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In this paper, a topology for a grid-connected generation system, based on two doubly fed induction machines, is presented. The proposed scheme is implemented using an indirect matrix converter (IMC) consisting of an input stage, a three-to-two matrix converter, and two output stages consisting of a pair of voltage source inverters. The input stage is connected to the grid and provides the required dc voltage for the output stages. Space vector modulation (SVM) is used for the input stage producing the maximum dc voltage, with unity power factor operation at the IMC grid-side input. Each of the output converters is connected to the rotor of a DFIM. The rotor currents of each machine are vector controlled for fast dynamic response and tight torque control. Moreover, the SVM algorithm used for the inverters is designed to provide soft switching operation in the input converter. Simulation and experimental results obtained from a 2.5-kW experimental prototype are presented. Steady-state and transient operation is discussed with the system running at below and above synchronous speed. The results demonstrate the feasibility of the proposed scheme for variable speed energy systems.
Date of Publication: Oct. 2009