A modular power unit and method suitable for four-quadrant cascade frequency conversion

Abstract

The present invention provides a modular power unit and method suitable for four-quadrant cascade frequency conversion; the modular power unit consists of a power unit module and a capacitor module; the power unit module includes two small-volume power modules, a power unit housing and a metal cavity of a control circuit board; the power unit main circuit adopts single-phase PWM rectification and single-phase H-bridge inversion; the secondary winding structure of the transformer of the four-quadrant high-voltage frequency conversion system adopting the modular power unit is simple, and the design of a power unit input reactor-free four-quadrant H-bridge cascade multi-level high-voltage frequency conversion system is more efficiently realized, and the rectification and inversion IGBT power modules are symmetrically arranged in the two small-volume power modules, which greatly reduces the complexity of the power unit design and improves the modularization level of the power unit; the present invention provides a highly reliable and low-cost modular power unit and method.

Description

Technical Field

[0001] The present invention belongs to the technical field of four-quadrant H-bridge cascade multi-level high-voltage frequency conversion systems, and in particular relates to a modular power unit and method suitable for four-quadrant cascade frequency conversion. Background Art

[0002] In a four-quadrant H-bridge cascaded multi-level high-voltage inverter system, the design of the power unit directly affects key factors such as the cost, reliability, compatibility, and ease of maintainability of the entire high-voltage inverter system.

[0003] The power unit principle currently used in the four-quadrant H-bridge cascade multi-level high-voltage frequency conversion system is as follows: Figure 1 As shown in the figure, the high-voltage inverter's multi-winding phase-shifting transformer T1 isolates, steps down, and phase-shifts the input three-phase high-voltage power supply through multiple three-phase output extended triangle secondary windings Ux, Vx, and Wx, then supplies it to each power unit. A three-phase power unit input reactor Lnx is connected in series between the multi-winding phase-shifting transformer's secondary winding and the power unit to implement four-quadrant PWM rectification control. The rectifier circuit of a four-quadrant H-bridge cascaded multi-level high-voltage inverter power unit generally uses three-phase PWM rectification, while the inverter circuit uses single-phase H-bridge inverter. The DC output side of the rectifier circuit and the DC input side of the inverter circuit are connected to the DC link capacitor C, and resistor R is used to discharge the capacitor. The unit control circuit board controls the rectifier and inverter IGBT power modules of the power unit through the rectifier IGBT driver board and inverter IGBT driver board, respectively.

[0004] In a four-quadrant H-bridge cascaded multilevel high-voltage inverter system, the main components that significantly impact system cost are the multi-winding phase-shifting transformer, the power unit input three-phase reactor, and the power unit's IGBT power module. For the multi-winding phase-shifting transformer, the use of a three-phase output Yanbian triangle secondary winding design requires more metal and insulation material, and a more complex winding process, significantly impacting transformer cost. As for the power unit input reactor, since each power unit requires a three-phase input reactor, for example, a 6kV four-quadrant H-bridge cascaded multilevel high-voltage inverter system with five power units per phase would require 15 three-phase input reactors. This not only significantly impacts system cost but also hinders system size reduction. For the power unit, three-phase PWM rectification requires the use of three half-bridge IGBT power modules. Not only is the number of IGBT power modules large, but the rectification and inverter IGBT drive circuit boards cannot be interchangeable. In addition, the safety distances of more components must be considered when designing the power unit, and more metal connectors and insulating parts must be used, which significantly affects the cost, volume and complexity of the power unit.

[0005] Currently, there are two main design approaches for power units in H-bridge cascaded multi-level high-voltage frequency conversion systems: an integrated power unit and a power unit with separate power modules and capacitors. The integrated power unit integrates the key components of the power unit into a single unit. Specifically, the three-phase rectifier power module and H-bridge inverter power module are placed on a single heat sink. The remaining key components, including the support capacitors, and the heat sink are then placed in a single cavity, forming an integrated power unit. This makes it easier to achieve low stray inductance for some key main power metal connectors, improving the reliability of the power unit. The power unit with separate power modules and capacitors is designed by placing the three-phase rectifier power module and H-bridge inverter power module on a single heat sink. The remaining components, excluding the support capacitors, and the heat sink are placed in a single cavity, forming a single power module. The module is then connected to the support capacitors via DC metal connectors, allowing the support capacitors to be separated from the power module, reducing the weight and volume of the power module.

[0006] The integrated power unit has too many power components installed on a single heat sink, making the assembly process complicated. The power unit is large and heavy, making it difficult to transport and assemble, and resulting in high maintenance costs. It is also not conducive to modular production, improving heat dissipation capabilities, and has low compatibility. Although power units with separate power modules and capacitors reduce the size and weight of the power module to a certain extent, due to the large number of rectifier and inverter power modules within the power unit, the size and weight of the power module formed after being arranged on a single heat sink are still relatively large. The main power metal connector between the power module and the supporting capacitor is long, making it difficult to achieve a low stray inductance effect on the key DC metal connector, affecting the reliability of the power unit. Summary of the Invention

[0007] In view of the deficiencies in the prior art, the present invention provides a modular power unit and method suitable for four-quadrant cascade frequency conversion, which is low-cost, highly reliable, highly compatible, and easy to maintain.

[0008] The technical solution of the present invention is: a modular power unit and method suitable for four-quadrant cascade frequency conversion, wherein the modular power unit is composed of a power unit module and a capacitor module; the power unit module and the capacitor module are arranged front to back, with the power unit module in front and the capacitor module in the back; the power unit module includes a left-side small-volume power module and a right-side small-volume power module; the two small-volume power modules respectively include a left-side radiator and a right-side radiator; the heat dissipation surfaces of the left-side radiator and the right-side radiator are symmetrically arranged with a single-phase PWM rectifier module and a single-phase H-bridge inverter module; the single-phase PWM rectifier module and the single-phase H-bridge inverter module ... The phase H-bridge inverter modules respectively adopt a single-phase PWM rectifier circuit and a single-phase H-bridge inverter circuit; the single-phase PWM rectifier module includes a first single-phase PWM rectifier module and a second single-phase PWM rectifier module; the single-phase H-bridge inverter module includes a first single-phase H-bridge inverter module and a second single-phase H-bridge inverter module; the first single-phase PWM rectifier module and the first single-phase H-bridge inverter module are arranged on the left radiator; the second single-phase PWM rectifier module and the second single-phase H-bridge inverter module are arranged on the right radiator; the single-phase PWM rectifier module is arranged at the lower part of the radiator; and the single-phase H-bridge inverter module is arranged at the upper part of the radiator.

[0009] The single-phase PWM rectifier module is connected to the AC input metal connection terminal via an AC input metal connector, and is connected to the DC output metal connection terminal via a DC output metal connector. The AC input metal connector is an aluminum busbar, a copper busbar, or a cable. The DC output metal connector is a copper or aluminum laminated composite busbar, a copper busbar, or an aluminum busbar. The AC input metal connection terminal includes a first AC input metal connection terminal and a second AC input metal connection terminal. The DC output metal connection terminal includes a first DC output metal connection terminal and a second DC output metal connection terminal. The first AC input metal connection terminal and the second AC input metal connection terminal are respectively connected to the two ends of the secondary single-phase output winding of the multi-winding transformer of the frequency conversion system. The secondary winding of the multi-winding transformer adopts a single-phase winding, does not require phase shifting between windings, and does not adopt a complex Yanbian triangle three-phase output winding. At the same time, by increasing the impedance of the secondary winding of the multi-winding transformer to replace the power unit three-phase input reactor, a four-quadrant H-bridge cascade multi-level high-voltage frequency conversion system without a power unit input reactor is realized.

[0010] The single-phase H-bridge inverter module is connected to the DC input metal connection terminal through a DC input metal connector, and is connected to the AC output metal connection terminal through an AC output metal connector; the AC output metal connector is an aluminum busbar or a copper busbar; the DC input metal connector is a laminated composite busbar of copper or aluminum; the DC input metal connection terminal includes a first DC input metal connection terminal and a second DC input metal connection terminal; the AC output metal connection terminal includes a first AC output metal connection terminal and a second AC output metal connection terminal; the first AC input metal connection terminal and the first DC output metal connection terminal are installed on the left side of the small-volume power module; the second AC input metal connection terminal and the second DC output metal connection terminal are installed on the right side of the small-volume power module.

[0011] The single-phase PWM rectifier module and the single-phase H-bridge inverter module are composed of a half-bridge packaged IGBT power module; the positive and negative terminals of the half-bridge packaged IGBT power module are installed with surge absorption capacitors; the half-bridge packaged IGBT power module can adopt a non-parallel or parallel structure according to the capacity requirements of the inverter.

[0012] The IGBT power module adopts a 62mm package or an EconoDUAL half-bridge package IGBT power module.

[0013] The capacitor module of the power unit includes a capacitor group composed of several single metal film capacitors; the capacitor group is connected to the DC output metal connection terminal and the DC input metal connection terminal respectively through capacitor metal connectors; a capacitor group base is provided at the bottom of the capacitor group, and the capacitor group base supports the capacitor group at the bottom; the discharge resistor is arranged behind the capacitor group base; the discharge resistor is connected to the positive and negative terminals of the capacitor group through a cable.

[0014] The power unit module includes a power unit housing; the small-volume power module is symmetrically installed vertically on both sides of the power unit housing, wherein the heat dissipation surfaces of the radiators on the left and right sides of the small-volume power module are installed relative to each other; the power unit housing is preferably made of insulating material in a four-quadrant cascaded frequency conversion system with a capacity below 800KVA to facilitate reducing the insulation distance requirements between power units, thereby reducing the volume of the high-voltage frequency conversion system; the power unit housing is preferably made of metal material in a four-quadrant cascaded frequency conversion system with a capacity above 800KVA to facilitate shielding the electromagnetic interference of the high-voltage frequency conversion system.

[0015] The power unit module includes a metal cavity for a control circuit board; the metal cavity for the control circuit board is installed on the outside of the power unit housing; the interior of the metal cavity for the control circuit board is provided with a unit control circuit board, a power circuit board, a rectifier IGBT driver board, and an inverter IGBT driver board; the circuit boards in the metal cavity for the control circuit board are connected by wiring; the rectifier IGBT driver board, the inverter IGBT driver board and the single-phase PWM rectifier IGBT power module and the single-phase H-bridge inverter IGBT power module are connected by cables; the rectifier IGBT driver board and the inverter IGBT driver board are universal and can be replaced with each other.

[0016] Beneficial effects of the present invention:

[0017] (1) The four-quadrant H-bridge cascade multi-level high-voltage frequency conversion system adopts the above-mentioned modular power unit and method, which can simplify the secondary winding of the multi-winding transformer of the frequency converter from the original Yanbian triangle three-phase output to single-phase output, and there is no phase shift angle requirement between the secondary windings of the transformer. This not only greatly simplifies the winding structure and manufacturing process of the multi-winding transformer, but also makes the design method of replacing the input inductor by increasing the secondary winding impedance of the multi-winding transformer simpler. It is easier to realize the four-quadrant H-bridge cascade multi-level high-voltage frequency conversion system without the need for expensive power unit input inductors, simplifies the four-quadrant high-voltage frequency conversion main power circuit, and has obvious advantages in reducing the cost and volume of the four-quadrant H-bridge cascade multi-level high-voltage frequency conversion system.

[0018] (2) The use of the above-mentioned modular power unit and method not only reduces the number and cost of the power unit rectifier IGBT power modules, but also reduces the number of metal connectors and insulating parts used in the power unit, reducing the complexity of the power unit design. In the four-quadrant H-bridge cascade multi-level high-voltage frequency conversion application within a certain power range, it has obvious advantages in reducing the cost and volume of the inverter power unit.

[0019] (3) By adopting the above-mentioned modular power unit and method, it is relatively easy to symmetrically arrange the single-phase PWM rectifier module and the single-phase H-bridge inverter module of the power unit on two small-volume heat sinks, thereby improving the modularization and standardization of the power unit and increasing the proportion of common metal connectors in the power unit, which is convenient for the production and maintenance of the power unit. In addition, the rectifier and inverter IGBT driver boards are common, which has obvious advantages in reducing the cost of the power unit.

[0020] (4) The use of the above-mentioned modular power unit and method can significantly reduce the volume of a single power module, facilitate the low-inductance design of the key DC metal connectors between the power module and the supporting capacitor module, and improve the reliability of the power unit.

[0021] (5) By adopting the above modular power unit and method, the heat dissipation capacity of the air-cooled radiator can be more efficiently utilized, the heat dissipation problem of the rectifier and inverter IGBT power modules can be more easily solved, and the power expansion capability of the power unit can be improved.

[0022] (6) For the same four-quadrant H-bridge cascade multi-level high-voltage frequency converter, the above-mentioned modular power unit and method are used, which not only realizes the interchangeability between power units in the frequency converter, but also the left and right small-volume power modules in different power units can be replaced with each other respectively, and the power unit has obvious advantages in compatibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the principle of a commonly used power unit in a four-quadrant H-bridge cascaded multi-level high-voltage frequency conversion system.

[0024] Figure 2 Schematic diagram of the principle of the modular power unit and method of the present invention.

[0025] Figure 3 This is a schematic diagram of the principle of a high-voltage frequency conversion system using modular power units in the present invention.

[0026] Figure 4 It is a structural diagram of the power module in the present invention.

[0027] Figure 5 It is a schematic diagram of the partial structure of the casing in the present invention.

[0028] Figure 6 This is a schematic diagram of the modular power unit structure in the present invention. DETAILED DESCRIPTION

[0029] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The description of the exemplary embodiments is merely illustrative and is in no way intended to limit the present invention and its application or use. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the present invention thorough and complete and to fully convey the scope of the present invention to those skilled in the art. It should be noted that unless otherwise specifically stated, the relative arrangement of parts and steps, the composition of materials, numerical expressions, and numerical values ​​set forth in these embodiments should be interpreted as being merely exemplary and not as limiting.

[0030] The terms "first", "second" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different parts. The terms "include" or "comprises" and similar terms mean that the elements before the term include the elements listed after the term, and do not exclude the possibility of also including other elements. The terms "upper", "lower", "left", "right", "front", "back" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0031] like Figures 2 to 6 As shown, a modular power unit and method suitable for four-quadrant cascade frequency conversion: the modular power unit includes a power unit module 1 and a capacitor module 2; the power unit module 1 and the capacitor module 2 are arranged front to back, with the power unit 1 in front and the capacitor module 2 in the back.

[0032] The power unit module 1 includes a small-volume power module 11 on the left and a small-volume power module 12 on the right; the small-volume power modules 11 and 12 respectively include a left heat sink 110 and a right heat sink 120; the left heat sink 110 and the right heat sink 120 respectively include a heat dissipation surface 1101 of the heat sink; the heat dissipation surfaces 1101 of the two heat sinks 110 and 120 are symmetrically arranged with a single-phase PWM rectifier module 111 and a single-phase H-bridge inverter module 112; the single-phase PWM rectifier module 111 The single-phase H-bridge inverter module 112 and the single-phase H-bridge inverter module 111 respectively adopt a single-phase PWM rectifier circuit and a single-phase H-bridge inverter circuit; the single-phase PWM rectifier module 111 comprises a first single-phase PWM rectifier module 1111A and a second single-phase PWM rectifier module 1111B; the single-phase H-bridge inverter module 112 comprises a first single-phase H-bridge inverter module 1121A and a second single-phase H-bridge inverter module 1121B; the first single-phase PWM rectifier module 1111A and the first single-phase H-bridge inverter module 1121A are arranged on the left side. heat sink 110; a second single-phase PWM rectifier module 1111B and a second single-phase H-bridge inverter module 1121B are arranged on the right heat sink 120; the single-phase PWM rectifier module 111 and the single-phase H-bridge inverter module 112 are composed of a half-bridge packaged IGBT power module 15; surge absorption capacitors 117 are installed at the positive and negative terminals of the half-bridge packaged IGBT power module 15; the half-bridge packaged IGBT power module 15 can adopt a non-parallel or parallel structure according to the capacity requirements of the inverter. A preferred embodiment is to adopt a 62mm or EconoDUAL half-bridge packaged IGBT power module, specifically, the FF200R17KE4 or FF200R17ME4; adopting this method, the number and cost of the power unit rectifier IGBT power modules are reduced, the complexity of the power unit design is reduced, and it is easier to realize the symmetrical arrangement of the rectifier and inverter power modules on the left and right heat sinks, more efficiently utilizing the heat dissipation capacity of the air-cooled heat sink, and improving the modularity of the power unit.

[0033] The single-phase PWM rectifier module 111 and the single-phase H-bridge inverter module 112 are arranged above and below the heat dissipation surface 1101 of the radiator; the single-phase PWM rectifier module 111 is arranged at the lower part of the heat dissipation surface 1101 of the radiator, and the single-phase H-bridge inverter module 112 is arranged at the upper part of the heat dissipation surface 1101 of the radiator; because the power consumption of the single-phase PWM rectifier module 111 is greater than that of the single-phase H-bridge inverter module 112, this arrangement can further fully utilize the heat dissipation performance of the air-cooled radiator, easily achieve the shortest distance between the single-phase H-bridge inverter module 112 and the capacitor metal connector 24, and help improve the reliability of the power unit.

[0034] The single-phase PWM rectifier module 111 is connected to the AC input metal connection terminal 1131 through the AC input metal connection member 113; the single-phase PWM rectifier module 111 is connected to the DC output metal connection terminal 1141 through the DC output metal connection member 114; the AC input metal connection terminal 1131 includes a first AC input metal connection terminal 1131A and a second AC input metal connection terminal 1131B; the DC output metal connection terminal 1141 includes a first DC output metal connection terminal 1141A and a second DC output metal connection terminal 1141B.

[0035] The first AC input metal connection terminal 1131A and the second AC input metal connection terminal 1131B are respectively connected to the two ends of the secondary single-phase output winding of the multi-winding transformer 4; the secondary single-phase output winding of the multi-winding transformer 4 is divided into three groups: Ux, Vx, and Wx. Figure 3 As shown in the figure, taking a 6KV voltage-level high-voltage frequency conversion system as an example, 5 power units are required on each output side of the high-voltage frequency converter U, V, and W. Then, each secondary side of the multi-winding transformer U, V, and W has 5 sets of single-phase output windings, for a total of 15 sets of single-phase output windings. The secondary winding of the multi-winding transformer is simplified from the commonly used Yanbian triangle three-phase output to a single-phase output winding, and no phase shift angle is required between the secondary windings of the transformer. Since the secondary winding of the multi-winding transformer has a simple single-phase output structure, it is relatively easy to replace the expensive three-phase input reactor of the power unit by increasing the impedance of the transformer secondary winding, so that the power unit of the high-voltage frequency conversion system does not need to be equipped with an expensive three-phase input reactor. This greatly simplifies the structure of the multi-winding transformer and the four-quadrant high-voltage frequency conversion main power circuit.

[0036] The single-phase H-bridge inverter module 112 is connected to the DC input metal connection terminal 1151 through the DC input metal connection member 115; the DC input metal connection terminal 1151 includes a first DC input metal connection terminal 1151A and a second DC input metal connection terminal 1151B; the single-phase H-bridge inverter module 112 is connected to the AC output metal connection terminal 1161 through the AC output metal connection member 116; the AC output metal connection terminal 1161 includes a first AC output metal connection terminal 1161A and a second AC output metal connection terminal 1161B.

[0037] The first AC input metal connection terminal 1131A and the first DC output metal connection terminal 1141A are installed on the left small-volume power module 11; the second AC input metal connection terminal 1131B and the second DC output metal connection terminal 1141B are installed on the right small-volume power module 12; this method reduces the number of metal connectors and insulating parts used in the power unit, increases the proportion of common metal connectors in the power unit, and enables the left and right small-volume power modules in different power units to be replaced with each other, thereby improving the compatibility and maintainability of the power unit.

[0038] The capacitor module 2 of the power unit includes a capacitor group 21 composed of several single metal film capacitors; the capacitor group 21 is connected to the DC output metal connection terminal 1141 and the DC input metal connection terminal 1151 respectively through the capacitor metal connector 24; the power unit module and the capacitor module can be easily separated or assembled together by disassembling and assembling the fixing metal screws between the DC output metal connection terminal 1141, the DC input metal connection terminal 1151 and the capacitor metal connector 24, which facilitates the assembly and maintenance of the power unit; a capacitor group base 22 is provided at the bottom of the capacitor group 2, and the capacitor group base 22 supports the capacitor group 21 at the bottom; the discharge resistor 23 is arranged behind the capacitor group base 22; the discharge resistor 23 is connected to the positive and negative terminals of the capacitor group 21 through a cable.

[0039] The power unit module 1 includes a power unit housing 13; the small-volume power modules 11 and 12 are symmetrically installed vertically on both sides of the inside of the power unit housing 13, wherein the radiators on the left and right sides of the small-volume power modules are arranged and the rectifier and inverter power modules are installed opposite to each other on the side; the power unit housing 13 is preferably made of insulating material in high-voltage frequency conversion systems with a capacity below 800KVA to facilitate reducing the insulation distance requirements between power units, thereby reducing the volume of the power cabinet of the high-voltage frequency conversion system; the power unit housing 13 is preferably made of metal material in high-voltage frequency conversion systems with a capacity above 800KVA to facilitate shielding the electromagnetic interference of the high-voltage frequency conversion system.

[0040] The power unit module 1 includes a control circuit board metal cavity 14; the control circuit board metal cavity 14 is installed on the outside of the power unit housing 13; the inside of the control circuit board metal cavity 14 is provided with a unit control circuit board 141, a power circuit board 142, a rectifier IGBT driver board 143, and an inverter IGBT driver board 144; the circuit boards in the control circuit board metal cavity are connected by wiring; the rectifier IGBT driver board 143, the inverter IGBT driver board 144 and the half-bridge packaged bridge IGBT power module are connected by cables; among them, the unit control circuit board 141, the power circuit board 142, the rectifier IGBT driver board 143, and the inverter IGBT driver board 144 are all components in the prior art, so their functions and structures are no longer repeated.

[0041] Thus far, various embodiments of the present invention have been described in detail. To avoid obscuring the concept of the present invention, some details well known in the art have not been described. Based on the above description, those skilled in the art can fully understand how to implement the technical solutions disclosed herein.

[0042] The above-described embodiments represent only some embodiments of the present invention. Although the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art may make various modifications and improvements without departing from the scope of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A modular power unit suitable for four-quadrant cascade frequency conversion, characterized by: The modular power unit is composed of a power unit module and a capacitor module; the power unit module and the capacitor module are arranged front and back, with the power unit module in front and the capacitor module in the back; the power unit module includes a small-volume power module on the left and a small-volume power module on the right; the two small-volume power modules respectively include a left radiator and a right radiator; the heat dissipation surfaces of the left radiator and the right radiator are symmetrically arranged with a single-phase PWM rectifier module and a single-phase H-bridge inverter module; the single-phase PWM rectifier module and the single-phase H-bridge inverter module respectively adopt single-phase PWM Rectifier circuit and single-phase H-bridge inverter circuit; the single-phase PWM rectifier module includes a first single-phase PWM rectifier module and a second single-phase PWM rectifier module; the single-phase H-bridge inverter module includes a first single-phase H-bridge inverter module and a second single-phase H-bridge inverter module; the first single-phase PWM rectifier module and the first single-phase H-bridge inverter module are arranged on the left radiator; the second single-phase PWM rectifier module and the second single-phase H-bridge inverter module are arranged on the right radiator; the single-phase PWM rectifier module is arranged at the bottom of the radiator; the single-phase H-bridge inverter module is arranged at the top of the radiator; The single-phase PWM rectifier module is connected to the AC input metal connection terminal via an AC input metal connector, and is connected to the DC output metal connection terminal via a DC output metal connector. The AC input metal connector is an aluminum busbar, a copper busbar, or a cable. The DC output metal connector is a copper or aluminum laminated composite busbar, a copper busbar, or an aluminum busbar. The AC input metal connection terminal includes a first AC input metal connection terminal and a second AC input metal connection terminal. The DC output metal connection terminal includes a first DC output metal connection terminal and a second DC output metal connection terminal. The first AC input metal connection terminal and the second AC input metal connection terminal are respectively connected to the two ends of the secondary single-phase output winding of the multi-winding transformer of the frequency conversion system. The secondary winding of the multi-winding transformer adopts a single-phase winding, does not require phase shifting between windings, and does not adopt a complex Yanbian triangle three-phase output winding. At the same time, by increasing the impedance of the secondary winding of the multi-winding transformer to replace the power unit three-phase input reactor, a four-quadrant H-bridge cascade multi-level high-voltage frequency conversion system without a power unit input reactor is realized.

2. A modular power unit suitable for four-quadrant cascade frequency conversion according to claim 1, characterized in that: The single-phase H-bridge inverter module is connected to the DC input metal connection terminal through a DC input metal connector, and is connected to the AC output metal connection terminal through an AC output metal connector; the AC output metal connector is an aluminum busbar or a copper busbar; the DC input metal connector is a laminated composite busbar of copper or aluminum; the DC input metal connection terminal includes a first DC input metal connection terminal and a second DC input metal connection terminal; the AC output metal connection terminal includes a first AC output metal connection terminal and a second AC output metal connection terminal; the first AC input metal connection terminal and the first DC output metal connection terminal are installed on the left side of the small-volume power module; the second AC input metal connection terminal and the second DC output metal connection terminal are installed on the right side of the small-volume power module.

3. The modular power unit suitable for four-quadrant cascade frequency conversion according to claim 1, characterized in that: The single-phase PWM rectifier module and the single-phase H-bridge inverter module are composed of a half-bridge packaged IGBT power module; the positive and negative terminals of the half-bridge packaged IGBT power module are installed with surge absorption capacitors; the half-bridge packaged IGBT power module can adopt a non-parallel or parallel structure according to the capacity requirements of the inverter.

4. The modular power unit suitable for four-quadrant cascade frequency conversion according to claim 3, characterized in that: The IGBT power module adopts a 62mm package or an EconoDUAL half-bridge package IGBT power module.

5. The modular power unit suitable for four-quadrant cascade frequency conversion according to claim 1, characterized in that: The capacitor module of the power unit includes a capacitor group composed of a plurality of single metal film capacitors; the capacitor group is connected to the DC output metal connection terminal and the DC input metal connection terminal through capacitor metal connectors; a capacitor group base is provided at the bottom of the capacitor group to support the capacitor group; The discharge resistor is arranged behind the base of the capacitor group; the discharge resistor is connected to the positive and negative terminals of the capacitor group through cables.

6. The modular power unit suitable for four-quadrant cascade frequency conversion according to claim 1, characterized in that: The power unit module includes a power unit housing; the small-volume power modules are symmetrically installed vertically on both sides of the power unit housing, wherein the heat dissipation surfaces of the radiators on the left and right sides of the small-volume power modules are installed opposite to each other; the power unit housing is made of insulating material in a four-quadrant cascaded frequency conversion system with a capacity below 800KVA to facilitate reducing the insulation distance requirements between power units, thereby reducing the volume of the high-voltage frequency conversion system; the power unit housing is made of metal material in a four-quadrant cascaded frequency conversion system with a capacity above 800KVA to facilitate shielding the electromagnetic interference of the high-voltage frequency conversion system.

7. The modular power unit suitable for four-quadrant cascade frequency conversion according to claim 1, characterized in that: The power unit module includes a metal cavity for a control circuit board; the metal cavity for the control circuit board is installed on the outside of the power unit housing; the interior of the metal cavity for the control circuit board is provided with a unit control circuit board, a power circuit board, a rectifier IGBT driver board, and an inverter IGBT driver board; the circuit boards in the metal cavity for the control circuit board are connected by wiring; the rectifier IGBT driver board, the inverter IGBT driver board and the single-phase PWM rectifier IGBT power module and the single-phase H-bridge inverter IGBT power module are connected by cables; the rectifier IGBT driver board and the inverter IGBT driver board are universal and can be replaced with each other.

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