Computational Investigation of Starting Characteristics of An Induction Machine

An induction machine consumes a very high inrush current during start-up, which can be potentially damaging to the machine itself and to the appliances connected. In the past, various studies focused on analytical and experimental techniques for direct on line start, star delta starting and V/Hz control methods. However, this paper provides and compares computational simulations of these methods and investigates techniques to avoid high starting current and develop the starting characteristics of an induction machine. For the V/Hz control relationships, the paper shows modeling of a six-step inverter by simulating the system with different values of ramp rates for the excitation frequency. Governing relations between the DC link voltage source amplitude and frequency are formulated and constant V/Hz control is used to maintain the magnetizing flux at its rated value for each steady-state excitation frequency and load. A comparison between all the proposed methods shows that constant V/Hz control operation is capable of producing a softer starting procedure than direct on-line starting and star-delta starting. However, it is not suitable for very high frequency ramp rate