Real-time simulation zero current judgment method for power electronic system

Abstract

The invention belongs to the technical field of real-time simulation of power electronic topology, and relates to a method for judging real-time simulation zero current of a power electronic system. The method comprises the following steps: configuring a blocking judgment module for the diode switching circuit; determining the switching state judgment logic of the diode switching circuit; constructing a mathematical calculation model of the diode switching circuit and performing real-time simulation; when the current zero crossing point of the diode is detected, the blocking judgment module outputs a blocking signal to control the diode to enter a blocking state; and in the blocking state, continuously monitoring the voltage at the two ends of the uncontrolled device and the direction and amplitude of the virtual electromotive force, and when it is detected that the voltage direction is consistent with the direction of the virtual electromotive force and the voltage amplitude exceeds a preset conduction threshold value, releasing the blocking signal and controlling the diode to enter the conduction state again. According to the method, the zero-point current state and the conduction state of the uncontrolled device can be accurately identified on the premise of not increasing the simulation step length and the number of iterations, and the stability and the accuracy of real-time simulation are remarkably improved.

Description

Technical Field

[0001] This application belongs to the field of real-time simulation technology of power electronic topology, and specifically relates to a method for determining zero-point current in real-time simulation of power electronic systems without iterative calculation. Background Technology

[0002] In real-time simulations, due to the limitation of the step size, it is usually only possible to obtain the previous moment. and the next moment after one step. The simulation system cannot capture the current value itself, but it cannot capture the current change between the two. For some uncontrolled devices (such as diodes), their conduction and cutoff states are entirely determined by the current direction. In a rectifier circuit composed of such devices connected in parallel, the device conducts in the forward direction when the current is greater than zero, conducts in the reverse direction when the current is less than zero, and is only completely turned off when the current is equal to zero. If the instant of the current zero-crossing occurs between two sampling times, the simulation system will not be able to detect the current zero-crossing phenomenon. Uncontrolled devices that should be turned off will be misjudged as still conducting, resulting in alternating forward and reverse conduction and causing current oscillations. Traditional methods usually correct this error through a finite number of iterative calculations.

[0003] Therefore, there is an urgent need for a technical solution to overcome or mitigate at least one of the aforementioned defects in the existing technology. Summary of the Invention

[0004] The purpose of this application is to provide a method for determining zero-point current in real-time simulation of power electronic systems, so as to solve the problem that it is difficult to capture the current crossing zero point state in real-time simulation and the stability problem caused by zero-point current oscillation in the existing technology.

[0005] The technical solution of this application is:

[0006] A method for determining zero-point current in real-time simulation of a power electronic system includes:

[0007] Configure a blocking detection module for diode switching circuits to detect the current state of uncontrolled devices;

[0008] Determine the switching state judgment logic of the diode switching circuit to distinguish the conduction, turn-off and blocking states of the uncontrolled device under different current directions;

[0009] Based on the switching state judgment logic, a mathematical calculation model of the diode switching circuit is constructed and real-time simulation is performed to determine whether the diode current has crossed zero.

[0010] When the diode current crosses zero, the blocking judgment module outputs a blocking signal to control the diode to enter the blocking state, so as to avoid the uncontrolled device from being falsely turned on and the current oscillation caused by the failure to capture the zero current.

[0011] A virtual electromotive force is introduced as an auxiliary criterion. The virtual electromotive force is the maximum port potential difference that the converter power supply side can provide under the current topology without considering the influence of energy storage components. It is used to characterize the equivalent driving voltage potential energy of the uncontrolled rectifier branch.

[0012] In the blocking state, the voltage across the uncontrolled device and the direction and amplitude of the virtual electromotive force are continuously monitored. When the voltage direction is detected to be consistent with the direction of the virtual electromotive force and the voltage amplitude exceeds the preset conduction threshold, the blocking signal is released, and the diode is controlled to re-enter the conduction state, thereby realizing the dynamic recovery of the uncontrolled device.

[0013] In at least one embodiment of this application, the virtual electromotive force is calculated as follows:

[0014] Without considering the influence of energy storage components, at each discrete moment in the real-time simulation, when the converter is in a non-conducting state, the open-circuit voltage input to the converter port (p+, p-) is extracted. This voltage is taken as the maximum port potential difference that the converter power supply side can provide at that moment, and is defined as the virtual electromotive force in the discontinuous state at that moment:

[0015] U vf (t)= U p+ (t)-U p- (t)

[0016] Among them, U p- U p+ This represents the node potential of the power supply-side equivalent network at that moment.

[0017] In at least one embodiment of this application, the diode switching circuit is a single-phase diode uncontrolled rectifier circuit;

[0018] During the positive half-cycle of the power supply, diodes D1 and D4 are forward biased and conduct, while diodes D2 and D3 are reverse biased and turn off.

[0019] During the negative half-cycle of the power supply, diodes D1 and D4 are turned off due to reverse voltage, while diodes D2 and D3 are turned on due to forward voltage.

[0020] Initially, the voltage across the capacitor is 0. As the power supply voltage increases, current flows through the load resistor R and the capacitor C. When the power supply voltage is less than the voltage across the capacitor C, the capacitor C begins to discharge. When the power supply voltage is greater than the voltage across the capacitor C, it continues to charge the capacitor C, and this cycle repeats.

[0021] In at least one embodiment of this application, the switching state determination logic of the single-phase diode uncontrolled rectifier circuit is as follows:

[0022] In a single-phase diode uncontrolled rectifier circuit with two phase arms, the switching state signal of phase a is Hsa, and the switching state signal of phase b is Hsb. The values ​​of the switching state signals are:

[0023] When the upper bridge arm switch is turned on and the lower bridge arm switch is turned off in phase a, Hsa=1; when the upper bridge arm switch is turned off and the lower bridge arm switch is turned on, Hsa=0.

[0024] When the upper bridge arm switch is on and the lower bridge arm switch is off in phase b, Hsb=1; when the upper bridge arm switch is off and the lower bridge arm switch is on, Hsb=0.

[0025] In at least one embodiment of this application, the mathematical calculation model of the single-phase diode uncontrolled rectifier circuit is as follows:

[0026]

[0027] When diodes D1 and D4 are turned on, i s >0, u 12 >0;

[0028] When diodes D2 and D3 are turned on, i s <0, u 12 <0;

[0029] Where Ls is the leakage inductance of the secondary winding of the traction transformer, i s e is the power supply current. s Rs is the power supply voltage, and u is the equivalent resistance of the secondary winding of the traction transformer. 12 For the bridge arm voltage, u a1 Let u be the voltage of phase a bridge arm. b1 For the voltage of phase b bridge arm, u dc For the load voltage, i dc Let i be the load current. R Let i be the load resistance current. C Where C is the capacitor current, C is the capacitance, and R is the load resistance.

[0030] In at least one embodiment of this application, when a diode current is detected to cross zero, the blocking determination module outputs a blocking signal to control the diode to enter a blocking state, including:

[0031] When the load voltage u dc The absolute value of is greater than the absolute value of the virtual electromotive force, and the power supply current i s When the diode current approaches zero, determine that the diode current has crossed the zero point;

[0032] The blocking judgment module outputs a blocking signal BL=0, forcibly turning off the bridge arm switch and controlling the diode to enter the blocking state;

[0033] In the blocking state, the load current i dc and power supply current i s Forced to zero, bridge arm voltage u 12 The voltage value remains the same as the voltage value at the previous simulation time.

[0034] In at least one embodiment of this application, the diode switching circuit is an NPC-type three-level rectifier circuit, and each phase arm of the NPC-type three-level rectifier circuit includes four switching elements, four freewheeling diodes, and two box-type diodes.

[0035] In at least one embodiment of this application, the switching state determination logic of the NPC-type three-level circuit is as follows:

[0036] When T1 and T2 are turned on, regardless of the direction of the current in phase A, the bridge arm of phase A operates in state P.

[0037] When T3 and T4 are turned on, regardless of the direction of the current in phase A, the bridge arm of phase A operates in the N state;

[0038] When T3 is turned on and the current of phase A is positive, the phase A bridge arm is in the 0 state;

[0039] When T2 is turned on and the current of phase A is negative, the phase A bridge arm is in the 0 state.

[0040] When T3 is turned off and the current of phase A is positive, the phase A bridge arm operates in state P.

[0041] When T2 is turned off and the current of phase A is negative, the phase A bridge arm operates in the N state;

[0042] Among them, T1, T2, T3, and T4 are the switching elements of the A-phase bridge arm.

[0043] In at least one embodiment of this application, the mathematical calculation model of the NPC-type three-level rectifier circuit is as follows:

[0044] Each phase arm of the NPC-type three-level rectifier circuit is equivalent to a three-way switch S. a ;in,

[0045] The operating state of the NPC-type three-level rectifier circuit is as follows:

[0046] If T1=1, T2=1, then S a =1;

[0047] If T3=1 and T4=1, then S a =-1;

[0048] If T2=1, T1=0, and i a <0, then S a =0;

[0049] If T3=1, T4=0, and i a If S ≥ 0, then a =0;

[0050] If T2=0, T1=0, and i a <0, then S a =-1;

[0051] If T3=0, T4=0, and i a If S ≥ 0, then a =1;

[0052] The output voltage and current are obtained based on the different operating states of the NPC-type three-level rectifier circuit:

[0053] When S a When =1:

[0054]

[0055] When S a When =0:

[0056]

[0057] When S a When =-1:

[0058]

[0059] Among them, i a Let u be the phase A current. a i1 is the voltage at the A-phase bridge arm port to ground, i2 is the current in the upper bridge arm, i1 is the current in the lower bridge arm, u1 is the voltage at point P, and u2 is the voltage at point N.

[0060] In at least one embodiment of this application, when a diode current is detected to cross zero, the blocking determination module outputs a blocking signal to control the diode to enter a blocking state, including:

[0061] when When the diode current crosses zero, the blocking judgment module outputs a lockout signal Block=0, forcibly turning off the bridge arm switch and controlling the diode to enter the blocking state.

[0062] At other times, the blocking judgment module outputs a blocking signal Block=1;

[0063] Under the blocking state, the phase A current and phase A voltage satisfy:

[0064]

[0065] Among them, i a Let e ​​be the phase A current. a This is the voltage of phase A power supply.

[0066] The invention has at least the following beneficial technical effects:

[0067] The real-time simulation zero-point current judgment method for power electronic systems in this application solves the stability problem caused by zero-point current oscillation by adding an additional blocking judgment module. After the diode current is detected to be crossing zero, the module is made to enter the blocking state. The self-starting process of a single-phase diode uncontrolled rectifier circuit and an NPC-type three-level rectifier circuit are used as examples. Attached Figure Description

[0068] Figure 1 This is a schematic diagram of a real-time simulation zero-point current determination method for power electronic systems according to one embodiment of this application;

[0069] Figure 2 This is a single-phase diode uncontrolled rectifier circuit diagram according to one embodiment of this application;

[0070] Figure 3 This is a single-phase diode uncontrolled rectifier circuit diagram with diodes D1 and D4 in the on state according to one embodiment of this application;

[0071] Figure 4 This is a single-phase diode uncontrolled rectifier circuit diagram with diodes D2 and D3 in the conducting state according to one embodiment of this application;

[0072] Figure 5 This is a circuit diagram of a single-phase diode uncontrolled rectifier circuit in the capacitor discharge state according to one embodiment of this application;

[0073] Figure 6 In one embodiment of this application, when R=10Ω, the current i in the single-phase diode uncontrolled rectifier circuit is determined by adding a blocking judgment module, a traditional mathematical model, and a Simulink model. s Waveform comparison chart;

[0074] Figure 7 In one embodiment of this application, when R = infinity, the current i in the single-phase diode uncontrolled rectifier circuit is determined by adding a blocking judgment module, a traditional mathematical model, and a Simulink model. s Waveform comparison chart;

[0075] Figure 8 In one embodiment of this application, when R=10Ω, the load voltage u of the single-phase diode uncontrolled rectifier circuit is determined by adding a blocking judgment module, a traditional mathematical model, and a Simulink model. dc Waveform comparison chart;

[0076] Figure 9In one embodiment of this application, when R = infinity, the load voltage u of the single-phase diode uncontrolled rectifier circuit is determined by adding a blocking judgment module, a traditional mathematical model, and a Simulink model. dc Waveform comparison chart;

[0077] Figure 10 This is a circuit diagram of an NPC-type three-level rectifier according to one embodiment of this application;

[0078] Figure 11 This is a circuit diagram showing the operating state of phase A of an NPC-type three-level rectifier circuit according to one embodiment of this application;

[0079] Figure 12 This is an equivalent model of the A-phase bridge arm of an NPC-type three-level rectifier circuit according to one embodiment of this application;

[0080] Figure 13 This is a circuit diagram of the operating state of an NPC-type three-level rectifier circuit during self-starting according to one embodiment of this application;

[0081] Figure 14 This is a comparison diagram of the output voltage waveforms of an NPC-type three-level rectifier circuit and a Simulink model according to one embodiment of this application;

[0082] Figure 15 This is a comparison diagram of the output voltage waveforms of the mathematical model and the Simulink model of an NPC-type three-level rectifier circuit according to one embodiment of this application;

[0083] Figure 16 This is a comparison diagram of the current waveforms during self-starting of an NPC-type three-level rectifier circuit with an added blocking judgment module, a traditional mathematical model, and a Simulink model, according to one embodiment of this application.

[0084] Figure 17 This is a comparison diagram of the output voltage waveforms of an NPC-type three-level rectifier circuit with an added blocking judgment module, a traditional mathematical model, and a Simulink model during self-starting, according to one embodiment of this application.

[0085] Figure 18 This is a real-time simulation flowchart of one embodiment of this application. Detailed Implementation

[0086] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0087] The following is in conjunction with the appendix Figures 1 to 18 This application will be described in further detail.

[0088] This application provides a method for determining zero-point current in real-time simulation of a power electronic system, including the following steps:

[0089] Configure a blocking detection module for diode switching circuits to detect the current state of uncontrolled devices;

[0090] Determine the switching state judgment logic of the diode switching circuit to distinguish the conduction, turn-off and blocking states of uncontrolled devices under different current directions;

[0091] Based on the switching state judgment logic, a mathematical calculation model of the diode switching circuit is constructed and real-time simulation is performed to determine whether the diode current has crossed zero.

[0092] When the diode current crosses zero, the blocking judgment module outputs a blocking signal to control the diode to enter the blocking state, so as to avoid the uncontrolled device from being falsely turned on and the current oscillation caused by the failure to capture the current zero point.

[0093] Virtual electromotive force is introduced as an auxiliary criterion. Virtual electromotive force is the maximum port potential difference that the converter power supply side can provide under the current topology without considering the influence of energy storage components. It is used to characterize the equivalent drive voltage potential energy of the uncontrolled rectifier branch.

[0094] In the blocking state, the voltage across the uncontrolled device and the direction and amplitude of the virtual electromotive force are continuously monitored. When the voltage direction is detected to be consistent with the direction of the virtual electromotive force and the voltage amplitude exceeds the preset conduction threshold, the blocking signal is released, and the diode is controlled to re-enter the conduction state, thereby realizing the dynamic recovery of the uncontrolled device.

[0095] The principle of the real-time simulation zero-point current determination method for power electronic systems in this application is as follows: Figure 1As shown, if the blocking state is not correctly captured at the zero-crossing of the current, the blocking judgment module forces the switch to enter the blocking state. The virtual electromotive force is calculated as follows:

[0096] Without considering the influence of energy storage components, at each discrete moment in the real-time simulation, when the converter is in a non-conducting state, the open-circuit voltage input to the converter port (p+, p-) is extracted. This voltage is taken as the maximum port potential difference that the converter power supply side can provide at that moment, and is defined as the virtual electromotive force in the discontinuous state at that moment:

[0097] U vf (t)=U p+ (t)-U p- (t)

[0098] Among them, U p- U p+ This represents the node potential of the power supply-side equivalent network at that moment.

[0099] In one embodiment of this application, using Figure 2 Taking the diode switching circuit shown as an example, the method for determining zero-point current in real-time simulation of the power electronic system in this application will be explained. Figure 2 As shown, the diode switching circuit is a single-phase diode uncontrolled rectifier circuit. For ease of analysis, the effect of magnetic circuit saturation of the traction transformer is ignored, and the traction transformer is considered equivalent to a voltage source. s i is the power supply voltage. s Rs is the power supply current, Ls is the equivalent resistance of the secondary winding of the traction transformer, Ls is the leakage inductance of the secondary winding of the traction transformer, D1, D2, D3, and D4 are diodes, R is the load resistance, and C is the capacitor.

[0100] According to the circuit diagram, during the positive half-cycle of the power supply, diodes D1 and D4 are forward-biased and conduct, while diodes D2 and D3 are reverse-biased and turn off. During the negative half-cycle of the power supply, diodes D1 and D4 are reverse-biased and turn off, while diodes D2 and D3 are forward-biased and conduct.

[0101] Initially, the voltage across the capacitor is 0. As the power supply voltage increases, current flows through the load resistor R and the capacitor C (charging the capacitor). Since the voltage across the capacitor cannot change abruptly, when the power supply voltage is less than the voltage across capacitor C, capacitor C begins to discharge. When the power supply voltage is greater than the voltage across capacitor C, it will continue to charge capacitor C, and this cycle repeats.

[0102] A diode is a semiconductor device controlled by the voltage and current across its terminals. When a diode is forward biased, it begins to conduct; when the current flowing through the device becomes zero, the diode turns off; when a diode is reverse biased, it remains in the off state. This example models a diode using an ideal switch as a model.

[0103] In this embodiment, the switching state determination logic of the single-phase diode uncontrolled rectifier circuit is as follows:

[0104] In a single-phase diode uncontrolled rectifier circuit with two phase arms, the switching state signal of phase a is Hsa, and the switching state signal of phase b is Hsb. The values ​​of the switching state signals are:

[0105] When in phase a bridge arm, if the upper bridge arm switch is on and the lower bridge arm switch is off, Hsa = 1; if the upper bridge arm switch is off and the lower bridge arm switch is on, H sa =0;

[0106] When the upper bridge arm switch is turned on and the lower bridge arm switch is turned off in phase b, H sb =1; Upper arm switch is off, lower arm switch is on, H sb =0.

[0107] In this embodiment, the mathematical calculation model of the single-phase diode uncontrolled rectifier circuit is as follows:

[0108]

[0109] like Figure 3 As shown, when diodes D1 and D4 are turned on, i s >0, u 12 >0;

[0110] like Figure 4 As shown, when diodes D2 and D3 are conducting, i s <0, u 12 <0;

[0111] Where Ls is the leakage inductance of the secondary winding of the traction transformer, i s e is the power supply current. s Rs is the power supply voltage, and u is the equivalent resistance of the secondary winding of the traction transformer. 12 For the bridge arm voltage, u a1 Let u be the voltage of phase a bridge arm. b1 For the voltage of phase b bridge arm, u dc For the load voltage, i dc Let i be the load current. R Let i be the load resistance current. C Where C is the capacitor current, C is the capacitance, and R is the load resistance.

[0112] In this embodiment, when the diode current is detected to cross zero, the blocking judgment module outputs a blocking signal to control the diode to enter the blocking state, including:

[0113] The virtual electromotive force (EMF) refers to the maximum port voltage difference that the converter's power supply side can provide under the current topology, without considering the influence of energy storage components such as inductors and capacitors in the circuit. It is used to characterize the equivalent drive voltage potential energy of the uncontrolled rectifier branch; this voltage reflects the theoretical upper limit of the rectifier branch under ideal conduction conditions, directly determined by the power supply voltage. In this example, the virtual EMF is the power supply voltage e. s The absolute value. When the load voltage u dc The absolute value is greater than the power supply voltage e s The absolute value of, and the power supply current i s When the diode current approaches zero, determine that the diode current has crossed the zero point;

[0114] The blocking judgment module outputs a blocking signal BL=0, forcibly turning off the bridge arm switch and controlling the diode to enter the blocking state;

[0115] In the blocking state, the load current i dc and power supply current i s Forced to zero, bridge arm voltage u 12 The voltage value remains the same as the voltage value at the previous simulation time.

[0116] When the capacitor voltage is about to reach the threshold and charging continues, due to the step size limitation, the capacitor charges beyond the threshold in the next moment, at which point the capacitor voltage is greater than the voltage on the left side of the switch. In traditional real-time simulation, the capacitor discharges to the load resistor in the next moment, such as... Figure 5 As shown, after a discharge step, the capacitor voltage will drop below the voltage on the left side of the switch, and the power supply will recharge the capacitor, repeating this cycle continuously.

[0117] After adding the blocking detection module, when the absolute value of the load voltage is detected to be greater than the absolute value of the power supply voltage, and the current i s When the switch approaches zero, a lock / unlock signal is given to forcibly shut it off.

[0118] Because when the current i s When the voltage is close to zero, the power supply voltage can be essentially equated to the voltage on the left side of the switch, at which point the capacitor is about to reach its charging threshold. When the absolute value of the load voltage is greater than the absolute value of the power supply voltage, it indicates that the capacitor voltage has been overcharged, and the polarity of the voltage across the switch changes, meaning the current i... s Since the current has already passed zero, and the switch remains in the off state when the current is equal to 0, a lock signal is given at this time to forcibly turn off the switch.

[0119] Add a latching signal BL. When the switch is in the blocked state, BL=0, i dc =is =0, bridge arm voltage u 12 Equal to the voltage at the previous moment:

[0120]

[0121] Conversely, BL=1:

[0122]

[0123] like Figure 6-9 As shown, a comparison of the output waveforms of the single-phase diode uncontrolled rectifier circuit after adding the blocking judgment module and the existing model is presented. By comparing the single-phase diode uncontrolled rectifier circuit with the traditional modeling and simulation, it can be seen that this application can effectively avoid the oscillation problem caused by zero-point current, improve numerical stability, and better achieve the desired ideal state.

[0124] In another embodiment of this application, the diode switching circuit is an NPC-type three-level rectifier circuit. The converter's operating principle is analyzed as follows: Figure 10 As shown, the diode-mounted rectifier, also known as a neutral-point-mounted rectifier, is an NPC-type three-level rectifier circuit. Each phase arm includes four switching elements, four freewheeling diodes, and two mounting diodes. The midpoints of the two series-connected devices are connected through the mounting diodes and the midpoint of the DC-side capacitors. The mounting diodes provide a current path to prevent short circuits in the capacitors when the switching transistors are on. The circuit is based on a two-level rectifier, but the number of DC-side capacitors is increased to two, the number of switching transistors per phase arm is increased from two to four, and mounting diodes are added to each phase arm. This adds a zero level to the existing positive and negative voltage levels, creating a three-level circuit, which improves the output voltage waveform quality.

[0125] The characteristics of a diode box-type rectifier include:

[0126] 1) The DC-side voltage value of each switching device is reduced to half of the DC-side voltage value, which improves waveform quality and reduces switching frequency;

[0127] 2) The rate of voltage rise is reduced to half that of a two-level converter;

[0128] 3) The increase in the number of output voltage levels reduces the relative amplitude of each level, thus reducing voltage variation, current ripple, and electromagnetic interference.

[0129] 4) When the output voltage of one of the three phases is zero, current flows into or out of the midpoint of the DC side capacitor. When the inflow and outflow currents are not equal, the voltages of the upper and lower capacitors are not equal, the midpoint potential drifts, and the output voltage waveform quality is affected.

[0130] 5) The switching frequencies of power devices on the same bridge arm are different. Compared with the power switches in the middle of the bridge arm, the power switches in the middle of the bridge arm have a much longer conduction time and bear a heavier load. This results in different utilization rates of the switching devices.

[0131] In this embodiment, the switching state determination logic of the NPC-type three-level circuit is as follows:

[0132] When T1 and T2 are turned on, regardless of the direction of the current in phase A, the bridge arm of phase A operates in state P.

[0133] When T3 and T4 are turned on, regardless of the direction of the current in phase A, the bridge arm of phase A operates in the N state;

[0134] When T3 is turned on and the current of phase A is positive, the phase A bridge arm is in the 0 state;

[0135] When T2 is turned on and the current of phase A is negative, the phase A bridge arm is in the 0 state.

[0136] When T3 is turned off and the current of phase A is positive, the phase A bridge arm operates in state P.

[0137] When T2 is turned off and the current of phase A is negative, the phase A bridge arm operates in the N state;

[0138] Among them, T1, T2, T3, and T4 are the switching elements of the A-phase bridge arm.

[0139] like Figure 11-12 As shown, taking phase A of an NPC-type three-level rectifier circuit as an example, its operating state is analyzed, with the priority order for judging the operating state from front to back:

[0140] 1) When T1 and T2 are turned on, (assuming the current in phase A is i) a (The direction of flow into the rectifier is positive, and vice versa is negative). At this time, regardless of i... a Whether the value is positive or negative, the circuit operates in the P state. Ignore the transistor voltage drop; at this time, u... a =u1, u1= u PO Among them, neutral point O is grounded, V O =0;

[0141] 2) When T3 and T4 are turned on, regardless of the current in phase A... Whether positive or negative, the circuit operates in the N state. Ignore the transistor voltage drop; at this time, u... a =u2, where u2= u PO ;

[0142] 3) When T3 is on, and i a When it is positive, the current i a Flowing through T3, D 14The current flows to the neutral point O, at which point the circuit operates in state O. Ignoring the transistor voltage drop, u... a =0;

[0143] 4) When T2 is on, and i a When it is negative, the current i a Flowing through T2, D 13 Flow to neutral point At this time, the circuit is operating in the 0 state, and the voltage drop across the transistor is negligible. At this time, u a =0;

[0144] 5) When T3 is off, and i a When it is positive, the current i a The circuit can only reach point P through D2 and D1. At this time, the circuit operates in state P. Ignore the voltage drop across the transistor. At this point, u... a =u1;

[0145] 6) When T2 is off, and i a When it is negative, the current i a The circuit can only reach point N through D3 and D4. At this point, the circuit operates in state N. Ignoring the transistor voltage drop, u... a =u2.

[0146] In this embodiment, the mathematical calculation model of the NPC-type three-level rectifier circuit is as follows:

[0147] Each phase arm of the NPC-type three-level rectifier circuit is equivalent to a three-way switch S. a ;

[0148] When S a When connected to point P, the circuit operates in state P. At this time, let S... a =1, when S a When connected to point O, the circuit operates in state O. At this time, let S... a =0, when S a When connected to point N, the circuit operates in state N. At this point, let S... a =-1. The operating state of the circuit is determined by switch T and i. a A joint decision.

[0149] The operating states of the NPC-type three-level rectifier circuit are as follows:

[0150] 1) If T1=1, T2=1, then S a =1;

[0151] 2) If T3=1 and T4=1, then S a =-1;

[0152] 3) If T2=1, T1=0, and i a <0, then S a =0;

[0153] 4) If T3=1, T4=0, and i a If S ≥ 0, then a =0;

[0154] 5) If T2=0, T1=0, and i a <0, then S a =-1;

[0155] 6) If T3=0, T4=0, and i a If S ≥ 0, then a =1;

[0156] The output voltage and current are obtained based on the different operating states of the NPC-type three-level rectifier circuit:

[0157] When S a When =1:

[0158]

[0159] When S a When =0:

[0160]

[0161] When S a When =-1:

[0162]

[0163] Among them, i a Let u be the phase A current. a i1 is the voltage at the A-phase bridge arm port to ground, i2 is the current in the upper bridge arm, i1 is the current in the lower bridge arm, u1 is the voltage at point P, and u2 is the voltage at point N.

[0164] The virtual electromotive force is:

[0165] U vf = max(|U ab |, |U bc |, |U ca |)

[0166] Furthermore, when no control signal is input to the NPC topology, the circuit will automatically start up. At this time, T1, T2, ..., T12 are all 0. The circuit will then operate in states as shown in 5) and 6), depending on the direction of the current. The power supply charges C1 and C2 through D1, D2, D3, and D4. Figure 13 As shown.

[0167] Taking phase A as an example, when i a When the absolute value of the voltage is close to 0, it means the capacitor is about to reach the charging threshold. When the absolute value of the capacitor voltage is detected to be greater than the virtual electromotive force U...vf When the voltage across the switch changes sign, meaning the current crosses zero during this period, the switch can be directly opened, putting the circuit in a blocking state. To maintain this blocking state, a latching signal (Block) can be added.

[0168] In this embodiment, when the diode current crosses zero, the blocking judgment module outputs a blocking signal to control the diode to enter the blocking state, including:

[0169] when When the diode current crosses zero, the blocking judgment module outputs a lockout signal Block=0, forcibly turning off the bridge arm switch and controlling the diode to enter the blocking state.

[0170] At other times, the blocking judgment module outputs a blocking signal Block=1;

[0171] In the blocking state, the voltage and current of phase A bridge arm are corrected according to the block size:

[0172]

[0173] Among them, i a Let e ​​be the phase A current. a This is the voltage of phase A power supply.

[0174] like Figure 14-17 As shown, a comparison diagram of the output waveforms of the NPC-type three-level rectifier circuit after adding the blocking judgment module and the existing model is presented. By comparing the NPC-type three-level rectifier circuit with traditional modeling and simulation, it can be seen that this application can effectively avoid the oscillation problem caused by zero-point current, improve numerical stability, and better achieve the desired ideal state.

[0175] like Figure 18 As shown, a real-time simulation process is provided.

[0176] This application presents a real-time simulation method for zero-point current determination in power electronic systems. This method involves configuring a blocking judgment module for the diode switching circuit; establishing switching state judgment logic to determine the conduction, turn-off, and blocking states of the device under different current directions; constructing a mathematical calculation model of the diode switching circuit based on the judgment logic and performing real-time simulation to determine whether the diode current has crossed zero; when a current zero-point crossing is detected, the blocking judgment module outputs a latching signal, controlling the diode to enter the blocking state; in the blocking state, the direction and amplitude of the voltage across the device and the virtual electromotive force are continuously monitored; when a preset conduction condition is met, the latching signal is released, and the device is controlled to conduct again. By introducing the concept of virtual electromotive force, without considering the influence of energy storage components such as inductors and capacitors, the maximum output voltage of the uncontrolled rectifier unit is extracted as an auxiliary criterion, achieving joint judgment based on current direction and virtual electromotive force. This method can accurately identify the zero-point current state and conduction state of uncontrolled devices without increasing the simulation step size and iteration count, significantly improving the stability and accuracy of real-time simulation.

[0177] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for determining zero current in real-time simulation of power electronic systems, characterized by, Comprise: A blocking judgment module is configured for the diode switching circuit to detect the current state of the uncontrolled device; Switching state judgment logic of the diode switching circuit is determined to distinguish the on, off and blocking states of the uncontrolled device under different current directions; Based on the switching state judgment logic, a mathematical calculation model of the diode switching circuit is constructed and real-time simulation is performed to determine whether the diode current has zero-crossing; When the diode current zero-crossing point is detected, the blocking judgment module outputs a blocking signal to control the diode to enter the blocking state, so as to avoid the mis-conduction of the uncontrolled device and current oscillation caused by the failure to capture the current zero-crossing point; A virtual electromotive force is introduced as an auxiliary criterion, which is the maximum port potential difference that the converter power supply side can provide under the current topology without considering the influence of the energy storage element, and is used to represent the equivalent driving voltage potential energy of the uncontrolled rectifier branch; In the blocking state, the voltage across the uncontrolled device and the direction and amplitude of the virtual electromotive force are continuously monitored. When the voltage direction is consistent with the direction of the virtual electromotive force, and the voltage amplitude exceeds the preset conduction threshold, the blocking signal is released to control the diode to re-enter the conduction state, thereby realizing the dynamic recovery of the uncontrolled device.

2. The method of claim 1, wherein the zero current determination is performed in real time. The calculation method of the virtual electromotive force is: Under the condition of not considering the influence of the energy storage element, at each discrete time in real-time simulation, when the converter is in the non-conduction state, the open-circuit voltage input to the converter port (p+, p-) is extracted, which is defined as the virtual electromotive force under the intermittent state at this moment, and is the maximum port potential difference that the converter power supply side can provide at this moment: U vf (t)=U p+ (t)-U p- (t) where U p- , U p+ is the node potential of the power supply side equivalent network at this moment.

3. The method of claim 2, wherein the zero current determination is performed in real time. The diode switching circuit is a single-phase diode uncontrolled rectifier circuit; During the positive half cycle of the power supply, diodes D1 and D4 are turned on under forward voltage, and diodes D2 and D3 are turned off under reverse voltage; During the negative half cycle of the power supply, diodes D1 and D4 are turned off under reverse voltage, and diodes D2 and D3 are turned on under forward voltage; At the initial moment, the voltage across the capacitor is 0, and as the power supply voltage rises, the current flows through the load resistor R and the capacitor C; when the power supply voltage is less than the voltage across the capacitor C, the capacitor C begins to discharge; when the power supply voltage is greater than the voltage across the capacitor C, the capacitor C will continue to be charged, and the cycle will be repeated.

4. The method of claim 3, wherein the zero current determination is performed in real time. The switching state judgment logic of the single-phase diode uncontrolled rectifier circuit is: In the two-phase bridge arms of the single-phase diode uncontrolled rectifier circuit, the switching state signal of the a-phase bridge arm is Hsa, and the switching state signal of the b-phase bridge arm is Hsb, and the value of the switching state signal is: When the upper bridge arm switch is turned on and the lower bridge arm switch is turned off in the a-phase bridge arm, Hsa=1; when the upper bridge arm switch is turned off and the lower bridge arm switch is turned on, Hsa=0; When the upper bridge arm switch is turned on and the lower bridge arm switch is turned off in the b-phase bridge arm, Hsb=1; when the upper bridge arm switch is turned off and the lower bridge arm switch is turned on, Hsb=0.

5. The method of claim 4, wherein the zero current determination is performed in real time. The mathematical calculation model of the single-phase diode uncontrolled rectifier circuit is: When diodes D1 and D4 are on, i s > 0, u 12 > 0; When diodes D2 and D3 are on, i s <0, u 12 <0; where Ls is the leakage inductance of the secondary winding of the traction transformer, i s is the supply current, e s is the supply voltage, Rs is the equivalent resistance of the secondary winding of the traction transformer, u 12 is the bridge arm voltage, u a1 is the a-phase bridge arm voltage, u b1 is the b-phase bridge arm voltage, u dc is the load voltage, i dc is the load current, i R is the load resistance current, i C is the capacitor current, C is the capacitor, R is the load resistance.

6. The method of claim 5, wherein the zero current determination is performed in real time. When the diode current zero-crossing point is detected, the blocking judgment module outputs a blocking signal to control the diode to enter the blocking state, including: When the load voltage u dc is greater than the absolute value of the virtual electromotive force, and the power supply current i s is close to zero, it is determined that the diode current zero-crossing point has occurred. The blocking judging module outputs a blocking signal BL=0 to force the bridge arm switch to be turned off and control the diode to be in a blocking state. In the blocking state, the load current i dc and the supply current i s are forced to zero, and the bridge arm voltage u 12 remains at the voltage value of the previous simulation instant.

7. The method of claim 2, wherein the zero current determination is performed in real time. The diode switching circuit is an NPC three-level rectifier circuit, and each phase bridge arm of the NPC three-level rectifier circuit comprises four switching elements, four freewheeling diodes and two clamping diodes.

8. The method of claim 7, wherein the zero current determination is performed in real time. The switching state judging logic of the NPC three-level circuit is as follows: When T1 and T2 are turned on, the A-phase bridge arm works in a P state regardless of the direction of the A-phase current; When T3 and T4 are turned on, the A-phase bridge arm works in an N state regardless of the direction of the A-phase current; When T3 is turned on and the A-phase current is positive, the A-phase bridge arm works in an O state; When T2 is turned on and the A-phase current is negative, the A-phase bridge arm works in an O state; When T3 is turned off and the A-phase current is positive, the A-phase bridge arm works in a P state; When T2 is turned off and the A-phase current is negative, the A-phase bridge arm works in an N state; Wherein, T1, T2, T3 and T4 are switching elements of the A-phase bridge arm.

9. The method of claim 8, wherein the zero current determination is performed in real time. The mathematical calculation model of the NPC three-level rectifier circuit is as follows: Each phase bridge arm of the NPC type three-level rectifier circuit is equivalent to a three-way switch S a ; wherein, The working state of the NPC three-level rectifier circuit is as follows: If T1 = 1, T2 = 1, then S a = 1. If T3 = 1, T4 = 1, then S a = -1; If T2 = 1, T1 = 0, and i a < 0, then S a = 0; If T3 = 1, T4 = 0, and i a ≥ 0, then S a = 0; If T2 = 0, T1 = 0, and i a < 0, then S a = -1; If T3 = 0, T4 = 0, and i a ≥ 0, then S a = 1; According to different working states of the NPC three-level rectifier circuit, the output voltage and current are obtained as follows: When S a = 1: When S a = 0: When S a = -1: Wherein, i a is the A-phase current, u a is the A-phase bridge arm port voltage, i1 is the current of the upper bridge arm, i2 is the current of the lower bridge arm, u1 is the P-point voltage, and u2 is the N-point voltage.

10. The method of claim 9, wherein the zero current determination is performed in real time. When the diode current zero-crossing point is detected, the blocking judging module outputs a blocking signal to control the diode to be in a blocking state, comprising: When the diode current zero-crossing point is determined, the blocking determination module outputs a blocking signal Block=0 to force the bridge arm switch to be turned off and control the diode to enter a blocking state. At other times, the blocking judging module outputs a blocking signal Block=1; In the blocking state, the A-phase circuit and the A-phase voltage satisfy: where i a is the A-phase current, e a is the A-phase supply voltage.

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