Cascade multi-level converter

Abstract

The invention relates to a cascade multi-level convertor, which comprises a pulse width modulation rectifier and a control unit, wherein the input end of the pulse width modulation rectifier is connected with a power grid; the output end of the pulse width modulation rectifier is connected with direct current buses; the direct current buses are connected with the input end of an inverter; the inverter supplies power to an alternating current motor; and the control unit carries out information interaction with the pulse width modulation rectifier to balance the voltages at two ends of the pulse width modulation rectifier and a plurality of capacitance voltages between the direct current buses and to make a power grid input power factor be 1, and controls the inverter to output a frequency-variable alternating current. The cascade multi-level convertor does not require a phase-shifting transformer, is small in volume, light in weight, low in cost, capable of operating in four quadrants,obvious in economic benefits and suitable to be popularized and used.

Description

technical field [0001] The invention relates to a topology structure of a power electronic high-voltage large-capacity multilevel converter, in particular to a cascaded multilevel converter. Background technique [0002] High-voltage and large-capacity AC motors are widely used in industrial fields such as steel rolling, papermaking, cement, coal, railways, and ships. The frequency conversion and speed regulation of AC motors by multi-level technology can not only achieve the purpose of energy saving, but also improve the process conditions, production efficiency and product quality. [0003] At present, there are mainly two types of multilevel converters for frequency conversion and speed regulation of high-power AC motors: one is a medium-voltage three-level converter using diode clamping, and the other is an H-bridge cascaded high-voltage multi-level converter. level shifter. Three-level converters control AC motors with a voltage of 3kV and below, while H-bridge cascad...

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Problems solved by technology

[0004] Although the transformer in the three-level converter is relatively simple, and the harmonics of the output voltage are also low, the three-level converter has the problem of difficulty in applying high voltage (generally, high voltage refers to 6kV ~ 10kV). The capacitor voltage of the level converter is also difficult to achieve balance

However, there are also some problems in the H-bridge cascaded multilevel converter. For example, since the front end of each power unit in the H-bridge cascaded multilevel converter uses a diode uncontrolled rectification, the AC motor braking At this time, the converter cannot achieve four-quadrant operation, that is, the energy is fed back to the grid; in addition, the phase-shifting transformer has many taps, and the weight and volume are large, and the cost is high

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