CN112001142B - Real-time simulation method of half-bridge type modular multilevel converter - Google Patents
Real-time simulation method of half-bridge type modular multilevel converter Download PDFInfo
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- CN112001142B CN112001142B CN202010714120.3A CN202010714120A CN112001142B CN 112001142 B CN112001142 B CN 112001142B CN 202010714120 A CN202010714120 A CN 202010714120A CN 112001142 B CN112001142 B CN 112001142B
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
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- G06F30/30—Circuit design
- G06F30/36—Circuit design at the analogue level
- G06F30/367—Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
- H02M7/53875—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with analogue control of three-phase output
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Abstract
The invention discloses a real-time simulation method of a half-bridge type modular multilevel converter, which comprises the following steps: constructing an equivalent circuit model of the half-bridge type modular multilevel converter; initializing system parameters of the equivalent circuit model; updating the states of two power electronic switches and input bridge arm current of each power module in the MMC; obtaining the current of a switch branch circuit, the current of a bridge arm inductance equivalent branch circuit and the current of a module capacitor branch circuit at the current simulation moment; updating the voltage of each branch and the current of each branch according to the voltage-current relationship of each branch; obtaining bridge arm current of each bridge arm equivalent circuit; judging whether the current simulation duration reaches a preset threshold value, if so, ending the simulation; if not, the current simulation duration is increased by one simulation step length so as to continue the next simulation calculation. The invention can realize the decoupling of the power module and the bridge arm loop and avoid the fault current error caused by the large and small step decoupling mode in the simulation calculation.
Description
Technical Field
The invention relates to the technical field of simulation, in particular to a real-time simulation method of a half-bridge type modular multilevel converter.
Background
Flexible direct-current power transmission based on a Modular Multilevel Converter (MMC) has the advantages of active and reactive independent control, stable direct-current voltage, less alternating-current voltage harmonic waves, small occupied area and the like, so that the flexible direct-current power transmission has been widely applied to aspects of large-capacity remote power transmission, asynchronous networking, renewable energy grid connection and the like in recent years. The modularized multi-level converter is generally composed of thousands of power modules with similar structures and functions, each power module comprises a plurality of power electronic switching devices, and the modularized multi-level converter has the characteristics of complex structure and high control difficulty. In order to guarantee the reliability of the flexible direct-current transmission system, a digital real-time simulation system is generally required to perform sufficient semi-physical simulation tests on the flexible direct-current protection system in a factory and before production so as to verify that related functions and performances meet design requirements. The digital real-time simulation model of the MMC is a key part of the whole simulation system.
The existing MMC real-time simulation model is generally based on a large step size simulation calculation mode, namely, an MMC model is divided into a bridge arm model and a sub-module model through decoupling, the large step size (20-100 mu s) is adopted in a CPU to complete the simulation calculation of the bridge arm model, and the small step size (0.5-2 mu s) is adopted in an FPGA to complete the simulation calculation of the sub-module model. By adopting the mode, the real-time simulation problem of a large number of power electronic switch systems is effectively solved. However, the large error is also easily caused by the large-and-small step decoupling mode under some extreme conditions, for example, when a bridge arm is short-circuited, the short-circuit current rise rate is large, and the module response is delayed due to the asynchronous calculation mode of the bridge arm and the module large-and-small step, and finally the fault current error is large.
Disclosure of Invention
The embodiment of the invention aims to provide a real-time simulation method of a half-bridge type modular multilevel converter, and provides an MMC (modular multilevel converter) small-step real-time simulation equivalent circuit model which can be completely calculated by adopting an FPGA (field programmable gate array) so as to decouple a power module and a bridge arm loop and avoid fault current errors caused by a large-step decoupling mode in simulation calculation.
In order to achieve the above object, an embodiment of the present invention provides a real-time simulation method for a half-bridge type modular multilevel converter, including the following steps:
constructing an equivalent circuit model of the half-bridge type modular multilevel converter; the equivalent circuit model comprises six identical bridge arm equivalent circuits, each bridge arm equivalent circuit comprises two switch branches and a bridge arm inductance equivalent branch, each switch branch comprises a first equivalent resistor, a first controlled current source and a controlled voltage source, and each bridge arm inductance equivalent branch comprises a second equivalent resistor and a second controlled current source;
initializing system parameters of the equivalent circuit model to start electromagnetic transient simulation calculation of the half-bridge type modular multilevel converter;
updating the states of two power electronic switches and input bridge arm current of each power module in the half-bridge type modular multilevel converter to obtain port voltage and capacitance current of each power module;
acquiring the current of the switch branch, the current of the bridge arm inductance equivalent branch and the current of the module capacitor branch at the current simulation moment; the module capacitor branch is equivalent to a module capacitor in the power module and comprises a third equivalent resistor and a third controlled current source, and the third equivalent resistor is connected with the third controlled current source in parallel;
updating the voltage of each branch and the current of each branch according to the voltage-current relationship of each branch; each branch comprises the switch branch, the bridge arm inductance equivalent branch and the module capacitor branch;
obtaining bridge arm current of each bridge arm equivalent circuit;
judging whether the current simulation duration reaches a preset threshold value, if so, outputting three-phase current and direct current of alternating current, and finishing simulation; and if not, increasing the current simulation duration by a preset simulation step length so as to continuously update the states of the two power electronic switches of each power module in the half-bridge type modular multilevel converter and the input bridge arm current.
Preferably, the two switch branches of the bridge arm equivalent circuit are connected in parallel, one end of each switch branch is connected with one end of the bridge arm inductance equivalent branch, the other end of each switch branch is connected with a direct-current positive electrode port or a direct-current negative electrode port, and the other end of the bridge arm inductance equivalent branch is connected with one port of three-phase alternating current.
Preferably, one end of the first equivalent resistor is connected to the dc positive port and one end of the first controlled current source, the other end of the first equivalent resistor is connected to the other end of the first controlled current source and one end of the controlled voltage source, the other end of the controlled voltage source is connected to one end of the second equivalent resistor and one end of the second controlled current source, the other end of the second equivalent resistor is connected to one port of the three-phase alternating current, and the other end of the second controlled current source is connected to one port of the three-phase alternating current.
Preferably, initializing system parameters of the equivalent circuit model specifically includes:
determining a simulation step length according to a preset on-state inductance of the switch branch circuit and a preset off-state capacitance of the switch branch circuit; wherein the simulation step length is
Δ t is the simulation step, L eq For a predetermined conduction inductance of the switching branch, C eq The switching-off capacitance is a preset switching-off capacitance of the switching branch circuit;
determining the resistance value of the first equivalent resistor according to the simulation step length; wherein the first equivalent resistor has a resistance value of
Or
R S1 Is the resistance value of the first equivalent resistor;
determining the resistance value of the second equivalent resistor and the resistance value of the third equivalent resistor according to the bridge arm inductance value of the half-bridge type modular multilevel converter, the capacitance value of the module capacitor and the simulation step length; wherein the resistance value of the second equivalent resistor is
The resistance value of the third equivalent resistor is
R L Is the resistance value, R, of the second equivalent resistor C And L is the resistance value of the third equivalent resistor, L is the inductance value of the bridge arm, and C is the capacitance value of the module capacitor.
Preferably, the updating the states and the input bridge arm currents of the two power electronic switches of each power module in the half-bridge modular multilevel converter to obtain the port voltage and the capacitor current of each power module specifically includes:
inputting a switch control signal according to simulation requirements, and updating the states of two power electronic switches of each power module in the half-bridge type modular multilevel converter;
determining the port voltage of each power module as the voltage of the module capacitor or 0 according to the states of two power electronic switches in each power module;
and obtaining the capacitance current of the module capacitor according to the input bridge arm current and the states of the two power electronic switches in each power module.
Preferably, the voltage of the controlled voltage source is
Wherein, U 1 Is the voltage of the controlled voltage source, U 1_k The terminal voltage of the kth power module in the half-bridge type modular multilevel converter is represented, n is the module number of the power module in the half-bridge type modular multilevel converter, and k is larger than or equal to 1 and smaller than or equal to n.
Preferably, the obtaining of the current of the switch branch, the current of the bridge arm inductance equivalent branch, and the current of the module capacitor branch at the current simulation time specifically includes:
according to the resistance value of the first equivalent resistor,Obtaining a current value of the first controlled current source in the switch branch circuit at the current simulation moment by the current value flowing through the first equivalent resistor and the voltage values at two ends of the first equivalent resistor at the previous simulation moment; wherein when U is S1(t-Δt) >At the time of 0, the number of the first electrode,
when U is turned S1(t-Δt) When the content is less than or equal to 0,
U S1(t-Δt) the voltage value of the two ends of the first equivalent resistor, ih, at the last simulation moment S1 For the current value of the first controlled current source at the present simulation time, ib 1(t-Δt) The value of the current flowing through the first equivalent resistor at the last simulation moment is obtained;
obtaining the current value of the second controlled current source in the equivalent branch of the bridge arm inductor at the current simulation moment according to the resistance value of the second equivalent resistor, the current value flowing through the second equivalent resistor at the last simulation moment and the voltage values at two ends of the second equivalent resistor; wherein the calculation formula is
U L(t-Δt) For the voltage value, ih, across the second equivalent resistor at the last simulation moment L For the current value of the second controlled current source at the present simulation time, ib L(t-Δt) The value of the current flowing through the second equivalent resistor at the last simulation moment is obtained;
obtaining a current value of the third controlled current source in the module capacitor branch at the current simulation moment according to the resistance value of the third equivalent resistor, the current value flowing through the third equivalent resistor at the last simulation moment and the voltage values at the two ends of the third equivalent resistor; wherein the calculation formula is
U C(t-Δt) The voltage value of the two ends of the third equivalent resistor, ih, at the last simulation moment C Is that whenCurrent value of the third controlled current source at pre-simulation time, ib C(t-Δt) The value of the current flowing through the third equivalent resistor at the last simulation moment is obtained.
Preferably, the updating the voltage of each branch and the current of each branch according to the voltage-current relationship of each branch specifically includes:
obtaining the voltage of each branch and the bridge arm current at the current simulation moment according to the voltage-current relationship of the switch branch, the voltage-current relationship of the equivalent branch of the bridge arm inductance, the voltage-current relationship of the module capacitor branch and the voltage-current relationship existing in the bridge arm loop; wherein the voltage-current relationship of the switch branch comprises U S1 ＝R S1 (Ih S1 +i 1 ) The voltage-current relationship of the equivalent branch of the bridge arm inductor comprises U L ＝R L (Ih L + i), the voltage-current relationship of the module capacitor branch comprises U C ＝R C (I C +Ih C ) The voltage-current relation existing in the bridge arm loop comprises i = i 1 +i 2 And v a +U L +U 1 +U S1 ＝V p ，U S1 For the voltage value, i, across the first equivalent resistor at the current simulation moment 1 For the current flowing through the switching branch in which the first equivalent resistor is located, i 2 I is the current of the bridge arm at the current simulation moment, U L For the voltage value, U, across the second equivalent resistor at the present simulation moment C The voltage value I of the two ends of the third equivalent resistor at the current simulation moment C Is the capacitance current, v, of the module capacitance a Phase voltage of a phase of alternating current V p Positive electrode to ground voltage;
updating the current of each branch at the current simulation moment according to the voltage of each branch at the current simulation moment; wherein the current value of the first equivalent resistor flowing through the switch branch circuit is
Ib 1 For the current simulationThe current value flowing through the first equivalent resistor is marked, and the current value of the first equivalent resistor flowing through the equivalent branch of the bridge arm inductance is
Ib L The current value of the third equivalent resistor flowing through the module capacitor branch is equal to the current value of the current flowing through the second equivalent resistor at the current simulation moment
Ib C And the current value of the current flowing through the third equivalent resistor at the current simulation moment.
Preferably, the outputting three-phase current of the alternating current and the direct current specifically includes:
calculating three-phase current of the alternating current according to the bridge arm current of each bridge arm equivalent circuit;
according to the phase current of the three phases of the alternating current, calculating to obtain direct current positive pole current and direct current negative pole current;
and outputting three-phase current of alternating current, direct positive current and direct negative current.
Compared with the prior art, the real-time simulation method of the half-bridge type modular multilevel converter provided by the embodiment of the invention provides an equivalent circuit model which can be completely calculated by adopting an FPGA (field programmable gate array) and is used for MMC (modular multilevel converter) small-step real-time simulation, so that the decoupling of a power module and a bridge arm loop is realized, and the fault current error caused by a large-step decoupling mode and a small-step decoupling mode in simulation calculation is avoided.
Drawings
Fig. 1 is a schematic flowchart of a real-time simulation method for a half-bridge type modular multilevel converter according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a topology of a half-bridge type modular multilevel converter according to an embodiment of the present invention;
fig. 3 is a schematic diagram of an equivalent circuit model of a half-bridge type modular multilevel converter according to an embodiment of the present invention;
fig. 4 is a simplified flowchart of a real-time simulation method for a half-bridge type modular multilevel converter according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a schematic flow chart of a real-time simulation method of a half-bridge modular multilevel converter according to an embodiment of the present invention is shown, where the method includes steps S1 to S7:
s1, constructing an equivalent circuit model of a half-bridge type modular multilevel converter; the equivalent circuit model comprises six identical bridge arm equivalent circuits, each bridge arm equivalent circuit comprises two switch branches and a bridge arm inductance equivalent branch, each switch branch comprises a first equivalent resistor, a first controlled current source and a controlled voltage source, and each bridge arm inductance equivalent branch comprises a second equivalent resistor and a second controlled current source;
s2, initializing system parameters of the equivalent circuit model to start electromagnetic transient simulation calculation of the half-bridge type modular multilevel converter;
s3, updating the states of two power electronic switches of each power module in the half-bridge type modular multilevel converter and the input bridge arm current to obtain the port voltage and the capacitance current of each power module;
s4, obtaining the current of the switch branch, the current of the bridge arm inductance equivalent branch and the current of the module capacitor branch at the current simulation moment; the module capacitor branch is equivalent to a module capacitor in the power module and comprises a third equivalent resistor and a third controlled current source, and the third equivalent resistor and the third controlled current source are connected in parallel;
s5, updating the voltage of each branch and the current of each branch according to the voltage-current relationship of each branch; each branch comprises the switch branch, the bridge arm inductance equivalent branch and the module capacitor branch;
s6, obtaining bridge arm current of each bridge arm equivalent circuit;
s7, judging whether the current simulation duration reaches a preset threshold value, if so, outputting three-phase current and direct current of alternating current, and finishing simulation; and if not, increasing the current simulation duration by a preset simulation step length so as to continuously update the states of the two power electronic switches of each power module in the half-bridge type modular multilevel converter and the input bridge arm current.
It should be noted that, referring to fig. 2, a schematic diagram of a topology structure of a half-bridge type modular multilevel converter according to an embodiment of the present invention is shown. As shown in fig. 2, the Modular Multilevel Converter (MMC) is connected to the three-phase ac port and the dc positive and negative ports. Each MMC comprises six bridge arms, and each bridge arm comprises a bridge arm inductor and n half-bridge type power modules connected in series. Each half-bridge power module contains two power electronic switches and a module capacitor. Each power electronic switch is composed of an Insulated gate bipolar power tube (IGBT) and a diode connected in anti-parallel. The on/off of the two switches is controlled to control the input or the exit of the module capacitor, so that the bridge arm voltage and the bridge arm current are controlled, and alternating current-direct current power conversion is realized.
The existing MMC real-time simulation model is generally based on a large-step size simulation calculation mode, namely, an MMC model is divided into a bridge arm model and a sub-module model through decoupling, the simulation calculation of the bridge arm model is completed by adopting a large step size in a CPU, and the simulation calculation of the sub-module model is completed by adopting a small step size in an FPGA (field programmable gate array), but the large-step size decoupling mode easily causes large errors under some extreme working conditions, for example, when a bridge arm short circuit occurs, the short circuit current rise rate is large, and the asynchronous calculation mode of the bridge arm and the module large step size causes the module response to be delayed, and finally causes the large fault current error.
In order to solve the problems, the invention provides an MMC small-step real-time simulation model which can be completely calculated by adopting an FPGA. Referring to fig. 3, it is a schematic diagram of an equivalent circuit model of a half-bridge type modular multilevel converter provided in an embodiment of the present invention, where each bridge arm inductance is equivalent to an equivalent resistor and an accompanying historical current source, n series half-bridge type power modules are equivalent to two parallel switch branches, and each switch branch is composed of an equivalent voltage source, an equivalent resistor, and an accompanying historical current source. In the simulation calculation, because the relevant data of the module capacitor in the half-bridge type power module is needed, each module capacitor is also subjected to equivalent processing, which is equivalent to an equivalent resistor and an accompanying historical current source, and the circuit structure of a dashed box at the right side in fig. 3 is referred to. It should be noted that the equivalent circuit of the module capacitor is only needed in the calculation, and is not drawn in the equivalent circuit model of the MMC, and is already embodied in the equivalent voltage source of the switching branch.
The real-time simulation method of the half-bridge type modular multilevel converter provided by the embodiment of the invention comprises the following specific steps:
constructing an equivalent circuit model of the half-bridge type modular multilevel converter; the equivalent circuit model includes six identical bridge arm equivalent circuits, each bridge arm equivalent circuit includes two switch branches and a bridge arm inductance equivalent branch, each switch branch includes a first equivalent resistor, a first controlled current source and a controlled voltage source, and the bridge arm inductance equivalent branch includes a second equivalent resistor and a second controlled current source, which can be seen in detail in the circuit structure on the left side of fig. 3.
And initializing system parameters of the equivalent circuit model to start electromagnetic transient simulation calculation of the half-bridge type modular multilevel converter. The system parameters of the equivalent circuit model are initialized in order to enable the equivalent circuit model and the MMC to have the same external characteristics, and meanwhile, the simulation time length and the simulation step length are set.
And updating the states of two power electronic switches of each power module in the half-bridge modular multilevel converter and the input bridge arm current to obtain the port voltage and the capacitance current of each power module. Because the states of the two power electronic switches and the bridge arm current of each power module of the MMC directly affect the voltage and the current of each branch in the equivalent circuit model, the original characteristic data of the MMC needs to be used as the original data of the simulation calculation.
Obtaining the current of a switch branch circuit, the current of a bridge arm inductance equivalent branch circuit and the current of a module capacitor branch circuit at the current simulation moment; the module capacitor branch is equivalent to a module capacitor in the power module and comprises a third equivalent resistor and a third controlled current source, and the third equivalent resistor and the third controlled current source are connected in parallel;
updating the voltage of each branch and the current of each branch at the next simulation moment according to the voltage-current relationship of each branch; each branch comprises a switch branch, a bridge arm inductance equivalent branch and a module capacitor branch.
According to the voltage of each branch and the current of each branch, the bridge arm current of each bridge arm equivalent circuit can be calculated, and therefore the bridge arm current of each bridge arm equivalent circuit can be obtained.
Judging whether the current simulation duration reaches a preset threshold value, if so, outputting three-phase current and direct current of alternating current, and finishing simulation; if not, increasing the current simulation duration by a preset simulation step length to continuously update the states of the two power electronic switches of each power module in the half-bridge type modular multilevel converter and the input bridge arm current, namely, returning to the step S3.
In order to more intuitively understand the simulation steps of the present invention, the embodiment of the present invention further provides a simplified schematic flow chart of a real-time simulation method of a half-bridge type modular multilevel converter, and refer to fig. 4 specifically.
The embodiment of the invention provides a real-time simulation method of a half-bridge type modular multilevel converter, which provides an equivalent circuit model of MMC small-step real-time simulation capable of completely adopting FPGA calculation so as to decouple a power module and a bridge arm loop and avoid fault current errors caused by a large-step decoupling mode in simulation calculation.
As an improvement of the above scheme, the two switch branches of the bridge arm equivalent circuit are connected in parallel, one end of each switch branch is connected with one end of the bridge arm inductance equivalent branch, the other end of each switch branch is connected with a dc positive port or a dc negative port, and the other end of the bridge arm inductance equivalent branch is connected with one port of three-phase alternating current.
Specifically, referring to fig. 3, two switch branches of the bridge arm equivalent circuit are connected in parallel, one end of each switch branch is connected to one end of the bridge arm inductance equivalent branch, the other end of each switch branch is connected to a dc positive terminal or a dc negative terminal, and the other end of the bridge arm inductance equivalent branch is connected to one port of three-phase ac power. The other end of the switch branch equivalent to the bridge arm equivalent circuit of the upper bridge arm is connected with a direct current positive electrode port, and the other end of the switch branch equivalent to the bridge arm equivalent circuit of the lower bridge arm is connected with a direct current negative electrode port.
As an improvement of the foregoing scheme, one end of the first equivalent resistor is connected to the dc positive port and one end of the first controlled current source, the other end of the first equivalent resistor is connected to the other end of the first controlled current source and one end of the controlled voltage source, the other end of the controlled voltage source is connected to one end of the second equivalent resistor and one end of the second controlled current source, the other end of the second equivalent resistor is connected to one port of the three-phase alternating current, and the other end of the second controlled current source is connected to one port of the three-phase alternating current.
Specifically, referring to fig. 3, each switching branch includes a first equivalent resistor, a first controlled current source, and a controlled voltage source, and the bridge arm inductance equivalent branch includes a second equivalent resistor and a second controlled current source. The specific connection relationship between the switch branch and the bridge arm inductance equivalent branch is described by taking a bridge arm equivalent circuit equivalent to an upper bridge arm as an example, wherein one end of a first equivalent resistor is connected with a direct current positive electrode port and one end of a first controlled current source respectively, the other end of the first equivalent resistor is connected with the other end of the first controlled current source and one end of a controlled voltage source respectively, the other end of the controlled voltage source is connected with one end of a second equivalent resistor and one end of a second controlled current source respectively, the other end of the second equivalent resistor is connected with one port of three-phase alternating current, and the other end of the second controlled current source is connected with one port of three-phase alternating current. That is to say, after the first equivalent resistor and the first controlled current source are connected in parallel to form a whole, one end of the whole is connected with the positive direct current port, the other end of the whole is connected with one end of the controlled voltage source, and the other end of the controlled voltage source is connected with the equivalent branch of the bridge arm inductor.
As an improvement of the above scheme, initializing system parameters of the equivalent circuit model specifically includes:
determining a simulation step length according to a preset on-state inductance of the switch branch and a preset off-state capacitance of the switch branch; wherein the simulation step length is
Δ t is the simulation step length, L eq For a predetermined conduction inductance of the switching branch, C eq The switching-off capacitance is a preset switching-off capacitance of the switching branch circuit;
determining the resistance value of the first equivalent resistor according to the simulation step length; wherein the first equivalent resistor has a resistance value of
Or
R S1 Is the resistance value of the first equivalent resistor;
determining the resistance value of the second equivalent resistor and the resistance value of the third equivalent resistor according to the bridge arm inductance value of the half-bridge type modular multilevel converter, the capacitance value of the module capacitor and the simulation step length; wherein, the second, etcThe resistance value of the effective resistor is
The resistance value of the third equivalent resistor is
R L Is the resistance value, R, of the second equivalent resistance C And L is the resistance value of the third equivalent resistor, L is the inductance value of the bridge arm, and C is the capacitance value of the module capacitor.
Specifically, a simulation step length is determined according to a preset on-state inductance of a switch branch and a preset off-state capacitance of the switch branch; wherein the simulation step length is
Δ t is the simulation step length, L eq The conduction inductance of a predetermined switching branch, C eq Is the turn-off capacitance of the preset switch branch. The half-bridge power module of MMC comprises two power electronic switches, and the conducted switches are equivalent to a conduction inductor L of a switch branch eq In general, L eq The smaller the better, the switched-off switch is equivalent to the switched-off capacitor C of the switch branch eq In general C eq The larger the better. But both of them are satisfied
Determining the resistance value of the first equivalent resistor according to the simulation step length; wherein the first equivalent resistor has a resistance value of
Or
R S1 Is the resistance value of the first equivalent resistor. Similarly, the other first equivalent resistor of the bridge arm equivalent circuit has a resistance value of
Or
Determining the resistance value of the second equivalent resistor and the resistance value of the third equivalent resistor according to the bridge arm inductance value of the half-bridge type modular multilevel converter, the capacitance value of the module capacitor and the simulation step length; wherein the resistance value of the second equivalent resistor is
The third equivalent resistor has a resistance value of
R L Is the resistance value of the second equivalent resistor, R C L is the bridge arm inductance, i.e., the inductance of the bridge arm inductor in fig. 2, and C is the capacitance of the module capacitor, i.e., the capacitance of the module capacitor in the dashed frame in fig. 2.
As an improvement of the above scheme, the updating states and input bridge arm currents of two power electronic switches of each power module in the half-bridge type modular multilevel converter to obtain a port voltage and a capacitance current of each power module specifically includes:
inputting a switch control signal according to simulation requirements, and updating the states of two power electronic switches of each power module in the half-bridge type modular multilevel converter;
determining the port voltage of each power module as the voltage of the module capacitor or 0 according to the states of two power electronic switches in each power module;
and obtaining the capacitance current of the module capacitor according to the input bridge arm current and the states of the two power electronic switches in each power module.
Specifically, switch control signals are input according to simulation requirements, and the states of two power electronic switches of each power module in the half-bridge type modular multilevel converter are updated. The switch control signal is inputted through an external controller. Generally, the switch control signal is 1, indicating that the power electronic switch is in an on state; the switch control signal is 0, indicating that the power electronic switch is off.
And determining the port voltage of each power module as the voltage of the module capacitor or 0 according to the states of the two power electronic switches in each power module.
And obtaining the capacitance current of the module capacitor according to the input bridge arm current and the states of the two power electronic switches in each power module.
In order to obtain the port voltage of each power module and the capacitance current of the module capacitor more intuitively according to the state of each power electronic switch, the invention provides an attached table as shown in table 1, wherein the attached table lists the corresponding relation between various switch states and the port voltage of the power module and the capacitance current of the module capacitor. Generally, the data of the first 5 columns are input, and then the data of the last three columns can be output, that is, the capacitance current of the module capacitor and the port voltage of the power module can be obtained by looking up table 1, where U is 1 K and U 2 And (k) is the port voltage of the kth power module corresponding to the two switch branches of the bridge arm equivalent circuit respectively.
TABLE 1 correspondence between various switch states and port voltage of power module and capacitance current of module capacitor
In table 1, S1 and S2 are two power electronic switches shown in fig. 2, where "1" in the S1-S2 columns represents an on signal, "0" represents an off signal, "plus" in the i column represents a positive arm current, and "-" represents a negative arm current, and the positive direction of the current is based on the direction of the arrow in fig. 3.
As an improvement of the above scheme, the voltage of the controlled voltage source is
Wherein, U 1 Is the voltage of the controlled voltage source, U 1_k For the kth power in the half-bridge type modular multilevel converterAnd the port voltage of the module, n is the number of the modules of the power module in the half-bridge modular multilevel converter, and k is more than or equal to 1 and less than or equal to n.
In particular, the voltage of the controlled voltage source is
Wherein, U 1 For the voltage of a controlled voltage source, U 1_k The voltage of a port of a kth power module in the half-bridge type modular multilevel converter is defined, n is the number of modules of the power module in the half-bridge type modular multilevel converter, namely n is the number of modules of an MMC bridge arm connected in series, and is generally 100-500, wherein k is more than or equal to 1 and less than or equal to n.
As an improvement of the above scheme, the obtaining of the current of the switch branch, the current of the equivalent branch of the bridge arm inductance, and the current of the module capacitor branch at the current simulation time specifically includes:
obtaining a current value of the first controlled current source in the switch branch circuit at the current simulation moment according to the resistance value of the first equivalent resistor, the current value flowing through the first equivalent resistor at the previous simulation moment and the voltage values at two ends of the first equivalent resistor; wherein, when U S1(t-Δt) >At the time of 0, the number of the first,
when U is formed S1(t-Δt) When the content is less than or equal to 0,
U S1(t-Δt) the voltage value of the two ends of the first equivalent resistor, ih, at the last simulation moment S1 For the current value of the first controlled current source at the present simulation time, ib 1(t-Δt) The value of the current flowing through the first equivalent resistor at the last simulation moment is obtained;
obtaining the current value of the second controlled current source in the bridge arm inductance equivalent branch at the current simulation moment according to the resistance value of the second equivalent resistor, the current value flowing through the second equivalent resistor at the previous simulation moment and the voltage values at two ends of the second equivalent resistor; wherein the calculation formula is
U L(t-Δt) For the voltage value, ih, across the second equivalent resistor at the last simulation moment L For the current value of the second controlled current source at the present simulation time, ib L(t-Δt) The current value flowing through the second equivalent resistor at the last simulation moment is obtained;
obtaining a current value of the third controlled current source in the module capacitor branch at the current simulation time according to the resistance value of the third equivalent resistor, the current value flowing through the third equivalent resistor at the previous simulation time and the voltage values at two ends of the third equivalent resistor; wherein the calculation formula is
U C(t-Δt) The voltage value of the two ends of the third equivalent resistor, ih, at the last simulation moment C For the current value of the third controlled current source at the present simulation time, ib C(t-Δt) The value of the current flowing through the third equivalent resistor at the last simulation moment is obtained.
Specifically, the current value of the first controlled current source in the switch branch at the current simulation moment is obtained according to the resistance value of the first equivalent resistor, the current value flowing through the first equivalent resistor at the previous simulation moment and the voltage values at the two ends of the first equivalent resistor; wherein when U is S1(t-Δt) >At the time of 0, the number of the first,
when U is turned S1(t-Δt) When the content is less than or equal to 0,
U S1(t-Δt) is the voltage value, ih, across the first equivalent resistor at the last simulation moment S1 For the current value of the first controlled current source at the present simulation time, ib 1(t-Δt) The value of the current flowing through the first equivalent resistor at the last simulation moment. That is to say, in the simulation calculation, the electricity of the switch branch at the current simulation time is calculated and obtained through the voltage value and the current value of the switch branch at the previous simulation timeThe current value, i.e. the updated historical current.
Obtaining the current value of a second controlled current source in the lower bridge arm inductance equivalent branch at the current simulation moment according to the resistance value of the second equivalent resistor, the current value flowing through the second equivalent resistor at the previous simulation moment and the voltage values at the two ends of the second equivalent resistor; wherein the calculation formula is
U L(t-Δt) The voltage value of the two ends of the second equivalent resistor, ih, at the previous simulation moment L For the current value of the second controlled current source at the present simulation time, ib L(t-Δt) The value of the current flowing through the second equivalent resistor at the last simulation moment. In other words, in the simulation calculation, the current value of the bridge arm inductance equivalent branch at the current simulation time, that is, the updated historical current, is calculated according to the voltage value and the current value of the bridge arm inductance equivalent branch at the previous simulation time.
Obtaining the current value of a third controlled current source in the module capacitor branch at the current simulation moment according to the resistance value of the third equivalent resistor, the current value flowing through the third equivalent resistor at the previous simulation moment and the voltage values at two ends of the third equivalent resistor; wherein the calculation formula is
U C(t-Δt) The voltage value, ih, across the third equivalent resistor at the previous simulation time C For the current value of the third controlled current source at the present simulation time, ib C(t-Δt) The value of the current flowing through the third equivalent resistor at the last simulation moment. In other words, in the simulation calculation, the current value of the module capacitor branch at the current simulation time, that is, the updated historical current, is calculated according to the voltage value and the current value of the module capacitor branch at the previous simulation time.
As an improvement of the above scheme, the updating the voltage of each branch and the current of each branch according to the voltage-current relationship of each branch specifically includes:
according to the voltage-current relationship of the switch branch circuit, the voltage-current relationship of the equivalent branch circuit of the bridge arm inductance and the modeObtaining the voltage and the bridge arm current of each branch at the current simulation moment according to the voltage-current relationship of the block capacitor branches and the voltage-current relationship existing in the bridge arm loop; wherein the voltage-current relationship of the switch branch comprises U S1 ＝R S1 (Ih S1 +i 1 ) The voltage-current relationship of the bridge arm inductance equivalent branch comprises U L ＝R L (Ih L + i), the voltage-current relationship of the module capacitor branch comprises U C ＝R C (I C +Ih C ) The voltage-current relation existing in the bridge arm loop comprises i = i 1 +i 2 And v a +U L +U 1 +U S1 ＝V p ，U S1 For the voltage value, i, across the first equivalent resistor at the current simulation moment 1 For the current flowing through the switching branch in which the first equivalent resistor is located, i 2 I is the current of the bridge arm at the current simulation moment, U L For the voltage value, U, across the second equivalent resistor at the present simulation moment C The voltage value I of the two ends of the third equivalent resistor at the current simulation moment C Is the capacitance current, v, of the module capacitance a Phase voltage of a phase of alternating current V p Is the positive electrode to ground voltage;
updating the current of each branch at the current simulation moment according to the voltage of each branch at the current simulation moment; wherein the current value of the first equivalent resistor flowing through the switch branch circuit is
Ib 1 The current value of the first equivalent resistance flowing through the bridge arm inductance equivalent branch is the current value of the first equivalent resistance flowing through the bridge arm inductance equivalent branch at the current simulation moment
Ib L The current value of the third equivalent resistor flowing through the module capacitor branch is equal to the current value of the current flowing through the second equivalent resistor at the current simulation moment
Ib C And the current value of the current flowing through the third equivalent resistor at the current simulation moment.
Specifically, the voltage and the bridge arm current of each branch at the current simulation moment are obtained according to the voltage-current relationship of a switch branch, the voltage-current relationship of a bridge arm inductance equivalent branch, the voltage-current relationship of a module capacitor branch and the voltage-current relationship existing in a bridge arm loop; wherein, the voltage-current relationship of the switch branch circuit comprises U S1 ＝R S1 (Ih S1 +i 1 ) The voltage-current relationship of the equivalent branch of the bridge arm inductance comprises U L ＝R L (Ih L + i), the voltage-current relationship of the module capacitor branch includes U C ＝R C (I C +Ih C ) The voltage-current relation existing in the bridge arm loop comprises i = i 1 +i 2 And v a +U L +U 1 +U S1 ＝V p ，U S1 Is the voltage value i at the two ends of the first equivalent resistor at the current simulation moment 1 Is the current flowing through the switch branch in which the first equivalent resistor is located, i 2 I is the current of the other switch branch of the equivalent circuit of the bridge arm, U is the current of the bridge arm at the current simulation moment L For the voltage value, U, across the second equivalent resistor at the present simulation moment C Is the voltage value, I, across the third equivalent resistor at the current simulation moment C Is the capacitance current of the module capacitor, v a Here, the phase voltage of the ac a-phase is calculated only by way of example, and is not to be construed as a limitation to the phase voltage of the ac a-phase, and similarly, the phase voltages of the ac b-phase and the c-phase are calculated similarly. V p For positive to ground, and likewise, when the switching branch is connected to a DC negative, that V p Should be negative to ground, and should not be considered as limiting positive to ground. The step is to update the branch voltage of each branch at the current simulation moment.
Updating the current of each branch at the current simulation moment according to the voltage of each branch at the current simulation moment; wherein, the openingThe current value of the first equivalent resistor flowing in the off branch circuit is
Ib 1 The current value of the first equivalent resistor flowing through the bridge arm inductance equivalent branch is the current value of the first equivalent resistor flowing through the bridge arm inductance equivalent branch at the current simulation moment
Ib L The current value of the third equivalent resistor flowing through the module capacitor branch is equal to the current value of the current flowing through the second equivalent resistor at the current simulation moment
Ib C The current value flowing through the third equivalent resistor at the current simulation moment is shown. The step is to update the branch current of each branch at the current simulation moment.
As an improvement of the above scheme, the outputting three-phase current of alternating current and direct current specifically includes:
calculating three-phase current of alternating current according to the bridge arm current of each bridge arm equivalent circuit;
calculating to obtain direct current positive current and direct current negative current according to the three-phase current of the alternating current;
and outputting three-phase current of the alternating current, direct positive current and direct negative current.
Specifically, the phase current of three phases of the alternating current is calculated according to the bridge arm current of each bridge arm equivalent circuit, and the calculation formula is as follows:
in the formula i a 、i b 、i c Three-phase currents i corresponding to the alternating current a phase, b phase and c phase respectively ap 、i an The bridge arm current of an upper bridge arm and the bridge arm current of a lower bridge arm which are connected with an alternating current a phase are respectively bp 、i bn Bridge arm current of an upper bridge arm and bridge arm current of a lower bridge arm which are connected with an alternating current b phase are respectively cp 、i cn The bridge arm current of the upper bridge arm and the bridge arm current of the lower bridge arm are respectively connected with the alternating current c phase.
According to the phase current of three phases of alternating current, direct current positive current and direct current negative current are obtained through calculation, and the calculation formula is as follows:
in the formula i p 、i n Is direct positive and negative current.
Phase current i of three phases of alternating current a 、i b 、i c d.C. positive electrode current i p And a direct negative electrode current i n And outputting the data.
To sum up, the real-time simulation method for the half-bridge modular multilevel converter provided by the embodiment of the invention provides a complete calculation equivalent circuit suitable for half-bridge MMC small-step modeling, realizes decoupling of a full-bridge power module and a bridge arm loop based on an ideal transformer method, and fully utilizes the parallel calculation advantages of an FPGA (field programmable gate array) in the power module part; solving the power module switch state based on a table look-up method, avoiding iterative computation, thereby not needing a CPU, but directly adopting an FPGA (field programmable gate array) and realizing the calculation by small step programming, and avoiding precision loss caused by switching of large step and small step; based on the anti-parallel switch branch, the natural phase change of the bridge arm current at the zero crossing point is realized, and the zero crossing point error is avoided. The method is based on the trapezoidal integration method, gives complete electromagnetic transient simulation calculation steps of the MMC small-step model, and has the advantages of high calculation precision and high speed. The method based on the invention can more accurately simulate the dynamic characteristics of the MMC under various working conditions, thereby improving the research and development and test effects of the control protection system.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (9)
1. A real-time simulation method of a half-bridge type modular multilevel converter is characterized by comprising the following steps:
constructing an equivalent circuit model of the half-bridge type modular multilevel converter; the equivalent circuit model comprises six identical bridge arm equivalent circuits, each bridge arm equivalent circuit comprises two switch branches and a bridge arm inductance equivalent branch, each switch branch comprises a first equivalent resistor, a first controlled current source and a controlled voltage source, and each bridge arm inductance equivalent branch comprises a second equivalent resistor and a second controlled current source;
initializing system parameters of the equivalent circuit model to start electromagnetic transient simulation calculation of the half-bridge type modular multilevel converter;
updating the states of two power electronic switches and input bridge arm current of each power module in the half-bridge type modular multilevel converter to obtain port voltage and capacitance current of each power module;
obtaining the current of the switch branch, the current of the bridge arm inductance equivalent branch and the current of the module capacitor branch at the current simulation moment; the module capacitor branch is equivalent to a module capacitor in the power module and comprises a third equivalent resistor and a third controlled current source, and the third equivalent resistor and the third controlled current source are connected in parallel;
updating the voltage of each branch and the current of each branch according to the voltage-current relationship of each branch; each branch comprises the switch branch, the bridge arm inductance equivalent branch and the module capacitor branch;
obtaining bridge arm current of each bridge arm equivalent circuit;
judging whether the current simulation duration reaches a preset threshold value, if so, outputting three-phase current and direct current of alternating current, and finishing simulation; and if not, increasing the current simulation duration by a preset simulation step length so as to continuously update the states of the two power electronic switches of each power module in the half-bridge type modular multilevel converter and the input bridge arm current.
2. The real-time simulation method of the half-bridge type modular multilevel converter according to claim 1, wherein two switch branches of the bridge arm equivalent circuit are connected in parallel, one end of each switch branch is connected with one end of the bridge arm inductance equivalent branch, the other end of each switch branch is connected with a direct current positive port or a direct current negative port, and the other end of the bridge arm inductance equivalent branch is connected with one port of three-phase alternating current.
3. The method for real-time simulation of a half-bridge type modular multilevel converter according to claim 2, wherein one end of the first equivalent resistor is connected to the dc positive terminal and one end of the first controlled current source, the other end of the first equivalent resistor is connected to the other end of the first controlled current source and one end of the controlled voltage source, the other end of the controlled voltage source is connected to one end of the second equivalent resistor and one end of the second controlled current source, the other end of the second equivalent resistor is connected to one port of the three-phase alternating current, and the other end of the second controlled current source is connected to one port of the three-phase alternating current.
4. The real-time simulation method of the half-bridge modular multilevel converter according to claim 1, wherein initializing system parameters of the equivalent circuit model specifically comprises:
determining a simulation step length according to a preset on-state inductance of the switch branch circuit and a preset off-state capacitance of the switch branch circuit; wherein the simulation step length is
Δ t is the simulation step length, L eq For a predetermined conduction inductance of the switching branch, C eq The switching-off capacitance is a preset switching-off capacitance of the switching branch circuit;
determining the resistance value of the first equivalent resistor according to the simulation step length; wherein the first equivalent resistor has a resistance value of
Or
R S1 Is the resistance value of the first equivalent resistor;
determining the resistance value of the second equivalent resistor and the resistance value of the third equivalent resistor according to the bridge arm inductance value of the half-bridge type modular multilevel converter, the capacitance value of the module capacitor and the simulation step length; wherein the resistance value of the second equivalent resistor is
The resistance value of the third equivalent resistor is
R L Is the resistance value, R, of the second equivalent resistor C And L is the resistance value of the third equivalent resistor, L is the inductance value of the bridge arm, and C is the capacitance value of the module capacitor.
5. The method for real-time simulation of a half-bridge modular multilevel converter according to claim 4, wherein the updating the states and input leg currents of the two power electronic switches of each power module in the half-bridge modular multilevel converter to obtain the port voltage and the capacitor current of each power module comprises:
inputting a switch control signal according to simulation requirements, and updating the states of two power electronic switches of each power module in the half-bridge type modular multilevel converter;
determining the port voltage of each power module as the voltage of the module capacitor or 0 according to the states of two power electronic switches in each power module;
and obtaining the capacitance current of the module capacitor according to the input bridge arm current and the states of the two power electronic switches in each power module.
6. The method for real-time simulation of a half-bridge modular multilevel converter according to claim 5, wherein the voltage of the controlled voltage source is
Wherein, U 1 Is the voltage of the controlled voltage source, U 1_k The terminal voltage of the kth power module in the half-bridge type modular multilevel converter is represented, n is the module number of the power module in the half-bridge type modular multilevel converter, and k is larger than or equal to 1 and smaller than or equal to n.
7. The real-time simulation method of the half-bridge type modular multilevel converter according to claim 6, wherein the obtaining of the current of the switching branch, the current of the bridge arm inductance equivalent branch, and the current of the module capacitance branch at the current simulation time specifically includes:
obtaining a current value of the first controlled current source in the switch branch circuit at the current simulation moment according to the resistance value of the first equivalent resistor, the current value flowing through the first equivalent resistor at the last simulation moment and the voltage values at the two ends of the first equivalent resistor; wherein when U is S1(t-Δt) >At the time of 0, the number of the first electrode,
when U is formed S1(t-Δt) When the content is less than or equal to 0,
U S1(t-Δt) the voltage value of the two ends of the first equivalent resistor, ih, at the last simulation moment S1 For the current value of the first controlled current source at the present simulation time, ib 1(t-Δt) The value of the current flowing through the first equivalent resistor at the last simulation moment is obtained;
obtaining the current value of the second controlled current source in the bridge arm inductance equivalent branch at the current simulation moment according to the resistance value of the second equivalent resistor, the current value flowing through the second equivalent resistor at the previous simulation moment and the voltage values at two ends of the second equivalent resistor; wherein the calculation formula is
U L(t-Δt) For the voltage value, ih, across the second equivalent resistor at the last simulation moment L For the current value of the second controlled current source at the present simulation moment, ib L(t-Δt) The current value flowing through the second equivalent resistor at the last simulation moment is obtained;
obtaining a current value of the third controlled current source in the module capacitor branch at the current simulation time according to the resistance value of the third equivalent resistor, the current value flowing through the third equivalent resistor at the previous simulation time and the voltage values at two ends of the third equivalent resistor; wherein the calculation formula is
U C(t-Δt) The voltage value of the two ends of the third equivalent resistor, ih, at the last simulation moment C For the current value of the third controlled current source at the present simulation time, ib C(t-Δt) The value of the current flowing through the third equivalent resistor at the last simulation moment is obtained.
8. The method for real-time simulation of a half-bridge modular multilevel converter according to claim 7, wherein the updating of the voltage of each branch and the current of each branch according to the voltage-current relationship of each branch specifically comprises:
obtaining the current simulation moment according to the voltage-current relationship of the switch branch, the voltage-current relationship of the equivalent branch of the bridge arm inductance, the voltage-current relationship of the module capacitance branch and the voltage-current relationship existing in the bridge arm loopThe voltage of each branch and the bridge arm current; wherein the voltage-current relationship of the switch branch comprises U S1 ＝R S1 (Ih S1 +i 1 ) The voltage-current relationship of the equivalent branch of the bridge arm inductor comprises U L ＝R L (Ih L + i), the voltage-current relationship of the module capacitor branch comprises U C ＝R C (I C +Ih C ) The voltage-current relation existing in the bridge arm loop comprises i = i 1 +i 2 And v a +U L +U 1 +U S1 ＝V p ，U S1 For the voltage value, i, across the first equivalent resistor at the current simulation moment 1 Is the current flowing through the switch branch in which the first equivalent resistor is located, i 2 I is the current of the other switch branch of the bridge arm equivalent circuit at the current simulation moment, U L For the voltage value, U, across the second equivalent resistor at the present simulation moment C Is the voltage value, I, across the third equivalent resistor at the current simulation time C Is the capacitance current, v, of the module capacitance a Phase voltage of a phase of alternating current V p Is the positive electrode to ground voltage;
updating the current of each branch at the current simulation moment according to the voltage of each branch at the current simulation moment; wherein the current value of the first equivalent resistor flowing through the switch branch circuit is
Ib 1 The current value of the first equivalent resistance flowing through the bridge arm inductance equivalent branch is the current value of the first equivalent resistance flowing through the bridge arm inductance equivalent branch at the current simulation moment
Ib L The current value of the third equivalent resistor flowing through the module capacitor branch is equal to the current value of the current flowing through the second equivalent resistor at the current simulation moment
Ib C And the current value of the current flowing through the third equivalent resistor at the current simulation moment.
9. The real-time simulation method of the half-bridge type modular multilevel converter according to claim 1, wherein the outputting three-phase current and direct current of alternating current specifically comprises:
calculating three-phase current of the alternating current according to the bridge arm current of each bridge arm equivalent circuit;
calculating to obtain direct current positive current and direct current negative current according to the three-phase current of the alternating current;
and outputting three-phase current of alternating current, direct positive current and direct negative current.
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