Unidirectional power transmission high power density module and modular medium voltage frequency converter

Abstract

The invention discloses a high-power-density module for unidirectional power transmission and a modular medium-voltage frequency converter. The high-power-density module for unidirectional power transmission is composed of a grid-side full-bridge circuit, a high-frequency converter, an LC resonance branch, a multi-winding high-frequency transformer, a high-frequency diode circuit and a machine-side full-bridge circuit. A direct-current port of the grid-side / machine-side full-bridge circuit is connected with a direct-current port of the high-frequency converter and a direct-current port of the high-frequency diode circuit respectively, and an alternating-current port of the high-frequency converter and an alternating-current port of the high-frequency diode circuit are connected with a winding of the high-frequency transformer through LC resonance branches respectively. The modularized medium-voltage frequency converter comprises M high-power-density modules, and alternating-current ports of network-side / machine-side full-bridge circuits of all the modules are connected in series / in parallel to form a network-side three-phase alternating-current port and a machine-side n-phase alternating-current port. According to the invention, the number of IGBTs is effectively reduced, the capacitance value of the capacitor is reduced, and the size of the transformer is reduced, so that the transformer has the characteristics of low cost and high power density.

Description

Technical Field

[0001] The invention relates to the technical field of power electronic electric energy conversion, and in particular to a high power density module for unidirectional power transmission and a modular medium voltage frequency converter. Background Art

[0002] Series H-bridge converter (CHB) and modular multilevel converter (MMC) are widely used medium voltage high power inverters with unidirectional power transmission.

[0003] The series H-bridge converter (CHB) consists of an industrial frequency transformer, a distributed rectifier, and a series H-bridge inverter. However, this topology has a relatively serious power density problem, which is mainly reflected in the expensive industrial frequency transformer and large-capacity DC-side capacitor. The industrial frequency transformer is used to generate the isolated low-voltage AC source required by the distributed rectifier. Since the transformer is directly connected to the medium-voltage power grid, its operating frequency is low, which causes volume and cost problems. The DC-side capacitor between the distributed rectifier and the H-bridge inverter needs to buffer the fluctuating power generated on the motor side. At low frequencies, it generates serious capacitor voltage fluctuations, so a large capacitor is required to buffer it, causing volume and cost problems. The modular multilevel converter (MMC) removes the expensive industrial frequency transformer, but because it requires the midpoint of six bridge arms to form a three-phase AC output, the number of switching devices and capacitors increases to 2 times and 4 times the original. In addition, because it is used for low-speed operation of the motor load, the DC capacitor in each module still needs to buffer the serious double-frequency fluctuation power, resulting in the problem of large capacitance. Therefore, the cost problem caused by switching devices and capacitors is more serious. The above disadvantages limit the application of CHB and MMC in medium voltage and high power unidirectional motor drive systems.

[0004] Therefore, medium voltage high power inverter with unidirectional power transmission urgently needs to develop a new generation of low-cost unidirectional high power density converter. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the present invention proposes a high power density module and a modular medium voltage inverter for unidirectional power transmission, which can effectively reduce costs and improve power density.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A high power density module for unidirectional power transmission, comprising a grid-side full-bridge circuit, a high-frequency converter, an LC resonant branch, a multi-winding high-frequency transformer, a high-frequency diode circuit and a machine-side full-bridge circuit;

[0008] When there are three grid-side full-bridge circuits, three high-frequency converters, n high-frequency diode circuits, n machine-side full-bridge circuits, (3+n) LC resonant branches, and a (3+n)-winding high-frequency transformer, a first high-power density module for unidirectional power transmission is formed;

[0009] Among them, the DC ports of the three grid-side full-bridge circuits are respectively connected to the DC ports of the three high-frequency converters, and the AC ports of the three high-frequency converters are respectively connected to the three windings of the high-frequency transformer through three LC resonant branches; the remaining n windings of the high-frequency transformer are respectively connected to the AC ports of the n high-frequency diode circuits through n LC resonant branches, and the DC ports of the n high-frequency diode circuits are connected to the DC ports of the n machine-side full-bridge circuits through n DC capacitors.

[0010] The grid-side full-bridge circuit has one of two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs;

[0011] The high-frequency converter and the high-frequency diode circuit are of two structural types; the first type is that the high-frequency converter is composed of an IGBT full-bridge circuit, and the high-frequency diode circuit is composed of a diode full-bridge circuit; the second type is that the high-frequency converter is composed of an IGBT half-bridge circuit, and the high-frequency diode circuit is composed of a diode half-bridge circuit;

[0012] A modular medium-voltage inverter for unidirectional power transmission is composed of M high-power density modules for unidirectional power transmission; the AC ports of three grid-side full-bridge circuits of all high-power density modules are connected in series or in parallel to form three grid-side single-phase AC ports, the three grid-side single-phase AC ports are connected in Y-type to form a grid-side three-phase AC port, and the grid-side three-phase AC port is connected to an AC power grid through a filtering inductor; the AC ports of n machine-side single-phase full-bridge circuits of all high-power density modules are connected in series or in parallel to form n machine-side single-phase AC ports, the n machine-side single-phase AC ports are connected in Y-type to form a machine-side n-phase AC port, and the machine-side n-phase AC port is connected to an n-phase motor.

[0013] When there are three grid-side full-bridge circuits, three high-frequency converters, (4+n) LC resonant branches, a multi-winding high-frequency transformer with (4+n) windings, and n high-frequency diode circuits and machine-side full-bridge circuits, a second high-power density module with unidirectional power transmission is formed;

[0014] Among them, the DC ports of the three grid-side full-bridge circuits are connected to the DC ports of the three high-frequency converters, and the AC ports of the three high-frequency converters are connected to the three windings of the high-frequency transformer through three LC resonant branches; the n windings of the high-frequency transformer are connected to the AC ports of the n high-frequency diode circuits through n LC resonant branches, and the DC ports of the n high-frequency diode circuits are connected to the DC ports of the n machine-side full-bridge circuits. The (4+n)th winding of the high-frequency transformer is connected to the interface circuit through the LC resonant branch;

[0015] The grid-side full-bridge circuit has one of two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs;

[0016] The high-frequency converter and the high-frequency diode circuit are of two structural types; the first type is that the high-frequency converter is composed of an IGBT full-bridge circuit, and the high-frequency diode circuit is composed of a diode full-bridge circuit; the second type is that the high-frequency converter is composed of an IGBT half-bridge circuit, and the high-frequency diode circuit is composed of a diode half-bridge circuit;

[0017] The structure of the interface circuit is one of two types: the first structure is a direct-connection wire type, and the interface circuit constitutes a high-frequency AC port; the second structure is an IGBT full-bridge circuit or an IGBT half-bridge circuit, and the interface circuit constitutes a high-frequency DC port.

[0018] A modular medium-voltage inverter for unidirectional power transmission, comprising M high-power density modules of the second type for unidirectional power transmission; the AC ports of three grid-side full-bridge circuits of the M high-power density modules are connected in series or in parallel to form three grid-side single-phase AC ports, the three grid-side single-phase AC ports are connected in Y-type to form a grid-side three-phase AC port, the grid-side three-phase AC port is connected to an AC grid via a filtering inductor; the AC ports of n machine-side single-phase full-bridge circuits of the M high-power density modules are connected in series or in parallel to form n machine-side single-phase AC ports, the n machine-side single-phase AC ports are connected in Y-type to form a machine-side n-phase AC port, the machine-side n-phase AC port is connected to an n-phase motor; the high-frequency AC ports or high-frequency DC ports of the M high-power density modules are connected in parallel to form a common high-frequency bus.

[0019] When there is one grid-side full-bridge circuit, one high-frequency converter, three LC resonant branches, a multi-winding high-frequency transformer, a three-winding high-frequency transformer, one high-frequency diode circuit, and one machine-side full-bridge circuit, a third high-power density module with unidirectional power transmission is formed;

[0020] The DC sides of the grid-side full-bridge circuit and the machine-side full-bridge circuit are respectively connected to the DC sides of the high-frequency converter and the high-frequency diode circuit, and the AC sides of the high-frequency converter and the high-frequency diode circuit are respectively connected to the two windings of the high-frequency transformer through an LC resonant branch to form a grid-side circuit and a machine-side circuit; the third winding of the high-frequency transformer is connected in series with the LC resonant branch to the interface circuit;

[0021] The grid-side full-bridge circuit has one of two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs;

[0022] The high-frequency converter and the high-frequency diode circuit are of two structural types; the first type is that the high-frequency converter is composed of an IGBT full-bridge circuit, and the high-frequency diode circuit is composed of a diode full-bridge circuit; the second type is that the high-frequency converter is composed of an IGBT half-bridge circuit, and the high-frequency diode circuit is composed of a diode half-bridge circuit;

[0023] The structure of the interface circuit is one of two types of structures: the first structure is a direct-connection wire type, and the interface circuit constitutes a high-frequency AC port; the second structure is a full-bridge circuit or a half-bridge circuit, and the interface circuit constitutes a high-frequency DC port.

[0024] A modular medium voltage inverter with unidirectional power transmission, which is composed of 3M high power density modules of the third unidirectional power transmission, and the modular medium voltage inverter has an M-layer structure, and each layer is composed of three high power density modules;

[0025] The AC ports of the grid-side full-bridge circuit and the machine-side full-bridge circuit of the first high-power density module in each layer are connected in series or in parallel to form a grid-side / machine-side single-phase AC port, and the same is true for the second and third modules; the three grid-side / machine-side single-phase AC ports are connected in a Y-type to form a grid-side / machine-side three-phase AC port; the grid-side three-phase AC port is connected to the AC grid through a filtering inductor, and the machine-side three-phase AC port is connected to a three-phase motor; the high-frequency AC ports or high-frequency DC ports of the three high-power density modules in each layer are connected in parallel to form a common high-frequency bus, and the common high-frequency busbars between the layers are connected in parallel.

[0026] When there is one grid-side full-bridge circuit, one high-frequency converter, nine LC resonant branches, a multi-winding high-frequency transformer, one three-phase three-winding high-frequency transformer, one high-frequency diode circuit, and one machine-side full-bridge circuit, a fourth high-power density module for unidirectional power transmission is formed;

[0027] The DC sides of the grid-side and machine-side full-bridge circuits are respectively connected to the DC sides of the high-frequency converter and high-frequency diode circuit, and the AC sides of the high-frequency converter and high-frequency diode circuit are respectively connected to two pairs of three-phase windings of the high-frequency transformer through three LC resonant branches, forming a grid-side circuit and a machine-side circuit. The third pair of three-phase windings of the high-frequency transformer is connected in series with the LC resonant branch to the interface circuit;

[0028] The grid-side full-bridge circuit has one of two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs;

[0029] The high-frequency converter is a three-phase IGBT half-bridge circuit; the high-frequency diode circuit is a three-phase diode circuit; the interface circuit includes two structures, the first structure is a direct-connection wire type, and the interface circuit constitutes a three-phase high-frequency AC port; the second structure is a three-phase IGBT half-bridge circuit, and the interface circuit constitutes a high-frequency DC port.

[0030] A modular medium-voltage inverter for unidirectional power transmission for motor driving, composed of 3M high-power density modules of the fourth type for unidirectional power transmission, the grid-side full-bridge circuit and the AC ports of the machine-side full-bridge circuit of the first high-power density module in each layer are connected in series or in parallel to form a grid-side / machine-side single-phase AC port, and the second and third modules are connected in the same way; the three grid-side / machine-side single-phase AC ports are connected in a Y-type to form a grid-side / machine-side three-phase AC port; the grid-side three-phase AC port is connected to the AC grid through a filtering inductor, and the machine-side three-phase AC port is connected to a three-phase motor, the three-phase high-frequency AC ports or high-frequency DC ports of the three high-power density modules in each layer are connected in parallel to form a common high-frequency bus, and the common high-frequency busbars between the layers are connected in parallel.

[0031] The high power density module with unidirectional power transmission is used for motor driving.

[0032] The modular medium voltage inverter with unidirectional power transmission is used for motor driving.

[0033] Beneficial effects of the present invention:

[0034] 1) The modular medium voltage inverter of the present invention has the advantage of low cost. This is reflected in the switching devices, DC capacitors and transformers. The present invention replaces part of the IGBT with a diode circuit, thereby reducing the cost of the switching devices. The present invention uses the path provided by the high-frequency transformer to offset the three-phase fluctuating power, thereby reducing the capacitance of the DC side capacitor and reducing the cost of the capacitor. The operating frequency of the transformer is increased from the original industrial frequency to a high frequency of tens or hundreds of kilohertz, which reduces the material consumption of the transformer and reduces the cost of the transformer magnetic parts.

[0035] 2) The modular medium voltage inverter of the present invention has the characteristics of high power density, which is reflected in the transformer and capacitor. The increase in the operating frequency of the transformer not only reduces the use of materials, but also greatly reduces the volume of this part. The capacitance of the DC link capacitor is reduced, and the original large capacitance electrolytic capacitor can be replaced with a small capacitance film capacitor, which reduces the total volume of the DC link capacitor. Therefore, the present invention improves the power density of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the topological structure of a high power density module for unidirectional power transmission according to the first embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the topological structure of a modular medium-voltage inverter with first unidirectional power transmission according to the present invention.

[0038] Figure 3 This is a schematic diagram of the topological structure of a high power density module for unidirectional power transmission according to the second embodiment of the present invention.

[0039] Figure 4 This is a schematic diagram of the topological structure of a modular medium-voltage inverter with second unidirectional power transmission according to the present invention.

[0040] Figure 5 This is a schematic diagram of the topological structure of a high power density module for unidirectional power transmission according to the third embodiment of the present invention.

[0041] Figure 6 This is a schematic diagram of a third topological structure of a modular medium-voltage inverter with unidirectional power transmission according to the present invention.

[0042] Figure 7 This is a schematic diagram of the topological structure of a high power density module for unidirectional power transmission according to the fourth embodiment of the present invention.

[0043] Figure 8 This is a schematic diagram of a fourth topological structure of a modular medium-voltage inverter with unidirectional power transmission according to the present invention.

[0044] Fig. 9 It is a simulation waveform diagram of the motor speed and torque, the machine-side AC output voltage and output current, the grid-side input voltage and input current, the multi-winding high-frequency transformer port voltage and winding current, and the DC-side capacitor voltage during the starting process of the medium-voltage asynchronous motor of the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0046] The present invention relates to four high power density modules for unidirectional power transmission of motor driving and four corresponding modular medium voltage inverters. The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments.

[0047] like Figure 1 As shown in (a), a high power density module for unidirectional power transmission for motor drive includes three grid-side full-bridge circuits, three high-frequency converters, (3+n) LC resonant branches, a (3+n) winding high-frequency transformer, n high-frequency diode circuits and n machine-side full-bridge circuits; the DC ports of the three grid-side full-bridge circuits are respectively connected to the three DC ports of the high-frequency converter, and the AC ports of the three high-frequency converters are respectively connected to the three windings of the high-frequency transformer through three LC resonant branches; the remaining n windings of the high-frequency transformer are respectively connected to the AC ports of the n high-frequency diode circuits through n LC resonant branches, and the DC ports of the n high-frequency diode circuits are connected to the DC ports of the n machine-side full-bridge circuits through n DC capacitors. Figure 1 As shown in (b), the grid-side full-bridge circuit includes two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs. Figure 1 As shown in (c), the high-frequency converter and the high-frequency diode circuit include two structural types. The first type is that the high-frequency converter is composed of an IGBT full-bridge circuit, and the high-frequency diode circuit is composed of a diode full-bridge circuit; the second type is that the high-frequency converter is composed of an IGBT half-bridge circuit, and the high-frequency diode circuit is composed of a diode half-bridge circuit;

[0048] like Figure 2 As shown, a modular medium voltage inverter for unidirectional power transmission of motor driving is composed of M Figure 1 The high power density module for unidirectional power transmission shown in the figure is composed of; the AC ports of the three grid-side full-bridge circuits of all high power density modules are connected in series or in parallel to form three grid-side single-phase AC ports. The AC ports of the n machine-side full-bridge circuits of all high power density modules are connected in series or in parallel to form n machine-side single-phase AC ports. The three grid-side single-phase AC ports are connected in Y-type to form a grid-side three-phase AC port, and the n single-phase phase-side AC ports are connected in Y-type to form a machine-side n-phase AC port; the grid-side three-phase AC port is connected to the AC grid through a filter inductor, and the machine-side n-phase AC port is connected to an n-phase motor.

[0049] like Figure 3As shown in (a), a high power density module for unidirectional power transmission of motor drive includes three grid-side full-bridge circuits, three high-frequency converters, (4+n) LC resonant branches, a (4+n) winding high-frequency transformer, n high-frequency diode circuits, n machine-side full-bridge circuits and an interface circuit; the grid-side full-bridge circuit, the high-frequency converter and the high-frequency diode circuit are connected to the Figure 1 The structure is exactly the same as Figure 3 As shown in (b) and (c), the structure of the interface circuit is divided into two types: the first structure is a direct-connection wire type, and the interface circuit constitutes a high-frequency AC port; the second structure is a full-bridge circuit or a half-bridge circuit, and the interface circuit constitutes a high-frequency DC port;

[0050] like Figure 4 As shown, a modular medium voltage inverter for unidirectional power transmission of motor driving is composed of M Figure 3 The high power density module structure of unidirectional power transmission shown in the figure; the interconnection method of the grid-side full-bridge circuit and the AC side of the machine-side full-bridge circuit of all high power density modules and Figure 2 The high-frequency AC ports or high-frequency DC ports (V1, V2) of the M high-power density modules are connected in parallel to form a common high-frequency bus.

[0051] like Figure 5 As shown, a high power density module for unidirectional power transmission of motor drive includes a grid-side full-bridge circuit, a high-frequency converter, three LC resonant branches, a three-winding high-frequency transformer, a high-frequency diode circuit, a machine-side full-bridge circuit and an interface circuit; the grid-side full-bridge circuit, the high-frequency converter and the high-frequency diode circuit are connected to the Figure 1 The structure of the interface circuit is exactly the same as Figure 3 The structure is completely consistent;

[0052] like Figure 6 As shown, a modular medium voltage inverter for one-way power transmission for motor driving is characterized by: Figure 5 The high power density modules shown are composed of modular medium voltage inverters with M layers, and each layer is composed of three high power density modules. The AC ports of the grid-side full-bridge circuit and the machine-side full-bridge circuit of the first high power density module of each layer are connected in series or in parallel to form a grid-side / machine-side single-phase AC port, and the second and third modules are connected in parallel; then the three grid-side / machine-side single-phase AC ports are connected in a Y-type to form a grid-side / machine-side three-phase AC port; the grid-side three-phase AC port is connected to the AC grid through a filter inductor, and the machine-side three-phase AC port is connected to a three-phase motor. The high-frequency AC ports or high-frequency DC ports (V1, V2) of the three high power density modules in each layer are connected in parallel to form a common high-frequency bus, and the common high-frequency bus between each layer is connected in parallel.

[0053] like Figure 7 As shown in (a), a high power density module for unidirectional power transmission of motor drive includes a grid-side full-bridge circuit, a high-frequency converter, 9 LC resonant branches, a three-phase three-winding high-frequency transformer, a high-frequency diode circuit, a machine-side full-bridge circuit and an interface circuit; the grid-side full-bridge circuit and Figure 1 The structure is exactly the same as in the above; the high-frequency converter is a three-phase half-bridge circuit; the high-frequency diode circuit is a three-phase diode circuit; Figure 7 As shown in (b) and (c), the interface circuit includes two structures. The first structure is a direct-connection wire type, and the interface circuit constitutes a three-phase high-frequency AC port; the second structure is a three-phase half-bridge circuit, and the interface circuit constitutes a high-frequency DC port;

[0054] like Figure 8 As shown in the figure, a modular medium voltage inverter for one-way power transmission of motor driving: composed of 3M Figure 7 The high power density module structure of unidirectional power transmission shown in the figure, the connection method of the AC port of the grid-side full-bridge circuit and the machine-side full-bridge circuit of all high power density modules is the same as Figure 6 The three-phase high-frequency AC ports or high-frequency DC ports of the three high-power density modules in each layer are connected in parallel to form a common high-frequency bus, and the common high-frequency bus between the layers are connected in parallel.

[0055] The following is a detailed description with reference to specific embodiments.

[0056] The embodiment of the present invention is designed as follows: Figure 1 and Figure 2 , each high power density module consists of three grid-side full-bridge circuits, three high-frequency converters, six LC resonant branches, a six-winding high-frequency transformer, three high-frequency diode circuits and three machine-side full-bridge circuits. The grid-side full-bridge circuit structure is that the two lower switch tubes of the full-bridge circuit are diodes, and the two upper switch tubes are IGBTs. The high-frequency converter and the high-frequency diode circuit are composed of a half-bridge IGBT circuit and a half-bridge diode circuit. The number of modules for the modular medium-voltage inverter design is 4. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0057] The parameters of the modular medium-voltage inverter designed with the above ideas are summarized in Table 1. The MATLAB / Simulink simulation model constructed based on this fully achieves the expected design goals and realizes the control function.

[0058] Table 1 Specific parameters of modular medium voltage inverter

[0059]

[0060] Fig. 9The figure shows the dynamic process simulation waveform of the converter when the motor operating frequency changes from 0Hz to 60Hz. The sub-figure (a) is the motor speed ω r Waveform; sub-figure (b) is the output voltage v of the modular medium voltage inverter u Waveform, sub-figure (c) is the three-phase grid current i in Waveform, sub-figure (d) is the terminal voltage v of the multi-winding high-frequency transformer ha Waveform, sub-figure (e) is the resonant current i ha Waveform, sub-figure (f) is the grid input voltage v a Waveform, sub-graph (g) is the grid-side DC capacitor voltage v ca ,v cb ,v cc Waveform, sub-graph (h) is the DC capacitor voltage v on the generator side cu ,v cv ,v cw Waveform. After the simulation starts, the modular medium-voltage inverter supplies energy to the motor to establish a magnetic field. When the simulation time is 0.9s, the motor speed setting value suddenly changes from 0 to the rated speed (1189RPM), the motor speed gradually increases, the waveform of the output voltage gradually changes to multi-level, and the frequency of the output current gradually increases with the increase of the speed. The inverter obtains energy from the medium-voltage power grid. As the speed increases, the peak value of the current input from the power grid gradually increases. Throughout the process, the high-frequency converter and the high-frequency diode circuit have been operating at a high frequency of 50% duty cycle, and the resonant current and the zero-crossing time of the high-frequency port voltage are consistent. At the same time, the fluctuation voltage of both the grid-side capacitor and the DC link capacitor on the machine side is small. In the entire speed range, the amplitude of the voltage fluctuation on the DC side capacitor capacitance is always controlled within 5%. It can be seen that the modular medium-voltage inverter proposed in the present invention reduces the capacitance of the DC link capacitor. At the same time, this scheme uses a large number of high-frequency diode circuits, which reduces the cost of switching devices as a whole, and verifies the feasibility, low cost and high power density advantages of the proposed scheme.

[0061] The above are only preferred embodiments of the present invention and do not limit the present invention in any way. Any simple modifications, changes and equivalent structural changes made to the above embodiments based on the technical essence of the present invention are still within the protection scope of the technical solution of the present invention.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art can still modify or make equivalent substitutions to the specific implementation schemes of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention.

[0063] The above content is a further detailed description of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, they can also make several simple deductions or substitutions, which should be regarded as belonging to the protection scope of the present invention determined by the submitted claims.

Claims

1. A high power density module for unidirectional power transmission, characterized in that: It includes a grid-side full-bridge circuit, a high-frequency converter, an LC resonant branch, a multi-winding high-frequency transformer, a high-frequency diode circuit and a machine-side full-bridge circuit; Three grid-side full-bridge circuits, three high-frequency converters, (3+n) LC resonant branches, a (3+n) winding high-frequency transformer, n high-frequency diode circuits and n machine-side full-bridge circuits constitute the first high-power density module for unidirectional power transmission; Among them, the DC ports of the three grid-side full-bridge circuits are connected to the DC ports of the three high-frequency converters, and the AC ports of the three high-frequency converters are connected to the three windings of the high-frequency transformer through three LC resonant branches respectively; the remaining n windings of the high-frequency transformer are connected to the AC ports of the n high-frequency diode circuits through n LC resonant branches respectively, and the DC ports of the n high-frequency diode circuits are connected to the DC ports of the n machine-side full-bridge circuits.

2. A high power density module for unidirectional power transmission according to claim 1, characterized in that: The grid-side full-bridge circuit is one of the following two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs; The high-frequency converter and high-frequency diode circuit are of one of the following two structural types: the first type is that the high-frequency converter is composed of an IGBT full-bridge circuit, and the high-frequency diode circuit is composed of a diode full-bridge circuit; the second type is that the high-frequency converter is composed of an IGBT half-bridge circuit, and the high-frequency diode circuit is composed of a diode half-bridge circuit.

3. A modular medium voltage inverter with unidirectional power transmission, comprising M high power density modules for unidirectional power transmission according to claim 1; the AC ports of the three grid-side full-bridge circuits of all high power density modules are connected in series or in parallel to form three grid-side single-phase AC ports, the three grid-side single-phase AC ports are connected in Y-type to form a grid-side three-phase AC port, and the grid-side three-phase AC port is connected to the AC grid through a filter inductor. The AC ports of the n machine-side full-bridge circuits of all high power density modules are connected in series or in parallel to form n machine-side single-phase AC ports, the n machine-side single-phase AC ports are connected in Y-type to form a machine-side n-phase AC port, and the machine-side n-phase AC port is connected to an n-phase motor.

4. A high power density module for unidirectional power transmission, characterized in that: When there are three grid-side full-bridge circuits, three high-frequency converters, (4+n) LC resonant branches, a multi-winding high-frequency transformer is a (4+n)-winding high-frequency transformer, and n high-frequency diode circuits and n machine-side full-bridge circuits, a second high-power density module with unidirectional power transmission is formed; The DC ports of the three grid-side full-bridge circuits are connected to the DC ports of the three high-frequency converters, and the AC ports of the three high-frequency converters are respectively connected to the three windings of the high-frequency transformer through three LC resonant branches; the n windings of the high-frequency transformer are respectively connected to the AC ports of the n high-frequency diode circuits through n LC resonant branches, and the DC ports of the n high-frequency diode circuits are connected to the DC ports of the n machine-side full-bridge circuits, and the (4+n)th winding of the high-frequency transformer is connected to the interface circuit through the LC resonant branch; The grid-side full-bridge circuit is one of the following two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs; The high-frequency converter and the high-frequency diode circuit are of one of the following two structural types; the first type is that the high-frequency converter is composed of an IGBT full-bridge circuit, and the high-frequency diode circuit is composed of a diode full-bridge circuit; the second type is that the high-frequency converter is composed of an IGBT half-bridge circuit, and the high-frequency diode circuit is composed of a diode half-bridge circuit; The structure of the interface circuit is one of the following two types of structures: the first structure is a direct-connection wire type, and the interface circuit constitutes a high-frequency AC port; the second structure is an IGBT full-bridge circuit or an IGBT half-bridge circuit, and the interface circuit constitutes a high-frequency DC port.

5. A modular medium-voltage inverter with unidirectional power transmission, comprising M high-power density modules of the second type of unidirectional power transmission as described in claim 4; the AC ports of the three grid-side full-bridge circuits of the M high-power density modules are connected in series or in parallel to form three grid-side single-phase AC ports, and the three grid-side single-phase AC ports are Y-connected to form a grid-side three-phase AC port, and the grid-side three-phase AC port is connected to the AC power grid through a filtering inductor; the AC ports of n machine-side full-bridge circuits of the M high-power density modules are connected in series or in parallel to form n machine-side single-phase AC ports, and the n machine-side single-phase AC ports are Y-connected to form a machine-side n-phase AC port, and the machine-side n-phase AC port is connected to an n-phase motor; the high-frequency AC ports or high-frequency DC ports of the M high-power density modules are connected in parallel to form a common high-frequency bus.

6. A high power density module for unidirectional power transmission, characterized in that: When there is one grid-side full-bridge circuit, one high-frequency converter, three LC resonant branches, a multi-winding high-frequency transformer, a three-winding high-frequency transformer, one high-frequency diode circuit, and one machine-side full-bridge circuit, a third high-power density module with unidirectional power transmission is formed; The DC sides of the grid-side full-bridge circuit and the machine-side full-bridge circuit are respectively connected to the DC sides of the high-frequency converter and the high-frequency diode circuit, and the AC sides of the high-frequency converter and the high-frequency diode circuit are respectively connected to the two windings of the high-frequency transformer through an LC resonant branch to form a grid-side circuit and a machine-side circuit; the third winding of the high-frequency transformer is connected in series with the LC resonant branch to the interface circuit; The grid-side full-bridge circuit is one of the following two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs; The high-frequency converter and the high-frequency diode circuit are of one of the following two structural types; the first type is that the high-frequency converter is composed of an IGBT full-bridge circuit, and the high-frequency diode circuit is composed of a diode full-bridge circuit; the second type is that the high-frequency converter is composed of an IGBT half-bridge circuit, and the high-frequency diode circuit is composed of a diode half-bridge circuit; The structure of the interface circuit is one of the following two types of structures: the first structure is a direct-connection wire type, and the interface circuit constitutes a high-frequency AC port; the second structure is a full-bridge circuit or a half-bridge circuit, and the interface circuit constitutes a high-frequency DC port.

7. A modular medium voltage inverter with unidirectional power transmission, comprising 3M high power density modules of the third type of unidirectional power transmission according to claim 6, wherein the modular medium voltage inverter has an M-layer structure, and each layer is composed of three high power density modules; The AC ports of the grid-side full-bridge circuit and the machine-side full-bridge circuit of the first high-power density module in each layer are connected in series or in parallel to form a grid-side / machine-side single-phase AC port, and the same is true for the second and third modules; the three grid-side / machine-side single-phase AC ports are connected in a Y-type to form a grid-side / machine-side three-phase AC port; the grid-side three-phase AC port is connected to the AC grid through a filter inductor, and the machine-side three-phase AC port is connected to a three-phase motor. The high-frequency AC ports or high-frequency DC ports of the three high-power density modules in each layer are connected in parallel to form a common high-frequency bus, and the common high-frequency buses between layers are connected in parallel.

8. A high power density module for unidirectional power transmission, characterized in that: When there is one grid-side full-bridge circuit, one high-frequency converter, nine LC resonant branches, a multi-winding high-frequency transformer, one three-phase three-winding high-frequency transformer, one high-frequency diode circuit, and one machine-side full-bridge circuit, a fourth high-power density module for unidirectional power transmission is formed; Among them, the DC sides of the grid-side and machine-side full-bridge circuits are respectively connected to the DC sides of the high-frequency converter and the high-frequency diode circuit, and the AC sides of the high-frequency converter and the high-frequency diode circuit are respectively connected to two pairs of three-phase windings of the high-frequency transformer through three LC resonant branches, forming a grid-side circuit and a machine-side circuit; the third pair of three-phase windings of the high-frequency transformer is connected in series with the LC resonant branch to the interface circuit; The grid-side full-bridge circuit is one of the following two structural types: the first structure is that the upper switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the lower switch tubes of the two half-bridges are IGBTs; the second structure is that the lower switch tubes of the two half-bridges of the full-bridge circuit are diodes, and the upper switch tubes of the two half-bridges are IGBTs; The high-frequency converter is a three-phase IGBT half-bridge circuit; the high-frequency diode circuit is a three-phase diode circuit; the interface circuit is one of the following two structural types: the first structure is a direct-connected wire type, and the interface circuit constitutes a three-phase high-frequency AC port; the second structure is a three-phase IGBT half-bridge circuit, and the interface circuit constitutes a high-frequency DC port.

9. A modular medium-voltage inverter for unidirectional power transmission for motor driving, composed of 3M high-power density modules of the fourth type of unidirectional power transmission according to claim 8, the AC ports of the grid-side / machine-side full-bridge circuit of the first high-power density module in each layer are connected in series or in parallel to form a grid-side / machine-side single-phase AC port, and the same applies to the second and third modules; the three grid-side / machine-side single-phase AC ports are connected in Y shape to form a grid-side / machine-side three-phase AC port; the grid-side three-phase AC port is connected to the AC power grid through a filtering inductor, and the machine-side three-phase AC port is connected to a three-phase motor, the three-phase high-frequency AC ports or high-frequency DC ports of the three high-power density modules in each layer are connected in parallel to form a common high-frequency bus, and the common high-frequency busbars between the layers are connected in parallel.

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