and system for direct-drive wind turbine" (CN111478365B) uses fuzzy control to coordinate the droop coefficient Kf and the damping coefficient D, but because the two are strongly coupled in the transfer function, increasing D will weaken the droop regulation ability, resulting in a power oscillation amplitude of 15%, and the damping-droop coupling problem has not been solved.

[0009] The invention patent titled "Grid-connected inverter transient stability control method and device based on virtual synchronous machine" (CN114552675A) introduces virtual impedance to compensate for circulating current differences, but fixed virtual impedance values lead to output voltage distortion rate > 5% when the load changes dynamically, and the circulating current peak value reaches 22% of the rated current, and the multi-machine parallel circulating current problem has not been solved.

[0010] The invention patent titled "A virtual synchronous machine adaptive control method based on output differential feedback" (CN108418256B) relies on pre-synchronization phase matching, but the phase-locked loop lock loss rate is > 25% in a weak grid, and the phase jump during switching causes an impact current of 2 times the rated value, and the on-off grid switching transient impact problem has not been solved.

[0011] However, the existing VSG technology cannot achieve decoupling control of the damping characteristics and droop characteristics in grid-connected mode, and it is difficult to simultaneously consider the relationship between dynamic response and steady-state current sharing in off-grid parallel mode, and there is a transition process in on-off grid switching. This paper proposes a virtual synchronous machine control method that uses a combination of inverter output frequency and grid frequency feedback control methods to independently adjust the active-frequency droop coefficient and the virtual damping coefficient, achieving decoupling control. SUMMARY

[0012] The technical problem to be solved by the present application is the deficiency of the prior art, and the present application provides a self-synchronous voltage source control method based on independent adjustment of damping and droop coefficients, which can be applied to a distributed new energy power grid, and is characterized in that a combination feedback control method of inverter output frequency and grid frequency is adopted to independently adjust the active-frequency droop coefficient and the virtual damping coefficient, so as to achieve decoupling control and effectively guarantee high-quality power supply of the new energy power generation unit.

[0013] The purpose of the present application is achieved. The present application provides a self-synchronous voltage source control method based on independent adjustment of damping and droop coefficients, and the circuit topology involved in the control method includes a DC power supply, a grid-connected inverter, an LC filter and a three-phase grid; the control method comprises the following steps:

[0014] Step 1, obtaining the bridge arm side inductance current dq axis components i Ld , i Lq , output voltage dq axis components u d , u q and output current dq axis components i d , i q by real-time sampling and coordinate conversion, and calculating output voltage zero sequence components u0 and output current zero sequence components i0;

[0015] Step 2, calculating the active power instantaneous value p and the reactive power instantaneous value q according to the output voltage dq axis components u d , u q and the output current dq axis components i d , i q , then performing smoothing filtering, and calculating the active power deviation ΔP and the reactive power deviation ΔQ;

[0016] Step 3, generating the virtual synchronous machine output angular frequency ω by a power-frequency control equation; integrating the output angular frequency ω to generate the virtual synchronous machine output vector angle θ;

[0017] Step 4, calculating the steady-state active power according to the closed-loop transfer function model of the active power outer loop; by designing the active-frequency droop coefficient m and the virtual damping coefficient D, the steady-state active power is only determined by m, so as to realize independent adjustment of m and D;

[0018] Step 5, converting the reactive power deviation ΔQ into the voltage adjustment amount Δu by the reactive-voltage droop coefficient n; superimposing the voltage adjustment amount Δu and the output voltage zero sequence component u0 to generate the terminal voltage amplitude instruction E*, and realizing reactive-voltage droop control;

[0019] Step 6, sampling the actual output voltage of the grid-connected inverter regulated and controlled above, generating dq-axis modulation voltage command according to the sampling result and terminal voltage amplitude command E* through voltage-current double-loop control, and obtaining three-phase modulation wave signal through coordinate transformation, driving the inverter switching device through SPWM module.

[0020] Preferably, the sampling and coordinate transformation of step 1 include: collecting the inductor current i La at the bridge arm side of the grid-connected inverter in real time Lb , the output voltage u Lc of the grid-connected point a , and the output current i b ; c Then, through coordinate transformation, obtaining the dq-axis components of the inductor current i a at the bridge arm side b , the dq-axis components of the output voltage u c , and the dq-axis components of the output current i Ld ; Lq d q d q ;

[0021] The calculation formula of the output voltage zero sequence component u0 and the output current zero sequence component i0 is:

[0022] Preferably, the implementation process of step 2 is as follows:

[0023] First, calculating the active power instantaneous value p and the reactive power instantaneous value q, the expressions are:

[0024] p = u d × i d + u q × i q

[0025] q = u q × i d - u d × i q

[0026] Secondly, using half power frequency period sliding average filtering to obtain the smoothed active power P e and the smoothed reactive power Q e :

[0027]

[0028] Where T is the sliding window length, τ is the time integral variable, and t is the current time;

[0029] ​​​​The active power deviation ΔP and the reactive power deviation ΔQ are calculated, and the expressions are respectively:

[0030] ΔP = P ref - P e

[0031] ΔQ = Q ref - Q e

[0032] wherein P ref is the active power set value; Q ref is the reactive power reference value generated by using the voltage-reactive power droop characteristic, Q ref = Q0 + K v (u n - u ref ), wherein Q0 is the reactive power reference term, K v is the voltage adjustment coefficient, u n is the rated voltage, and u ref is the voltage rated reference value.

[0033] Preferably, the expression of the power-frequency control equation in step 3 is:

[0034] ΔP = P0 - p = m (ω0 - ω) + D1ω - D2ω g + Jsω

[0035] wherein P0 is the active power reference term, m is the power-frequency droop coefficient, ω is the virtual synchronous machine output angular frequency, ω0 is the rated angular frequency, ω g is the grid angular frequency, D1 is the virtual self-damping coefficient, D2 is the virtual mutual damping coefficient, s is the Laplace operator, and J is the virtual rotational inertia.

[0036] The virtual synchronous machine output angular frequency ω is integrated to generate a virtual synchronous machine output vector angle θ, θ = ∫ω.

[0037] Preferably, the expression of the closed-loop transfer function model of the active power outer loop in step 4 is:

[0038]

[0039] wherein P(s) is the active power closed-loop output, and G(s) is the open-loop transfer function, and the expression is:

[0040]

[0041] wherein K s is the synchronous controller gain, and D is the virtual damping, D = D1 = D2.

[0042] When the system enters steady state, Laplace operator s tends to 0, at this time Jω0ms 2 tends to 0, (1+mD)s tends to 0, at this time the limit value G(0) of the open-loop transfer function when the system enters steady state is obtained, G(0)=1 / m, G(0) is substituted into the closed-loop transfer function model of the active power outer loop to obtain the steady-state active power output P(0), and the expression is:

[0043]

[0044] The power-frequency droop coefficient m is defined as being much greater than 1, that is, 1+(1 / m)≈1, at this time the expression of the steady-state active power output P(0) is rewritten as:

[0045]

[0046] Preferably, the calculation formula of the voltage adjustment amount Δu in step 5 is Δu=n×ΔQ; the terminal voltage amplitude instruction E * is calculated as: E * =u0+Δu.

[0047] Preferably, the dq-axis modulation voltage instruction in step 6 is denoted as u d，ref , u q，ref , and the implementation process is as follows:

[0048] First, the actual output voltage u 0，a , u 0,b , u 0，c of the grid-connected inverter after the above adjustment and control is obtained by sampling, and the dq-axis components u 0,d , u 0，q of the actual output voltage of the grid-connected inverter are obtained through coordinate conversion;

[0049] The dq-axis active control error signal Δu d , Δu q is obtained through the voltage loop control equation, and the expression is:

[0050] Δu d =E * -u 0，d

[0051] Δu q =0-u 0,q

[0052] The dq-axis reference current value I d,ref , I q，ref is generated through the voltage loop PI controller, and the expression is:

[0053]

[0054] wherein, Kp，v K is a proportional coefficient of the voltage loop i，v t is a time variable

[0055] The dq-axis current error Δi is obtained through the current loop control equation d Δi q The expression is:

[0056] Δi d = I d，ref -i Ld

[0057] Δi q = I q，ref -i Lq

[0058] The dq-axis modulation voltage command u is generated through the current loop PI controller and the dynamic decoupling compensation term d，ref u q，ref The expression is:

[0059]

[0060] K is a proportional coefficient of the current loop p，c K is an integral coefficient of the current loop i，c L is the inductance of the LC filter.

[0061] Compared with the prior art, the beneficial effects of the present application are as follows:

[0062] 1. The combined feedback control can realize independent adjustment of the active-frequency droop coefficient and the virtual damping coefficient, achieving decoupling control, effectively solving the problem of coupling of damping and droop characteristics in traditional virtual synchronous generator control, and improving the adaptability and stability of the system.

[0063] 2. Independent adjustment of the droop and damping coefficients can precisely control the steady-state power distribution and optimize the dynamic oscillation suppression capability of the system, ensuring the stability of the grid frequency.

[0064] 3. Independent adjustment of the reactive-power-voltage droop control enhances the active support capability of the distributed power supply to the grid voltage, improving the voltage stability of the system.

[0065] 4. The method only needs local electrical quantity measurement and does not need to rely on complex communication networks, and the control strategy is simple and reliable, easy to implement and suitable for various grid scenarios with high proportion of new energy access. BRIEF DESCRIPTION OF DRAWINGS

[0066] Figure 1 is the control diagram of the independent adjustment stage of m and D in the present application through the closed-loop transfer function model of the active power outer loop

[0067] Figure 2 This is the control diagram for the reactive power-voltage droop control stage in this invention;

[0068] Figure 3 This is the control diagram for the voltage and current dual-loop control stage in this invention;

[0069] Figure 4 This refers to the circuit topology involved in the control method of this invention;

[0070] Figure 5 This is the steady-state simulation waveform diagram of the present invention;

[0071] Figure 6 This is a simulation waveform diagram of load mutation in this invention. Detailed Implementation

[0072] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0073] Figure 4 This is the circuit topology involved in the control method of the present invention. As can be seen from the figure, the circuit topology involved in the control method includes a DC power supply, a grid-connected inverter, an LC filter, a grid-side equivalent impedance, and a three-phase power grid connected in series.

[0074] Depend on Figure 4 As can be seen, a DC-side filter capacitor C is also connected in parallel between the DC power supply and the grid-connected inverter. dc The LC filter includes a bridge arm-side filter inductor L1 and a passive damping resistor R. c And filter capacitor C1. The grid-side equivalent impedance includes the grid-side equivalent resistance R. g Equivalent inductance L on the grid side g .in addition, Figure 4 Middle,U dc For DC power supply, e a ,e b ,e c It is a three-phase power grid.

[0075] In this embodiment, C dc =0.045F, L1=0.3mH, R c =0.001Ω, Ci = 200uF, R g =0.001Ω, L g =1mH,U dc =1500V,

[0076] Figure 1 This is the control diagram of the independent adjustment stage of m and D in this invention, which is achieved through the closed-loop transfer function model of the active power outer loop. Figure 2This is the control diagram for the reactive power-voltage droop control stage in this invention; Figure 3 This is the control diagram for the voltage and current dual-loop control stage in this invention. Figures 1-3 As can be seen, the present invention provides a self-synchronizing voltage source control method based on independent adjustment of damping and droop coefficients, comprising the following steps:

[0077] Step 1: Obtain the dq-axis component i of the inductor current on the bridge arm side through real-time sampling and coordinate transformation. Ld i Lq Output voltage dq-axis component u d ,u q and the dq-axis component of the output current i d i q The zero-sequence component of the output voltage u0 and the zero-sequence component of the output current i0 are calculated.

[0078] In this embodiment, the sampling and coordinate transformation in step 1 includes: real-time acquisition of the inductor current i on the bridge arm side of the grid-connected inverter. La i Lb i Lc Output voltage u at the grid connection point a u b ,u c and output current i a i b i c Then, the dq-axis component i of the inductor current on the bridge arm side is obtained through coordinate transformation. Ld i Lq Output voltage dq-axis component u d u q and the dq-axis component of the output current i d i q ;

[0079] The formulas for calculating the zero-sequence component u0 of the output voltage and the zero-sequence component i0 of the output current are:

[0080] Step 2, based on the dq-axis component u of the output voltage d u q and the dq-axis component of the output current i d i q The instantaneous values ​​of active power p and reactive power q are calculated, then smoothed and filtered, and the active power deviation ΔP and reactive power deviation ΔQ are calculated.

[0081] In this embodiment, the implementation process of step 2 is as follows:

[0082] First, calculate the instantaneous value of active power p and the instantaneous value of reactive power q, expressed as:

[0083] p = u d x i d + u q x i q

[0084] q = u q x i d - u d x i q

[0085] Secondly, the semi-power frequency cycle moving average filter is adopted to obtain the smooth active power P e and the smooth reactive power Q e :

[0086]

[0087] wherein T is the length of the sliding window, τ is the time integral variable, and t is the current time.

[0088] In the embodiment, T = 1 / 50Hz = 0.02s.

[0089] The active power deviation Δp and the reactive power deviation ΔQ are calculated, and the expressions are respectively:

[0090] Δp = P ref - P e

[0091] ΔQ = Q ref - Q e

[0092] In the formula, P ref is the active power set value; Q ref is the reactive reference value generated by using the voltage-reactive droop characteristic, Q ref = Q0 + K v (u n - u ref ), wherein Q0 is the reactive power reference item, K v is the voltage adjustment coefficient, u n is the rated voltage, and u ref is the voltage rated reference value.

[0093] P ref = 500kW, Q ref = 0kVar, and K v = 0.001V / Var.

[0094] Step 3, the virtual synchronous machine output angular frequency ω is generated by the power-frequency control equation; the virtual synchronous machine output vector angle θ is generated by integrating the output angular frequency ω.

[0095] In this embodiment, the expression of the power-frequency control equation described in step 3 is:

[0096] ΔP=P0-p=m(ω0-ω)+D1ω-D2ω g +Jsω

[0097] wherein P0 is the active power reference term, m is the power-frequency droop coefficient, ω is the VSG output angular frequency, ω0 is the rated angular frequency, ω g is the grid angular frequency, D1 is the virtual self-damping coefficient, D2 is the virtual mutual-damping coefficient, s is the Laplace operator, and J is the virtual moment of inertia;

[0098] The virtual synchronous machine output angular frequency ω is integrated to generate the virtual synchronous machine output vector angle θ, θ=∫ω.

[0099] m=0.5rad / W, ω0=314rad / s, D1=2.5, D2=2.0, J=0.0003kg·m 2

[0100] Step 4, according to the closed-loop transfer function model of the active power outer loop, the steady-state active power is calculated; by designing the active-frequency droop coefficient m and the virtual damping coefficient D, the steady-state active power is determined only by m, and independent adjustment of m and D is realized.

[0101] In this embodiment, the expression of the closed-loop transfer function model of the active power outer loop described in step 4 is:

[0102]

[0103] wherein P(s) is the active power closed-loop output, and G(s) is the open-loop transfer function, and the expression thereof is:

[0104]

[0105] In the formula, K s is the synchronous controller gain, D is the virtual damping, and D=D1=D2;

[0106] When the system enters the steady state, the Laplace operator s tends to 0, at this time Jω0ms 2 tends to 0, and (1+mD)s tends to 0, at this time the limit value of the open-loop transfer function when the system enters the steady state G(0) is obtained, G(0)=1 / m, and G(0) is substituted into the closed-loop transfer function model of the active power outer loop to obtain the steady-state active power output P(0), and the expression is:

[0107]

[0108] The power-frequency droop coefficient m is defined to be much greater than 1, i.e. 1+(1 / m)≈1, and the expression of the steady-state active power output P(0) is rewritten as:

[0109]

[0110] Step 5: The reactive power deviation ΔQ=Q0-Q is converted into a voltage adjustment amount Δu by the reactive power-voltage droop coefficient n; Q is the output reactive power; the voltage adjustment amount Δu is superimposed with the output voltage zero sequence component u0 to generate the terminal voltage amplitude instruction E*, and the reactive power-voltage droop control is realized.

[0111] In the embodiment, the calculation formula of the voltage adjustment amount Δu is Δu=n×ΔQ, and the calculation formula of the terminal voltage amplitude instruction E* is E*=u0+Δu.

[0112] It should be noted that the reactive power-voltage droop coefficient n independently adjusts the dynamic response of the reactive power and the voltage amplitude, and does not affect the steady-state characteristics of the active power-frequency droop control.

[0113] n=0.001 V / Var, u0=565 V

[0114] Step 6: The actual output voltage of the grid-connected inverter after the above adjustment and control is sampled; according to the sampling result and the terminal voltage amplitude instruction E*, the dq-axis modulation voltage instruction is generated through the voltage-current double-loop control, and the three-phase modulation wave signal is obtained through coordinate transformation, and the inverter switching device is driven through the SPWM module.

[0115] In the embodiment, the dq-axis modulation voltage instruction is denoted as u d，ref , u q，ref , and the implementation process is as follows:

[0116] First, the actual output voltage u 0,a , u 0，b , u 0，c of the grid-connected inverter after the above adjustment and control is obtained through sampling, and the dq-axis components u 0，d , u 0,q of the grid-connected inverter actual output voltage are obtained through coordinate conversion;

[0117] The dq-axis active control error signals Δu d , Δu q are obtained through the voltage loop control equation, and the expression is:

[0118] Δu d =E*-u 0,d

[0119] Δu q =0-u 0，q

[0120] The dq-axis reference current value I is generated by a voltage loop PI controller d，ref , I q，ref , and the expression is:

[0121]

[0122] Wherein, K p，v is a voltage loop proportional coefficient, K i，v is a voltage loop integral coefficient, and t is a time variable;

[0123] The dq-axis current error Δi is obtained by a current loop control equation d , Δi q , and the expression is:

[0124] Δi d = I d，ref -i Ld

[0125] Δi q = I q，ref -i Lq

[0126] The dq-axis modulation voltage command u is generated by a current loop PI controller and a dynamic decoupling compensation term d，ref , u q，ref , and the expression is:

[0127]

[0128] Wherein, K p，c is a current loop proportional coefficient, K i，c is a current loop integral coefficient, and L is the inductance of the filter inductor in the LC filter.

[0129] In the embodiment, K p，v = 10, K i,v = 100, K p，c = 0.01, and K i，c = 0.133.

[0130] In order to verify the beneficial effects of the present application, simulation is performed. Figure 5 is a steady-state simulation waveform of the present application, the DC side voltage U dc = 1500V, and the inverter side output three-phase voltage is The output active power is P(0) = 500kW, and the frequency is ω0 = 314.14 rad / s.

[0131] Figure 6is the load mutation simulation waveform of the application, the output power is P(0) = 500kW in the steady state, the load is mutated to 700kW at 2s, at this time the output three-phase voltage is The output active power is P(1) = 700kW, the frequency is ω1 = 313.95 rad / s, and the frequency is reduced by 0.19 rad / s compared with the steady state frequency.

Claims

1. A self-synchronous voltage source control method based on independent adjustment of damping and droop coefficients, the circuit topology involved in the control method comprising a DC power source, a grid-connected inverter, an LC filter and a three-phase power grid; characterized in that, The control method comprises the following steps: Step 1, obtain the dq-axis components i of the inductor current on the bridge arm side by real-time sampling and coordinate transformation Ld , Lq , d , q , d , q , and calculate the zero-sequence components u0 of the output voltage and i0 of the output current; Step 2, according to the output voltage dq axis component u d , u q and the output current dq axis component i d , i q , the active power instantaneous value p and the reactive power instantaneous value q are calculated, then the smoothing filter is carried out, and the active power deviation ΔP and the reactive power deviation ΔQ are calculated; Step 3, generating the virtual synchronous machine output angular frequency ω by a power-frequency control equation; and integrating the output angular frequency ω to generate a virtual synchronous machine output vector angle θ; Step 4, calculating the steady-state active power according to a closed-loop transfer function model of an active power outer loop; and by designing an active-frequency droop coefficient m and a virtual damping coefficient D, making the steady-state active power only determined by m, and realizing independent adjustment of m and D; Step 5, convert reactive power deviation AQ to voltage adjustment amount Du by reactive-voltage droop coefficient n; superimpose voltage adjustment amount Du and output voltage zero sequence component u0 to generate terminal voltage amplitude instruction E * , realize reactive-voltage droop control; Step 6, the grid-connected inverter actual output voltage after the above adjustment and control is sampled, and according to the sampling result and the terminal voltage amplitude instruction E * , the dq-axis modulation voltage instruction is generated through the voltage-current double-loop control, and the three-phase modulation wave signal is obtained through the coordinate transformation, and the inverter switching device is driven through the SPWM module.

2. The self-synchronous voltage source control method based on independent adjustment of damping and droop coefficients according to claim 1, characterized in that, The sampling and coordinate transformation in step 1 include: real-time acquisition of grid-connected inverter bridge arm side inductor current i La , i Lb , i Lc , output voltage u a , u b , u c and output current i a , i b , i c Then, through coordinate transformation, the bridge arm side inductor current dq axis component i Ld , i Lq , output voltage dq axis component u d , u q and output current dq axis component i d , i q ; The calculation formula of the output voltage zero sequence component u0 and the output current zero sequence component i0 is:

3. The self-synchronized voltage source control method based on independent adjustment of damping and droop coefficients according to claim 1, characterized in that, The implementation process of the step 2 is as follows: First, calculating an active power instantaneous value p and a reactive power instantaneous value q, and the expressions are as follows: p = u d x i d + u q x i q q = u q x i d - u d x i q Secondly, the semi-power frequency cycle moving average filter is adopted to obtain the smooth active power P e and the smooth reactive power Q e : Wherein, T is a sliding window length, τ is a time integral variable, and t is a current time; Calculating an active power deviation ΔP and a reactive power deviation ΔQ, and the expressions are as follows: ΔP = P ref - P e ΔQ = Q ref - Q e where P ref is the active power setpoint; Q ref is the reactive power reference generated with the voltage-reactive power droop characteristic, Q ref = Q0+ Kv v (u n - u ref ), where Q0is the reactive power base term, Kv is the voltage droop coefficient, u n is the nominal voltage, and u ref is the voltage nominal reference.

4. The self-synchronized voltage source control method based on independent adjustment of damping and droop coefficients according to claim 1, characterized in that, The expression of the power-frequency control equation in the step 3 is as follows: ΔP = P0- p = m(ω0- ω) + D1ω - D2ω g + Jsω where P0 is the active power reference term, m is the power-frequency droop coefficient, ω is the VSM output angular frequency, ω0 is the rated angular frequency, ω g is the grid angular frequency, D1 is the virtual self-damping coefficient, D2 is the virtual mutual-damping coefficient, s is the Laplace operator, and J is the virtual moment of inertia. Integrating the virtual synchronous machine output angular frequency ω to generate a virtual synchronous machine output vector angle θ, θ = ∫ ω.

5. The self-synchronized voltage source control method based on independent adjustment of damping and droop coefficients according to claim 4, characterized in that, The expression of the closed-loop transfer function model of the active power outer loop in the step 4 is as follows: Wherein, P(s) is an active power closed-loop output, and G(s) is an open-loop transfer function, and the expression is as follows: In the formula, K s is the gain of the synchronization controller, and D is the virtual damping, D = D1 = D2. When the system enters steady state, Laplace operator s tends to 0, at this time Jω0ms 2 Tends to 0, (1+mD)s tends to 0, at this time the limit value G(0) of open loop transfer function when the system enters steady state is obtained, G(0)=1 / m, G(0) is substituted into the closed loop transfer function model of active power outer loop, and steady state active power output P(0) is obtained, and the expression is: Defining that the power-frequency droop coefficient m is much greater than 1, that is, 1 + (1 / m) ≈ 1, and at this time, the expression of the steady-state active power output P(0) is rewritten as:

6. The self-synchronized voltage source control method based on independent adjustment of damping and droop coefficients according to claim 1, characterized in that, The calculation formula of the voltage adjustment amount Δu described in Step 5 is Δu = n x ΔQ; and the calculation formula of the terminal voltage amplitude command E is E = u0+ Δu. * The calculation formula of the terminal voltage amplitude command E is E = u0+ Δu.

7. The self-synchronized voltage source control method based on independent adjustment of damping and droop coefficients according to claim 6, characterized in that, The dq-axis modulation voltage command described in Step 6 is denoted as u d，ref , u q，ref , is implemented as follows: Firstly, the actual output voltage u of the grid-connected inverter after the above adjustment and control is obtained by sampling 0,a , u 0,b , u 0,c , and the dq-axis components u of the actual output voltage of the grid-connected inverter are obtained through coordinate conversion 0，d , u 0，q ; The dq-axis active control error signal Δu is obtained by the voltage loop control equation d , Δu q , and the expression is: Δu d = E * - u 0,d Δu q = 0 - u 0,q The dq-axis reference current values I are generated by a voltage loop PI controller d，ref , I q，ref , the expression is: I d，ref = K p，v Δu d + K i，v ∫Δu d dt I q，ref = K p,v Δu q + K i，v ∫Δu q dt where K p，v is the voltage loop proportional coefficient, K i，v is the voltage loop integral coefficient, and t is the time variable. The dq-axis current error Δi is obtained by the current loop control equation d , Δi q , and the expression is: Δi d = I d，ref - i Ld Δi q = I q，ref - i Lq The dq-axis modulation voltage instruction u is generated by a current loop PI controller and a dynamic decoupling compensation term d，ref , u q，ref , The expression is: u d，ref = K p，c Δi d + K i，c ∫Δi d dt - ωLi Lq + u 0，d u q，ref = K p，c Δi q + K i，c ∫Δi q d t - ωLi Ld where K p，c is the current loop proportional coefficient, K i，c is the current loop integral coefficient, and L is the inductance of the filter inductor in the LC filter.

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