Voltage and frequency stability control method for voltage-type converter of energy storage in microgrid based on coordinated control theory

Abstract

The present application relates to the voltage frequency stability control method of the droop control of the energy storage voltage type converter in the microgrid based on the cooperative control theory, compared with the prior art, the technical deficiency of the output voltage and frequency of the energy storage voltage type converter caused by the load change of the microgrid is solved.The present application comprises the following steps: based on the rated active power and the rated reactive power of the energy storage voltage type converter, the output voltage angle frequency and the voltage amplitude given value of the energy storage voltage type converter, the droop control equation of the energy storage voltage type converter is established; the improved droop control of the fusion of the nonlinear stability controller and the droop control is proposed, the improved droop control equation is established; the nonlinear stability controller is designed; the delay link is designed to monitor the load disturbance of the microgrid; the voltage frequency stability control is realized.The dynamic control performance and the robustness of the energy storage voltage type converter of the droop control are improved at the same time, and the voltage and frequency fluctuation caused by the load change of the microgrid is inhibited.

Description

Technical Field

[0001] This invention relates to the field of power electronic converter control technology, specifically a voltage frequency stabilization control method for energy storage voltage-type converters in microgrids based on cooperative control theory. Background Technology

[0002] With the continuous development of renewable energy utilization technologies, a large number of power electronic converters have been connected to the power system, and control technologies to ensure the stable operation of power electronic converters have attracted research attention. Microgrids (MG) provide an effective means of seamlessly integrating loads, distributed generation units (DG), and energy storage systems (ESS), where DG and ESS are connected to the MG through voltage-source converters (VSC). To ensure that the MG has the characteristics of flexible structure, plug-and-play, and scalable capacity, while reasonably sharing the load among units, droop control is widely used for the control of voltage-source converters in the MG. However, voltage-source converters based on droop control lack inertial support for the microgrid, and load uncertainty may affect the stable operation of the microgrid, especially when the MG is islanded, load changes can cause large fluctuations in the output voltage and frequency of the voltage-source converters.

[0003] To address the aforementioned issues, some scholars have proposed adding feedforward control to the droop control, introducing voltage and frequency fluctuations into the feedforward control to suppress the output voltage and frequency fluctuations of the voltage-source converter caused by changes in microgrid load. However, introducing feedforward control makes the control structure more complex and also affects the steady-state control performance of the voltage-source converter. Other scholars have proposed adding power derivative to the droop control to improve the dynamic control performance of the voltage-source converter. However, when the microgrid load fluctuates significantly, the introduction of power derivative can cause large fluctuations in the output voltage and frequency of the voltage-source converter, and may even cause instability in islanded microgrids.

[0004] Cooperative control theory is the application of synergetics in the field of control, with its core idea being the principle of directed self-organization. The principle of directed self-organization refers to designing a cooperative controller within a system satisfying dissipative structures using cooperative control theory. This controller enables the system's state variables to cooperate with each other, and the system's control objective is achieved through the design of its dynamic evolution process towards equilibrium. Cooperative control theory provides a novel control method for nonlinear systems. Some researchers have combined cooperative control with direct power control to achieve accurate control of grid-injected power by distributed generation units.

[0005] Therefore, it is urgent to solve and make key breakthroughs in the key technologies of combining coordinated control and droop control, and cleverly utilizing the theory of coordinated control to solve the large fluctuations in voltage and frequency of voltage-source converters caused by changes in microgrid load. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies in the large fluctuations in output voltage and frequency of energy storage voltage converters caused by changes in microgrid load, and to provide a technical solution for stable voltage and frequency control of microgrid droop control based on cooperative control theory.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A voltage frequency stabilization control method for droop control of energy storage voltage-source converters in microgrids based on cooperative control theory includes the following steps:

[0009] Based on the rated active power and rated reactive power of the energy storage voltage converter, the output voltage angular frequency and voltage amplitude setpoint of the energy storage voltage converter, the droop control equation of the energy storage voltage converter is established.

[0010] An improved droop control equation is established: An improved droop control is proposed that integrates the designed nonlinear stable controller with droop control, resulting in the improved droop control equation.

[0011] Design a nonlinear stability controller: Taking the stability of the output voltage amplitude and voltage angular frequency of the energy storage voltage converter under load disturbance as the control objective, a nonlinear stabilizer is designed based on the cooperative control theory.

[0012] Design a delay element to monitor load disturbances in the microgrid;

[0013] Voltage and frequency stabilization control: When the load is disturbed, the output power, output voltage amplitude, and voltage angular frequency reference values ​​of the energy storage voltage converter are used as inputs to the nonlinear stabilizer. The compensation values ​​of the output voltage amplitude and voltage angular frequency of the energy storage voltage converter are generated through collaborative control. An improved droop control that integrates the nonlinear stability controller and droop control is proposed to achieve stable control of the voltage frequency of the energy storage voltage converter.

[0014] The steps for establishing the droop control equations for the energy storage voltage source converter are as follows:

[0015] Assuming the line impedance between the energy storage voltage source converter and the point of common coupling is inductive, the active and reactive power outputs of the energy storage voltage source converter in the microgrid are:

[0016]

[0017] Where P and Q are the active power and reactive power output of the energy storage voltage source converter, respectively, and U and U are the reactive power output of the converter. pcc These represent the output voltage amplitude and the point of common coupling voltage amplitude of the energy storage voltage converter, respectively; δ is the phase angle between the output voltage of the energy storage voltage converter and the point of common coupling voltage; X is the line inductance;

[0018] Based on the relationship between the output power, output voltage, and point of common coupling voltage of the energy storage voltage converter, the droop control equation for the energy storage voltage converter under inductive line impedance is established as follows:

[0019]

[0020] Where ω and U are the output voltage angular frequency and voltage amplitude of the energy storage voltage converter, respectively; P0 and Q0 are the rated active power and rated reactive power of the energy storage voltage converter, respectively; ω0 and U0 are the output rated voltage angular frequency and rated voltage amplitude of the energy storage voltage converter, respectively; and m and n are the angular frequency droop coefficient and voltage droop coefficient, respectively.

[0021] The improved droop control equation is established as follows:

[0022]

[0023] Where ω and U are the output voltage angular frequency and voltage amplitude of the energy storage voltage converter, respectively; P and Q are the active power and reactive power output of the energy storage voltage converter, respectively; P0 and Q0 are the rated active power and rated reactive power, respectively; ω0 and U0 are the rated voltage angular frequency and rated voltage amplitude output of the energy storage voltage converter, respectively; m and n are the angular frequency droop coefficient and voltage droop coefficient, respectively; Δω and ΔU are the compensation amounts for the voltage amplitude and voltage angular frequency of the energy storage voltage converter output by the nonlinear stabilizer designed based on cooperative control theory, respectively. c This is the cutoff frequency of the low-pass filter.

[0024] The design of the nonlinear stable controller includes the following steps:

[0025] A nonlinear stabilizer is designed using collaborative control theory, with the macrovariable designed as follows:

[0026]

[0027] In the formula, k1 and k2 are positive parameters, and ω ref U ref P is the reference value for the output voltage angular frequency and voltage amplitude of the energy storage voltage source converter. ref Q refω and U are the reference values ​​for the active and reactive power output of the energy storage voltage converter during stable operation, respectively. ω and U are the angular frequency and voltage amplitude of the output voltage of the energy storage voltage converter, respectively. P and Q are the active and reactive power output of the energy storage voltage converter, respectively.

[0028] The expressions for the reference values ​​of the output voltage angular frequency and voltage amplitude of the energy storage voltage converter are as follows:

[0029]

[0030]

[0031] Where P0 and Q0 are the rated active power and rated reactive power of the energy storage voltage converter, respectively; ω0 and U0 are the rated voltage angular frequency and rated voltage amplitude of the energy storage voltage converter, respectively; m and n are the angular frequency droop coefficient and voltage droop coefficient, respectively; and T... z To delay the time, the output power is compared with the output power of the previous moment through a delay circuit to monitor load disturbances;

[0032] Based on the theory of cooperative control, when the load changes, in order to ensure that the energy storage voltage source converter can converge to the manifold ψ under the action of cooperative control, i =0, the dynamic evolution process is defined as:

[0033]

[0034] Among them, T i These are the design parameters of the nonlinear stabilizer, where k1 and k2 are positive parameters, and (·) is their derivative.

[0035] The compensation values ​​Δω and ΔU for the voltage amplitude and voltage angular frequency of the energy storage voltage-type converter output by the nonlinear stabilizer are obtained:

[0036] Substituting equations (3), (4), (5), and (6) into equation (7), we obtain the compensation amounts Δω and ΔU for the voltage amplitude and voltage angular frequency of the energy storage voltage-type converter output by the nonlinear stabilizer, and we have:

[0037]

[0038] Where Δω and ΔU are the compensation quantities for the voltage amplitude and voltage angular frequency of the energy storage voltage converter output by the nonlinear stabilizer designed based on cooperative control theory, respectively. c This is the cutoff frequency of the low-pass filter; the output of the nonlinear stabilizer is 0 during steady-state operation, which does not affect the steady-state operation of the system; when the delay circuit detects load disturbances in the microgrid, the nonlinear stabilizer outputs compensation for the voltage amplitude and voltage angular frequency of the energy storage voltage converter, suppressing the voltage and frequency fluctuations of the energy storage voltage converter caused by changes in microgrid load;

[0039] To reduce high-order harmonics caused by power measurement, the active and reactive power outputs of the energy storage voltage converter in the input of the nonlinear stabilizer are subjected to low-pass filtering.

[0040] Adaptive k in nonlinear stabilizers i The determination;

[0041] In order to adaptively generate k i Set it to:

[0042]

[0043] a i b i Let ω be a positive parameter, and || be the absolute value. When ω is related to the reference value of the angular frequency of the output voltage of the energy storage voltage-type converter, ω... ref The greater the phase difference, the larger k1 becomes, thus limiting the change in voltage angular frequency;

[0044] When U is related to the reference value U of the output voltage amplitude of its energy storage voltage source converter ref The greater the phase difference, the larger k2 becomes, thus limiting the change in voltage amplitude.

[0045] As ω approaches the reference value of the output voltage angular frequency of the energy storage voltage-type converter, ref The smaller k1 is, the faster the dynamic response speed of the voltage angular frequency;

[0046] As U approaches the reference value U of the output voltage amplitude of the energy storage voltage converter... ref The smaller k2 is, the faster the dynamic response speed of the voltage amplitude.

[0047] Beneficial effects

[0048] The present invention provides a voltage and frequency stabilization control method for energy storage voltage-type converters in microgrids based on cooperative control theory. Compared with the prior art, this method simultaneously improves the dynamic control performance and robustness of energy storage voltage-type converters under droop control, and suppresses voltage and frequency fluctuations caused by changes in microgrid load.

[0049] The present invention has the following advantages:

[0050] 1. A nonlinear stabilizer designed based on the theory of cooperative control, whose inputs are the output voltage angular frequency, voltage amplitude, active power and reactive power of the energy storage voltage converter, allows to be implemented in a distributed manner without the need for any information interaction between distributed units in the microgrid, thereby improving the flexibility and reliability of microgrid operation.

[0051] 2. The proposed microgrid droop control voltage-frequency stability control method based on cooperative control theory not only enables the energy storage voltage converter to have good dynamic and steady-state control performance, but also has strong robustness to microgrid load changes.

[0052] 3. The proposed improved droop control method, which integrates a nonlinear stability controller and droop control, can maintain the stable output voltage frequency of the energy storage voltage converter when the microgrid load changes significantly. It can also adaptively adjust the output voltage frequency of the energy storage voltage converter to quickly recover to a steady state when the microgrid load change weakens or ends. Attached Figure Description

[0053] Figure 1 This is a sequence diagram of the method of the present invention;

[0054] Figure 2 This is a schematic diagram of the control structure of a droop control voltage frequency stabilization control method based on cooperative control theory according to the present invention.

[0055] Figure 3 This is a graph showing the continuous variation of the adaptive coefficients;

[0056] Figure 4 The circuit model diagram is shown below for a droop control voltage frequency stabilization control method based on cooperative control theory according to the present invention.

[0057] Figure 5 A comparison chart of inverter output voltage frequencies when load changes, with and without a stabilizer in droop control.

[0058] Figure 6 The diagram illustrates the output values ​​of a stabilizer when the load changes in droop control.

[0059] Figure 7 A comparison of inverter output voltage frequencies when a three-phase short circuit occurs in droop control with and without a stabilizer.

[0060] Figure 8 A comparison of output voltage and frequency without an adaptive stabilizer in droop control. Detailed Implementation

[0061] To provide a better understanding of the structural features and effects achieved by the present invention, a detailed description is provided below, accompanied by preferred embodiments and accompanying drawings:

[0062] In collaborative control, the design of macro variables determines its control effect, and appropriate control target reference values ​​need to be selected for these macro variables. However, when droop control operates in islanded mode, load changes are unpredictable, leading to inaccurate determination of the control target reference value. In this invention, the power reference value is designed as the output power after a delay element. By monitoring load changes through the delay element, the influence of load disturbances on the inverter's output angular frequency and voltage amplitude can be effectively suppressed.

[0063] like Figure 1 and Figure 2 As shown, the present invention provides a method for stabilizing the voltage frequency of a voltage-source converter for energy storage in a microgrid based on cooperative control theory, comprising the following steps:

[0064] The first step is to establish the droop control equations for the energy storage voltage converter based on its rated active power and rated reactive power, as well as the output voltage angular frequency and voltage amplitude setpoints.

[0065] Establishing the droop control equations for the inverter includes the following steps:

[0066] (1) Assuming the line impedance between the energy storage voltage converter and the point of common coupling is inductive, the active power and reactive power output of the energy storage voltage converter in the microgrid are:

[0067]

[0068] Where P and Q are the active power and reactive power output of the energy storage voltage source converter, respectively, and U and U are the reactive power output of the converter. pcc These represent the output voltage amplitude of the energy storage voltage converter and the voltage amplitude at the point of common coupling, respectively; δ is the phase angle between the output voltage of the energy storage voltage converter and the voltage at the point of common coupling; X is the line inductance.

[0069] The active power output of an energy storage voltage converter is related to the phase angle of the output voltage, while the reactive power output is related to the amplitude of the output voltage. The relationship between the phase angle δ and the angular frequency ω is ω=dδ / dt.

[0070] (2) Based on the relationship between the output power, output voltage, and point of common coupling voltage of the energy storage voltage converter, the droop control equation for the energy storage voltage converter under the condition that the line impedance exhibits inductive characteristics is established as follows:

[0071]

[0072] Where ω and U are the output voltage angular frequency and voltage amplitude of the energy storage voltage converter, respectively; P0 and Q0 are the rated active power and rated reactive power of the energy storage voltage converter, respectively; ω0 and U0 are the output rated voltage angular frequency and rated voltage amplitude of the energy storage voltage converter, respectively; and m and n are the angular frequency droop coefficient and voltage droop coefficient, respectively.

[0073] The second step is to establish an improved droop control equation: the designed nonlinear stabilizer is integrated with the droop control to obtain the improved droop control equation.

[0074] An improved droop control method that integrates a nonlinear stability controller with droop control is proposed, and the improved droop control equation is established as follows:

[0075]

[0076] Where ω and U are the output voltage angular frequency and voltage amplitude of the energy storage voltage converter, respectively; P and Q are the active power and reactive power output of the energy storage voltage converter, respectively; P0 and Q0 are the rated active power and rated reactive power, respectively; ω0 and U0 are the rated voltage angular frequency and rated voltage amplitude output of the energy storage voltage converter, respectively; m and n are the angular frequency droop coefficient and voltage droop coefficient, respectively; Δω and ΔU are the compensation amounts for the voltage amplitude and voltage angular frequency of the energy storage voltage converter output by the nonlinear stabilizer designed based on cooperative control theory, respectively. c This is the cutoff frequency of the low-pass filter.

[0077] The third step is to design a nonlinear stability controller: taking the stability of the output voltage amplitude and voltage angular frequency of the energy storage voltage converter under load disturbance as the control objective, a nonlinear stabilizer is designed based on the cooperative control theory.

[0078] (1) The core of cooperative control theory is to design a control manifold based on the system's state variables. This control manifold contains the desired performance indicators of the system, causing the system to converge to an equilibrium state along the control manifold. Assume the target system is represented by the following nonlinear differential equation:

[0079]

[0080] Where x is the system state variable; Δu is the control variable; and t is time. The macro variable ψ is defined as a function of the state variable, and the goal of cooperative control is to make the system converge from any point in the state space to the control manifold ψ=(x,t)=0 in finite time.

[0081] The dynamic evolution process of macro variable convergence is defined as follows:

[0082]

[0083] T is a design parameter that determines the convergence speed; the smaller the value of T, the faster the system's dynamic response. Substituting the macro variables into the convergence equation, we can derive the control law that makes the system state converge to the manifold ψ=(x,t)=0.

[0084] Specifically, the nonlinear stabilizer control method based on cooperative control theory includes the following aspects:

[0085] Referring to the nonlinear differential equation representation of equation (4), equation (3) can be rewritten as:

[0086]

[0087] A nonlinear stabilizer is designed using cooperative control theory. When the DG system is subjected to load disturbances, the stabilizer outputs Δω and ΔU can be automatically adjusted to maintain droop control stability during dynamic processes, while preventing the introduction of steady-state errors. The stabilizer output must be zero in steady state. A linear combination of angular frequency and active power, voltage and reactive power is used as a macrovariable.

[0088]

[0089] In the formula, k1 and k2 are positive parameters, and ω ref U ref P is the reference value for the output voltage angular frequency and voltage amplitude of the energy storage voltage source converter. ref Q ref Here, ω and U represent the reference values ​​for the active and reactive power outputs of the energy storage voltage source converter during stable operation, respectively. P and Q represent the active and reactive power outputs of the energy storage voltage source converter, respectively. The expressions for the reference values ​​of the output voltage angular frequency and voltage amplitude of the energy storage voltage source converter are:

[0090]

[0091]

[0092] Where P0 and Q0 are the rated active power and rated reactive power of the energy storage voltage converter, respectively; ω0 and U0 are the rated voltage angular frequency and rated voltage amplitude of the energy storage voltage converter, respectively; m and n are the angular frequency droop coefficient and voltage droop coefficient, respectively. The reference values ​​for the angular frequency and voltage amplitude are ω0 and U0, respectively. ref U ref Obtained from traditional droop control, this ensures that the angular frequency and amplitude of the inverter's output voltage in steady state are consistent with those of traditional droop control, guaranteeing that each unit shares the load reasonably according to its capacity. Power reference value P ref Q refIt is not a static constant; it changes with the load. Therefore, its reference value is obtained from the output power through a delay circuit, T. z The delay time is used to compare the output power with the output power of the previous moment to monitor load disturbances. This ensures that the stabilizer will suppress load power fluctuations and improve system dynamic performance after the system converges to the control manifold.

[0093] (2) Based on the theory of cooperative control, when the load changes, in order to ensure that the energy storage voltage converter can converge to the manifold ψ under the action of cooperative control, i =0, to ensure that the system converges to the control manifold under the action of cooperative control, the dynamic evolution process of the macro variables is defined as follows:

[0094]

[0095] Among them, T i These are the design parameters of the nonlinear stabilizer, which determine the time for the manifold to converge to the equilibrium point. k1 and k2 are positive parameters, and (·) is their derivative.

[0096] Substituting equations (6)(7)(8)(9) into (10), we obtain the compensation amounts Δω and ΔU for the voltage amplitude and voltage angular frequency of the energy storage voltage converter output by the nonlinear stabilizer.

[0097] The output compensation is then added to the droop control to ensure that the system approaches and converges to the control manifold ψ. i =0, and move along the control manifold.

[0098] (3) Set the expression for the stabilizer output compensation as follows:

[0099]

[0100] Where Δω and ΔU are the compensation quantities for the voltage amplitude and voltage angular frequency of the energy storage voltage converter output by the nonlinear stabilizer designed based on cooperative control theory, respectively. c The output of the nonlinear stabilizer is 0 when the low-pass filter is in steady state, which does not affect the steady-state operation of the system. When the delay circuit detects load disturbances in the microgrid, the nonlinear stabilizer outputs compensation for the voltage amplitude and voltage angular frequency of the energy storage voltage converter, suppressing the voltage and frequency fluctuations of the energy storage voltage converter caused by changes in the microgrid load.

[0101] (4) In order to reduce the high-order harmonics caused by the measured power, the active power and reactive power output of the energy storage voltage type converter in the input of the nonlinear stabilizer are subjected to low-pass filtering.

[0102] Let T iThis determines the speed at which the stabilizer converges to 0. The smaller the value, the faster the convergence and the shorter the time to reach the target state; the larger the value, the slower the convergence and the longer the time to reach the target state.

[0103] (5) Adaptive k in nonlinear stabilizers i The determination; such as Figure 3 As shown, the macro variable formula (7) can be represented as a straight line passing through the origin with a slope of -1 / k. i The origin is the steady-state operating point, and the state variables will move along this straight line and eventually converge to the origin.

[0104] In order to adaptively generate k i Set it to:

[0105]

[0106] a i b i Let ω be a positive parameter and || be the absolute value. When ω and U are related to the angular frequency and amplitude reference value ω of the energy storage voltage-type converter output voltage... ref U ref The greater the difference, the larger k1 and k2 become, which can be represented by a straight line with a smaller slope. A smaller slope can limit load fluctuations, but the dynamic response is slower. As the output voltage angular frequency and amplitude ω, U of the energy storage voltage converter approach the reference value, k1 and k2 become smaller, and the trajectory slope increases with k i The slope of the trajectory increases as k decreases. Adaptation is a continuous process, and the trajectory slope changes constantly. On the other hand, when ω and U are close to a given value, the error is small, the working point moves towards the origin, and the trajectory slope increases with k. i The smaller the ω and U values, the faster the dynamic response speed. This adaptive control law limits the impact of load fluctuations, such as sudden load changes or line faults, during transient processes where the errors of ω and U are large. When the errors of ω and U are small, such as during line fault recovery, it can make a rapid transient response.

[0107] Adaptive k i Substituting into equation (8), we can obtain a result that is more accurate than when k is fixed. i Faster transient response.

[0108] The fourth step is to design a delay element to monitor the load disturbance of the microgrid. Using traditional methods, the delay element is used to monitor the load disturbance status of the microgrid in order to perform stable voltage and frequency control.

[0109] The fifth step is the stable control of voltage and frequency: When the load is disturbed, the output power, output voltage amplitude, and voltage angular frequency reference values ​​of the energy storage voltage converter are used as inputs to the nonlinear stabilizer. Through collaborative control, the compensation quantities of the output voltage amplitude and voltage angular frequency of the energy storage voltage converter are generated. An improved droop control that integrates the nonlinear stabilizer controller with droop control is proposed to achieve stable control of the voltage frequency of the energy storage voltage converter.

[0110] A simulation model of multiple inverters in parallel was built using Matlab / Simulink software, such as... Figure 4 As shown, each of the two inverters supplies power to its local load, and simultaneously supplies power to a common load via the PCC connection line. Two case studies are established to verify whether the improved droop control strategy, which introduces a cooperative control stabilizer, has good control performance under load changes and line faults, and whether it can achieve inverter output voltage frequency stability under load changes and line faults.

[0111] In the two simulation examples, at the initial moment of the first example, the inverter supplies power to its local load. At 0.5s, the common coupling point connects to common load 1; at 1.3s, it connects to common load 2; and at 1.35s, it disconnects from common load 2. At the initial moment of the second example, the inverter supplies power to the load, and a three-phase short-circuit fault occurs at 1s. The fault occurs at... Figure 4 At the common load 1 shown, the faulty line is disconnected at 1.1s.

[0112] from Figure 5 As can be seen, without the coordinated control stabilizer, load changes cause frequency oscillations, and there is a lack of suppression of rapid voltage changes, affecting the stability of the inverter. This shows that the droop control has a weak ability to suppress load fluctuations. After the coordinated control stabilizer is introduced, the frequency oscillations caused by load changes are significantly reduced, and rapid voltage changes are suppressed. This shows that it can maintain the stability of the inverter's output voltage frequency.

[0113] from Figure 6 As can be seen, the stabilizer only outputs when the system fluctuates, and outputs zero in steady state, thus not generating steady-state error.

[0114] from Figure 7 As can be seen, without the introduction of the coordinated control stabilizer, a three-phase short circuit fault will cause a large frequency oscillation and a rapid voltage drop; after the introduction of the coordinated control stabilizer, the fault suppression capability is improved, and the system stability is enhanced.

[0115] from Figure 8 As can be seen from this, adding adaptive k i After parameter adjustment, the stabilizer still maintains good stabilization performance for load changes and line faults, and reaches steady state faster after fluctuations and faults occur, quickly tracking the voltage and frequency setting.

[0116] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection claimed by the appended claims and their equivalents is defined.

Claims

1. A voltage-frequency stabilization control method for droop control of energy storage voltage-type converters in microgrids based on cooperative control theory, characterized in that, Includes the following steps: 11) Based on the rated active power and rated reactive power of the energy storage voltage converter, the output voltage angular frequency and voltage amplitude setpoint of the energy storage voltage converter, establish the droop control equation of the energy storage voltage converter. 12) Establishing an improved droop control equation: An improved droop control is proposed that integrates the designed nonlinear stable controller with droop control, resulting in an improved droop control equation. 13) Design a nonlinear stabilizer: Taking the stability of the output voltage amplitude and voltage angular frequency of the energy storage voltage converter under load disturbance as the control objective, design a nonlinear stabilizer based on the cooperative control theory; The design of the nonlinear stable controller includes the following steps: 131) Design a nonlinear stabilizer using cooperative control theory, with the macro variables designed as follows: ， In the formula, , It is a positive parameter. , These are reference values ​​for the output voltage angular frequency and voltage amplitude of the energy storage voltage-source converter. , These are reference values ​​for the output active and reactive power of the energy storage voltage source converter during stable operation. , These represent the angular frequency and voltage amplitude of the output voltage of the energy storage voltage-source converter, respectively. , These are the active power and reactive power output by the energy storage voltage converter, respectively. The expressions for the reference values ​​of the output voltage angular frequency and voltage amplitude of the energy storage voltage converter are as follows: ， ， in, , These are the rated active power and rated reactive power of the energy storage voltage source converter, respectively. , These are the angular frequency and rated voltage amplitude of the energy storage voltage-type converter output voltage, respectively. and These are the angular frequency droop factor and the voltage droop factor, respectively. The delay time is used to compare the output power with the output power of the previous moment to monitor load disturbances. 132) Based on the theory of cooperative control, when the load changes, in order to ensure that the energy storage voltage source converter can converge to the manifold under the action of cooperative control, The dynamic evolution process is defined as follows: ， in, These are the design parameters for nonlinear stabilizers. , For positive parameters, Its derivative; 133) Obtain the compensation amount for the voltage amplitude and voltage angular frequency of the energy storage voltage-type converter output from the nonlinear stabilizer. , : Substituting equations (3), (4), (5), and (6) into equation (7), we obtain the compensation amounts for the voltage amplitude and voltage angular frequency of the energy storage voltage-type converter output by the nonlinear stabilizer. , And there are: ， in , These represent the compensation amounts for the voltage amplitude and voltage angular frequency of the energy storage voltage-type converter output from the nonlinear stabilizer designed based on cooperative control theory. This is the cutoff frequency of the low-pass filter; the output of the nonlinear stabilizer is 0 during steady-state operation, which does not affect the steady-state operation of the system; when the delay circuit detects load disturbances in the microgrid, the nonlinear stabilizer outputs compensation for the voltage amplitude and voltage angular frequency of the energy storage voltage converter, suppressing the voltage and frequency fluctuations of the energy storage voltage converter caused by changes in microgrid load; 134) To reduce high-order harmonics caused by the measured power, the active and reactive power outputs of the energy storage voltage converter in the input of the nonlinear stabilizer are subjected to low-pass filtering. 135) Adaptive in nonlinear stabilizers The determination; To adaptively generate Set it to: ， , It is a positive parameter. For absolute value, when Reference value of output voltage angular frequency of energy storage voltage converter The greater the difference, The larger the value, the more limited the variation in voltage angular frequency; when Its energy storage voltage converter output voltage amplitude reference value The greater the difference, The larger the value, the more limited the variation in voltage amplitude; when The closer it is to the reference value of the output voltage angular frequency of the energy storage voltage-type converter , The smaller the value, the faster the dynamic response speed of the voltage angular frequency; when The closer it is to the reference value of the output voltage amplitude of the energy storage voltage converter , The smaller the value, the faster the dynamic response of the voltage amplitude; 14) Design a delay mechanism to monitor load disturbances in the microgrid; 15) Stable control of voltage frequency: When the load is disturbed, the output power, output voltage amplitude and voltage angular frequency reference values ​​of the energy storage voltage converter are used as inputs to the nonlinear stabilizer. The compensation amount of the output voltage amplitude and voltage angular frequency of the energy storage voltage converter is generated through collaborative control. An improved droop control that integrates the nonlinear stabilizer controller and droop control is proposed to achieve stable control of the voltage frequency of the energy storage voltage converter.

2. The voltage-frequency stabilization control method for droop control of energy storage voltage-type converters in microgrids based on cooperative control theory according to claim 1, characterized in that, The steps for establishing the droop control equations for the energy storage voltage source converter are as follows: 21) Assuming the line impedance between the energy storage voltage converter and the point of common coupling is inductive, the active and reactive power outputs of the energy storage voltage converter in the microgrid are: ， in, , These represent the active power and reactive power output of the energy storage voltage source converter, respectively. , These are the output voltage amplitude and the point of common coupling voltage amplitude of the energy storage voltage-type converter, respectively. The phase angle between the output voltage of the energy storage voltage converter and the voltage at the point of common coupling. For line inductance; 22) Based on the relationship between the output power, output voltage, and point of common coupling voltage of the energy storage voltage-type converter, the droop control equation for the energy storage voltage-type converter with inductive line impedance is established as follows: ， in, , These are the angular frequency and voltage amplitude of the output voltage of the energy storage voltage-type converter, respectively. , These are the rated active power and rated reactive power of the energy storage voltage converter, respectively. , These are the angular frequency and rated voltage amplitude of the output rated voltage of the energy storage voltage-type converter, respectively. and These are the angular frequency droop coefficient and the voltage droop coefficient, respectively.

3. The voltage-frequency stabilization control method for droop control of energy storage voltage-type converters in microgrids based on cooperative control theory according to claim 1, characterized in that, An improved droop control method is proposed, which integrates a nonlinear stability controller with droop control. The improved droop control equation is established as follows: ， in, , These are the angular frequency and voltage amplitude of the output voltage of the energy storage voltage-type converter, respectively. , These are the active power and reactive power output by the energy storage voltage converter, respectively. , These are the rated active power and the rated reactive power, respectively. , These are the angular frequency and rated voltage amplitude of the output rated voltage of the energy storage voltage-type converter, respectively. and These are the angular frequency droop coefficient and the voltage droop coefficient, respectively. , These represent the compensation amounts for the voltage amplitude and voltage angular frequency of the energy storage voltage-type converter output from the nonlinear stabilizer designed based on cooperative control theory. This is the cutoff frequency of the low-pass filter.

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