阅读说明：本技术 一种级联型灵活交流链变换器拓扑结构 (Topological structure of cascade flexible alternating current chain converter ) 是由 刘闯 蔡国伟 朱炳达 张瀚文 郭东波 王艺博 于 2019-10-16 设计创作，主要内容包括：本发明公开了一种级联型灵活交流链变换器拓扑结构,包括三相交流电源、3个功率调节单元、3个Buck型直接式AC-AC变换器UT-AC、三相多绕组隔离变压器、3个LC低通滤波器；其中,每个功率调节单元由两个双极性直接式AC-AC变换器BT-AC组成。本发明的拓扑结构能够控制互联馈线之间的潮流,实现配电网馈线的柔性互联故障情况下,可以实现对于隔离负载的恢复供电；通过对配电网中馈线的柔性互联,能够提高分布式发电在配电网中的渗透率,提高配电网的电能质量和供电可靠性。(The invention discloses a topological structure of a cascade flexible alternating current chain converter, which comprises a three-phase alternating current power supply, 3 power regulating units, 3 Buck type direct AC-AC converters UT-AC, a three-phase multi-winding isolation transformer and 3 LC low-pass filters, wherein the three-phase direct AC-AC converters UT-AC are connected with the three-phase multi-winding isolation transformer; wherein each power conditioning unit consists of two bipolar direct AC-AC converters BT-AC. The topological structure can control the power flow among the interconnected feeders, and can realize the recovery power supply of the isolated load under the condition of flexible interconnection faults of the feeder of the power distribution network; through the flexible interconnection of the feeders in the power distribution network, the permeability of distributed power generation in the power distribution network can be improved, and the power quality and the power supply reliability of the power distribution network are improved.)

1. A topological structure of a cascade flexible alternating current chain converter is characterized in that: the three-phase direct AC-AC converter comprises a three-phase AC power supply, 3 power adjusting units, 3 Buck type direct AC-AC converters UT-AC, a three-phase multi-winding isolation transformer and 3 LC low-pass filters; each power regulating unit consists of two bipolar direct AC-AC converters BT-AC;

a feeder terminal node A, B, C three-phase AC power source is connected to the primary side of the three-phase multi-winding isolation transformer; the secondary side of the three-phase multi-winding isolation transformer comprises 9 windings, each single-phase comprises 3 windings, and each single-phase comprises 3 windings which are respectively and correspondingly used for supplying power for 1 UT-AC and 2 BT-AC; the negative electrode of the output port of the A-phase UT-AC converter is connected with the positive electrode of the output port of the B-phase BT-AC converter; the negative electrode of the output port of the B-phase BT-AC converter is connected with the positive electrode of the output port of the C-phase BT-AC converter; the positive electrode of the output port of the A-phase UT-AC converter and the negative electrode of the output port of the C-phase BT-AC converter form an output two-port, the positive electrode of the output two-port is connected to the tail end of the other feeder line, and the negative electrode of the output two-port and the negative electrodes of the other two-phase output two-port are connected to a point N2;

the B, C phase was grafted to phase A.

2. The cascaded flexible ac link converter topology of claim 1, wherein: the power regulating unit of the phase A consists of two bipolar direct AC-AC converters BT-AC; a secondary side winding Tb2 of the phase B transformer is the alternating current input of the BT-AC converter Ba; a secondary side winding Tc2 of the phase C transformer is the alternating current input of the BT-AC converter Ca; the negative electrode of the Ba output two-port of the converter is connected with the positive electrode of the Ca output two-port of the converter to form a power conversion unit applied to the A phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of the two output ports of the converter Ba, and the cathode of the power conversion unit is the cathode of the two output ports of the converter Ca;

the B-phase power regulating unit consists of two bipolar direct AC-AC converters; the secondary side winding Ta3 of the phase A transformer is the alternating current input of the BT-AC converter Ab; a secondary side winding Tc3 of the C phase transformer is an alternating current input of the BT-AC converter Cb; the negative electrode of the two output ports of the converter Ab is connected with the positive electrode of the two output ports of the converter Cb to form a power conversion unit applied to the B phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of the output two ports of the converter Ab, and the cathode of the power conversion unit is the cathode of the output two ports of the converter Cb;

the power regulating unit of the C phase consists of two bipolar direct AC-AC converters; a secondary side winding Ta4 of the phase A transformer is an alternating current input of the BT-AC converter Ac; a secondary side winding Tb4 of the phase B transformer is the alternating current input of the BT-AC converter Bc; the negative electrode of the AC output two-port of the converter is connected with the positive electrode of the Bc output two-port of the converter to form a power conversion unit applied to the C phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of two output ports of the converter Ac, and the cathode of the power conversion unit is the cathode of two output ports of the converter Bc.

3. The cascaded flexible ac link converter topology of claim 1, wherein: the bipolar direct AC-AC converter BT-AC consists of an input filter capacitor, an H bridge and a signal control unit; the H bridge is composed of a positive bridge arm and a negative bridge arm;

the input filter capacitor is a high-frequency thin-film capacitor; one end of the input filter capacitor is connected with the anode of the single-phase alternating current input, and the other end of the input filter capacitor is connected with the cathode of the single-phase alternating current input; each bridge arm of the H bridge consists of 4 full-control power switch tubes and 1 clamping capacitor; one end of the positive and negative bridge arms is connected with the positive pole of the single-phase alternating current power supply, and the other end of the positive and negative bridge arms is connected with the negative pole; the positive and negative bridge arms have an output port to ground, and the two bridge arms form two-end output ports.

4. As claimed inThe bipolar direct AC-AC converter BT-AC of claim 3, characterized in that: the fully-controlled power switch tube of the positive-polarity bridge arm is S from top to bottom in sequence₂、S₁、S_1c、S_2c；S₂Is connected with the positive electrode of the single-phase alternating current power supply, and the collector is connected with S₁Is connected with the collector of the collector; s₁Emitter and S_1cCollector electrode connection of S_1cEmitter and S_2cThe emitter of (3) is connected; s_2cThe collector of the single-phase alternating current power supply is connected with the negative electrode of the single-phase alternating current power supply; clamping capacitor C₃One end and S₁Is connected with the collector of the other end of the collector and S_1cThe emitting electrodes are connected; the output end of the positive bridge arm is connected with a switch tube S₁Emitter and S_1cIs led out between the collectors.

5. A bipolar direct AC-AC converter BT-AC according to claim 3, wherein: the fully-controlled power switch tube forming the negative bridge arm is S from top to bottom_2p、S_1p、S_1cp、S_2cp；S_2pIs connected with the positive electrode of the single-phase alternating current power supply, and the collector is connected with S_1pIs connected with the collector of the collector; s_1pEmitter and S_1cpIs connected with the collector of the collector; s_1cpEmitter and S_2cpThe emitter of (3) is connected; s_2cpThe collector of the single-phase alternating current power supply is connected with the negative electrode of the single-phase alternating current power supply; clamping capacitor C₂Clamped in the switching tube S_1pCollector electrode of (1) and S_1cpIs led out from between the emitters.

6. The cascaded flexible ac link converter topology of claim 1, wherein: the Buck type direct AC-AC converter UT-AC has one phase; the Buck type direct AC-AC converter UT-AC consists of an alternating current input power supply, two input capacitors and four fully-controlled power switch tubes IGBT; the negative electrode of the capacitor C1 is connected with the positive electrode of the capacitor C2; the positive electrode of the capacitor C1 is connected with the positive electrode of the power supply; the negative electrode of the capacitor C2 is connected with the negative electrode of the power supply; the four IGBTs are T1, T2, T3 and T4 from top to bottom in sequence; the collector of T1 is connected with the positive electrode of C1, and the emitter is connected with the collector of T2; the emitter of T2 is connected to the emitter of T3; the collector of T3 is connected with the emitter of T4; the collector of the T4 is connected with the negative electrode of the capacitor C2; the cathode of the C1 is connected with the emitter of the T2; the emitter of the T1 is the positive output of the bridge arm, the collector of the T3 is the negative output of the bridge arm, and the two ports form two output ports of the UT-AC of the Buck type direct AC-AC converter.

7. The cascaded flexible ac link converter topology of claim 1, wherein: the phase A input winding of the three-phase multi-winding isolation transformer is Ta1, the phase A output winding is Ta2, Ta3 and Ta4, and the transformation ratio is Ta 1: ta 2: ta 3: ta4 ═ 2: 2: 1: 1; the phase B input winding is Tb1, the phase B output winding is Tb2, Tb3 and Tb4, and the transformation ratio is Tb 1: tb 2: tb 3: tb4 ═ 2: 2: 1: 1; the phase C input winding is Tc1, the phase C output winding is Tc2, Tc3 and Tc4, the transformation ratio is Tc 1: tc 2: tc 3: tc4 ═ 2: 2: 1: 1; all windings of the transformer are isolated.

8. The cascaded flexible ac link converter topology of claim 1, wherein: one for each phase of the LC low-pass filter; the LC low-pass filter consists of an output filter inductor and an output filter capacitor; the inductor L and the capacitor C form two ports; and the input two ports of the LC low-pass filter are connected with the output two ports of each cascaded module, and the output port is the voltage output port of each phase.

9. The cascaded flexible ac link converter topology of claim 1, wherein: a terminal node A, B, C of a feeder line is connected with input windings Ta1, Tb1 and Tc1 of a three-phase multi-winding isolation transformer correspondingly; the phase A is connected with the anode of the winding Ta1, the phase B is connected with the anode of the winding Tb1, and the phase C is connected with the anode of the winding Tc 1; the negative electrodes of the windings Ta1, Tb1 and Tc1 are connected together, and the connection point is N1; a secondary side winding Ta2 of the phase A transformer is connected with the input end of a Buck type direct AC-AC converter Aa, a winding Ta3 is connected with the input end of a BT-AC converter Ab, and a winding Ta4 is connected with the input end of the BT-AC converter Ac; a secondary side winding Tb2 of the phase-B transformer is connected with the input end of the BT-AC converter Ba, a winding Tb3 is connected with the input end of the Buck type direct AC-AC converter Bb, and a winding Tb4 is connected with the input end of the BT-AC converter Bc; a secondary side winding Tc2 of the C phase transformer is connected with the input end of the BT-AC converter Ca, a winding Tc3 is connected with the input end of the BT-AC converter Cb, and a winding Tc4 is connected with the input end of the Buck type direct AC-AC converter Cc; the cathode of the output port of the Aa converter is connected with the anode of the output port of the Ba converter, and the cathode of the output port of the Ba converter is connected with the anode of the output port of the Ca converter; the negative pole of the output port of the Ab converter is connected with the positive pole of the output port of the Bb converter, and the negative pole of the output port of the Bb converter is connected with the positive pole of the output port of the Cb converter; the negative pole of the output port of the Ac converter is connected with the positive pole of the output port of the Bc converter, and the negative pole of the output port of the Bc converter is connected with the positive pole of the output port of the Cc converter; the negative electrode of the output port of the Ca converter, the negative electrode of the output port of the Cb converter and the negative electrode of the output port of the Cc converter are connected together, and the connection point is N2; aa. Ba and Ca share one LC filter; ab. Bb and Cb share one LC filter; ac. Bc and Cc share one LC filter; the input two ports of each phase of filter are connected with the output two ports of all the cascaded modules of each phase; the positive pole of the output port of the Aa converter, the positive pole of the output port of the Ab converter and the positive pole of the output port of the Ac converter are A, B, C three-phase voltage outputs correspondingly and are connected to the tail end of the other feeder line.

Technical Field

The invention belongs to the technical field of flexible interconnection of power distribution networks, and particularly relates to a topological structure of a cascade flexible alternating current chain converter.

Background

The rapid increase of the grid-connected capacity of distributed renewable energy power generation, the large-scale access of novel loads represented by electric vehicles, the continuous change of power structures and types and the increasingly diversified load characteristics have widely and profound influences on the current power distribution network. The main performance is as follows: the power flow direction is increasingly complex, the load fluctuation is aggravated, the single power supply radial structure is changed into an active network structure, the problem of electric energy quality such as voltage out-of-limit is increasingly prominent, and the power supply reliability is reduced. The renewable energy power generation represented by photovoltaic and wind power has typical intermittence and randomness, the change rate of the power generation output along with the time scale and the geographical range is relatively high, the time sequence characteristics of the output and the load of the renewable energy on the same feeder line determine the dislocation of the high-output time period and the heavy-load time period of the renewable energy, and the power quality and the renewable energy consumption of a power distribution network are adversely affected. In addition, the operation of the power distribution network also faces the problems of ring opening and ring closing of the electromagnetic looped network, improvement of the balance degree of the load rate, optimal control of reactive voltage, avoidance of short-time power supply interruption and the like. Around these problems, researchers at home and abroad propose various solutions such as real-time reconstruction, active power distribution network layered distributed control and demand side response. However, flexible interconnection of power distribution networks is an important basis for implementing the above solutions, and conventional interconnection methods lack sufficient controllability and flexibility. Current distribution networks typically rely on sectionalizing and tie switches and transformer taps for interconnection. The sectional switch and the interconnection switch only have two states of opening and closing, the response speed is generally in the second level, the opening and closing action times are also clearly limited, the adjustment capability is not provided, and the short-circuit current can be increased. The distribution transformer is a scheme with adjustment capability by adding taps, but the adjustment flexibility by adopting taps is limited, the adjustment range is narrow, and the adjustment precision is low. Therefore, the traditional equipment of the current power distribution network cannot meet the operation requirements of the current power distribution network on intellectualization, refinement and real-time operation.

Along with the rapid development of power electronic transformation technology, the distribution network flexible interconnection equipment based on the power electronic technology receives extensive attention and research, compares with traditional interconnection switch, and the flexible interconnection equipment based on the power electronic technology not only possesses two kinds of states of opening and shutting, does not have the restriction of mechanical type switch action number of times moreover, has increased the continuous controllable state of power, has concurrently that the operation is flexible to be switched, control mode characteristics such as nimble various. The flexible direct-current transmission system draws much attention, and researchers consider whether VSC-HVDC can be used for an urban power distribution network before and after 2003, but because an IGBT series converter is required to be adopted, the research difficulty is high, the manufacturing cost is high, the loss is high, and therefore related research only stays at the conceptual level. The british university of empire and state university provides a Soft normal-Open Point (SNOP) concept, the SNOP can accurately control the active power and the reactive power of feeders on two sides connected with the SNOP, the power supply mode of the traditional power distribution network in closed-loop design and Open-loop operation is changed, the power supply reliability of the power distribution network is improved, and the balance degree of load factor is improved. At present, SNOP equipment based on a Modular Multilevel Converter (MMC) topological structure becomes a mainstream technology, and the MMC is used for new energy grid connection or power transmission network partition interconnection in a plurality of projects at home and abroad due to the advantage that the MMC can be produced in a modular mode. However, some of the characteristics of VSC-HVDC of the MMC type may be detrimental to its application in the distribution network. The MMC adopts two-stage power conversion of AC/DC/AC based on a fully-controlled device (such as IGBT), so that the efficiency of a converter is reduced, and the difficulty of fault protection of a direct current side is increased. Furthermore, a large number of dc side capacitors must be used in the MMC topology, which results in an excessively large and costly equipment. The SNOP equipment based on MMC has the great advantage that asynchronous interconnection can be realized, but almost no demand is made in the aspect of power distribution network.

Disclosure of Invention

The invention aims to provide a topological structure of a cascade flexible alternating current chain converter, which can control the power flow among interconnected feeders and realize the flexible interconnection of the feeders of a power distribution network.

The technical scheme adopted by the invention is that the topological structure of the cascade flexible alternating current chain converter comprises a three-phase alternating current power supply, 3 power adjusting units, 3 Buck type direct AC-AC converters UT-AC, a three-phase multi-winding isolation transformer and 3 LC low-pass filters; each power regulating unit consists of two bipolar direct AC-AC converters BT-AC;

a feeder terminal node A, B, C three-phase AC power source is connected to the primary side of the three-phase multi-winding isolation transformer; the secondary side of the three-phase multi-winding isolation transformer comprises 9 windings, each single-phase comprises 3 windings, and each single-phase comprises 3 windings which are respectively and correspondingly used for supplying power for 1 UT-AC and 2 BT-AC; the negative electrode of the output port of the A-phase UT-AC converter is connected with the positive electrode of the output port of the B-phase BT-AC converter; the negative electrode of the output port of the B-phase BT-AC converter is connected with the positive electrode of the output port of the C-phase BT-AC converter; the positive electrode of the output port of the A-phase UT-AC converter and the negative electrode of the output port of the C-phase BT-AC converter form an output two-port, the positive electrode of the output two-port is connected to the tail end of the other feeder line, and the negative electrode of the output two-port and the negative electrodes of the other two-phase output two-port are connected to a point N2;

the B, C phase was grafted to phase A.

The invention is also characterized in that:

the power regulating unit of the A phase consists of two bipolar direct AC-AC converters BT-AC; a secondary side winding Tb2 of the phase B transformer is the alternating current input of the BT-AC converter Ba; a secondary side winding Tc2 of the phase C transformer is the alternating current input of the BT-AC converter Ca; the negative electrode of the Ba output two-port of the converter is connected with the positive electrode of the Ca output two-port of the converter to form a power conversion unit applied to the A phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of the two output ports of the converter Ba, and the cathode of the power conversion unit is the cathode of the two output ports of the converter Ca;

the power regulating unit of the B phase consists of two bipolar direct AC-AC converters; the secondary side winding Ta3 of the phase A transformer is the alternating current input of the BT-AC converter Ab; a secondary side winding Tc3 of the C phase transformer is an alternating current input of the BT-AC converter Cb; the negative electrode of the two output ports of the converter Ab is connected with the positive electrode of the two output ports of the converter Cb to form a power conversion unit applied to the B phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of the output two ports of the converter Ab, and the cathode of the power conversion unit is the cathode of the output two ports of the converter Cb;

the power regulating unit of the C phase consists of two bipolar direct AC-AC converters; a secondary side winding Ta4 of the phase A transformer is an alternating current input of the BT-AC converter Ac; a secondary side winding Tb4 of the phase B transformer is the alternating current input of the BT-AC converter Bc; the negative electrode of the AC output two-port of the converter is connected with the positive electrode of the Bc output two-port of the converter to form a power conversion unit applied to the C phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of two output ports of the converter Ac, and the cathode of the power conversion unit is the cathode of two output ports of the converter Bc.

The bipolar direct AC-AC converter BT-AC consists of an input filter capacitor, an H bridge and a signal control unit; the H bridge is composed of a positive bridge arm and a negative bridge arm;

the input filter capacitor is a high-frequency thin-film capacitor; one end of the input filter capacitor is connected with the anode of the single-phase alternating current input, and the other end of the input filter capacitor is connected with the cathode of the single-phase alternating current input; each bridge arm of the H bridge consists of 4 full-control power switch tubes and 1 clamping capacitor; one end of the positive and negative bridge arms is connected with the positive pole of the single-phase alternating current power supply, and the other end of the positive and negative bridge arms is connected with the negative pole; the positive and negative bridge arms have an output port to ground, and the two bridge arms form two-end output ports.

The fully-controlled power switch tube of the positive-polarity bridge arm is S from top to bottom in sequence₂、S₁、S_1c、S_2c；S₂Is connected with the positive electrode of the single-phase alternating current power supply, and the collector is connected with S₁Is connected with the collector of the collector; s₁Emitter and S_1cCollector electrode connection of S_1cEmitter and S_2cThe emitter of (3) is connected; s_2cThe collector of the single-phase alternating current power supply is connected with the negative electrode of the single-phase alternating current power supply; clamping capacitor C₃One end and S₁Is connected with the collector of the other end of the collector and S_1cThe emitting electrodes are connected; the output end of the positive bridge arm is connected with a switch tube S₁Emitter and S_1cIs led out between the collectors.

Fully-controlled power forming negative-polarity bridge armThe switch tube is S from top to bottom_2p、S_1p、S_1cp、S_2cp；S_2pIs connected with the positive electrode of the single-phase alternating current power supply, and the collector is connected with S_1pIs connected with the collector of the collector; s_1pEmitter and S_1cpIs connected with the collector of the collector; s_1cpEmitter and S_2cpThe emitter of (3) is connected; s_2cpThe collector of the single-phase alternating current power supply is connected with the negative electrode of the single-phase alternating current power supply; clamping capacitor C₂Clamped in the switching tube S_1pCollector electrode of (1) and S_1cpIs led out from between the emitters.

One for each phase of the Buck type direct AC-AC converter UT-AC; the Buck type direct AC-AC converter UT-AC consists of an alternating current input power supply, two input capacitors and four fully-controlled power switch tubes IGBT; the negative electrode of the capacitor C1 is connected with the positive electrode of the capacitor C2; the positive electrode of the capacitor C1 is connected with the positive electrode of the power supply; the negative electrode of the capacitor C2 is connected with the negative electrode of the power supply; the four IGBTs are T1, T2, T3 and T4 from top to bottom in sequence; the collector of T1 is connected with the positive electrode of C1, and the emitter is connected with the collector of T2; the emitter of T2 is connected to the emitter of T3; the collector of T3 is connected with the emitter of T4; the collector of the T4 is connected with the negative electrode of the capacitor C2; the cathode of the C1 is connected with the emitter of the T2; the emitter of the T1 is the positive output of the bridge arm, the collector of the T3 is the negative output of the bridge arm, and the two ports form two output ports of the UT-AC of the Buck type direct AC-AC converter.

The phase A input winding of the three-phase multi-winding isolation transformer is Ta1, the phase A output winding is Ta2, Ta3 and Ta4, and the transformation ratio is Ta 1: ta 2: ta 3: ta4 ═ 2: 2: 1: 1; the phase B input winding is Tb1, the phase B output winding is Tb2, Tb3 and Tb4, and the transformation ratio is Tb 1: tb 2: tb 3: tb4 ═ 2: 2: 1: 1; the phase C input winding is Tc1, the phase C output winding is Tc2, Tc3 and Tc4, the transformation ratio is Tc 1: tc 2: tc 3: tc4 ═ 2: 2: 1: 1; all windings of the transformer are isolated.

One for each phase of the LC low pass filter; the LC low-pass filter consists of an output filter inductor and an output filter capacitor; the inductor L and the capacitor C form two ports; and the input two ports of the LC low-pass filter are connected with the output two ports of each cascaded module, and the output port is the voltage output port of each phase.

A terminal node A, B, C of a feeder line is connected with input windings Ta1, Tb1 and Tc1 of a three-phase multi-winding isolation transformer correspondingly; the phase A is connected with the anode of the winding Ta1, the phase B is connected with the anode of the winding Tb1, and the phase C is connected with the anode of the winding Tc 1; the negative electrodes of the windings Ta1, Tb1 and Tc1 are connected together, and the connection point is N1; a secondary side winding Ta2 of the phase A transformer is connected with the input end of a Buck type direct AC-AC converter Aa, a winding Ta3 is connected with the input end of a BT-AC converter Ab, and a winding Ta4 is connected with the input end of the BT-AC converter Ac; a secondary side winding Tb2 of the phase-B transformer is connected with the input end of the BT-AC converter Ba, a winding Tb3 is connected with the input end of the Buck type direct AC-AC converter Bb, and a winding Tb4 is connected with the input end of the BT-AC converter Bc; a secondary side winding Tc2 of the C phase transformer is connected with the input end of the BT-AC converter Ca, a winding Tc3 is connected with the input end of the BT-AC converter Cb, and a winding Tc4 is connected with the input end of the Buck type direct AC-AC converter Cc; the cathode of the output port of the Aa converter is connected with the anode of the output port of the Ba converter, and the cathode of the output port of the Ba converter is connected with the anode of the output port of the Ca converter; the negative pole of the output port of the Ab converter is connected with the positive pole of the output port of the Bb converter, and the negative pole of the output port of the Bb converter is connected with the positive pole of the output port of the Cb converter; the negative pole of the output port of the Ac converter is connected with the positive pole of the output port of the Bc converter, and the negative pole of the output port of the Bc converter is connected with the positive pole of the output port of the Cc converter; the negative electrode of the output port of the Ca converter, the negative electrode of the output port of the Cb converter and the negative electrode of the output port of the Cc converter are connected together, and the connection point is N2; aa. Ba and Ca share one LC filter; ab. Bb and Cb share one LC filter; ac. Bc and Cc share one LC filter; the input two ports of each phase of filter are connected with the output two ports of all the cascaded modules of each phase; the positive pole of the output port of the Aa converter, the positive pole of the output port of the Ab converter and the positive pole of the output port of the Ac converter are A, B, C three-phase voltage outputs correspondingly and are connected to the tail end of the other feeder line.

The invention has the beneficial effects that:

(1) compared with the traditional AC-AC converter topological structure, the BT-AC converter adopted by the structure can realize safe current conversion without a lossy RC buffer circuit and a special current conversion strategy, so that the reliability of the converter is improved;

(2) the power conversion unit of the invention works in buck/boost mode no matter what angle and amplitude voltage is output, except for the locking mode, the output current is not interrupted; meanwhile, the output voltage range is wide, the phase angle range is 360 degrees, and the amplitude range can be adjusted randomly along with the transformer transformation ratio;

(3) compared with the SOP adopting SSSC, the invention can continuously and flexibly adjust the active power and the reactive power between the feeders, and the power adjusting range can be improved along with the change of the transformer; in addition, the regulation of the active power and the reactive power is decoupled within a certain range, and the independent control of the active power and the reactive power can be realized;

(4) when a fault occurs, the Buck type direct AC-AC converter can be used for disconnecting the two feeder lines, so that the protection of a power grid and a load is realized, and uninterrupted power supply can be provided for the load;

(5) compared with other types of SOPs, the invention has no direct current link and no energy storage equipment, does not need to convert electric energy for many times, has better stability, improves the efficiency and the reliability of the device, and effectively reduces the volume and the cost of the device;

(6) the topological structure can control the power flow among the interconnected feeders, and can realize the recovery power supply of the isolated load under the condition of flexible interconnection faults of the feeder of the power distribution network; through the flexible interconnection of the feeders in the power distribution network, the permeability of distributed power generation in the power distribution network can be improved, and the power quality and the power supply reliability of the power distribution network are improved.

Drawings

FIG. 1 is a schematic diagram of the electrical connections of the converter topology of the present invention;

FIG. 2 is a schematic diagram of the connection of the converter topology of the present invention in a feeder;

FIG. 3 is a schematic diagram of the electrical connections of the power conditioning units in the converter topology of the present invention;

FIG. 4 is a topology block diagram of a BT-AC converter in the converter topology of the present invention;

FIG. 5 is a control schematic of the BT-AC converter in the converter topology of the present invention;

FIG. 6 is a block diagram of the topology of the UT-AC converter in the converter topology of the present invention;

FIG. 7 is a voltage regulation schematic of the converter topology of the present invention;

fig. 8 shows the transformer transformation ratio of 1 in the converter topology of the present invention: 1: 1: voltage compensation range diagram at 1;

FIG. 9 is a schematic diagram of an LC low pass filter in the converter topology of the present invention;

FIG. 10 is a graph of the amplitude modulated value mode output positive polarity compensation voltage waveform of the converter topology of the present invention;

FIG. 11 is a graph of an amplitude modulated value mode output negative polarity compensation voltage waveform for a converter topology of the present invention;

FIG. 12 is a phase modulation mode hysteretic compensation output voltage waveform diagram of a converter topology of the present invention;

FIG. 13 is a phase modulation mode lead compensated output voltage waveform diagram of the converter topology of the present invention;

FIG. 14 is a graph of the phase shift voltage regulation mode output voltage waveform of the converter topology of the present invention;

fig. 15 is a graph of the output waveform of the converter topology of the present invention with resistive loading.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1 and fig. 2, the topology structure of the cascade-type flexible AC chain converter of the present invention includes a three-phase AC power supply, 3 power conditioning units, 3 Buck-type direct AC-AC converters UT-AC, a three-phase multi-winding isolation transformer, and 3 LC low-pass filters; each power regulating unit consists of two bipolar direct AC-AC converters BT-AC;

a feeder terminal node A, B, C three-phase AC power source is connected to the primary side of the three-phase multi-winding isolation transformer; the secondary side of the three-phase multi-winding isolation transformer comprises 9 windings, each single-phase comprises 3 windings, and each single-phase comprises 3 windings which are respectively and correspondingly used for supplying power for 1 UT-AC and 2 BT-AC; the negative electrode of the output port of the A-phase UT-AC converter is connected with the positive electrode of the output port of the B-phase BT-AC converter; the negative electrode of the output port of the B-phase BT-AC converter is connected with the positive electrode of the output port of the C-phase BT-AC converter; the positive electrode of the output port of the A-phase UT-AC converter and the negative electrode of the output port of the C-phase BT-AC converter form an output two-port, the positive electrode of the output two-port is connected to the tail end of the other feeder line, and the negative electrode of the output two-port and the negative electrodes of the other two-phase output two-port are connected to a point N2;

B. the phase C is connected with the phase A.

As shown in fig. 3, the power conditioning unit of phase a is composed of two bipolar direct AC-AC converters BT-AC; a secondary side winding Tb2 of the phase B transformer is the alternating current input of the BT-AC converter Ba; a secondary side winding Tc2 of the phase C transformer is the alternating current input of the BT-AC converter Ca; the negative electrode of the Ba output two-port of the converter is connected with the positive electrode of the Ca output two-port of the converter to form a power conversion unit applied to the A phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of the two output ports of the converter Ba, and the cathode of the power conversion unit is the cathode of the two output ports of the converter Ca;

the power regulating unit of the B phase consists of two bipolar direct AC-AC converters; the secondary side winding Ta3 of the phase A transformer is the alternating current input of the BT-AC converter Ab; a secondary side winding Tc3 of the C phase transformer is an alternating current input of the BT-AC converter Cb; the negative electrode of the two output ports of the converter Ab is connected with the positive electrode of the two output ports of the converter Cb to form a power conversion unit applied to the B phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of the output two ports of the converter Ab, and the cathode of the power conversion unit is the cathode of the output two ports of the converter Cb;

the power regulating unit of the C phase consists of two bipolar direct AC-AC converters; a secondary side winding Ta4 of the phase A transformer is an alternating current input of the BT-AC converter Ac; a secondary side winding Tb4 of the phase B transformer is the alternating current input of the BT-AC converter Bc; the negative electrode of the AC output two-port of the converter is connected with the positive electrode of the Bc output two-port of the converter to form a power conversion unit applied to the C phase; the output of the power conversion unit is two ports, the anode of the power conversion unit is the anode of two output ports of the converter Ac, and the cathode of the power conversion unit is the cathode of two output ports of the converter Bc.

The bipolar direct AC-AC converter BT-AC consists of an input filter capacitor, an H bridge and a signal control unit; the H bridge is composed of a positive bridge arm and a negative bridge arm;

the input filter capacitor is a high-frequency thin-film capacitor; one end of the input filter capacitor is connected with the anode of the single-phase alternating current input, and the other end of the input filter capacitor is connected with the cathode of the single-phase alternating current input; each bridge arm of the H bridge consists of 4 full-control power switch tubes and 1 clamping capacitor; one end of the positive and negative bridge arms is connected with the positive pole of the single-phase alternating current power supply, and the other end of the positive and negative bridge arms is connected with the negative pole; the positive and negative bridge arms have an output port to ground, and the two bridge arms form two-end output ports.

The fully-controlled power switch tube of the positive-polarity bridge arm is S from top to bottom in sequence₂、S₁、S_1c、S_2c；S₂Is connected with the positive electrode of the single-phase alternating current power supply, and the collector is connected with S₁Is connected with the collector of the collector; s₁Emitter and S_1cCollector electrode connection of S_1cEmitter and S_2cThe emitter of (3) is connected; s_2cThe collector of the single-phase alternating current power supply is connected with the negative electrode of the single-phase alternating current power supply; clamping capacitor C₃One end and S₁Is connected with the collector of the other end of the collector and S_1cThe emitting electrodes are connected; the output end of the positive bridge arm is connected with a switch tube S₁Emitter and S_1cIs led out between the collectors.

The fully-controlled power switch tube forming the negative bridge arm is S from top to bottom_2p、S_1p、S_1cp、S_2cp；S_2pIs connected with the positive electrode of the single-phase alternating current power supply, and the collector is connected with S_1pIs connected with the collector of the collector; s_1pEmitter and S_1cpIs connected with the collector of the collector; s_1cpEmitter and S_2cpThe emitter of (3) is connected; s_2cpThe collector of the single-phase alternating current power supply is connected with the negative electrode of the single-phase alternating current power supply; clamping capacitor C₂Clamped in the switching tube S_1pCollector electrode of (1) and S_1cpIs led out from between the emitters.

FIG. 4 shows a bipolar direct AC-AC converter BT-an AC topology; as can be seen from FIG. 7, the input of the BT-AC converter is connected to a single-phase AC power supply, and the converter obtains 50Hz sinusoidal AC power V from the power supply_inAnd the electric energy is converted by a BT-AC converter and then is transmitted to the input end of an LC low-pass filter, and the 50Hz sine alternating current is obtained after filtering.

FIG. 5 is a schematic diagram of the control of a bipolar direct AC-AC inverter BT-AC; wherein Vin is the input voltage of a single-phase power frequency alternating current power supply, and d1 and d2 are the modulation ratios of a positive bridge arm and a negative bridge arm of the AC-AC converter respectively; uc is frequency 12 kHz; a triangular carrier of peaks 0 to 1; the input voltage Vin is compared with the 0 potential to generate a square wave signal of 50Hz, the modulation wave is compared with the triangular carrier to generate another square wave signal, the two square wave signals are subjected to logical operation to generate a PWM (pulse-width modulation) driving signal for driving the corresponding switching tube, when the driving signal is at a high level, the corresponding switching tube is switched on, and when the driving signal is at a 0 level, the corresponding switching tube is switched off.

As shown in fig. 6, the Buck-type direct AC-AC converter UT-AC has one phase per phase; the Buck type direct AC-AC converter UT-AC consists of an alternating current input power supply, two input capacitors and four fully-controlled power switch tubes IGBT; the negative electrode of the capacitor C1 is connected with the positive electrode of the capacitor C2; the positive electrode of the capacitor C1 is connected with the positive electrode of the power supply; the negative electrode of the capacitor C2 is connected with the negative electrode of the power supply; the four IGBTs are T1, T2, T3 and T4 from top to bottom in sequence; the collector of T1 is connected with the positive electrode of C1, and the emitter is connected with the collector of T2; the emitter of T2 is connected to the emitter of T3; the collector of T3 is connected with the emitter of T4; the collector of the T4 is connected with the negative electrode of the capacitor C2; the cathode of the C1 is connected with the emitter of the T2; the emitter of the T1 is the positive output of the bridge arm, the collector of the T3 is the negative output of the bridge arm, and the two ports form two output ports of the UT-AC of the Buck type direct AC-AC converter.

The phase A input winding of the three-phase multi-winding isolation transformer is Ta1, the phase A output winding is Ta2, Ta3 and Ta4, and the transformation ratio is Ta 1: ta 2: ta 3: ta4 ═ 2: 2: 1: 1; the phase B input winding is Tb1, the phase B output winding is Tb2, Tb3 and Tb4, and the transformation ratio is Tb 1: tb 2: tb 3: tb4 ═ 2: 2: 1: 1; the phase C input winding is Tc1, the phase C output winding is Tc2, Tc3 and Tc4, the transformation ratio is Tc 1: tc 2: tc 3: tc4 ═ 2: 2: 1: 1; all windings of the transformer are isolated.

One for each phase of the LC low pass filter; the LC low-pass filter consists of an output filter inductor and an output filter capacitor; the inductor L and the capacitor C form two ports; and the input two ports of the LC low-pass filter are connected with the output two ports of each cascaded module, and the output port is the voltage output port of each phase.

As shown in fig. 1 and fig. 2, a three-phase ac power supply at a feed line end node A, B, C is respectively connected to input windings Ta1, Tb1 and Tc1 of a three-phase multi-winding isolation transformer; the phase A is connected with the anode of the winding Ta1, the phase B is connected with the anode of the winding Tb1, and the phase C is connected with the anode of the winding Tc 1; the negative electrodes of the windings Ta1, Tb1 and Tc1 are connected together, and the connection point is N1; a secondary side winding Ta2 of the phase A transformer is connected with the input end of a Buck type direct AC-AC converter Aa, a winding Ta3 is connected with the input end of a BT-AC converter Ab, and a winding Ta4 is connected with the input end of the BT-AC converter Ac; a secondary side winding Tb2 of the phase-B transformer is connected with the input end of the BT-AC converter Ba, a winding Tb3 is connected with the input end of the Buck type direct AC-AC converter Bb, and a winding Tb4 is connected with the input end of the BT-AC converter Bc; a secondary side winding Tc2 of the C phase transformer is connected with the input end of the BT-AC converter Ca, a winding Tc3 is connected with the input end of the BT-AC converter Cb, and a winding Tc4 is connected with the input end of the Buck type direct AC-AC converter Cc; the cathode of the output port of the Aa converter is connected with the anode of the output port of the Ba converter, and the cathode of the output port of the Ba converter is connected with the anode of the output port of the Ca converter; the negative pole of the output port of the Ab converter is connected with the positive pole of the output port of the Bb converter, and the negative pole of the output port of the Bb converter is connected with the positive pole of the output port of the Cb converter; the negative pole of the output port of the Ac converter is connected with the positive pole of the output port of the Bc converter, and the negative pole of the output port of the Bc converter is connected with the positive pole of the output port of the Cc converter; the negative electrode of the output port of the Ca converter, the negative electrode of the output port of the Cb converter and the negative electrode of the output port of the Cc converter are connected together, and the connection point is N2; aa. Ba and Ca share one LC filter; ab. Bb and Cb share one LC filter; ac. Bc and Cc share one LC filter; the input two ports of each phase of filter are connected with the output two ports of all the cascaded modules of each phase; the positive pole of the output port of the Aa converter, the positive pole of the output port of the Ab converter and the positive pole of the output port of the Ac converter are A, B, C three-phase voltage outputs correspondingly and are connected to the tail end of the other feeder line.

(A)

According to the voltage expected by the load side, the present invention can have various combinations of PWM modulation modes, as shown in table 1:

TABLE 1 PWM modulation scheme

(II)

FIG. 4 is a schematic diagram of the voltage regulation of the present invention; taking phase A as an example, displaying the phase A in a plane phasor coordinate system; UA1, UB1 and UC1 are three-phase voltage phasors; -UA1, -UB1, -UC1 are three-phase voltage phasors in opposite directions; d1 UB1, D2 UC1 are output voltage phasors of the two BT-AC converters; uout is the voltage phasor output by the power conversion unit, namely the vector composition of D1 UB1 and D2 UC 1; UA2 is the total voltage output of phase A, which is composed of Uout and UA1 vector;

the graph (a) shows that the device works in a negative-polarity voltage regulator mode, the phase of input and output voltage is unchanged, and the amplitude is reduced;

the device works in a positive polarity voltage regulator mode, so that the phase of input and output voltage is unchanged, and the amplitude is reduced;

the graph (c) shows that the device works in a phase shifter mode, and the amplitude of the input voltage and the amplitude of the output voltage are unchanged, and the phase is changed; and (d) the device works in a phase-shifting voltage-regulating mode to realize that both input and output voltages and amplitudes are changed.

(III)

Fig. 5(a) shows when the transformer transformation ratio is Ta 1: ta 2: ta 3: ta4 ═ 1: 1: 1: the compensation range of the A phase voltage at 1; VcN and-VcN are input voltage phasors for the C phase; VbN and-VbN are input voltage phasors for phase B; the output voltage phasor of the power conversion unit, namely the voltage phasor compensated to the phase A, starts from the origin, and the end point is in the diamond (including the diamond boundary);

the diagram (b) shows the three-phase voltage compensation range, and the transformation ratio of each phase transformer is 1: 1: 1: 1.

(IV)

FIG. 9 is a circuit schematic of an LC low pass filter; wherein for the inductance L_fCan flow through direct current to block alternating current, particularly high-frequency alternating current; capacitor C_fAlternating current can be circulated to block direct current, and the aims of filtering high-frequency harmonic waves and ensuring the output of high-quality 50Hz sine alternating current voltage are finally achieved by designing LC parameters. Wherein L is_fAnd C_fWith reference to the following formula:

wherein, ω is_LIs the cut-off angular frequency, V, of the LC filter₀To output a voltage, ω₁Is the angular frequency of the input ac power.

(V)

In order to better verify the superiority of the invention, a single-phase application function model machine is built, and the parameters of the model machine are shown in the following table 2:

TABLE 2 prototype parameters

Name (R)	Numerical value
		Transformation ratio of transformer	2∶2∶1∶1
Number of BT-AC converters	2
		Buck type direct AC-AC conversionNumber of devices	1
Range of input voltage effective value	[180V，240V]/50Hz
		Target effective value of single-phase output phase voltage	220V
Rated power	5kW
		Frequency of switching tube	12kHz
IGBT	FF300R 12KS4；FF600R 12KS4
		Output filter inductor L of single AC converterf	0.3mH
Output filter capacitor Cf	20uF
		Capacitors C1, C2	20uF

(VI)

FIG. 10 is a graph of an AM output positive polarity compensation voltage waveform; UAO, UBU and UO are input voltage, compensation voltage and total output voltage respectively; 11-15, where IO is the total output current;

as can be seen from fig. 10 and 11, the device can realize constant phase and regulate voltage;

fig. 12 and 13 show that the device can realize constant voltage and phase adjustment;

it can be seen from fig. 14 and 15 that the device can realize phase-shifting voltage regulation and work normally with load;

in conclusion, the invention can realize flexible regulation of node voltage and power and has certain protection function.