Droop control and stability analysis method of grid-connected inverter based on differential passivity

Abstract

The present invention discloses a droop control and stability analysis method of a grid-type inverter based on differential passivity, and belongs to the field of electrical engineering. Under the background of high-penetration new energy, the present invention proposes a droop control and stability analysis method of a grid-type inverter based on differential passivity, aiming at the characteristics of strong dynamic characteristics and poor stability of new energy power generation systems. The droop control method increases the input power differential on the basis of traditional droop control, so that it has input differential passivity, and then verifies the stability of the inverter system through the Lyapunov stability criterion, and maintains the stability of the inverter system by modifying the parameters. The present invention is not only simple to implement, but also solves the problems of insufficient dynamic performance and strong conservatism under traditional passive control of the inverter. At the same time, it proposes a controller design method based on input differential passivity and a method for analyzing the stability of the inverter from the inverter equipment itself, which effectively improves the dynamic characteristics of the system.

Description

Technical Field

[0001] The invention belongs to the field of electrical engineering and relates to a differential passive-based grid-type inverter droop control and stability analysis method. Background Art

[0002] In the context of high penetration of new energy, a large number of distributed devices with power electronic converters as interfaces are continuously connected to the power system. Due to the intermittent and random nature of new energy generation and output fluctuations, the power system often presents weak grid characteristics, which has a negative impact on system stability. Therefore, the research on stable control of new energy grid-connected converters has received more and more attention.

[0003] The article entitled "Research on Impedance Adaptive Dual-Mode Control of Grid-connected Inverters for High Penetration Renewable Energy Generation" (Li Ming. Research on Impedance Adaptive Dual-Mode Control of Grid-connected Inverters for High Penetration Renewable Energy Generation [D]. Hefei University of Technology, 2020.) introduces the characteristics of inverter control in different modes under weak power grids. Among them, traditional grid-connected inverters usually adopt current control and are connected to the grid through a phase-locked loop, becoming a grid-following grid-connected mode. However, the grid impedance often fluctuates greatly under weak power grids, resulting in a decrease in the stability margin of traditional grid-following inverters or even instability. Compared with traditional current source mode grid-connected inverters, grid-connected modes based on droop or virtual synchronous generator control can operate stably under weak power grids.

[0004] In addition, grid-connected inverters in renewable energy systems such as wind power and photovoltaic power are often affected by factors such as failures, maintenance and expansion, and the inverters are randomly switched on and off and plug-and-play. At this time, the structure and parameters of the equivalent power grid seen at the grid-connected point of the grid-connected inverter show nonlinear changes. Moreover, as the penetration rate of new energy increases, the nonlinear dynamic characteristics will become more and more complex, and the stability and safety of the system will be severely challenged.

[0005] In response to high grid impedance and nonlinear grid structure / parameter changes, some scholars have proposed passive control based on nonlinear control theory. The key feature of the passivity theory is that the new system obtained by interconnecting multiple passive subsystems will remain passive and stable. Therefore, due to this natural characteristic, passive control is particularly suitable for the expansion of a single machine to a multi-machine system, thereby effectively coping with the plug-and-play of inverters. In particular, the differential passivity theory developed on the basis of traditional input and output passivity will further improve the dynamic performance and control conservatism of the system, and has been studied in some ways, such as:

[0006] 1) The paper entitled “Power shaping: A new paradigm for stabilization of nonlinear RLC circuits” (R. Ortega, D. Jeltsema and JM A Scherpen, Power shaping: a new paradigm for stabilization of nonlinear RLC circuits[J], in IEEE Transactions on Automatic Control, vol. 48, no. 10, pp. 1762-1767, Oct. 2003.) proposes a control method based on power shaping passiveness for RLC circuits by performing differential operations at the system ports, which has a better dynamic process.

[0007] 2) Titled "Distributed Stability Conditions for Power Systems With Heterogeneous Nonlinear Bus Dynamics" (P. Yang, F. Liu, Z. Wang and C. Shen, Distributed Stability Conditions for Power Systems With Heterogeneous Nonlinear Bus Dynamics [J], in IEEE Transactions on Power Systems, vol. 35, no. 3, pp. 2313-2324, May 2020.) By adding differentials at the output port, the stable operation of the heterogeneous renewable energy power generation system based on output differential passive is also obtained. However, it is considered from the system perspective and then the stability parameter conditions of the controller are obtained.

[0008] In summary, the prior art has the following problems:

[0009] (1) The inverter passive control mentioned in the existing literature is based on traditional passive control, which has average dynamic performance and is highly conservative;

[0010] (2) The existing literature does not involve the design of a differential passive controller and its stability analysis method for scenarios with high grid impedance and nonlinear grid changes, starting from the grid-connected inverter equipment itself. Summary of the invention

[0011] The technical problem to be solved by the present invention is: the problem of insufficient dynamic performance and strong conservatism of traditional passive control of inverters, and a method for analyzing the stability of inverters is proposed.

[0012] The object of the present invention is achieved in this way. The present invention provides a differential passive grid-type inverter droop control method, wherein the inverter involved in the droop control strategy includes a DC source, a three-phase inverter bridge, and an LCL filter connected in series in sequence, and the LCL filter includes a bridge arm side inductor, a filter capacitor, and a grid side inductor;

[0013] The steps of the droop control method are as follows:

[0014] Step 1.1, establish the inverter grid-type droop control model with power differential term and record it as the control model, and its expression is:

[0015]

[0016] Among them, P is the instantaneous value of the inverter output active power, Q is the instantaneous value of the inverter output reactive power, P * The reference value of the inverter output active power is given, Q * Give a reference value for the inverter output reactive power, is the differential of the instantaneous value P of the inverter output active power, is the differential of the instantaneous value Q of the inverter output reactive power, ω is the instantaneous value of the inverter output voltage frequency, ω * is the reference value of the inverter output voltage frequency, V is the instantaneous value of the inverter output voltage amplitude, V * is the given reference value of the inverter output voltage amplitude, m is the active power loop droop coefficient, n is the reactive power loop droop coefficient, δ1 is the coefficient of the power loop input active power differential term, and δ2 is the coefficient of the power loop input reactive power differential term;

[0017] Step 1.2, according to the control model established in step 1.1, a differential passive grid-connected inverter droop control method is given;

[0018] Sampling bridge arm side current i L 、Filter capacitor voltage uo , grid-side current i o ;

[0019] According to the bridge arm current i obtained by sampling L And the filter capacitor voltage u o , after instantaneous power calculation and power filtering, we get active power P and reactive power Q, the calculation formulas are:

[0020]

[0021] Among them, V d is the d-axis component of the inverter output voltage, V q is the q-axis component of the inverter output voltage, I d is the d-axis component of the inverter output current, I q is the q-axis component of the inverter output current, s is the Laplace operator, ω c is the filter cutoff frequency;

[0022] According to the control model in step 1.1, the instantaneous value of the inverter output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V are obtained, and their calculation formulas are as follows:

[0023]

[0024] According to the instantaneous value of the inverter output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V, the SPWM wave is generated through the voltage and current double closed-loop control to control the on and off of each switch tube in the three-phase inverter bridge, so that the inverter emits a voltage corresponding to the instantaneous value of the output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V to achieve the control purpose.

[0025] The present invention also provides a differential passivity-based grid-type inverter droop control stability analysis method, which performs stability judgment on an inverter that adopts the differential passivity-based grid-type inverter droop control method; the inverter controlled by the differential passivity-based inverter grid-type inverter droop control method is recorded as a currently running inverter system, and the steps of the stability analysis method are as follows:

[0026] Step 2.1, determine whether the current inverter system meets the input differential passivity

[0027] Step 2.1.1, according to the control model established in step 1.1, determine the storage function S(x) and supply rate ω(t) of the currently operating inverter system, and their expressions are:

[0028]

[0029]

[0030] Among them, t is any time in the operation of the current inverter system, u is the input variable, is the differential of the input variable, for The transpose of , x is the state variable, y is the output variable, and the expressions of input variable u and output variable y are:

[0031]

[0032] Step 2.1.2, introduce the gradient function corresponding to the storage function S(x) and the Hessian matrix The expressions are:

[0033]

[0034]

[0035] in is the Hamiltonian operator;

[0036] Let x * is the balance point of the current inverter system, x * =(P * , Q * ,ω * , V * ) T , assuming that the current inverter system is operating at the equilibrium point x * At, the Hessian matrix And meet

[0037] Step 2.1.3, record the time derivative of the storage function S(x) as The criterion for the current inverter system to meet the input differential passivity is: Let the equilibrium point x * The external state variable is x′, and the equilibrium point is x * The outer Hessian matrix satisfy At the equilibrium point x * The storage function S(x * ) is a local minimum, and

[0038] When the currently running inverter system does not satisfy the input differential passivity, adjust the parameters in the control model so that the currently running inverter system satisfies the input differential passivity; when the currently running inverter system satisfies the input differential passivity, proceed to step 2.2;

[0039] Step 2.2: Determine whether the current inverter system meets asymptotic stability.

[0040] The Lyapunov function V(x) of the currently running inverter system is introduced as:

[0041]

[0042] The equilibrium point x * The Lyapunov function at is denoted as V(x * ), the differential of the Lyapunov function V(x) is expressed as The criterion for the current inverter system to meet the asymptotic stability is: when V(x * )=0, and x≠x * When V(x)>0, and

[0043] The currently running inverter system does not meet the asymptotic stability. Adjust the parameters in the control model to make the currently running inverter system meet the asymptotic stability. The currently running inverter system meets the asymptotic stability, and this analysis is completed.

[0044] Preferably, the specific operation method of adjusting the parameters in the control model so that the currently running inverter system satisfies the input differential passivity is:

[0045] When the equilibrium point x * The outer Hessian matrix Dissatisfied When the active power loop droop coefficient m and reactive power loop droop coefficient n in the control model are adjusted, the balance point x * The outer Hessian matrix satisfy

[0046] When the equilibrium point x * The outer Hessian matrix At the equilibrium point x * The storage function S(x * ) is a local minimum, but does not satisfy When the input active power differential coefficient δ1 and the input reactive power differential coefficient δ2 in the droop control model are adjusted, Established.

[0047] Preferably, the specific operation method of adjusting the parameters in the control model so that the currently running inverter system meets the asymptotic stability is:

[0048] Adjust the input active power differential coefficient δ1, input reactive power differential coefficient δ2, active power loop droop coefficient m and reactive power loop droop coefficient n in the control model so that when V(x * )=0, and x≠x * When V(x)>0, and

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] 1. The droop control method provided by the present invention is simple to implement, and only needs to add an input power differential term in the droop control link to effectively suppress power oscillation;

[0051] 2. The present invention adopts a grid-type droop control method that satisfies input differential passivity. It is a nonlinear passive control based on power loop design. Different from the traditional linear passive control based on voltage and current double closed-loop design, it can improve the stability under weak power grid and the adaptability to nonlinear changes of power grid, and improve the dynamic performance of grid-connected inverter;

[0052] 3. The stability analysis method adopted by the present invention utilizes the Lyapunov stability criterion to enable the input differential passive method to reduce conservatism while achieving stability;

[0053] 4. The differential passivity proposed in the existing literature is mostly based on the perspective of the power system, usually the grid-connected inverter equipment is equivalent to a node with voltage and phase information, and the use of differential passivity to guide the design of the grid-connected inverter controller is not considered. The innovation of the present invention is that starting from the grid-connected inverter equipment itself, it can realize the differential passive controller design and its stability analysis method under the scenario of high grid impedance and nonlinear grid change. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is an overall control structure diagram of the droop control method of the present invention.

[0055] Figure 2 It is a control block diagram of the power loop in the droop control method of the present invention.

[0056] Figure 3 This is an input-output equivalent structure diagram of a single inverter system of the droop control method described in the present invention.

[0057] Figure 4 This is a schematic diagram of the structure of an inverter three-machine system using the droop control method adopted by the present invention.

[0058] Figure 5 for Figure 4 Each inverter in the system adopts the traditional droop control method, and the active power waveform changes of the three machines under system disturbance are shown.

[0059] Figure 6 for Figure 4 Each inverter in the system adopts the traditional droop control method, and the reactive power waveform changes of the three machines under system disturbance are shown.

[0060] Figure 7for Figure 4 Each inverter in the system adopts the droop control method of the present invention, and the active power waveform changes of the three machines under system disturbance are shown.

[0061] Figure 8 for Figure 4 Each inverter in the system adopts the droop control method of the present invention, and the reactive power waveform change diagram of the three machines under system disturbance. DETAILED DESCRIPTION

[0062] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0063] Figure 1 is the overall control structure diagram of the droop control method of the present invention, Figure 2 is a control block diagram of the power loop in the droop control method of the present invention, Figure 3 This is the input and output equivalent structure diagram of a single inverter system of the droop control method of the present invention. Figure 1 , Figure 2 and Figure 3 It can be seen that the present invention provides a method for controlling inverter grid droop based on differential passivity. The inverter involved in the droop control method includes a DC source, a three-phase inverter bridge, and an LCL filter connected in series in sequence, and the LCL filter includes a bridge arm side inductor, a filter capacitor, and a grid side inductor.

[0064] exist Figure 1 In the figure, L1 is the inductance on the bridge arm side, C is the filter capacitor, L2 is the grid side inductance, PCC is the common coupling point, E is the DC source, and ∑ is the three-phase inverter bridge.

[0065] The steps of the droop control method are as follows:

[0066] Step 1.1, establish the inverter grid-type droop control model with power differential term and record it as the control model, and its expression is:

[0067]

[0068] Among them, P is the instantaneous value of the inverter output active power, Q is the instantaneous value of the inverter output reactive power, P * The reference value of the inverter output active power is given, Q * Give a reference value for the inverter output reactive power, is the differential of the instantaneous value P of the inverter output active power, is the differential of the instantaneous value Q of the inverter output reactive power, ω is the instantaneous value of the inverter output voltage frequency, ω * is the given reference value of the inverter output voltage frequency, V is the instantaneous value of the inverter output voltage amplitude, V *is the given reference value of the inverter output voltage amplitude, m is the active power loop droop coefficient, n is the reactive power loop droop coefficient, δ1 is the coefficient of the power loop input active power differential term, and δ2 is the coefficient of the power loop input reactive power differential term.

[0069] Step 1.2, according to the control model established in step 1.1, a differential passive inverter grid droop control method is given;

[0070] Sampling bridge arm side current i L 、Filter capacitor voltage u o , grid-side current i o ;

[0071] According to the bridge arm current i obtained by sampling L And the filter capacitor voltage u o , after instantaneous power calculation and power filtering, we get active power P and reactive power Q, the calculation formulas are:

[0072]

[0073] Among them, V d is the d-axis component of the inverter output voltage, V q is the q-axis component of the inverter output voltage, I d is the d-axis component of the inverter output current, I q is the q-axis component of the inverter output current, s is the Laplace operator, ω c is the filter cutoff frequency.

[0074] According to the control model in step 1.1, the instantaneous value of the inverter output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V are obtained, and their calculation formulas are as follows:

[0075]

[0076] According to the instantaneous value of the inverter output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V, the SPWM wave is generated through the voltage and current double closed-loop control to control the on and off of each switch tube in the three-phase inverter bridge, so that the inverter emits a voltage corresponding to the instantaneous value of the output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V to achieve the control purpose.

[0077] The present invention also provides a method for analyzing the stability of inverter grid droop control based on differential passivity, and performs stability judgment on an inverter that adopts the inverter grid droop control method based on differential passivity.

[0078] The inverter controlled by the inverter grid droop control method based on differential passivity is recorded as the current operating inverter system, and the steps of the stability analysis method are as follows:

[0079] Step 2.1, determine whether the current inverter system meets the input differential passivity

[0080] Step 2.1.1, according to the control model established in step 1.1, determine the storage function S(x) and supply rate ω(t) of the currently operating inverter system, and their expressions are:

[0081]

[0082]

[0083] Among them, t is any time in the operation of the current inverter system, u is the input variable, is the differential of the input variable, for The transpose of , x is the state variable, y is the output variable, and the expressions of input variable u and output variable y are:

[0084]

[0085] Step 2.1.2, introduce the gradient function corresponding to the storage function S(x) and the Hessian matrix The expressions are:

[0086]

[0087]

[0088] in is the Hamiltonian operator;

[0089] Let x * is the balance point of the current inverter system, x * =(P * , Q * ,ω * , V * ) T , assuming that the current inverter system is operating at the equilibrium point x * At, the Hessian matrix And meet

[0090] Step 2.1.3, record the time derivative of the storage function S(x) as The criterion for the current inverter system to meet the input differential passivity is: Let the equilibrium point x * The external state variable is x′, and the equilibrium point is x * The outer Hessian matrix satisfy At the equilibrium point x * The storage function S(x* ) is a local minimum, and

[0091] When the currently running inverter system does not satisfy the input differential passivity, adjust the parameters in the control model so that the currently running inverter system satisfies the input differential passivity; when the currently running inverter system satisfies the input differential passivity, proceed to step 2.2;

[0092] In this embodiment, the specific operation method of adjusting the parameters in the control model so that the currently running inverter system satisfies the input differential passivity is:

[0093] When the equilibrium point x * The outer Hessian matrix Dissatisfied When the active power loop droop coefficient m and reactive power loop droop coefficient n in the control model are adjusted, the balance point x * The outer Hessian matrix satisfy

[0094] When the equilibrium point x * The outer Hessian matrix Yes, at the equilibrium point x * The storage function S(x * ) is a local minimum, but does not satisfy When the input active power differential coefficient δ1 and the input reactive power differential coefficient δ2 in the droop control model are adjusted, Established.

[0095] Step 2.2: Determine whether the current inverter system meets asymptotic stability.

[0096] Introducing the Lyapunov function of the currently operating inverter system for:

[0097]

[0098] The equilibrium point x * The Lyapunov function at is denoted as V(x * ), the differential of the Lyapunov function V(x) is expressed as The criterion for the current inverter system to meet the asymptotic stability is: when V(x * )=0, and x≠x * When V(x)>0, and

[0099] The currently running inverter system does not meet the asymptotic stability. Adjust the parameters in the control model to make the currently running inverter system meet the asymptotic stability. The currently running inverter system meets the asymptotic stability, and this analysis is completed.

[0100] In this embodiment, the specific operation method of adjusting the parameters in the control model so that the currently running inverter system meets the asymptotic stability is:

[0101] Adjust the input active power differential coefficient δ1, input reactive power differential coefficient δ2, active power loop droop coefficient m and reactive power loop droop coefficient n in the control model so that when V(x * )=0, and x≠x * When V(x)>0, and

[0102] In order to verify the inverter grid droop control method based on differential passivity provided by the present invention, simulation was carried out.

[0103] Figure 4 The schematic diagram of the structure of the inverter 3-machine system of the droop control method of the present invention. As can be seen from the figure, the inverter 3-machine system includes 3 distributed power sources DG connected to the system through the inverter and 6 loads, wherein the first distributed power source is recorded as DG1, the second distributed power source is recorded as DG2, and the third distributed power source is recorded as DG3. The 6 loads are respectively recorded as load 1, load 2, load 3, load 4, load 5 and load 6. Among them, load 6 simulates disturbance and is connected to the system during the operation of the current inverter system to simulate the load mutation condition.

[0104] The relevant electrical parameters for this simulation are set as follows: The active power reference value of DG1 is Active power reference value of DG2 Active power reference value of DG3 The reference value of reactive power of DG1 is The reference value of reactive power of DG2 is The reference value of reactive power of DG3 is Inverter output voltage frequency given reference value ω * =314rad / s, the inverter output voltage amplitude is given by reference value V * =380V, DG1 active power loop droop coefficient m DG1 =1×10 -4 , DG2 active power loop droop coefficient m DG2 =1.5×10 -4 , DG3 active power loop droop coefficient m DG3 =1×10 -4 , DG1 reactive power loop droop coefficient nDG1 =3×10 -4 , DG2 reactive power loop droop coefficient n DG2 =2×10 -4 , DG3 reactive power loop droop coefficient n DG3 =3×10 -4 , the power differential coefficient of DG1 is δ DG1 =2×10 -6 , the power differential coefficient of DG2 is δ DG2 =3×10 -6 , the power differential coefficient of DG3 is δ DG3 =2×10 -6 .

[0105] Figure 5 for Figure 4 Each inverter in the system adopts the traditional droop control method, and the active power waveform of the three machines changes under system disturbance. It can be seen from the figure that at time 2 seconds, load 6 is connected to the system to simulate the disturbance, and the active power waveform has obvious oscillation.

[0106] Figure 6 for Figure 4 Each inverter in the system adopts the traditional droop control method, and the reactive power waveform of the three machines changes under system disturbance. It can be seen from the figure that at time 2 seconds, load 6 is connected to the system to simulate the disturbance, and the reactive power waveform has obvious oscillation.

[0107] Figure 7 for Figure 4 Each inverter in the system adopts the droop control method of the present invention, and the active power waveform change diagram of the three machines under system disturbance. It can be seen from the figure that at time 2 seconds, load 6 is connected to the system to simulate the disturbance, and the active power waveform oscillation under the traditional droop control is effectively suppressed.

[0108] Figure 8 for Figure 4 Each inverter in the system adopts the droop control method of the present invention, and the reactive power waveform change diagram of the three machines under system disturbance. As can be seen from the figure, at time 2 seconds, load 6 is connected to the system to simulate the disturbance, and the reactive power waveform oscillation under the traditional droop control is effectively suppressed.

[0109] In summary, Figure 7 , Figure 8 The simulation waveform shown is consistent with the stability proof result of the present invention, which effectively suppresses the oscillation of active power and reactive power under system disturbance and improves the stability of the system.

Claims

1. A differential passive grid-connected inverter droop control stability analysis method, characterized in that: To determine the stability of the inverter using the differential passive grid-connected inverter droop control method; The inverter involved in the droop control method comprises a DC source, a three-phase inverter bridge, and an LCL filter connected in series in sequence, wherein the LCL filter comprises a bridge arm side inductor, a filter capacitor, and a grid side inductor; The steps of the differential passive grid-type inverter droop control method are as follows: Step 1.1, establish the inverter grid-type droop control model with power differential term and record it as the control model, and its expression is: Among them, P is the instantaneous value of the inverter output active power, Q is the instantaneous value of the inverter output reactive power, P * The reference value of the inverter output active power is given, Q * Give a reference value for the inverter output reactive power, is the differential of the instantaneous value P of the inverter output active power, is the differential of the instantaneous value Q of the inverter output reactive power, ω is the instantaneous value of the inverter output voltage frequency, ω * is the given reference value of the inverter output voltage frequency, V is the instantaneous value of the inverter output voltage amplitude, V * is the given reference value of the inverter output voltage amplitude, m is the active power loop droop coefficient, n is the reactive power loop droop coefficient, δ1 is the coefficient of the power loop input active power differential term, and δ2 is the coefficient of the power loop input reactive power differential term; Step 1.2, according to the control model established in step 1.1, a differential passive grid-connected inverter droop control method is given; Sampling bridge arm side current i L 、Filter capacitor voltage u o , grid-side current i o ; According to the bridge arm current i obtained by sampling L And the filter capacitor voltage u o , after instantaneous power calculation and power filtering, we get active power P and reactive power Q, the calculation formulas are: Among them, V d is the d-axis component of the inverter output voltage, V q is the q-axis component of the inverter output voltage, I d is the d-axis component of the inverter output current, I q is the q-axis component of the inverter output current, s is the Laplace operator, ω c is the filter cutoff frequency; According to the control model in step 1.1, the instantaneous value of the inverter output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V are obtained, and their calculation formulas are as follows: According to the instantaneous value of the inverter output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V, the SPWM wave is generated through the voltage and current double closed-loop control to control the on and off of each switch tube in the three-phase inverter bridge, so that the inverter emits a voltage corresponding to the instantaneous value of the output voltage frequency ω and the instantaneous value of the inverter output voltage amplitude V to achieve the purpose of control; The inverter using the differential passive grid-type inverter droop control method is recorded as the current operating inverter system, and the steps of the stability analysis method are as follows: Step 2.1, determine whether the current inverter system meets the input differential passivity Step 2.1.1, according to the control model established in step 1.1, determine the storage function S(x) and supply rate ω(t) of the currently operating inverter system, and their expressions are: Among them, t is any time in the operation of the current inverter system, u is the input variable, is the differential of the input variable, for The transpose of , x is the state variable, y is the output variable, and the expressions of input variable u and output variable y are: Step 2.1.2, introduce the gradient function ▽S(x) and Hessian matrix ▽ corresponding to the storage function S(x) 2 S(x), whose expressions are: Where ▽ is the Hamiltonian operator; Let x * is the balance point of the current inverter system, x * =(P * ,Q * ,ω * ,V * ) T , assuming that the current inverter system is operating at the equilibrium point x * At, the Hessian matrix ▽ 2 S(x)=▽ 2 S(x * ), and satisfies ▽S(x * )=0; Step 2.1.3, record the time derivative of the storage function S(x) as The criterion for the current inverter system to meet the input differential passivity is: Let the equilibrium point x * The external state variable is x′, and the equilibrium point x * The Hessian matrix outside 2 S(x′) satisfies ▽ 2 When S(x′)>0, at the equilibrium point x * The storage function S(x*) is a local minimum, and When the currently running inverter system does not satisfy the input differential passivity, adjust the parameters in the control model so that the currently running inverter system satisfies the input differential passivity; when the currently running inverter system satisfies the input differential passivity, proceed to step 2.2; Step 2.2: Determine whether the current inverter system meets asymptotic stability. The Lyapunov function V(x) of the currently running inverter system is introduced as: The equilibrium point x * The Lyapunov function at is denoted as V(x * ), the differential of the Lyapunov function V(x) is expressed as The criterion for the current inverter system to meet the asymptotic stability is: when V(x * )=0, and x≠x * When V(x)>0, and The currently running inverter system does not meet the asymptotic stability. Adjust the parameters in the control model to make the currently running inverter system meet the asymptotic stability. The currently running inverter system meets the asymptotic stability, and this analysis is completed.

2. The differential passive grid-connected inverter droop control stability analysis method according to claim 1 is characterized in that: The specific operation method of adjusting the parameters in the control model so that the currently running inverter system meets the input differential passivity is: When the equilibrium point x * The Hessian matrix outside 2 S(x′) does not satisfy ▽ 2 When S(x′)>0, adjust the active power loop droop coefficient m and reactive power loop droop coefficient n in the control model so that the balance point x * The Hessian matrix outside 2 S(x′) satisfies ▽ 2 S(x′)>0; When the equilibrium point x * The Hessian matrix outside 2 When S(x′)>0, at the equilibrium point x * The storage function S(x*) is a local minimum, but does not satisfy When the input active power differential coefficient δ1 and the input reactive power differential coefficient δ2 in the droop control model are adjusted, Established.

3. The differential passive grid-connected inverter droop control stability analysis method according to claim 1, characterized in that: The specific operation method of adjusting the parameters in the control model so that the currently running inverter system meets asymptotic stability is: Adjust the input active power differential coefficient δ1, input reactive power differential coefficient δ2, active power loop droop coefficient m and reactive power loop droop coefficient n in the control model so that when V(x * )=0, and x≠x * When V(x)>0, and

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