Unit cascade type high-voltage frequency converter adopting multi-power unit parallel structure

Abstract

The utility model relates to a unit cascade type high-voltage frequency converter adopting a multi-power unit parallel structure, which comprises an input multi-winding transformer and at least three power units, and each power unit comprises at least two subunits. Each subunit is provided with three alternating-current input terminals, two alternating-current output terminals and two direct-current bus voltage output terminals, the three alternating-current input terminals of one subunit serve as a first group of input terminals of the power unit, the three alternating-current output terminals of the other subunit serve as a second group of input terminals of the power unit, and the subunits are identical in circuit structure. Two groups of input terminals of each power unit are respectively connected with a corresponding secondary winding of the transformer, one end of each group of power units which are sequentially connected in series through alternating current output terminals is used as an output end of the high-voltage frequency converter to be connected to a motor, and the other end is used as a center node of the high-voltage frequency converter after being connected. According to the utility model, a multi-power unit parallel connection structure is adopted, so that the overall output current level of the unit cascade type high-voltage frequency converter is increased.

Description

TECHNICAL FIELD

[0001] The utility model relates to a kind of high voltage frequency converter for frequency control, in particular to a kind of unit cascade high voltage frequency converter using the parallel structure of multiple power units, applied to motor frequency drive field. BACKGROUND

[0002] Unit cascade high voltage frequency converter has the advantages of small input and output harmonic, easy to realize high voltage output etc., is one of the mainstream topologies of current domestic high voltage frequency converter market, the scheme can realize the output of higher voltage grade of whole machine by the number of series power unit, but the grade of frequency converter whole machine output current is limited by the rated current of power device, there is no better solution at present. In the application occasion of larger motor current, if single frequency converter whole machine cannot satisfy the rated current demand of electric motor, the traditional scheme is to design the motor as double-winding motor or adopt the parallel mode of frequency converter whole machine, both need to consider the power balance control of two frequency converter whole machines, control algorithm is complex and multiple frequency converters parallel lead to transmission system occupies larger volume, system cost is also higher. CONTENT OF UTILITY MODEL

[0003] The utility model aims at solving the defects of prior art, designs a kind of unit cascade high voltage frequency converter using the parallel structure of multiple power units, by the way of using parallel structure to the power unit of unit cascade high voltage frequency converter, increase the output current grade of frequency converter whole machine.

[0004] This utility model is implemented as follows: a cascaded high-voltage frequency converter with a multi-power unit parallel structure, characterized in that: the high-voltage frequency converter has a power unit cascaded topology, including one input multi-winding transformer and several power units. The input multi-winding transformer is a three-phase multi-winding transformer, with the primary side of the multi-winding transformer serving as the input terminal of the high-voltage frequency converter. Each phase has n power units, for a total of 3n power units across 3 phases. The secondary side of the transformer is equipped with a secondary winding, where n is a natural number greater than or equal to 1. Each power unit includes at least two sub-units, and each sub-unit has three AC input terminals, two AC output terminals, and two DC bus voltage output terminals, namely, a positive DC bus voltage output terminal DC+ and a negative DC bus voltage output terminal DC-. The three AC input terminals of one subunit serve as the first set of input terminals for the power unit, and the three AC input terminals of another subunit serve as the second set of input terminals for the power unit. Any one of the AC output terminals of each subunit is also connected to a current-sharing reactor. The circuit structure of each subunit is the same, which is a three-phase input, single-phase output AC-DC-AC voltage source converter structure. Each power unit is connected to the secondary winding of the three-phase multi-winding transformer through its own input terminals. Each group of power units is connected in series through its two AC output terminals. One end of the series-connected circuit serves as the output terminal of the high-voltage frequency converter and is connected to the motor. The other end is led out from the AC output terminal of the subunit connected to the current-sharing reactor and connected together to serve as the central node N of the high-voltage frequency converter.

[0005] When the transformer has 6n secondary windings, the two sets of input terminals of each power unit are connected one-to-one with the secondary windings of the three-phase multi-winding transformer. When the transformer has 3n secondary windings, the two sets of input terminals of each power unit are connected in parallel after being connected to an input current-sharing reactor, and the parallel connection ends are then connected to the corresponding secondary windings of the three-phase multi-winding transformer. The current-sharing reactor is an iron-core reactor or an air-core reactor.

[0006] The positive and negative DC bus voltage output terminals of each subunit in the power unit are not connected to each other, forming an independent DC bus structure for each subunit. Alternatively, the positive DC bus voltage output terminals of each subunit in the power unit are connected in sequence, and the negative DC bus voltage output terminals are also connected in sequence, forming a parallel connection structure for the DC buses of each subunit.

[0007] The first structure of the sub-unit in the power unit: The sub-unit includes six diodes, a first DC energy storage capacitor C1, and four controlled power electronic switches. The six diodes are, in order, diodes D1 to D6. The four controlled power electronic switches are, in order, fully controlled power electronic switches S1 to S4. Diodes D1 and D4, D3 and D6, and D5 and D2 are connected in series in pairs and then in parallel. Simultaneously, the series-connected lines each have three AC input terminals for the sub-unit, and the parallel-connected lines are... The two DC bus voltage output terminals of the sub-unit are respectively the positive DC bus voltage output terminal DC+ and the negative DC bus voltage output terminal DC-, forming a three-phase full-bridge uncontrolled rectifier structure. The first DC energy storage capacitor C1 is connected between the two DC bus voltage output terminals of the sub-unit. The first fully controlled power electronic switch S1 and the second fully controlled power electronic switch S2, the fully controlled power electronic switch S3 and the fully controlled power electronic switch S4 are connected in series in pairs, and the two ends of the series connection are respectively connected to the two DC bus voltage output terminals of the sub-unit. The two series connection lines are also provided with two AC output terminals of the sub-unit, forming a single-phase H-bridge inverter structure.

[0008] The second structure of the sub-unit in the power unit: The sub-unit includes six diodes, a second DC energy storage capacitor C2, a braking resistor R1, and five controlled power electronic switches. The six diodes are, in order, the eleventh diode D11 to the seventeenth diode D17. The five controlled power electronic switches are, in order, the fifth fully controlled power electronic switch S5 to the ninth fully controlled power electronic switch S9. The eleventh diode D11 and the fourteenth diode D14, the thirteenth diode D13 and the sixteenth diode D16, and the fifteenth diode D15 and the twelfth diode D12 are connected in series in pairs and then in parallel. Simultaneously, the lines connecting the series-connected pairs are respectively provided with the three AC input terminals of the sub-unit. The two ends of the series-connected and then parallel-connected pairs serve as the DC bus voltage output terminals of the sub-unit. The positive DC bus voltage output terminal is DC+. The negative DC bus voltage output terminal DC- forms a three-phase full-bridge uncontrolled rectifier structure. The second DC energy storage capacitor C2 is connected between the two DC bus voltage output terminals of the sub-unit. The fifth fully controlled power electronic switch S5 and the sixth fully controlled power electronic switch S6, the seventh fully controlled power electronic switch S7 and the eighth fully controlled power electronic switch S8 are connected in series in pairs, and the two ends of the series connection are respectively connected to the two DC bus voltage output terminals of the sub-unit. The two series connection lines are also provided with the two AC output terminals of the sub-unit, forming a single-phase H-bridge inverter structure. The braking resistor R1 and the seventeenth diode D17 are connected in parallel, one end of which is connected to the negative DC bus voltage output terminal DC-, and the other end is connected in series with the ninth fully controlled power electronic switch S9 and then connected to the positive DC bus voltage output terminal DC+, forming a DC chopper braking structure.

[0009] The third structure of the sub-unit in the power unit: The sub-unit includes an input filter assembly (Filter), ten fully controlled power electronic switches, and a third DC energy storage capacitor C3. The ten fully controlled power electronic switches are, in order, the eleventh fully controlled power electronic switch S11 to the sixteenth fully controlled power electronic switch S16 and the thirty-first fully controlled power electronic switch S31 to the thirty-fourth fully controlled power electronic switch S34. The eleventh fully controlled power electronic switch S11 and the fourteenth fully controlled power electronic switch S14, the thirteenth fully controlled power electronic switch S13 and the sixteenth fully controlled power electronic switch S16, and the fifteenth fully controlled power electronic switch S15 and the twelfth fully controlled power electronic switch S12 are connected in series in pairs and then in parallel. Each series-connected line is then connected to the output terminal of the filter assembly (Filter). The input terminals of the filter component serve as the three AC input terminals of the sub-unit. The two ends of the series-connected and then parallel-connected terminals serve as the DC bus voltage output terminals of the sub-unit: a positive DC bus voltage output terminal (DC+) and a negative DC bus voltage output terminal (DC-), forming a three-phase active rectifier structure. The two ends of the third DC energy storage capacitor C3 are respectively connected to the two DC bus voltage output terminals of the sub-unit. The thirty-first fully controlled power electronic switch S31, the thirty-second fully controlled power electronic switch S32, the thirty-third fully controlled power electronic switch S33, and the thirty-fourth fully controlled power electronic switch S34 are each connected in series in pairs, and the two ends of these series connections are then respectively connected to the two DC bus voltage output terminals of the sub-unit. The series-connected lines also have two AC output terminals of the sub-unit, forming a single-phase H-bridge inverter structure. The filter component uses an L, LC, or LCL low-pass filter.

[0010] The subunit is also equipped with a bypass switch K1, the two ends of which are respectively connected to the two AC output terminals of the subunit to form a subunit with automatic bypass function.

[0011] The beneficial effects of this utility model are:

[0012] 1. By connecting multiple power units in a cascaded high-voltage frequency converter in parallel, the output current of the entire frequency converter can be increased. The power units can use existing mature technologies, and the solution is simple to implement and easy to operate.

[0013] 2. Compared with the traditional scheme of connecting multiple frequency converters in parallel, the frequency converter system of this utility model has a smaller footprint and lower cost in motor frequency conversion drive. Attached Figure Description

[0014] Figure 1This is a schematic diagram of the independent DC bus structure of the two sub-units in the power unit of this utility model.

[0015] Figure 2 This is a schematic diagram of the parallel connection structure of the two sub-unit DC buses in the power unit of this utility model.

[0016] Figure 3 This is a schematic diagram of the structure of a subunit embodiment 1 of the power unit in this utility model.

[0017] Figure 4 This is a schematic diagram of the structure of a subunit embodiment 2 of the power unit in this utility model.

[0018] Figure 5 This is a schematic diagram of the structure of the power unit subunit embodiment 3 in this utility model.

[0019] Figure 6 This is a schematic diagram of the structure of the subunit embodiment 4 of the power unit in this utility model.

[0020] Figure 7 This is a schematic diagram of the structure of embodiment 5 of the power unit in this utility model.

[0021] Figure 8 This is a schematic diagram of the structure of a subunit of the power unit in Embodiment 6 of this utility model.

[0022] Figure 9 This is a schematic diagram of the topology of the cascaded high-voltage frequency converter with a multi-power unit parallel structure according to Embodiment 7.

[0023] Figure 10 This is a schematic diagram of the topology of the cascaded high-voltage frequency converter with a multi-power unit parallel structure according to Embodiment 8.

[0024] In the diagram: 1. Three-phase phase-shifting transformer; 2. Power unit group; 3. Motor. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] According to the appendix Figures 1-10This utility model relates to a cascaded high-voltage frequency converter employing a multi-power unit parallel structure. The high-voltage frequency converter includes one input multi-winding transformer (i.e., a three-phase phase-shifting transformer 1) and several power units. These power units constitute a power unit group 2. The power units of the high-voltage frequency converter are power units of a cascaded high-voltage frequency converter, and each power unit employs at least two parallel-connected sub-units, representing a mature solution for cascaded high-voltage frequency converter power units. The high-voltage frequency converter features a cascaded power unit topology.

[0027] According to the appendix Figure 1 Each power unit in the high-voltage frequency converter of this utility model has at least two sub-units. Taking the setting of two sub-units as an example, it includes a first sub-unit Cell1, a second sub-cell2, and a first current-sharing reactor L1 and a second current-sharing reactor L2 respectively connected to the two sub-units. The circuit structure of the first sub-unit Cell1 and the second sub-unit Cell2 is the same, which is a three-phase input, single-phase output AC-DC-AC voltage source converter structure.

[0028] Each of the aforementioned sub-units has three AC input terminals, two AC output terminals, and two DC bus voltage output terminals, namely the positive DC bus voltage output terminal DC+ and the negative DC bus voltage output terminal DC-.

[0029] The three AC input terminals of the first sub-unit Cell1 are U1, V1 and W1, which serve as the first set of input terminals for the power unit of the high-voltage frequency converter. The two AC output terminals are the first AC output terminal T11 and the second AC output terminal T21, and the two DC bus voltage output terminals are the positive DC bus voltage output terminal DC+ and the negative DC bus voltage output terminal DC-.

[0030] The three AC input terminals of the second sub-unit Cell2 are U2, V2 and W2, which serve as the second set of input terminals for the power unit of the high-voltage frequency converter. The two AC output terminals are the third AC output terminal T12 and the fourth AC output terminal T22, and the two DC bus voltage output terminals are the positive DC bus voltage output terminal DC+ and the negative DC bus voltage output terminal DC-.

[0031] The first AC output terminal T11 of the first sub-unit Cell1 is connected to the third AC output terminal T12 of the second sub-unit Cell2 and serves as the first output terminal BT1 of the high-voltage inverter power unit. The second AC output terminal T21 of the first sub-unit Cell1 is connected to one end of the first current-sharing reactor L1. The fourth AC output terminal T22 of the second sub-unit Cell2 is connected to one end of the second current-sharing reactor L2. The other end of the first current-sharing reactor L1 is connected to the other end of the second current-sharing reactor L2 and serves as the second output terminal BT2 of the high-voltage inverter power unit.

[0032] The first current-sharing reactor L1 and the second current-sharing reactor L2 can also be respectively located on the connection circuit of the first AC output terminal T11 of the first sub-unit Cell1 and the third AC output terminal T12 of the second sub-unit Cell2.

[0033] The function of the first current-sharing reactor L1 and the second current-sharing reactor L2 is to reduce the circulating current of a single sub-unit output. When the output voltage frequency is low (e.g., output frequency < 100Hz), an iron-core reactor can be used to reduce the reactor size; when the output voltage frequency is high (e.g., output frequency ≥ 100Hz), an air-core reactor is preferable to avoid severe high-frequency heating of the reactor core. Furthermore, the drive pulses of the two sub-unit outputs can be controlled by synchronous pulse drive to further reduce the size of the current-sharing reactor.

[0034] According to the appendix Figure 1 The positive and negative DC bus voltage output terminals of the first sub-unit Cell1 and the second sub-unit Cell2 are not connected to each other, forming an independent DC bus structure for each sub-unit. When this connection method is adopted, the two sets of input terminals of the high-voltage frequency converter power unit can be powered by the same transformer winding or by two separate transformer windings. Since the DC bus of the unit is independent, there is no input circulating current problem, and there is no need to consider the impedance matching problem of the two sets of inputs. The transformer winding and the power unit input terminals can be directly connected by cable or copper busbar.

[0035] Depending on the rated current requirement of the motor to be driven, if two sub-units cannot meet the rated current requirement of the motor, three or more sub-units can be connected in parallel. The implementation method is similar to that of the two-sub-unit parallel structure.

[0036] According to the appendix Figure 2 This is a schematic diagram of the parallel connection of the DC buses of two sub-units in the power unit of this utility model, and is related to the attached diagram. Figure 1Compared to the previous structure, the positive DC bus voltage output terminal of the first sub-unit Cell1 is connected to the positive DC bus voltage output terminal of the second sub-unit Cell2, and the negative DC bus voltage output terminal of the first sub-unit Cell1 is connected to the negative DC bus voltage output terminal of the second sub-unit Cell2, forming a parallel connection of the DC buses of the two sub-units. When this connection method is adopted, the two sets of input terminals of the high-voltage frequency converter power unit can be powered by the same transformer winding or by two different secondary windings. Since the DC buses of the two sub-units are connected in parallel, there will be an input current sharing problem. It is necessary to consider the impedance matching of the two sets of inputs. The transformer and the input terminals of the power unit can be connected by cables or copper busbars of equal impedance, or an input current sharing reactor can be added to achieve input impedance matching. Example 1

[0037] According to the appendix Figure 3 The first structural form of the sub-unit in the power unit:

[0038] Taking the first sub-unit Cell1 as an example, the sub-unit includes six diodes (i.e., first diode D1 to sixth diode D6), a first DC energy storage capacitor C1, and four controlled power electronic switches (i.e., first fully controlled power electronic switch S1 to fourth fully controlled power electronic switch S4). The first diode D1 and fourth diode D4, the third diode D3 and sixth diode D6, and the fifth diode D5 and second diode D2 are connected in series in pairs and then in parallel. Simultaneously, the lines connecting the first diode D1 and fourth diode D4, the third diode D3 and sixth diode D6, and the fifth diode D5 and second diode D2 in series in pairs are respectively provided with the three AC input terminals U1, V1, and W1 of the sub-unit. The two ends of the series-connected and then parallel-connected terminals serve as the DC bus voltage output terminals of the sub-unit (i.e., positive DC bus voltage output terminal DC+ and negative DC bus voltage output terminal DC-), forming a three-phase full-bridge uncontrolled rectifier structure. The first DC energy storage capacitor C1 is connected between the two DC bus voltage output terminals of the sub-unit. The first fully controlled power electronic switch S1 and the second fully controlled power electronic switch S2, the fully controlled power electronic switch S3 and the fully controlled power electronic switch S4 are connected in series in pairs, and the two ends of the series connection are respectively connected to the two DC bus voltage output terminals of the sub-unit. The series connection lines are also provided with the first AC output terminal T11 and the second AC output terminal T21 of the sub-unit, forming a single-phase H-bridge inverter structure. Example 2

[0039] According to the appendix Figure 4 The second structural form of the sub-unit in the power unit:

[0040] Taking the first subunit Cell1 as an example, based on the structure of Embodiment 1, the subunit is further equipped with a bypass switch K1. The two ends of the bypass switch K1 are connected to the first AC output terminal T11 and the second AC output terminal T21 of the subunit, respectively, forming a subunit with automatic bypass function to improve system reliability. The bypass switch K1 adopts a mechanical switch such as a contactor or an electronic switch such as a power semiconductor. During normal operation, the bypass switch K1 of each subunit is in the open state; when a subunit fails, the bypass switch K1 of each subunit automatically closes, bypassing the subunit it belongs to. The control module in the frequency converter system, through existing technology control algorithms such as center point offset, can drive the motor to continue running within the allowable range of the output voltage capability. Example 3

[0041] According to the appendix Figure 5 The third structural form of the sub-unit in the power unit:

[0042] Taking the first subunit Cell1 as an example, the subunit includes six diodes (i.e., the eleventh diode D11 to the seventeenth diode D17), a second DC energy storage capacitor C2, a braking resistor R1, and five controlled power electronic switches (i.e., the fifth fully controlled power electronic switch S5 to the ninth fully controlled power electronic switch S9). The eleventh diode D11 and the fourteenth diode D14, the thirteenth diode D13 and the sixteenth diode D16, and the fifteenth diode D15 and the twelfth diode D12 are connected in series in pairs and then in parallel. Simultaneously, the lines connecting the eleventh diode D11 and the fourteenth diode D14, the thirteenth diode D13 and the sixteenth diode D16, and the fifteenth diode D15 and the twelfth diode D12 in series with each other are respectively provided with the three AC input terminals U1, V1 and W1 of the sub-unit. The two ends of the series-connected and then parallel-connected terminals serve as the DC bus voltage output terminals of the sub-unit (i.e., positive DC bus voltage output terminal DC+ and negative DC bus voltage output terminal DC-), forming a three-phase full-bridge uncontrolled rectifier structure. The second DC energy storage capacitor C2 is connected between the two DC bus voltage output terminals of the sub-unit. The fifth fully controlled power electronic switch S5 and the sixth fully controlled power electronic switch S6, the seventh fully controlled power electronic switch S7 and the eighth fully controlled power electronic switch S8 are connected in series in pairs, and the two ends of the series connection are respectively connected to the two DC bus voltage output terminals of the sub-unit. The series connection lines are also provided with the first AC output terminal T11 and the second AC output terminal T21 of the sub-unit, forming a single-phase H-bridge inverter structure.

[0043] The braking resistor R1 is connected in parallel with the seventeenth diode D17, with one end connected to the negative DC bus voltage output terminal DC-, and the other end connected in series with the ninth fully controlled power electronic switch S9 and then connected to the positive DC bus voltage output terminal DC+, forming a DC chopper braking structure. When the subunit absorbs braking power, the braking power is consumed through the braking resistor R1, thereby suppressing the DC bus voltage surge. Example 4

[0044] According to the appendix Figure 6 The fourth structural form of the sub-unit in the power unit:

[0045] Taking the first subunit Cell1 as an example, the subunit is based on the structure of Embodiment 3 and is further provided with a bypass switch K1. The location and function of the bypass switch K1 are the same as those in Embodiment 2.

[0046] Example 5

[0047] According to the appendix Figure 7 The fifth structural form of the sub-unit in the power unit:

[0048] Taking the first subunit Cell1 as an example, the subunit includes an input filter component Filter, ten fully controlled power electronic switches (i.e., the eleventh fully controlled power electronic switch S11 to the sixteenth fully controlled power electronic switch S16, the thirty-first fully controlled power electronic switch S31 to the thirty-fourth fully controlled power electronic switch S34), and a third DC energy storage capacitor C3. The eleventh fully controlled power electronic switch S11 and the fourteenth fully controlled power electronic switch S14, the thirteenth fully controlled power electronic switch S13 and the sixteenth fully controlled power electronic switch S16, and the fifteenth fully controlled power electronic switch S15 and the twelfth fully controlled power electronic switch S12 are connected in series in pairs and then in parallel. Meanwhile, the... The lines connecting the eleventh fully controlled power electronic switch S11 with the fourteenth fully controlled power electronic switch S14, the thirteenth fully controlled power electronic switch S13 with the sixteenth fully controlled power electronic switch S16, and the fifteenth fully controlled power electronic switch S15 with the twelfth fully controlled power electronic switch S12 in series are then connected to the output terminal of the filter assembly Filter. The input terminals of the filter assembly Filter serve as the three AC input terminals U1, V1, and W1 of the sub-unit. The two ends of the series-connected and parallel-connected terminals serve as the DC bus voltage output terminals (i.e., the positive DC bus voltage output terminal DC+ and the negative DC bus voltage output terminal DC-) of the sub-unit, forming a three-phase active rectification structure. The two ends of the third DC energy storage capacitor C3 are respectively connected to the two DC bus voltage output terminals of the sub-unit. The thirty-first fully controlled power electronic switch S31 and the thirty-second fully controlled power electronic switch S32, the thirty-third fully controlled power electronic switch S33 and the thirty-fourth fully controlled power electronic switch S34 are connected in series in pairs, and the two ends of the series connection are respectively connected to the two DC bus voltage output terminals of the sub-unit. The series connection lines are also provided with the first AC output terminal T11 and the second AC output terminal T21 of the sub-unit, forming a single-phase H-bridge inverter structure.

[0049] When the subunit absorbs braking power, the braking power is fed back to the grid through a three-phase active rectifier structure, thereby suppressing DC bus voltage rise. The filter component typically uses a low-pass filter with an L, LC, or LCL structure. When the leakage reactance of the secondary winding of the input multi-winding transformer is sufficiently large (e.g., greater than 4%), the transformer's leakage reactance can be used to replace the filter component in this embodiment, thus simplifying the transformer system structure.

[0050] When the two sets of input terminals of the high-voltage frequency converter power unit are powered by the same transformer winding, the eleventh fully controlled power electronic switch S11 to the sixteenth fully controlled power electronic switch S16 should adopt a synchronous drive pulse control mode to reduce the size of the filter assembly or to achieve the purpose of using the leakage reactance of the transformer to replace the filter assembly in this embodiment. Example 6

[0051] According to the appendix Figure 8 The sixth structural form of the sub-unit in the power unit:

[0052] Taking the first subunit Cell1 as an example, the subunit is further provided with a bypass switch K1 based on the structure of embodiment 5. The setting position and function of the bypass switch K1 are the same as those in embodiment 2. Example 7

[0053] According to the appendix Figure 9 The schematic diagram of the topology of the unit-cascaded high-voltage frequency converter with the multi-power unit parallel structure of this utility model is shown. In this embodiment, each phase uses n power units (n is a natural number ≥ 1), and there are a total of 3n power units for 3 phases, namely the first group of power units A1……An, the second group of power units B1……Bn, and the third group of power units C1……Cn. The secondary side of the transformer is provided with 6n secondary windings.

[0054] The high-voltage frequency converter is a power unit cascaded topology structure, which is a three-phase structure, including one input multi-winding transformer and a power unit group 2 consisting of 3n power units. The input multi-winding transformer is a three-phase multi-winding transformer. In this embodiment, a three-phase phase-shifting transformer 1 is used.

[0055] The power unit adopts a structure in which each power unit has an independent DC bus for its sub-units (as shown in the attached diagram). Figure 1 As shown), each power unit adopts the single power unit topology described in Example 1 (as shown in the attached diagram). Figure 3 (As shown). The primary winding of the multi-winding transformer serves as the input terminal of the high-voltage frequency converter, and it has 6n secondary windings. The 3n power units are divided into 3 groups, each containing n power units (i.e., power units A1...An are the first group of power units, power units B1...Bn are the second group of power units, and power units C1...Cn are the third group of power units). The two sets of input terminals of each power unit are connected one-to-one with the secondary windings of the three-phase phase-shifting transformer 1. Each group of power units is connected in series through its first output terminal BT1 and second output terminal BT2. One end of the series-connected circuit serves as the output terminal of the high-voltage frequency converter and is connected to the motor 3. The other end of the three groups of power units connected in series is connected together as the central node N of the high-voltage frequency converter. Example 8

[0056] According to the appendix Figure 10 This is a schematic diagram of the topology of the cascaded high-voltage frequency converter with a multi-power unit parallel structure according to this utility model. In this embodiment, each phase of power unit group 2 uses n power units (n is a natural number ≥ 1), and there are a total of 3n power units in 3 phases, namely the first group of power units A1...An, the second group of power units B1...Bn, and the third group of power units C1...Cn. The transformer secondary side has 3n secondary windings.

[0057] The high-voltage frequency converter is a power unit cascaded topology with a three-phase structure, including one input multi-winding transformer and 3n power units. Each input terminal of each power unit is connected to an input current sharing reactor. The input multi-winding transformer is a three-phase multi-winding transformer. In this embodiment, a three-phase phase-shifting transformer 1 is used.

[0058] The power unit is connected in parallel with the DC bus of each power unit's sub-units (as shown in the attached diagram). Figure 2 As shown), each power unit adopts the single power unit topology described in Example 1 (as shown in the attached diagram). Figure 3(As shown). The primary winding of the multi-winding transformer serves as the input terminal of the high-voltage frequency converter. The multi-winding transformer has 3n secondary windings. The 3n power units are divided into 3 groups, each group containing n power units (i.e., power units A1...An are the first group of power units, power units B1...Bn are the second group of power units, and power units C1...Cn are the third group of power units). The two sets of input terminals of each power unit are respectively connected to input current sharing reactors. There are a total of 6n input current sharing reactors. That is, the two sets of input terminals of power unit A1 in the first group of power units are respectively connected to input current sharing reactor LA. The two sets of input terminals of power unit An are connected to input current sharing reactors LAn1 and LAn2 respectively, and so on. Similarly, the two sets of input terminals of power unit B1 in the second group of power units are connected to input current sharing reactors LB11 and LB12 respectively, and so on. The two sets of input terminals of power unit Bn are connected to input current sharing reactors LBn1 and LBn2 respectively. The two sets of input terminals of power unit C1 in the third group of power units are connected to input current sharing reactors LC11 and LC12 respectively. ...The two sets of input terminals of the power unit Cn are respectively connected to the input current sharing reactor LCn1 and the input current sharing reactor LCn2, and then connected in parallel with the two input current sharing reactors connected to the two input terminals of each power unit. Then they are connected to the corresponding secondary winding of the three-phase phase-shifting transformer 1. Each power unit is connected in series through its first output terminal BT1 and second output terminal BT2. One end of the series-connected circuit is connected to the motor 3 as the output terminal of the high-voltage frequency converter, while the other end of the three power units connected in series is connected together as the central node N of the high-voltage frequency converter.

[0059] The above-described embodiments of a single power unit are merely preferred embodiments of this utility model, used to provide a detailed explanation of the utility model, and are not intended to limit the utility model. The power units in the high-voltage frequency converter with multiple power units connected in parallel according to this utility model can adopt different structures depending on the actual situation, including but not limited to the specific embodiments exemplified in this utility model. Those skilled in the art will obviously make various equivalent modifications, changes, and substitutions to the specific implementation methods based on the disclosure of this utility model, and such equivalent modifications, changes, and substitutions should all fall within the protection scope of this utility model. The protection scope of this utility model is determined by the description in the claims of this application.

Claims

1. A cascaded high-voltage frequency converter employing a multi-power unit parallel structure, characterized in that: The high-voltage frequency converter is a power unit cascaded topology, including one input multi-winding transformer and several power units. The input multi-winding transformer is a three-phase multi-winding transformer, with the primary winding of the multi-winding transformer serving as the input terminal of the high-voltage frequency converter. Each phase has n power units, for a total of 3n power units across the three phases. The secondary winding of the transformer is provided with a secondary winding, where n is a natural number greater than or equal to 1. Each power unit includes at least two sub-units. Each sub-unit has three AC input terminals, two AC output terminals, and two DC bus voltage output terminals, namely a positive DC bus voltage output terminal (DC+) and a negative DC bus voltage output terminal (DC-). The three AC input terminals of one sub-unit serve as the power input terminals. The first set of input terminals of the unit, and the three AC input terminals of the other sub-unit serve as the second set of input terminals of the power unit. Any one of the AC output terminals of each sub-unit is also connected to a current-sharing reactor. The circuit structure of each sub-unit is the same, which is a three-phase input, single-phase output AC-DC-AC voltage source converter structure. Each power unit is connected to the secondary winding of the multi-winding transformer through its own input terminal. Each set of power units is connected in series through its two AC output terminals. One end of the series-connected circuit serves as the output terminal of the high-voltage frequency converter and is connected to the motor. The other end is led out from the AC output terminal of the sub-unit connected to the current-sharing reactor and connected together to serve as the center node (N) of the high-voltage frequency converter.

2. A cascaded high-voltage frequency converter with a multi-power unit parallel structure as described in claim 1, characterized in that: The transformer is equipped with 6n secondary windings, and the two sets of input terminals of each power unit are respectively connected to the secondary windings of the multi-winding transformer.

3. A cascaded high-voltage frequency converter with a multi-power unit parallel structure as described in claim 1, characterized in that: The transformer is equipped with 3n secondary windings. The two sets of input terminals of each power unit are connected in parallel after being connected to the input current sharing reactor. The parallel connection ends are then connected to the corresponding secondary windings of the multi-winding transformer.

4. A cascaded high-voltage frequency converter employing a multi-power unit parallel structure as described in claim 1, 2, or 3, characterized in that: The positive and negative DC bus voltage output terminals of each subunit in the power unit are not connected to each other, forming an independent DC bus structure for each subunit. Alternatively, the positive DC bus voltage output terminals of each subunit in the power unit are connected in sequence, and the negative DC bus voltage output terminals are also connected in sequence, forming a parallel connection structure for the DC buses of each subunit.

5. A cascaded high-voltage frequency converter employing a multi-power unit parallel structure as described in claim 1, 2, or 3, characterized in that... The sub-unit structure of the power unit is as follows: The sub-unit comprises six diodes, a first DC energy storage capacitor (C1), and four controlled power electronic switches. The six diodes are, in order, diodes one through six (D6). The four controlled power electronic switches are, in order, fully controlled power electronic switches one through four (S4). Diodes one through four (D4), three through six (D6), and five through two (D2) are connected in series and then in parallel. Each of the series-connected lines has three AC input terminals for the sub-unit, which are also connected in series and then in parallel. The two ends of the circuit serve as the DC bus voltage output terminals of the sub-unit, namely the positive DC bus voltage output terminal (DC+) and the negative DC bus voltage output terminal (DC-), forming a three-phase full-bridge uncontrolled rectifier structure. The first DC energy storage capacitor (C1) is connected between the two DC bus voltage output terminals of the sub-unit. The first fully controlled power electronic switch (S1) and the second fully controlled power electronic switch (S2), and the fully controlled power electronic switch (S3) and the fully controlled power electronic switch (S4) are connected in series in pairs, and the two ends of the series connection are then connected to the two DC bus voltage output terminals of the sub-unit. The two series-connected lines are also provided with the two AC output terminals of the sub-unit, forming a single-phase H-bridge inverter structure.

6. A cascaded high-voltage frequency converter employing a multi-power unit parallel structure as described in claim 1, 2, or 3, characterized in that... The sub-unit structure of the power unit is as follows: The sub-unit includes six diodes, a second DC energy storage capacitor (C2), a braking resistor (R1), and five controllable power electronic switches. The six diodes are, in order, the eleventh diode (D11) to the seventeenth diode (D17), and the five controllable power electronic switches are, in order, the fifth fully controllable power electronic switch (S5) to the ninth fully controllable power electronic switch (S9). The eleventh diode (D11) and the fourteenth diode (D14), the thirteenth diode (D13) and the sixteenth diode (D16), and the fifteenth diode (D15) and the twelfth diode (D12) are connected in series in pairs and then in parallel. At the same time, the lines connected in series in pairs are respectively provided with three AC input terminals of the sub-unit. The two ends of the series-connected and then parallel-connected lines serve as the DC bus voltage output terminals and the positive DC bus voltage output terminals (DC+) of the sub-unit. The negative DC bus voltage output terminal (DC-) forms a three-phase full-bridge uncontrolled rectifier structure. The second DC energy storage capacitor (C2) is connected between the two DC bus voltage output terminals of the sub-unit. The fifth fully controlled power electronic switch (S5) and the sixth fully controlled power electronic switch (S6), the seventh fully controlled power electronic switch (S7) and the eighth fully controlled power electronic switch (S8) are connected in series in pairs, and the two ends of the series connection are respectively connected to the two DC bus voltage output terminals of the sub-unit. The two series connection lines are also provided with the two AC output terminals of the sub-unit, forming a single-phase H-bridge inverter structure. The braking resistor (R1) and the seventeenth diode (D17) are connected in parallel, one end of which is connected to the negative DC bus voltage output terminal (DC-), and the other end is connected in series with the ninth fully controlled power electronic switch (S9) and then connected to the positive DC bus voltage output terminal (DC+), forming a DC chopper braking structure.

7. A cascaded high-voltage frequency converter with a multi-power unit parallel structure as described in claim 1, 2, or 3, characterized in that... The sub-unit structure of the power unit is as follows: The sub-unit includes an input filter assembly (Filter), ten fully controlled power electronic switches, and a third DC energy storage capacitor (C3). The ten fully controlled power electronic switches are, in order, the eleventh fully controlled power electronic switch (S11) to the sixteenth fully controlled power electronic switch (S16) and the thirty-first fully controlled power electronic switch (S31) to the thirty-fourth fully controlled power electronic switch (S34). The eleventh fully controlled power electronic switch (S11) and the fourteenth fully controlled power electronic switch (S14), the thirteenth fully controlled power electronic switch (S13) and the sixteenth fully controlled power electronic switch (S16), and the fifteenth fully controlled power electronic switch (S15) and the twelfth fully controlled power electronic switch (S12) are connected in series in pairs and then in parallel. Each series-connected line is then connected to the output terminal of the filter assembly (Filter). The input terminals of the filter component serve as the three AC input terminals of the sub-unit. The two ends of the series connection and parallel connection serve as the DC bus voltage output terminals of the sub-unit, namely the positive DC bus voltage output terminal (DC+) and the negative DC bus voltage output terminal (DC-), forming a three-phase active rectification structure. The two ends of the third DC energy storage capacitor (C3) are respectively connected to the two DC bus voltage output terminals of the sub-unit. The thirty-first fully controlled power electronic switch (S31) and the thirty-second fully controlled power electronic switch (S32), the thirty-third fully controlled power electronic switch (S33) and the thirty-fourth fully controlled power electronic switch (S34) are respectively connected in series in pairs, and the two ends of the series connection are respectively connected to the two DC bus voltage output terminals of the sub-unit. The two series-connected lines are also provided with the two AC output terminals of the sub-unit, forming a single-phase H-bridge inverter structure.

8. A cascaded high-voltage frequency converter with a multi-power unit parallel structure as described in claim 1, 2, or 3, characterized in that... The sub-unit structure of the power unit: The sub-unit is further provided with a bypass switch (K1), the two ends of which are respectively connected to the two AC output terminals of the sub-unit to form a sub-unit with automatic bypass function.

9. A cascaded high-voltage frequency converter with a multi-power unit parallel structure as described in claim 1 or 3, characterized in that: The current-sharing reactor is either an iron-core reactor or an air-core reactor.

10. A cascaded high-voltage frequency converter with a multi-power unit parallel structure according to claim 7, characterized in that: The filter component described herein is a low-pass filter with an L, LC, or LCL structure.

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