Modular multi-level four-quadrant frequency converter and control method thereof

Abstract

The invention relates to a modular multi-level four-quadrant frequency converter and a control method thereof, which can effectively suppress the fluctuation of sub-module capacitance voltage at low speed, reduce size and cost and belong to the field of power electronics. The modular multi-level four-quadrant frequency converter comprises a network-side modular multilevel converter, a machine-sidemodular multilevel converter and a bi-directional switch. The bi-directional switch comprises a forward switch and a reverse switch. The forward and reverse switches are connected in series on a DC bus between the network-side modular multilevel converter and the machine-side modular multilevel converter. The forward switch adopts full-control power electronic devices, while the reverse switch adopts semi-control power electronic devices or uncontrollable devices. Or, the forward switch adopts semi-controlled power electronic devices, and the reverse switch adopts full-controlled power electronic devices or semi-controlled power electronic devices or uncontrollable devices. According to the invention, a common-mode voltage is prevented from being introduced to a motor end, the current stress of a bridge arm will not be additionally increased, and a DC side does not need an additional filtering device.

Description

technical field [0001] The invention relates to a modular multilevel converter, in particular to a modular multilevel four-quadrant frequency converter and a control method thereof, belonging to the field of power electronics. Background technique [0002] The pumped storage power station has the characteristics of flexible, fast and reliable operation, and it undertakes important tasks such as peak and valley filling and frequency regulation in the power grid. Most of the traditional pumped storage units are synchronous generator motor units, which have problems such as speed regulation or speed change of hydro-generators. The four-quadrant frequency converter can effectively realize the variable speed operation of the pumped storage unit, and improve the system efficiency and stability. Modular multilevel converter (MMC) is especially suitable for high-voltage energy storage such as pumped storage due to its advantages of modular structure, multi-level voltage output, con...

AI Technical Summary

Problems solved by technology

However, the former will cause serious common-mode voltage problems at the motor end, and the common-mode current introduced at the same time will increase the current stress of the MMC bridge arm and aggravate losses; while the latter will cause intermittent current on the DC side and cause serious harmonic problems. , it is necessary to add an additional filtering device on the DC side

In addition, none of these schemes considered the four-quadrant operation

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