Virtual impedance parameter setting method and related device for network construction type converter

Abstract

The virtual impedance parameter setting method comprises the following steps: determining control system parameters: filter inductance L, parasitic resistance R, filter capacitance C, rotational inertia J, damping coefficient D, power grid line equivalent inductance Lg and power grid line equivalent resistance Rg; establishing a Lyapunov energy function containing three state variables delta, omega and E by adopting an undetermined gradient method; and a control system parameter is substituted into the Lyapunov energy function to draw an attraction domain when a fault occurs, a stability boundary is determined by adjusting a virtual impedance parameter value, and then a virtual impedance parameter setting boundary value is obtained. Under single voltage loop amplitude control, a phase angle of an active link and a voltage dynamic process of a reactive link are considered at the same time, an overall Lyapunov energy function of the system is formed, and a virtual impedance parameter setting method is provided, so that when a superior power grid is disturbed, a network-forming type energy storage power station can realize the optimal control of the system within a current limiting range. And the grid-connected point voltage is actively and effectively supported.

Description

Technical Field

[0001] The invention belongs to the field of power system control, and in particular relates to a method for setting virtual impedance parameters of a grid-connected converter. Background Art

[0002] Due to the intermittent and instability of new energy sites, the power system under the background of high proportion of new energy presents the characteristics of low inertia and weak damping, which brings great challenges to the stability of the system. In practical applications, traditional centralized grid-type energy storage power stations do not have active support performance. In the face of sudden transient conditions such as voltage sag and phase jump, it is unable to provide fast power response. Many scholars have gradually paid attention to the application of centralized grid-type energy storage, and proposed that under grid-type control, it can show voltage source characteristics to the outside, and can adjust the loop virtual rotation inertia and virtual damping parameters to provide flexible inertia support and damping characteristics for the system, thereby enhancing system stability.

[0003] The inventors have found that the grid-type single voltage loop amplitude control only performs feedback control of the grid-connected point voltage, takes the inverter output filter as a whole as the controlled object, and directly generates the internal potential reference signal through conversion. The single voltage loop amplitude control has a large equivalent output impedance and can improve the small signal stability of the system. However, the single voltage loop amplitude control lacks direct control of the grid-connected current, so the control itself does not have the current limiting capability, which is prone to transient overcurrent problems. Limiting fault current and adding virtual impedance are effective suppression methods, while existing research is basically based on voltage and current dual-loop control. In terms of single voltage loop amplitude control, some scholars have optimized and improved the active loop to accelerate the internal potential of the inverter to follow the grid voltage changes in the case of voltage sag and suppress overcurrent, but there is a lack of research on methods for designing virtual impedance based on single voltage loop amplitude control. Summary of the invention

[0004] Based on this, the present invention provides a method for setting virtual impedance parameters of a grid-type converter, which is applied to centralized grid-type control superimposed virtual impedance under single voltage loop amplitude control.

[0005] The inventor has found through research that after superimposing virtual impedance control, the transient stability of the system needs to be considered. For the transient stability analysis of power systems, commonly used theoretical methods include the equal area rule, phase diagram analysis method, Lyapunov energy function method, etc. The physical meaning of the equal area rule is to compare the acceleration area formed by converting the kinetic energy of the motor rotor into potential energy with the deceleration area. If the deceleration area is larger than the acceleration area, the system tends to be stable. Grid-type control is different from synchronous motors, and is greatly affected by control algorithms and parameters. When applying the equal area rule, the dynamic regulation process of the voltage by the grid-type control loop is usually not considered, and after triggering the current limiting control, the acceleration and deceleration area is difficult to accurately draw. The phase diagram analysis method is generally used to determine the convergence solution problem of the second-order constant coefficient differential equation. When applied to the transient stability analysis of grid-type energy storage, the second-order constant coefficient differential equation of the power angle is usually established through the active loop, and the voltage amplitude signal generated by the reactive loop is taken as a constant value, but the voltage dynamic process is ignored during the voltage sag process and the system cannot be accurately described.

[0006] The Lyapunov energy function method is a method for analyzing the stability of nonlinear systems. It uses the concept of mechanical energy to construct an equation that can describe the energy change of the system, and judges the stability of the system through the change of this function over time. The 1958 literature first proposed the application of the Lyapunov method to the instantaneous stability judgment of the power system. The advantage of this method is that it can perform stability analysis of high-order nonlinear power systems and establish a general Lyapunov equation suitable for single-machine infinite systems and dual-machine power systems. In terms of the stability of grid-type control systems, most of the existing literature is based on the traditional voltage and current dual-loop control basis for analysis. The voltage loop is considered as constant voltage control, ignoring the voltage dynamic process, and the relevant literature describes that adding a virtual impedance link for current limiting will affect the transient stability of the system.

[0007] This invention takes the centralized grid-type energy storage power station as the research object. On the basis of the single voltage loop amplitude control, in order to ensure that the current is within the safe range and avoid damage to the switching devices, the virtual impedance control is superimposed to suppress the transient fault current. By establishing the Lyapunov energy function, the system potential energy equipotential surface is drawn, and the virtual impedance parameters are adjusted using the attraction domain range before and after the fault. The final simulation results verify the effectiveness of the single voltage loop amplitude control superimposed virtual impedance control, as well as the correctness of the virtual impedance parameter adjustment method.

[0008] The present invention simulates and establishes the Lyapunov energy function V(δ, ω, E) by considering the three state variables δ, ω, E obtained by the active power and reactive power loops, and analyzes the transient behavior of the overall network control. The core of the method for constructing the energy function is the undetermined gradient method, which is actually a reverse derivation method. First, the differential term is explored, and then the energy function is constructed. The energy function is used to draw the attraction domain when a fault occurs, and the stability boundary is determined by adjusting the virtual impedance parameter value, so as to obtain the virtual impedance parameter setting boundary.

[0009] The technical solution adopted by the present invention is: a method for setting virtual impedance parameters of a grid-type converter, which is applied to a grid-type control system under a single voltage loop amplitude control considering a voltage dynamic response process, and the method comprises:

[0010] Determine the control system parameters: filter inductance L, parasitic resistance R, filter capacitor C, moment of inertia J, damping coefficient D, equivalent inductance of the power grid line L g , grid line equivalent resistance R g ;

[0011] Considering the three state variables δ, ω, and E obtained from the active power loop and the reactive power loop, the Lyapunov energy function V(δ, ω, E) containing the three state variables δ, ω, and E is established using the undetermined gradient method; δ is the phase angle difference between the inverter voltage and the grid voltage; ω is the actual angular frequency; E is the potential inside the inverter;

[0012] The control system parameters are introduced into the Lyapunov energy function V (δ, ω, E) to draw the attraction domain when a fault occurs, and the stability boundary is determined by adjusting the virtual impedance parameter value, thereby obtaining the virtual impedance parameter setting boundary value.

[0013] The establishment of the Lyapunov energy function V(δ, ω, E) containing three state variables δ, ω, and E includes:

[0014] Determine active loop control equation and reactive loop control equation;

[0015] Calculate the actual output active power P and reactive power Q of the system;

[0016] According to the active loop control equation and the calculated active power P, construct the partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω; according to the reactive loop control equation and the calculated reactive power Q, construct the partial differential term of the energy function V with respect to the potential E inside the inverter;

[0017] The partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the internal potential E of the inverter are integrated with respect to the variables δ, ω, and E, and a Lyapunov energy function V (δ, ω, E) containing the state variables δ, ω, and E is established.

[0018] The active loop control equation is shown in the following equation (1), and the reactive loop control equation is shown in the following equation (2):

[0019]

[0020] E=k v ∫(k q (Q ref -Q)+U gref -U pccmag ) (2)

[0021] Where P ref , Q ref are the set active power command value and reactive power command value respectively, P and Q are the actual output active power and reactive power respectively (calculated after detecting the grid connection point voltage Upcc); U gref is the rated value of the grid voltage, ω0 is the rated angular frequency of the system, ω is the actual angular frequency, k q is the reactive voltage droop coefficient; U pccmag is the voltage amplitude at the grid connection point, k v is the voltage regulation factor.

[0022] The actual output active power P and reactive power Q are calculated by the following formula (3):

[0023]

[0024] U g is the grid voltage, R t is the overall equivalent resistance of the system, X t is the overall equivalent reactance of the system.

[0025] Because the system impedance is generally inductive, and X t >R t , R t / (R t 2 +X t 2 ) is small, the actual output active power P and reactive power Q can be calculated by the following formula (4) simplified from formula (3):

[0026]

[0027] The partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω is shown in the following equation (5):

[0028]

[0029] The partial differential term of the energy function V with respect to the potential E inside the inverter is shown in equation (6):

[0030]

[0031] The “integrating the partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the potential E inside the inverter with respect to the variables δ, ω, and E, and establishing the Lyapunov energy function V (δ, ω, E) containing the state variables δ, ω, and E” includes:

[0032] According to the partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the potential E inside the inverter, the differential form of the overall energy function is formed:

[0033]

[0034] Formula (7) is the differential of the overall Lyapunov energy function V. The differential term of the energy function is regarded as the system damping. The differential term of the constructed energy function is less than or equal to zero. The case where the differential term of the energy function is less than zero means the energy dissipation process of the system, and the system has a local asymptotic stable point.

[0035] According to the method of undetermined coefficients, the Lyapunov energy function is derived, assuming That is, the gradient of the energy function. According to the mathematical relationship between the function and the gradient in formula (8), the energy function V is integrated with respect to the variables δ, ω, and E:

[0036]

[0037]

[0038] Formula (9) and Formula (10) are the integral results of the energy function V with respect to variables δ, ω, and E, respectively. The integral results are simplified and combined to obtain the Lyapunov energy function V containing state variables δ, ω, and E, as shown in Formula (11):

[0039]

[0040] In formula (11), X t =X+X v +X g ; R t =R+R v +R g ;

[0041] X, X g , X v They represent filter reactance, grid line equivalent reactance, and virtual reactance respectively; X = jωL, X g =jωL g , X v =jωL v ; L, L g , L v Respectively represent filter inductance, grid line equivalent inductance, and virtual inductance; R, R g , R v They represent the parasitic resistance of the filter inductor, the equivalent resistance of the power grid line, and the virtual resistance respectively.

[0042] The “substituting the control system parameters into the Lyapunov energy function V(δ, ω, E) to draw the attraction domain when the fault occurs, and determining the stability boundary by adjusting the virtual impedance parameter value, thereby obtaining the virtual impedance parameter setting boundary value” includes:

[0043] Substitute the control system parameters into the Lyapunov energy function V(δ, ω, E), draw the system energy function equipotential diagram, and determine the system attraction domain; by adjusting the virtual impedance parameter value X v With R v , determine whether the attraction domain exists, obtain the change boundary of the attraction domain, determine the stability boundary, and then obtain the parameter adjustment boundary of the virtual impedance.

[0044] The present invention also provides a virtual impedance parameter setting device for a grid-type converter, which is applied to a grid-type control system under a single voltage loop amplitude control considering a voltage dynamic response process, and the device comprises:

[0045] Determine the control system parameter determination module, which is used to determine the control system parameters: filter inductance L, parasitic resistance R, filter capacitor C, moment of inertia J, damping coefficient D, equivalent inductance L of the power grid line g , grid line equivalent resistance R g ;

[0046] The energy function establishment module is used to consider the three state variables δ, ω, and E obtained from the active power loop and the reactive power loop, and use the undetermined gradient method to establish the Lyapunov energy function V (δ, ω, E) containing the three state variables δ, ω, and E; δ is the phase angle difference between the inverter voltage and the grid voltage; ω is the actual angular frequency; E is the potential inside the inverter;

[0047] The parameter setting module is used to bring the control system parameters into the Lyapunov energy function V (δ, ω, E) to draw the attraction domain when a fault occurs, determine the stability boundary by adjusting the virtual impedance parameter value, and then obtain the virtual impedance parameter setting boundary value.

[0048] The energy function establishment module is specifically used for:

[0049] Determine active loop control equation and reactive loop control equation;

[0050] Calculate the actual output active power P and reactive power Q of the system;

[0051] According to the active loop control equation and the calculated active power P, construct the partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω; according to the reactive loop control equation and the calculated reactive power Q, construct the partial differential term of the energy function V with respect to the potential E inside the inverter;

[0052] The partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the internal potential E of the inverter are integrated with respect to the variables δ, ω, and E, and a Lyapunov energy function V (δ, ω, E) containing the state variables δ, ω, and E is established.

[0053] The parameter setting module is specifically used for:

[0054] The control system parameters are introduced into the Lyapunov energy function V (δ, ω, E), and the equipotential diagram of the system energy function is drawn to determine the system attraction domain; by adjusting the virtual impedance parameter value, it is judged whether the attraction domain exists, the change boundary of the attraction domain is obtained, the stability boundary is determined, and then the parameter adjustment boundary of the virtual impedance is obtained.

[0055] On the other hand, the present invention provides an electronic device, characterized in that it includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the processor executes the computer program, it implements the method for setting the virtual impedance parameters of the grid-type converter described in the first aspect.

[0056] Another aspect of the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for setting virtual impedance parameters of a grid-connected converter as described in the first aspect.

[0057] The present invention focuses on the stable operation of centralized grid-type energy storage power stations, especially their response strategies in the face of voltage sags. In order to optimize the active control capability of the power station, the present invention adopts single voltage loop amplitude control as the active control strategy for grid-type energy storage, and analyzes the specific response of the voltage and current at the grid connection point of the power station under voltage sag conditions. On this basis, virtual impedance is introduced to optimize the control of the power station. This optimization method aims to enable the grid-type energy storage power station to actively and effectively support the grid connection point voltage within the current limit range when the upper power grid is disturbed.

[0058] Compared with the prior art, the beneficial effect of the present invention is that compared with the phase plane method, in the process of voltage sag of the upper power grid, only the dynamic process of the phase angle in the active synchronization link is considered, and the change of the potential amplitude in the inverter is ignored. Under the control of the single voltage loop amplitude, the present invention simultaneously considers the phase angle of the active link and the voltage dynamic process of the reactive link, forms the Lyapunov energy function of the whole system, analyzes the transient behavior of the grid-type control, makes transient stability judgment, and proposes a maximum range analysis method for setting virtual impedance parameters. Compared with the traditional analysis system transient, the phase plane method of the second-order constant coefficient differential equation established can obtain a smaller virtual impedance range. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The invention draws a network-type three-dimensional potential energy distribution diagram and a system equipotential surface diagram based on the Lyapunov energy function.

[0060] Figure 2 The active power reference values ​​of the present invention are respectively P ref =10kW, P ref =12kW, P ref =15kW, grid voltage U g =U gn , the potential energy equipotential surfaces of the system.

[0061] Figure 3 The present invention shows that when a voltage failure of the upper power grid occurs and the power grid voltage temporarily drops to 0.2pu, potential energy equipotential surfaces of the system before and after adding virtual impedance are shown.

[0062] Figure 4 The invention provides a meshed single voltage loop amplitude control, a single voltage loop amplitude control superimposed virtual impedance output current effective value comparison and a voltage drop depth comparison during the upper voltage drop period.

[0063] Figure 5 During the upper voltage drop period of the present invention, when the virtual impedance value is set to 2, 4, and 6, the grid connection point drop depth comparison and the output current effective value comparison are shown.

[0064] Figure 6 The three-phase grid-connected point current waveforms are compared during the upper voltage drop period of the present invention when no virtual impedance is added, the virtual impedance value is reasonable, and the virtual impedance is too large.

[0065] Figure 7 Schematic diagram of active control strategy for grid-type energy storage.

[0066] Figure 8 Block diagram of virtual impedance control superimposed on single voltage loop amplitude control. DETAILED DESCRIPTION

[0067] In order to scientifically and systematically determine the optimal parameter range of virtual impedance, the present invention mainly uses the system Lyapunov energy function considering the voltage dynamic response process as a single voltage loop amplitude control grid-type converter virtual impedance parameter setting method. This function can not only serve as a basis for judging the transient stability of the system, but also provides a new perspective to observe and evaluate the operating status of the system.

[0068] The present invention provides a method for adjusting virtual impedance parameters of a grid-type converter with single voltage loop amplitude control. The method is applied to a grid-type system under single voltage amplitude control that takes into account a voltage dynamic response process. The virtual impedance parameters are adjusted using a Lyapunov energy function. The method for establishing a system Lyapunov energy function that takes into account a voltage dynamic response process adopted by the present invention aims to use the transient stability of a grid-type energy storage power station when facing power disturbances such as voltage sag as a method for adjusting the range of virtual impedance parameters.

[0069] A first aspect of the present invention provides a method for setting virtual impedance parameters of a grid-type converter, which is applied to a grid-type control system under a single voltage loop amplitude control considering a voltage dynamic response process. The method comprises the following steps:

[0070] S1. Determine the control system parameters: filter inductance L, parasitic resistance R, filter capacitor C, moment of inertia J, damping coefficient D, line parameter L g , R g , obtain the system grid-connected point output voltage U pcc And the current value I pcc ; These parameters are subsequently substituted into the derived energy function to specifically set the virtual impedance;

[0071] S2. Write the control loop equation of the system according to the active-frequency control link and reactive-voltage and single voltage loop amplitude control. pcc In the case of weak grid, it is approximately equal to the potential value inside the inverter, I pcc The difference between the potential in the inverter and the grid voltage can be divided by the equivalent impedance for conversion, which is used for subsequent formula conversion. pcc ,I pcc The actual output active power P and reactive power Q of the system can be obtained through the power calculation module, and the active loop synchronization process can be constructed by simulating the virtual synchronous motor control loop;

[0072] S3. According to the grid-type active power-frequency synchronization link equation in S2, the calculated actual output active power P is substituted, and after multiplying both sides of the active power loop equation by dδ / dt, the partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω is defined;

[0073] S4. According to the grid-type reactive-voltage and single voltage loop amplitude control link equations in S2, the calculated actual output reactive power Q is substituted and multiplied by dE / dt to define the partial differential term of the potential E inside the inverter under the grid-type single voltage loop amplitude control;

[0074] S5. Construct a gradient of the energy function assuming that the differential terms obtained in S3 and S4 are the gradients of the energy function. According to the mathematical relationship between the function and the gradient, the partial differential terms of the energy function obtained in S3 with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function obtained in S4 with respect to the potential E inside the inverter are integrated with respect to each variable of the energy function V, and a Lyapunov energy function including the state variables δ, ω, and E is established.

[0075] S6. Based on the corresponding system parameters in S1 and the Lyapunov energy function established in S5, and by substituting the system parameters, draw the equipotential diagram of the system energy function and determine the system attraction domain. Add virtual impedance Z based on the filter inductance and grid impedance v , which means that the equivalent increase in grid impedance is Z+Z g +Z v The virtual impedance parameters are dynamically adjusted to draw the system attraction and determine the stability boundary, and the virtual impedance parameter setting boundary value is obtained.

[0076] In S2, the centralized grid-type energy storage adopts power synchronization mode, which shows voltage source characteristics to the outside. It can adjust the loop virtual rotation inertia and virtual damping parameters to provide flexible inertia support and damping characteristics for the system, and enhance system stability. The grid-type control obtains the phase signal θ through active power synchronization mode, and the reactive loop obtains the voltage amplitude reference signal U ref , as the inner loop voltage command. The control equations of the active loop and reactive loop can be written as

[0077]

[0078] E=k v ∫(k q (Q ref -Q)+U gref -U pccmag ) (2)

[0079] In formula (1) and (2), P ref , Q ref U is the set active power command value, P and Q are the actual output active power and reactive power detected by the grid connection point. gref is the rated value of the grid voltage, ω0 is the rated angular frequency of the system, ω is the actual angular frequency, k q is the reactive voltage droop coefficient. pccmag is the voltage amplitude at the grid connection point, k v is the voltage regulation factor.

[0080] The S2 can calculate the actual output active power and reactive power of the system based on the centralized grid-connected equivalent circuit:

[0081]

[0082] Where, E is the potential inside the inverter, U g is the grid voltage, R t , X t is the overall equivalent resistance and reactance of the system. After adding the virtual impedance, the equivalent impedance of the system increases accordingly. δ is the phase angle difference between the inverter voltage and the grid voltage.

[0083] In formula (2), the system impedance is generally inductive, and X t >R t , R t / (R t 2 +X t 2 ) ratio is small, the active power and reactive power can be simplified to calculate:

[0084]

[0085] The S3 is the differential term of the Lyapunov function with respect to the phase angle difference δ, which needs to be derived according to the active loop control formula (1), ignoring the damping term, and it can be obtained:

[0086]

[0087] The S4 is a dynamic process of adding the potential inside the inverter into the Lyapunov energy function. It needs to be derived according to the reactive loop control formula (2). The differential term of the potential E inside the inverter under the grid-type single voltage loop amplitude control is:

[0088]

[0089] Formula (7) is the differential of the overall Lyapunov energy function, which is the system damping. The differential term of the constructed energy function is less than or equal to zero, which is the energy dissipation of the system. The system has a local asymptotic stable point.

[0090] assumed That is, the gradient of the energy function. The process described in S5 needs to be derived based on the mathematical relationship between the function and the gradient:

[0091]

[0092]

[0093] Formulas (9) and (10) are the integral calculations of the phase angle δ and the internal potential E, respectively. Finally, the Lyapunov energy function (Formula (11)) containing the state variables δ, ω, and E is established as the transient stability criterion under the amplitude control of the grid-type single voltage loop.

[0094]

[0095] The actual analysis process of S6 is based on the transient stability analysis process of Lyapunov energy function, which usually adopts the Russell principle. The mathematical theory of the Russell principle is: for a scalar function V(x) with a continuous first-order partial derivative, assuming that in the bounded region Ω l ∈{V(x)<l,l> 0} satisfies dV(x) / dt≤0; R is the region Ω l The set of points that satisfy dV(x) / dt=0. According to the transient stability analysis process of Lyapunov energy function, the established Lyapunov energy function (Formula (11)) can be used to draw the three-dimensional potential energy distribution diagram of the system and the two-dimensional potential energy equipotential surface diagram of E and δ using MATLAB. The maximum closed equipotential surface in the equipotential diagram is used as the maximum attraction domain estimate, and the energy is zero, which corresponds to the equilibrium point of the system. Corresponding to the established Lyapunov energy function (Formula (11)), the bounded area formed by dV(x) / dt=0 is drawn as the maximum attraction domain estimate, and the energy is zero, which corresponds to the equilibrium point of the system. Generally speaking, after the system is disturbed, if the system state is still within the attraction domain, the system state will gradually stabilize. Under the filter impedance Z and the grid impedance Z g Add virtual impedance Z based on v , the equivalent increase in grid impedance is Z+Z g +Z v ; Among them, Z=|R+jωL|, Z g =|R g +jωL g |, Z v =|R v +jωL v ,|where R, R g , R v They represent the parasitic resistance of the filter inductor, the equivalent resistance of the power grid line, and the virtual resistance, respectively. g , L v represent the filter inductance, equivalent inductance of the power grid line, and virtual inductance respectively; in formula (11), the filter impedance, virtual impedance and line impedance are uniformly represented: X t =X+X v +X g (X=jωL、X g =jωL g , X v =jωLv They are called filter reactance, grid line equivalent reactance, and virtual reactance respectively), R t =R+R v +R g The addition of virtual impedance is equivalent to connecting impedance in series in the original equivalent circuit of the system. By adjusting the parameter value of virtual impedance, the change boundary of the attraction domain is obtained, and the parameter adjustment boundary of virtual impedance is further obtained.

[0096] The present invention uses MATLAB simulation software to simulate and verify the single voltage loop amplitude control strategy and the virtual impedance optimization method for the network type. The system fault is set to the voltage of the upper grid drops to 0.2pu at 0.2s. It is mainly through observing the effective value domain of the output voltage and the grid connection point voltage depth during the voltage sag. The active support capability of the network control and the virtual impedance current limiting performance are judged.

[0097] Adding virtual impedance control on the basis of networked single voltage loop control is equivalent to connecting impedance in series in the original equivalent circuit of the system, increasing the equivalent impedance between the potential inside the inverter and the grid voltage, which will affect the transient stability of the system. The present invention uses the Lyapunov energy function of the networked single voltage loop amplitude control as the transient stability criterion.

[0098] The existing transient stability research strategy mainly considers the voltage and current dual-loop control basis, and considers the voltage loop as constant voltage control, ignoring the voltage dynamic process. The present invention chooses to consider the three state variables δ, ω, E obtained by the active and reactive loops on the basis of single voltage loop amplitude control, simulates and establishes the Lyapunov energy function V (δ, ω, E), and analyzes the transient behavior of the overall network control. The method of constructing the energy function can adopt the undetermined gradient method, which is actually a reverse derivation method, first exploring the differential term, and then constructing the energy function.

[0099] In the actual analysis process, the established Lyapunov energy function is mainly used to draw the potential energy equipotential surface of the network-type system. The bounded area formed by dV(x) / dt=0, that is, the closed equipotential surface, is used as the maximum attraction domain estimate, where the energy calculated by the Lyapunov function is zero, corresponding to the equilibrium point of the system. Generally speaking, after the system is disturbed, if the system state is still within the attraction domain, the system state will gradually stabilize. The three-dimensional potential energy distribution diagram and potential energy equipotential surface drawn according to the proposed energy function are shown in Figure 2. Figure 1 As shown in , the maximum range of the red closed curve in the potential energy equipotential surface corresponds to the maximum attraction domain range of the system.

[0100] In the present invention, the system-related simulation data is set as follows:

[0101] Table 1 Simulation system related parameters

[0102]

[0103] Figure 2 Potential energy equipotential diagram of the process of increasing the active power reference value. As the active power reference value gradually increases, the range of the attraction domain gradually decreases, and the system stability decreases. Figure 3 When the grid voltage drops to 0.2pu, the potential energy isopotential diagrams before and after adding virtual impedance. Gradually increasing the virtual impedance value, the attraction domain also decreases, and the system stability range decreases. It is deduced that the maximum virtual impedance is set to about 56.76Ω, so that the attraction domain does not exist, that is, the system does not have a stable operating point.

[0104] according to Figure 4 The simulation results show that the grid-connected inverter uses a single voltage loop amplitude control to achieve active support for the grid-connected point voltage under voltage sag conditions. When virtual impedance is not added, the overcurrent is very large. On the basis of single voltage loop amplitude control, virtual impedance is added to effectively suppress the overcurrent, but the active support capability of the grid-connected inverter is sacrificed. The comparison values ​​of the voltage drop depth and current amplitude of the grid-connected point before and after adding virtual impedance are shown below:

[0105] Table 2 Comparison of simulation results between single voltage loop amplitude control and single voltage loop amplitude superimposed virtual impedance control

[0106]

[0107] Figure 5 The virtual impedance value is gradually increased, and the current gradually decreases, but at the same time, the voltage drop depth of the grid connection point increases, and the active support capacity of the amplitude control of the grid-type single voltage loop is reduced. For the specific parameter setting of the virtual impedance, it can be calculated based on the current limit range and transient stability. First, the rated current effective value is calculated to be about 13.58A during stable operation. During the fault period, the allowable range of the fault through-current is set to 2 times the rated current of 27.16A, and the overall value of the virtual impedance Zv is calculated to be 6Ω. In order to more effectively suppress transient current, set X / R=4.

[0108] Figure 6 It can also be observed from the three-phase current of the grid-connected point that setting a reasonable virtual impedance value can effectively suppress the current, but when the virtual impedance value is increased to the maximum boundary range, the current waveform of the grid-connected point has been distorted, seriously affecting the grid stability.

[0109] Table 3 Comparison of simulation results when adding different virtual impedance parameters to voltage sag

[0110]

[0111] The embodiment of the present invention further provides a virtual impedance parameter setting device for a grid-type converter, which is applied to a grid-type control system under a single voltage loop amplitude control considering a voltage dynamic response process, and the device comprises:

[0112] Determine the control system parameter determination module, which is used to determine the control system parameters: filter inductance L, parasitic resistance R, filter capacitor C, moment of inertia J, damping coefficient D, equivalent inductance L of the power grid line g , grid line equivalent resistance R g ;

[0113] The energy function establishment module is used to consider the three state variables δ, ω, and E obtained from the active power loop and the reactive power loop, and use the undetermined gradient method to establish the Lyapunov energy function V (δ, ω, E) containing the three state variables δ, ω, and E; δ is the phase angle difference between the inverter voltage and the grid voltage; ω is the actual angular frequency; E is the potential inside the inverter;

[0114] The parameter setting module is used to bring the control system parameters into the Lyapunov energy function V (δ, ω, E) to draw the attraction domain when a fault occurs, determine the stability boundary by adjusting the virtual impedance parameter value, and then obtain the virtual impedance parameter setting boundary value.

[0115] The energy function establishment module is specifically used for:

[0116] Determine active loop control equation and reactive loop control equation;

[0117] Calculate the actual output active power P and reactive power Q of the system;

[0118] According to the active loop control equation and the calculated active power P, construct the partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω; according to the reactive loop control equation and the calculated reactive power Q, construct the partial differential term of the energy function V with respect to the potential E inside the inverter;

[0119] The partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the internal potential E of the inverter are integrated with respect to the variables δ, ω, and E, and a Lyapunov energy function V (δ, ω, E) containing the state variables δ, ω, and E is established.

[0120] The parameter setting module is specifically used for:

[0121] The control system parameters are introduced into the Lyapunov energy function V (δ, ω, E), and the equipotential diagram of the system energy function is drawn to determine the system attraction domain; by adjusting the virtual impedance parameter value, it is judged whether the attraction domain exists, the change boundary of the attraction domain is obtained, the stability boundary is determined, and then the parameter adjustment boundary of the virtual impedance is obtained.

[0122] On the other hand, the present invention provides an electronic device, characterized in that it includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and when the processor executes the computer program, it implements the method for setting the virtual impedance parameters of the grid-type converter described in the first aspect.

[0123] Another aspect of the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the method for setting virtual impedance parameters of a grid-connected converter as described in the first aspect.

[0124] The present invention studies the virtual impedance parameter setting method of the grid-type converter under the single voltage loop amplitude control, takes the centralized grid-type energy storage power station as the research object, adopts the single voltage loop amplitude control as the grid-type active control strategy, and adds virtual impedance on the basis of control to optimize the control in the face of voltage sag. The present invention mainly establishes the system Lyapunov energy function considering the voltage dynamic response process under the grid-type single voltage loop amplitude control as a judgment method for the transient stability of the system. The system potential energy equipotential surface is drawn, and the change of the attraction domain when adding virtual impedance in the case of a fault is used to propose a method for the virtual impedance setting range, so that the grid-type energy storage can actively support the grid connection point voltage within the current limit range in the face of voltage sag.

Claims

1. A method for setting virtual impedance parameters of a grid-connected converter, characterized in that: A networked control system is applied to a single voltage loop amplitude control considering a voltage dynamic response process, the method comprising: Determine the control system parameters: filter inductance L, parasitic resistance R, filter capacitor C, moment of inertia J, damping coefficient D, equivalent inductance of the power grid line L g , grid line equivalent resistance R g ; Considering the three state variables δ, ω, and E obtained from the active power loop and the reactive power loop, a Lyapunov energy function V(δ, ω, E) containing the three state variables δ, ω, and E is established; δ is the phase angle difference between the inverter voltage and the grid voltage; ω is the actual angular frequency; E is the potential inside the inverter; The control system parameters are introduced into the Lyapunov energy function V (δ, ω, E) to draw the attraction domain when a fault occurs, and the stability boundary is determined by adjusting the virtual impedance parameter value, thereby obtaining the virtual impedance parameter setting boundary value.

2. The method for setting virtual impedance parameters of a grid-connected converter according to claim 1, characterized in that: The establishment of the Lyapunov energy function V(δ, ω, E) containing three state variables δ, ω, and E includes: Determine active loop control equation and reactive loop control equation; Calculate the actual output active power P and reactive power Q of the system; According to the active loop control equation and the calculated active power P, construct the partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω; according to the reactive loop control equation and the calculated reactive power Q, construct the partial differential term of the energy function V with respect to the potential E inside the inverter; The partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the internal potential E of the inverter are integrated with respect to the variables δ, ω, and E, and a Lyapunov energy function V (δ, ω, E) containing the state variables δ, ω, and E is established.

3. The method for setting virtual impedance parameters of a grid-connected converter according to claim 2, characterized in that: The active loop control equation is shown in the following equation (1), and the reactive loop control equation is shown in the following equation (2): E=kv∫(kq(Qref-Q)+Ugref-Upccmag) (2) Where P ref , Q ref are the set active power command value and reactive power command value respectively, P and Q are the actual output active power and reactive power respectively; U gref is the rated value of the grid voltage, ω0 is the rated angular frequency of the system, ω is the actual angular frequency, k q is the reactive voltage droop coefficient; U pccmag is the voltage amplitude at the grid connection point, k v is the voltage regulation factor.

4. The method for setting virtual impedance parameters of a grid-connected converter according to claim 2, characterized in that: The actual output active power P and reactive power Q are calculated by the following formula (3): U g is the grid voltage, R t is the overall equivalent resistance of the system, X t is the overall equivalent reactance of the system.

5. The method for setting virtual impedance parameters of a grid-connected converter according to claim 4, characterized in that: The actual output active power P and reactive power Q can be calculated by the following formula (4) simplified from formula (3):

6. The method for setting virtual impedance parameters of a grid-connected converter according to claim 5, characterized in that: The partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω is shown in the following equation (5): The partial differential term of the energy function V with respect to the potential E inside the inverter is shown in equation (6):

7. The method for setting virtual impedance parameters of a grid-connected converter according to claim 6, characterized in that: The “integrating the partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the potential E inside the inverter with respect to the variables δ, ω, and E, and establishing the Lyapunov energy function V (δ, ω, E) containing the state variables δ, ω, and E” includes: According to the partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the potential E inside the inverter, the differential form of the overall energy function is formed: Formula (7) is the differential of the overall Lyapunov energy function V; According to the mathematical relationship between the function and the gradient in formula (8), the energy function V is integrated with respect to the variables δ, ω, and E: Formula (9) and Formula (10) are the integral results of the energy function V with respect to variables δ, ω, and E, respectively. The integral results are simplified and combined to obtain the Lyapunov energy function V containing state variables δ, ω, and E, as shown in Formula (11): In formula (11), X t =X+X v +X g ; R t =R+R v +R g ; X, X g , X v They represent filter reactance, grid line equivalent reactance, and virtual reactance respectively; X = jωL, X g =jωL g , X v =jωL v ; L, L g , L v Respectively represent filter inductance, grid line equivalent inductance, and virtual inductance; R, R g , R v They represent the parasitic resistance of the filter inductor, the equivalent resistance of the power grid line, and the virtual resistance respectively.

8. The method for setting virtual impedance parameters of a grid-connected converter according to claim 7, characterized in that: The "substituting the control system parameters into the Lyapunov energy function V(δ, ω, E) to draw the attraction domain when the fault occurs, determining the stability boundary by adjusting the virtual impedance parameter value, and then obtaining the virtual impedance parameter setting boundary value" includes: Substitute the control system parameters into the Lyapunov energy function V(δ, ω, E), draw the system energy function equipotential diagram, and determine the system attraction domain; by adjusting the virtual impedance parameter value X v With R v , determine whether the attraction domain exists, obtain the change boundary of the attraction domain, determine the stability boundary, and then obtain the parameter adjustment boundary of the virtual impedance.

9. A virtual impedance parameter setting device for a grid-type converter, characterized in that: A network control system is applied to a single voltage loop amplitude control considering a voltage dynamic response process, the device comprising: Determine the control system parameter determination module, which is used to determine the control system parameters: filter inductance L, parasitic resistance R, filter capacitor C, moment of inertia J, damping coefficient D, equivalent inductance L of the power grid line g , grid line equivalent resistance R g ; The energy function establishment module is used to consider the three state variables δ, ω, and E obtained from the active power loop and the reactive power loop, and establish the Lyapunov energy function V (δ, ω, E) containing the three state variables δ, ω, and E; δ is the phase angle difference between the inverter voltage and the grid voltage; ω is the actual angular frequency; and E is the potential inside the inverter; The parameter setting module is used to bring the control system parameters into the Lyapunov energy function V (δ, ω, E) to draw the attraction domain when a fault occurs, determine the stability boundary by adjusting the virtual impedance parameter value, and then obtain the virtual impedance parameter setting boundary value.

10. The virtual impedance parameter setting device for a grid-type converter according to claim 9, characterized in that: The energy function establishment module is specifically used for: Determine active loop control equation and reactive loop control equation; Calculate the actual output active power P and reactive power Q of the system; According to the active loop control equation and the calculated active power P, construct the partial differential term of the energy function V with respect to the phase angle difference δ and the angular velocity ω; according to the reactive loop control equation and the calculated reactive power Q, construct the partial differential term of the energy function V with respect to the potential E inside the inverter; The partial differential terms of the energy function V with respect to the phase angle difference δ and the angular velocity ω, and the partial differential terms of the energy function V with respect to the internal potential E of the inverter are integrated with respect to the variables δ, ω, and E, and a Lyapunov energy function V (δ, ω, E) containing the state variables δ, ω, and E is established.

11. The virtual impedance parameter setting device for a grid-type converter according to claim 9, characterized in that: The parameter setting module is specifically used for: The control system parameters are introduced into the Lyapunov energy function V (δ, ω, E), and the equipotential diagram of the system energy function is drawn to determine the system attraction domain; by adjusting the virtual impedance parameter value, it is judged whether the attraction domain exists, the change boundary of the attraction domain is obtained, the stability boundary is determined, and then the parameter adjustment boundary of the virtual impedance is obtained.

12. An electronic device, characterized in that: The method comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the method for setting virtual impedance parameters of a grid-connected converter as described in any one of claims 1 to 8 is implemented.

13. A non-transitory computer-readable storage medium having a computer program stored thereon, wherein when the computer program is executed by a processor, the method for setting virtual impedance parameters of a grid-connected converter according to any one of claims 1 to 8 is implemented.

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