Design of a Dynamic Voltage Restorer to Suppress Torque Pulsation for the Wind-Driven Induction Generator Operating under Unbalanced Distribution Systems

With the high dependence of global economies on fossil fuels and the concern about the environment, interest in the use of renewable energy resources has intensified. In this trend towards the diversification of the energy market, wind power is demanded to be more cost-competitive attributed to the nature of inexhaustible and freely available all over the world. The variable speed wind generator systems, being capable of accommodating wind turbine to a widespread operating speed for the purpose of aerodynamic efficiency optimization, have been favored lately. Squirrel-cage induction generators are known as a variable speed machine in which the stator circuit can be directly connected to the power grid without the need of frequency converter. The advantages of this structure such as simple control scheme, robust construction, and low-initial and run-time cost have gained some momentum lately as compared to doubly-fed induction generators. However, the impact of unbalanced source voltage on stator circuit coupled with the need for excitation current lead to the poor voltage regulation which is the root for the torque pulsation and the degeneration of power efficiency. To improve the stator voltage quality for the IG, a dynamic voltage restorer (DVR) configured with a six-leg voltage-sourced inverter (VSI) is mandatory to alleviate the unbalanced rate and the voltage fluctuation of the distribution system. Two approaches including reactive voltage compensation and minimum voltage compensation will be adopted for the DVR controller in order to restore the stator voltage profile. To further alleviate the negative impact of unbalanced components on the IG, the symmetric components which resolved from the three-phase instantaneous quantities would be regarded as the magnitude and phase references for the DVR controller before inserting its output voltage to the power line. A laboratory prototype, based on a 3kVA DVR, will be implemented to compensate the terminal voltage of an IG in this project. Since the material of the proposed system is made in Taiwan, the superiority, such as low cost and excellent voltage quality, over traditional the IG system in the market will be expected.

Project ID:PB10207-1891
External Project ID:NSC102-2221-E182-030