Electromagnetic transient modeling simulation method and system for cascaded H-bridge converter

Abstract

The invention discloses an electromagnetic transient modeling simulation method and system for a cascaded H-bridge converter. The method comprises the following steps: respectively calculating a capacitance accompanying circuit and an inductance accompanying circuit of an H-bridge unit; dividing the operation state of the half-bridge circuit in the H-bridge unit, and determining an on-off state table of the half-bridge circuit according to the operation state; based on the capacitance accompanying circuit and the on-off state table, respectively establishing a step length average on-off model of the H-bridge unit in a normal state and a detailed on-off model of the H-bridge unit in an abnormal state; calculating a first Thevenin equivalent circuit based on a step length average switch model; calculating a second Thevenin equivalent circuit based on the detailed switch model; based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductance adjoint circuit, a Norton equivalent circuit of the cascaded H bridge arm is calculated; determining a bridge arm current based on a Norton equivalent circuit of a cascaded H bridge arm; and calculating a direct current voltage and a diode voltage of each H-bridge unit based on the bridge arm current.

Description

Technical Field

[0001] The present invention relates to the technical field of electromagnetic transient simulation, and more specifically, to an electromagnetic transient modeling simulation method and system for a cascaded H-bridge converter. Background Art

[0002] In recent years, electromagnetic transients simulation (EMT) has become an indispensable part in the study of transient dynamic characteristics of complex power electronic equipment and the safety and stability analysis and planning of power systems.

[0003] like Figure 1 The multilevel converter based on cascaded H-bridge (CHB) shown in the figure is a new type of high-voltage and high-power converter with the advantages of large transmission power, high system efficiency, and good waveform quality. It has been a research hotspot in recent years. Its typical application scenarios include modular multilevel converter MMC, cascaded H-bridge static VAR generator CHB-SVG, cascaded H-bridge energy storage CHB-BESS, etc. They have the characteristics of high voltage level, large power capacity, large number of cascade units, and large number of switches. When developing and analyzing this type of CHB converter, electromagnetic transient simulation software such as PSModel, PSCAD, and MATLAB are required for calculation. In order to analyze the harmonics output by the CHB converter and the dynamic characteristics during faults, it is necessary to simulate the turn-on and turn-off process of PWM waves and IGBT / diodes in detail. For example, in CHB-SVG, which is widely used in new energy stations, since more than 30 H-bridge units are connected in series (for MMC, the number may reach several hundred), if one wants to use a detailed model based on discrete switching elements for simulation, the circuit matrix of a single SVG will be as high as hundreds of orders, and the elements of the circuit matrix will change frequently, resulting in a huge calculation time problem.

[0004] Therefore, an electromagnetic transient modeling and simulation method for cascaded H-bridge converters is needed. Summary of the invention

[0005] The present invention proposes an electromagnetic transient modeling and simulation method and system for a cascaded H-bridge converter, so as to solve the problem of how to efficiently perform modeling and simulation of the cascaded H-bridge converter.

[0006] In order to solve the above problem, according to one aspect of the present invention, a method for electromagnetic transient modeling and simulation of a cascaded H-bridge converter is provided, the method comprising:

[0007] Calculate the capacitive accompanying circuit of the H-bridge unit capacitor and the inductive accompanying circuit of the bridge arm inductance respectively;

[0008] Dividing the operating states of the half-bridge circuits in the H-bridge unit, and determining a switch state table of the half-bridge circuits according to the operating states;

[0009] Based on the capacitor accompanying circuit and the switch state table, a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state are respectively established;

[0010] Based on the step-average switching model, calculating a first Thevenin equivalent circuit of the average switching model of the H-bridge unit in a normal state;

[0011] Based on the detailed switch model, calculating a second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state;

[0012] Calculate the Norton equivalent circuit of the cascaded H-bridge bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit;

[0013] Determine the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm;

[0014] The DC voltage and the diode voltage of each H-bridge unit are calculated based on the bridge arm current.

[0015] Preferably, respectively calculating the capacitance accompanying circuit of the H-bridge unit capacitance and the inductance accompanying circuit of the bridge arm inductance comprises:

[0016] Determine the companion point G of the capacitor C and the accompanying current source J C The values ​​are:

[0017]

[0018] Determine the accompanying conductance G of the inductor L and the accompanying current source J L The values ​​are:

[0019]

[0020] J L =i n-1 ,

[0021] Where C is the capacitance; h is the simulation step length; u n-1 is the voltage across the capacitor at time n-1. ; L is the inductance; i n-1 is the current of the inductor at time n-1.

[0022] Preferably, the operating state of the half-bridge circuit in the H-bridge unit is divided, and a switch state table of the half-bridge circuit is determined according to the operating state, including:

[0023] When the upper bridge arm of the half-bridge circuit is turned on and the lower bridge arm is turned off, it is determined to be in the capacitor input state, and the switch state is represented by the binary number 10; when the upper bridge arm of the bridge circuit is turned off and the lower bridge arm is turned on, it is determined to be in the capacitor bypass state, and the switch state is represented by the binary number 01; when both the upper and lower bridge arms of the half-bridge circuit are turned on, it is determined to be in the capacitor short-circuit state, and the switch state is represented by the binary number 11; when both the upper and lower bridge arms of the half-bridge circuit are turned off, it is determined to be in the capacitor input state, determined to be in the circuit open state, and the switch state is represented by the binary number 00;

[0024] According to the IGBT gate signal, DC voltage e and diode voltage u D1 and u D2 Determine the operating status of the half-bridge circuit.

[0025] Preferably, based on the capacitor accompanying circuit and the switch state table, a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state are established respectively, including:

[0026] Under normal conditions, the two half-bridge circuits in the H-bridge unit are replaced with the step average model, and the capacitor is equivalent to the capacitor companion circuit to obtain the step average model of the H-bridge unit under normal conditions; wherein, the on-resistance R is connected in series at the unit port. on To simulate conduction losses in detailed models;

[0027] In the abnormal state, the upper and lower bridge arms of the two half-bridge circuits in the H-bridge unit are modeled with binary resistors to obtain a detailed switch model of the H-bridge unit in the abnormal state; the conductance of the bridge arm is determined by the switch state table. When the bridge arm is turned on, the bridge arm conductance is the on-state conductance G on When the bridge arm is turned off, the bridge arm conductance is the off conductance G off .

[0028] Preferably, based on the step-average switch model, calculating a first Thevenin equivalent circuit of the average switch model of the H-bridge unit in a normal state comprises:

[0029] Determine the first Thevenin equivalent resistance R eq1 ,include:

[0030]

[0031] Determine the first Thevenin equivalent voltage source E eq1 ,include:

[0032]

[0033] Where k is the controlled source coefficient of the H-bridge unit; U p and U nis the voltage at nodes p and n; i is the AC current; G C and J c is the discretized circuit parameter of the capacitor; the subscripts 1 and 2 of k and i are used to distinguish the two half-bridge circuits of the H-bridge unit.

[0034] Preferably, based on the detailed switch model, calculating a second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state includes:

[0035] Determine the second Thevenin equivalent resistance R eq2 for:

[0036]

[0037] Determine the second Thevenin equivalent voltage source E eq2 for:

[0038] E eq2 =J eq R eq2 ,

[0039]

[0040] Among them, J eq is the Norton equivalent current; Y 11 -Y 22 are the four block matrices of the H-bridge circuit conductivity matrix; J2 is the second block vector of the H-bridge circuit current column vector; G1-G4 are the conductances of the bridge arms; J C It is the current source of the capacitor discretization circuit.

[0041] Preferably, the calculation of the Norton equivalent circuit of the cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit comprises:

[0042] The Norton equivalent circuit parameters of the cascaded H-bridge arm are determined as:

[0043]

[0044] Among them, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq is the current source of the Norton equivalent circuit of the cascaded H-bridge arm; i represents the i-th H-bridge unit on the bridge arm; R LARM and E LARM is the accompanying circuit parameter of the bridge arm inductance; R eqi is the Thevenin equivalent resistance of the ith unit; U eqi is the Thevenin equivalent voltage source of the ith unit.

[0045] Preferably, determining the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm comprises:

[0046] The Norton equivalent circuit of the cascaded H-bridge bridge arm is superimposed into the system equation and input into the electromagnetic transient simulation program to solve the node voltage equation of the system to obtain the node voltage u at both ends of the bridge arm. ARM1 and u ARM2 , according to the Norton equivalent circuit of the bridge arm, the bridge arm current i1 is calculated as:

[0047] i1=(u ARM2 -u ARM1 )G armeq +J armeq ,

[0048] Among them, u ARM1 and u ARM2 are the voltages of bridge arm nodes 1 and 2, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq It is the current source of the Norton equivalent circuit of the cascaded H-bridge arm.

[0049] Preferably, the DC voltage and the diode voltage of each H-bridge unit are calculated based on the bridge arm current, comprising:

[0050] Determine the DC voltage of the i-th H-bridge unit in the normal state as:

[0051] Determine the port voltage of each H-bridge unit in the abnormal state as:

[0052] u celli =E eqi -i1R eqi ,

[0053]

[0054] Determine the DC voltage under abnormal conditions:

[0055] e i =u n2i -u p2i ,

[0056] Determine the diode voltage under abnormal conditions:

[0057]

[0058] Wherein, the subscript i represents the i-th H-bridge unit in the cascaded H-bridge; u p2 is the voltage difference between node p and node 2; u n2 is the voltage difference between node n and node 2; U p , U nU1, U2 are the voltages of nodes p, n, and 2 respectively; G1-G4 are the conductances of the bridge arms; G C and J C is the conductance and current source of the capacitor discretization circuit; u D1 -u D4 is the voltage of diodes 1 to 4; u cell is the H-bridge port voltage; i1 is the bridge arm current; k1 and k2 are the controlled source coefficients of the first and second half bridges of the H-bridge respectively.

[0059] According to another aspect of the present invention, there is provided an electromagnetic transient modeling and simulation system for a cascaded H-bridge converter, the system comprising:

[0060] A companion circuit calculation unit, used for respectively calculating a capacitance companion circuit of the H-bridge unit capacitance and an inductance companion circuit of the bridge arm inductance;

[0061] A state division unit, used to divide the operating state of the half-bridge circuit in the H-bridge unit, and determine a switch state table of the half-bridge circuit according to the operating state;

[0062] A model building unit, used to build a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state, respectively, based on the capacitor accompanying circuit and the switch state table;

[0063] A first Thevenin equivalent unit, used for calculating a first Thevenin equivalent circuit of an average switching model of an H-bridge unit in a normal state based on the step-average switching model;

[0064] A second Thevenin equivalent unit, used for calculating a second Thevenin equivalent circuit of the detailed switching model of the H-bridge unit in an abnormal state based on the detailed switching model;

[0065] A Norton equivalent unit, used for calculating a Norton equivalent circuit of a bridge arm of a cascaded H bridge based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit;

[0066] A bridge arm current calculation unit, used for determining the bridge arm current based on a Norton equivalent circuit of the cascaded H-bridge bridge arm;

[0067] A voltage calculation unit is used to calculate the DC voltage and the diode voltage of each H-bridge unit based on the bridge arm current.

[0068] Preferably, the accompanying circuit calculation unit is used to calculate the capacitance accompanying circuit of the H-bridge unit capacitance and the inductance accompanying circuit of the bridge arm inductance, respectively, and includes:

[0069] Determine the companion point G of the capacitor C and the accompanying current source J C The values ​​are:

[0070]

[0071] Determine the accompanying conductance G of the inductor L and the accompanying current source J L The values ​​are:

[0072]

[0073] J L =i n-1 ,

[0074] Where C is the capacitance; h is the simulation step length; u n-1 is the voltage across the capacitor at time n-1. ; L is the inductance; i n-1 is the current of the inductor at time n-1.

[0075] Preferably, the state division unit divides the operating state of the half-bridge circuit in the H-bridge unit and determines a switch state table of the half-bridge circuit according to the operating state, including:

[0076] When the upper bridge arm of the half-bridge circuit is turned on and the lower bridge arm is turned off, it is determined to be in the capacitor input state, and the switch state is represented by the binary number 10; when the upper bridge arm of the bridge circuit is turned off and the lower bridge arm is turned on, it is determined to be in the capacitor bypass state, and the switch state is represented by the binary number 01; when both the upper and lower bridge arms of the half-bridge circuit are turned on, it is determined to be in the capacitor short-circuit state, and the switch state is represented by the binary number 11; when both the upper and lower bridge arms of the half-bridge circuit are turned off, it is determined to be in the capacitor input state, determined to be in the circuit open state, and the switch state is represented by the binary number 00;

[0077] According to the IGBT gate signal, DC voltage e and diode voltage u D1 and u D2 Determine the operating status of the half-bridge circuit.

[0078] Preferably, the model building unit, based on the capacitor accompanying circuit and the switch state table, respectively builds a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state, including:

[0079] Under normal conditions, the two half-bridge circuits in the H-bridge unit are replaced with the step average model, and the capacitor is equivalent to the capacitor companion circuit to obtain the step average model of the H-bridge unit under normal conditions; wherein, the on-resistance R is connected in series at the unit port. on To simulate conduction losses in detailed models;

[0080] In the abnormal state, the upper and lower bridge arms of the two half-bridge circuits in the H-bridge unit are modeled with binary resistors to obtain a detailed switch model of the H-bridge unit in the abnormal state; the conductance of the bridge arm is determined by the switch state table. When the bridge arm is turned on, the bridge arm conductance is the on-state conductance G on When the bridge arm is turned off, the bridge arm conductance is the off conductance G off .

[0081] Preferably, the first Thevenin equivalent unit calculates the first Thevenin equivalent circuit of the average switch model of the H-bridge unit in a normal state based on the step-average switch model, including:

[0082] Determine the first Thevenin equivalent resistance R eq1 ,include:

[0083]

[0084] Determine the first Thevenin equivalent voltage source E eq1 ,include:

[0085]

[0086] Where k is the controlled source coefficient of the H-bridge unit; U p and U n is the voltage at nodes p and n; i is the AC current; G C and J c is the discretized circuit parameter of the capacitor; the subscripts 1 and 2 of k and i are used to distinguish the two half-bridge circuits of the H-bridge unit.

[0087] Preferably, the second Thevenin equivalent unit calculates the second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state based on the detailed switch model, including:

[0088] Determine the second Thevenin equivalent resistance R eq2 for:

[0089]

[0090] Determine the second Thevenin equivalent voltage source E eq2 for:

[0091] E eq2 =J eq R eq2 ,

[0092]

[0093] Among them, J eq is the Norton equivalent current; Y 11 -Y 22are the four block matrices of the H-bridge circuit conductivity matrix; J2 is the second block vector of the H-bridge circuit current column vector; G1-G4 are the conductances of the bridge arms; J C It is the current source of the capacitor discretization circuit.

[0094] Preferably, the Norton equivalent unit calculates the Norton equivalent circuit of the cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit, including:

[0095] The Norton equivalent circuit parameters of the cascaded H-bridge arm are determined as:

[0096]

[0097] Among them, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq is the current source of the Norton equivalent circuit of the cascaded H-bridge arm; i represents the i-th H-bridge unit on the bridge arm; R LARM and E LARM is the accompanying circuit parameter of the bridge arm inductance; R eqi is the Thevenin equivalent resistance of the ith unit; U eqi is the Thevenin equivalent voltage source of the ith unit.

[0098] Preferably, the bridge arm current determining unit determines the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm, comprising:

[0099] The Norton equivalent circuit of the cascaded H-bridge bridge arm is superimposed into the system equation and input into the electromagnetic transient simulation program to solve the node voltage equation of the system to obtain the node voltage u at both ends of the bridge arm. ARM1 and u ARM2 , according to the Norton equivalent circuit of the bridge arm, the bridge arm current i1 is calculated as:

[0100] i1=(u ARM2 -u ARM1 )G armeq +J armeq ,

[0101] Among them, u ARM1 and u ARM2 are the voltages of bridge arm nodes 1 and 2, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq It is the current source of the Norton equivalent circuit of the cascaded H-bridge arm.

[0102] Preferably, the voltage calculation unit calculates the DC voltage and the diode voltage of each H-bridge unit based on the bridge arm current, including:

[0103] Determine the DC voltage of the i-th H-bridge unit in the normal state as:

[0104] Determine the port voltage of each H-bridge unit in the abnormal state as:

[0105] u celli =E eqi -i1R eqi ,

[0106]

[0107] Determine the DC voltage under abnormal conditions:

[0108] e i =u n2i -u p2i ,

[0109] Determine the diode voltage under abnormal conditions:

[0110]

[0111] Wherein, the subscript i represents the i-th H-bridge unit in the cascaded H-bridge; u p2 is the voltage difference between node p and node 2; u n2 is the voltage difference between node n and node 2; U p , U n U1, U2 are the voltages of nodes p, n, and 2 respectively; G1-G4 are the conductances of the bridge arms; G C and J C is the conductance and current source of the capacitor discretization circuit; u D1 -u D4 is the voltage of diodes 1 to 4; u cell is the H-bridge port voltage; i1 is the bridge arm current; k1 and k2 are the controlled source coefficients of the first and second half bridges of the H-bridge respectively.

[0112] The present invention provides an electromagnetic transient modeling and simulation method and system for a cascaded H-bridge converter, comprising: respectively calculating a capacitance companion circuit of an H-bridge unit capacitor and an inductance companion circuit of a bridge arm inductance; dividing the operating state of a half-bridge circuit in the H-bridge unit, and determining a switch state table of the half-bridge circuit according to the operating state; respectively establishing a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state based on the capacitance companion circuit and the switch state table; calculating a first Thevenin equivalent circuit of an average switch model of the H-bridge unit in a normal state based on the step average switch model; calculating a second Thevenin equivalent circuit of a detailed switch model of the H-bridge unit in an abnormal state based on the detailed switch model; calculating a Norton equivalent circuit of a cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductance companion circuit; determining a bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge arm; and calculating a DC voltage and a diode voltage of each H-bridge unit based on the bridge arm current. The method of the present invention can be calculated faster while maintaining the same calculation accuracy as the small step-size detailed model, and does not need to perform additional interpolation and variable step-size processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0113] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0114] Figure 1 It is a structural schematic diagram of a cascaded H-bridge converter;

[0115] Figure 2 is a flow chart of an electromagnetic transient modeling and simulation method 200 for a cascaded H-bridge converter according to an embodiment of the present invention;

[0116] Figure 3 is a schematic diagram of a companion model of capacitance and inductance according to an embodiment of the present invention;

[0117] Figure 4 A topological diagram of a half-bridge circuit according to an embodiment of the present invention;

[0118] Figure 5 A circuit diagram of a half-bridge circuit in a start-up state according to an embodiment of the present invention;

[0119] Figure 6 is a circuit diagram of a half-bridge circuit in bypass state according to an embodiment of the present invention;

[0120] Figure 7 is a circuit diagram of a half-bridge circuit in a short-circuit state according to an embodiment of the present invention;

[0121] Figure 8 is a circuit diagram of an open circuit state of a half-bridge circuit according to an embodiment of the present invention;

[0122] Fig. 9 A schematic diagram of a step-average model of a half-bridge circuit according to an embodiment of the present invention;

[0123] Fig.10 Schematic diagram of a step average switching model of an H-bridge unit in a normal state according to an embodiment of the present invention;

[0124] Fig.11 is a Thevenin equivalent circuit diagram of an H-bridge unit according to an embodiment of the present invention;

[0125] Fig.12 is a schematic diagram of a detailed switch model of an H-bridge unit in an abnormal state according to an embodiment of the present invention;

[0126] Fig.13 A Norton equivalent circuit diagram of a cascaded H-bridge arm according to an embodiment of the present invention;

[0127] Fig.14 A simulation flow chart according to an embodiment of the present invention;

[0128] Fig.15 A schematic diagram of the structure of an SVG test circuit according to an embodiment of the present invention;

[0129] Fig.16 (a) and (b) are respectively simulation waveform comparison diagrams according to embodiments of the present invention;

[0130] Fig.17 (a), (b) and (c) are reactive power comparison diagrams according to embodiments of the present invention;

[0131] Fig.18 Schematic diagram of the structure of an electromagnetic transient modeling and simulation system 1800 for a cascaded H-bridge converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0132] Now, exemplary embodiments of the present invention are described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0133] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0134] Figure 2 FIG. 2 is a flow chart of an electromagnetic transient modeling and simulation method 200 for a cascaded H-bridge converter according to an embodiment of the present invention. Figure 2 As shown, the electromagnetic transient modeling and simulation method of the cascaded H-bridge converter provided by the embodiment of the present invention can be calculated faster while maintaining the same calculation accuracy as the small-step detailed model, and no additional interpolation and variable step processing are required. The electromagnetic transient modeling and simulation method 200 of the cascaded H-bridge converter provided by the embodiment of the present invention starts from step 201. In step 201, the capacitive accompanying circuit of the H-bridge unit capacitor and the inductive accompanying circuit of the bridge arm inductor are calculated respectively.

[0135] Preferably, respectively calculating the capacitance accompanying circuit of the H-bridge unit capacitance and the inductance accompanying circuit of the bridge arm inductance comprises:

[0136] Determine the companion point G of the capacitor C and the accompanying current source J C The values ​​are:

[0137]

[0138] Determine the accompanying conductance G of the inductor L and the accompanying current source J L The values ​​are:

[0139]

[0140] J L =i n-1 ,

[0141] Where C is the capacitance; h is the simulation step length; u n-1 is the voltage across the capacitor at time n-1. ; L is the inductance; i n-1 is the current of the inductor at time n-1.

[0142] In the present invention, the electromagnetic transient simulation software discretizes by applying the numerical integration method, converting the capacitance and inductance into a Norton companion circuit represented by the conductance G and the current source J, or a Thevenin companion circuit represented by the resistance R and the voltage source E, such as Figure 3 shown.

[0143] Here, let the voltage across the capacitor be u, the current be i, and the capacitance be C. The state equation of the capacitor is:

[0144]

[0145] When using the backward Euler method to perform n-1 to n When numerically integrating , we obtain the following formula:

[0146]

[0147] Here, h is the simulation step size.

[0148] According to formula (2), the accompanying conductance G of the capacitor can be obtained C and the accompanying current source J C The values ​​are:

[0149]

[0150] Similarly, let the voltage across the inductor be u, the current be i, and the inductance be L. The accompanying conductance G of the inductor can be obtained L and the accompanying current source J L The values ​​are:

[0151]

[0152] J L =i n-1 (6)

[0153] like Figure 3 As shown, the Norton circuit form can also be equivalently converted to the Thevenin circuit form:

[0154]

[0155] In step 202, the operating states of the half-bridge circuits in the H-bridge unit are divided, and a switch state table of the half-bridge circuits is determined according to the operating states.

[0156] Preferably, the operating state of the half-bridge circuit in the H-bridge unit is divided, and a switch state table of the half-bridge circuit is determined according to the operating state, including:

[0157] When the upper bridge arm of the half-bridge circuit is turned on and the lower bridge arm is turned off, it is determined to be in the capacitor input state, and the switch state is represented by the binary number 10; when the upper bridge arm of the bridge circuit is turned off and the lower bridge arm is turned on, it is determined to be in the capacitor bypass state, and the switch state is represented by the binary number 01; when both the upper and lower bridge arms of the half-bridge circuit are turned on, it is determined to be in the capacitor short-circuit state, and the switch state is represented by the binary number 11; when both the upper and lower bridge arms of the half-bridge circuit are turned off, it is determined to be in the capacitor input state, determined to be in the circuit open state, and the switch state is represented by the binary number 00;

[0158] According to the IGBT gate signal, DC voltage e and diode voltage u D1 and u D2 Determine the operating status of the half-bridge circuit.

[0159] Since the H-bridge unit is composed of two half-bridge circuits and a DC side capacitor, the present invention only considers taking out Figure 4 The single half-bridge circuit shown divides the possible operating states of the half-bridge circuit into:

[0160] (1) The capacitor is connected to the circuit in the forward direction. This state is called input. Figure 5 As shown in the figure, the upper arm of the half-bridge circuit is turned on, and the lower arm is turned off. The switch state is represented by the binary number 10.

[0161] (2) Capacitor bypass. From the perspective of the unit port characteristics, it is a small resistor. This state is called bypass. Figure 6 As shown in the figure, the upper arm of the half-bridge circuit is turned off, the lower arm is turned on, and the switch state is represented by the binary number 01.

[0162] (3) Capacitor short circuit. At this time, the capacitor voltage becomes 0. This state is called short circuit. Figure 7 As shown. The upper and lower arms of the half-bridge circuit are both turned on, and the switch state is represented by the binary number 11.

[0163] (4) Circuit is open. From the characteristics of the unit port, it is a large resistance. This state only occurs when the lock is closed and e ≥ u ≥ 0. This state is called an open circuit, such as Figure 8 The upper and lower arms of the half-bridge circuit are both turned off, and the switch state is represented by the binary number 00.

[0164] In the present invention, a switch state table of the half-bridge circuit is formed according to the specified half-bridge circuit state definition. At a certain moment, the state of the half-bridge circuit is determined by the following variables: (1) IGBT gate signal; (2) DC voltage e; (3) diode voltage u D1 and u D2 .

[0165] Table 1 Half-bridge circuit switch state table

[0166]

[0167] Table 1 shows the switch state table corresponding to the gate signal and circuit state. For the first binary number, 0 indicates an abnormal state and 1 indicates a normal state; for the second and third binary numbers, they indicate the operating state of the half-bridge circuit specified in step 1. The switch state table determines which state the H-bridge unit is in based on the gate signal, DC voltage, and diode voltage. By determining the state of the half-bridge circuit in this way, it is possible to convert it into a correct equivalent circuit while maintaining the diode nonlinear characteristics of the half-bridge circuit.

[0168] The present invention utilizes a half-bridge switch state table to model all possible switch states of the H-bridge and can retain the nonlinear characteristics of the diode of the H-bridge.

[0169] In step 203, based on the capacitor accompanying circuit and the switch state table, a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state are respectively established.

[0170] Preferably, based on the capacitor accompanying circuit and the switch state table, a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state are established respectively, including:

[0171] Under normal conditions, the two half-bridge circuits in the H-bridge unit are replaced with the step average model, and the capacitor is equivalent to the capacitor companion circuit to obtain the step average model of the H-bridge unit under normal conditions; wherein, the on-resistance R is connected in series at the unit port. on To simulate conduction losses in detailed models;

[0172] In the abnormal state, the upper and lower bridge arms of the two half-bridge circuits in the H-bridge unit are modeled with binary resistors to obtain a detailed switch model of the H-bridge unit in the abnormal state; the conductance of the bridge arm is determined by the switch state table. When the bridge arm is turned on, the bridge arm conductance is the on-state conductance G on When the bridge arm is turned off, the bridge arm conductance is the off conductance G off .

[0173] The present invention makes comprehensive use of the advantages of the step average model and the detailed switch model. The cascade H-bridge is modeled as a step average model in a normal state. The step average model can efficiently process switch events without interpolation, extend the simulation time step by more than 10 times without reducing the accuracy, and reasonably reproduce harmonics. In an abnormal state, it is modeled as a detailed switch model. The detailed switch model can correctly simulate the nonlinear characteristics of the diode in an abnormal state.

[0174] In the present invention, the input capacitor is accompanied by a circuit model and a switch state table to establish an averaged switch model (AS) of a normal state H-bridge unit. Fig. 9 As shown in Figure 1, it represents the step average model of the half-bridge circuit in the normal state. In a simulation interval of step size h, the time when the upper bridge arm is turned on is T p , the conduction time of the lower bridge arm is T n , T p The ratio of h (T u / h) is k, k∈[0,1].

[0175] Usually, the cascade H-bridge adopts carrier phase shift control. The IGBT gate signal is generated by comparing the carrier (usually a triangular wave) with the modulation wave. The electromagnetic transient simulation software can obtain the precise switching time of the gate signal ON and OFF by linearly interpolating the carrier and the modulation wave, and then obtain T according to the established switch state table. p and T n , and thus calculate the corresponding k in each h interval.

[0176] In T p During this period, the AC side output voltage e( Figure 5 ), in T n During the period, the output voltage is 0( Figure 6 ). Therefore, the average output AC voltage u at step length h interval is

[0177] u=ke (9)

[0178] Where: e represents DC voltage.

[0179] Similarly, in T p During this period, the AC side current i flows Figure 4 The path shown. l During the period Figure 5 Therefore, the average output DC current i p 、i n for

[0180] i p =ki (10)

[0181] i n =(1-k)i (11)

[0182] Where: i represents the AC current. From the AC side, the half-bridge circuit can be considered as a voltage source that outputs the voltage of equation (9). From the DC side, the half-bridge circuit can be considered as a current source that outputs the currents of equations (10) and (11). When expressed as an equivalent circuit, the half-bridge circuit can be equivalent to: Fig. 9 The equivalent circuit shown in Figure 1 is shown in Figure 1. Using the modified node analysis method, Fig. 9 The equation of the equivalent circuit can be expressed as:

[0183]

[0184] The same idea also applies to the H-bridge unit. Replace the two half-bridge circuits in the H-bridge unit with the step average model, and equate the capacitor to the companion circuit derived in step 1 to obtain the step average model of the H-bridge unit, as shown in Fig.10 As shown. In the equivalent circuit, the on-resistance R is connected in series with the unit port. onTo simulate the conduction losses in the detailed model, the subscripts 1 and 2 of k and i are used to distinguish the two half-bridge circuits of the H-bridge unit.

[0185] In the present invention, a detailed switch model of the H-bridge unit in an abnormal state can also be established according to the input capacitor accompanying circuit model and the switch state table. In the abnormal state, the H-bridge unit is modeled as a detailed switch model. In the detailed switch model, the upper and lower bridge arms of the half-bridge circuit are both modeled with binary resistors. The detailed switch model of the H-bridge unit is as follows: Fig.12 As shown. Among them, the conductance of the bridge arm is determined by the switch state table. When the bridge arm is turned on, the conductance of the bridge arm is the on-state conductance G on When the bridge arm is turned off, the bridge arm conductance is the off conductance G off Among them, G on The typical value is 1 / 0.01S, G off The typical value is 1 / 10 6 S.

[0186] In step 204, based on the step-average switch model, a first Thevenin equivalent circuit of the average switch model of the H-bridge unit in a normal state is calculated.

[0187] Preferably, based on the step-average switch model, calculating a first Thevenin equivalent circuit of the average switch model of the H-bridge unit in a normal state comprises:

[0188] Determine the first Thevenin equivalent resistance R eq1 ,include:

[0189]

[0190] Determine the first Thevenin equivalent voltage source E eq1 ,include:

[0191]

[0192] Where k is the controlled source coefficient of the H-bridge unit; U p and U n is the voltage at nodes p and n; i is the AC current; G C and J c is the discretized circuit parameter of the capacitor; the subscripts 1 and 2 of k and i are used to distinguish the two half-bridge circuits of the H-bridge unit.

[0193] In the present invention, after the step-average switching model is determined, the first Thevenin equivalent circuit of the average switching model of the H-bridge unit in a normal state is calculated according to the step-average switching model.

[0194] In the present invention, the Thevenin equivalent circuit of the normal state step average model of the H-bridge unit is as follows: Fig.11 As shown.C Set to 0 and calculate the Thevenin equivalent resistance R eq , the calculation formula of the H-bridge unit port voltage is:

[0195]

[0196] According to the H-bridge unit port voltage u in formula (13): cell The relationship between the first Thevenin equivalent resistance R and the port current i2 can be obtained. eq :

[0197]

[0198] Let i1=i2=0, and find the first Thevenin equivalent voltage source E eq for:

[0199]

[0200] In step 205, based on the detailed switch model, a second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state is calculated.

[0201] Preferably, based on the detailed switch model, calculating a second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state includes:

[0202] Determine the second Thevenin equivalent resistance R eq2 for:

[0203]

[0204] Determine the second Thevenin equivalent voltage source E eq2 for:

[0205] E eq2 =J eq R eq2 ,

[0206]

[0207] Among them, J eq is the Norton equivalent current; Y 11 -Y 22 are the four block matrices of the H-bridge circuit conductivity matrix; J2 is the second block vector of the H-bridge circuit current column vector; G1-G4 are the conductances of the bridge arms; J C It is the current source of the capacitor discretization circuit.

[0208] In the present invention, based on the detailed switch model of the H-bridge unit in the abnormal state, the Thevenin equivalent circuit of the H-bridge unit in the abnormal state is calculated. The specific method of solving the Thevenin equivalent circuit parameters is as follows:

[0209] Fig.12 The circuit equation is:

[0210]

[0211] Taking node 2 as the reference node, cross out the second row and the second column of equation (16) to obtain:

[0212]

[0213] Simplify formula (17) into formula (18):

[0214]

[0215] The second Thevenin equivalent resistance R eq The calculation formula is:

[0216]

[0217] Norton equivalent current source J eq The calculation formula is:

[0218]

[0219] The second Thevenin equivalent voltage source E eq The calculation formula is:

[0220] E eq =J eq R eq (twenty one)

[0221] The present invention establishes the Thevenin equivalent model of the average switch model under normal state and the detailed switch model under abnormal state respectively. The establishment of the Thevenin model reduces the original circuit equation of hundreds of orders to only 2 orders, greatly reduces the dimension of the circuit matrix, and improves the simulation efficiency without losing any accuracy.

[0222] In step 206, a Norton equivalent circuit of a cascaded H-bridge arm is calculated based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit.

[0223] Preferably, the calculation of the Norton equivalent circuit of the cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit comprises:

[0224] The Norton equivalent circuit parameters of the cascaded H-bridge arm are determined as:

[0225]

[0226] Among them, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; Jarmeq is the current source of the Norton equivalent circuit of the cascaded H-bridge arm; i represents the i-th H-bridge unit on the bridge arm; R LARM and E LARM is the accompanying circuit parameter of the bridge arm inductance; R eqi is the Thevenin equivalent resistance of the ith unit; U eqi is the Thevenin equivalent voltage source of the ith unit.

[0227] In the present invention, the Norton equivalent circuit of the cascaded H-bridge arm is calculated based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor accompanying circuit of the H-bridge unit. As described above, the present invention models all cases of the H-bridge unit. In the cascaded H-bridge arm, multiple units are connected in series. In addition, one bridge arm inductor is also connected in series in the bridge arm. If the number of units in each bridge arm is N, the modeling of the bridge arm is as follows: Fig.13 As shown. The Norton equivalent circuit parameters of the H-bridge arm can be obtained as follows:

[0228]

[0229] Where i represents the i-th H-bridge unit on the bridge arm, R LARM and E LARM is the accompanying circuit parameter of the bridge arm inductance (obtained from the step-average switching model).

[0230] In step 207 , the bridge arm current is determined based on the Norton equivalent circuit of the cascaded H-bridge bridge arm.

[0231] Preferably, determining the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm comprises:

[0232] The Norton equivalent circuit of the cascaded H-bridge bridge arm is superimposed into the system equation and input into the electromagnetic transient simulation program to solve the node voltage equation of the system to obtain the node voltage u at both ends of the bridge arm. ARM1 and u ARM2 , according to the Norton equivalent circuit of the bridge arm, the bridge arm current i1 is calculated as:

[0233] i1=(u ARM2 -u ARM1 )G armeq +J armeq ,

[0234] Among them, u ARM1 and u ARM2 are the voltages of bridge arm nodes 1 and 2, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq It is the current source of the Norton equivalent circuit of the cascaded H-bridge arm.

[0235] In the present invention, the Norton equivalent circuits of the bridge arms of the cascaded H bridge are superimposed into the system equation, and the node voltage equations of the system are solved by inputting them into the electromagnetic transient simulation program to obtain the node voltages u at both ends of the bridge arm. ARM1 and u ARM2 . According to the Norton equivalent circuit of the bridge arm, calculate the bridge arm current i1:

[0236] i1=(u ARM2 -u ARM1 )G armeq +J armeq (twenty four)

[0237] Among them, u ARM1 and u ARM2 are the voltages of bridge arm nodes 1 and 2, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq It is the current source of the Norton equivalent circuit of the cascaded H-bridge arm.

[0238] In step 208 , the DC voltage and the diode voltage of each H-bridge unit are calculated based on the bridge arm current.

[0239] Preferably, the DC voltage and the diode voltage of each H-bridge unit are calculated based on the bridge arm current, comprising:

[0240] Determine the DC voltage of the i-th H-bridge unit in the normal state as:

[0241] Determine the port voltage of each H-bridge unit in the abnormal state as:

[0242] u celli =E eqi -i1R eqi ,

[0243]

[0244] Determine the DC voltage under abnormal conditions:

[0245] e i =u n2i -u p2i ,

[0246] Determine the diode voltage under abnormal conditions:

[0247]

[0248] Wherein, the subscript i represents the i-th H-bridge unit in the cascaded H-bridge; u p2 is the voltage difference between node p and node 2; u n2 is the voltage difference between node n and node 2; U p , Un U1, U2 are the voltages of nodes p, n, and 2 respectively; G1-G4 are the conductances of the bridge arms; G C and J C is the conductance and current source of the capacitor discretization circuit; u D1 -u D4 is the voltage of diodes 1 to 4; u cell is the H-bridge port voltage; i1 is the bridge arm current; k1 and k2 are the controlled source coefficients of the first and second half bridges of the H-bridge respectively.

[0249] In the present invention, the DC voltage e and the diode voltage u are solved according to the bridge arm current i1. D1 to u D4 .

[0250] in,

[0251] (1) Under normal conditions, the DC voltage calculation formula of the i-th unit is:

[0252]

[0253] The subscript i represents the i-th unit of the cascaded H-bridge, and the same applies below.

[0254] (2) Abnormal status:

[0255] The calculation formula for the port voltage of each unit is:

[0256] u celli =E eqi -i1R eqi (26)

[0257]

[0258] The DC voltage calculation formula under abnormal conditions is:

[0259] e i =u n2i -u p2i (29)

[0260] The calculation formula of diode voltage under abnormal condition is:

[0261]

[0262] Wherein, the subscript i represents the i-th H-bridge unit in the cascaded H-bridge; u p2 is the voltage difference between node p and node 2; u n2 is the voltage difference between node n and node 2; U p , U n U1, U2 are the voltages of nodes p, n, and 2 respectively; G1-G4 are the conductances of the bridge arms; G C and JC is the conductance and current source of the capacitor discretization circuit; u D1 -u D4 is the voltage of diodes 1 to 4; u cell is the H-bridge port voltage; i1 is the bridge arm current; k1 and k2 are the controlled source coefficients of the first and second half bridges of the H-bridge respectively.

[0263] The simulation process of the present invention is as follows Fig.14 The model proposed in the present invention utilizes the Thevenin equivalent principle, and the calculation results are strictly equal to the calculation results of the average switch detailed model without Thevenin equivalent processing. Taking a single-bridge 39-unit CHB-SVG stand-alone test system as an example, the test circuit is as follows Fig.15 The simulation waveform comparison results are shown in Fig.16 As shown, Fig.16 (a) and (b) are schematic diagrams of SVG bridge arm voltage / kV (one cycle) and SVG bridge arm voltage / kV (local magnification), respectively. It can be seen that the calculation results of the proposed model and the average switch detailed model are completely consistent, and the simulation curves of the two overlap, so they look like one curve. This shows the correctness of the proposed model applying the Thevenin equivalent principle.

[0264] As shown in Table 2, the efficiency comparison results of the CHB-SVG single-machine test system simulation time of 10s are given. It can be seen that for H-bridge units of different sizes, the calculation time of the proposed model is much shorter than that of the detailed switch model. For a single-phase CHB-SVG with 100 H-bridge units, the speedup ratio can reach 24 times. This shows that the proposed model can be calculated faster than the detailed switch model.

[0265] Table 2 Simulation efficiency comparison table

[0266]

[0267] In addition, the proposed model can accurately simulate the harmonics and dynamic characteristics of the converter during faults without the need for additional interpolation or variable step size processing. Taking a CHB-SVG with 39 H-bridge units in a single bridge arm as an example, the reactive power comparison results of the proposed model and the detailed switch model are shown in Figure 2. Fig.17 As shown in (a), (b) and (c), they represent the reactive power output by SVG, the reactive power output by SVG / Mvar (locally amplified during steady state) and the reactive power output by SVG / Mvar (locally amplified during fault recovery). It can be seen that the simulation accuracy of the proposed model at 50μs is close to that of the detailed model at 1μs, and is significantly higher than that of the detailed model at 50μs, indicating that the proposed model can extend the simulation time step by more than 10 times without reducing the accuracy and reproduce the harmonics reasonably.

[0268] Fig.18 FIG. 1 is a schematic diagram of the structure of an electromagnetic transient modeling simulation system 1800 for a cascaded H-bridge converter according to an embodiment of the present invention. Fig.18 As shown, the electromagnetic transient modeling and simulation system 1800 of the cascaded H-bridge converter provided in an embodiment of the present invention includes: a companion circuit calculation unit 1801, a state division unit 1802, a model establishment unit 1803, a first Thevenin equivalent unit 1804, a second Thevenin equivalent unit 1805, a Norton equivalent unit 1806, a bridge arm current calculation unit 1807 and a voltage calculation unit 1808.

[0269] Preferably, the companion circuit calculation unit 1801 is used to calculate the capacitance companion circuit of the H-bridge unit capacitor and the inductance companion circuit of the bridge arm inductance respectively.

[0270] Preferably, the accompanying circuit calculation unit 1801 is used to calculate the capacitance accompanying circuit of the H-bridge unit capacitance and the inductance accompanying circuit of the bridge arm inductance, respectively, including:

[0271] Determine the companion point G of the capacitor C and the accompanying current source J C The values ​​are:

[0272]

[0273] Determine the accompanying conductance G of the inductor L and the accompanying current source J L The values ​​are:

[0274]

[0275] J L =i n-1 ,

[0276] Where C is the capacitance; h is the simulation step length; u n-1 is the voltage across the capacitor at time n-1. ; L is the inductance; i n-1 is the current of the inductor at time n-1.

[0277] Preferably, the state division unit 1802 is used to divide the operating state of the half-bridge circuit in the H-bridge unit, and determine a switch state table of the half-bridge circuit according to the operating state.

[0278] Preferably, the state division unit 1802 divides the operating state of the half-bridge circuit in the H-bridge unit, and determines a switch state table of the half-bridge circuit according to the operating state, including:

[0279] When the upper bridge arm of the half-bridge circuit is turned on and the lower bridge arm is turned off, it is determined to be in the capacitor input state, and the switch state is represented by the binary number 10; when the upper bridge arm of the bridge circuit is turned off and the lower bridge arm is turned on, it is determined to be in the capacitor bypass state, and the switch state is represented by the binary number 01; when both the upper and lower bridge arms of the half-bridge circuit are turned on, it is determined to be in the capacitor short-circuit state, and the switch state is represented by the binary number 11; when both the upper and lower bridge arms of the half-bridge circuit are turned off, it is determined to be in the capacitor input state, determined to be in the circuit open state, and the switch state is represented by the binary number 00;

[0280] According to the IGBT gate signal, DC voltage e and diode voltage u D1 and u D2 Determine the operating status of the half-bridge circuit.

[0281] Preferably, the model building unit 1803 is used to build a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state, respectively, based on the capacitor accompanying circuit and the switch state table.

[0282] Preferably, the model building unit 1803 builds a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state based on the capacitor accompanying circuit and the switch state table, respectively, including:

[0283] Under normal conditions, the two half-bridge circuits in the H-bridge unit are replaced with the step average model, and the capacitor is equivalent to the capacitor companion circuit to obtain the step average model of the H-bridge unit under normal conditions; wherein, the on-resistance R is connected in series at the unit port. on To simulate conduction losses in detailed models;

[0284] In the abnormal state, the upper and lower bridge arms of the two half-bridge circuits in the H-bridge unit are modeled with binary resistors to obtain a detailed switch model of the H-bridge unit in the abnormal state; the conductance of the bridge arm is determined by the switch state table. When the bridge arm is turned on, the bridge arm conductance is the on-state conductance G on When the bridge arm is turned off, the bridge arm conductance is the off conductance G off .

[0285] Preferably, the first Thevenin equivalent unit 1804 is used to calculate a first Thevenin equivalent circuit of an average switching model of the H-bridge unit in a normal state based on the step-average switching model.

[0286] Preferably, the first Thevenin equivalent unit 1805 calculates the first Thevenin equivalent circuit of the average switching model of the H-bridge unit in the normal state based on the step-average switching model, including:

[0287] Determine the first Thevenin equivalent resistance R eq1,include:

[0288]

[0289] Determine the first Thevenin equivalent voltage source E eq1 ,include:

[0290]

[0291] Where k is the controlled source coefficient of the H-bridge unit; U p and U n is the voltage at nodes p and n; i is the AC current; G C and J c is the discretized circuit parameter of the capacitor; the subscripts 1 and 2 of k and i are used to distinguish the two half-bridge circuits of the H-bridge unit.

[0292] Preferably, the second Thevenin equivalent unit 1805 is used to calculate a second Thevenin equivalent circuit of the detailed switching model of the H-bridge unit in an abnormal state based on the detailed switching model.

[0293] Preferably, the second Thevenin equivalent unit 1805 calculates the second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state based on the detailed switch model, including:

[0294] Determine the second Thevenin equivalent resistance R eq2 for:

[0295]

[0296] Determine the second Thevenin equivalent voltage source E eq2 for:

[0297] E eq2 =J eq R eq2 ,

[0298]

[0299] Among them, J eq is the Norton equivalent current; Y 11 -Y 22 are the four block matrices of the H-bridge circuit conductivity matrix; J2 is the second block vector of the H-bridge circuit current column vector; G1-G4 are the conductances of the bridge arms; J C It is the current source of the capacitor discretization circuit.

[0300] Preferably, the Norton equivalent unit 1806 is used to calculate the Norton equivalent circuit of the cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit.

[0301] Preferably, the Norton equivalent unit 1806 calculates the Norton equivalent circuit of the cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit, including:

[0302] The Norton equivalent circuit parameters of the cascaded H-bridge arm are determined as:

[0303]

[0304] Among them, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq is the current source of the Norton equivalent circuit of the cascaded H-bridge arm; i represents the i-th H-bridge unit on the bridge arm; R LARM and E LARM is the accompanying circuit parameter of the bridge arm inductance; R eqi is the Thevenin equivalent resistance of the ith unit; U eqi is the Thevenin equivalent voltage source of the ith unit.

[0305] Preferably, the bridge arm current calculation unit 1807 is used to determine the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm.

[0306] Preferably, the bridge arm current determining unit 1807 determines the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm, including:

[0307] The Norton equivalent circuit of the cascaded H-bridge bridge arm is superimposed into the system equation and input into the electromagnetic transient simulation program to solve the node voltage equation of the system to obtain the node voltage u at both ends of the bridge arm. ARM1 and u ARM2 , according to the Norton equivalent circuit of the bridge arm, the bridge arm current i1 is calculated as:

[0308] i1=(u ARM2 -u ARM1 )G armeq +J armeq ,

[0309] Among them, u ARM1 and u ARM2 are the voltages of bridge arm nodes 1 and 2, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq It is the current source of the Norton equivalent circuit of the cascaded H-bridge arm.

[0310] Preferably, the voltage calculation unit 1808 is used to calculate the DC voltage and the diode voltage of each H-bridge unit based on the bridge arm current.

[0311] Preferably, the voltage calculation unit 1808 calculates the DC voltage and the diode voltage of each H-bridge unit based on the bridge arm current, including:

[0312] Determine the DC voltage of the i-th H-bridge unit in the normal state as:

[0313] Determine the port voltage of each H-bridge unit in the abnormal state as:

[0314] u celli =E eqi -i1R eqi ,

[0315]

[0316] Determine the DC voltage under abnormal conditions:

[0317] e i =u n2i -u p2i ,

[0318] Determine the diode voltage under abnormal conditions:

[0319]

[0320]

[0321] Wherein, the subscript i represents the i-th H-bridge unit in the cascaded H-bridge; u p2 is the voltage difference between node p and node 2; u n2 is the voltage difference between node n and node 2; U p , U n U1, U2 are the voltages of nodes p, n, and 2 respectively; G1-G4 are the conductances of the bridge arms; G C and J C is the conductance and current source of the capacitor discretization circuit; u D1 -u D4 is the voltage of diodes 1 to 4; u cell is the H-bridge port voltage; i1 is the bridge arm current; k1 and k2 are the controlled source coefficients of the first and second half bridges of the H-bridge respectively.

[0322] The electromagnetic transient modeling and simulation system 1800 of the cascaded H-bridge converter according to the embodiment of the present invention corresponds to the electromagnetic transient modeling and simulation method 200 of the cascaded H-bridge converter according to another embodiment of the present invention, and will not be described in detail here.

[0323] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0324] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise therein. All references to "a / said / the [means, components, etc.]" are to be openly interpreted as at least one instance of said means, components, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily have to be performed in the exact order disclosed, unless explicitly stated otherwise.

[0325] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0326] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0327] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0328] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0329] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. An electromagnetic transient modeling and simulation method for a cascaded H-bridge converter, characterized in that: The method comprises: Calculate the capacitive accompanying circuit of the H-bridge unit capacitor and the inductive accompanying circuit of the bridge arm inductance respectively; Dividing the operating states of the half-bridge circuits in the H-bridge unit, and determining a switch state table of the half-bridge circuits according to the operating states; Based on the capacitor accompanying circuit and the switch state table, a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state are respectively established; Based on the step-average switching model, calculating a first Thevenin equivalent circuit of the average switching model of the H-bridge unit in a normal state; Based on the detailed switch model, calculating a second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state; Calculate the Norton equivalent circuit of the cascaded H-bridge bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit; Determine the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm; The DC voltage and the diode voltage of each H-bridge unit are calculated based on the bridge arm current.

2. The method according to claim 1, characterized in that Calculate the capacitive accompanying circuit of the H-bridge unit capacitor and the inductive accompanying circuit of the bridge arm inductance respectively, including: Determine the companion point G of the capacitor C and the accompanying current source J C The values ​​are: Determine the accompanying conductance G of the inductor L and the accompanying current source J L The values ​​are: J L =i n-1 , Where C is the capacitance; h is the simulation step length; u n-1 is the voltage across the capacitor at time n-1. ; L is the inductance; i n-1 is the current of the inductor at time n-1.

3. The method according to claim 1, characterized in that The operating state of the half-bridge circuit in the H-bridge unit is divided, and a switch state table of the half-bridge circuit is determined according to the operating state, including: When the upper bridge arm of the half-bridge circuit is turned on and the lower bridge arm is turned off, it is determined to be in the capacitor input state, and the switch state is represented by the binary number 10; when the upper bridge arm of the bridge circuit is turned off and the lower bridge arm is turned on, it is determined to be in the capacitor bypass state, and the switch state is represented by the binary number 01; when both the upper and lower bridge arms of the half-bridge circuit are turned on, it is determined to be in the capacitor short-circuit state, and the switch state is represented by the binary number 11; when both the upper and lower bridge arms of the half-bridge circuit are turned off, it is determined to be in the capacitor input state, determined to be in the circuit open state, and the switch state is represented by the binary number 00; According to the IGBT gate signal, DC voltage e and diode voltage u D1 and u D2 Determine the operating status of the half-bridge circuit.

4. The method according to claim 1, characterized in that Based on the capacitor accompanying circuit and the switch state table, a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state are respectively established, including: Under normal conditions, the two half-bridge circuits in the H-bridge unit are replaced with the step average model, and the capacitor is equivalent to the capacitor companion circuit to obtain the step average model of the H-bridge unit under normal conditions; wherein, the on-resistance R is connected in series at the unit port. on To simulate conduction losses in detailed models; In the abnormal state, the upper and lower bridge arms of the two half-bridge circuits in the H-bridge unit are modeled with binary resistors to obtain a detailed switch model of the H-bridge unit in the abnormal state; the conductance of the bridge arm is determined by the switch state table. When the bridge arm is turned on, the bridge arm conductance is the on-state conductance G on When the bridge arm is turned off, the bridge arm conductance is the off conductance G off .

5. The method according to claim 1, characterized in that Based on the step-average switching model, a first Thevenin equivalent circuit of the average switching model of the H-bridge unit in a normal state is calculated, including: Determine the first Thevenin equivalent resistance R eq1 ,include: Determine the first Thevenin equivalent voltage source E eq1 ,include: Where k is the controlled source coefficient of the H-bridge unit; U p and U n is the voltage at nodes p and n; i is the AC current; G C and J c is the discretized circuit parameter of the capacitor; the subscripts 1 and 2 of k and i are used to distinguish the two half-bridge circuits of the H-bridge unit.

6. The method according to claim 1, characterized in that Based on the detailed switch model, a second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state is calculated, including: Determine the second Thevenin equivalent resistance R eq2 for: Determine the second Thevenin equivalent voltage source E eq2 for: Among them, J eq is the Norton equivalent current; Y 11 -Y 22 are the four block matrices of the H-bridge circuit conductivity matrix; J2 is the second block vector of the H-bridge circuit current column vector; G1-G4 are the conductances of the bridge arms; J C It is the current source of the capacitor discretization circuit.

7. The method according to claim 1, characterized in that The step of calculating the Norton equivalent circuit of the cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit comprises: The Norton equivalent circuit parameters of the cascaded H-bridge arm are determined as: Among them, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq is the current source of the Norton equivalent circuit of the cascaded H-bridge arm; i represents the i-th H-bridge unit on the bridge arm; R LARM and E LARM is the accompanying circuit parameter of the bridge arm inductance; R eqi is the Thevenin equivalent resistance of the ith unit; U eqi is the Thevenin equivalent voltage source of the ith unit.

8. The method according to claim 1, characterized in that Determine the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge arm, including: The Norton equivalent circuit of the cascaded H-bridge bridge arm is superimposed into the system equation and input into the electromagnetic transient simulation program to solve the node voltage equation of the system to obtain the node voltage u at both ends of the bridge arm. ARM1 and u ARM2 , according to the Norton equivalent circuit of the bridge arm, the bridge arm current i1 is calculated as: i1=(u ARM2 -u ARM1 )G armeq +J armeq , Among them, u ARM1 and u ARM2 are the voltages of bridge arm nodes 1 and 2, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq It is the current source of the Norton equivalent circuit of the cascaded H-bridge arm.

9. The method according to claim 1, characterized in that: Calculating the DC voltage and the diode voltage of each H-bridge unit based on the bridge arm current includes: Determine the DC voltage of the i-th H-bridge unit in the normal state as: Determine the port voltage of each H-bridge unit in the abnormal state as: you celli =E eqi -i1R eqi , Determine the DC voltage under abnormal conditions: yes i =in n2i -in p2i , Determine the diode voltage under abnormal conditions: Wherein, the subscript i represents the i-th H-bridge unit in the cascaded H-bridge; u p2 is the voltage difference between node p and node 2; u n2 is the voltage difference between node n and node 2; U p , U n U1, U2 are the voltages of nodes p, n, and 2 respectively; G1-G4 are the conductances of the bridge arms; G C and J C is the conductance and current source of the capacitor discretization circuit; u D1 -u D4 is the voltage of diodes 1 to 4; u cell is the H-bridge port voltage; i1 is the bridge arm current; k1 and k2 are the controlled source coefficients of the first and second half bridges of the H-bridge respectively.

10. An electromagnetic transient modeling and simulation system for a cascaded H-bridge converter, characterized in that: The system comprises: A companion circuit calculation unit, used for respectively calculating a capacitance companion circuit of the H-bridge unit capacitance and an inductance companion circuit of the bridge arm inductance; A state division unit, used to divide the operating state of the half-bridge circuit in the H-bridge unit, and determine a switch state table of the half-bridge circuit according to the operating state; A model building unit, used to build a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state, respectively, based on the capacitor accompanying circuit and the switch state table; A first Thevenin equivalent unit, used for calculating a first Thevenin equivalent circuit of an average switching model of an H-bridge unit in a normal state based on the step-average switching model; A second Thevenin equivalent unit, used for calculating a second Thevenin equivalent circuit of the detailed switching model of the H-bridge unit in an abnormal state based on the detailed switching model; A Norton equivalent unit, used for calculating a Norton equivalent circuit of a cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit; A bridge arm current calculation unit, used for determining the bridge arm current based on a Norton equivalent circuit of the cascaded H-bridge bridge arm; A voltage calculation unit is used to calculate the DC voltage and the diode voltage of each H-bridge unit based on the bridge arm current.

11. The system according to claim 10, characterized in that The accompanying circuit calculation unit is used to calculate the capacitance accompanying circuit of the H-bridge unit capacitance and the inductance accompanying circuit of the bridge arm inductance, respectively, including: Determine the companion point G of the capacitor C and the accompanying current source J C The values ​​are: Determine the accompanying conductance G of the inductor L and the accompanying current source J L The values ​​are: J L =i n-1 , Where C is the capacitance; h is the simulation step length; u n-1 is the voltage across the capacitor at time n-1. ; L is the inductance; i n-1 is the current of the inductor at time n-1.

12. The system according to claim 10, characterized in that A state division unit divides the operating state of the half-bridge circuit in the H-bridge unit and determines a switch state table of the half-bridge circuit according to the operating state, including: When the upper bridge arm of the half-bridge circuit is turned on and the lower bridge arm is turned off, it is determined to be in the capacitor input state, and the switch state is represented by the binary number 10; when the upper bridge arm of the bridge circuit is turned off and the lower bridge arm is turned on, it is determined to be in the capacitor bypass state, and the switch state is represented by the binary number 01; when both the upper and lower bridge arms of the half-bridge circuit are turned on, it is determined to be in the capacitor short-circuit state, and the switch state is represented by the binary number 11; when both the upper and lower bridge arms of the half-bridge circuit are turned off, it is determined to be in the capacitor input state, determined to be in the circuit open state, and the switch state is represented by the binary number 00; According to the IGBT gate signal, DC voltage e and diode voltage u D1 and u D2 Determine the operating status of the half-bridge circuit.

13. The system according to claim 10, characterized in that The model building unit builds a step average switch model of the H-bridge unit in a normal state and a detailed switch model of the H-bridge unit in an abnormal state based on the capacitor accompanying circuit and the switch state table, respectively, including: Under normal conditions, the two half-bridge circuits in the H-bridge unit are replaced with the step average model, and the capacitor is equivalent to the capacitor companion circuit to obtain the step average model of the H-bridge unit under normal conditions; wherein, the on-resistance R is connected in series at the unit port. on To simulate conduction losses in detailed models; In the abnormal state, the upper and lower bridge arms of the two half-bridge circuits in the H-bridge unit are modeled with binary resistors to obtain a detailed switch model of the H-bridge unit in the abnormal state; the conductance of the bridge arm is determined by the switch state table. When the bridge arm is turned on, the bridge arm conductance is the on-state conductance G on When the bridge arm is turned off, the bridge arm conductance is the off conductance G off .

14. The system according to claim 10, characterized in that The first Thevenin equivalent unit calculates the first Thevenin equivalent circuit of the average switching model of the H-bridge unit in a normal state based on the step average switching model, including: Determine the first Thevenin equivalent resistance R eq1 ,include: Determine the first Thevenin equivalent voltage source E eq1 ,include: Where k is the controlled source coefficient of the H-bridge unit; U p and U n is the voltage at nodes p and n; i is the AC current; G C and J c is the discretized circuit parameter of the capacitor; the subscripts 1 and 2 of k and i are used to distinguish the two half-bridge circuits of the H-bridge unit.

15. The system according to claim 10, characterized in that The second Thevenin equivalent unit calculates the second Thevenin equivalent circuit of the detailed switch model of the H-bridge unit in an abnormal state based on the detailed switch model, including: Determine the second Thevenin equivalent resistance R eq2 for: Determine the second Thevenin equivalent voltage source E eq2 for: E eq2 =J eq R eq2 , Among them, J eq is the Norton equivalent current; Y 11 -Y 22 are the four block matrices of the H-bridge circuit conductivity matrix; J2 is the second block vector of the H-bridge circuit current column vector; G1-G4 are the conductances of the bridge arms; J C It is the current source of the capacitor discretization circuit.

16. The system according to claim 10, characterized in that The Norton equivalent unit calculates the Norton equivalent circuit of the cascaded H-bridge arm based on the first Thevenin equivalent circuit, the second Thevenin equivalent circuit and the inductor companion circuit, including: The Norton equivalent circuit parameters of the cascaded H-bridge arm are determined as: Among them, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq is the current source of the Norton equivalent circuit of the cascaded H-bridge arm; i represents the i-th H-bridge unit on the bridge arm; R LARM and E LARM is the accompanying circuit parameter of the bridge arm inductance; R eqi is the Thevenin equivalent resistance of the ith unit; U eqi is the Thevenin equivalent voltage source of the ith unit.

17. The system according to claim 10, characterized in that The bridge arm current determination unit determines the bridge arm current based on the Norton equivalent circuit of the cascaded H-bridge bridge arm, including: The Norton equivalent circuit of the cascaded H-bridge bridge arm is superimposed into the system equation and input into the electromagnetic transient simulation program to solve the node voltage equation of the system to obtain the node voltage u at both ends of the bridge arm. ARM1 and u ARM2 , according to the Norton equivalent circuit of the bridge arm, the bridge arm current i1 is calculated as: i1=(u ARM2 -u ARM1 )G armeq +J armeq , Among them, u ARM1 and u ARM2 are the voltages of bridge arm nodes 1 and 2, G armeq is the conductance of the Norton equivalent circuit of the cascaded H-bridge arm; J armeq It is the current source of the Norton equivalent circuit of the cascaded H-bridge arm.

18. The system according to claim 10, characterized in that A voltage calculation unit, which calculates the DC voltage and the diode voltage of each H-bridge unit based on the bridge arm current, comprises: Determine the DC voltage of the i-th H-bridge unit in the normal state as: Determine the port voltage of each H-bridge unit in the abnormal state as: you celli =E eqi -i1R eqi , Determine the DC voltage under abnormal conditions: yes i =in n2i -in p2i , Determine the diode voltage under abnormal conditions: Wherein, the subscript i represents the i-th H-bridge unit in the cascaded H-bridge; u p2 is the voltage difference between node p and node 2; u n2 is the voltage difference between node n and node 2; U p , U n U1, U2 are the voltages of nodes p, n, and 2 respectively; G1-G4 are the conductances of the bridge arms; G C and J C is the conductance and current source of the capacitor discretization circuit; u D1 -u D4 is the voltage of diodes 1 to 4; u cell is the H-bridge port voltage; i1 is the bridge arm current; k1 and k2 are the controlled source coefficients of the first and second half bridges of the H-bridge respectively.

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