CN115276434B - Electric energy router with full-bridge submodule and control method thereof - Google Patents

Electric energy router with full-bridge submodule and control method thereof Download PDF

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Publication number
CN115276434B
CN115276434B CN202210082750.2A CN202210082750A CN115276434B CN 115276434 B CN115276434 B CN 115276434B CN 202210082750 A CN202210082750 A CN 202210082750A CN 115276434 B CN115276434 B CN 115276434B
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voltage
phase
bridge
current
arm
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CN115276434A (en
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鲁思兆
刘娅奇
李思奇
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Kunming University of Science and Technology
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Kunming University of Science and Technology
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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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/26—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents
    • H02H3/28—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to difference between voltages or between currents; responsive to phase angle between voltages or between currents involving comparison of the voltage or current values at two spaced portions of a single system, e.g. at opposite ends of one line, at input and output of apparatus
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac 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

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention relates to an electric energy router with a full-bridge submodule, which comprises a high-voltage stage, an isolation stage and a low-voltage stage, wherein the high-voltage stage comprises a three-phase four-bridge arm MMC, a three-phase six-bridge arm MMC and a half-bridge unit, the isolation stage is formed by a plurality of series resonance DC/DC converters, the low-voltage stage adopts a three-phase full-bridge inverter structure, the high-voltage stage, the isolation stage and the low-voltage stage are connected in parallel, P+ and N-are the positive and negative poles of a high-voltage direct current port, two public high-voltage direct current buses are led out from P+ and N-points, and the two public high-voltage direct current buses are respectively connected with the two ends of the high-voltage direct current port. Aiming at the problem that when the third phase of the traditional three-phase four-bridge arm MMC consists of a capacitor phase, the capacitor phase is uncontrollable, and when a short circuit fault of the high-voltage direct-current side occurs, the capacitor of the C phase can discharge to damage the converter, and the C phase consists of a half-bridge unit. A carrier phase shift modulation strategy is provided for the C-phase half-bridge unit, under the provided modulation strategy, the port voltage of the C-phase half-bridge unit is constantly equal to the voltage of the high-voltage direct-current side, and the higher harmonic wave of the high-voltage direct-current side is reduced.

Description

Electric energy router with full-bridge submodule and control method thereof
Technical Field
The invention relates to the technical field of power electronic converters, in particular to an electric energy router with a full-bridge submodule and a control method thereof.
Background
The energy internet is an energy system which deeply fuses a new energy technology and an information technology, aims to solve the environmental problems caused by shortage of energy and fossil fuel, continuously increases the proportion of distributed new energy in energy consumption, requires more AC/DC conversion links when a large amount of distributed new energy is added into a power grid, and becomes more flexible, complex and intelligent in operation of the power distribution network. Compared with the traditional power frequency transformer, the electric energy router can be conveniently connected into new energy grid-connected equipment, so that the plug and play of the new energy grid-connected equipment is realized, the capacity of the power distribution network for receiving distributed new energy is improved, and the controllable distribution of electric energy can be performed by utilizing the multiport characteristic of the electric energy router. Compared with the fault on the alternating current side, the fault of the direct current system is faster to propagate, and the relay protection requirement is higher, so that the fault on the direct current side is a key problem to be faced by the fault protection of the power distribution network. Three main methods for clearing short-circuit faults on the direct current side: the first method for disconnecting the alternating current system through the alternating current circuit breaker is long in action time, and cannot realize rapid protection of direct current side faults; the second method for cutting off the fault point through the direct current breaker has the advantages of low on-state loss and the like, but requires additional equipment cost; and thirdly, the direct current side fault self-clearing method is controlled by the converter, and the direct current side fault self-clearing is realized by utilizing the rapid switching characteristic of the power electronic device. The high-voltage stage of the existing power electronic converter adopts an MMC based on a half-bridge sub-module, the structure does not have the capacity of clearing short-circuit faults on the high-voltage direct-current side, a breaker can only be used for clearing fault currents, the cost is high, and the other disadvantage is that the utilization rate of direct-current voltage of the half-bridge MMC is low, and larger voltage fluctuation on the high-voltage direct-current side cannot be processed.
Disclosure of Invention
The invention aims to solve the technical problem of higher cost caused by the fact that a breaker is additionally arranged in a power electronic converter in the prior art to remove fault current.
In order to solve the technical problems, the technical scheme of the invention is as follows: the utility model provides a contain electric energy router of full bridge submodule piece which innovation point lies in: the high-voltage power supply comprises a high-voltage stage, an isolation stage and a low-voltage stage, wherein the high-voltage stage comprises a three-phase four-bridge arm MMC, a three-phase six-bridge arm MMC and a half-bridge unit, the isolation stage is formed by a plurality of series resonance DC/DC converters, the low-voltage stage adopts a three-phase full-bridge inverter structure, the high-voltage stage, the isolation stage and the low-voltage stage are connected in parallel, P+ and N-are the positive and negative poles of a high-voltage direct current port, and two public high-voltage direct current buses are led out from P+ and N-points and are respectively connected with two ends of the high-voltage direct current port.
Further, the direct current ports of the three-phase four-bridge arm MMC and the three-phase six-bridge arm MMC of the high-voltage stage are connected in parallel, and the high-voltage stage comprises two alternating current ports of 10kV and 20 kV;
The 20kV high-voltage alternating-current port is connected with a three-phase six-bridge-arm MMC topological structure based on a full-bridge sub-module, each phase of the three-phase six-bridge-arm MMC is U, V, W phases, each three phase is formed by sequentially connecting an upper bridge arm, two bridge arm inductors L arm and a lower bridge arm in series, each upper bridge arm and each lower bridge arm are obtained by connecting N full-bridge sub-modules in series, the 20kV high-voltage alternating-current port is provided with a three-phase voltage source and three inductors L 0, the cathodes of the three-phase voltage sources are connected with each other, the anodes of the three-phase voltage sources are respectively connected with one ends of three inductors L 0, and the other ends of the three inductors L 0 are respectively connected between two bridge arm inductors L arm of the three phases;
The 10kV high-voltage alternating-current port is connected with a three-phase four-bridge arm MMC topological structure and a half-bridge unit structure, phases of the three-phase four-bridge arm MMC topological structure and the half-bridge unit structure are A, B, C phases respectively, a A, B phase is formed by a three-phase four-bridge arm MMC based on a Quan Qiaozi module, a C phase is formed by a half-bridge unit, A, B phases are formed by sequentially connecting an upper bridge arm, two bridge arm inductors L arm and a lower bridge arm in series, the upper bridge arm and the lower bridge arm are formed by connecting N full-bridge submodules in series, the 10kV high-voltage alternating-current port is provided with a three-phase voltage source and three inductors L 0, the cathodes of the three-phase voltage source are connected with each other, the anodes of the three-phase voltage source are respectively connected with one ends of three inductors L 0, and the other ends of two inductors L 0 corresponding to A, B are respectively connected between two bridge arm inductors L arm of the A, B phases;
The half-bridge unit comprises an upper half-bridge arm, two arm inductors L arm and a lower half-bridge arm, wherein the upper half-bridge arm, the two arm inductors L arm and the lower half-bridge arm are sequentially connected in series, the other end of the inductor L 0 corresponding to C is connected between the two arm inductors L arm, and the upper half-bridge arm and the lower half-bridge arm are respectively formed by connecting M+1 half-bridge modules in series.
Further, when the alternating current side is in a voltage level of 10kV, the voltage level of the direct current side is +/-10 kV, and on the premise that the modulation ratio is 1.414 when the alternating current side of the three-phase four-bridge arm MMC of the full-bridge submodule is connected with a 10kV alternating current power grid.
Furthermore, the number N of the full-bridge submodules is determined by the voltage class of the high-voltage direct-current side and the withstand voltage class of the adopted device, and the voltage of the high-voltage direct-current side can be born when the normal operation is required to be ensured.
Further, the isolation level is divided into an isolation upper bridge arm and an isolation lower bridge arm, the isolation upper bridge arm and the isolation lower bridge arm are respectively formed by connecting M+1 isolation level submodules in series, the isolation level submodules are serial resonance DC/DC converters, a plurality of serial resonance DC/DC converters are connected in a serial-in parallel-out mode, the isolation level is close to a half-bridge unit of the high-voltage level, each isolation level submodule corresponds to one half-bridge unit, and the corresponding isolation level submodule and the half-bridge unit share a capacitor in the half-bridge unit.
Furthermore, the magnitude of M is determined by the voltage class of the high-voltage direct-current side and the voltage class of the adopted device, and the voltage of the high-voltage direct-current side can be born when the normal operation is required to be ensured.
Furthermore, the low-voltage stage is composed of a three-phase full-bridge inverter, the output ends of the plurality of isolation stage series resonance DC/DC converters are connected in parallel to be used as the input ends of the three-phase full-bridge inverter together, the output ends of the plurality of isolation stage series resonance DC/DC converters are connected with 700V low-voltage direct current ports in parallel, and the three-phase line voltage of the low-voltage stage is 380V low-voltage.
The technical scheme of the invention also comprises a control method of the electric energy router with the full-bridge submodule, which is characterized in that: the method comprises a three-phase six-bridge-arm MMC control method, a three-phase four-bridge-arm MMC control method, a half-bridge unit control method, an isolation level control method, a low-voltage level control method and a direct current side fault protection method, and specifically comprises the following steps:
S1: the three-phase six-bridge arm MMC control method comprises the following specific steps:
s11: setting a current reference value under a dq coordinate system;
s12: collecting three-phase current values of a high-voltage alternating current side, and enabling the collected three-phase current under a static U, V and W coordinate system to pass through a dq converter to obtain current values under a dq coordinate system;
S13: the current reference value under the dq coordinate system is differenced with the current value obtained in the step S12, and then the voltage control instruction under the dq coordinate system is obtained after current loop control;
S14: the voltage control instruction under the dq coordinate system obtained in the step S13 is processed by a dq inverse converter to obtain U, V, W three-phase voltage control instructions;
s2: the three-phase four-bridge arm MMC control method comprises the following specific steps:
s21: setting a three-phase current reference value and sampling time, and collecting a three-phase current value and a three-phase voltage value of a high-voltage alternating-current side;
s22: the three-phase current reference value and the acquired three-phase current value are subjected to difference and then multiplied by a proportionality coefficient Kp to obtain the voltage drop on the loop inductance;
setting the bridge arm inductance in the high voltage stage to be L arm, the power supply inductance to be L 0, and the sampling time to be T, the proportionality coefficient Kp is expressed as:
KP＝[(L0+Larm/2)/T]*0.5
s23: the voltage drop on the loop inductance is differenced with the acquired three-phase voltage value, and a three-phase voltage reference instruction is obtained;
S24: superposing the three-phase voltage reference instruction obtained in the step S23 with a common-mode voltage with the same amplitude as that of the C-phase voltage reference instruction and opposite phases to obtain A, B, C three-phase voltage control instructions;
s3: the half-bridge unit control method comprises the following specific steps:
S31: selecting a proper submodule number M+1 according to the high-voltage direct-current voltage and the withstand voltage grade of the selected power switching device;
s32: determining the duty ratio d of the driving pulse of the power switch tube according to the number of the submodules determined in the step S31;
The half-bridge unit comprises an upper half-bridge arm, two arm inductors L arm and a lower half-bridge arm, wherein the upper half-bridge arm and the lower half-bridge arm are respectively formed by connecting M+1 half-bridge units in series, M units are conducted at each moment of each half-bridge unit by adjusting the duty ratio, the conducted M power units jointly bear the direct-current voltage of U dc/2, U dc is the high-voltage direct-current side voltage, the rated voltage of the isolation level high-voltage side is U dc/2M, the upper half-bridge arm and the lower half-bridge arm are symmetrical, the phase-shifting modulation principle is the same, in the phase-shifting modulation method, the driving signal duty ratio of the half-bridge unit is d, and the port output voltage U sp of the M+1 units of the upper half-bridge arm of the C phase is:
Because the upper bridge arm of the C-phase half bridge needs to bear half of the high-voltage direct-current voltage, the output voltages of the ports of M+1 units of the upper bridge arm of the C-phase half bridge can be written as follows:
the duty ratio d has the following relation with the number M+1 of half-bridge units used in the phase C:
S33: determining phase shift angle between adjacent cells The carrier between two adjacent units has a phase shift angle/>The method comprises the following steps:
S34: and (3) formulating a modulation strategy of the C-phase half-bridge unit: in the same bridge arm, C 1-CM+1 represents M+1 triangular carriers, and a phase shift angle exists between two adjacent units Comparing M+1 triangular carriers with the modulation ratio to obtain driving pulses of M+1 half-bridge units;
s4: the isolation level control method comprises the following specific steps:
s41: setting the switching frequency of the power switching tube to be equal to the resonance frequency;
s42: the driving signals of the two H bridges on the primary side and the secondary side are square waves with the duty ratio of 50%, and no phase shift angle exists between the driving signals on the primary side and the secondary side;
S43: the upper power switch tube and the lower power switch tube in the primary and secondary side H bridge are controlled to conduct complementarily, and the diagonal lines conduct simultaneously;
S5: the low-voltage level control method comprises the following specific steps:
s51: setting a current reference value under a dq coordinate system;
S52: collecting three-phase current values of a low-voltage alternating-current side, and obtaining current values of a dq coordinate system by the collected three-phase current values of static a, b and c coordinate systems through a dq converter;
s53: the current reference value under the dq coordinate system is differenced with the current value obtained in the step S52, and then the voltage control instruction value under the dq coordinate system is obtained after current loop control;
S54: the voltage control command value under the dq coordinate system obtained in the step S53 is processed by a dq inverse converter to obtain a, b and c three-phase voltage control command values;
S6: the direct current side fault protection method comprises the following specific steps:
S61: setting a protection action threshold of the direct-current side fault electric quantity;
S62: when the energy-collecting router fails, the failure electric quantity value caused by the failure;
S63: comparing the fault electrical quantity value obtained in the step S62 with a protection action threshold value, and locking all power switch tubes in the electric energy router if the collected fault electrical quantity value is greater than the protection threshold value;
S64: and collecting fault electrical values after locking of the power switch tubes, and unlocking all the power switch tubes in the electric energy router if the collected fault electrical values are smaller than a protection action threshold value, so that the system is restored to normal operation.
Compared with the prior art, the invention has the beneficial effects that:
(1) Aiming at the fact that a breaker is required to be additionally arranged on a power electronic converter to cut off direct-current short-circuit fault current, the invention provides an electric energy router with a full-bridge submodule, and the direct-current short-circuit fault current can be cut off through control of the converter.
(2) Aiming at the problem that when the third phase of the traditional three-phase four-bridge arm MMC consists of a capacitor phase, the capacitor phase is uncontrollable, and when a short circuit fault of the high-voltage direct-current side occurs, the capacitor of the C phase can discharge to damage the converter, and the C phase consists of a half-bridge unit. A carrier phase shift modulation strategy is provided for the C-phase half-bridge unit, under the provided modulation strategy, the port voltage of the C-phase half-bridge unit is constantly equal to the voltage of the high-voltage direct-current side, and the higher harmonic wave of the high-voltage direct-current side is reduced.
(3) Aiming at the control requirements of the energy Internet on multiple ports, multiple directions and the like of electric energy, the electric energy router topology with the full-bridge submodule can realize active control of power flow among all ports.
(4) According to the electric energy router with the full-bridge submodule, after the high-voltage side direct-current bipolar short circuit fault occurs and all power switching tubes are blocked, the counter electromotive force provided by the full-bridge submodule capacitor is larger than the alternating-current line voltage amplitude, and finally, the complete blocking of the converter can be realized through the single-phase conductivity of the anti-parallel diode.
Drawings
Fig. 1 is a block diagram of an electric energy router with full-bridge submodules according to the present invention.
Fig. 2 is a phase shift modulation method of a C-phase half-bridge unit carrier wave in the present invention.
Fig. 3a shows a phase a capacitive discharge circuit.
Fig. 3b shows an equivalent loop of the a-phase capacitive discharge loop.
Fig. 4 is a A, B-phase current equivalent loop in the latched state.
Fig. 5 is a A, C-phase current equivalent loop in the latched state.
Fig. 6 is a fault isolation control strategy for a power router including full-bridge sub-modules.
Fig. 7 is a graph of the C-phase half-bridge cell port voltage and bridge arm voltage waveforms in an embodiment.
Fig. 8 is an example of isolating transformer primary and secondary side voltage and current waveforms.
Fig. 9 is a waveform of the voltage and current output from the high voltage 10kV ac port during normal operation in an embodiment.
Fig. 10 is a waveform of the voltage and current output from the high voltage 20kV ac port during normal operation in an embodiment.
Fig. 11 is a waveform of the low voltage 380V ac port output line voltage and current during normal operation in an embodiment.
Fig. 12 is a waveform of the output voltage of the low voltage 700V dc port during normal operation in the embodiment.
Fig. 13 is a waveform of a hvdc port current in an embodiment with a hvdc side fault.
Fig. 14 is a waveform of a high voltage 10kV ac port current for a high voltage dc side fault in an embodiment.
Fig. 15 is a waveform of a high voltage 20kV ac port current for a high voltage dc side fault in an embodiment.
Fig. 16 is a waveform of a low voltage 380V ac port current for a high voltage dc side fault in an embodiment.
Fig. 17 is a waveform of a hvdc port voltage for a hvdc side failure in an embodiment.
Fig. 18 is a waveform of a high voltage 10kV ac port voltage for a high voltage dc side fault in an embodiment.
Fig. 19 is a waveform of a high voltage 20kV ac port voltage for a high voltage dc side fault in an embodiment.
FIG. 20 is a waveform of the AC port voltage at low voltage 380V in an embodiment with a high voltage DC side fault
Fig. 21 shows a high-voltage dc side fault, and the capacitor voltages of the upper arm submodules of the a-phase and the b-phase are blocked in the embodiment.
Fig. 22 is a dc voltage during self-cleaning of a high voltage dc side fault in an embodiment.
Detailed Description
The invention will be further described with reference to the drawings and the specific examples.
The invention provides an electric energy router with a full-bridge submodule and a high-voltage direct-current side fault protection method thereof, and the specific structure of the electric energy router is shown in figure 1 and comprises a high-voltage stage, an isolation stage and a low-voltage stage. The high-voltage stage comprises a three-phase four-bridge arm MMC, a three-phase six-bridge arm MMC and a half-bridge unit, the isolation stage is formed by a plurality of series resonance DC/DC converters, the low-voltage stage adopts a three-phase full-bridge inverter structure, the high-voltage stage, the isolation stage and the low-voltage stage are connected in parallel, P+ and N-are the positive and negative poles of a high-voltage direct current port, two public high-voltage direct current buses are led out from the P+ and N-points, and the two public high-voltage direct current buses are respectively connected with the two ends of the high-voltage stage direct current port.
The high-voltage stage of the invention connects the direct current ports of the three-phase four-bridge arm MMC and the three-phase six-bridge arm MMC in parallel to provide a common high-voltage direct current port for the access of the distributed new energy. The high-voltage stage comprises two alternating current ports of 10kV and 20kV, and interconnection of a 10kV/20kV power distribution network can be achieved. The 20kV high-voltage alternating-current port is connected with a three-phase six-bridge-arm MMC topological structure based on a full-bridge sub-module, each phase of the three-phase six-bridge-arm MMC is U, V, W phases, the three phases are formed by sequentially connecting an upper bridge arm, two bridge arm inductors L arm and a lower bridge arm in series, each upper bridge arm and each lower bridge arm are obtained by connecting N full-bridge sub-modules in series, the 20kV high-voltage alternating-current port is provided with a three-phase voltage source and three inductors L 0, the cathodes of the three-phase voltage sources are connected with each other, the anodes of the three high-voltage alternating-current ports are respectively connected with one ends of the three inductors L 0, and the other ends of the three inductors L 0 are respectively connected between two bridge arm inductors L arm of the three phases. The 10kV high-voltage alternating current port is connected with a three-phase four-bridge arm MMC topological structure and a half-bridge unit structure, phases of the three-phase four-bridge arm MMC topological structure and the half-bridge unit structure are A, B, C phases respectively, A, B phases are formed by a three-phase four-bridge arm MMC based on a Quan Qiaozi module, C phases are formed by a half-bridge unit, A, B phases are formed by sequentially connecting an upper bridge arm, two bridge arm inductors L arm and a lower bridge arm in series, the upper bridge arm and the lower bridge arm are obtained by connecting N full-bridge submodules in series, the 10kV high-voltage alternating current port is provided with a three-phase voltage source and three inductors L 0, the cathodes of the three-phase voltage source are connected with each other, the anodes of the three inductors L 0 are connected with one ends of the three inductors L 0 respectively, and the other ends of the two inductors L 0 corresponding to the A, B are connected between two bridge arm inductors L arm of A, B phases respectively. The half-bridge unit comprises an upper half-bridge arm, two arm inductors L arm and a lower half-bridge arm, wherein the upper half-bridge arm, the two arm inductors L arm and the lower half-bridge arm are sequentially connected in series, the other end of the inductor L 0 corresponding to C is connected between the two arm inductors L arm, and the upper half-bridge arm and the lower half-bridge arm are respectively formed by connecting M+1 half-bridge modules in series.
When the alternating current side is in a voltage level of 10kV, the voltage level of the direct current side is +/-10 kV, and on the premise that the modulation ratio is 1.414 when the alternating current side of the three-phase four-bridge arm MMC of the full-bridge submodule is connected with a 10kV alternating current power grid. The number N of the full-bridge submodules is determined by the voltage class of the high-voltage direct-current side and the voltage class of the adopted device, and the voltage of the high-voltage direct-current side can be born when the normal operation is required.
The isolation level is divided into an isolation upper bridge arm and an isolation lower bridge arm, the isolation upper bridge arm and the isolation lower bridge arm are respectively formed by connecting M+1 isolation level sub-modules in series, the isolation level sub-modules are serial resonance DC/DC converters, a plurality of serial resonance DC/DC converters are connected in a serial-in parallel-out mode, the isolation level is close to a half-bridge unit of a high-voltage level, each isolation level sub-module corresponds to one half-bridge unit, the corresponding isolation level sub-modules and the half-bridge units share a capacitor in the half-bridge unit, the phenomenon that the capacitor phase is uncontrollable when the C phase is formed by the capacitor and the capacitor discharges when a high-voltage direct-current side short circuit occurs is avoided, and when the high-voltage direct-current side short circuit fault occurs, the self-clearing of the direct-current fault can be realized through a locking switch device. The size of M is determined by the voltage class of the high-voltage direct-current side and the voltage class of the adopted device, and the voltage of the high-voltage direct-current side can be born when the normal operation is required.
The low-voltage stage is composed of a three-phase full-bridge inverter, the output ends of a plurality of isolation stage series resonance DC/DC converters are connected in parallel to be used as the input end of the three-phase full-bridge inverter, the output ends of the plurality of isolation stage series resonance DC/DC converters are connected with a 700V low-voltage direct current port in parallel, and the three-phase line voltage of the low-voltage stage is 380V low voltage.
The invention also provides a control method of the electric energy router with the full-bridge submodule, which specifically comprises the following steps: the three-phase six-bridge arm MMC control method, the three-phase four-bridge arm MMC control method, the half-bridge unit control method, the isolation level control method, the low-voltage level control method and the direct current side fault protection method specifically comprise the following steps:
S1: the three-phase six-bridge arm MMC control method comprises the following specific steps:
s11: setting a current reference value under a dq coordinate system;
s12: collecting three-phase current values of a high-voltage alternating current side, and enabling the collected three-phase current under a static U, V and W coordinate system to pass through a dq converter to obtain current values under a dq coordinate system;
S13: the current reference value under the dq coordinate system is differenced with the current value obtained in the step S12, and then the voltage control instruction under the dq coordinate system is obtained after current loop control;
S14: the voltage control instruction under the dq coordinate system obtained in the step S13 is processed by a dq inverse converter to obtain U, V, W three-phase voltage control instructions;
s2: the three-phase four-bridge arm MMC control method comprises the following specific steps:
s21: setting a three-phase current reference value and sampling time, and collecting a three-phase current value and a three-phase voltage value of a high-voltage alternating-current side;
s22: the three-phase current reference value and the acquired three-phase current value are subjected to difference and then multiplied by a proportionality coefficient Kp to obtain the voltage drop on the loop inductance;
setting the bridge arm inductance in the high voltage stage to be L arm, the power supply inductance to be L 0, and the sampling time to be T, the proportionality coefficient Kp is expressed as:
KP＝[(L0+Larm/2)/T]*0.5
s23: the voltage drop on the loop inductance is differenced with the acquired three-phase voltage value, and a three-phase voltage reference instruction is obtained;
S24: superposing the three-phase voltage reference instruction obtained in the step S23 with a common-mode voltage with the same amplitude as that of the C-phase voltage reference instruction and opposite phases to obtain A, B, C three-phase voltage control instructions;
s3: the half-bridge unit control method comprises the following specific steps:
S31: selecting a proper submodule number M+1 according to the high-voltage direct-current voltage and the withstand voltage grade of the selected power switching device;
s31: determining the duty ratio d of the driving pulse of the power switch tube according to the number of the submodules determined in the step S31;
The half-bridge unit comprises an upper half-bridge arm, two arm inductances L arm and a lower half-bridge arm, wherein the upper half-bridge arm and the lower half-bridge arm are respectively formed by connecting M+1 half-bridge units in series, M units are conducted at each moment of each arm of the half-bridge unit by adjusting the duty ratio, and the conducted M power units jointly bear direct current voltage of U dc/2 (U dc is high-voltage direct current side voltage), then rated voltage of the isolation level high-voltage side (namely rated value of port voltage of the half-bridge unit) is U dc/2M, the upper half-bridge arm and the lower half-bridge arm are symmetrical, the phase-shifting modulation principle is the same, in the phase-shifting modulation method, driving signal duty ratio of the half-bridge unit is d, and port output voltage U sp of M+1 units of the upper half-bridge arm of the C phase-shifting half-bridge is as follows:
Because the upper bridge arm of the C-phase half bridge needs to bear half of the high-voltage direct-current voltage, the output voltages of the ports of M+1 units of the upper bridge arm of the C-phase half bridge can be written as follows:
the duty ratio d has the following relation with the number M+1 of half-bridge units used in the phase C:
S33: determining phase shift angle between adjacent cells The carrier between two adjacent units has a phase shift angle/>The method comprises the following steps:
S34: and (3) formulating a modulation strategy of the C-phase half-bridge unit: in the same bridge arm, C 1-CM+1 represents M+1 triangular carriers, and a phase shift angle exists between two adjacent units The driving pulse of m+1 half-bridge units is obtained by comparing m+1 triangular carriers with the modulation ratio, as shown in fig. 2, which is a schematic diagram of the proposed carrier phase-shift modulation.
S4: the isolation level control method comprises the following specific steps:
s41: setting the switching frequency of the power switching tube to be equal to the resonance frequency;
s42: the driving signals of the two H bridges on the primary side and the secondary side are square waves with the duty ratio of 50%, and no phase shift angle exists between the driving signals on the primary side and the secondary side;
S43: the upper power switch tube and the lower power switch tube in the primary and secondary side H bridge are controlled to conduct complementarily, and the diagonal lines conduct simultaneously;
S5: the low-voltage level control method comprises the following specific steps:
s51: setting a current reference value under a dq coordinate system;
S52: collecting three-phase current values of a low-voltage alternating-current side, and obtaining current values of a dq coordinate system by the collected three-phase current values of static a, b and c coordinate systems through a dq converter;
s53: the current reference value under the dq coordinate system is differenced with the current value obtained in the step S52, and then the voltage control instruction value under the dq coordinate system is obtained after current loop control;
S54: the voltage control command value under the dq coordinate system obtained in the step S53 is processed by a dq inverse converter to obtain a, b and c three-phase voltage control command values;
S6: the direct current side fault protection method comprises the following specific steps:
S61: setting protection action threshold value of direct current side fault electric quantity
S62: when the electric energy router fails, acquiring a failure electric quantity value caused by the failure;
S63: comparing the fault electrical quantity value obtained in the step S62 with a protection action threshold value, and locking all power switch tubes in the electric energy router if the collected fault electrical quantity value is greater than the protection threshold value;
S64: and collecting fault electrical values after locking of the power switch tubes, and unlocking all the power switch tubes in the electric energy router if the collected fault electrical values are smaller than a protection action threshold value, so that the system is restored to normal operation.
To further describe the power router including the full-bridge sub-module and the control method thereof, the present invention is described below with reference to specific embodiments:
the invention has a + -10 kV high-voltage direct current port, a 10kV high-voltage alternating current port, a 20kV high-voltage alternating current port, a 700V low-voltage direct current port and a 380V low-voltage alternating current port.
Unlike the half-bridge sub-module, the full-bridge sub-module can output negative level, and terminal voltages of the upper and lower bridge arm sub-modules of the three-phase four-bridge arm MMC based on Quan Qiaozi modules and the three-phase six-bridge arm MMC based on Quan Qiaozi modules need to meet:
In the middle of Representing capacitor voltage constraint of full-bridge submodule of three-phase four-bridge arm MMC, wherein/>Representing the capacity voltage constraint of the full-bridge submodule of the three-phase six-bridge arm MMC, U An is the phase voltage of the A phase of the alternating current side, U Un is the phase voltage of the U phase of the alternating current side, N is the number of submodules, in the built simulation, the number N of the full-bridge submodules in each bridge arm is 10, and the selection range of the capacity voltage constraint of the submodule can be calculated according to the formula, so that the constraint in the example is represented as:
After the high-voltage direct-current side fails, the failure process of the electric energy router with the full-bridge submodule is divided into two stages, and the full-bridge submodule and the isolation stage input capacitor in the first stage discharge, so that bridge arm current is rapidly increased, and the current flowing through components exceeds a protection threshold value to trigger the protection action of the system. The second stage is a short-circuit fault protection stage after the switching tube is locked, and a counter electromotive force is provided for the capacitor of the full-bridge submodule, so that the two sides of the diode form a turn-off voltage, and the short-circuit fault current at the high-voltage direct-current side cannot flow through the diode.
Taking phase A in the topology of the electric energy router with the full-bridge submodule as an example, assuming the capacitance value of the submodule as C, analyzing a capacitor discharge loop of the submodule before locking. Fig. 3 is a phase a capacitor discharge loop and its equivalent circuit. In fig. 3 (a), i A is an a-phase input ac current, u A is an a-phase input ac voltage, u p、un represents a series voltage of upper and lower arm submodules, i f represents a fault current, L arm represents an arm inductance, and R represents an arm resistance. For the first stage of the sub-module capacitive discharge, the simplified equivalent circuit is shown in fig. 3 (b). At this time, a second-order discharge circuit is formed by the short-circuit resistor, the submodule capacitor, the bridge arm inductor and the bridge arm resistor. Where C eq represents the equivalent capacitance, R f represents the shorting resistance, u c (0) represents the initial value of the submodule capacitor voltage, and i c (0) represents the initial current value.
In general, (2 R+R f) is much smaller than in practical systemsTherefore, the secondary oscillation discharging circuit of the RLC can be formed by a submodule capacitor, a short circuit resistor and a bridge arm inductor. And the upper bridge arm inductance, the lower bridge arm inductance and the resistor are connected in series into a loop, and the equivalent inductance and the equivalent resistor are respectively 2L arm and 2R. Because of the module switching, the upper bridge arm submodule capacitance and the lower bridge arm submodule capacitance are equivalent to parallel connection, and the equivalent capacitance C eq is represented by the following formula:
Assuming that the switching tube is not locked at the moment of failure, the system transmits power normally, and the capacitance voltage u c meets the differential equation:
According to the differential equation, let the initial value of the capacitor voltage of the single-phase sub-module be U dc, and the initial current be the dc current I 0, the calculation formulas of the capacitor voltage U c and the fault current I f during the dc short-circuit fault can be expressed as follows:
wherein,
Where τ 1 denotes the discharge loop time constant, ω denotes the resonant angular frequency, and α denotes the discharge loop initial phase angle.
From the formulas of the capacitor voltage u c and the fault current i f during the direct current short circuit fault, the capacitor voltage of the submodule is rapidly reduced and the fault current is rapidly increased before the switching tube is locked in the first stage. The fault current is proportional to the capacitance value and inversely proportional to the number of submodules and the bridge arm inductance. When the system voltage class is determined, the smaller the bridge arm inductance and the number of submodules, the larger the fault current. In addition, the larger the capacitance value is, the more energy is stored, and the larger the short-circuit current is when the short-circuit occurs, so that the formula corresponds to the physical process of the actual circuit.
After the second stage switching tube is locked, the full-bridge submodule can be equivalently connected with the submodule capacitor in series, and the C-phase half-bridge unit can be equivalently connected with the diode in series, and the upper bridge arm and the lower bridge arm are connected through the bridge arm inductor. The three-phase six-bridge-arm MMC based on Quan Qiaozi modules has the self-clearing capacity of high-voltage direct-current faults, so that whether the three-phase four-bridge-arm MMC and the C-phase half-bridge unit based on Quan Qiaozi modules have the self-clearing capacity of high-voltage direct-current faults is a key for measuring whether the electric energy router with the full-bridge submodules has the fault ride-through capacity of the high-voltage direct-current side. Because the current paths formed by the three-phase four-bridge arm MMC and the C-phase half-bridge unit are asymmetric, the following discussion will be divided into two cases, and the specific case analysis is as follows:
T1: in the first case, the freewheel loop is constituted by A, B phases:
(1) Fig. 4 shows the A, B-phase current equivalent loop in the latched state. R L represents line resistance, L L represents line inductance, and L 0 represents ac power supply inductance. If the impedance is ignored, the closed alternating current system feeds through the anti-parallel diode, the submodule capacitor, the bridge arm inductance, the high-voltage direct current fault channel and the direct current system. The submodule capacitance in the feed path will provide a back emf that will reduce the fault current to zero using the reverse blocking of the diode.
(2) In order to ensure that the power switch tube is completely locked, the back electromotive force provided by the neutron module capacitor of the A, B-phase bridge arm is larger than the amplitude of the alternating current line voltage, and finally, the complete locking of the converter is realized through the single-phase conductivity of the anti-parallel diode. At this time, the back emf that needs to be provided by the submodule capacitance can be expressed as:
Where u cn represents the rated capacitance voltage of the sub-module, and u An represents the ac side a-phase voltage amplitude.
T2: in the second case, the freewheel loop is composed of A, C phases:
(1) Fig. 5 shows the A, C-phase current equivalent circuit in the closed state. Only the submodule capacitors of the a-phase upper bridge arm in the feed-through loop provide back electromotive force.
(2) In order to ensure that the power switch tube is completely locked, the back electromotive force provided by the capacitance of the sub-module of the bridge arm on the phase A should be larger than the amplitude of the alternating current line voltage. At this time, the back emf that needs to be provided by the submodule capacitance can be expressed as:
Therefore, the first condition is constantly established when the second condition is satisfied for the current path formed by the three-phase four-bridge arm MMC and the C-phase half-bridge module.
Under the condition that the redundant submodules of the system are not considered, N submodules are input in each phase through the modulation strategy, and the superposition value of the output voltages of all input submodules is equal to the high-voltage direct-current side voltage, and the output voltages can be expressed by the following formula:
Nucn＝Udc
Wherein U dc represents the high-voltage dc side voltage.
When the system operates normally, m represents the modulation ratio, and in the three-phase four-bridge arm MMC, the requirement for the amplitude value between the high-voltage direct current bus voltage and the alternating current side phase voltage is satisfied:
the back emf provided by the submodule capacitor satisfies the following relationship with the ac side phase voltage magnitude:
According to the analysis, the modulation ratio m is 1.414, so that the back electromotive force provided by the submodule capacitor is larger than the amplitude of the alternating-current side phase voltage, and the high-voltage direct-current side short-circuit protection can be realized through the three-phase four-bridge arm MMC and C-phase half-bridge unit structure.
The fault isolation control strategy of the power router with the full-bridge submodule is shown in fig. 6. In the early stage of the high-voltage direct-current side fault occurrence, the fault electric quantity does not reach the protection action threshold, and the electric energy router works in a normal state. When the system detects the direct current fault action threshold, all switching tubes in the electric energy router are locked, and fault short-circuit current is cleared through counter electromotive force provided by the capacitor and single-phase conductivity of the diode. And for the temporary faults, the system is recovered to normal operation after the IGBT is unlocked. For permanent faults, it is necessary to open the ac circuit breaker for isolation maintenance.
In order to illustrate the effectiveness of the electric energy router structure with the full-bridge submodule, in steady operation, a high-voltage direct current port is arranged in a simulation model to input 8MW of active power, a 10kV high-voltage alternating current port outputs 1.8MW of active power, a 20kV high-voltage alternating current port outputs 6MW of active power, a 380kV low-voltage alternating current port outputs 0.2MW of active power, and the low-voltage direct current port does not transmit power.
In the built simulation, each half-bridge arm has 5 sub-modules, so that 10 half-bridge units are arranged in total, the rated value of the port voltage of each half-bridge unit is 2500V, and the method is based on the formula/>The duty ratio d of the half-bridge unit is calculated to be 4/5, and the phase shift angle/>, between adjacent unitsIn the case of pi/3, fig. 7 shows waveforms of input port voltage u 1 of the first half bridge unit and input port voltage u 2 of the second half bridge unit of the C-phase upper bridge, and voltage uH of the upper bridge arm of the half bridge, where the amplitude of the input port voltage is 2500V, the duty ratio is 4/5, and the voltage of the upper bridge arm of the half bridge is 10kV, which is half of the high-voltage dc input voltage. Fig. 8 shows waveforms of a primary voltage u pri, a primary current i pri, a secondary voltage u sec, and a secondary current i pri of a isolation transformer in a series resonant DC/DC converter. From the figure, it can be seen that the voltage waveforms at both sides of the isolation transformer are identical in phase and vary in magnitude according to the transformation ratio (2500:700). The absolute value of the amplitude of the primary side high voltage waveform is 2500, and the absolute value of the amplitude of the secondary side low voltage waveform is 700.
To illustrate that the proposed power router architecture is capable of controlling power flow, the high voltage dc port input active power is changed to 4MW, the 10kv high voltage ac port output power is changed from 1.8MW to 0.9MW, the 20kv high voltage ac port output power is changed from 6MW to 3MW, and the 380v low voltage ac port output power is changed from 0.2MW to 0.1MW at 0.5 s. Fig. 9-12 are waveforms of output line voltage and current for each port when the system is in normal operation. From the simulation waveforms of fig. 9-12, it can be known that the power flow between the ports can reach balance, and the proposed electric energy router with the full-bridge submodule can realize coordinated control of the power flow of each port.
In order to illustrate the effectiveness of the proposed electric energy router structure with the full-bridge submodule on the short-circuit protection of the high-voltage direct-current side, the high-voltage stage of the electric energy router structure with the full-bridge submodule in the simulation model works in an inversion mode, the active power of the system is 8MW, and when the time t sc = 0.5s, the short-circuit fault occurs on the high-voltage direct-current side of the system, and the short-circuit resistance is 1 omega. And (3) taking action delay caused by system fault identification and the like into consideration, and locking driving signals of all switches in the electric energy router structure containing the full-bridge submodule after the short circuit fault occurs for 400 mu s.
Fig. 13-16 are waveforms of output currents of ports of the power router before and after blocking. As can be seen from fig. 13, the high-voltage dc side current rises instantaneously when a short-circuit fault occurs, and the inverter is immediately shut down after the fault occurs, so that the high-voltage dc side current gradually drops to zero. As can be seen from fig. 14, 15 and 16, after the converter is locked, due to the output inductance on the ac side, the currents on the three ac sides gradually decay to zero after freewheeling through the inductance, and it is verified that the electric energy router structure of the proposed full-bridge submodule can realize high-voltage dc side short-circuit protection through the locked power device.
Fig. 17-20 are waveforms of output line voltages of ports of the power router before and after blocking, when the high voltage dc side fails. The high-voltage dc side voltage waveform is shown in fig. 17. As can be seen from the simulation, when a short-circuit fault on the high-voltage dc side occurs, the voltage on the high-voltage dc side rapidly decreases. When the high-voltage direct-current side short-circuit fault occurs, since the high-voltage alternating-current side is connected to the three-phase alternating-current power supply, the high-voltage alternating-current side line voltage waveform becomes a power line voltage waveform, as shown in fig. 18, 19 and 20.
Fig. 21 is a waveform of the capacitor voltage of the upper arm sub-module of the a-phase before and after blocking when the high voltage dc side fails. In the first stage after the fault occurs, the capacitance of the submodule is briefly discharged, and the capacitance voltage of the submodule is slightly reduced. In the second stage after the fault occurs, according to the current path in fig. 4, the capacitance of the sub-module of the a-phase upper bridge arm is in a charging state, and the capacitance voltage of the sub-module is slightly raised. After the direct current at the high voltage side becomes zero, the capacitance voltage of the submodule remains unchanged, and conditions are provided for the follow-up converter to resume normal operation.
Assuming that the system has a high-side direct-current bipolar short-circuit fault at 0.5s, all IGBTs are immediately blocked after 400 mus, the fault duration is 0.2s, the fault disappears at 0.7s, and all IGBTs are unblocked. The simulation results are shown in fig. 22. As can be seen from fig. 22, after the high-side dc bipolar failure occurs, the high-side dc voltage rapidly drops to zero. After the fault current is cleared, the switching tube is unlocked, under the control of the control system, the high-voltage direct-current side voltage is restored to the +/-10 kV voltage level after short oscillation, and the system resumes normal power transmission. According to the analysis, when the bipolar grounding short-circuit fault occurs, the electric energy router with the full-bridge sub-module can cut off fault current by means of the blocking converter, so that the high-voltage direct-current side fault can be cut off and isolated, normal operation can be quickly recovered after the fault occurs, and the electric energy router with the full-bridge sub-module has good self-clearing capacity for the high-voltage direct-current side fault.
The specific embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present invention.

Claims (7)

1. An electric energy router that contains full bridge submodule, its characterized in that: the high-voltage power supply comprises a high-voltage stage, an isolation stage and a low-voltage stage, wherein the high-voltage stage comprises a three-phase four-bridge arm MMC, a three-phase six-bridge arm MMC and a half-bridge unit, the isolation stage is formed by a plurality of series resonance DC/DC converters, the low-voltage stage adopts a three-phase full-bridge inverter structure, the high-voltage stage, the isolation stage and the low-voltage stage are connected in parallel, P+ and N-are the positive and negative poles of a high-voltage direct current port, two public high-voltage direct current buses are led out from the P+ and N-points, and are respectively connected with the two ends of the high-voltage direct current port;
The direct current ports of the three-phase four-bridge arm MMC and the three-phase six-bridge arm MMC of the high-voltage stage are connected in parallel, and the high-voltage stage comprises two alternating current ports of 10kV and 20 kV;
The 20kV high-voltage alternating-current port is connected with a three-phase six-bridge-arm MMC topological structure based on a full-bridge sub-module, each phase of the three-phase six-bridge-arm MMC is U, V, W phases, three phases are respectively formed by sequentially connecting an upper bridge arm, two bridge arm inductors L arm and a lower bridge arm in series, the upper bridge arm and the lower bridge arm are respectively obtained by connecting N full-bridge sub-modules in series, the 20kV high-voltage alternating-current port is provided with a three-phase voltage source and three inductors L 0, the cathodes of the three-phase voltage source are mutually connected, the anodes of the three voltage source are respectively connected with one ends of the three inductors L 0, and the other ends of the three inductors L 0 are respectively connected between two bridge arm inductors L arm of the three phases;
The three-phase four-bridge arm MMC topology structure and the half-bridge unit structure are connected to a 10kV high-voltage alternating-current port, each phase of the three-phase four-bridge arm MMC topology structure and the half-bridge unit structure is A, B, C phases respectively, the A, B phase is composed of a Quan Qiaozi module-based three-phase four-bridge arm MMC, the C phase is composed of a half-bridge unit, the A, B phases are formed by sequentially connecting an upper bridge arm, two bridge arm inductors L arm and a lower bridge arm in series, the upper bridge arm and the lower bridge arm are formed by connecting N full-bridge submodules in series, the 10kV high-voltage alternating-current port is provided with a three-phase voltage source and three inductors L 0, the cathodes of the three-phase voltage source are connected with each other, the anodes of the three-phase voltage source are respectively connected with one ends of three inductors L 0, and the other ends of two inductors L 0 corresponding to A, B are respectively connected between two bridge arm inductors L arm of A, B phases;
The half-bridge unit comprises an upper half-bridge arm, two arm inductors L arm and a lower half-bridge arm, wherein the upper half-bridge arm, the two arm inductors L arm and the lower half-bridge arm are sequentially connected in series, the other end of the inductor L 0 corresponding to C is connected between the two arm inductors L arm, and the upper half-bridge arm and the lower half-bridge arm are respectively formed by connecting M+1 half-bridge modules in series.
2. A power router comprising a full-bridge sub-module as claimed in claim 1, wherein: when the alternating current side is in a voltage level of 10kV, the voltage level of the direct current side is +/-10 kV, and on the premise that the modulation ratio is 1.414 when the alternating current side of the three-phase four-bridge arm MMC adopting the full-bridge submodule is connected with a 10kV alternating current power grid.
3. A power router comprising a full-bridge sub-module as claimed in claim 1, wherein: the number N of the full-bridge submodules is determined by the voltage class of the high-voltage direct-current side and the voltage class of the adopted device, and the voltage of the high-voltage direct-current side can be born when the normal operation is required.
4. A power router comprising a full-bridge sub-module as claimed in claim 1, wherein: the isolation level is divided into an isolation upper bridge arm and an isolation lower bridge arm, the isolation upper bridge arm and the isolation lower bridge arm are respectively formed by connecting M+1 isolation level submodules in series, the isolation level submodules are serial resonance DC/DC converters, a plurality of serial resonance DC/DC converters are connected in a serial-in parallel-out mode, the isolation level is close to a half-bridge unit of the high-voltage level, each isolation level submodule corresponds to one half-bridge unit, and the corresponding isolation level submodule and the half-bridge unit share a capacitor in the half-bridge unit.
5. A power router comprising a full bridge sub-module according to claim 1 or 4, wherein: the magnitude of M is determined by the voltage class of the high-voltage direct-current side and the voltage withstand class of the adopted device, and can bear the voltage of the high-voltage direct-current side when the normal operation is required.
6. The full-bridge sub-module-containing power router of claim 5, wherein: the low-voltage stage consists of a three-phase full-bridge inverter, the output ends of a plurality of isolation stage series resonance DC/DC converters are connected in parallel and jointly serve as the input ends of the three-phase full-bridge inverter, the output ends of the plurality of isolation stage series resonance DC/DC converters are connected with 700V low-voltage direct current ports in parallel, and the three-phase line voltage of the low-voltage stage is 380V low voltage.
7. A method of controlling a power router having a full-bridge sub-module as claimed in any one of claims 1 to 6, wherein: the method comprises a three-phase six-bridge-arm MMC control method, a three-phase four-bridge-arm MMC control method, a half-bridge unit control method, an isolation level control method, a low-voltage level control method and a direct current side fault protection method, and specifically comprises the following steps:
S1: the three-phase six-bridge arm MMC control method comprises the following specific steps:
s11: setting a current reference value under a dq coordinate system;
s12: collecting three-phase current values of a high-voltage alternating current side, and enabling the collected three-phase current under a static U, V and W coordinate system to pass through a dq converter to obtain current values under a dq coordinate system;
S13: the current reference value under the dq coordinate system is differenced with the current value obtained in the step S12, and then the voltage control instruction under the dq coordinate system is obtained after current loop control;
S14: the voltage control instruction under the dq coordinate system obtained in the step S13 is processed by a dq inverse converter to obtain U, V, W three-phase voltage control instructions;
s2: the three-phase four-bridge arm MMC control method comprises the following specific steps:
s21: setting a three-phase current reference value and sampling time, and collecting a three-phase current value and a three-phase voltage value of a high-voltage alternating-current side;
s22: the three-phase current reference value and the acquired three-phase current value are subjected to difference and then multiplied by a proportionality coefficient Kp to obtain the voltage drop on the loop inductance;
setting the bridge arm inductance in the high voltage stage to be L arm, the power supply inductance to be L 0, and the sampling time to be T, the proportionality coefficient Kp is expressed as:
KP＝[(L0+Larm/2)/T]*0.5
s23: the voltage drop on the loop inductance is differenced with the acquired three-phase voltage value, and a three-phase voltage reference instruction is obtained;
S24: superposing the three-phase voltage reference instruction obtained in the step S23 with a common-mode voltage with the same amplitude as that of the C-phase voltage reference instruction and opposite phases to obtain A, B, C three-phase voltage control instructions;
s3: the half-bridge unit control method comprises the following specific steps:
S31: selecting a proper submodule number M+1 according to the high-voltage direct-current voltage and the withstand voltage grade of the selected power switching device;
s32: determining the duty ratio d of the driving pulse of the power switch tube according to the number of the submodules determined in the step S31;
The half-bridge unit comprises an upper half-bridge arm, two arm inductors L arm and a lower half-bridge arm, wherein the upper half-bridge arm and the lower half-bridge arm are respectively formed by connecting M+1 half-bridge units in series, M units are conducted at each moment of each half-bridge unit by adjusting the duty ratio, the conducted M power units jointly bear the direct-current voltage of U dc/2, U dc is the high-voltage direct-current side voltage, the rated voltage of the isolation level high-voltage side is U dc/2M, the upper half-bridge arm and the lower half-bridge arm are symmetrical, the phase-shifting modulation principle is the same, in the phase-shifting modulation method, the driving signal duty ratio of the half-bridge unit is d, and the port output voltage U sp of the M+1 units of the upper half-bridge arm of the C phase is:
Because the upper bridge arm of the C-phase half bridge needs to bear half of the high-voltage direct-current voltage, the output voltages of the ports of M+1 units of the upper bridge arm of the C-phase half bridge can be written as follows:
the duty ratio d has the following relation with the number M+1 of half-bridge units used in the phase C:
S33: determining phase shift angle between adjacent cells The carrier between two adjacent units has a phase shift angle/>The method comprises the following steps:
S34: and (3) formulating a modulation strategy of the C-phase half-bridge unit: in the same bridge arm, C 1-CM+1 represents M+1 triangular carriers, and a phase shift angle exists between two adjacent units Comparing M+1 triangular carriers with the modulation ratio to obtain driving pulses of M+1 half-bridge units;
s4: the isolation level control method comprises the following specific steps:
s41: setting the switching frequency of the power switching tube to be equal to the resonance frequency;
s42: the driving signals of the two H bridges on the primary side and the secondary side are square waves with the duty ratio of 50%, and no phase shift angle exists between the driving signals on the primary side and the secondary side;
S43: the upper power switch tube and the lower power switch tube in the primary and secondary side H bridge are controlled to conduct complementarily, and the diagonal lines conduct simultaneously;
S5: the low-voltage level control method comprises the following specific steps:
s51: setting a current reference value under a dq coordinate system;
S52: collecting three-phase current values of a low-voltage alternating-current side, and obtaining current values of a dq coordinate system by the collected three-phase current values of static a, b and c coordinate systems through a dq converter;
s53: the current reference value under the dq coordinate system is differenced with the current value obtained in the step S52, and then the voltage control instruction value under the dq coordinate system is obtained after current loop control;
S54: the voltage control command value under the dq coordinate system obtained in the step S53 is processed by a dq inverse converter to obtain a, b and c three-phase voltage control command values;
S6: the direct current side fault protection method comprises the following specific steps:
S61: setting a protection action threshold of the direct-current side fault electric quantity;
S62: when the energy-collecting router fails, the failure electric quantity value caused by the failure;
S63: comparing the fault electrical quantity value obtained in the step S62 with a protection action threshold value, and locking all power switch tubes in the electric energy router if the collected fault electrical quantity value is greater than the protection threshold value;
S64: and collecting fault electrical values after locking of the power switch tubes, and unlocking all the power switch tubes in the electric energy router if the collected fault electrical values are smaller than a protection action threshold value, so that the system is restored to normal operation.
CN202210082750.2A 2022-01-28 2022-01-28 Electric energy router with full-bridge submodule and control method thereof Active CN115276434B (en)

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