A network-configuration type multi-converter modeling method based on sub-microsecond simulation

Abstract

This invention discloses a modeling method for grid-type multi-converter based on sub-microsecond simulation, belonging to the field of converter modeling and simulation technology. The method involves discretizing the switching elements to construct a generalized constant admittance switching model based on the LC equivalent circuit. Then, by discretizing the system state matrix, an extended modeling from a single converter to a multi-converter system is achieved. Furthermore, by combining the inertia characteristics of a virtual synchronous generator, a complete grid-type multi-converter model including control elements is established. Finally, a simulation model of the grid-type multi-converter system is built in PSCAD / EMTDC, verifying the correctness and effectiveness of the method. This invention demonstrates good applicability and stability in integrating the generalized constant admittance switching model with the inertia characteristics of a virtual synchronous generator at a sub-microsecond simulation step size. It significantly improves the simulation accuracy and efficiency while achieving rapid convergence of transient processes in the grid-type multi-converter and active support for grid voltage and frequency.

Description

Technical Field

[0001] This invention relates to the technical field of converter modeling and simulation, and in particular to a method for modeling network-type multi-converter based on sub-microsecond simulation. Background Technology

[0002] Against the backdrop of increasing electricity demand and intensifying environmental pressures, the application scenarios for new energy sources and power electronic equipment are expanding rapidly. Multi-converter systems, with their higher generation capacity and power electronic equipment utilization rates, are gradually replacing traditional synchronous generator-dominated distribution systems. However, current converter control mostly employs grid-following (GFL) strategies, whose synchronization relies on phase-locked loops (PLLs), which can easily lead to stability issues in weak grid environments. Therefore, in grids with low physical inertia, grid-forming (GFM) control is more suitable. This method achieves autonomous synchronization without PLLs, 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 converters to support the grid in a timely manner during voltage and frequency fluctuations. However, its transient stability still has certain limitations, making it crucial to improve its dynamic response capability. Currently, modeling of converter switching processes often employs L / C equivalent circuits or binary resistor models. These methods require recalculating the admittance matrix for each switching state change, significantly increasing the computational complexity of multi-converter systems. Furthermore, transient errors during switching can easily lead to additional power losses, reducing system response speed and making the system susceptible to external circuit influences, thus weakening real-time simulation accuracy. As the switching frequencies of new power electronic switching devices continue to increase, the additional losses during switching processes also gradually increase. Traditional modeling methods struggle to accurately characterize switching transient processes at sub-microsecond simulation steps, limiting the system's ability to rapidly support the grid's inertial demands.

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

[0005] To address the shortcomings of existing technologies, this invention discloses a modeling method for grid-type multi-converters based on sub-microsecond simulation. This method constructs a generalized switching constant admittance model based on LC equivalent circuit for grid-type converters, and combines the inertia characteristics of virtual synchronous generators to achieve accurate modeling of multi-converters. This solves the problems of slow response speed and low simulation accuracy of existing models during transient processes, and significantly reduces the power loss generated in sub-microsecond simulations.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A modeling method for network-type multi-converters based on sub-microsecond simulation includes:

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

[0009] To ensure that the equivalent admittance Y of the generalized constant admittance switch model is equal in the on and off states, the converter has ideal response characteristics under steady-state conditions. Under ideal response characteristics, the discrete system state matrix of a single grid-type converter is obtained by sorting, and the modeling of the single grid-type converter is completed. This state matrix consists of voltage coefficient α and current coefficient β.

[0010] The discrete system state matrix of a single grid-type converter is extended 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 then simplified to obtain the simplified discrete system state matrix of n grid-type converters, thus completing the modeling of a single integrated grid-type multi-converter.

[0011] Based on the single-unit integrated grid-type multi-converter model, the inertia characteristics of the virtual synchronous generator are combined to obtain the control pulse signal, improve the control system model, and construct a complete grid-type multi-converter system model.

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

[0013] Furthermore, to ensure that the equivalent admittance Y of the generalized constant admittance switch model is equal in both the on and off states, the converter possesses ideal response characteristics under steady-state conditions. Under these ideal response characteristics, the discrete system state matrix of a single grid-type converter is obtained through simplification, thus completing the modeling of the single grid-type converter. The specific method is as follows:

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

[0015] Based on the equivalent admittance condition of the switch, the independent half-bridge circuits in the single-phase and three-phase full-bridge circuits of a single converter are analyzed. The voltage-current relationship equation is obtained through KCL. After the equation is rearranged into the 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 as follows:

[0017]

[0018] In the formula: L p For filter inductance; C p It is a voltage regulator capacitor.

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

[0020]

[0021] In the formula: t represents the current time, t-Δt represents the time before Δt; U c1 U c2 I is the capacitor voltage; h1 I h2 U1 and U2 are the upper and lower bridge arm currents, respectively; U0 is the equivalent admittance; U0 is the bridge arm midpoint voltage; I0 is the inductor current; I1(t) and I2(t) are the upper and lower bridge arm output currents, 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; and C is the constant matrix.

[0022] Furthermore, the discrete system state matrix of the single converter can be obtained from 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 extended to a multi-converter system. Combining this 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 then 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 system. Specifically, this includes:

[0026] By using the voltage-current relationship state equation for a single converter, the relationship state equation for n converters connected in parallel is derived as follows:

[0027]

[0028] Among them, U 11 U 21 、…、U n1These represent the upper bridge arm voltages of the 1st, 2nd, ..., nth converters, respectively; I 11 I 21 ... I n2 These are the lower bridge arm currents of the 1st, 2nd, ..., nth converters, respectively; A n Let C be the state matrix of the discrete system. n It is a constant matrix;

[0029] When n converters are connected in parallel, the voltage at the grid connection point is determined by the output current of the two converters, exhibiting dynamic coupling characteristics of voltage coupling.

[0030] By applying the state equations relating the voltage and current of multiple converters and considering dynamic coupling characteristics, the discrete system state matrix A of n grid-type converters is obtained. n for:

[0031]

[0032] Where: α1, α2, ..., α n Let β1, β2, ..., βn be the current conduction coefficients of the 1st, 2nd, ..., nth converters, respectively. n These are the voltage turn-off coefficients for the 1st, 2nd, ..., nth converters, respectively. L i R i These 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 can be represented as follows:

[0034]

[0035] Let α1 = ... = α n =α * , β1=…=β n =β * Furthermore, the line inductance and resistance of each converter are equal, and the state matrix A n The system is stable when the absolute value of the eigenvalues ​​reaches its maximum, at which point α * β * For the optimal parameters, 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 point, the historical current source parameters are the optimal parameters for the multi-converter switching model.

[0039] Furthermore, based on the single-unit integrated grid-type multi-converter model, and combined with the inertia characteristics of a virtual synchronous generator, control pulse signals are obtained to improve the control system model, thus constructing a complete grid-type multi-converter system model, specifically including:

[0040] The converter output voltage and current are collected in real time, and the instantaneous active power and reactive power are calculated and used as inputs for the virtual synchronous generator.

[0041] Combining the inertia characteristics of a virtual synchronous generator, based on the calculated instantaneous active and reactive power, and by employing virtual synchronous generator control, including virtual active-frequency control and virtual reactive-voltage control, the vector value of the output electromotive force is calculated. The calculated vector value of the output electromotive force 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] The optimized dynamic performance parameters are input into the PWM module to generate pulse signals and control the switching state of the converter.

[0043] Construct a complete network-type multi-converter system model.

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

[0045]

[0046] In the formula, P′ represents the input active power; P ref P0 is the input active power reference value; ω is the electromagnetic power; ω is the actual angular velocity; ref Angular velocity reference value; J is virtual moment of inertia; D is damping coefficient; δ is the power angle of the virtual synchronizer; Δθ is the power angle variation; K a K is the frequency adjustment coefficient. a = -ΔP / Δω, where ΔP is the change in output active power; This represents the change in angular frequency.

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

[0048]

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

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

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

[0052]

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

[0054] When the load changes, the expression for the frequency change with the 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 , For the total load change, γ i Let Δω be the power angle coefficient of the i-th converter. i Let Δω be the angular frequency change of the i-th converter output. c This represents the change in angular frequency 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 modeling method and system for a network-type multi-converter based on sub-microsecond simulation, which takes into account the voltage and 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 the transient dynamic response, and significantly reduces the power loss under sub-microsecond simulation conditions.

[0061] (2) The network-type multi-converter model based on sub-microsecond simulation provided by this 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 modeling method and system for network-type multi-converter 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 new power distribution systems.

[0063] (4) The present invention provides a modeling method and system for grid-type multi-converters based on sub-microsecond simulation. The grid-type converter enables power electronic equipment to actively support grid voltage and frequency by simulating the dynamic characteristics of synchronous generators. Attached Figure Description

[0064] Figure 1 This is a flowchart of the present invention;

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

[0066] Figure 3 This 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 This is a comparison chart of the output power response curves of the present invention;

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

[0070] Figure 7 This is a hardware diagram of an electronic device according to an embodiment. Detailed Implementation

[0071] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. The present invention will be further described below with reference to specific embodiments.

[0072] Example 1:

[0073] A modeling method for network-type multi-converters based on sub-microsecond simulation, such as Figure 1 As shown, it includes:

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

[0075] To ensure that the equivalent admittance Y of the generalized constant admittance switch model is equal in the on and off states, the converter has ideal response characteristics under steady-state conditions. Under ideal response characteristics, the discrete system state matrix of a single grid-type converter is obtained by sorting, and the modeling of the single grid-type converter is completed. This state matrix consists of voltage coefficient α and current coefficient β.

[0076] The discrete system state matrix of a single grid-type converter is extended 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 then simplified to obtain the simplified discrete system state matrix of n grid-type converters, thus completing the modeling of a single integrated grid-type multi-converter.

[0077] Based on the single-unit integrated grid-type multi-converter model, the inertia characteristics of the virtual synchronous generator are combined to obtain the control pulse signal, improve the control system model, and construct a complete grid-type multi-converter system model.

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

[0079] Furthermore, to ensure that the equivalent admittance Y of the generalized constant admittance switch model is equal in both the on and off states, the converter possesses ideal response characteristics under steady-state conditions. Under these ideal response characteristics, the discrete system state matrix of a single grid-type converter is obtained through simplification, thus completing the modeling of the single grid-type converter. The specific method is as follows:

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

[0081] Based on the equivalent admittance condition of the switch, the independent half-bridge circuits in the single-phase and three-phase full-bridge circuits of a single converter are analyzed. The voltage-current relationship equation is obtained through KCL. After the equation is rearranged into the 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 as follows:

[0083]

[0084] In the formula: L p For filter inductance; C p It is a voltage regulator capacitor.

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

[0086]

[0087] In the formula: t represents the current time, t-Δt represents the time before Δt; U c1 U c2 I is the capacitor voltage; h1 I h2 U1 and U2 are the upper and lower bridge arm currents, respectively; U0 is the equivalent admittance; U0 is the bridge arm midpoint voltage; I0 is the inductor current; I1(t) and I2(t) are the upper and lower bridge arm output currents, 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; and C is the constant matrix.

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

[0089]

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

[0091] Furthermore, the discrete system state matrix of a single grid-type converter is extended to a multi-converter system. Combining this 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 then 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 system. Specifically, this includes:

[0092] By using the voltage-current relationship state equation for a single converter, the relationship state equation for n converters connected in parallel is derived as follows:

[0093]

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

[0095] When n converters are connected in parallel, the voltage at the grid connection point is determined by the output current of the two converters, exhibiting dynamic coupling characteristics of voltage coupling.

[0096] By applying the state equations relating the voltage and current of multiple converters and considering dynamic coupling characteristics, the discrete system state matrix A of n grid-type converters is obtained. n for:

[0097]

[0098] Where: α1, α2, ..., α n Let β1, β2, ..., βn be the current conduction coefficients of the 1st, 2nd, ..., nth converters, respectively. n These are the voltage turn-off coefficients for the 1st, 2nd, ..., nth converters, respectively. L i R i These 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 can be represented as follows:

[0100]

[0101] Let α1 = ... = α n =α * , β1=…=β n =β* Furthermore, the line inductance and resistance of each converter are equal, and the state matrix A n The system is stable when the absolute value of the eigenvalues ​​reaches its maximum, at which point α * β * For the optimal parameters, 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 point, the historical current source parameters are the optimal parameters for the multi-converter switching model.

[0105] Furthermore, based on the single-unit integrated grid-type multi-converter model, and combined with the inertia characteristics of a virtual synchronous generator, control pulse signals are obtained to improve the control system model, thus constructing a complete grid-type multi-converter system model, specifically including:

[0106] The converter output voltage and current are collected in real time, and the instantaneous active power and reactive power are calculated and used as inputs for the virtual synchronous generator.

[0107] Combining the inertia characteristics of a virtual synchronous generator, based on the calculated instantaneous active and reactive power, and by employing virtual synchronous generator control, including virtual active-frequency control and virtual reactive-voltage control, the vector value of the output electromotive force is calculated. The calculated vector value of the output electromotive force 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] The optimized dynamic performance parameters are input into the PWM module to generate pulse signals and control the switching state of the converter.

[0109] Construct a complete network-type multi-converter system model.

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

[0111]

[0112] In the formula, P′ represents the input active power; P ref P0 is the input active power reference value; ω is the electromagnetic power; ω is the actual angular velocity; refAngular velocity reference value; J is virtual moment of inertia; D is damping coefficient; δ is the power angle of the virtual synchronizer; Δθ is the power angle variation; K a K is the frequency adjustment coefficient. a = -ΔP / Δω, where ΔP is the change in output active power; This represents the change in angular frequency.

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

[0114]

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

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

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

[0118]

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

[0120] When the load changes, the expression for the frequency change with the 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 , For the total load change, γ i Let Δω be the power angle coefficient of the i-th converter. i Let Δω be the angular frequency change of the i-th converter output. c This represents the change in angular frequency at the grid connection point.

[0125] Furthermore, the present invention also includes a computer device, comprising 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, it implements the method described above.

[0126] The present invention also includes a storage medium storing a computer program that, when executed by a processor, implements the method described above.

[0127] The simulation model of the network-type multi-converter system in this implementation case is as follows: Figure 3 As shown, the main circuit of the simulation model adopts a three-phase bridge circuit, and a system simulation model containing 10 three-phase converter circuits is built. Due to the high switching frequency of the multiple converters, the simulation step size is set to 900 ns, achieving a sub-microsecond simulation step size, and the simulation time is set to 0.8 s. All models are set with the same parameter conditions; the specific simulation model parameters are shown in Table 1.

[0128] Table 1 Simulation Specific Parameters

[0129]

[0130] According to the present invention, a modeling method and system for network-type multi-converters based on sub-microsecond simulation is proposed, and the simulation of Case 1 is performed in PSCAD. In order to demonstrate the superiority and accuracy of the proposed model (FAS), it is compared with the binary resistor switch model (PSCAD) and the traditional L / C switch model (LC) used by the PSCAD simulation software.

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

[0132] During the operation of a grid-type multi-converter system, the output power response curve is as follows: Figure 5As shown in the figure, the active power slowly increases and eventually stabilizes at 0.4MW. This indicates 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–0.42s) was added to a converter in the original system. Upon the fault, the power decreased rapidly. After the fault was cleared in 0.42s, the steady-state recovery time of the LC model was approximately 22.533ms, while that of the FAS model was approximately 20.723ms, representing an improvement of about 8%. This demonstrates that the FAS model achieves faster output power convergence. Additionally, the FAS model exhibits smaller active power errors, better aligning with the PSCAD model.

[0134] If an active step of 0.2 MW is applied to the system at t = 0.3 s, then the active step is removed at t = 0.5 s. Figure 6 The figure shows the AC side voltage response curve of phase A of the converter. As can be seen from the figure, the voltage drops rapidly after the system is disturbed for 0.3s, but under the grid-type control strategy, the voltage responds quickly and recovers to a steady state. In addition, it can be seen from the figure that 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 model is 98.12%, as shown in Table 2. The FAS model in this case study employs a generalized constant admittance switch modeling method based on the LC equivalent circuit. Its parameter settings are independent and unaffected by external conditions. Compared to the LC model, this model exhibits lower losses during simulation. Furthermore, by incorporating the inertia characteristics of a virtual synchronous generator, it can more accurately simulate the dynamic response of the multi-converter system, accurately reflecting the operating characteristics of the grid-type multi-converter system and demonstrating higher simulation accuracy. In addition, the FAS model has a significant advantage in simulation time, greatly shortening the simulation duration and thus improving simulation efficiency.

[0136] Table 2 Comparison of Simulation Models

[0137]

[0138] Please see Figure 7 See below for reference. Figure 7 To describe an electronic device 40 according to this embodiment of the present invention. Figure 7 The electronic device 40 shown is merely an example and should not impose any limitation on the functionality and scope of use of the embodiments of the present invention.

[0139] like Figure 7As shown, the electronic device 40 is manifested in the form of a general-purpose computing device. The 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 storage unit 42 and processing unit 41).

[0140] The storage unit stores program code, which can be executed by the processing unit 41 to perform the steps described in the "Embodiment Methods" section of this specification according to various exemplary embodiments of the present invention.

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

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

[0143] Bus 43 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0144] Electronic device 40 can also communicate with one or more external devices (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 40, and / or with any device that enables electronic device 40 to communicate with one or more other computing devices (e.g., router, modem, etc.). This communication can be performed through input / output (I / O) interface 44. Furthermore, electronic device 40 can also communicate with one or more networks (e.g., local area network (LAN), wide area network (WAN), and / or public networks, such as the Internet) through network adapter 45. Figure 7 As shown, network adapter 45 communicates with other modules of electronic device 40 via bus 43. It should be understood that, although... Figure 7 As not shown, other hardware and / or software modules may be used in conjunction with 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] From the above description of the embodiments, those skilled in the art will readily understand that the exemplary embodiments described herein can be implemented by software or by combining software with necessary hardware. Therefore, the technical solutions according to the embodiments of this disclosure can be embodied in the form of a software product, which can be stored in a non-volatile storage medium (such as a CD-ROM, USB flash drive, external hard drive, etc.) or on a network, including several instructions to cause a computing device (such as a personal computer, server, terminal device, or network device, etc.) to execute the methods according to the embodiments of this disclosure.

[0146] Finally, it should be noted that this computer simulation model can also be loaded onto a computer or other programmable data processing equipment, causing a series of operational steps to be executed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 Steps of a specified function in one or more processes.

[0147] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions 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 network-type multi-converters based on sub-microsecond simulation, characterized in that, include: The switching model of a single grid-type converter is equivalent to the on and off states of the switch. By discretizing the switching elements, a generalized constant admittance switching model based on the LC equivalent circuit is constructed. To ensure that the equivalent admittance Y of the generalized constant admittance switch model is equal in both the on and off states, the converter exhibits ideal response characteristics under steady-state conditions. Under these ideal response characteristics, the discrete system state matrix of a single-unit grid-connected converter is obtained through simplification, thus completing the modeling of the single-unit grid-connected converter. This state matrix consists of voltage coefficients. Current coefficient constitute; The discrete system state matrix of a single grid-type converter is extended 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 then simplified to obtain the simplified discrete system state matrix of n grid-type converters, thus completing the modeling of a single integrated grid-type multi-converter. Based on a single-unit integrated grid-connected multi-converter model, and incorporating the inertia characteristics of a virtual synchronous generator, control pulse signals are obtained to refine the control system model, thus constructing a complete grid-connected multi-converter system model. Specifically, this includes: real-time acquisition of converter output voltage and current, calculation of instantaneous active and reactive power as input to the virtual synchronous generator; combining the inertia characteristics of the virtual synchronous generator, and based on the calculated instantaneous active and reactive power, using virtual synchronous generator control (including virtual active-frequency control and virtual reactive-voltage control), calculating the vector value of the output electromotive force (EMF), using the calculated output EMF vector value as input, aligning it with the grid reference signal through coordinate transformation, and optimizing dynamic performance under dual closed-loop control of the current and voltage loops; inputting the optimized dynamic performance parameters into the PWM module to generate pulse signals to control the converter switching state; and constructing a complete grid-connected multi-converter system model. Based on the established system model, a simulation model of the network-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 size. The real-time acquisition of converter output voltage and current, and the calculation of instantaneous active and reactive power, are used as inputs to the virtual synchronous generator. When calculating instantaneous active power, the effects of multiple grid-connected converters connected in parallel in a high-impedance grid environment and load changes need to be considered. Specifically: In a high-impedance power grid environment, when the line impedance is inductive, the active power change equation of the converter is: In the formula, E c E is the voltage at the grid connection point. i Let X be the output voltage of the i-th converter. i Let i be the total reactance of the i-th converter. The power angle change of the virtual synchronous machine of the i-th converter; When the load changes, the expression for the frequency change with the load is: The active power change equation of the converter is: Where γ is the total power angle coefficient, γ = γ1 + … + γ n , For the total load change, γ i Let be the power angle coefficient of the i-th converter. The change in angular frequency of the output of the i-th converter. This represents the change in angular frequency at the grid connection point.

2. The method for modeling a network-type multi-converter based on sub-microsecond simulation according to claim 1, characterized in that, To ensure that the equivalent admittance Y of the generalized constant admittance switch model is equal in both the on and off states, the converter exhibits ideal response characteristics under steady-state conditions. Under these ideal response characteristics, the discrete system state matrix of a single grid-connected converter is obtained through simplification, thus completing the modeling of the single grid-connected converter. The specific method is as follows: When the equivalent admittance Y of the generalized constant admittance switching model is equal in the on and off states, the converter energy storage and voltage regulation components are treated as independent power sources during the transient process of the switching model to obtain the specific equivalent admittance conditions. Based on the specific switching equivalent admittance condition, the independent half-bridge circuits in single-phase and three-phase full-bridge circuits are analyzed in a single converter. The voltage-current relationship equation is obtained through KCL. After the equation is rearranged into the voltage-current relationship state equation, the discrete system state matrix of a single grid-type converter is obtained.

3. The method for modeling a network-type multi-converter based on sub-microsecond simulation according to claim 2, characterized in that, The specific equivalent admittance condition is as follows: In the formula: L p For filter inductance; C p Y is the voltage regulator capacitor; Y0 is the equivalent admittance.

4. The method for modeling a network-type multi-converter 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 as follows: In the formula: t represents the current time. U represents the time Δt before; c1 U c2 I is the capacitor voltage; h1 I h2 U1 and U2 are the upper and lower bridge arm currents, respectively; U1 and U2 are the upper and lower bridge arm voltages, respectively; Y0 is the equivalent admittance; U0 is the bridge arm midpoint voltage; I0 is the inductor current; , These are the output currents of the upper and lower bridge arms, respectively. Voltage coefficients under different states; Let A represent the current coefficients under different states, B represent the system state matrix, C represent the control matrix, and C represent the constant matrix.

5. The method for modeling a network-type multi-converter based on sub-microsecond simulation according to claim 2, characterized in that, The discrete system state matrix of the single grid-type converter can be obtained from 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 network-type multi-converter based on sub-microsecond simulation according to claim 1, characterized in that, This paper derives the extension of the discrete system state matrix of a single grid-connected converter to a multi-converter system. Combining this with the dynamic coupling characteristics of the grid-connected multi-converter system, the discrete system state matrix of n grid-connected converters is obtained. This is then simplified to obtain the simplified discrete system state matrix of n grid-connected converters, completing the modeling of a single integrated grid-connected multi-converter system. Specifically, this includes: By using the voltage-current relationship state equation for a single converter, the voltage-current relationship state equation for multiple converters connected in parallel is derived as follows: Among them, U 11 U 21 、…、U n1 These represent the upper bridge arm voltages of the 1st, 2nd, ..., nth converters, respectively; I 11 I 21 ... I n2 These are the lower bridge arm currents of the 1st, 2nd, ..., nth converters, respectively; A n Let C be the state matrix of the discrete system. n It is a constant matrix; When n converters are connected in parallel, the voltage at the grid connection point is determined by the output current of the two converters, exhibiting dynamic coupling characteristics of voltage coupling. By applying the state equations relating the voltage and current of multiple converters and considering dynamic coupling characteristics, the discrete system state matrix A of n grid-type converters is obtained. n for: Where: α1, α2, ..., α n Let β1, β2, ..., βn be the current conduction coefficients of the 1st, 2nd, ..., nth converters, respectively. n These are the voltage turn-off coefficients for the 1st, 2nd, ..., nth converters, respectively. L i R i These 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 can be represented as follows: Let α1 = ... = α n =α * , β1=…=β n =β * Furthermore, the line inductance and resistance of each converter are equal, and the state matrix A n The system is stable when the absolute value of the eigenvalues ​​reaches its maximum, at which point α * β * For the optimal parameters, the corresponding historical current source expression is: At this point, the historical current source parameters are the optimal parameters for the multi-converter switching model.

7. The method for modeling a network-type multi-converter based on sub-microsecond simulation according to claim 1, characterized in that, The virtual active power-frequency control method is as follows: In the formula, P is the input active power; ref P0 is the input active power reference value; ω is the electromagnetic power; ω is the actual angular velocity; ref δ is the reference value for angular velocity; J is the virtual moment of inertia; D is the damping coefficient; δ is the power angle of the virtual synchronizer. For the change of work angle; K a This is the frequency adjustment coefficient, i.e. Where ΔP is the change in output active power; This represents the change in angular frequency.

8. The method for modeling a network-type multi-converter based on sub-microsecond simulation according to claim 1, characterized in that, The virtual reactive power-voltage control method is as follows: In the formula, E is the electromotive force output by the virtual synchronous generator control; K s K is the integral coefficient; b This is the voltage regulation coefficient, i.e. Where ΔQ is the change in output reactive power; ΔU is the change in output voltage, U ref Q is the output voltage reference value; Q0 is the output reactive power; Q ref This is the reference value for output reactive power.

Images