Cascaded frequency converter

Abstract

The utility model provides a cascaded frequency converter. The cascaded frequency converter comprises a transformer, the transformer comprises a primary side coil and a secondary side coil, and the primary side coil can be connected with a power grid; a plurality of power unit groups, each power unit group comprises a plurality of cascaded power units, the plurality of power units are connected with the secondary coil, and each power unit comprises a capacitor connected with the DC bus; one end of the resistor is connected with the tap of the primary coil, and the other end is connected with the neutral point of the primary coil; and the switch is connected in parallel with the resistor. According to the cascade type frequency converter, the switch can take electricity from the tap of the primary side coil of the transformer, automatic triggering of the switch can be achieved, no extra control circuit is needed to control on-off of the switch, the switch and the control circuit do not need to be electrically connected, insulation design does not need to be strengthened, and cost is reduced. The size, cost and installation difficulty of the switch can be reduced.

Description

TECHNICAL FIELD

[0001] The utility model relates to variable frequency device technical field especially, and it is a kind of cascaded variable frequency device. BACKGROUND

[0002] Variable-frequency Drive (VFD) is through changing motor output voltage frequency and voltage amplitude to control motor power control equipment. Variable-frequency Drive is widely used in fan, water pump, belt conveyor, experimental power supply and other scenes. In order to reduce the influence of surge on power grid and variable-frequency Drive safety at the moment of power-on, some variable-frequency Drive increases pre-charging function in high-voltage side, and traditional pre-charging switch and resistance are arranged between user power grid (for example, 10kV) and transformer of variable-frequency Drive, and switch action is controlled by control system (for example, PLC), and this way has high requirement to pre-charging switch, and it needs to select switch with insulation level meeting enhanced insulation or double insulation, otherwise electric shock accident is easy to cause. In order to prevent the occurrence of this accident, main circuit and control circuit of switch need to be designed with enhanced insulation, but this will increase the size, cost and installation difficulty of switch. Therefore, a new technical scheme is needed to solve the above technical problems.

[0003] The content of the background section merely represents the technical knowledge of the inventor, and does not necessarily represent the prior art in the field. CONTENT OF THE UTILITY MODEL

[0004] In view of one or more of the problems existing in the prior art, the utility model provides a kind of cascaded variable frequency device, including: transformer, the transformer includes primary winding and secondary winding, wherein the primary winding can be connected power grid;Multiple power unit groups, each power unit group includes cascaded multiple power units, the multiple power units connect the secondary winding, each power unit includes the capacitor connected to DC bus;Resistance, one end of the resistance is connected with the tap of the primary winding, and the other end is connected with the neutral point of the primary winding;And switch, the switch is connected in parallel with the resistance.

[0005] Optionally, the first end and the second end of the switch are connected in parallel with the resistance, and the control end of the switch is connected with the tap, and the transformer provides trigger voltage signal to the switch through the tap.

[0006] Optionally, the number of resistances is multiple, one end of each resistance is connected with one of the taps, and the other end is connected with the neutral point;The number of switches is multiple, the first end and the second end of each switch are connected in parallel with one of the resistances respectively, and the control end of each switch is connected with a pair of the taps of the same phase primary winding.

[0007] Optionally, the number of resistors is one, one end of the resistor is connected to the tap, and the other end is connected to the neutral point; the number of switches is multiple, and the multiple switches include a first switch and a second switch, wherein the first end and the second end of the second switch are connected in parallel to the resistor, and the first end and the second end of the first switch and the second switch are respectively connected to one of the taps and the neutral point, and the control ends of the first switch and the second switch are respectively connected to a pair of the taps of the same phase original coil of the transformer.

[0008] Optionally, the switch is turned off, and the transformer precharges the capacitor through the resistor; and when the precharging of the capacitor by the transformer is completed, the switch is turned on.

[0009] Optionally, the cascaded frequency converter further comprises a step-down module connected to the tap and the switch.

[0010] Optionally, the tap includes one or more of a center tap, a ±10% tap, a ±5% tap, or a ±2.5% tap.

[0011] Optionally, the power unit includes a control unit connected to the capacitor, which can monitor the charging time and / or voltage of the capacitor.

[0012] Optionally, the cascaded frequency converter further comprises a main control module connected to the control unit, and the control unit can communicate the charging time and / or voltage to the main control module.

[0013] The cascaded frequency converter of the utility model, the switch can take electricity from the tap of the original coil of the transformer, can realize automatic triggering of the switch, does not need to set up additional control circuit to control the on-off of the switch, the switch and the control circuit do not need electrical connection, do not need to consider strengthening insulation design, can reduce the size, cost and installation difficulty of the switch. BRIEF DESCRIPTION OF DRAWINGS

[0014] The accompanying drawings are included to provide a further understanding of the utility model, and constitute a part of the specification, and are used together with the embodiments of the utility model to explain the utility model, and do not constitute the limitation to the utility model. In the drawings:

[0015] Figure 1 A schematic view of a cascaded frequency converter according to some embodiments of the utility model is shown.

[0016] Figure 2 A schematic view of a cascaded frequency converter according to some embodiments of the utility model is shown. Figure 1 A partial schematic view of the cascaded frequency converter of the embodiment is shown.

[0017] Figure 3A schematic diagram of a power unit without bypass function according to some embodiments of the present application is shown.

[0018] Figure 4 A schematic diagram of a power unit with bypass function according to some embodiments of the present application is shown.

[0019] Figure 5 A schematic diagram of a cascaded frequency converter according to some embodiments of the present application is shown.

[0020] Figure 6 A schematic diagram of a cascaded frequency converter according to some embodiments of the present application is shown. Figure 5 A partial schematic diagram of a cascaded frequency converter according to some embodiments of the present application is shown.

[0021] Figure 7 A schematic diagram of a cascaded frequency converter according to some embodiments of the present application is shown.

[0022] Figure 8 A schematic diagram of a cascaded frequency converter according to some embodiments of the present application is shown. DETAILED DESCRIPTION

[0023] In the following, only certain exemplary embodiments are simply described. As those skilled in the art will realize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present application. The drawings and description are therefore to be considered an exemplification of the application, and not a limitation thereof.

[0024] In the description of the present application, it is to be understood that the orientations or positional relationships indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", and the like are based on the orientations or positional relationships shown in the drawings, and are merely for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements indicated must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise specifically limited.

[0025] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "coupling" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for mutual communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model according to the specific circumstances.

[0026] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0027] The following provides many different embodiments or examples for implementing various structures of this invention. To simplify the invention, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0028] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0029] The utility model provides a kind of cascaded frequency converter.The cascaded frequency converter includes transformer, multiple power unit groups, resistance and switch.Transformer includes primary winding and secondary winding, wherein primary winding can be connected power grid.Each power unit group includes cascaded multiple power units, and the multiple power units are connected secondary winding.Each power unit includes the capacitor connected direct current bus.The resistance one end connects the tap of primary winding, and the other end connects the neutral point of primary winding.The switch is connected in parallel with resistance.The cascaded frequency converter of the utility model, switch can take electricity from the tap of transformer primary winding, can realize the automatic triggering of switch, without setting additional control circuit to control the on-off of switch, switch and control circuit do not need electrical connection, without considering strengthening insulation design, can reduce the size, cost and installation difficulty of switch.

[0030] Figure 1 A schematic diagram of a cascaded frequency converter according to some embodiments of the utility model is shown. Figure 2 A schematic diagram of Figure 1 A partial schematic diagram of a cascaded frequency converter of an embodiment is shown. Figure 3 A schematic diagram of a power unit without bypass function according to some embodiments of the utility model is shown. Figure 4 A schematic diagram of a power unit with bypass function according to some embodiments of the utility model is shown. Figure 5 A schematic diagram of a cascaded frequency converter according to some embodiments of the utility model is shown. Figure 6 A schematic diagram of Figure 5 A partial schematic diagram of a cascaded frequency converter of an embodiment is shown. In the following, reference is made to Figures 1 to 6 The cascaded frequency converter of the utility model is introduced.

[0031] In some embodiments, as Figures 1 to 4 shown, the cascaded frequency converter 10 includes transformer 11, multiple power unit groups 12, resistance and switch.Transformer 11 includes primary winding 111 and secondary winding 113 and iron core 112.Primary winding 111 can be connected to power grid E (for example, 10kV / 50Hz, etc.).Primary winding 111 includes A, B, C three-phase coils.Secondary winding 113 can be connected to multiple power unit groups 12.Each power unit group 12 includes cascaded multiple power units 121 (one purple rectangle represents one power unit, one row of power units constitutes one power unit group, and three rows of power units constitute three power unit groups).Three power unit groups form three-phase output terminals U, V, W of cascaded frequency converter 10.Three-phase output terminals U, V, W can be connected to motor M.Multiple power units 121 are connected to secondary winding 113.Electric energy provided by power grid E is transmitted to power unit 121 through transformer 11.Each power unit 121 includes capacitor C1-Cn connected to direct current bus (DC+, DC-), and n is a positive integer.

[0032] In some embodiments, the switch includes a first terminal, a second terminal, and a control terminal. The first terminal and the second terminal of the switch are connected in parallel with the resistor. The control terminal of the switch is connected to the tap. The transformer provides a trigger voltage signal to the switch through the tap. That is, the switch can take power from the tap to achieve on-off control. The tap can include one or more of a center tap (0% tap), ±10% tap, ±5% tap, or ±2.5% tap, or other taps. Preferably, the control terminal of the switch can be connected to the tap adjacent to the resistor connected in parallel with the switch, which can reduce the potential difference and reduce the insulation requirement of the switch.

[0033] The utility model discloses not limit the quantity of resistance and switch. In some embodiments, the number of resistors can be multiple, and the number of switches can be multiple. The specifications of the plurality of resistors can be the same. The specifications of the plurality of switches can be the same. One end of each resistor is connected to one of the taps, and the other end is connected to the neutral point. The first end and the second end of each switch are connected in parallel with one of the resistors, respectively. The control terminal of each switch is connected to a pair of taps of the same phase primary coil, respectively. Exemplarily, as shown in Figure 1 and Figure 2 The cascaded frequency converter 10 includes resistors R1, R2, R3 and switches K1, K2, K3. The resistors R1, R2, R3 are connected to taps A1, B1, C1 at one end and to the neutral point N at the other end. The taps A1, B1, C1 can be ±10% taps, ±5% taps, or ±2.5% taps, or 0% taps. The first terminals 1 and the second terminals 2 of the switches K1, K2, K3 are connected in parallel with the resistors R1, R2, R3, respectively. The control terminal g1 of the switch K1 is connected to the taps A1, A0. The control terminal g2 of the switch K2 is connected to the taps B1, B0. The control terminal g3 of the switch K3 is connected to the taps C1, C0. The taps A0, B0, C0 are 0% taps. Alternatively, the control terminal g1 can be connected to the taps A2, A0. The control terminal g2 can be connected to the taps B2, B0. The control terminal g3 can be connected to the taps C2, C0. The taps A2, B2, C2 can be ±10% taps, ±5% taps, or ±2.5% taps, which are opposite to the taps A1, B1, C1. Alternatively, the control terminal g1 can be connected to the taps A1, A2. The control terminal g2 can be connected to the taps B1, B2. The control terminal g3 can be connected to the taps C1, C2. It should be noted that, Figure 1 and Figure 2In some embodiments, the number of resistors can be one. The number of switches can be multiple. One end of the resistor is connected to a tap, and the other end is connected to a neutral point. The multiple switches include a first switch and a second switch. The first end and the second end of the second switch are connected in parallel to the resistor. The first end and the second end of the first switch and the second switch are respectively connected to one of the taps and the neutral point. The control ends of the first switch and the second switch are respectively connected to a pair of taps of the same phase primary coil. For example, as shown in FIG. 1, the first switch K1 and the second switch K2 are connected to the same phase primary coil L1. The control end g1 of the first switch K1 is connected to the tap A1 and the tap A0. The control end g2 of the second switch K2 is connected to the tap B1 and the tap B0. The first end 1 and the second end 2 of the second switch K2 are connected in parallel to the resistor R2. The first end 1 and the second end 2 of the first switch K1 are respectively connected to the tap A1 and the neutral point N. The first switch K1 and the second switch K2 can be two independent single-phase switches. Alternatively, the first switch K1 and the second switch K2 can be a combined two-phase switch. In addition, the resistor R2 can include one resistor, or can include multiple resistors in series and / or parallel. In practical applications, it can be set according to the needs.

[0034] In some embodiments, the number of resistors can be one. The number of switches can be multiple. One end of the resistor is connected to a tap, and the other end is connected to a neutral point. The multiple switches include a first switch and a second switch. The first end and the second end of the second switch are connected in parallel to the resistor. The first end and the second end of the first switch and the second switch are respectively connected to one of the taps and the neutral point. The control ends of the first switch and the second switch are respectively connected to a pair of taps of the same phase primary coil. For example, as shown in FIG. 1, the first switch K1 and the second switch K2 are connected to the same phase primary coil L1. The control end g1 of the first switch K1 is connected to the tap A1 and the tap A0. The control end g2 of the second switch K2 is connected to the tap B1 and the tap B0. The first end 1 and the second end 2 of the second switch K2 are connected in parallel to the resistor R2. The first end 1 and the second end 2 of the first switch K1 are respectively connected to the tap A1 and the neutral point N. The first switch K1 and the second switch K2 can be two independent single-phase switches. Alternatively, the first switch K1 and the second switch K2 can be a combined two-phase switch. In addition, the resistor R2 can include one resistor, or can include multiple resistors in series and / or parallel. In practical applications, it can be set according to the needs. Figure 5 Figure 6 In some embodiments, the number of resistors can be one. The number of switches can be multiple. One end of the resistor is connected to a tap, and the other end is connected to a neutral point. The multiple switches include a first switch and a second switch. The first end and the second end of the second switch are connected in parallel to the resistor. The first end and the second end of the first switch and the second switch are respectively connected to one of the taps and the neutral point. The control ends of the first switch and the second switch are respectively connected to a pair of taps of the same phase primary coil. For example, as shown in FIG. 1, the first switch K1 and the second switch K2 are connected to the same phase primary coil L1. The control end g1 of the first switch K1 is connected to the tap A1 and the tap A0. The control end g2 of the second switch K2 is connected to the tap B1 and the tap B0. The first end 1 and the second end 2 of the second switch K2 are connected in parallel to the resistor R2. The first end 1 and the second end 2 of the first switch K1 are respectively connected to the tap A1 and the neutral point N. The first switch K1 and the second switch K2 can be two independent single-phase switches. Alternatively, the first switch K1 and the second switch K2 can be a combined two-phase switch. In addition, the resistor R2 can include one resistor, or can include multiple resistors in series and / or parallel. In practical applications, it can be set according to the needs. Figure 5 Figure 6 In some embodiments, the number of resistors can be one. The number of switches can be multiple. One end of the resistor is connected to a tap, and the other end is connected to a neutral point. The multiple switches include a first switch and a second switch. The first end and the second end of the second switch are connected in parallel to the resistor. The first end and the second end of the first switch and the second switch are respectively connected to one of the taps and the neutral point. The control ends of the first switch and the second switch are respectively connected to a pair of taps of the same phase primary coil. For example, as shown in FIG. 1, the first switch K1 and the second switch K2 are connected to the same phase primary coil L1. The control end g1 of the first switch K1 is connected to the tap A1 and the tap A0. The control end g2 of the second switch K2 is connected to the tap B1 and the tap B0. The first end 1 and the second end 2 of the second switch K2 are connected in parallel to the resistor R2. The first end 1 and the second end 2 of the first switch K1 are respectively connected to the tap A1 and the neutral point N. The first switch K1 and the second switch K2 can be two independent single-phase switches. Alternatively, the first switch K1 and the second switch K2 can be a combined two-phase switch. In addition, the resistor R2 can include one resistor, or can include multiple resistors in series and / or parallel. In practical applications, it can be set according to the needs.

[0035] ​​In some embodiments, transformer 11 can precharge capacitors C1 to Cn of power unit 121. After the cascaded frequency converter 10 is connected to the user's power grid E (e.g., 10kV / 50Hz), transformer 11 first precharges capacitors C1 to Cn through resistors R1 and / or R2 and / or R3 with current limiting. After precharging is completed, switches K1 and / or K2 and / or K3 automatically close to complete power-on, thereby reducing the surge current of high voltage in the internal circuit of the cascaded frequency converter, reducing the mechanical stress generated by thermal stress and electrodynamics, improving the safety and reliability of the cascaded frequency converter, and optimizing the selection of components such as rectifier bridges, fuses, and power unit bus capacitors to reduce costs.

[0036] In some embodiments, the resistor can act as a current limiter. The switch can be used as a pre-charging switch. The switch is open by default. The transformer pre-charges the capacitor while the switch is open. Once the transformer has completed pre-charging the capacitor, the switch turns on. Figures 1 to 4 As shown, switches K1, K2, and K3 are open by default. After the cascaded frequency converter 10 is powered on, the electrical energy provided by the grid E is transmitted to the power unit 121 through the primary coil 111, resistors R1, R2, and R3, and the secondary coil 113, thereby pre-charging capacitors C1 to Cn. As capacitors C1 to Cn gradually complete their charging, the current gradually decreases, the voltage across the resistors gradually decreases, and the voltages across taps A0 and A1, B0 and B1, and C0 and C1 gradually increase, gradually approaching the operating voltages of switches K1, K2, and K3. When the transformer 11 completes the pre-charging of capacitors C1 to Cn, the voltage across taps A0 and A1 reaches the operating voltage of switch K1, the voltage across taps B0 and B1 reaches the operating voltage of switch K2, and the voltage across taps C0 and C1 reaches the operating voltage of switch K3. Switches K1, K2, and K3 then conduct, and resistors R1, R2, and R3 are bypassed. This achieves automatic triggering of switches K1, K2, and K3 without the need for additional control circuits to control their on / off states, nor does it require reinforced insulation design for the switches and their control circuits. This reduces the size and cost of the switches and facilitates installation. Taps A0, B0, and C0 are center taps (0% taps). Taps A1, B1, and C1 can be ±10%, ±5%, or ±2.5%, etc. It should be noted that this example uses the control terminal g1 of switch K1 connected to taps A1 and A0, the control terminal g2 of switch K2 connected to taps B1 and B0, and the control terminal g3 of switch K3 connected to taps C1 and C0. It should be understood that the example of connecting the control terminal g1 of switch K1 to taps A2 and A0 (or A2 and A1), the control terminal g2 of switch K2 to taps B2 and B0 (or B2 and B1), and the control terminal g3 of switch K3 to taps C2 and C0 (or C2 and C1) is similar. Similarly, for exampleFigures 2 to 6 As shown, the switches K1 and K2 are off by default. After the cascade frequency converter 10 is powered on, the power provided by the power grid E is transmitted to the power unit 121 through the primary coil 111, the resistor R2 and the secondary coil 113, thereby pre-charging the capacitors C1-Cn. When the transformer 11 completes the pre-charging of the capacitors C1-Cn, the voltage across the taps A0 and A1 reaches the operating voltage of the switch K1, and the voltage across the taps B0 and B1 reaches the operating voltage of the switch K2, and the switches K1 and K2 are turned on, and the resistor R2 is bypassed. In this way, the automatic triggering of the switches K1 and K2 is achieved. The taps A0 and B0 are center taps (0% taps). The taps A1 and B1 can be ±10% taps, ±5% taps, or ±2.5% taps, etc. It should be noted that, here, the control end g1 of the switch K1 is connected to the taps A1 and A0, and the control end g2 of the switch K2 is connected to the taps B1 and B0, which are exemplary described. It should be understood that the control end g1 of the switch K1 is connected to the taps A2 and A0 (or A2 and A1), and the control end g2 of the switch K2 is connected to the taps B2 and B0 (or B2 and B1), which are similar to the examples.

[0037] In some embodiments, the cascade frequency converter can further include a voltage reduction module. The voltage reduction module is connected to the taps and the switches. The voltage reduction module can reduce the voltage at the taps of the transformer to a safe voltage that the switches can withstand, avoiding overvoltage burnout of the switches. The voltage reduction module can include a voltage reduction circuit, including but not limited to a switching power supply (for example, a buck circuit), or can be realized by transformer voltage reduction, etc. In actual application, it can be set according to the needs.

[0038] Figure 7 A schematic diagram of a cascade frequency converter according to some embodiments of the present application is shown. As shown, Figure 7 The input side of the voltage reduction module 13 is connected to the center tap A0 and the tap A1 (or A0 and A2; or A1 and A2). The output side of the voltage reduction module 13 is connected to the switches K1 and K2 respectively. The voltage reduction module 13 can take power from the A-phase tap, reduce the voltage and output to the switches K1 and K2. Alternatively, the input side of the voltage reduction module 13 can also be connected to the center tap B0 and the tap B1 (or B0 and B2; or B1 and B2) (not shown in the figure for convenience), take power from the B-phase tap, reduce the voltage and output to the switches K1 and K2. Alternatively, the input side of the voltage reduction module 13 can also be connected to the center tap C0 and the tap C1 (or C0 and C2; or C1 and C2) (not shown in the figure for convenience), take power from the C-phase tap, reduce the voltage and output to the switches K1 and K2. The taps A0, B0 and C0 are center taps (0% taps). The taps A1, B1 and C1 can be ±10% taps, ±5% taps, or ±2.5% taps, etc. It should be noted that, Figure 7In this embodiment, switches K1 and K2 can be independent or integrated. Switches K1 and K2 can each use a separate step-down module, or they can share a single step-down module. When each switch uses a separate step-down module, the input and output sides of each step-down module are connected to the same-phase tap and switch, respectively, drawing power from the same-phase tap and outputting a stepped-down voltage to the same-phase switch. When all switches share a single step-down module, the input side of the step-down module is connected to one or more phase taps, and the output side is connected to each switch, drawing power from the tap and outputting a stepped-down voltage to each switch.

[0039] Figure 8 A schematic diagram of a cascaded frequency converter according to some embodiments of the present invention is shown. For example... Figure 8 As shown, exemplarily, the input side of the step-down module 13 is connected to the center tap A0 and tap A1 (or A0, A2; or A1, A2), drawing power from the A-phase tap and stepping it down before outputting it to switches K1, K2, and K3. The output side of the step-down module 13 is connected to switches K1, K2, and K3 respectively. Optionally, the input side of the step-down module 13 can be connected to the center tap B0 and tap B1 (or B0, B2; or B1, B2) (not shown in the figure for convenience), drawing power from the B-phase tap and stepping it down before outputting it to switches K1, K2, and K3. Optionally, the input side of the step-down module 13 is also connected to the center tap C0 and tap C1 (or C0, C2; or C1, C2) (not shown in the figure for convenience). Taps A0, B0, and C0 are center taps (0% taps), drawing power from the C-phase tap and stepping it down before outputting it to switches K1, K2, and K3. Taps A1 (or A2), B1 (or B2), and C1 (or C2) can be ±10%, ±5%, or ±2.5%, etc. It should be noted that... Figure 8 In this embodiment, switches K1, K2, and K3 can be independent or integrated. Switches K1, K2, and K3 can each use a separate step-down module, or they can share a single step-down module. When each switch uses a separate step-down module, the input and output sides of each module are connected to the tap changer and the switch of the same phase, respectively, drawing power from the tap changer and outputting a stepped-down voltage to the switch of the same phase. When all switches share a single step-down module, the input side of the module is connected to one or more phase tap changers, and the output side is connected to each switch, drawing power from the tap changer and outputting a stepped-down voltage to each switch.

[0040] In some embodiments, the power unit 121 includes a control unit (not shown). The control unit is connected to capacitors C1 to Cn and can monitor the charging time and / or voltage of capacitors C1 to Cn.

[0041] In some embodiments, the cascaded frequency converter further comprises a main control module. The main control module is connected with the control units of the power units (not shown in the figure), and the two can communicate with each other. The control units can communicate the charging time and / or voltage of the capacitors to the main control module. As shown in Figure 3 , Figure 4 , Figure 7 and Figure 8 , the cascaded frequency converter 10 further comprises a main control module 14. The main control module 14 is connected with the control units of the power units 121, and the two can communicate with each other. The control units can communicate the charging time and / or voltage of the capacitors C1-Cn to the main control module 14. The main control module 14 can send control commands to the control units.

[0042] In some embodiments, as shown in Figure 4 , the power unit 121 comprises a bypass switch Thy1 arranged at the output end of the power unit 121. When the bypass switch Thy1 is turned on, the power unit 121 is bypassed. When the bypass switch Thy1 is turned off, the power unit 121 is not bypassed. The control unit is connected with the bypass switch Thy1, and can control the on-off of the bypass switch Thy1 based on the control command of the main control module 14.

[0043] In some embodiments, as shown in Figure 3 and Figure 4 , the power unit 121 can further comprise fuses Fuse1, Fuse2, diodes D1-D10, and insulated gate bipolar transistors IGBT1-IGBT4. The control unit is connected with the control electrodes G1-G4 of the IGBT1-IGBT4, and can control the on-off of the IGBT1-IGBT4 based on the control command of the main control module 14.

[0044] In some embodiments, as shown in Figure 7 and Figure 8 , the cascaded frequency converter 10 can further comprise one or more of a human machine interface (HMI), a drive advisor (DA), and a programmable logic controller (PLC). The HMI, DA, and PLC are connected with the main control module 14, and can communicate with one or more of the main control module 14 and the control units of the power units 121 to share data information.

[0045] In some embodiments, the control terminals g1 / g2 / g3 of the switches K1 / K2 / K3 can be connected to at least one of the main control module 14, the control units, the HMI, the DA, and the PLC, so as to be controlled to be triggered. In actual applications, it can be set according to requirements. These are all within the protection scope of the utility model.

[0046] In some embodiments, the main control module / control unit can include a control circuit, a central processing unit (CPU), a micro control unit (MCU), a digital signal processor (DSP), other general purpose processors, an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, and the like components and circuits.

[0047] In some embodiments, the switches K1 / K2 / K3 / K4 / bypass switch Thy1 can include any switch device that can play the same or similar role, such as a field effect transistor (FET), a bipolar junction transistor (BJT), a relay (RELAY), a silicon controlled rectifier (SCR), a contactor, a circuit breaker, a potentiometer, a mechanical switch, etc. The FET can be a metal-oxide-semiconductor field-effect transistor (MOSFET). The MOSFET can be a P-channel metal-oxide-semiconductor field-effect transistor (PMOS). Alternatively, the FET can be an N-channel metal-oxide-semiconductor field-effect transistor (NMOS). The MOSFET can be a silicon carbide (SIC) MOSFET, a gallium nitride (GaN) MOSFET, or other power device with lower loss, higher efficiency, and better performance. In actual applications, it can be determined according to the needs. These are within the protection scope of the present application.

[0048] The cascade frequency converter, the resistance and the switch are arranged between the tap and the neutral point of the primary coil of the transformer, one end of the resistance is connected with the tap of the primary coil, the other end is connected with the neutral point of the primary coil, the control end of the switch is connected with the tap, the switch and the resistance can take electricity from the tap, the switch can realize automatic triggering, an additional control circuit is not needed to control the on-off of the switch, the switch and the control circuit do not need to be electrically connected, the insulation design needs not to be strengthened, the size, the cost and the installation difficulty of the switch can be reduced.

[0049] It should be noted that, although several modules of the cascade frequency converter are mentioned in the foregoing detailed description, such a division is merely not mandatory. Indeed, according to the embodiments of the present application, the features and functions of two or more modules described above can be implemented in one module. Conversely, the features and functions of one module described above can be further divided into modules.

[0050] It should be noted that the present application can only include Figures 1-8 any one or more features of any one or more embodiments. In other words, not all the features shown must be implemented in the cascade frequency converter of the present application.

[0051] Finally, it should be noted that: the above only describes the preferred embodiments of the present application, and is not intended to limit the present application, although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement for part of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A cascade inverter characterized by comprising: Comprising: a transformer, the transformer comprising a primary coil and a secondary coil, wherein the primary coil is connectable to a power grid; a plurality of power unit groups, each of the power unit groups comprising a plurality of power units connected in cascade, the plurality of power units being connected to the secondary coil, each of the power units comprising a capacitor connected to a DC bus; a plurality of resistors, each of the resistors having one end connected to a tap of the primary coil and another end connected to a neutral point of the primary coil; and a plurality of switches, each of the switches being connected in parallel to one of the resistors. A first end and a second end of each of the switches are connected in parallel to one of the resistors, a control end of each of the switches is connected to a pair of the taps of the primary coil of the same phase.

2. The cascaded frequency converter of claim 1, wherein, The number of the resistors is one, one end of the resistor is connected to the tap, and the other end is connected to the neutral point. The number of the switches is multiple, and the multiple switches comprise a first switch and a second switch. The first end and the second end of the second switch are connected in parallel to the resistor. The first end and the second end of the first switch and the second switch are respectively connected to one of the taps and the neutral point. The control end of the first switch and the second switch is respectively connected to a pair of the taps of the primary coil of the same phase.

3. The cascaded frequency converter of claim 2, wherein, The switch is turned off, and the transformer pre-charges the capacitor through the resistor. When the pre-charging of the capacitor by the transformer is completed, the switch is turned on.

4. The cascaded frequency converter of claim 1, wherein, Further comprising:

5. The cascade frequency inverter according to any one of claims 1 to 4, characterized in that, a step-down module, the step-down module being connected to the tap and the switch.

6. The cascade frequency converter according to any one of claims 1 to 4, characterized in that The tap comprises one or more of a center tap, ±10% taps, ±5% taps, or ±2.5% taps. The power unit comprises a control unit, the control unit being connected to the capacitor and being capable of monitoring the charging time and / or voltage of the capacitor.

7. The cascade frequency inverter according to any one of claims 1 to 4, characterized by Further comprising:

8. The cascade frequency inverter according to any one of claims 1 to 4, characterized by a main control module, the main control module being connected to the control unit, and the control unit being capable of communicating the charging time and / or voltage to the main control module.

9. The cascaded frequency converter of claim 8, wherein, ​ ​

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