Transient simulation method and device for AC / DC hybrid system including flexible DC grid

Abstract

The present invention provides a method and device for transient simulation of an AC / DC hybrid system including a flexible DC grid, wherein the AC / DC hybrid system including the flexible DC grid includes an AC main grid, a DC and near-region AC grid, and an interface between the DC and near-region AC grid and the AC main grid. The method includes simulating the AC main grid using a large step size based on complex signal modeling with a step size greater than or equal to 1ms and less than or equal to 10ms; simulating the DC and near-region AC grid using a small step size based on real signal modeling with a step size greater than or equal to 10us and less than or equal to 50us; and converting complex signals into real signals at the interface between the DC and near-region AC grid and the AC main grid using Parker transformation to achieve conversion of simulation variables between the AC main grid and the DC and near-region AC grid. The present invention uses large and small step sizes and interface signal conversion to achieve efficient transient simulation of the AC / DC hybrid system including the flexible DC grid.

Description

Technical Field

[0001] The present invention relates to the technical field of power simulation, and in particular to a method and device for transient simulation of an AC / DC hybrid system including a flexible DC power grid. Background Art

[0002] Currently, there is no analytical method to accurately assess the safety and stability of large-scale AC / DC power systems including flexible DC grids. Therefore, power system controller design, planning, and operational research rely heavily on time-domain simulation of power systems. Fault dynamics in flexible DC grids are influenced by the switching processes of power electronic devices and controllers, and have relatively small timescales, making them difficult to accurately characterize using traditional electromechanical transient simulation. Electromagnetic transient simulation, however, can accurately simulate power system dynamics at microsecond scales and above, and is widely used in the design and operation of AC / DC power systems.

[0003] Traditional electromagnetic transient simulation programs suffer from very low simulation efficiency when simulating large-scale AC / DC systems that include flexible DC grids. This is primarily due to three reasons. First, the small time scales of DC devices and other components in the system necessitate a very small step size during simulation. Second, the addition of the DC grid adds tens of thousands of nodes, exploding the dimensionality of the system equations and significantly reducing simulation efficiency. Third, the inclusion of power electronics makes the system admittance matrix time-varying, requiring LU decomposition of the system's equivalent admittance matrix. This computationally expensive process for large systems.

[0004] Because traditional electromagnetic transient simulation processes fast-changing transient signals, even with multi-rate simulation, the step size of each partition cannot be too large. This means that conventional techniques cannot perform electromagnetic transient simulation efficiently and can introduce other problems. Summary of the Invention

[0005] The present invention provides a transient simulation method for an AC / DC hybrid system including a flexible DC power grid, which is used to solve the defect of low simulation efficiency in the prior art and achieve efficient simulation.

[0006] In a first aspect, the present invention provides a transient simulation method for an AC / DC hybrid system including a flexible DC grid, wherein the AC / DC hybrid system including the flexible DC grid includes an AC main grid, a DC and nearby AC grids, and an interface between the DC and nearby AC grids and the AC main grid, including:

[0007] The AC main grid is simulated using a large step size based on complex signal modeling and a step size greater than or equal to 1ms and less than or equal to 10ms;

[0008] The DC and near-area AC power grids are simulated using a small step size of 10 us and 50 us based on real signal modeling;

[0009] The interface between the DC and near-region AC power grid and the AC main grid is subjected to Park transformation to convert complex signals into real signals to realize conversion of simulation variables between the AC main grid and the DC and near-region AC power grid.

[0010] According to a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention, wherein the AC main grid is simulated using a large step size based on complex signal modeling and with a step size greater than or equal to 1ms and less than or equal to 10ms, specifically comprising:

[0011] Simulating each component of the AC main grid using the first model to obtain a large-step-size simulation model of each component based on complex signal modeling with a step size greater than or equal to 1 ms and less than or equal to 10 ms;

[0012] Based on the large-step simulation model of each component, a large-step simulation model of the AC main grid based on complex signal modeling with a step length greater than or equal to 1ms and less than or equal to 10ms is constructed.

[0013] According to a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention, wherein the DC and nearby AC grids include a flexible DC converter station, the DC and nearby AC grids are simulated using a small step size of greater than or equal to 10 us and less than or equal to 50 us based on real signal modeling, specifically:

[0014] Modeling the submodule capacitance of the flexible DC converter station using the medium rectangular integration method to obtain a discretized simulation model of the submodule capacitance based on real signal modeling with a small step size greater than or equal to 10 us and less than or equal to 50 us;

[0015] The bridge arm inductance of the flexible DC converter station is modeled using the trapezoidal method and the medium rectangular integration method to obtain a discretized simulation model of the bridge arm inductance based on real signal modeling and with a small step size greater than or equal to 10 us and less than or equal to 50 us;

[0016] Modeling other components in the DC and nearby AC power grids using a node analysis method to obtain simulation models of the other components based on real signal modeling with a small step size greater than or equal to 10 μs and less than or equal to 50 μs;

[0017] Combined with the discretization model of the submodule capacitor, the discretization model of the bridge arm inductance and the simulation models of other components, a real signal modeling of the DC and near-zone AC power grid is constructed, and a simulation model with a small step size greater than or equal to 10us and less than or equal to 50us is constructed.

[0018] According to a transient simulation method for an AC / DC hybrid system including a flexible DC power grid provided by the present invention, the method further comprises: modeling the flexible DC converter station using the trapezoidal method and the medium rectangular integration method to obtain a simulation model of the DC and near-zone AC power grids with a constant admittance matrix.

[0019] According to a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention, when the propagation time corresponding to the tie line between the DC and nearby AC grids and the AC main grid is greater than the simulation step size of the AC main grid and the DC and nearby AC grids, a transmission line decoupling method is used to convert simulation variables on both sides.

[0020] Alternatively, when the propagation time corresponding to the tie line is less than the simulation step of the AC main grid and the DC and near-zone AC grid, the multi-region Thevenin equivalence method MATE is used to perform asynchronous coordination to convert the simulation variables on both sides.

[0021] According to a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention, the first model is:

[0022]

[0023] Where, ω s is the shift frequency, k is the scale factor, Δt is the integration step, e E (t) is the complex envelope signal of e(t), u E (t) is the complex envelope signal of u(t), where u(t) is the input variable at time t, e(t) is the output signal at time t, and e E (t+Δt) is the complex envelope signal of e(t+Δt), u E (t+Δt) is the complex envelope signal of u(t+Δt), u(t+Δt) is the input variable at time t+Δt, and e(t+Δt) is the output signal at time t+Δt.

[0024] In a second aspect, the present invention provides a transient simulation device for an AC / DC hybrid system including a flexible DC grid, wherein the AC / DC hybrid system including the flexible DC grid includes an AC main grid, a DC and nearby AC grids, and an interface between the DC and nearby AC grids and the AC main grid, including:

[0025] A first processing module is used to simulate the AC main network using a large step size based on complex signal modeling and a step size greater than or equal to 1ms and less than or equal to 10ms;

[0026] The second processing module is used to simulate the DC and nearby AC power grids using a small step size of greater than or equal to 10 us and less than or equal to 50 us based on real signal modeling;

[0027] The third processing module is used to apply Park transformation to the interface between the DC and nearby AC power grids and the AC main grid, converting complex signals into real signals and vice versa to achieve coupling between the AC main grid and the DC and nearby AC power grids.

[0028] According to a transient simulation device for an AC / DC hybrid system including a flexible DC power grid provided by the present invention, the first processing module is specifically configured to:

[0029] Simulating each component of the AC main grid using the first model to obtain a large-step-size simulation model of each component based on complex signal modeling with a step size greater than or equal to 1 ms and less than or equal to 10 ms;

[0030] Based on the large-step simulation model of each component based on complex signal modeling and with a step length greater than or equal to 1ms and less than or equal to 10ms, a large-step simulation model of the AC main grid based on complex signal modeling and with a step length greater than or equal to 1ms and less than or equal to 10ms is constructed.

[0031] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the transient simulation method for an AC / DC hybrid system containing a flexible DC grid as described above are implemented.

[0032] The present invention also provides a non-transient computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the transient simulation method of an AC / DC hybrid system containing a flexible DC grid as described above are implemented.

[0033] The present invention provides a transient simulation method and device for an AC / DC hybrid system including a flexible DC grid. The AC / DC hybrid system including a flexible DC grid includes an AC main grid, a DC and near-region AC grid, and an interface between the DC and near-region AC grid and the AC main grid. The method includes: simulating the AC main grid using a large step size based on complex signal modeling with a step size greater than or equal to 1ms and less than or equal to 10ms; improving simulation efficiency by using a large step size for systems with slowly changing signals. Simulating the DC and near-region AC grid using a small step size based on real signal modeling with a step size greater than or equal to 10us and less than or equal to 50us; improving simulation accuracy by using a small step size for the DC and near-region AC grid. Using Parker transformation at the interface between the DC and near-region AC grid and the AC main grid to convert complex signals into real signals and vice versa, achieving conversion of simulation variables between the AC main grid and the DC and near-region AC grid. By converting real and complex signals, signal exchange between the AC main grid and the DC and nearby AC power grids is achieved, thereby making the transient simulation of the AC / DC hybrid system containing the flexible DC power grid more accurate. Furthermore, the present invention achieves efficient simulation through large-step modeling, small-step modeling, and the exchange of signals between the two power grids. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0035] Figure 1 It is a flow chart of a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention;

[0036] Figure 2 Schematic diagram of the spectrum of the original signal and the complex signal provided by the present invention;

[0037] Figure 3 Schematic diagram of the spectrum of the analytical signal and the analytical envelope signal provided by the present invention;

[0038] Figure 4 It is a topological structure circuit diagram and a submodule circuit diagram of the MMC provided by the present invention;

[0039] Figure 5 is an equivalent circuit diagram of a submodule of the MMC provided by the present invention;

[0040] Figure 6 This is a transient simulation flow chart of an AC / DC hybrid system including a flexible DC grid provided by the present invention;

[0041] Figure 7 It is a structural schematic diagram of a transient simulation device for an AC / DC hybrid system including a flexible DC power grid provided by the present invention;

[0042] Figure 8 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0043] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below 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 ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0044] The following combination Figure 1-Figure 3 A transient simulation method for an AC / DC hybrid system including a flexible DC grid is described in an embodiment of the present invention. The AC / DC hybrid system including the flexible DC grid includes an AC main grid, a DC and nearby AC grids, and interfaces between the DC and nearby AC grids and the AC main grid, including:

[0045] The AC main grid is simulated using a large step size based on complex signal modeling and a step size greater than or equal to 1ms and less than or equal to 10ms;

[0046] The DC and near-area AC power grids are simulated using a small step size of 10 us and 50 us based on real signal modeling;

[0047] The interface between the DC and near-region AC power grid and the AC main grid is subjected to Park transformation to convert complex signals into real signals to realize conversion of simulation variables between the AC main grid and the DC and near-region AC power grid.

[0048] Specifically, AC power grids are modeled based on complex signal electromagnetic transient modeling technology. Complex signal modeling can transform fast-changing signals in AC systems into slowly changing signals. When the signals in the system change slowly, a larger simulation step size can be used to simulate the system. In an AC system, the electrical quantity s(t) can be expressed as:

[0049]

[0050] Where t is time, angular frequency ω c =2πf c , f c is the fundamental frequency; is the initial phase angle; A(t) is the signal amplitude; Δω(t) is the fluctuation of angular frequency, and s(t) is a signal with a double-sided spectrum.

[0051] s S (t)=s(t)+js T (t) (2)

[0052] Where: s s The imaginary part s of (t) T (t) is a signal orthogonal to s(t), which can be obtained by performing a mathematical transformation T[s] on s(t). In the embodiment of the present invention, Hilbert transform is used to perform an orthogonal transformation on s(t) to obtain s T (t), and then get s s (t). s(t) and s s The spectrum of (t) is as follows Figure 3 shown.

[0053] It can be seen that the complex signal s s The spectrum of (t) is centered at the angular frequency +ω c To obtain a signal with a frequency concentrated near 0, multiply both sides of formula (2) by That is, frequency shift conversion, ω s is the shift frequency. Take ω s Equal to the system angular frequency ω c , we can get the complex envelope signal, the spectrum of the complex signal and the complex envelope signal is as follows Figure 3 shown.

[0054] Depend on Figure 2 It can be found that s E The spectrum of s(t) is concentrated near 0 Hz, with the maximum frequency much lower than the frequency of the original signal s(t). According to Shannon's sampling theorem, when simulating the complex envelope signal obtained after frequency shift transformation, a larger step size can be used to improve simulation efficiency. In this embodiment of the present invention, a large step size simulation based on complex signal modeling is used, with a step size of 1 to 10 ms.

[0055] For DC and near-region AC power grids, corresponding models are constructed based on real-number signals, where the step size is generally 10us to 50us.

[0056] During the DC and near-field AC grid simulation, a tie-line decoupling-based interface with the AC main grid simulation is also required. During simulation, the injected current for the DC and near-field simulation is first calculated based on the voltage and current on the AC main grid side of the tie line, as well as the resistance, inductance, capacitance, and propagation delay of the transmission line. Then, the injected current on the main grid side is calculated based on the voltage and current on the DC near-field side of the tie line, and the AC main grid simulation is performed for the next time step.

[0057] In the embodiment of the present invention, complex signal simulation is adopted for the AC main grid, so it involves the conversion between the complex signals of the AC main grid and the real signals of the DC and near-zone AC power grids. Regarding the Park transformation: From a mathematical point of view, the Park transformation is nothing, it is just a coordinate transformation, from the abc coordinate to the dq0 coordinate, ua, ub, uc, ia, ib, ic, magnetic flux a, magnetic flux b, magnetic flux c are all transformed into the dq0 coordinate, and can be reversed if necessary. From a physical point of view, the Park transformation is to equate the projection of the ia, ib, ic currents on the α and β axes to the d and q axes, and to equate the currents on the stator to the direct and quadrature axes. For the steady state, after such an equivalence, iq, id are just constants. The conversion method is introduced as follows:

[0058] The complex signal can be converted into a real signal using (3):

[0059]

[0060] Where s Eabc is a complex signal, s abc is the corresponding real number signal, Re(.) means taking a real number.

[0061] Since the Hilbert transform is a non-causal transform, it is rather troublesome to use an instantaneous real signal to generate a corresponding complex signal. The following introduces a convenient method for generating a complex signal and designs a method for converting a real signal into a complex envelope signal as shown in formula (4):

[0062]

[0063] Where,

[0064]

[0065] The present invention provides a transient simulation method for an AC / DC hybrid system including a flexible DC grid. The AC / DC hybrid system including a flexible DC grid includes an AC main grid, a DC and near-region AC grid, and an interface between the DC and near-region AC grid and the AC main grid. The method includes: simulating the AC main grid using a large step size based on complex signal modeling with a step size greater than or equal to 1ms and less than or equal to 10ms; improving simulation efficiency by using a large step size for systems with slowly changing signals. Simulating the DC and near-region AC grid using a small step size based on real signal modeling with a step size greater than or equal to 10us and less than or equal to 50us; improving simulation accuracy by using a small step size for the DC and near-region AC grid. Using Parker transformation at the interface between the DC and near-region AC grid and the AC main grid to convert complex signals into real signals and vice versa, achieving conversion of simulation variables between the AC main grid and the DC and near-region AC grid. By converting real and complex signals, signal exchange between the AC main grid and the DC and nearby AC power grids is achieved, thereby making the transient simulation of the AC / DC hybrid system containing the flexible DC power grid more accurate. Furthermore, the present invention achieves efficient simulation through large-step modeling, small-step modeling, and the exchange of signals between the two power grids.

[0066] According to a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention, wherein the AC main grid is simulated using a large step size based on complex signal modeling and with a step size greater than or equal to 1ms and less than or equal to 10ms, specifically comprising:

[0067] Simulating each component of the AC main grid using the first model to obtain a large-step-size simulation model of each component based on complex signal modeling with a step size greater than or equal to 1 ms and less than or equal to 10 ms;

[0068] Based on the large-step simulation model of each component, a large-step simulation model of the AC main grid based on complex signal modeling with a step length greater than or equal to 1ms and less than or equal to 10ms is constructed.

[0069] Specifically, based on the complex signal modeling method, a complex signal electromagnetic transient model of the AC power grid can be established. All components obtained in the AC main grid can be expressed by differential equations. Without loss of generality, consider the following differential equation:

[0070]

[0071] Where u is the input variable, k is the scale factor, and e is the output signal. The differential equation represented by the complex envelope signal can be obtained through frequency shift transformation:

[0072]

[0073] Where, e E(t) is the complex envelope signal of e(t), u E (t) is the complex envelope signal of u(t). Using the trapezoidal method to discretize, we can get

[0074]

[0075] In the formula, ω s is the shift frequency, k is the scale factor, Δt is the integration step, e E (t) is the complex envelope signal of e(t), u E (t) is the complex envelope signal of u(t), where u(t) is the input variable at time t, e(t) is the output signal at time t, and e E (t+Δt) is the complex envelope signal of e(t+Δt), u E (t+Δt) is the complex envelope signal of u(t+Δt).

[0076] According to the modeling method shown in equations (6)-(8), a large-step simulation model of all components of the AC main network can be quickly constructed. Then, a large-scale simulation model of the AC main network is constructed based on all components of the constructed AC main network.

[0077] According to a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention, wherein the DC and nearby AC grids include a flexible DC converter station, the DC and nearby AC grids are simulated using a small step size of greater than or equal to 10 us and less than or equal to 50 us based on real signal modeling, specifically:

[0078] Modeling the submodule capacitance of the flexible DC converter station using the medium rectangular integration method to obtain a discretized simulation model of the submodule capacitance based on real signal modeling with a small step size greater than or equal to 10 us and less than or equal to 50 us;

[0079] The bridge arm inductance of the flexible DC converter station is modeled using the trapezoidal method and the medium rectangular integration method to obtain a discretized simulation model of the bridge arm inductance based on real signal modeling and with a small step size greater than or equal to 10 us and less than or equal to 50 us;

[0080] Modeling other components in the DC and nearby AC power grids using a node analysis method to obtain simulation models of the other components based on real signal modeling with a small step size greater than or equal to 10 μs and less than or equal to 50 μs;

[0081] Combined with the discretization model of the submodule capacitor, the discretization model of the bridge arm inductance and the simulation models of other components, a real signal modeling of the DC and near-zone AC power grid is constructed, and a simulation model with a small step size greater than or equal to 10us and less than or equal to 50us is constructed.

[0082] Specifically, in HVDC transmission, the converter used in the flexible DC converter station is generally a modular multilevel converter (MMC). The topology of MMC is as follows: Figure 4 As shown, Figure 4 (a) is the topology of MMC, where each bridge arm is composed of N submodules (SM) connected in series. The structure of the submodule is as follows: Figure 4 (b) shown. Figure 1 In the figure, L0 is the bridge arm reactance, R0 is the bridge arm resistance, and the submodule consists of two groups of IGBT / diode switches and a capacitor.

[0083] Figure 4 The submodule shown in (b) can be equivalent to the following in electromagnetic transient simulation: Figure 5 In the circuit shown in the figure, R1 and R2 are equivalent resistors, C SM The switch is represented by a resistor. When the switch is on, it is equivalent to a small resistor, and when the switch is off, it is equivalent to a large resistor.

[0084] If the resistance of the switch is considered to be ∞ when it is turned off, then according to Figure 2 It can be found that the dynamic process of the capacitance of the submodule in the bridge arm can be expressed as:

[0085]

[0086] Where C SMi is the capacitance of the submodule put into operation at that moment, v ci is the capacitor voltage of the submodule, i arm is the bridge arm current. The dynamic process of the bridge arm inductance can be expressed as:

[0087]

[0088] Among them, R0 is generally 0, and the rest can be calculated as follows:

[0089]

[0090] N is the number of submodules, R oni is the on-state resistance of the switch in the i-th sub-module. Whether the sub-module is put into operation is determined by the controller.

[0091] K = [1 … 1 … 1] n (12)

[0092] v c (t)=[v c1 (t) … v ci (t) … v cn (t)] n (13)

[0093] Where n is the number of self-drawn fast cards, v is ci is the voltage of the capacitor of the i-th submodule. Using the middle rectangular integration method to discretize the differential equation (9) of the submodule capacitance, we can obtain:

[0094]

[0095] By using the trapezoidal method to discretize the differential equation (10) of the bridge arm inductance, we can obtain:

[0096]

[0097] Since the accuracy of the medium rectangular integration format is consistent with that of the trapezoidal integration format, the medium rectangular integration formula can be used to replace Replace with And sorting it out we get:

[0098]

[0099] Where R arm =R0+R eq , L arm = L0, it can be found that the equivalent conductance of the bridge arm Δt / (R arm Δt+2L arm ) is kept constant during the numerical integration calculation process, which can avoid frequent LU decomposition of the admittance matrix. In formula (16), the historical current source i hist It can be expressed as:

[0100]

[0101] According to equations (14) and (16), it can be found that if the submodule capacitance differential equation is discretized using the middle rectangular integral formula, and the bridge arm inductance is discretized using the middle rectangular integral formula and the trapezoidal integral formula, then the calculation of the dynamic process of the submodule capacitance and the dynamic process of the bridge arm inductance can be decoupled, and the numerical integration process of the two differs by half a time step. During the calculation, the two can be calculated alternately. After the submodule capacitance voltage at time t+Δt / 2 is calculated, the bridge arm inductance current at time t+Δt can be calculated, and then the capacitance voltage at time t+3Δt / 2 can be calculated. During the calculation process, the calculation of the submodule capacitance voltage is decoupled from the calculation of the bridge arm current, and they always differ by half a time step. This modeling method can be called a half-step delay decoupling modeling method.

[0102] The simulation model for DC and near-region AC grid components other than the capacitors and inductors in the flexible DC converter station is constructed using the node analysis method. The basic guiding principle of the node analysis method is to replace the unknown branch voltages with unknown node voltages to establish circuit equations, thereby reducing the number of simultaneous equations. A node voltage refers to the voltage between an independent node and a dependent node. The node analysis method applies Kirchhoff's current law to establish node current equations, then uses node voltages to represent branch currents and finally solves for the node voltages.

[0103] Since the step size adopted in the above modeling method is a small step size of 10us and less than or equal to 50us, the discretization model of the sub-module capacitance, the discretization model of the bridge arm inductance and the simulation models of other components are combined to construct the real number signal modeling of the DC and near-zone AC power grids, and a simulation model with a small step size of greater than or equal to 10us and less than or equal to 50us.

[0104] According to a transient simulation method for an AC / DC hybrid system including a flexible DC power grid provided by the present invention, the method further comprises: modeling the flexible DC converter station using the trapezoidal method and the medium rectangular integration method to obtain a simulation model of the DC and near-zone AC power grids with a constant admittance matrix.

[0105] Specifically, since the accuracy of the medium rectangular integration format is consistent with that of the trapezoidal integration format, the medium rectangular integration formula can be used to replace Replace with And sorting it out we get:

[0106]

[0107] Where R arm =R0+R eq , L arm = L0, it can be found that the equivalent conductance of the bridge arm Δt / (R arm Δt+2L arm ) remains constant during the numerical integration calculation, which can avoid frequent LU decomposition of the admittance matrix.

[0108] According to a transient simulation method for an AC / DC hybrid system including a flexible DC grid provided by the present invention, when the propagation time corresponding to the tie line between the DC and nearby AC grids and the AC main grid is greater than the simulation step size of the AC main grid and the DC and nearby AC grids, a transmission line decoupling method is used to convert simulation variables on both sides.

[0109] Alternatively, when the propagation time corresponding to the tie line is less than the simulation step of the AC main grid and the DC and near-zone AC grid, the multi-region Thevenin equivalence method MATE is used to perform asynchronous coordination to convert the simulation variables on both sides.

[0110] Specifically, the embodiment of the present invention adopts transmission line decoupling or MATE method to convert the simulation variables on both sides at the interface. When the propagation time corresponding to the tie line is greater than the step size of the power grids on both sides, transmission line decoupling is adopted. When the propagation time corresponding to the tie line is less than the simulation step size, MATE is adopted for asynchronous coordination.

[0111] It should be noted that the traditional MATE method cannot guarantee both accuracy and efficiency when simulating AC / DC systems including DC grids. This is because the equivalent admittance of the DC converter station varies with time in traditional simulations. However, since the DC converter station in the present invention is modeled using a half-step delay decoupling method, the admittance matrix remains constant during DC and near-grid simulations, eliminating the accuracy issues associated with the MATE method.

[0112] In summary, if Figure 6 As shown, in the rapid electromagnetic transient simulation process for a hybrid AC / DC system with a flexible DC grid in an embodiment of the present invention, when simulating the DC and near-region AC grids, the control system first calculates whether the submodule is enabled or disabled, followed by the dynamic process of the converter station submodule. During each calculation step, the dynamic processes of each submodule do not affect each other, and the calculations are performed in parallel. The historical current source of each component is then calculated, and the node voltage equations are solved. During the DC and near-region AC grid simulation process, an interface with the AC main grid simulation is also established through tie-line decoupling.

[0113] The AC main grid simulation uses a large-step complex signal simulation process, which is basically the same as the traditional electromagnetic transient simulation process based on node analysis. The difference lies in the calculation of the equivalent node admittance matrix and historical current source. The specific steps for each time step of the complex signal electromagnetic transient simulation are as follows:

[0114] Step 1: Initialize the AC main network simulation, including setting the simulation step size, frequency shift, etc.

[0115] Step 2: Calculate the equivalent nodal admittance matrix considering the frequency shift;

[0116] Step 3: Calculate the historical current source of each component of the AC main grid based on the node voltage and branch current;

[0117] Step 4: Calculate the node injection current;

[0118] Step 5: Solve the node voltage equation of the AC main grid based on the node admittance matrix, historical current source, and injected current to obtain the system node voltage.

[0119] Step 6: Calculate the current in each branch of the AC main grid and proceed to the next step of solution.

[0120] It should be noted that when forming the node admittance matrix and solving the historical current source, it is necessary to consider the impact of the DC side on the AC grid based on the interface between the AC main grid and the DC nearby grid mentioned above.

[0121] It should be noted that the simulation step size of the AC main grid is large, while the simulation step size of the DC and nearby power grids is small. In DC simulation, the interpolation algorithm can be used to obtain the interface variables of the DC system at each time step.

[0122] Compared with the existing electromagnetic transient simulation technology for AC / DC hybrid systems containing flexible DC power grids, the present invention can adopt a larger simulation step size for the AC main grid, has an error-free interface, a constant system equivalent admittance matrix, and a low system dimension. These advantages enable the proposed electromagnetic transient simulation technology to achieve greatly improved efficiency while ensuring accuracy.

[0123] like Figure 7 As shown, a transient simulation device for an AC / DC hybrid system including a flexible DC grid is provided. The AC / DC hybrid system including the flexible DC grid includes an AC main grid, a DC and nearby AC grids, and interfaces between the DC and nearby AC grids and the AC main grid. The device is characterized by comprising:

[0124] The first processing module 71 is configured to simulate the AC main grid using a large step size based on complex signal modeling and a step size greater than or equal to 1 ms and less than or equal to 10 ms;

[0125] The second processing module 72 is configured to simulate the DC and nearby AC power grids using a small step size greater than or equal to 10 us and less than or equal to 50 us based on real signal modeling;

[0126] The third processing module 73 is configured to apply Park transformation to the interface between the DC and nearby AC power grids and the AC main grid, converting complex signals into real signals and vice versa to achieve coupling between the AC main grid and the DC and nearby AC power grids.

[0127] Since the device provided in the embodiment of the present invention can be used to execute the method described in the above embodiment, its working principle and beneficial effects are similar, so they will not be described in detail here. For specific details, please refer to the introduction of the above embodiment.

[0128] According to a transient simulation device for an AC / DC hybrid system including a flexible DC power grid provided by the present invention, the first processing module 71 is specifically configured to:

[0129] Simulating each component of the AC main grid using the first model to obtain a large-step-size simulation model of each component based on complex signal modeling with a step size greater than or equal to 1 ms and less than or equal to 10 ms;

[0130] Based on the large-step simulation model of each component, a large-step simulation model of the AC main grid based on complex signal modeling with a step length greater than or equal to 1ms and less than or equal to 10ms is constructed.

[0131] According to a transient simulation device for an AC / DC hybrid system including a flexible DC grid provided by the present invention, wherein the DC and nearby AC grids include a flexible DC converter station, the second processing module 72 is specifically configured to:

[0132] Modeling the submodule capacitance of the flexible DC converter station using the medium rectangular integration method to obtain a discretized simulation model of the submodule capacitance based on real signal modeling with a small step size greater than or equal to 10 us and less than or equal to 50 us;

[0133] The bridge arm inductance of the flexible DC converter station is modeled using the trapezoidal method and the medium rectangular integration method to obtain a discretized simulation model of the bridge arm inductance based on real signal modeling and with a small step size greater than or equal to 10 us and less than or equal to 50 us;

[0134] Modeling other components in the DC and nearby AC power grids using a node analysis method to obtain simulation models of the other components based on real signal modeling with a small step size greater than or equal to 10 μs and less than or equal to 50 μs;

[0135] Combined with the discretization model of the submodule capacitor, the discretization model of the bridge arm inductance and the simulation models of other components, a real signal modeling of the DC and near-zone AC power grid is constructed, and a simulation model with a small step size greater than or equal to 10us and less than or equal to 50us is constructed.

[0136] According to the present invention, a transient simulation device for an AC / DC hybrid system including a flexible DC power grid is provided, wherein the device is further used to: model the flexible DC converter station using the trapezoidal method and the medium rectangular integration method to obtain a simulation model of the DC and near-zone AC power grid with a constant admittance matrix.

[0137] According to the present invention, a transient simulation device for an AC / DC hybrid system including a flexible DC grid is provided, wherein, when the propagation time corresponding to the tie line of the interface between the DC and nearby AC grids and the AC main grid is greater than the simulation step size of the AC main grid and the DC and nearby AC grids, a transmission line decoupling method is used to perform mutual conversion of simulation variables on both sides;

[0138] Alternatively, when the propagation time corresponding to the tie line is less than the simulation step of the AC main grid and the DC and near-zone AC grid, the multi-region Thevenin equivalence method MATE is used to perform asynchronous coordination to convert the simulation variables on both sides.

[0139] According to a transient simulation device for an AC / DC hybrid system including a flexible DC grid provided by the present invention, the first model used in the first processing module 71 is:

[0140]

[0141] Where, ω s is the shift frequency, k is the scale factor, Δt is the integration step, e E (t) is the complex envelope signal of e(t), u E (t) is the complex envelope signal of u(t), where u(t) is the input variable at time t, e(t) is the output signal at time t, and e E (t+Δt) is the complex envelope signal of e(t+Δt), u E (t+Δt) is the complex envelope signal of u(t+Δt), u(t+Δt) is the input variable at time t+Δt, and e(t+Δt) is the output signal at time t+Δt.

[0142] Figure 8 An example of a physical structure diagram of an electronic device is shown below. Figure 8 As shown, the electronic device may include: a processor (processor) 810, a communication interface (Communications Interface) 820, a memory (memory) 830 and a communication bus 840, wherein the processor 810, the communication interface 820, and the memory 830 communicate with each other through the communication bus 840. The processor 810 can call the logic instructions in the memory 830 to execute a transient simulation method for an AC / DC hybrid system including a flexible DC grid, wherein the AC / DC hybrid system including the flexible DC grid includes an AC main grid, a DC and near-region AC grid, and an interface between the DC and near-region AC grid and the AC main grid. The method includes: simulating the AC main grid using a large step size based on complex signal modeling with a step size greater than or equal to 1 ms and less than or equal to 10 ms; simulating the DC and near-region AC grid using a small step size based on real signal modeling with a step size greater than or equal to 10 us and less than or equal to 50 us; and using a Park transform on the interface between the DC and near-region AC grid and the AC main grid to convert complex signals into real signals and realize conversion of simulation variables between the AC main grid and the DC and near-region AC grid.

[0143] In addition, the logic instructions in the above-mentioned memory 830 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when sold or used as an independent product. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or the part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0144] On the other hand, the present invention also provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer can execute the transient simulation method of the AC / DC hybrid system containing a flexible DC power grid provided by the above methods. The AC / DC hybrid system containing a flexible DC power grid includes an AC main grid, a DC and near-region AC power grid, and an interface between the DC and near-region AC power grid and the AC main grid. The method includes: simulating the AC main grid using a large step size based on complex signal modeling with a step size greater than or equal to 1ms and less than or equal to 10ms; simulating the DC and near-region AC power grid using a small step size based on real signal modeling with a step size greater than or equal to 10us and less than or equal to 50us; and using Park transformation on the interface between the DC and near-region AC power grid and the AC main grid to convert complex signals and real signals into each other to realize the conversion of simulation variables of the AC main grid and the DC and near-region AC power grid.

[0145] On the other hand, the present invention also provides a non-transient computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to execute the above-mentioned transient simulation methods for an AC / DC hybrid system containing a flexible DC power grid, wherein the AC / DC hybrid system containing a flexible DC power grid includes an AC main grid, a DC and near-region AC power grid, and an interface between the DC and near-region AC power grid and the AC main grid. The method includes: simulating the AC main grid using a large step size based on complex signal modeling with a step size greater than or equal to 1ms and less than or equal to 10ms; simulating the DC and near-region AC power grid using a small step size based on real signal modeling with a step size greater than or equal to 10us and less than or equal to 50us; and using Park transformation on the interface between the DC and near-region AC power grid and the AC main grid to convert complex signals and real signals into each other to realize conversion of simulation variables of the AC main grid and the DC and near-region AC power grid.

[0146] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, i.e., they may be located in one location or distributed across multiple network units. Some or all of the modules may be selected based on actual needs to achieve the objectives of the present embodiment. Persons of ordinary skill in the art will be able to understand and implement the present invention without inventive effort.

[0147] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, or of course, by hardware. Based on this understanding, the essence of the above technical solution or the part that contributes to the existing technology can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a magnetic disk, an optical disk, etc., and includes a number of instructions for enabling a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or certain parts of the embodiments.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. 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 of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A transient simulation method for an AC / DC hybrid system including a flexible DC grid, wherein the AC / DC hybrid system including the flexible DC grid comprises an AC main grid, a DC and nearby AC grids, and interfaces between the DC and nearby AC grids and the AC main grid, characterized in that: include: The AC main grid is simulated using a large step size based on complex signal modeling and a step size greater than or equal to 1ms and less than or equal to 10ms; The DC and near-area AC power grids are simulated using a small step size of 10 us and 50 us based on real signal modeling; Using Park transformation on the interface between the DC and near-region AC power grid and the AC main grid, converting complex signals into real signals and vice versa to achieve conversion of simulation variables between the AC main grid and the DC and near-region AC power grid; The DC and near-region AC power grids include flexible DC converter stations, and the DC and near-region AC power grids are simulated using real signal modeling with a small step size greater than or equal to 10 us and less than or equal to 50 us, specifically: Modeling the submodule capacitance of the flexible DC converter station using the medium rectangular integration method to obtain a discretized simulation model of the submodule capacitance based on real signal modeling with a small step size greater than or equal to 10 us and less than or equal to 50 us; The bridge arm inductance of the flexible DC converter station is modeled using the trapezoidal method and the medium rectangular integration method to obtain a discretized simulation model of the bridge arm inductance based on real signal modeling and with a small step size greater than or equal to 10 us and less than or equal to 50 us; Modeling other components in the DC and nearby AC power grids using a node analysis method to obtain simulation models of the other components based on real signal modeling with a small step size greater than or equal to 10 μs and less than or equal to 50 μs; Combined with the discretization model of the submodule capacitor, the discretization model of the bridge arm inductance and the simulation models of other components, a real signal modeling of the DC and near-zone AC power grid is constructed, and a simulation model with a small step size greater than or equal to 10us and less than or equal to 50us is constructed.

2. The transient simulation method of an AC / DC hybrid system including a flexible DC grid according to claim 1, characterized in that: The simulation of the AC main network using a large step size based on complex signal modeling and a step size greater than or equal to 1 ms and less than or equal to 10 ms specifically includes: Simulating each component of the AC main grid using the first model to obtain a large-step simulation model of each component based on complex signal modeling and with a step length greater than or equal to 1 ms and less than or equal to 10 ms; Based on the large-step simulation model of each component, a large-step simulation model of the AC main grid based on complex signal modeling with a step length greater than or equal to 1ms and less than or equal to 10ms is constructed.

3. The transient simulation method of an AC / DC hybrid system including a flexible DC grid according to claim 1, characterized in that: The method further includes: modeling the flexible DC converter station using the trapezoidal method and the medium rectangular integration method to obtain a simulation model of the DC and near-zone AC power grids with a constant admittance matrix.

4. The transient simulation method of an AC / DC hybrid system including a flexible DC grid according to claim 1, characterized in that: When the propagation time corresponding to the tie line of the interface between the DC and nearby AC power grid and the AC main grid is greater than the simulation step size of the AC main grid and the DC and nearby AC power grid, the simulation variables on both sides are converted to each other by using a transmission line decoupling method; Alternatively, when the propagation time corresponding to the tie line is less than the simulation step of the AC main grid and the DC and near-zone AC grid, the multi-region Thevenin equivalence method MATE is used to perform asynchronous coordination to convert the simulation variables on both sides.

5. The transient simulation method of an AC / DC hybrid system including a flexible DC grid according to claim 2, characterized in that: The first model is: ； Where, ω s is the shift frequency, k is the scaling factor, ∆ t is the integration step size, e E ( t )yes e ( t )’s complex envelope signal, u E ( t )yes u ( t ), where u ( t )yes t The input variables at time, e ( t )for t The output signal at time e E (t+∆ t )yes e ( t +∆ t )’s complex envelope signal, u E (t+∆ t )yes u ( t +∆ t ), u ( t +∆ t ) yes t +∆ t The input variables at time, e ( t +∆ t )yes t +∆ t Output signal at the moment.

6. A transient simulation device for an AC / DC hybrid system including a flexible DC grid, wherein the AC / DC hybrid system including the flexible DC grid comprises an AC main grid, a DC and nearby AC grids, and an interface between the DC and nearby AC grids and the AC main grid, characterized in that: include: A first processing module is used to simulate the AC main network using a large step size based on complex signal modeling and a step size greater than or equal to 1ms and less than or equal to 10ms; The second processing module is used to simulate the DC and nearby AC power grids using a small step size of greater than or equal to 10 us and less than or equal to 50 us based on real signal modeling; a third processing module, configured to apply Park transformation to the interface between the DC and nearby AC power grids and the AC main grid, converting complex signals into real signals and vice versa to achieve coupling between the AC main grid and the DC and nearby AC power grids; The DC and near-area AC power grids include a flexible DC converter station, and the second processing module is specifically used to model the submodule capacitance of the flexible DC converter station using a medium rectangular integration method to obtain a discretized simulation model of the submodule capacitance based on real signal modeling with a small step size greater than or equal to 10us and less than or equal to 50us; The bridge arm inductance of the flexible DC converter station is modeled using the trapezoidal method and the medium rectangular integration method to obtain a discretized simulation model of the bridge arm inductance based on real signal modeling and with a small step size greater than or equal to 10 us and less than or equal to 50 us; Modeling other components in the DC and nearby AC power grids using a node analysis method to obtain simulation models of the other components based on real signal modeling with a small step size greater than or equal to 10 μs and less than or equal to 50 μs; Combined with the discretization model of the submodule capacitor, the discretization model of the bridge arm inductance and the simulation models of other components, a real signal modeling of the DC and near-zone AC power grid is constructed, and a simulation model with a small step size greater than or equal to 10us and less than or equal to 50us is constructed.

7. The transient simulation device for an AC / DC hybrid system including a flexible DC grid according to claim 6, characterized in that: The first processing module is specifically configured to: Simulating each component of the AC main grid using the first model to obtain a large-step-size simulation model of each component based on complex signal modeling with a step size greater than or equal to 1 ms and less than or equal to 10 ms; Based on the large-step simulation model of each component based on complex signal modeling and with a step length greater than or equal to 1ms and less than or equal to 10ms, a large-step simulation model of the AC main grid based on complex signal modeling and with a step length greater than or equal to 1ms and less than or equal to 10ms is constructed.

8. An electronic 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 program, the steps of the transient simulation method of the AC / DC hybrid system including a flexible DC grid are implemented as described in any one of claims 1 to 5.

9. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method for transient simulation of an AC / DC hybrid system including a flexible DC grid are implemented as claimed in any one of claims 1 to 5.

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