CN109039128B - MMC submodule topological structure based on clamping and energy transfer circuit - Google Patents

MMC submodule topological structure based on clamping and energy transfer circuit Download PDF

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CN109039128B
CN109039128B CN201810889350.6A CN201810889350A CN109039128B CN 109039128 B CN109039128 B CN 109039128B CN 201810889350 A CN201810889350 A CN 201810889350A CN 109039128 B CN109039128 B CN 109039128B
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capacitor
voltage
diode
inductor
switch tube
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CN109039128A (en
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徐坤山
谢少军
陈文明
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Nanjing University of Aeronautics and Astronautics
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Nanjing University of Aeronautics and Astronautics
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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
    • H02M7/487—Neutral point clamped inverters

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  • Power Engineering (AREA)
  • Inverter Devices (AREA)
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Abstract

本发明公开了一种基于箝位和能量转移电路的MMC子模块拓扑结构，属于大功率变换器拓扑结构领域，该拓扑结构包括半桥电路、箝位电路和能量转移电路。本发明稳定性高，结构简单，本身具有电容电压控制能力，不需要传统的电容电压平衡控制；环流交流分量小，无需采用环流抑制策略。

Figure 201810889350

The invention discloses an MMC sub-module topology structure based on a clamping and energy transfer circuit, belonging to the field of high-power converter topology structure. The topology structure includes a half-bridge circuit, a clamping circuit and an energy transfer circuit. The invention has high stability, simple structure, and has the capability of controlling capacitance and voltage itself, and does not need traditional capacitance-voltage balance control; the circulating current AC component is small, and no circulating current suppression strategy is required.

Figure 201810889350

Description

MMC submodule topological structure based on clamping and energy transfer circuit
Technical Field
The invention relates to an MMC sub-module topological structure based on a clamping circuit and an energy transfer circuit, and belongs to the field of high-power converter topological structures.
Background
Modular Multilevel Converters (MMC) are widely used in the fields of flexible dc transmission systems, power quality management, energy storage, medium-high voltage power transmission, and the like, and are considered to be medium-high voltage high-power converters with the greatest development prospect. In the field of medium-high voltage high-power engineering, particularly in the field of power transmission and grid-connected converters, equipment is required to have high reliability, and even the equipment is required to have the capability of running without stopping when in failure. The MMC is a key device for completing energy conversion in the system, and the reliability of the MMC directly affects the reliability of the system. Because the sub-module is more in the MMC, the reliability of MMC can all be influenced to the reliability of every sub-module, leads to the reliability of MMC itself not high.
The direct connection of the upper and lower switching tubes is an important reason for failure of the MMC sub-module, and the conventional dead time is added to avoid the problem of reliability caused by the fact that switching signals are easily affected by factors such as interference and the like in the direct connection method of the upper and lower switching tubes. In addition, the MMC converter needs to adopt a balance control strategy to keep the sub-module capacitor voltage balance, so that the sub-module capacitor voltage information needs to be transmitted to the main controller by adopting optical fibers or other modes, the information transmission and control of the sub-module capacitor voltage increase the complexity of the system structure and the requirements of software and hardware resources of the main controller, and the working reliability of the converter is also influenced. The method for solving the direct connection and voltage balance problems is explored from the aspect of the sub-module structure, and the method has important significance for improving the working reliability of the MMC converter. This solution is not available in the prior art.
Disclosure of Invention
The purpose of the invention is as follows: the MMC converter has the problem of direct connection of bridge arm power tubes of a submodule which influences the working reliability, and therefore the invention provides an MMC submodule topological structure based on a clamping circuit and an energy transfer circuit.
The technical scheme is as follows: the MMC sub-module topological structure based on a clamping and energy transfer circuit is suitable for a modular multilevel converter based on a half-bridge sub-module and comprises a first power switch tube, a second power switch tube, a third switch tube, a fourth switch tube, first to third inductors, first to third diodes and first to third capacitors, wherein the first power switch tube and the second power switch tube comprise anti-parallel diodes; the emitter of the first power switch tube is connected with the collector of the second power switch tube, the collector of the first power switch tube is respectively connected with one end of the first inductor and the anode of the first diode, the other end of the first inductor, one end of the third inductor and the anode of the first capacitor are connected, the other end of the third inductor, the cathode of the third diode and the emitter of the third switch tube are connected, the collector of the third switch tube, the cathode of the second diode and the anode of the third capacitor are connected, the cathode of the first diode and one end of the second inductor are connected, the anode of the second capacitor is connected with the anode of the second diode, the other end of the second inductor and the collector of the fourth switching tube, and the emitter of the second power switching tube, the cathode of the first capacitor, the anode of the third diode, the cathode of the third capacitor, the emitter of the fourth switching tube and the cathode of the second capacitor are connected; and a collector and an emitter of the second power switch tube are respectively used as positive and negative output ends of the sub-module topological structure.
Has the advantages that:
(1) the submodule has the direct connection capability of a bridge arm switch tube and has high operation reliability;
(2) the submodule has the capacity of submodule capacitor voltage control, the traditional capacitor voltage balance control is not needed, the hardware structure of the system can be simplified, and the software design requirement can be reduced;
(3) the circulation alternating current component is small, and a circulation restraining strategy is not needed.
Drawings
FIG. 1 is a block diagram of a modular multilevel converter based on half-bridge sub-modules;
FIG. 2 is a topological structure diagram of the present invention;
FIG. 3 is a schematic diagram of the operation of the clamping circuit of the present invention;
FIG. 4 is a schematic diagram of the operation of the energy transfer circuit of the present invention;
FIG. 5 is a schematic diagram of the half bridge circuit of the present invention;
FIG. 6 is a control block diagram of a submodule of the present invention;
FIG. 7 is a steady state experimental waveform of the present invention;
fig. 8 is a waveform diagram of the through capability experiment of the present invention.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention.
As shown in fig. 1, each phase of the modular multilevel converter based on half-bridge sub-modules is formed by connecting an upper bridge arm and a lower bridge arm through two bridge arm inductors, each bridge arm includes N sub-modules, and the sub-modules are traditional sub-modules.
As shown in fig. 2, the topology of the present invention consists of a half-bridge circuit, a clamp circuit and an energy transfer circuit. The half-bridge circuit is composed of an inductor L1A capacitor C1And two NPN power switch tubes S containing anti-parallel diodes1And S2Composition L1Connecting capacitor C1Positive electrode of (2), L1The other end of the switch tube S is connected with a switch tube S1Collector electrode of, S1The emitter of (2) is connected with a switch tube S2Collector electrode of, S2Emitter electrode connection capacitor C1The negative electrode of (1).
The clamping circuit is composed of an inductor L1Two capacitors C1And C2And a power diode D1Are connected in series. Capacitor C2Is turning toPolar connection diode D1Negative electrode of (D)1Positive electrode of (2) is connected with an inductor L1Inductance L1The other end of the capacitor C is connected with a capacitor C1Positive electrode of (2), capacitor C1Negative pole of the capacitor C2The negative electrode of (1).
The energy transfer circuit is formed by cascading a voltage boosting circuit and a voltage reducing circuit, wherein the voltage boosting circuit is composed of two capacitors C2And C3An inductor L3A diode D3And a switching tube SZ2And (4) forming. Capacitor C2Positive electrode of (2) is connected with an inductor L2，L2The other end is connected with a switch tube SZ1Collector electrode of, SZ1Collector of the diode is connected with D2Positive electrode of (2), D2Negative pole of the capacitor C3Positive electrode of (2), capacitor C3Negative pole of (2) is connected with a switch tube SZ1An emitter of (1); the voltage reduction circuit is composed of two capacitors C1And C3An inductor L3A diode D3And a switching tube SZ2Composition is carried out; switch tube SZ2Is connected to the positive pole of a capacitor C, SZ2Emitter-connected diode D3Negative electrode of (1) and inductor L3，L3The other end of the capacitor C is connected with a capacitor C1Positive electrode of (2), capacitor C1Negative electrode of (2) is connected with a diode D3Anode of (2), diode D3Positive electrode of (2) is connected with a capacitor C3The negative electrode of (1).
As shown in fig. 3-5, which are schematic diagrams of the sub-module topology, in a half-bridge circuit when S is1And S2When conducting at the same time, the submodules are in a through state, C1Through L1Discharge, L1Increase in energy, C1The voltage drops, when the sub-module is switched from the through state to the non-through state, the clamping circuit starts to work, and the capacitor C1Continues through L1Discharge, D1Conduction, C1The voltage continues to drop, C2Voltage rises when L1Voltage vL1Plus C1Voltage vC1C or less2Voltage vC2When the output voltage of the submodule is vL1+vC1When v isL1Plus vC1Greater than vC2When the output voltage of the submodule is vC2(ii) a Capacitor C2Sub-module output voltages can be clamped; v. ofC1The bridge arm current rises when the bridge arm current is positive and falls when the bridge arm current is negative;
whether bridge arm current is positive or negative, C2The voltage continuously rises, when C is in the booster circuit2When the voltage is too high and is higher than the upper limit threshold value, SZ1Opening, C2Through L2Discharge when C2When the voltage is lower than the lower limit threshold value, SZ1Closing, D2Conduction, C2Through L2To C3Charging, C2Reduction in voltage, C3The voltage rises, the booster circuit will C2All energy increments of (2) are transferred to (C)3；
In addition, when the bridge arm current is negative, the capacitor C1Step-down, when C is in the step-down circuit1When the voltage is lower than the lower limit threshold value, SZ2Opening, C3Through L3To C1Discharging; when C is present1When the voltage is higher than the upper threshold, SZ2Closing, D3Conduction, L3By D3Free-wheeling loop feed C1And (6) charging. The voltage reduction unit realizes the conversion of C3Increased energy transfer to C1Above, in limit C3Maintaining C while applying voltage1The voltage is stable.
In order to keep the energy flowing through the sub-modules balanced, the inductances in the step-up and step-down circuits operate in an intermittent state.
FIG. 6 is a control block diagram of a submodule of the present invention. The submodule control strategy adopts a hysteresis comparison control strategy: (a) is shown in the figure when C2When the voltage is greater than the upper limit threshold value, the switch tube SZ1Is on when C2When the voltage is less than the lower threshold, the switch tube SZ1Closing;
(b) the figure is expressed as Sz2On and off condition, capacitor C3Voltage V ofc3When greater than the upper threshold, Vc1Control failure, Sz2Opening, Vc3When the upper limit threshold value is less than or equal to the lower limit threshold value, Vc1Control is effective in this stateIf Vc1Less than the lower threshold, Sz2Is turned on if Vc1Greater than the upper threshold value, Sz2Closing; vc3When the value is lower than the lower limit threshold value, Vc1Control failure, Sz2And closing. The circuit works at Vc1Controlling the active state.
Fig. 7 is a steady state experimental waveform of the present invention. As can be seen from fig. 7(a), the ac current amplitude is about 5A, and the harmonic content is only 2.1% and very small as calculated by the FFT of the oscilloscope. In fig. 7(b), the value of the circulating current fluctuation is 0.45A, which is 9% of the alternating current, indicating that the circulating current fluctuation is very small without the circulating current suppression algorithm. In FIG. 7(C), when the bridge arm current is positive, the capacitance C is set to zero2To C3Charging, C3The voltage is always increased, and C1Voltage quilt C2And (4) clamping. When the bridge arm current is negative, C1Voltage drop, C3To C1Charging, C3The voltage drops. C1The voltage is controlled and stabilized to fluctuate within the range of 23.5-25 v, C2The voltage is also stably controlled to fluctuate within the range of 28-30 v, C3The energy fluctuations are kept in balance.
Fig. 8 is a waveform diagram of the through capability experiment of the present invention. At t1At any moment, the upper and lower switch tubes of the submodule are conducted simultaneously, and the capacitor C1Discharge is initiated and its voltage begins to drop. After 25 mus, the direct connection state is changed into the normal working state, and the capacitor C1The voltage continues to drop and is supplied to C2Charging, C2The voltage rises. When the capacitance C2When the voltage is greater than the upper threshold, the capacitor C2Start to supply capacitor C3Charging, capacitance C3Rise in voltage, capacitance C2The voltage drops. And entering a normal working state after the process is finished.
It should be noted that the various features described in the above embodiments may be combined in any suitable manner without departing from the scope of the invention. The invention is not described in detail in order to avoid unnecessary repetition.

Claims (1)

1.基于箝位和能量转移电路的MMC子模块拓扑结构，其特征在于,包括两个含有反并联二极管的第一功率开关管和第二功率开关管，第三开关管，第四开关管，第一至第三电感，第一至第三二极管，以及第一至第三电容；第一功率开关管的发射极连接第二功率开关管的集电极，第一功率开关管的集电极分别连接第一电感的一端和第一二极管的阳极，第一电感的另一端、第三电感的一端、第一电容的正极相连接，第三电感的另一端、第三二极管的阴极、第三开关管的发射极相连接，第三开关管的集电极、第二二极管的阴极、第三电容的正极相连接，第一二极管的阴极、第二电感的一端、第二电容的正极相连接，第二二极管的阳极、第二电感的另一端、第四开关管的集电极相连接，第二功率开关管的发射极、第一电容的负极、第三二极管的阳极、第三电容的负极、第四开关管的发射极、第二电容的负极相连接；所述第二功率开关管的集电极和发射极分别作为子模块拓扑结构的正负输出端。1. based on the MMC sub-module topology of clamping and energy transfer circuit, it is characterized in that, comprises two first power switch tubes and second power switch tubes containing anti-parallel diodes, the third switch tube, the fourth switch tube, The first to third inductors, the first to third diodes, and the first to third capacitors; the emitter of the first power switch is connected to the collector of the second power switch, and the collector of the first power switch Connect one end of the first inductor and the anode of the first diode respectively, the other end of the first inductor, one end of the third inductor, and the positive electrode of the first capacitor are connected, and the other end of the third inductor and the anode of the third diode are connected. The cathode and the emitter of the third switch tube are connected, the collector of the third switch tube, the cathode of the second diode, and the anode of the third capacitor are connected, the cathode of the first diode, one end of the second inductor, The anode of the second capacitor is connected, the anode of the second diode, the other end of the second inductor, and the collector of the fourth switch are connected, the emitter of the second power switch, the cathode of the first capacitor, the third The anode of the diode, the cathode of the third capacitor, the emitter of the fourth switch tube, and the cathode of the second capacitor are connected; the collector and the emitter of the second power switch tube are respectively used as the positive and negative poles of the sub-module topology. output.
CN201810889350.6A 2018-08-07 2018-08-07 MMC submodule topological structure based on clamping and energy transfer circuit Expired - Fee Related CN109039128B (en)

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CN111585460A (en) * 2020-06-10 2020-08-25 南京工程学院 Modular multilevel converter submodule topological structure
CN111585459A (en) * 2020-06-10 2020-08-25 南京工程学院 Modular multilevel converter submodule topological structure based on bidirectional quasi-Z source and working method thereof

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