Research on DTC Control Strategy of Induction Starter/generator System

The advancement in power electronic makes the cage-type induction machine(IM) be suitable to be used as a starter/generator(S/G). Because the IM must start the engine to a high ignition speed with a low voltage battery, a method which employs delta-connection stator winding is proposed. Similarities and differences of basic direct torque control(DTC) in IM with delta-connection and starconnection stator winding are investigated. In order to convert the IM from starting mode to generating mode smoothly, a method by changing the direction of electromagnetic torque is presented. The disadvantage of basic DTC is that it has a big torque ripple. In generating mode, the torque ripple can cause voltage ripple. In order to decrease voltage ripple, DTC based on space vector modulation(SVM-DTC) is researched. Creation method of reference voltage vector which includes change trend and magnitude information of flux and torque is presented. Experimental results verify that the induction starter/generator system can successfully start the engine with the low voltage battery and can convert from starting mode to generating mode smoothly under basic-DTC. The system has a preferable stable and dynamic generation performance under SVM-DTC.