Switching-based control for a power converter

Abstract

A method for operating a power generation system that supplies power for application to a load is disclosed. The method may generally include receiving, at a power converter, an alternating current power generated by a generator operating at a speed that is substantially equal to its synchronous speed and converting, with the power converter, the alternating current power to an output power, wherein the power converter includes at least one switching element. In addition, the method may include receiving a control command to control a switching frequency of the at least one switching element and adjusting the switching frequency to an adjusted switching frequency that is substantially equal to a fundamental frequency of the load.

Description

FIELD OF THE INVENTION[0001]The present subject matter relates generally to power convertors for power generation systems and, more particularly, to a system and method for operating a power converter used in a DFIG wind turbine system when the generator is operated at speeds at or close to its synchronous speed.BACKGROUND OF THE INVENTION[0002]Power generation systems often include a power converter that is configured to convert an input power into a suitable power for application to a load, such as a generator, motor, electrical grid, or other suitable load. For instance, a power generation system, such as a wind turbine system, may include a power converter for converting variable frequency alternating current power generated at the generator into alternating current power at a grid frequency (e.g. 50 Hz or 60 Hz) for application to a utility grid. An exemplary power generation system may generate AC power using a wind-driven doubly fed induction generator (DFIG). A power convert...

AI Technical Summary

Benefits of technology

The present invention is directed to a power generation system that includes a generator and a power converter with at least one switching element. The system receives an alternating current power from the generator and converts it to an output power with the power converter. The controller of the system adjusts the switching frequency of the switching element to match the fundamental frequency of the load, which allows for a more efficient transfer of power. This invention is of particular use in wind turbine systems.

Problems solved by technology

However, as the rotor speed is increased or decreased towards the synchronous speed, such output parameters generally approach zero.

Because the transient thermal resistance of the IGBT increases at low frequency, the peak temperature of the rotor side IGBT increases at or near the synchronous speed, resulting in a reduction of the total output current capability of the rotor side of the converter.

In addition, operation of a DFIG generator at or near synchronous speed is even more complicated because current harmonics feed through the generator from the rotor side to the stator side and then directly to the transmission utility grid.

As the speed of the generator approaches the synchronous speed of a DFIG system, the thermal cycling of the IGBT junction increases, again based on the transient thermal resistance of the IGBT, which leads to the switching elements wearing out prematurely.

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