Medium voltage frequency conversion power circuit system

Abstract

The invention discloses a medium voltage frequency conversion power circuit system, which belongs to the technical field of electric power systems, and comprises a step-down transformer, a converter array and a step-up transformer which are sequentially connected in series, wherein the input end of the step-down transformer is connected with the output end of a three-phase supply of a medium voltage power grid, and the output end of the step-up transformer is a frequency conversion voltage output. The invention reduces the number of three-phase rectifiers and has balanced power, so the output voltage can be further improved, and the system has the advantages of simple integral structure, improved power grid side power factor and more perfect overall performance.

Description

technical field [0001] The invention relates to a system in the field of electric power technology, in particular to a medium-voltage variable-frequency power circuit system based on power balance and multi-stage series inverter. Background technique [0002] In the field of three-phase medium-voltage variable frequency speed regulation, the types of power electronic converters in use are cascaded frequency converters and three-level inverters in which voltage source inverters are connected in series. The former is a high-low-high type with a maximum voltage of 10kV. Its front stage generally uses an uncontrolled rectifier, and of course a three-phase controlled rectifier can also be used. The latter is a high-level type, and the current maximum voltage is only 3.3kV. The front stage generally uses an uncontrolled rectifier, and a three-level controllable rectifier can also be used. High-low-high type cascaded frequency converter, the general structure includes 3x stages of...

AI Technical Summary

Problems solved by technology

Theoretical analysis and practical use found that the cascaded inverter has the following problems: (1) The design of the step-down transformer is complicated, which is manifested by the design of the secondary winding winding and the low productivity; (2) The number of rectifiers is large; (3) The rectifiers are not controlled Unbalanced load requires large-capacity electrolytic capacitors, especially when a controllable rectifier is used; (4) The input current waveform of the uncontrolled rectifier is distorted, which increases the capacity of the step-down transformer; (4) The overall volume is large and the efficiency Low cost, high cost, complex control, and poor performance; (5) Higher voltage output requires more inverter series series

[0005] After analysis, the existing technologies all have the following defects: The first one: due to the unbalanced load of the uncontrolled rectifier bridge, the size of the energy storage capacitor in the DC circuit increases, the input current waveform is asymmetrical, and the stability is poor

The secondary of the step-down transformer must be designed into various connection groups, such as Y-type, zigzag type, etc., the design is complicated and the efficiency is low

Boosting is achieved solely by increasing the number of series, making the system huge and increasing the difficulty of control

The second type: the structure is relatively simple, but the control is still complicated, there is a problem of DC voltage imbalance, the supported power range is narrow, the supported output voltage range is not wide, and the secondary of the step-down transformer must also be designed as multi-Y type and triangular type, etc. , the design is somewhat complex and inefficient

The third type: Due to the complex structure and complicated controllability, it has not been applied

The fourth type: due to the unbalanced load of the matrix converter, the input current waveform is distorted, the original input current waveform is poor, the input current waveform is asymmetrical, and the stability is poor

The secondary of the step-down transformer must be designed into various connection groups, such as Y-type, zigzag type, etc., the design is complicated and the efficiency is low

Boosting is achieved solely by increasing the number of series, making the system huge and increasing the difficulty of control

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