Large-signal stability analysis method for micro-grid containing high-capacity hybrid energy storage system

Abstract

The invention discloses a large-signal stability analysis method for a micro-grid containing a high-capacity hybrid energy storage system. The method comprises the following steps: S1, establishing an equivalent circuit of each element in combination with a control strategy of each element in the micro-grid; s2, establishing an equivalent circuit model of the micro-grid and simplifying the equivalent circuit model; s3, based on the simplified equivalent circuit model, establishing a non-linear large-signal model of the micro-grid by applying a mixed potential function; s4, under the condition that control parameters of the energy storage bidirectional DC-DC converter are not considered, stability analysis is carried out on the microgrid; and S5, under the condition of considering the control parameters of the energy storage bidirectional DC-DC converter, carrying out stability analysis on the microgrid. According to the large-signal stability analysis method for the micro-grid containing the high-capacity hybrid energy storage system, parameters related to stability in the micro-grid are disclosed, the asymptotic stability domain of the micro-grid can be calculated, and a theoretical basis is provided for system parameter design.

Description

Technical Field

[0001] The present invention belongs to the technical field of microgrids, and more specifically relates to a large signal stability analysis method for a microgrid containing a large-capacity hybrid energy storage system. Background Art

[0002] Microgrids are composed of energy storage systems, distributed micro-sources, and some AC and DC loads. Most of the loads, distributed micro-sources, and energy storage systems are connected to the DC bus through converters. Since the instantaneous power of the closed-loop controlled DC load is controllable, it can be regarded as a dynamic load. When a disturbance occurs, it introduces positive feedback to the system, amplifies the disturbance signal, and affects the stability of the system. Due to its limited capacity, the microgrid system operating in an island is prone to instability under large disturbance conditions such as micro-source power fluctuations, load mutations, and mode switching. Therefore, it is necessary to ensure the large signal stability of the system. In order to compensate for the intermittent and seasonal characteristics of distributed micro-sources, large-capacity hybrid energy storage systems composed of batteries and supercapacitors are widely used in microgrid systems. Especially when the microgrid is operating in island mode, large-capacity hybrid energy storage has a great impact on the power supply performance of the system and can enhance the stability of the system.

[0003] However, at present, it is still impossible to quantitatively describe how energy storage systems enhance stability and how dynamic loads weaken stability. Therefore, it is necessary to conduct large-signal stability analysis on microgrids containing large-capacity hybrid energy storage systems, derive quantitative criteria, analyze the effects of energy storage systems and constant-power loads on stability, and ensure stable operation of microgrid systems under large disturbance conditions.

[0004] Existing literature on microgrid system stability analysis methods includes two categories: small signal stability analysis methods and large signal stability analysis methods. Among them, the small signal method appeared earlier, using linearization tools to linearize the nonlinear system near the steady-state operating point, and then perform stability analysis, which is relatively simple. However, in the case of large disturbances such as load power steps, working mode switching, and system failures, since the system has deviated from the original steady-state operating point, the small signal stability analysis method can only ensure the stability of the system near the original steady-state operating point, and cannot be applied to large disturbances.

[0005] Commonly used large signal stability analysis methods include Lyapunov method, Takagi-Sugeno fuzzy model research and mixed potential function analysis method (BM). Among them, Lyapunov analysis method is a large signal stability analysis method based on Lyapunov function, which can establish the stability domain of the system. However, since the actual system is often complex, it will face the problem of not being able to obtain the Lyapunov function. The Takagi-Sugeno fuzzy model method can estimate the specific stability domain of the system, but it cannot obtain quantitative stability criteria, and the stability analysis is not intuitive enough. The mixed potential function method proposed by Brayton-Moser is easier to establish a Lyapunov type energy function, apply the stability theorem, and obtain the large signal stability criterion, so it is widely used, but this method cannot obtain the stability domain of the system, and cannot intuitively reflect the role of each parameter on stability. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a large-signal stability analysis method for a microgrid containing a large-capacity hybrid energy storage system, which reveals the parameters related to stability in the microgrid and provides a theoretical basis for system parameter design.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A large signal stability analysis method for a microgrid containing a large capacity hybrid energy storage system, wherein the microgrid includes a DC bus, a large capacity battery group, a super capacitor, a distributed micro source, a resistive load and a constant power load, and the battery and the super capacitor are connected to the DC bus through multiple energy storage bidirectional DC-DC converters. The stability analysis method includes the following steps:

[0009] S1: Establish the equivalent circuit of each component in the microgrid based on the control strategy of each component;

[0010] S2: Establish and simplify the equivalent circuit model of the microgrid;

[0011] S3: Based on the simplified equivalent circuit model, the nonlinear large signal model of the microgrid is established by applying the mixed potential function;

[0012] S4: Perform stability analysis on the microgrid without considering the control parameters of the energy storage bidirectional DC-DC converter;

[0013] S5: Perform stability analysis on the microgrid considering the control parameters of the energy storage bidirectional DC-DC converter.

[0014] Furthermore, in step S1, multiple parallel bidirectional DC-DC converters of the battery pack adopt droop control to share power, and a single bidirectional DC-DC converter adopts double closed-loop control to maintain a constant DC bus voltage, which is equivalent to a voltage source; the supercapacitor adopts double closed-loop control of the reference power difference, which is equivalent to a controlled power source; the converter of the distributed micro source adopts MPPT control and outputs in constant current mode, which is equivalent to a power source; the constant power load is equivalent to a negative power source.

[0015] Further, in step S2, the equivalent circuit model of the microgrid includes a voltage source equivalent to a plurality of batteries and their cascaded bidirectional DC-DC converters, a controlled power source equivalent to a supercapacitor, a DC bus, a plurality of resistive loads, a power source equivalent to a distributed microsource, and a negative power source equivalent to a constant power load; the simplified equivalent circuit model of the microgrid includes a power source obtained by merging a voltage source equivalent to a battery and a DC-DC converter, a controlled power source equivalent to a supercapacitor, a DC bus, a resistive load, a power source equivalent to a distributed microsource, and a power source equivalent to a constant power load, wherein k is the equivalent internal resistance of the battery, and v b is the battery terminal voltage, i b is the battery output current, L is the inductance of the bidirectional DC / DC converter, P CPL is the power source equivalent to the distributed micro-source and the constant power load, R is the resistive load, C dc is the busbar support capacitance, v dc is the voltage of the DC bus.

[0016] Furthermore, in step S3, a nonlinear large signal model of the microgrid is established by applying the mixed potential function theory, including:

[0017] S3.1: Based on the simplified equivalent circuit model, the battery voltage v b The current potential function is

[0018]

[0019] S3.2: The voltage potential function of the supercapacitor is

[0020]

[0021] S3.3: Bus capacitance C dc The energy on can be expressed as

[0022]

[0023] S3.4: The battery voltage v b The current potential function, the voltage potential function of the supercapacitor, and the energy expression on the busbar capacitor are added together to obtain the mixed potential function large signal model of the model:

[0024]

[0025] S3.5: Combined with the unified expression of the mixed potential function: P(i,v) = -A(i) + B(v) + (i,γv-α), where A(i) represents the current potential function; B(v) represents the voltage potential function; (i,γv-α) is related to the circuit structure, and we can get:

[0026] The current potential function is

[0027] The voltage potential function is

[0028] S3.6: Combined with the standard form of the mixed potential function: Among them, i ρ 、v σ are the current variables and voltage variables in the mixed potential function, and the mixed potential function of the model is organized into the standard form of the mixed potential function of the microgrid:

[0029] Further, step S4 includes:

[0030] S4.1: Establish the voltage and current differential equations of the microgrid system and find the steady-state equilibrium operating point of the system;

[0031] S4.2: Without considering the control parameters of the energy storage converter, the third stability theorem of the mixed potential function is applied to obtain the large signal stability criterion of the microgrid;

[0032] S4.3: Establish the Lyapunov function of the microgrid and obtain the variation range of system parameters;

[0033] S4.4: Determine whether the microgrid has an asymptotically stable domain. If so, find the asymptotically stable domain of the microgrid based on the Lassalle invariance principle.

[0034] S4.5: Determine whether the steady-state equilibrium operating point of the system is within the asymptotic stability region.

[0035] Furthermore, step S4.2 includes:

[0036] S4.21: Take the second partial derivative of the current potential function A(i) and the voltage potential function B(v),

[0037] A(ii)=k

[0038]

[0039] Among them, A(ii) is the second-order partial derivative of the current potential function with respect to the current variable, and B(vv) is the second-order partial derivative of the voltage potential function with respect to the voltage variable;

[0040] S4.22: Solving the Matrix L -1 / 2 A ii (i)L -1 / 2 The minimum eigenvalue μ1 and the matrix C -1 / 2 B vv (v)C -1 / 2 The minimum eigenvalue μ2, where L represents the unit matrix of all inductance components in the circuit, and C represents the unit matrix of all capacitance components in the circuit. dc , calculated

[0041]

[0042]

[0043] S4.23: According to the third stability theorem of the mixed potential function, μ1+μ2>0, the stability criterion of the microgrid without considering the control parameters of the energy storage converter is obtained as follows:

[0044] Furthermore, according to the standard form of the hybrid potential function of the microgrid, the values ​​of μ1 and μ2, and the unified expression of the Lyapunov function:

[0045] The Lyapunov function of the microgrid is obtained as: According to the Lyapunov function, the voltage variation range and the current variation range can be obtained; the method for judging whether the microgrid has an asymptotically stable domain is as follows: within the voltage variation range and the current variation range, there is a region where the first-order derivative of the Lyapunov function with respect to time is less than zero and the Lyapunov function is greater than zero, then the microgrid has an asymptotically stable domain; the asymptotically stable domain of the microgrid is obtained according to the Lassalle invariance principle; and it is judged whether the steady-state equilibrium operating point of the system is within the asymptotically stable domain.

[0046] Further, step S5 includes:

[0047] S5.1: Establish the voltage and current differential equations of the microgrid system and find the steady-state equilibrium operating point of the system;

[0048] S5.2: Considering the control parameters of the energy storage converter, the third stability theorem of the mixed potential function is applied to obtain the large signal stability criterion of the microgrid;

[0049] S5.3: Establish the Lyapunov function of the microgrid and obtain the variation range of system parameters;

[0050] S5.4: Determine whether the microgrid has an asymptotically stable domain. If so, find the asymptotically stable domain of the microgrid based on the Lassalle invariance principle.

[0051] S5.5: Determine whether the steady-state equilibrium operating point of the system is within the asymptotic stability region.

[0052] Furthermore, step S5.2 includes:

[0053] S5.21: When considering the control parameters of the energy storage converter, the current potential function A(i) and the voltage potential function B(v) are respectively subjected to secondary partial derivatives. A(ii) is the second-order partial derivative of the current potential function with respect to the current variable, and B(vv) is the second-order partial derivative of the voltage potential function with respect to the voltage variable.

[0054]

[0055]

[0056] Where k is the virtual droop resistance, v dc is the voltage at the DC bus capacitor terminal, P CPL The power difference between the constant power load and the micro source, v b is the battery terminal voltage, i sc is the supercapacitor output current;

[0057] From the double closed-loop control strategy of the battery, we can know

[0058] v b =v dcref +k vp1 (i bref -i)+k vi1 (i bref -i)dt

[0059]

[0060] Among them, k vp1 is the voltage outer loop control parameter of the battery, k vi1 is the current inner loop control parameter of the battery, v dcref Reference value of DC bus capacitor terminal voltage, v b is the battery terminal voltage, i bref is the reference value of the battery current, i is the actual value of the battery current;

[0061] According to the control strategy and power conservation principle of supercapacitor bidirectional DC-DC converter

[0062] i L1 =i scref =k vp2 (P scref -i sc v dc )+k vi2 ∫(P scref -i sc v dc)dt

[0063] i sc v dc =i scl v SC

[0064] Among them, i sc is the high voltage side current of the supercapacitor, i scl is the low voltage side current of the supercapacitor, P scref is the power reference value of the supercapacitor, i scref is the current reference value of the supercapacitor, v SC is the supercapacitor terminal voltage, and i sc v dc Find the partial derivative, and we get

[0065]

[0066] S5.22: Solving the Matrix L -1 / 2 A ii (i)L -1 / 2 The minimum eigenvalue μ1 and the matrix C -1 / 2 B vv (v)C -1 / 2 The minimum eigenvalue μ2,

[0067]

[0068]

[0069] Among them, C dc is the bus capacitance, k is the droop coefficient of the energy storage system, k vp1 is the voltage outer loop control parameter of the battery, k vp2 is the power outer loop control parameter of the supercapacitor, v SC is the supercapacitor terminal voltage, v dc is the voltage at the DC bus capacitor terminal, P CPL is the difference power between the micro source and the constant power load;

[0070] S5.23: According to the third stability theorem of the mixed potential function, μ1+μ2>0, the stability criterion of the microgrid without considering the control parameters of the energy storage converter is:

[0071] Furthermore, according to the standard form of the hybrid potential function of the microgrid, the values ​​of μ1 and μ2, and the unified expression of the Lyapunov function:

[0072] The Lyapunov function of the microgrid is obtained as: According to the Lyapunov function, the voltage variation range and the current variation range can be obtained; the method to determine whether the microgrid has an asymptotically stable domain is: within the voltage variation range and the current variation range, there is a region where the first-order derivative of the Lyapunov function with respect to time is less than zero and the Lyapunov function is greater than zero, then the microgrid has an asymptotically stable domain; the asymptotically stable domain of the microgrid is obtained according to the Lassalle invariance principle, and it is determined whether the steady-state equilibrium operating point of the system is within the asymptotically stable domain.

[0073] Compared with the prior art, the large signal stability analysis method of a microgrid containing a large capacity hybrid energy storage system provided by the present invention first establishes the equivalent circuit of each component in the microgrid in combination with the control strategy of each component; establishes and simplifies the equivalent circuit model of the microgrid. Based on the simplified microgrid equivalent circuit model, a hybrid potential function is applied to establish a nonlinear large signal model of the microgrid; the third stability theorem of the hybrid potential function is applied to the nonlinear large signal model to obtain the large signal stability criterion of the microgrid, revealing the relationship between the system control parameters, filtering parameters, power consumption and power provided.

[0074] After the nonlinear large signal model of the microgrid is established by applying the mixed potential function, it is convenient to establish the Lyapunov function and find the asymptotic stability domain of the microgrid according to the Lassalle invariance principle, which provides an important theoretical basis for the system parameter design. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0076] Figure 1 A flow chart of a large signal stability analysis method for a microgrid including a large capacity hybrid energy storage system provided by the present invention;

[0077] Figure 2 It is the topological structure diagram of microgrid;

[0078] Figure 3 Simplified topology diagram for microgrid;

[0079] Figure 4 This is the control block diagram of the microgrid part;

[0080] Figure 5 This is the control block diagram of the battery converter;

[0081] Figure 6 is the equivalent circuit of the battery converter;

[0082] Figure 7 is the equivalent circuit of supercapacitor converter;

[0083] Figure 8 It is the block diagram of distributed micro-source control;

[0084] Fig. 9is the equivalent circuit of distributed micro-source;

[0085] Fig.10 This is the constant power load control block diagram;

[0086] Fig.11 It is the equivalent circuit of constant power load;

[0087] Fig.12 It is a microgrid model;

[0088] Fig.13 It is a simplified microgrid system model;

[0089] Fig.14 is the three-dimensional surface of the Lyapunov function changing with voltage and current when the energy storage control parameters are not considered;

[0090] Fig.15 is the asymptotic stability region of the microgrid without considering the energy storage control parameters;

[0091] Fig.16 The three-dimensional surface of the Lyapunov function as the voltage and current change when considering the energy storage control parameters;

[0092] Fig.17 is the asymptotic stability region of the microgrid when considering the energy storage control parameters;

[0093] Fig.18 This is the power waveform of the constant power load when the energy storage control parameters are not considered;

[0094] Fig.19 This is the output power waveform of the supercapacitor when the energy storage control parameters are not considered;

[0095] Fig. 20 The DC bus voltage waveform when the energy storage control parameters are not considered;

[0096] Fig.21 The power waveform of the battery pack when the energy storage control parameters are not considered;

[0097] Fig. 22 The power waveform of the constant power load when considering the energy storage control parameters;

[0098] Fig.23 The bus voltage waveform when considering the energy storage control parameters;

[0099] Fig.24 The output power waveform of the battery pack when considering the energy storage control parameters. DETAILED DESCRIPTION

[0100] The present invention is further described below in conjunction with the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0101] Please refer to Figure 1 , Figure 1 The flowchart of the large signal stability analysis method of a microgrid including a large capacity hybrid energy storage system provided by the present invention. The large signal stability analysis method of a microgrid including a large capacity hybrid energy storage system provided by the present invention comprises the following steps:

[0102] S1: Establish the equivalent circuit of each component in the microgrid based on the control strategy of each component;

[0103] S2: Establish and simplify the equivalent circuit model of the microgrid;

[0104] S3: Based on the simplified equivalent circuit model, the nonlinear large signal model of the microgrid is established by applying the mixed potential function;

[0105] S4: Perform stability analysis on the microgrid without considering the control parameters of the energy storage bidirectional DC-DC converter;

[0106] S5: Perform stability analysis on the microgrid considering the control parameters of the energy storage bidirectional DC-DC converter.

[0107] In step S1, an equivalent circuit of each component is established in combination with the control strategy of each component in the microgrid.

[0108] Figure 2 This is a microgrid topology diagram, including DC bus, battery, supercapacitor, wind power generation, photovoltaic power generation, AC load, DC load and power grid. The battery and supercapacitor are connected to the DC bus through a bidirectional DC-DC converter for energy storage. Figure 3 To simplify the topology diagram of the microgrid, the resistors are divided into constant power loads and resistive loads.

[0109] Figure 4This is a partial control block diagram of the microgrid, in which multiple parallel bidirectional DC-DC converters of the battery group use droop control to share power, a single bidirectional DC-DC converter uses dual closed-loop control, and the supercapacitor uses dual closed-loop control with reference to the power difference. In the microgrid system in island mode, the bidirectional DC-DC converter is used as the control unit, and droop control is used to provide voltage support for the bus; the distributed micro-source uses maximum power point tracking control (MPPT) to access the DC bus; the hybrid energy storage unit is connected to the DC bus through a bidirectional DC-DC converter to maintain a constant bus voltage, while the supercapacitor and the battery group are balanced through the converter, and according to the difference between the power emitted by the distributed micro-source and the power consumed by the load, the battery charge and discharge are automatically switched to maintain power balance.

[0110] Multiple parallel bidirectional DC-DC converters in the battery pack use droop control to share power equally, and a single bidirectional DC-DC converter uses dual closed-loop control, i.e., voltage and current dual closed-loop control, to maintain a constant DC bus voltage. The control block diagram is as follows: Figure 5 As shown, it is equivalent to a voltage source, and the equivalent circuit model is as follows Figure 6 As shown. The reference value of DC bus voltage V dc-ref and the actual value V dc For comparison, the PI regulator output is used as the reference value I of the current inner loop bat-ref Among them, when V dc-ref >V dc When V dc-ref <V dc When the energy storage device is charged, the DC bus voltage is reduced. Collect the battery current I bat and reference value I bat-ref After comparison, the PI regulator outputs the modulated wave, which is compared with the triangular carrier to adjust the duty cycle and output the control pulse. In order to make the charging and discharging switching process of the battery energy storage device smoother, the charging and discharging controllers are generally used to run in parallel, and the charging and discharging pulse switching is controlled according to the voltage difference to control the DC / DC converter.

[0111] According to the difference between the power generated by the distributed micro-source and the load power, the hybrid energy storage unit can be automatically switched between charging and discharging. DG , the load power consumption is P load , when P DG >P load When the power of the micro-source is greater than the power required by the load, the remaining power is absorbed by the battery, and the battery is in a charging state to maintain the power balance of the microgrid in the isolated operation. At this time, the power distribution can be expressed as

[0112] P DG -P load =P bat+P sc (1)

[0113] When P DG <P load When the power generated by the distributed micro-source is insufficient to maintain the load demand, the hybrid energy storage unit generates power to supplement it, and the battery is in discharge mode. At this time, the power flow of the system can be expressed as

[0114] P DG +P bat +P sc =P load (2)

[0115] In summary, hybrid energy storage units play a vital role in islanded microgrid systems.

[0116] The hybrid energy storage unit contains a battery and a supercapacitor. The power difference between the micro source and the load is passed through a low-pass filter (LPF), and the power is divided under appropriate filtering time constant conditions. The high-frequency power is used as the given power of the supercapacitor, and the low-frequency part is used as the given power of the battery. The hybrid energy storage system has the characteristics of high energy density of batteries and high power density of supercapacitors, which can greatly improve the working performance and service life of the energy storage system, and is widely used in microgrids.

[0117] Because the supercapacitor balances the high-frequency power, the control method of the power outer loop and the current inner loop is adopted, and the supercapacitor and the cascaded DC-DC converter can be equivalent to a controlled power source. sc The equivalent model is Figure 7 As shown, satisfy

[0118] i sc v dc =i SC v SC =P sc (3) Where i sc is the output current of the converter; v dc is the voltage of the DC bus; i SC is the output current of the supercapacitor; v SC is the terminal voltage of the supercapacitor.

[0119] The converter of the distributed micro-source adopts MPPT control, and its power characteristic is reverse constant power load. The maximum power output of MPPT is output through the controller and converter. cps and v dc ,like Figure 8 As shown. Since it adopts constant current mode output, it can be equivalent to power source P cps , the equivalent model is Fig. 9 As shown, satisfy

[0120] P cps =i cps v dc (4)

[0121] There are a large number of loads in the microgrid, which can be divided into resistive loads and constant power loads. They are all connected to the DC bus through the converter. The resistive load is represented by R; the constant power load is equivalent to a negative power source. The control block diagram is as follows Fig.10 As shown, the equivalent model is Fig.11 As shown in the figure, due to the closed-loop control, when the bus voltage increases, the load input current will decrease instead, and the power will remain constant, showing a constant power characteristic to the outside.

[0122]

[0123] Since both distributed micro-sources and constant power loads can be equivalent to power sources, they are combined into a power source P in the system equivalent model. CPL .

[0124] P CPL =∑P CPS +∑P CPL (6)

[0125] In summary, multiple parallel bidirectional DC-DC converters of the battery pack adopt droop control to share power, and a single bidirectional DC-DC converter adopts dual closed-loop control to maintain a constant DC bus voltage, which is equivalent to a voltage source; the supercapacitor adopts dual closed-loop control of the reference power difference, which is equivalent to a controlled power source; the converter of the distributed micro source adopts MPPT control and outputs in constant current mode, which is equivalent to a power source; the constant power load is equivalent to a negative power source.

[0126] In step S2, an equivalent circuit model of the microgrid is established and simplified.

[0127] Modeling of microgrid systems, such as Fig.12 The equivalent circuit model of the microgrid includes multiple batteries and their cascaded bidirectional DC-DC converter equivalent voltage sources, supercapacitor equivalent controlled power sources, DC bus, multiple resistive loads, distributed micro-source equivalent power sources, and constant power load equivalent power sources.

[0128] Simplifying the graphical model, we can obtain Fig.13 The simplified equivalent circuit model of the microgrid includes a voltage source equivalent to a battery and a DC-DC converter, a controlled power source equivalent to a supercapacitor, a DC bus, a resistive load, a power source equivalent to a distributed micro-source, and a power source equivalent to a constant power load.

[0129]

[0130] Among them, v b is the battery terminal voltage, k is the battery droop control coefficient, and a virtual droop resistor is introduced. b is the battery output current, L is the inductance of the bidirectional DC / DC converter, P CPL The power source equivalent to the distributed micro-source and the constant power load, R is the resistive load, C dc is the busbar support capacitance, v dc is the voltage of the DC bus.

[0131] In step S3, a nonlinear large signal model of the microgrid is established by applying the mixed potential function theory.

[0132] First, the hybrid potential function theory is introduced. The hybrid potential function theory was proposed by RK Rayton and JK Moser in 1964 and is widely used in nonlinear systems containing inductors, capacitors, resistors and negative impedance characteristic elements. The theory constructs a Lyapunov type energy function based on the studied circuit elements and topologies, which is called the hybrid potential function. Compared with other large signal stability analysis methods, the hybrid potential function theory can obtain quantitative stability criteria and is a nonlinear system stability analysis method that is highly compatible with power electronic converters.

[0133] The mixed potential function P is related to the circuit structure and can be uniformly expressed as:

[0134] P(i,v)=-A(i)+B(v)+(i,γv-α) (8)

[0135] Among them, A(i) represents the current potential function; B(v) represents the voltage potential function; (i,γv-α) is related to the circuit structure.

[0136] According to the description of mixed potential function theory, the steps of constructing mixed potential function are summarized as follows:

[0137] Write down the potential functions of non-energy storage components (resistors, power supplies, etc.) in the circuit, and directly list the current potential functions. For those that cannot be directly listed, express them in the form of voltage potential functions;

[0138] Calculate the energy absorbed by the capacitive elements in the system;

[0139] Operate the formulas obtained in step 1) and step 2) and write them in standard form;

[0140] The established mixed potential function can be expressed in the standard form shown in formula (9):

[0141]

[0142] Among them, i ρ 、vσ are the current variable and voltage variable in the mixed potential function.

[0143] Based on the obtained mixed potential function model and the circuit topology studied in this paper, the third stability theorem proposed by Brayton and Moser is applied to perform stability analysis. The theorem first defines:

[0144]

[0145]

[0146] A ii (i) is the second-order partial derivative of the current potential function with respect to the current variable; B vv (v) is the second-order partial derivative of the voltage potential function with respect to the voltage variable; μ1 is the matrix L -1 / 2 A ii (i)L -1 / 2 The minimum eigenvalue of C, where L represents the unit matrix of all inductance components in the circuit; μ2 is C -1 / 2 B vv (v)C -1 / 2 The minimum eigenvalue of , where C represents the identity matrix of all capacitive elements in the circuit. If for all i, v in the circuit:

[0147] μ1+μ2≥δ,δ>0 (13)

[0148] At the same time, when |i|+|v|→∞, equation (14) is satisfied: Then all solutions of the system under study will tend to the equilibrium point, and the system will eventually stabilize.

[0149]

[0150] Then there exists a convergence domain, which makes the system motion trajectory converge asymptotically to the steady-state equilibrium operating point.

[0151] Step S3 includes:

[0152] S3.1: Based on the simplified equivalent circuit model, establish the large signal model of the system, based on the current variable i b 、i sc , voltage variable v b 、v dc , k is the equivalent internal resistance of the battery, R is the resistive load, and the equivalent power source for the supercapacitor is P sc , the constant power load and the micro source are equivalent to the power source P CPL , C dc is the filter capacitor, and the terminal voltage is the bus voltage v dc .

[0153] Write the battery voltage v b The current potential function is

[0154]

[0155] S3.2: The voltage potential function of the supercapacitor is

[0156]

[0157] S3.3: Bus capacitance C dc The energy on can be expressed as

[0158]

[0159] S3.4: Add equations (15) to (17) to obtain:

[0160]

[0161] S3.5: Unified expression combining mixed potential function: P(i,v)=-A(i)+B(v)+(i,γv-α), where A(i)

[0162] represents the current potential function; B(v) represents the voltage potential function; (i,γv-α) is related to the circuit structure, and we can get:

[0163] The current potential function is

[0164]

[0165] The voltage potential function is

[0166]

[0167] S3.6: Combined with the standard form of the mixed potential function: Among them, i ρ 、v σ are the current variables and voltage variables in the mixed potential function, and the mixed potential function of the model is organized into the standard form of the mixed potential function of the microgrid:

[0168] S4: Perform stability analysis on the microgrid without considering the control parameters of the energy storage bidirectional DC-DC converter.

[0169] Step S4 includes:

[0170] S4.1: Establish the voltage and current differential equations of the microgrid system and find the steady-state equilibrium operating point of the system;

[0171] S4.2: Without considering the control parameters of the energy storage converter, the third stability theorem of the mixed potential function is applied to obtain the large signal stability criterion of the microgrid;

[0172] S4.3: Establish the Lyapunov function of the microgrid and obtain the variation range of system parameters;

[0173] S4.4: Determine whether the microgrid has an asymptotically stable domain. If so, find the asymptotically stable domain of the microgrid based on the Lassalle invariance principle.

[0174] S4.5: Determine whether the steady-state equilibrium operating point of the system is within the asymptotic stability region.

[0175] Step S4.2 includes:

[0176] S4.21: When the control parameters of the double closed loop of the livestock battery are not considered, the current potential function A(i) and the voltage potential function B(v) are respectively subjected to secondary partial derivatives, where A(ii) is the second-order partial derivative of the current potential function with respect to the current variable, and B(vv) is the second-order partial derivative of the voltage potential function with respect to the voltage variable.

[0177] A(ii)=k (22)

[0178]

[0179] S4.22: Solving the Matrix L -1 / 2 A ii (i)L -1 / 2 The minimum eigenvalue μ1 and the matrix C -1 / 2 B vv (v)C -1 / 2 The minimum eigenvalue μ2, where L represents the unit matrix of all inductance components in the circuit, and C represents the unit matrix of all capacitance components in the circuit. Figure 8 The equivalent model diagram shown in the figure shows that the system contains an inductor L and a capacitor C. dc , calculated

[0180]

[0181]

[0182] According to the stability theorem, in order to ensure the stability of the system under large disturbances, it is necessary to satisfy

[0183] μ1+μ2>0 (26)

[0184] From this we can get

[0185]

[0186] Equation (27) gives the large signal stability criterion of the microgrid with large-capacity hybrid energy storage. It can be seen from the criterion that the stability of the system is related to the filtering parameters, constant power load power, energy storage power, resistive load internal resistance and droop coefficient.

[0187] According to the standard form of the hybrid potential function of the microgrid, the values ​​of μ1 and μ2, and the unified expression of the Lyapunov function:

[0188] The Lyapunov function of the microgrid is obtained as:

[0189]

[0190] According to formula (28), P * The three-dimensional surface (i,v) changes with voltage and current, such as Fig.14 As shown, the voltage ranges from 0V to 800V, and the current ranges from -150A to 150A.

[0191] The method to determine whether the microgrid has an asymptotically stable domain is: within the voltage variation range and the current variation range, if there is a region where the first-order derivative of the Lyapunov function with respect to time is less than zero and the Lyapunov function is greater than zero, then the microgrid has an asymptotically stable domain.

[0192] According to the Lyapunov function in formula (28), its first-order derivative with respect to time can be obtained as

[0193]

[0194] Deriving equation (18) and its related parameters with respect to time yields

[0195]

[0196] Among them, v b is the battery terminal voltage, v dc is the bus terminal voltage, k is the virtual droop resistance, i is the battery output current, and L is the inductance in the DC / DC bidirectional converter.

[0197] By comparing equation (28) and equation (29), it can be seen that there is an asymptotically stable domain within the range of capacitor voltage and inductor current changes.

[0198] LaSalle's time-invariant principle is a generalization of Lyapunov's second method. For systems that do not depend on time, If f(x) is continuous and V(x) has a first-order continuous partial derivative with respect to x, then both of the following exist: in the region Ω, all V(x) < l (l > 0), that is, V(x) has an upper bound in the region Ω; and in the region Ω,

[0199] Satisfy the area The set of points is called R. M is defined as the largest invariant set contained in R. If the system starts in this region, then as t→∞ the system will converge to a point in the invariant set M.

[0200] According to the LaSalle time-invariant principle, the asymptotic stability domain of the microgrid system is obtained, as follows: Fig.15 As shown in the figure, the current range in the asymptotic stability domain is (-100A, 140A), and the voltage range is (310V, 430V). When a large disturbance occurs, the microgrid system can ensure stable operation in the stable domain.

[0201] The voltage and current differential equations of the microgrid system are established to find the steady-state equilibrium operating point of the system and determine whether the steady-state equilibrium operating point of the system is within the asymptotic stability domain. The voltage and current differential equations of the microgrid system are established as

[0202]

[0203] The steady-state working equilibrium point of the system can be obtained

[0204]

[0205] The power P is the power difference between the micro source and the constant power load and the supercapacitor.

[0206] P=P CPL -P sc (33)

[0207] The steady-state equilibrium operating point obtained by equation (33) is Fig.14 is within the asymptotically stable region shown.

[0208] Step S5: Perform stability analysis on the microgrid while considering the control parameters of the energy storage bidirectional DC-DC converter.

[0209] S5.1: Establish the voltage and current differential equations of the microgrid system and find the steady-state equilibrium operating point of the system;

[0210] S5.2: Considering the control parameters of the energy storage converter, the third stability theorem of the mixed potential function is applied to obtain the large signal stability criterion of the microgrid;

[0211] S5.3: Establish the Lyapunov function of the microgrid and obtain the variation range of system parameters;

[0212] S5.4: Determine whether the microgrid has an asymptotically stable domain. If so, find the asymptotically stable domain of the microgrid based on the Lassalle invariance principle.

[0213] S5.5: Determine whether the steady-state equilibrium operating point of the system is within the asymptotic stability region.

[0214] Furthermore, step S5.2 includes:

[0215] S5.21: When considering the control parameters of the energy storage converter, the current potential function A(i) and the voltage potential function B(v) are respectively subjected to secondary partial derivatives. A(ii) is the second-order partial derivative of the current potential function with respect to the current variable, and B(vv) is the second-order partial derivative of the voltage potential function with respect to the voltage variable.

[0216]

[0217]

[0218] Where k is the virtual droop resistance, v dc is the voltage at the DC bus capacitor terminal, P CPL The power difference between the constant power load and the micro source, v b is the battery terminal voltage, i sc is the supercapacitor output current;

[0219] From the double closed-loop control strategy of the battery, we can know

[0220] v b =v dcref +k vp1 (i bref -i)+k vi1 (i bref -i)dt (36)

[0221]

[0222] Among them, k vp1 is the voltage outer loop control parameter of the battery, k vi1 is the current inner loop control parameter of the battery, v dcref Reference value of DC bus capacitor terminal voltage, v b is the battery terminal voltage, i bref is the reference value of the battery current, i is the actual value of the battery current;

[0223] According to the control strategy and power conservation principle of supercapacitor bidirectional DC-DC converter

[0224] i L1 =i scref =k vp2 (P scref -i sc v dc )+k vi2 ∫(P scref -i sc v dc )dt (38)

[0225] i sc v dc =i scl v SC (39)

[0226] Among them, i sc is the high voltage side current of the supercapacitor, i scl is the low voltage side current of the supercapacitor, P scref is the power reference value of the supercapacitor, i scref is the current reference value of the supercapacitor, v SC is the supercapacitor terminal voltage, and i sc v dc Find the partial derivative, and we get

[0227]

[0228] S5.22: Solving the Matrix L -1 / 2 A ii (i)L -1 / 2 The minimum eigenvalue μ1 and the matrix C -1 / 2 B vv (v)C -1 / 2 The minimum eigenvalue μ2,

[0229] Matrix L -1 / 2 A(ii)L -1 / 2 and C -1 / 2 B(vv)C -1 / 2 They are

[0230]

[0231]

[0232] μ1 is the matrix L -1 / 2 A(ii)L -1 / 2 The minimum eigenvalue of , μ2 is the matrix C -1 / 2 B(vv)C -1 / 2 The minimum eigenvalue of can be calculated based on equations (41) and (42):

[0233]

[0234]

[0235] Among them, C dc is the bus capacitance, k is the droop coefficient of the energy storage system, k vp1 is the voltage outer loop control parameter of the battery, k vp2 is the power outer loop control parameter of the supercapacitor, v SC is the supercapacitor terminal voltage, v dc is the voltage at the DC bus capacitor terminal, PCPL is the difference power between the micro source and the constant power load.

[0236] S5.23: According to Lyapunov’s stability theorem, to ensure the stability of the system under large disturbances,

[0237] μ1+μ2>0 (45)

[0238] Right now

[0239]

[0240] Among them, C dc is the busbar support capacitance, and R is the resistive load value.

[0241] The voltage and current differential equations of the microgrid system are established to find the steady-state equilibrium operating point of the system. According to the standard form of the hybrid potential function of the microgrid, the values ​​of μ1 and μ2, and the unified expression of the Lyapunov function:

[0242] The Lyapunov function of the microgrid is obtained as: According to the Lyapunov function, the voltage variation range and the current variation range can be obtained; the method to determine whether the microgrid has an asymptotically stable domain is: within the voltage variation range and the current variation range, there is a region where the first-order derivative of the Lyapunov function with respect to time is less than zero and the Lyapunov function is greater than zero, then the microgrid has an asymptotically stable domain; the asymptotically stable domain of the microgrid is obtained according to the Lassalle invariance principle, and it is determined whether the steady-state equilibrium operating point of the system is within the asymptotically stable domain.

[0243] Microgrid system P considering the control parameters of energy storage converter * The three-dimensional surface (i, v) changes with the voltage and current variables, such as Fig.16 As shown. Combining the LaSalle time-invariant principle, the asymptotic stability domain of the microgrid system is obtained as follows Fig.17 As shown. Fig.16 It can be seen that the voltage range is between 0V and 800V, and the current range is between -150A and 150A. Fig.17 It can be seen that the steady-state operating point is also included in the asymptotic stability region. In this region, the current range is (-110A, 150A) and the voltage range is (320V, 480V).

[0244] Equations (27) and (46) respectively give the large signal stability criteria of the island mode microgrid system with and without considering the control parameters of the battery energy storage converter. When the system parameters meet the derived quantitative constraints, the system can be guaranteed to operate safely and stably under large disturbance conditions. Under the premise of ensuring the large disturbance stability of the islanded microgrid system, equation (46) is the control parameter k of the hybrid energy storage system converter. vp , droop coefficient k, filter parameter L and voltage stabilizing capacitor parameter C dc It provides an important theoretical basis for the design of

[0245] Experimental verification

[0246] The large signal stability analysis criterion of a microgrid with large-capacity hybrid energy storage is shown in equations (27) and (46). In order to verify the criterion, based on Figure 3 The system structure and control strategy shown in the figure were constructed using Matlab software. Fig.13 The AC-DC hybrid microgrid simulation platform in island mode is shown. The simulation model consists of distributed power supply, battery unit, supercapacitor, bidirectional DC-DC converter, constant power load, and hybrid energy storage system includes 2 groups of batteries and one group of supercapacitor. The following is a large disturbance stability test experiment on the analysis criteria of the microgrid containing large-capacity hybrid energy storage.

[0247] The parameters of the simulation model are shown in Table 1. The large disturbance signal in the simulation process is realized by the power step of the constant power load.

[0248] First, the large signal stability analysis criterion of the microgrid shown in formula (27) is verified. At 0.5s, the power of the constant power load steps from 2kW to 10kW, and at 1s, the power of the constant power load steps from 10kW to 30kW. The parameters are shown in Table 2. At 0.5s, the disturbance parameters meet the large signal stability criterion shown in formula (27), but at 1s, the disturbance parameters do not meet it.

[0249] Table 1 Microgrid system simulation parameters

[0250]

[0251]

[0252] Table 2 Parameters of microgrid system under different disturbance conditions

[0253]

[0254] Figure 18-Figure 21 They are constant power load power, supercapacitor output power, DC bus voltage and battery pack power. Fig.19The steady-state value of the DC bus voltage is 400V. At 0.5s, the constant power load power steps from 2kW to 10kW, and the power step range meets the large signal stability criterion. After the disturbance, the system has a power shortage, the hybrid energy storage system is activated, and the supercapacitor quickly outputs power to smooth high-frequency power fluctuations. As the battery output current gradually increases, the supercapacitor output current gradually returns to near zero. After a short fluctuation, the bus voltage returns to the rated value, and the microgrid system operates stably. At 1s, the constant power load power steps from 2kW to 30kW, and the power step range does not meet the large signal stability criterion. After the power step, the system has a power shortage, the bus voltage oscillates violently, the hybrid energy storage system composed of batteries and supercapacitors cannot work normally, and the microgrid system is difficult to operate stably.

[0255] First, the large signal stability analysis criterion of the microgrid shown in formula (46) is verified. When considering the influence of control parameters, two sets of simulation parameters are designed for comparison, as shown in Table 3. At 0.5s, the power of the constant power load steps from 2kW to 10kW, and at 1s, the power of the constant power load steps from 10kW to 80kW. Among them, at 0.5s, the system control parameters meet the large signal stability criterion shown in formula (46), at 1s, the control parameters do not meet the criterion, and at 1s, the energy storage converter control parameters are switched.

[0256] Table 3 Parameters of two groups of microgrid systems with different control parameters and the same disturbance conditions

[0257]

[0258] The constant power load power, bus voltage and battery output power obtained by simulation are as follows: Fig. 22 —24. As shown in the figure, in the initial stage, when the constant power load power is 2kW, the DC bus voltage is stable at 400V; when the constant power load power steps to 10kW, the DC bus voltage recovers to a stable value after a short fluctuation; but when the constant power load power steps to 80kW, since the power step range does not meet the large signal stability criterion shown in formula (46), the battery discharges, but cannot stabilize the DC bus voltage value, and the bus voltage drops severely to 160V, and the microgrid system cannot operate stably.

[0259] It can be seen from the above specific embodiments that the large signal stability analysis method of a microgrid containing a hybrid energy storage system provided by the present invention can accurately predict the stability of the microgrid.

[0260] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all these other variations or modifications.

Claims

1. A large signal stability analysis method for a microgrid containing a large capacity hybrid energy storage system, wherein the microgrid comprises a DC bus, a large capacity battery pack, a super capacitor, a distributed micro source, a resistive load and a constant power load, and the battery and the super capacitor are connected to the DC bus through a plurality of energy storage bidirectional DC-DC converters, characterized in that: The stability analysis method comprises the following steps: S1: Establish the equivalent circuit of each component in the microgrid based on the control strategy of each component; S2: Establish and simplify the equivalent circuit model of the microgrid; S3: Based on the simplified equivalent circuit model, the nonlinear large signal model of the microgrid is established by applying the mixed potential function; S4: Perform stability analysis on the microgrid without considering the control parameters of the energy storage bidirectional DC-DC converter; S5: Perform stability analysis on the microgrid considering the control parameters of the energy storage bidirectional DC-DC converter.

2. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 1, characterized in that: In step S1, multiple parallel bidirectional DC-DC converters of the battery pack adopt droop control to share power, and a single bidirectional DC-DC converter adopts double closed-loop control to maintain a constant DC bus voltage, which is equivalent to a voltage source; the supercapacitor adopts double closed-loop control of the reference power difference, which is equivalent to a controlled power source; the converter of the distributed micro source adopts MPPT control and outputs in constant current mode, which is equivalent to a power source; the constant power load is equivalent to a negative power source.

3. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 2, characterized in that: In step S2, the equivalent circuit model of the microgrid includes a voltage source equivalent to a plurality of batteries and their cascaded bidirectional DC-DC converters, a controlled power source equivalent to a supercapacitor, a DC bus, a plurality of resistive loads, a power source equivalent to a distributed microsource, and a negative power source equivalent to a constant power load; the simplified equivalent circuit model of the microgrid includes a power source obtained by merging a voltage source equivalent to a battery and a DC-DC converter, a controlled power source equivalent to a supercapacitor, a DC bus, a resistive load, a power source equivalent to a distributed microsource, and a power source equivalent to a constant power load, wherein k is a virtual droop resistor, v b is the battery terminal voltage, i b is the battery output current, L is the inductance of the bidirectional DC / DC converter, P CPL is the power source equivalent to the distributed micro-source and the constant power load, R is the resistive load, C dc is the busbar support capacitance, v dc is the voltage of the DC bus.

4. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 3, characterized in that: In step S3, a nonlinear large signal model of the microgrid is established by applying the mixed potential function theory, including: S3.1: Based on the simplified equivalent circuit model, the battery voltage v b The current potential function is S3.2: The voltage potential function of the supercapacitor is S3.3: Bus capacitance C dc The energy on can be expressed as S3.4: The battery voltage v b The large signal model of the mixed potential function obtained by adding the current potential function, the voltage potential function of the supercapacitor, and the energy expression on the busbar capacitor is: S3.5: Combined with the unified expression of the mixed potential function: P(i,v) = -A(i) + B(v) + (i,γv-α), where A(i) represents the current potential function; B(v) represents the voltage potential function; (i,γv-α) is related to the circuit structure, and we can get: The current potential function is The voltage potential function is S3.6: Combined with the standard form of the mixed potential function: Among them, i ρ 、v σ are the current variables and voltage variables in the mixed potential function, and the mixed potential function of the model is organized into the standard form of the mixed potential function of the microgrid:

5. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 4, characterized in that: Step S4 includes: S4.1: Establish the voltage and current differential equations of the microgrid system and find the steady-state equilibrium operating point of the system; S4.2: Without considering the control parameters of the energy storage converter, the third stability theorem of the mixed potential function is applied to obtain the large signal stability criterion of the microgrid; S4.3: Establish the Lyapunov function of the microgrid and obtain the variation range of system parameters; S4.4: Determine whether the microgrid has an asymptotically stable domain. If so, find the asymptotically stable domain of the microgrid based on the Lassalle invariance principle. S4.5: Determine whether the steady-state equilibrium operating point of the system is within the asymptotic stability region.

6. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 5, characterized in that: Step S4.2 includes: S4.21: Take the second partial derivative of the current potential function A(i) and the voltage potential function B(v), A(ii)=k Among them, A(ii) is the second-order partial derivative of the current potential function with respect to the current variable, and B(vv) is the second-order partial derivative of the voltage potential function with respect to the voltage variable; S4.22: Solving the Matrix L -1 / 2 A ii (i)L -1 / 2 The minimum eigenvalue μ1 and the matrix C -1 / 2 B vv (v)C -1 / 2 The minimum eigenvalue μ2, where L represents the unit matrix of all inductance components in the circuit, and C represents the unit matrix of all capacitance components in the circuit. dc , calculated S4.23: According to the third stability theorem of the mixed potential function, μ1+μ2>0, the stability criterion of the microgrid without considering the control parameters of the energy storage converter is:

7. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 6, characterized in that: According to the standard form of the hybrid potential function of the microgrid, the values ​​of μ1 and μ2, and the unified expression of the Lyapunov function: The Lyapunov function of the microgrid is obtained as: According to the Lyapunov function, the voltage variation range and the current variation range can be obtained; the method for judging whether the microgrid has an asymptotically stable domain is as follows: within the voltage variation range and the current variation range, there is a region where the first-order derivative of the Lyapunov function with respect to time is less than zero and the Lyapunov function is greater than zero, then the microgrid has an asymptotically stable domain; the asymptotically stable domain of the microgrid is obtained according to the Lassalle invariance principle; and it is judged whether the steady-state equilibrium operating point is within the asymptotically stable domain.

8. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 4, characterized in that: Step S5 includes: S5.1: Establish the voltage and current differential equations of the microgrid system and find the steady-state equilibrium operating point of the system; S5.2: Considering the control parameters of the energy storage converter, the third stability theorem of the mixed potential function is applied to obtain the large signal stability criterion of the microgrid; S5.3: Establish the Lyapunov function of the microgrid and obtain the variation range of system parameters; S5.4: Determine whether the microgrid has an asymptotically stable domain. If so, find the asymptotically stable domain of the microgrid based on the Lassalle invariance principle. S5.5: Determine whether the steady-state equilibrium operating point of the system is within the asymptotic stability region.

9. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 8, characterized in that: Step S5.2 includes: S5.21: When considering the control parameters of the energy storage converter, the current potential function A(i) and the voltage potential function B(v) are respectively subjected to secondary partial derivatives. A(ii) is the second-order partial derivative of the current potential function with respect to the current variable, and B(vv) is the second-order partial derivative of the voltage potential function with respect to the voltage variable. Where k is the virtual droop resistance, v dc is the voltage at the DC bus capacitor terminal, P CPL is the power difference between the constant power load and the micro source, v b is the battery terminal voltage, i sc is the supercapacitor output current; From the double closed-loop control strategy of the battery, we can know v b =v dcref +k vp1 (i bref -i)+k vi1 (i bref -i)dt Among them, k vp1 is the voltage outer loop control parameter of the battery, k vi1 is the current inner loop control parameter of the battery, v dcref Reference value of DC bus capacitor terminal voltage, v b is the battery terminal voltage, i bref is the reference value of the battery current, i is the actual value of the battery current; According to the control strategy and power conservation principle of supercapacitor bidirectional DC-DC converter and L1 =i scref =k vp2 (P scref -and sc in dc )+k vi2 ∫(P scref -and sc in dc )dt i sc v dc =i scl v SC Among them, i sc is the high voltage side current of the supercapacitor, i scl is the low voltage side current of the supercapacitor, P scref is the power reference value of the supercapacitor, i scref is the current reference value of the supercapacitor, v SC is the supercapacitor terminal voltage, and i sc v dc Find the partial derivative, and we get S5.22: Solving the Matrix L -1 / 2 A ii (i)L -1 / 2 The minimum eigenvalue μ1 and the matrix C -1 / 2 B vv (v)C -1 / 2 The minimum eigenvalue μ2, Among them, C dc is the bus capacitance, k is the virtual droop resistance (also the droop system of the energy storage system), k vp1 is the voltage outer loop control parameter of the battery, k vp2 is the power outer loop control parameter of the supercapacitor, v SC is the supercapacitor terminal voltage, v dc is the voltage at the DC bus capacitor terminal, P CPL is the difference power between the micro source and the constant power load; S5.23: According to the third stability theorem of the mixed potential function, μ1+μ2>0, the stability criterion of the microgrid without considering the control parameters of the energy storage converter is:

10. A method for analyzing large signal stability of a microgrid containing a large capacity hybrid energy storage system according to claim 9, characterized in that: According to the standard form of the hybrid potential function of the microgrid, the values ​​of μ1 and μ2, and the unified expression of the Lyapunov function: The Lyapunov function of the microgrid is obtained as: According to the Lyapunov function, the voltage variation range and the current variation range can be obtained; the method for judging whether the microgrid has an asymptotically stable domain is as follows: within the voltage variation range and the current variation range, there is a region where the first-order derivative of the Lyapunov function with respect to time is less than zero and the Lyapunov function is greater than zero, then the microgrid has an asymptotically stable domain; the asymptotically stable domain of the microgrid is obtained according to the Lassalle invariance principle; and it is judged whether the steady-state equilibrium operating point of the system is within the asymptotically stable domain.

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