Networking type multi-converter modeling method based on sub-microsecond simulation

Abstract

The invention discloses a sub-microsecond simulation-based network construction type multi-converter modeling method, and relates to the technical field of converter modeling and simulation. Discretizing a switch element, and constructing a generalized constant admittance switch model based on an LC equivalent circuit; then, expansion modeling from a single converter to a multi-converter system is realized through a discrete system state matrix, and a complete network-forming type multi-converter model including a control link is established in combination with inertia characteristics of a virtual synchronous generator; and finally, building a simulation model of the network construction type multi-converter system in the PSCAD / EMTDC, and verifying the correctness and effectiveness of the method. According to the method, the generalized constant admittance switch model and the inertia characteristic of the virtual synchronous generator are fused, good applicability and stability are achieved under the sub-microsecond-level simulation step length, the system simulation precision and efficiency are remarkably improved, and meanwhile rapid convergence of the transient process of the network construction type multi-converter and active supporting of the power grid voltage frequency are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field related to converter modeling and simulation, and in particular to a networked multi-converter modeling method based on sub-microsecond simulation. Background Art

[0002] Against the backdrop of growing electricity demand and increasing environmental pressure, the high-penetration application scenarios of new energy and power electronic equipment are continuously expanding. Multi-converter systems, with their higher power generation capacity and higher power electronic equipment utilization, are gradually replacing traditional synchronous generator-dominated distribution systems. However, current converter control mostly adopts a grid-following (GFL) strategy, whose synchronization relies on a phase-locked loop (PLL), which can easily cause stability issues in weak grid environments. Therefore, in low physical inertia grids, grid-forming (GFM) control is more suitable. This method can achieve autonomous synchronization without a phase-locked loop, while providing virtual inertia and damping, thereby improving system stability.

[0003] The core advantage of grid-based control lies in simulating the dynamic characteristics of synchronous generators, enabling the converter to promptly support the grid when voltage and frequency fluctuate. However, its transient stability still has certain limitations, so improving its dynamic response capability is crucial. Currently, the modeling of the converter switching process mostly uses L / C equivalent circuits or binary resistance models. Such methods require recalculating the admittance matrix every time the switch state changes, which significantly increases the computational complexity of the multi-converter system. In addition, transient errors during switching can easily lead to additional power loss, reduce the system response speed, and are easily affected by external circuits, weakening the real-time simulation accuracy. As the switching frequency of new power electronic switching devices continues to increase, the additional losses in the switching process are also gradually increasing. Traditional modeling methods find it difficult to accurately characterize the switching transient process at sub-microsecond simulation steps, which restricts the system's ability to quickly support the grid inertia requirements.

[0004] In summary, grid-connected converters require a more general and accurate modeling method to better reflect their support for the grid and dynamic response characteristics. Summary of the Invention

[0005] In response to the defects existing in the prior art, the present invention discloses a modeling method for a meshed multi-converter based on sub-microsecond simulation. This method constructs a generalized switch constant admittance model based on an LC equivalent circuit for the meshed converter, and combines the inertia characteristics of a virtual synchronous generator to achieve accurate modeling of the multi-converter. This solves the problems of slow response speed and low simulation accuracy of the existing model during transient processes, and significantly reduces the power loss generated in sub-microsecond simulation.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A modeling method for a meshed multi-converter based on sub-microsecond simulation, comprising:

[0008] The switch model of a single grid-type converter is equivalent to the switch on and off states. By discretizing the switch elements, a generalized constant admittance switch model based on the LC equivalent circuit is constructed.

[0009] The equivalent admittance Y of the generalized constant admittance switch model is ensured to be equal in both the on and off states, so that the converter has an ideal response characteristic under steady-state conditions. Under the ideal response characteristic, the discrete system state matrix of a single grid-type converter is obtained by sorting and completing the modeling of the single grid-type converter. The state matrix consists of the voltage coefficient α and the current coefficient β.

[0010] The discrete system state matrix of a single grid-type converter is derived to extend to a multi-converter system. Combined with the dynamic coupling characteristics of the grid-type multi-converter, the discrete system state matrix of n grid-type converters is obtained. This is simplified to obtain the simplified discrete system state matrix of n grid-type converters, completing the modeling of a single integrated grid-type multi-converter.

[0011] Based on the single integrated grid-type multi-converter model and combined with the inertia characteristics of the virtual synchronous generator, the control pulse signal is obtained, the control system model is improved, and a complete grid-type multi-converter system model is constructed.

[0012] Based on the established system model, a simulation model of the grid-type multi-converter system was built in PSCAD / EMTDC, and compared and verified with the multi-converter system based on the traditional L / C model at a sub-microsecond simulation step.

[0013] Furthermore, the equivalent admittance Y of the generalized constant admittance switch model is ensured to be equal in the on and off states, so that the converter has an ideal response characteristic under steady-state conditions. Under the ideal response characteristic, the discrete system state matrix of the single-unit grid-type converter is obtained by sorting out, and the modeling of the single-unit grid-type converter is completed. The specific method is as follows:

[0014] When the equivalent admittance Y of the generalized constant admittance switch model in the on and off states is equal, the converter energy storage and voltage stabilization components are considered as independent power sources during the transient process of the switch model to obtain the specific equivalent admittance condition.

[0015] Based on the switch equivalent admittance condition, in a single converter, the independent half-bridge circuits in the single-phase and three-phase full-bridge circuits are analyzed, and the voltage-current relationship equation is obtained through KCL. After the equation is organized into a voltage-current relationship state equation, the discrete system state matrix of a single grid-type converter is obtained.

[0016] Furthermore, the specific equivalent admittance condition is:

[0017]

[0018] Where: L p is the filter inductor; C p For the voltage stabilizing capacitor.

[0019] Furthermore, the voltage-current relationship equation and the voltage-current relationship state equation are respectively:

[0020]

[0021] Where: t represents the present time, t-Δt represents the time Δt ago; U c1 、U c2 is the capacitor voltage; I h1 , I h2 are the upper and lower arm currents respectively; U1 and U2 are the upper and lower arm voltages respectively; Y0 is the equivalent admittance; U0 is the midpoint voltage of the bridge arm; I0 is the inductor current; I1(t) and I2(t) are the output currents of the upper and lower arms respectively; α is the voltage coefficient under different states; β is the current coefficient under different states, A is the system state matrix, B is the control matrix; C is the constant matrix.

[0022] Furthermore, the discrete system state matrix of the single converter can be obtained according to the voltage-current relationship state equation:

[0023]

[0024] According to the above formula, the smaller the spectral radius of A, the faster the transient response of the system. When the spectral radius of A is less than 1, the system is stable, and when the spectral radius is greater than 1, the system is unstable.

[0025] Furthermore, the discrete system state matrix of a single grid-type converter is derived to extend to a multi-converter system. Combined with the dynamic coupling characteristics of the grid-type multi-converter, the discrete system state matrix of n grid-type converters is obtained. This is simplified to obtain the simplified discrete system state matrix of n grid-type converters, completing the modeling of a single integrated grid-type multi-converter. Specifically, the following steps are involved:

[0026] Through the state equation of the voltage and current relationship of a single converter, it is deduced that when n converters are connected in parallel, the state equation of the relationship is:

[0027]

[0028] Among them, U 11 、U 21 ,…,U n1are the upper arm voltages of the 1st, 2nd, ..., nth converters respectively; I 11 , I 21 ,…,I n2 are the lower arm currents of the 1st, 2nd, ..., nth converters respectively; A n is the discrete system state matrix, C n is a constant matrix;

[0029] When n converters are connected in parallel, the voltage at the grid connection point is determined by the output currents of the two converters, which has the dynamic coupling characteristic of voltage coupling.

[0030] The discrete system state matrix A of n grid-type converters is obtained by using the voltage-current relationship state equations of multiple converters and considering the dynamic coupling characteristics. n for:

[0031]

[0032] Where: α1, α2, …, α n are the current conduction coefficients of the first, second, ..., nth converters, β1, β2, ..., β n are the voltage turn-off coefficients of the 1st, 2nd, ..., nth converters respectively; L i 、R i are the line inductance and resistance of the i-th converter respectively;

[0033] Assuming the line impedance is infinite, the simplified discrete system state matrix of n grid-type converters is expressed as:

[0034]

[0035] Let α1=…=α n =α * , β1=…=β n =β * , and the line inductance and resistance of each converter are equal, the state matrix A n When the absolute value of the characteristic root reaches the maximum, the system is stable. * , β * is the optimal parameter, and the corresponding historical current source expression is:

[0036] I h_on (t) = α * Y sw U(t-Δt)-I(t-Δt)

[0037] I h_off (t) = Y sw U(t-Δt)+β * I(t-Δt)

[0038] At this time, the historical current source parameters are the optimal parameters of the multi-converter switch model.

[0039] Furthermore, based on the single integrated grid-type multi-converter model and combined with the inertia characteristics of the virtual synchronous generator, the control pulse signal is obtained, the control system model is improved, and a complete grid-type multi-converter system model is constructed, which specifically includes:

[0040] Collect the converter output voltage and current in real time, calculate the instantaneous active power and reactive power, and use them as the input of the virtual synchronous generator;

[0041] In combination with the inertia characteristics of the virtual synchronous generator, the vector value of the output electromotive force is calculated based on the calculated instantaneous active power and reactive power, and by adopting virtual synchronous generator control, including virtual active power-frequency control and virtual reactive power-voltage control. The calculated output electromotive force vector value is used as input, and the grid reference signal is aligned through coordinate transformation. The dynamic performance is optimized under dual closed-loop control of current loop and voltage loop.

[0042] Input the parameters after dynamic performance optimization into the PWM module to generate pulse signals to control the switching state of the converter;

[0043] Build a complete grid-type multi-converter system model.

[0044] Furthermore, the virtual reactive power-voltage control method is:

[0045]

[0046] Where, P' is the input active power; P ref is the input active power reference value; P0 is the electromagnetic power; ω is the actual angular velocity; ω ref is the angular velocity reference value; J is the virtual moment of inertia; D is the damping coefficient; δ is the power angle of the virtual synchronous machine; Δθ is the power angle change; K a is the frequency adjustment coefficient, that is, K a =-ΔP / Δω, where ΔP is the change in output active power; is the change in angular frequency.

[0047] Furthermore, the virtual reactive power-voltage control method is:

[0048]

[0049] Where, E is the electromotive force output by the virtual synchronous generator control; K s is the integral coefficient; K b is the voltage regulation coefficient, i.e. K b=-ΔQ / ΔU, where ΔQ is the change in output reactive power; ΔU is the change in output voltage, U ref is the output voltage reference value; Q0 is the output reactive power; Q ref is the output reactive power reference value.

[0050] Furthermore, the real-time acquisition of the converter output voltage and current, calculation of the instantaneous active power and reactive power, and the calculation of the instantaneous active power as the input of the virtual synchronous generator need to consider the impact of multiple grid-connected converters connected in parallel in a high-impedance grid environment and changes in load when calculating the instantaneous active power, specifically:

[0051] In a high-impedance grid environment, when the line impedance is inductive, the active power change equation of the converter is:

[0052]

[0053] Where, E c is the voltage at the grid connection point, E i is the output voltage of the i-th converter, X i is the total reactance of the i-th converter, Δδ i is the power angle change of the virtual synchronous machine of the i-th converter;

[0054] When the load changes, the corresponding expression for frequency change with load is:

[0055]

[0056] The active power change equation of the converter is:

[0057] ΔP i =γ i ∫(Δω i -Δω c )dt

[0058] Where γ is the total power angle coefficient, γ=γ1+…+γ n , is the total load change, γ i is the power angle coefficient of the i-th converter, Δω i is the angular frequency change of the output of the i-th converter, Δω c is the angular frequency change at the grid connection point.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The present invention provides a grid-type multi-converter modeling method and system based on sub-microsecond simulation, which takes into account the voltage-frequency support characteristics of the converter and the transient stability of the model during the simulation process, effectively improves the response speed during the transient process, overcomes the lag of the existing model in transient dynamic response, and significantly reduces the power loss under sub-microsecond simulation conditions.

[0061] (2) The grid-type multi-converter model based on sub-microsecond simulation provided by the present invention can better simulate the switching dynamic characteristics of the converter compared with the traditional L / C model.

[0062] (3) The present invention provides a grid-type multi-converter modeling method and system based on sub-microsecond simulation, which improves the system simulation accuracy and efficiency while maintaining system stability, and realizes sub-microsecond high-precision simulation of a new distribution system.

[0063] (4) The present invention provides a modeling method and system for a grid-type multi-converter based on sub-microsecond simulation. The grid-type converter simulates the dynamic characteristics of a synchronous generator, enabling power electronic equipment to have the ability to actively support the voltage and frequency of the grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 is a flow chart of the present invention;

[0065] Figure 2 is a two-level converter model under transient response of the present invention;

[0066] Figure 3 It is a simulation model topology diagram of the present invention;

[0067] Figure 4 This is a comparison diagram of the switching voltage waveforms of the present invention;

[0068] Figure 5 is a comparison diagram of the output power response curve of the present invention;

[0069] Figure 6 This is a comparison diagram of the AC voltage measurement response curve of the present invention;

[0070] Figure 7 is a hardware diagram of an electronic device according to an embodiment. DETAILED DESCRIPTION

[0071] The following is a clear and complete description of the technical solutions in the examples of the present invention, in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. The present invention is further described below with reference to specific embodiments.

[0072] Example 1:

[0073] A modeling method for meshed multi-converter based on sub-microsecond simulation, such as Figure 1 As shown, including:

[0074] The switch model of a single grid-type converter is equivalent to the switch on and off states. By discretizing the switch elements, a generalized constant admittance switch model based on the LC equivalent circuit is constructed.

[0075] The equivalent admittance Y of the generalized constant admittance switch model is ensured to be equal in both the on and off states, so that the converter has an ideal response characteristic under steady-state conditions. Under the ideal response characteristic, the discrete system state matrix of a single grid-type converter is obtained by sorting and completing the modeling of the single grid-type converter. The state matrix consists of the voltage coefficient α and the current coefficient β.

[0076] The discrete system state matrix of a single grid-type converter is derived to extend to a multi-converter system. Combined with the dynamic coupling characteristics of the grid-type multi-converter, the discrete system state matrix of n grid-type converters is obtained. This is simplified to obtain the simplified discrete system state matrix of n grid-type converters, completing the modeling of a single integrated grid-type multi-converter.

[0077] Based on the single integrated grid-type multi-converter model and combined with the inertia characteristics of the virtual synchronous generator, the control pulse signal is obtained, the control system model is improved, and a complete grid-type multi-converter system model is constructed.

[0078] Based on the established system model, a simulation model of the grid-type multi-converter system was built in PSCAD / EMTDC, and compared and verified with the multi-converter system based on the traditional L / C model at a sub-microsecond simulation step.

[0079] Furthermore, the equivalent admittance Y of the generalized constant admittance switch model is ensured to be equal in the on and off states, so that the converter has an ideal response characteristic under steady-state conditions. Under the ideal response characteristic, the discrete system state matrix of the single-unit grid-type converter is obtained by sorting out, and the modeling of the single-unit grid-type converter is completed. The specific method is as follows:

[0080] When the equivalent admittance Y of the generalized constant admittance switch model in the on and off states is equal, the converter energy storage and voltage stabilization components are considered as independent power sources during the transient process of the switch model to obtain the specific equivalent admittance condition.

[0081] Based on the switch equivalent admittance condition, in a single converter, the independent half-bridge circuits in the single-phase and three-phase full-bridge circuits are analyzed, and the voltage-current relationship equation is obtained through KCL. After the equation is organized into a voltage-current relationship state equation, the discrete system state matrix of a single grid-type converter is obtained.

[0082] Furthermore, the specific equivalent admittance condition is:

[0083]

[0084] Where: L p is the filter inductor; C p For the voltage stabilizing capacitor.

[0085] Furthermore, the voltage-current relationship equation and the voltage-current relationship state equation are respectively:

[0086]

[0087] Where: t represents the present time, t-Δt represents the time Δt ago; U c1 、U c2 is the capacitor voltage; I h1 , I h2 are the upper and lower arm currents respectively; U1 and U2 are the upper and lower arm voltages respectively; Y0 is the equivalent admittance; U0 is the midpoint voltage of the bridge arm; I0 is the inductor current; I1(t) and I2(t) are the output currents of the upper and lower arms respectively; α is the voltage coefficient under different states; β is the current coefficient under different states, A is the system state matrix, B is the control matrix; C is the constant matrix.

[0088] Furthermore, the discrete system state matrix of the single converter can be obtained according to the voltage-current relationship state equation:

[0089]

[0090] According to the above formula, the smaller the spectrum radius of A, the faster the system transient response. When the spectrum radius of A is less than 1, the system is stable. When the spectrum radius is greater than 1, the system is unstable. The two-level converter model under transient response is as follows: Figure 2 shown.

[0091] Furthermore, the discrete system state matrix of a single grid-type converter is derived to extend to a multi-converter system. Combined with the dynamic coupling characteristics of the grid-type multi-converter, the discrete system state matrix of n grid-type converters is obtained. This is simplified to obtain the simplified discrete system state matrix of n grid-type converters, completing the modeling of a single integrated grid-type multi-converter. Specifically, the following steps are involved:

[0092] Through the state equation of the voltage and current relationship of a single converter, it is deduced that when n converters are connected in parallel, the state equation of the relationship is:

[0093]

[0094] Among them, U 11 、U 21 ,…,U n1 are the upper arm voltages of the 1st, 2nd, ..., nth converters respectively; I 11 , I 21 ,…,I n2 are the lower arm currents of the 1st, 2nd, ..., nth converters respectively; A n is the discrete system state matrix, C n is a constant matrix;

[0095] When n converters are connected in parallel, the voltage at the grid connection point is determined by the output currents of the two converters, which has the dynamic coupling characteristic of voltage coupling.

[0096] The discrete system state matrix A of n grid-type converters is obtained by using the voltage-current relationship state equations of multiple converters and considering the dynamic coupling characteristics. n for:

[0097]

[0098] Where: α1, α2, …, α n are the current conduction coefficients of the first, second, ..., nth converters, β1, β2, ..., β n are the voltage turn-off coefficients of the 1st, 2nd, ..., nth converters respectively; L i 、R i are the line inductance and resistance of the i-th converter respectively;

[0099] Assuming the line impedance is infinite, the simplified discrete system state matrix of n grid-type converters is expressed as:

[0100]

[0101] Let α1=…=α n =α * , β1=…=β n =β* , and the line inductance and resistance of each converter are equal, the state matrix A n When the absolute value of the characteristic root reaches the maximum, the system is stable. * , β * is the optimal parameter, and the corresponding historical current source expression is:

[0102] I h_on (t) = α * Y sw U(t-Δt)-I(t-Δt)

[0103] I h_off (t) = Y sw U(t-Δt)+β * I(t-Δt)

[0104] At this time, the historical current source parameters are the optimal parameters of the multi-converter switch model.

[0105] Furthermore, based on the single integrated grid-type multi-converter model and combined with the inertia characteristics of the virtual synchronous generator, the control pulse signal is obtained, the control system model is improved, and a complete grid-type multi-converter system model is constructed, which specifically includes:

[0106] Collect the converter output voltage and current in real time, calculate the instantaneous active power and reactive power, and use them as the input of the virtual synchronous generator;

[0107] In combination with the inertia characteristics of the virtual synchronous generator, the vector value of the output electromotive force is calculated based on the calculated instantaneous active power and reactive power, and by adopting virtual synchronous generator control, including virtual active power-frequency control and virtual reactive power-voltage control. The calculated output electromotive force vector value is used as input, and the grid reference signal is aligned through coordinate transformation. The dynamic performance is optimized under dual closed-loop control of current loop and voltage loop.

[0108] Input the parameters after dynamic performance optimization into the PWM module to generate pulse signals to control the switching state of the converter;

[0109] Build a complete grid-type multi-converter system model.

[0110] Furthermore, the virtual reactive power-voltage control method is:

[0111]

[0112] Where, P' is the input active power; P ref is the input active power reference value; P0 is the electromagnetic power; ω is the actual angular velocity; ω refis the angular velocity reference value; J is the virtual moment of inertia; D is the damping coefficient; δ is the power angle of the virtual synchronous machine; Δθ is the power angle change; K a is the frequency adjustment coefficient, that is, K a =-ΔP / Δω, where ΔP is the change in output active power; is the change in angular frequency.

[0113] Furthermore, the virtual reactive power-voltage control method is:

[0114]

[0115] Where, E is the electromotive force output by the virtual synchronous generator control; K s is the integral coefficient; K b is the voltage regulation coefficient, i.e. K b =-ΔQ / ΔU, where ΔQ is the change in output reactive power; ΔU is the change in output voltage, U ref is the output voltage reference value; Q0 is the output reactive power; Q ref is the output reactive power reference value.

[0116] Furthermore, the real-time acquisition of the converter output voltage and current, calculation of the instantaneous active power and reactive power, and the calculation of the instantaneous active power as the input of the virtual synchronous generator need to consider the impact of multiple grid-connected converters connected in parallel in a high-impedance grid environment and changes in load when calculating the instantaneous active power, specifically:

[0117] In a high-impedance grid environment, when the line impedance is inductive, the active power change equation of the converter is:

[0118]

[0119] Where, E c is the voltage at the grid connection point, E i is the output voltage of the i-th converter, X i is the total reactance of the i-th converter, Δδ i is the power angle change of the virtual synchronous machine of the i-th converter;

[0120] When the load changes, the corresponding expression for frequency change with load is:

[0121]

[0122] The active power change equation of the converter is:

[0123] ΔP i =γ i ∫(Δω i -Δω c )dt

[0124] Where γ is the total power angle coefficient, γ=γ1+…+γ n , is the total load change, γ i is the power angle coefficient of the i-th converter, Δω i is the angular frequency change of the output of the i-th converter, Δω c is the angular frequency change at the grid connection point.

[0125] Furthermore, the present invention also includes a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the method described above is implemented.

[0126] The present invention also includes a storage medium on which a computer program is stored. When the computer program is executed by a processor, the method described above is implemented.

[0127] The simulation model of the grid-type multi-converter system in this implementation case is as follows Figure 3 As shown in Figure 1, the simulation model's main circuit uses a three-phase bridge circuit, creating a system simulation model containing 10 three-phase converter circuits. Due to the high switching frequency of the multiple converters, the simulation step size was set to 900 ns for each model, achieving a sub-microsecond simulation step size, and the simulation time was set to 0.8 s. All models were assigned the same parameters, as shown in Table 1.

[0128] Table 1 Simulation specific parameters

[0129]

[0130] Based on the proposed sub-microsecond simulation-based modeling method and system for a grid-type multi-converter, a simulation of Case 1 was performed in PSCAD. To demonstrate the superiority and accuracy of the proposed model (FAS), it was compared with the binary resistor switch model (PSCAD) and the traditional L / C switch model (LC) used in the PSCAD simulation software.

[0131] like Figure 4 As shown, during switching, the LC model exhibits a higher instantaneous switch voltage peak, indicating a larger error. Runtime results show that the LC model returns to steady state after switching in approximately 17.1 μs, while the FAS model takes approximately 6.3 μs, a 63% improvement in recovery time. This indicates that the FAS model converges faster. Furthermore, the figure shows that the FAS model is closer to the PSCAD model and better simulates the dynamic characteristics of an ideal switch than the LC model.

[0132] During the operation of the grid-type multi-converter system, the output power response curve is as follows: Figure 5As shown in the figure, the active power increases slowly and finally stabilizes at 0.4MW, which shows that the virtual synchronous generator control strategy can achieve effective power control and keep the system in a stable state.

[0133] Furthermore, a three-phase short-circuit fault (0.4s to 0.42s) was added to a converter in the original system. When the fault occurred, power rapidly decreased. After the fault was cleared at 0.42s, the LC model recovered to steady state in approximately 22.533ms, while the FAS model recovered in approximately 20.723ms, an improvement of approximately 8%. This indicates that the FAS model achieves faster output power convergence. Furthermore, the FAS model exhibits smaller active power errors, better aligning with the PSCAD model.

[0134] If at t = 0.3s, a 0.2MW active power step is given to the system; at t = 0.5s, the active power step is removed. Figure 6 Figure 2 shows the voltage response curve for the AC side of the converter phase A. As can be seen from the figure, after the system is disturbed 0.3 seconds later, the voltage drops rapidly. However, under the grid-based control strategy, the voltage quickly responds and returns to a stable state. Furthermore, the AC side output voltage waveform of the FAS model is closer to that of the PSCAD model, indicating that the established converter model has good accuracy in terms of voltage support response.

[0135] According to the relative error formula, the accuracy of the LC model is 96.05%, and the accuracy of the FAS is 98.12%, as shown in Table 2. The FAS model in this case adopts a generalized constant admittance switch modeling method based on the LC equivalent circuit. Its parameter settings are independent and not affected by external conditions. Compared with the LC model, this model has lower losses during the simulation process. At the same time, combined with the inertia characteristics of the virtual synchronous generator, it can more accurately simulate the dynamic response of the multi-converter system and accurately reflect the operating characteristics of the grid-type multi-converter system, showing high simulation accuracy. In addition, the FAS model has a significant advantage in simulation time, which can significantly shorten the simulation time and thus improve simulation efficiency.

[0136] Table 2 Comparison of simulation models

[0137]

[0138] See also Figure 7 , refer to the following Figure 7 An electronic device 40 according to this embodiment of the present invention will be described. Figure 7 The electronic device 40 shown is only an example and should not limit the functionality and scope of use of the embodiments of the present invention.

[0139] like Figure 7As shown, the electronic device 40 is a general-purpose computing device. Components of the electronic device 40 may include, but are not limited to, at least one processing unit 41, at least one storage unit 42, and a bus 43 connecting different system components (including the storage unit 42 and the processing unit 41).

[0140] The storage unit stores program codes, which can be executed by the processing unit 41, so that the processing unit 41 performs the steps according to various exemplary embodiments of the present invention described in the above “Example Method” section of this specification.

[0141] The storage unit 42 may include a readable medium in the form of a volatile storage unit, such as a random access memory unit (RAM) 421 and / or a cache memory unit 422 , and may further include a read-only memory unit (ROM) 423 .

[0142] The storage unit 42 may also include a program / utility 424 having a set (at least one) of program modules 425, such program modules 425 including but not limited to: an operating system, one or more application programs, other program modules, and program data, each of which or some combination may include an implementation of a network environment.

[0143] Bus 43 may represent one or more of several types of bus structures, including a memory unit bus or memory unit controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.

[0144] The electronic device 40 may also communicate with one or more external devices (e.g., keyboards, pointing devices, Bluetooth devices, etc.), one or more devices that enable a user to interact with the electronic device 40, and / or any device that enables the electronic device 40 to communicate with one or more other computing devices (e.g., routers, modems, etc.). Such communication may be performed via an input / output (I / O) interface 44. Furthermore, the electronic device 40 may also communicate with one or more networks (e.g., a local area network (LAN), a wide area network (WAN), and / or a public network, such as the Internet) via a network adapter 45. Figure 7 As shown, the network adapter 45 communicates with other modules of the electronic device 40 via the bus 43. Figure 7 Not shown, other hardware and / or software modules may be used in conjunction with the electronic device 40, including but not limited to microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup planning systems.

[0145] Through the description of the above embodiments, it is easy for those skilled in the art to understand that the example embodiments described herein can be implemented by software or by combining software with necessary hardware. Therefore, the technical solution according to the embodiments of the present disclosure can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (which can be a CD-ROM, a USB flash drive, a mobile hard disk, etc.) or on a network, and includes several instructions to enable a computing device (which can be a personal computer, a server, a terminal device, or a network device, etc.) to execute the method according to the embodiments of the present disclosure.

[0146] Finally, it should be noted that the computer simulation model can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for executing on the computer or other programmable device to implement the process. Figure 1 The steps of a specified function in a process or multiple processes.

[0147] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modeling method for a meshed multi-converter based on sub-microsecond simulation, characterized in that: include: The switch model of a single grid-type converter is equivalent to the switch on and off states. By discretizing the switch elements, a generalized constant admittance switch model based on the LC equivalent circuit is constructed. The equivalent admittance Y of the generalized constant admittance switch model is ensured to be equal in both the on and off states, so that the converter has an ideal response characteristic under steady-state conditions. Under the ideal response characteristic, the discrete system state matrix of a single grid-type converter is obtained by sorting and completing the modeling of the single grid-type converter. The state matrix consists of the voltage coefficient α and the current coefficient β. The discrete system state matrix of a single grid-type converter is derived to extend to a multi-converter system. Combined with the dynamic coupling characteristics of the grid-type multi-converter, the discrete system state matrix of n grid-type converters is obtained. This is simplified to obtain the simplified discrete system state matrix of n grid-type converters, completing the modeling of a single integrated grid-type multi-converter. Based on the single integrated grid-type multi-converter model and combined with the inertia characteristics of the virtual synchronous generator, the control pulse signal is obtained, the control system model is improved, and a complete grid-type multi-converter system model is constructed. Based on the established system model, a simulation model of the grid-type multi-converter system was built in PSCAD / EMTDC, and compared and verified with the multi-converter system based on the traditional L / C model at a sub-microsecond simulation step.

2. A meshed multi-converter modeling method based on sub-microsecond simulation according to claim 1, characterized in that: The equivalent admittance Y of the generalized constant admittance switch model is ensured to be equal in the on and off states, so that the converter has an ideal response characteristic under steady-state conditions. Under the ideal response characteristic, the discrete system state matrix of the single-unit grid-type converter is obtained by sorting out, and the modeling of the single-unit grid-type converter is completed. The specific method is as follows: When the equivalent admittance Y of the generalized constant admittance switch model in the on and off states is equal, the converter energy storage and voltage stabilization components are considered as independent power sources during the transient process of the switch model to obtain the specific equivalent admittance condition. Based on the specific switch equivalent admittance conditions, in a single converter, the independent half-bridge circuits in the single-phase and three-phase full-bridge circuits are analyzed, and the voltage-current relationship equation is obtained through KCL. After the equation is organized into a voltage-current relationship state equation, the discrete system state matrix of a single grid-type converter is obtained.

3. The method for modeling a meshed multi-converter based on sub-microsecond simulation according to claim 2, characterized in that: The specific equivalent admittance condition is: Where: L p is the filter inductor; C p For the voltage stabilizing capacitor.

4. A meshed multi-converter modeling method based on sub-microsecond simulation according to claim 3, characterized in that: The voltage-current relationship equation and the voltage-current relationship state equation are respectively: Where: t represents the present time, t-Δt represents the time Δt ago; U c1 、U c2 is the capacitor voltage; I h1 , I h2 are the upper and lower arm currents respectively; U1 and U2 are the upper and lower arm voltages respectively; Y0 is the equivalent admittance; U0 is the midpoint voltage of the bridge arm; I0 is the inductor current; I1(t) and I2(t) are the output currents of the upper and lower arms respectively; α is the voltage coefficient under different states; β is the current coefficient under different states, A is the system state matrix, B is the control matrix; C is the constant matrix.

5. The method for modeling a meshed multi-converter based on sub-microsecond simulation according to claim 2, characterized in that: The discrete system state matrix of the single converter can be obtained according to the voltage-current relationship state equation: According to the above formula, the smaller the spectral radius of A, the faster the transient response of the system. When the spectral radius of A is less than 1, the system is stable, and when the spectral radius is greater than 1, the system is unstable.

6. The method for modeling a meshed multi-converter based on sub-microsecond simulation according to claim 1, characterized in that: The discrete system state matrix of a single grid-type converter is derived to extend to a multi-converter system. Combined with the dynamic coupling characteristics of the grid-type multi-converter, the discrete system state matrix of n grid-type converters is obtained. This matrix is ​​simplified to obtain the simplified discrete system state matrix of n grid-type converters, completing the modeling of a single integrated grid-type multi-converter. Specifically, the following steps are involved: Based on the state equation of the voltage-current relationship of a single converter, it is deduced that when n converters are connected in parallel, the state equation of the voltage-current relationship of multiple converters is: Among them, U 11 、U 21 ,…,U n1 are the upper arm voltages of the 1st, 2nd, ..., nth converters respectively; I 11 , I 21 ,…,I n2 are the lower arm currents of the 1st, 2nd, ..., nth converters respectively; A n is the discrete system state matrix, C n is a constant matrix; When n converters are connected in parallel, the voltage at the grid connection point is determined by the output currents of the two converters, which has the dynamic coupling characteristic of voltage coupling. The discrete system state matrix A of n grid-type converters is obtained by using the voltage-current relationship state equations of multiple converters and considering the dynamic coupling characteristics. n for: Where: α1, α2, …, α n are the current conduction coefficients of the first, second, ..., nth converters, β1, β2, ..., β n are the voltage turn-off coefficients of the 1st, 2nd, ..., nth converters respectively; L i 、R i are the line inductance and resistance of the i-th converter respectively; Assuming the line impedance is infinite, the simplified discrete system state matrix of n grid-type converters is expressed as: Let α1=…=α n =α * , β1=…=β n =β * , and the line inductance and resistance of each converter are equal, the state matrix A n When the absolute value of the characteristic root reaches the maximum, the system is stable. * , β * is the optimal parameter, and the corresponding historical current source expression is: I h_on (t)=α * Y sw U(t-Δt)-I(t-Δt) I h_off (t)=Y sw U(t-Δt)+β * I(t-Δt) At this time, the historical current source parameters are the optimal parameters of the multi-converter switch model.

7. The method for modeling a meshed multi-converter based on sub-microsecond simulation according to claim 1, characterized in that: Based on the single integrated grid-type multi-converter model and combined with the inertia characteristics of the virtual synchronous generator, the control pulse signal is obtained, the control system model is improved, and a complete grid-type multi-converter system model is constructed. Specifically, it includes: Collect the converter output voltage and current in real time, calculate the instantaneous active power and reactive power, and use them as the input of the virtual synchronous generator; In combination with the inertia characteristics of the virtual synchronous generator, the vector value of the output electromotive force is calculated based on the calculated instantaneous active power and reactive power, and by adopting virtual synchronous generator control, including virtual active power-frequency control and virtual reactive power-voltage control. The calculated output electromotive force vector value is used as input, and the grid reference signal is aligned through coordinate transformation. The dynamic performance is optimized under dual closed-loop control of current loop and voltage loop. Input the parameters after dynamic performance optimization into the PWM module to generate pulse signals to control the switching state of the converter; Build a complete grid-type multi-converter system model.

8. The method for modeling a meshed multi-converter based on sub-microsecond simulation according to claim 7, characterized in that: The virtual reactive power-voltage control method is: Where, P' is the input active power; P ref is the input active power reference value; P0 is the electromagnetic power; ω is the actual angular velocity; ω ref is the angular velocity reference value; J is the virtual moment of inertia; D is the damping coefficient; δ is the power angle of the virtual synchronous machine; Δθ is the power angle change; K a is the frequency adjustment coefficient, that is, K a =-ΔP / Δω, where ΔP is the change in output active power; is the change in angular frequency.

9. The method for modeling a meshed multi-converter based on sub-microsecond simulation according to claim 7, characterized in that: The virtual reactive power-voltage control method is: Where, E is the electromotive force output by the virtual synchronous generator control; K s is the integral coefficient; K b is the voltage regulation coefficient, i.e. K b =-ΔQ / ΔU, where ΔQ is the change in output reactive power; ΔU is the change in output voltage, U ref is the output voltage reference value; Q0 is the output reactive power; Q ref is the output reactive power reference value.

10. The method for modeling a meshed multi-converter based on sub-microsecond simulation according to claim 7, characterized in that: The real-time acquisition of the converter output voltage and current, calculation of instantaneous active power and reactive power, and the calculation of instantaneous active power as the input of the virtual synchronous generator need to consider the impact of multiple grid-type converters connected in parallel in a high-impedance grid environment and load changes. Specifically: In a high-impedance grid environment, when the line impedance is inductive, the active power change equation of the converter is: Where, E c is the voltage at the grid connection point, E i is the output voltage of the i-th converter, X i is the total reactance of the i-th converter, Δδ i is the power angle change of the virtual synchronous machine of the i-th converter; When the load changes, the corresponding expression for frequency change with load is: The active power change equation of the converter is: ΔP i =c i ∫(See i -See c )dt Where γ is the total power angle coefficient, γ=γ1+…+γ n , is the total load change, γ i is the power angle coefficient of the i-th converter, Δω i is the angular frequency change of the output of the i-th converter, Δω c is the angular frequency change at the grid connection point.

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