A simulation method for eliminating oscillation and improving precision of switching action event

Abstract

The application discloses a simulation method for eliminating oscillation and improving precision of switching action event, first, based on topology before switching action, state quantity and non-state quantity at the moment are calculated; after detecting switching of the switch, the action moment is located through linear interpolation, and branch voltage and current at the moment are obtained; then, node admittance matrix is updated immediately, half-step backward Euler method is used to solve the solution at the moment, and state quantity approximation at the moment is obtained through backward extrapolation; the state quantity approximation is taken as a history item, non-state quantity at the moment is recalculated, and whether other switching commutation caused by mutation exists is judged, if yes, the foregoing steps are repeated; then, solutions at the moments are solved in sequence, and the solution at the moment is obtained through interpolation; finally, whether other switching action occurs in the interval is judged, if yes, the process is executed again. The method can effectively deal with multiple switching events under the fixed step length framework, suppress numerical oscillation, and significantly improve simulation precision.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic transient (EMT) simulation technology of power systems, and specifically relates to a simulation method for eliminating oscillations and improving simulation accuracy for switching action events. Background Technology

[0002] The "dual high" characteristics of new power systems—high proportion of renewable energy and high proportion of power electronic equipment—are becoming increasingly prominent. This trend towards power electronics in power systems places higher demands on the accuracy and efficiency of EMT simulation algorithms. Currently, the widely used fixed-step electromagnetic transient simulation algorithm based on the trapezoidal integral method, while computationally efficient, still suffers from several problems: first, it easily induces numerical oscillations during switching actions; second, the timing of switching actions is inaccurate; third, the instantaneous variable values ​​after switching actions are difficult to accurately solve; and fourth, the simulation accuracy decreases when multiple switching events occur within the same simulation step. These problems severely affect the reliability and practicality of the simulation results.

[0003] In existing technologies, researchers have employed strategies such as backward Euler method, multi-step interpolation, higher-order numerical integration methods, and re-initialization to suppress numerical oscillations. However, these strategies still suffer from low computational accuracy, low computational efficiency, limited applicability, and difficulty in handling concurrent events. Therefore, there is an urgent need to propose a novel simulation method that can effectively suppress oscillations while balancing accuracy and efficiency. Summary of the Invention

[0004] In order to overcome the problems existing in the prior art, the purpose of this invention is to provide a simulation method for eliminating oscillations and improving accuracy of switching action events. This method can effectively handle switching events, suppress numerical oscillations, support concurrent simulation of multiple events, and significantly improve computational accuracy within a fixed-step simulation framework.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A simulation method for eliminating oscillations and improving accuracy in switching action events, comprising the following steps:

[0007] Step 1: Use the nodal admittance matrix of the topology before the switch state change Solve The values ​​of state variables and non-state variables at each moment;

[0008] Step 2: After detecting the switch switching, determine the switch action time using linear interpolation. Meanwhile, interpolation is used to obtain the voltage and current of each branch at the moment of switch action; if multiple switch actions are detected, the first switch action event is processed first.

[0009] Step 3: In After the immediate switch to reactive switching action, the nodal admittance matrix of the topology is: And by using the Euler method after half a step, the solution is obtained. The values ​​of state variables and non-state variables at any given time;

[0010] Step 4: Apply the formula to all state variables. Perform backward extrapolation interpolation, where Represents all state variables. This represents the state quantities in the voltage and current of each branch at the moment of switch operation obtained through interpolation in step 2, i.e., the state quantities at the moment of switch operation before the change in circuit topology, and obtains the topology after switch operation. Approximate values ​​of the state variables at any given time;

[0011] Step 5: Using the approximate value obtained in the previous step as a historical term, re-solve using the Euler method after a half-step. The non-state values ​​at time t are used as the switching action times after the circuit topology change. The solution, and based on At any given time, determine if any other switches have commutated due to a sudden change in non-state variables. If so, return to step 3; otherwise, proceed to the next step.

[0012] Step 6: Solve the equations sequentially using the half-step backward Euler method and the trapezoidal method. and The values ​​of state variables and non-state variables at each moment;

[0013] Step 7: Obtain the switching action time after the instantaneous quantity generated by the switching action decays by back-out interpolation. The values ​​of state variables and non-state variables are obtained through extrapolation or interpolation. The values ​​of state variables and non-state variables at each moment;

[0014] Step 8: Determine if... arrive If there are other switching actions during the specified time period, then start from step 2 again; otherwise, end the process.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] Compared to traditional fixed-step trapezoidal geometry simulations, which are prone to numerical oscillations during switching actions, this invention employs two backward Euler methods to completely eliminate oscillations. Furthermore, compared to the fixed-step trapezoidal geometry and critical damping adjustment methods, which can lead to "shutdown" phenomena (where the voltage and current on the inductor drop to zero after the switch is opened) during forced commutation of controllable power electronic devices due to the switching action only being reflected after the step length is completed, this invention determines the switching action moment through interpolation and recalculates the values ​​that may change abruptly at the switching action moment, thus immediately reflecting changes in the circuit topology, avoiding "shutdown," and improving simulation accuracy. Compared to re-initializing using the switching theorem after locating the switching action moment, which requires multiple modifications to the node admittance matrix, this invention utilizes backward extrapolation interpolation and a half-step backward Euler method for re-initialization, requiring only one modification to the node admittance matrix, effectively reducing the computational load.

[0017] In summary, this invention effectively eliminates numerical oscillations and significantly improves simulation accuracy and practicality by combining backward extrapolation interpolation, re-initialization, and half-step backward Euler oscillation suppression strategies, and supports sequential processing of multiple events within the same simulation step. Attached Figure Description

[0018] Figure 1 This is a flowchart of the method of the present invention when encountering a switch action.

[0019] Figure 2 This is a circuit diagram for natural commutation at zero crossing.

[0020] Figure 3 This is a comparison of simulation results for a natural commutation circuit with a simulation step size of 10μs.

[0021] Figure 4 This is a comparison of simulation results for a natural commutation circuit with a simulation step size of 100μs.

[0022] Figure 5 This is a topology diagram of a forced commutation standard evaluation system.

[0023] Figure 6 This is a comparison of simulation results for a forced commutation circuit with a simulation step size of 10μs.

[0024] Figure 7 This is a comparison of simulation results for a forced commutation circuit with a simulation step size of 50μs.

[0025] Figure 8 This is a comparison of simulation results for a forced commutation circuit with a simulation step size of 100μs. Specific implementation methods

[0026] The invention will be further illustrated below using simulation examples.

[0027] like Figure 1 As shown, the present invention provides a simulation method for eliminating oscillations and improving accuracy in switching action events. The specific steps are as follows:

[0028] Step 1: Use the nodal admittance matrix of the topology before the switch state change Solve The values ​​of state variables and non-state variables at each moment;

[0029] Step 2: After detecting the switch switching, determine the switch action time using linear interpolation. Meanwhile, interpolation is used to obtain the voltage and current of each branch at the moment of switch action; if multiple switch actions are detected, the first switch action event is processed first.

[0030] Step 3: In After the immediate switch to reactive switching action, the nodal admittance matrix of the topology is: And by using the Euler method after half a step, the solution is obtained. The values ​​of state variables and non-state variables at any given time;

[0031] Step 4: Apply the formula to all state variables. Perform backward extrapolation interpolation, where Represents all state variables. This represents the state quantities in the voltage and current of each branch at the moment of switch operation obtained through interpolation in step 2, i.e., the state quantities at the moment of switch operation before the change in circuit topology, and obtains the topology after switch operation. Approximate values ​​of the state variables at time points; in step 4, backward outward interpolation is used to obtain the topology after the switch action. Approximate values ​​of the state variables at time points are obtained, and the solution is recalculated. The value of the moment, instead of directly using the moment before the switch action as in traditional methods. The value at time step is solved to improve the simulation accuracy.

[0032] Step 5: Using the approximate value obtained in the previous step as a historical term, re-solve using the Euler method after a half-step. The non-state values ​​at time t are used as the switching action times after the circuit topology change. The solution, and based on At time 5, the solution is used to determine if any other switches have commutated due to abrupt changes in non-state variables. If so, return to step 3; otherwise, proceed to the next step. In step 5, the solution is re-obtained using the Euler method after a half-step. The non-state values ​​at each time step are used to determine whether other diodes have commutated due to a sudden change in non-state values. If so, the solution is immediately recalculated instead of modifying the node admittance matrix when solving the next time step, thus ensuring that the switching action can be reacted immediately.

[0033] Step 6: Solve the equations sequentially using the half-step backward Euler method and the trapezoidal method. and The values ​​of state variables and non-state variables at each moment;

[0034] Step 7: Obtain the switching action time after the instantaneous quantity generated by the switching action decays by back-out interpolation. The values ​​of state variables and non-state variables are obtained through extrapolation or interpolation. The values ​​of state variables and non-state variables at each moment;

[0035] Step 8: Determine if... arrive If there are other switching actions during the specified time period, then start from step 2 again; otherwise, end the process.

[0036] Simulation Examples

[0037] To verify the effectiveness of the method of this invention, network equations were constructed on the MATLAB 2024b platform based on the improved nodal analysis method (MNA) for classical natural commutation circuits such as... Figure 2 The standard test system for forced commutation shown is as follows: Figure 5 The simulation results are shown and compared with those of the commonly used critical damping adjustment method (CDA) and PSCAD / EMTDC simulation results.

[0038] for Figure 2 The natural commutation circuit shown here represents an ideal AC voltage source with an effective value of 69V, an initial phase angle of 90°, and a frequency of 60Hz. SW represents a switch, and the resistance is set to be [value missing] when the switch is closed. When the switch is open, the resistance is , The resistance is 22.61. The resistor and the inductor on the right. The value is 19.72mH, and the resistor connected in parallel with it is... Resistance is 10MΩ The simulation step size was set to 10 μs and 100 μs respectively. The simulation results of different methods are as follows: Figure 3 and Figure 4 As shown in the figure, the vertical axis Inductance The voltage values ​​at both ends show that PSCAD exhibits small numerical oscillations at certain step lengths. After a period of time, the oscillations are eliminated by the oscillation elimination algorithm, but instantaneous errors still exist. In this example, although the CDA method does not exhibit numerical oscillations, the switching action can only be reacted after the step length ends, resulting in instantaneous errors. In contrast, the method of this invention can accurately locate the switching behavior at each step length without oscillations.

[0039] for Figure 5The forced commutation circuit shown here, where SW represents a controllable power electronic switch, is turned on at time 0, and at... SW is forcibly turned off at any time, and D represents the freewheeling diode, which automatically turns on when the forward voltage it withstands is greater than 1V. Simulation results of different methods are as follows: Figure 6 , Figure 7 and Figure 8 As shown in the figure, the vertical axis and They represent inductance respectively The voltage and current of the branch circuits are represented by theoretical curves, which show the results obtained through theoretical calculations. The figure indicates that the CDA method is prone to "shutdown" during forced commutation. The PSCAD results show significant errors as the step size increases, while the simulation results of the method of this invention almost completely overlap with the theoretical curves. Within a step size of 100μs, the voltage and current errors are both lower than... It exhibits higher accuracy and stability.

[0040] Based on the analysis of the above examples, the simulation method proposed in this invention can effectively suppress numerical oscillations, accurately handle switching events, and significantly improve the reliability and practicality of simulation results, making it suitable for high-precision power electronics simulation applications.

Claims

1. A simulation method for eliminating oscillations and improving accuracy in switching action events, characterized in that: The specific steps are as follows: Step 1: Use the nodal admittance matrix of the topology before the switch state change Solve The values ​​of state variables and non-state variables at each moment; Step 2: After detecting the switch switching, determine the switch action time using linear interpolation. Meanwhile, interpolation is used to obtain the voltage and current of each branch at the moment of switch action; if multiple switch actions are detected, the first switch action event is processed first. Step 3: In The node admittance matrix of the topology immediately after the reactive switch action. And by using the Euler method after half a step, the solution is obtained. The values ​​of state variables and non-state variables at any given time; Step 4: Apply the formula to all state variables. Perform backward extrapolation interpolation, where Represents all state variables. This represents the state quantities in the voltage and current of each branch at the moment of switch operation obtained through interpolation in step 2, i.e., the state quantities at the moment of switch operation before the change in circuit topology, and obtains the topology after switch operation. Approximate values ​​of the state variables at any given time; Step 5: Using the approximate value obtained in the previous step as a historical term, re-solve using the Euler method after a half-step. The non-state values ​​at time t are used as the switching action times after the circuit topology change. The solution, and based on At any given time, determine if any other switches have commutated due to a sudden change in non-state variables. If so, return to step 3; otherwise, proceed to the next step. Step 6: Solve the equations sequentially using the half-step backward Euler method and the trapezoidal method. and The values ​​of state variables and non-state variables at each moment; Step 7: Obtain the switching action time after the instantaneous quantity generated by the switching action decays by back-out interpolation. The values ​​of state variables and non-state variables are obtained through extrapolation or interpolation. The values ​​of state variables and non-state variables at each moment; Step 8: Determine if... arrive If there are other switching actions during the specified time period, then start from step 2 again; otherwise, end the process.

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