Improved Sensorless Phase Control of Stand-Alone Brushless Doubly-Fed Machine Under Unbalanced Loads for Ship Shaft Power Generation

The brushless doubly-fed machine (BDFM) without a brush and slip ring has some advantages of high operation reliability and less maintenance cost, which is very suitable for the ship shaft power generation. In this application, the BDFM mainly works on the stand-alone state, in which the power winding (PW) voltage should be controlled directly. The unbalanced load is a typical working state, which mostly results in the unbalance of PW voltage and affects the normal operation of loads severely. The sensorless control strategy can enhance the operation safety under extreme environment and cut down the cost effectively, which is highly desired to be applied in the BDFM-based ship shaft power generation. In this paper, an improved sensorless phase control strategy is proposed, which can work effectively under the unbalanced load condition. First, the sensorless operation is achieved by controlling the $q$-component of PW voltage, which can realize the phase control simultaneously. Then, the unbalanced compensation is designed in details. Finally, both simulation and experiments have demonstrated that, by the proposed method, the PW voltage phase can be controlled precisely and the voltage unbalance factor is lower than the permissible level.