A Phase Current Peak Prediction Technique to Increase the Output Power of Switched Reluctance Generators for Wind Turbines

Due to the lack of permanent magnets in a switched reluctance machine (SRM), it is an extremely attractive solution for renewable technologies. A compact switched reluctance generator (SRG) with high output power is not only desirable by wind turbines, but by a wide range of applications, such as the automotive, aerospace, and appliance industries. Maximizing the output power of an SRG involves operating the machine at high speeds in single pulse mode, during which a high back electromotive force (EMF) is established. As a result, the machine's phase current becomes uncontrollable as it enters into a state of positive feedback. Once in positive feedback, the phase current reaches its peak and falls only when the back EMF of the machine reduces. The machine's back EMF begins to reduce as the rotor approaches its unaligned position. During the operating period, protection of the drive circuit and its diodes is imperative; however, an unknown phase current peak value calls for either an over designed drive or the avoidance of the SRG's use in high speed single pulse mode, especially under positive feedback. This work presents a technique to predict the phase current peak by detecting an optimal turn-off angle, which leads to a more controllable SRG with reduced drive constraints and higher output power, all while maintaining the same size of the machine. Experimental and simulation results pertaining to the scenario of a wind turbine experiencing changing wind speeds are presented in this paper.