Modular multi-level inverter starting circuit and its starting and low-speed operation method

Abstract

The invention discloses a modularized multi-level inverter starting circuit and its starting and low-speed operation method. The starting circuit includes a DC power supply U dc , series switch, diode D1, auxiliary power supply E and improved modular multilevel inverter five parts, in which: auxiliary power supply E series diode D1 and DC power supply U dc The circuit connected in series with the series switch is connected in parallel to the DC terminal of the improved modular multilevel frequency converter. The invention reduces the voltage value of the DC side by adding an auxiliary power supply, thereby greatly reducing the capacitor voltage fluctuation of the sub-module, and can realize stable operation at an extremely low speed. Compared with the traditional method of injecting high-frequency components to reduce capacitor voltage fluctuations, on the one hand, the present invention does not need to apply a large-scale common-mode voltage to the motor, thereby ensuring the insulation safety and service life of the motor; on the other hand, it does not need to inject any The high-frequency circulating current can ensure that the current amplitude of the bridge arm is within the rated current and ensure the high efficiency of the converter.

Description

technical field [0001] The invention belongs to the technical field of power electronics, and relates to a start-up and low-speed operation method of a modular multi-level frequency converter, in particular to a start-up circuit of a modular multi-level frequency converter based on topology improvement and additional auxiliary power supply and its start-up and operation method. Low speed operation method. Background technique [0002] With the development of power electronics technology, especially the development of high-voltage frequency conversion technology, high-voltage frequency converters have been widely used in electric power, chemical industry, water supply, metallurgy, electric transportation and other industrial fields. Modular multilevel converter (MMC), as a converter topology suitable for high-voltage and high-power applications, has developed rapidly in recent years. Compared with the traditional high-voltage and large-capacity cascaded H-bridge inverter, MM...

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Problems solved by technology

This method also has two problems. One is that the function of the switch makes the current waveform on the DC side intermittent, which brings serious harmonic problems, and an additional filter device needs to be added on the DC side; As a result, the DC side voltage cannot be further reduced, and the capacitor voltage fluctuation will become large, making it impossible to achieve stable operation at extremely low speed or even zero speed, and to complete a reliable start-up process

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