Fast voltage interpolation method for electromagnetic transient simulation of power electronic device

Abstract

The invention discloses a rapid voltage interpolation method for electromagnetic transient simulation of a power electronic device, and the method comprises the steps: building an average model of a circuit according to the topology of different circuits; judging whether the current calculation point is the calculation point closest to the switching time or not; if the current calculation point is not the calculation point closest to the switching time, inputting a normal PWM signal to the switching tube; if the current calculation point is the calculation point closest to the switching time, calculating the magnitude of interpolation according to the values of the triangular carrier wave and the modulation wave at the calculation point, and inputting an interpolation signal between 0 and 1 to a switching tube; and integrating time by using a trapezoidal integration method according to the current voltage interpolation and the voltage interpolation at the previous moment, so as to ensure that the average value of the output voltage in one period is consistent with the actual condition. According to the method, interpolation is applied to the voltage near the voltage commutation moment, it is guaranteed that the simulation voltage is equivalent to the actual voltage on the equal-area method, and therefore accurate simulation of the electromagnetic transient state can be achieved.

Description

Technical Field

[0001] The invention relates to a method for electromagnetic transient simulation of power electronic devices, in particular to a fast voltage interpolation method for electromagnetic transient simulation of power electronic devices. Background Art

[0002] Nowadays, with the large-scale application of photovoltaic and wind power generation, there are more and more grid-connected inverters in power systems. The use of these inverters in the power grid may cause harmonic problems. Electromagnetic transient simulation is often used to study these harmonic problems. The switching model (SW) is a common simulation model in the electromagnetic transient model. In the switching model, the inverter is regarded as an ideal switch, which can simulate the switching operation of the power device. This model can simulate the harmonics caused by the switching operation very well. However, the switching model requires a very small time step to ensure the accuracy of the simulation. As long as there is such a switching device in the model, the time step of the entire system needs to be so small to match it, which increases the computational burden. The calculation time and calculation accuracy are contradictory and need to be weighed.

[0003] The average model was originally used for real-time simulation in order to simulate the characteristics of the inverter at a larger time step, especially to simulate higher harmonics. This method replaces each inverter pin with a controlled voltage source and then applies a pulse width modulated voltage wave to the AC side. Once switched, the voltage is corrected by an interpolation to reduce the error of the AC side current. The general average model is used for real-time simulation and requires the help of external hardware. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a fast voltage interpolation method for electromagnetic transient simulation of power electronic devices that can reduce the calculation time.

[0005] Technical solution: The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices described in the present invention comprises the following steps:

[0006] According to the topology of different circuits, an average model of the circuit is established;

[0007] Determine whether the current calculation point is the calculation point closest to the switching time;

[0008] If the current calculation point is not the calculation point closest to the switching time, a normal PWM signal is input to the switch tube;

[0009] If the current calculation point is the calculation point closest to the switching time, the interpolation value is calculated according to the values ​​of the triangular carrier and the modulation wave at this calculation point, and an interpolation signal between 0 and 1 is input to the switch tube;

[0010] Using the trapezoidal integration method, the time is integrated according to the current voltage interpolation and the voltage interpolation at the previous moment to ensure that the average value of the output voltage within a cycle is consistent with the actual situation.

[0011] Furthermore, according to the topology of different circuits, an average model of the circuit is established; specifically:

[0012] The average model of the Buck circuit includes the average model applicable to the CCM mode and the average model applicable to both the CCM mode and the DCM mode;

[0013] The average model of the three-phase inverter circuit is composed of the average models of multiple half-bridge circuits;

[0014] The average model of the three-level inverter circuit is composed of the average models of the three-level NPC half-bridge circuit.

[0015] Further, the average model suitable for the CCM mode includes a controlled voltage source and a controlled current source, wherein the controlled voltage source is at the output side and the controlled current source is at the input side for balancing power;

[0016] The average model applicable to both CCM mode and DCM mode includes a controlled voltage source, a controlled current source and a diode, wherein the controlled voltage source and the diode are connected at the output side and the controlled current source is at the input side.

[0017] Furthermore, the average model of the three-phase inverter circuit includes: two controlled voltage sources, two controlled current sources and two diodes, wherein a controlled voltage source and a diode are connected in series as a group, the two groups are connected in series, the middle point of the two groups is connected to the output side, and the current source is on the input side.

[0018] Furthermore, the average model of the three-level inverter circuit includes: two controlled voltage sources, two controlled current sources and two diodes, wherein a controlled voltage source and a diode are connected in series as a group, the two groups are connected in series, the middle point of the two groups is connected to the output side, and the current source is on the input side.

[0019] Furthermore, the controlled voltage source input in the average model is interpolated to obtain equivalent switching actions.

[0020] Furthermore, the switching time calculation formula is:

[0021]

[0022] Among them, t fall is the fall time of the waveform, t rise is the rise time of the waveform, t n is the current calculation point, t n-1 is the last calculated point, v* is the voltage reference value, v carrier is the triangular carrier, and h is the slope of the triangular carrier.

[0023] Furthermore, the interpolation value is calculated according to the values ​​of the triangular carrier and the modulated wave at the calculation point; specifically:

[0024]

[0025] in, and and the interpolation values ​​near the fall time and rise time, respectively. * is the sampling value of the modulation wave, v carrier is the triangular carrier, h is the slope of the triangular carrier, T s is the time step.

[0026] The system corresponding to the method of the present invention includes:

[0027] An average model building unit, used for building an average model of a circuit according to the topology of different circuits;

[0028] A judgment unit, judging whether the current calculation point is the calculation point closest to the switching time;

[0029] The interpolation unit is used to input a normal PWM signal to the switch tube if the current calculation point is not the calculation point closest to the switching time; if the current calculation point is the calculation point closest to the switching time, the interpolation value is calculated according to the values ​​of the triangular carrier and the modulation wave at this calculation point, and an interpolation signal between 0 and 1 is input to the switch tube;

[0030] The trapezoidal integration unit is used to use the trapezoidal integration method to integrate time according to the current voltage interpolation and the voltage interpolation at the previous moment, so as to ensure that the average value of the output voltage within one cycle is consistent with the actual situation.

[0031] The storage medium of the present invention stores a computer program, and when the computer program is executed by at least one processor, the steps of the fast voltage interpolation method for electromagnetic transient simulation of power electronic devices are implemented.

[0032] Beneficial effect: Compared with the prior art, the significant technical effect of the present invention is: by interpolating the switching signal during the switch state change, the integral of the output voltage over time under the trapezoidal integration method is kept consistent with the integral value under the actual situation, thereby compensating for the error generated by the switch model during the switch state change, thereby maintaining a certain accuracy at a larger time step, thereby reducing the calculation time. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1is a flow chart of the method of the present invention;

[0034] Figure 2 1 is a circuit topology diagram of Embodiment 1 of the present invention, wherein (a) is a circuit topology diagram applicable to the CCM mode; (b) is a circuit topology diagram applicable to the CCM mode and the DCM mode;

[0035] Figure 3 This is a circuit topology diagram of Embodiment 2 of the present invention;

[0036] Figure 4 This is a circuit topology diagram of Embodiment 3 of the present invention;

[0037] Figure 5 It is a schematic diagram of PWM wave generation in the present invention;

[0038] Figure 6 is a schematic diagram of the AC voltage level of the present invention;

[0039] Figure 7 The simulation curve diagram of the present invention; wherein (a) is a simulation curve of the output voltage measurement of the three-phase inverter circuit using the voltage interpolation method; (b) is a simulation curve of the output voltage measurement of the three-phase inverter circuit of the switch model; (c) is a spectrum diagram of the simulation curve of the output voltage measurement of the three-phase inverter circuit using the voltage interpolation method; (d) is a spectrum diagram of the simulation curve of the output voltage measurement of the three-phase inverter circuit of the switch model. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The voltage interpolation method of the present invention is a method that calculates the interpolation value based on a simple formula instead of averaging the switch signal through a hardware counter, which can reduce the calculation time. Since the proposed method no longer includes the "time averaging" process, the method is called the voltage interpolation method. The method changes the switch state (t fall and t rise ) before and after. The method includes: an equivalent model of the circuit under the average model, which is used to perform equivalent transformation of the output voltage according to the equal area method under different topologies; if the calculation point is not near the voltage reversal point, a normal PWM signal is input to the bridge arm; if the calculation point is near the voltage reversal point, an interpolation between 0 and 1 is input to the bridge arm; the size of the interpolation is calculated according to the value of the triangular carrier and the modulation wave at the calculation point; the trapezoidal integration method is used to ensure that the average value of the voltage within a cycle is consistent with the actual situation. Figure 1As shown, the specific steps include:

[0042] S1. Establish an average model of the circuit based on the circuit topology;

[0043] In the present invention, according to different circuit topologies, a corresponding average model can be used, and then a voltage interpolation method is used in the simulation, which is described below with a specific embodiment:

[0044] (1) Average model of the Buck circuit, including the average model applicable to CCM mode and the average model applicable to both CCM mode and DCM mode;

[0045] like Figure 2 As shown in (a), the average model applicable to CCM mode includes a controlled voltage source and a controlled current source. The controlled voltage source is on the output side and the controlled current source is on the input side to balance the power. Figure 2 The left part of (a) is the topology of the switching device in the Buck circuit, and the right part is the average model of this topology in CCM mode. v is the controlled voltage source, s is the interpolation, and v dc is the DC side voltage, i "c is a controlled current source, and i is the output measured current. Figure 2 As shown in (b), the average model applicable to CCM and DCM modes includes a controlled voltage source, a controlled current source and a diode. The controlled voltage source and the diode are connected on the output side, and the controlled current source is on the input side. Figure 2 The left part of (b) is the topology of the switching device in the Buck circuit, and the right part is the average model of the CCM and DCM modes of this topology. v is the controlled voltage source, s is the interpolation, and v dc is the DC side voltage, i "c is the controlled current source, i is the output measured current. The value of the controlled voltage source v is determined by the DC side voltage v dc and interpolation s determine the controlled current source i "c The value of is determined by the output measured current i and the interpolation value s. Figure 2 The circuit in (a) can only be used in CCM because it can deliver both forward and reverse currents i. Figure 2 The circuit in (b) limits the direction of the current i and can therefore be used in both DCM and CCM. The value of the controlled source is determined by the following formula: v = s·v dc ,i "c =s·i.

[0046] (2) The average model of the three-phase inverter circuit is composed of the average models of multiple half-bridge circuits;

[0047] See attached Figure 3The left part is the topology of the half-bridge circuit, and the right part is the average model of the half-bridge circuit. The average model isolates the input side and the output side, and replaces the switch action with a controlled source. The average model of the three-phase inverter circuit is composed of a half-bridge circuit. The half-bridge circuit can be regarded as the connection of two chopper circuits, so its average model can also be composed of two chopper circuits. The average model of the half-bridge circuit includes two controlled voltage sources v + and v - , two controlled current sources i "c + 、i "c - And two diodes, a controlled voltage source and a diode are connected in series as a group, the two groups are connected in series, the middle point of the two groups is connected to the output side, and the current source is on the input side. The value of the voltage source is determined by the DC side voltage v dc and interpolation, the value of the current source is determined by the output current i + and i - and interpolation. Their values ​​are: + =s + ·v dc , v - =s - ·v dc ,i "c + =s + ·i + ,i "c - =s - ·i - Among them, s + is the interpolation value of the upper bridge arm, s - is the interpolation value of the lower bridge arm, i + is the output current of the upper bridge arm, i - is the output current of the lower bridge arm.

[0048] (3) The average model of the three-level inverter circuit is composed of the average models of the three-level NPC half-bridge circuit;

[0049] See attached Figure 4 The left part is the topology of the three-level half-bridge circuit, and the right part is the average model of the three-level half-bridge circuit. The average model of the three-level circuit is composed of a three-level NPC type half-bridge circuit. By extending the two-level half-bridge structure to the three-level, the average model of the three-level NPC type half-bridge structure can be obtained, wherein the average model of the three-level NPC type half-bridge circuit includes two controlled voltage sources v + 、v - , two controlled current sources i "c1 、i "c2And two diodes, a controlled voltage source and a diode are connected in series as a group, the two groups are connected in series, the middle point of the two groups is connected to the output side, and the current source is on the input side. The interpolation of the four bridge arms from top to bottom is Controlled voltage source v + 、v - The value of the input voltage v dc1 、v dc2 and interpolation, the controlled current source i "c1 、i "c2 The value of the output current i + 、i - and interpolation. Their values ​​are:

[0050]

[0051] S2, judging whether the current calculation point is the calculation point closest to the switching time;

[0052] At the starting point of each cycle, each element in the circuit is calculated, and this point is called the calculation point.

[0053] S3, if the current calculation point is not the calculation point closest to the switching time, input a normal PWM signal to the switch tube;

[0054] S4. If the current calculation point is the calculation point closest to the switching time, the interpolation value is calculated according to the values ​​of the triangular carrier and the modulation wave at the calculation point, and an interpolation signal between 0 and 1 is input to the switch tube;

[0055] The principle of PWM wave generation is as follows Figure 5 As shown. The modulation wave is sampled synchronously to obtain the sampling value v of the modulation wave * , which is related to the triangular carrier v carrier Synchronous update, the slope h of the carrier is determined by the amplitude and frequency of the carrier. Based on these parameters, the following equation is obtained to calculate t fall and t rise :

[0056]

[0057] Among them, t fall is the waveform fall time, t rise is the waveform rise time, t n-1 and t n The distance t fall and t rise The nearest calculation point.

[0058] From (5) and (6), it can be seen that the exact switching time is obtained by calculation, so no matter how big the time step is, the exact switching time can be calculated by the formula.

[0059] The principle of calculating interpolation is as follows Figure 6 shown. Figure 6 The voltage v obtained by voltage interpolation method is shown ac_in0 The actual voltage v ac_ref The voltage interpolation method is used at t n-1 and t n Output interpolation voltage s fall V dc and rise V dc . Through the s fall V dc and rise V dc Assign appropriate values ​​so that v ac_in0 The shaded area in the ac_ref The shaded area in the figure is then, using trapezoidal integration, so that v ac_in0 The numerical integral of v is equal to ac_ref 's points.

[0060] S fall_ref represent Figure 6 The area of ​​the blue shaded part corresponds to v ac_ref From n-1 -T s / 2 to t n-1 +T s / 2. Its value is expressed by the following formula:

[0061]

[0062] Among them, V dc is the value of DC voltage, T s is the time step, t fall is the actual switching time, t n-1 is the distance t fall The nearest calculation point. Similarly, S rise_ref It is expressed by the following formula:

[0063]

[0064] Among them, t rise is the actual switching time, t n is the distance t rise The nearest calculation point. In addition, v ac_in0 The shaded area S in fall_in0 and S rise_in0 It is derived from the following formula:

[0065]

[0066] in, and Interpolation is the calculation point closest to the switching time, that is, the interpolation near the fall time and rise time, respectively.

[0067] In order to satisfy S in (7)-(10) fall_ref =S fall_in0 and S rise_ref =S rise_in0 ,get and Values:

[0068]

[0069] Substituting (5) into (11) and (6) into (12), we obtain and

[0070]

[0071] Among them, v * is the sampling value of the modulated wave, using synchronous sampling, along with the triangular carrier v carrier Update. The slope h of the carrier is determined by the amplitude and frequency of the carrier. When it is not near the switching time, the interpolation (include ) is the same as the signal in the switch model, which only has 0 and 1. Through this interpolation, the integral value of the voltage in the model can be made the same as the actual value.

[0072] S5. Use the trapezoidal integration method to integrate the time according to the current voltage interpolation and the voltage interpolation at the previous moment to ensure that the average value of the output voltage within one cycle is consistent with the actual situation.

[0073] The trapezoidal integration method calculates the area of ​​the output voltage over time based on the output voltage value at the current moment, the output voltage value at the previous moment and the time step, and is used to ensure that the integral value of the output voltage during the switch state change is consistent with the actual situation, so as to reduce the error caused by the switch state change and maintain the calculation accuracy at a larger time step.

[0074] Simulation experiment:

[0075] Figure 7 The voltage simulation curve of the output side of the three-phase two-level inverter circuit using the voltage interpolation method in one embodiment of the present invention is shown in FIG. The simulation time is set to 1s, the time step of the voltage interpolation method is set to 5μs, and the time step of the switch model is set to 1μs. Figure 7 (a) and Figure 7As can be seen in (b), the waveforms of the voltage interpolation method and the switch model are roughly the same, indicating that the selection of these time steps can simulate the current waveform more accurately. The calculation time of the voltage interpolation method is 4.1519s, and the calculation time of the switch model is 18.7633s. The voltage interpolation method greatly shortens the calculation time while having almost the same accuracy as the switch model. Figure 7 As shown in (c), the switching subharmonics can also be reflected in the voltage interpolation method. sw and 2f sw There is an obvious peak value of the harmonic component at Figure 7 Compared with (d), Figure 7 The curve in (c) is smoother because the step size of 5 μs is closer to the switching frequency f sw , the calculation point may be far away from the switching moment. In this way, the harmonics of the switching frequency will become lower and the harmonics of the surrounding frequencies will increase. If you want to make the harmonics more accurate, you can choose a smaller step size and increase the number of calculation points to approach the switching moment. However, this will increase the calculation time. How to choose the step size depends on the simulation requirements.

Claims

1. A fast voltage interpolation method for electromagnetic transient simulation of power electronic devices, characterized in that: The following steps are involved: According to the topology of different circuits, an average model of the circuit is established; Determine whether the current calculation point is the calculation point closest to the switching time; If the current calculation point is not the calculation point closest to the switching time, a normal PWM signal is input to the switch tube; If the current calculation point is the calculation point closest to the switching time, the interpolation value is calculated according to the values ​​of the triangular carrier and the modulation wave at this calculation point, and an interpolation signal between 0 and 1 is input to the switch tube; Using the trapezoidal integration method, the time is integrated according to the current voltage interpolation and the voltage interpolation at the previous moment to ensure that the average value of the output voltage within a cycle is consistent with the actual situation.

2. The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices according to claim 1, characterized in that: According to the topology of different circuits, an average model of the circuit is established; specifically: The average model of the Buck circuit includes the average model applicable to the CCM mode and the average model applicable to both the CCM mode and the DCM mode; The average model of the three-phase inverter circuit is composed of the average models of multiple half-bridge circuits; The average model of the three-level inverter circuit is composed of the average models of the three-level NPC half-bridge circuit.

3. The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices according to claim 2, characterized in that: The average model applicable to the CCM mode includes a controlled voltage source and a controlled current source, wherein the controlled voltage source is at the output side and the controlled current source is at the input side, for balancing the power; The average model applicable to both CCM mode and DCM mode includes a controlled voltage source, a controlled current source and a diode, wherein the controlled voltage source and the diode are connected at the output side and the controlled current source is at the input side.

4. The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices according to claim 2, characterized in that: The average model of the three-phase inverter circuit includes: two controlled voltage sources, two controlled current sources and two diodes, wherein a controlled voltage source and a diode are connected in series as a group, the two groups are connected in series, the middle point of the two groups is connected to the output side, and the current source is on the input side.

5. The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices according to claim 2, characterized in that: The average model of the three-level inverter circuit includes: two controlled voltage sources, two controlled current sources and two diodes, wherein a controlled voltage source and a diode are connected in series as a group, the two groups are connected in series, the middle point of the two groups is connected to the output side, and the current source is on the input side.

6. The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices according to claim 1, characterized in that: The controlled voltage source input in the average model is interpolated to obtain equivalent switching actions.

7. The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices according to claim 1, characterized in that: The switching time calculation formula is: Among them, t fall is the fall time of the waveform, t rise is the rise time of the waveform, t n is the current calculation point, t n-1 is the last calculated point, v * is the voltage reference value, v carrier is the triangular carrier, and h is the slope of the triangular carrier.

8. The fast voltage interpolation method for electromagnetic transient simulation of power electronic devices according to claim 1, characterized in that: According to the values ​​of the triangular carrier and the modulated wave at the calculation point, the size of the interpolation is calculated; specifically: in, and and the interpolation values ​​near the fall time and rise time, respectively. * is the sampling value of the modulation wave, v carrier is the triangular carrier, h is the slope of the triangular carrier, T s is the time step.

9. A fast voltage interpolation system for electromagnetic transient simulation of power electronic devices, characterized in that: include: An average model building unit, used for building an average model of a circuit according to the topology of different circuits; A judgment unit, judging whether the current calculation point is the calculation point closest to the switching time; The interpolation unit is used to input a normal PWM signal to the switch tube if the current calculation point is not the calculation point closest to the switching time; if the current calculation point is the calculation point closest to the switching time, the interpolation value is calculated according to the values ​​of the triangular carrier and the modulation wave at this calculation point, and an interpolation signal between 0 and 1 is input to the switch tube; The trapezoidal integration unit is used to use the trapezoidal integration method to integrate time according to the current voltage interpolation and the voltage interpolation at the previous moment, so as to ensure that the average value of the output voltage within one cycle is consistent with the actual situation.

10. A storage medium, characterized in that: The storage medium stores a computer program, which, when executed by at least one processor, implements the steps of the fast voltage interpolation method for electromagnetic transient simulation of power electronic devices as described in any one of claims 1 to 8.

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