Optimal Converter Rating for Brushless Doubly Fed Machines

This paper presents a systematic and practical approach to minimize the total of the machine side and the grid side converter currents, in order to minimize the cost, using per phase equivalent circuit model for D-180 prototype brushless doubly fed machine. The conventional approach for grid side converter control is only to keep the DC link voltage through active power flow. However, it is shown that utilizing the grid side converter capability in generating reactive power can reduce the total converter current. Furthermore, using capacitor bank to reduce the total converter current is investigated, and the optimal value of the capacitor to obtain the minimum converter current and the maximum output power simultaneously, is proposed. The optimization problem has been organized in three different approaches, i.e. 1) Conventional, 2) Using GSC for reactive power generation, and 3) Using capacitor bank. To evaluate the three approaches, comparison of side effects, including efficiency and output power were made