An improved CSI fed induction motor drive

Current source inverter (CSI) drives are preferred over voltage source inverter (VSI) drives in high power applications where fast dynamic response is not required. Conventional CSI drives have drawbacks such as resonance, instability at low speeds and high torque ripple, due to which their applications are restricted. This paper presents an improved CSI fed drive configuration that addresses these major drawbacks, as well as other power quality issues associated with the conventional drives. Two active power filters (APFs) are used in the proposed drive. The drive ensures sinusoidal waveforms at both the input and the output terminals. A simple CSI power circuit switching at fundamental frequency is used. Further, the use of a standard six-pulse SCR based rectifier eliminates the bulky and expensive input transformer, thus reducing the overall system cost. The proposed configuration is verified for a high power rating vector controlled induction motor drive. The design of the controllers and operation of the APFs are explained. Simulation results for the entire operating region of the drive including low speed operation and the field weakening region are presented. Finally, an important result regarding the presence of undesired circulating currents with the common DC bus for the two APFs, is also reported. The solution to avoid this problem is presented.