Sensorless, PWM-free starter/generator inverter topology for low inductance high speed PM machines

A low cost sensorless, PWM-free starter/generator inverter topology for high-speed low-inductance PM machine applications is presented. By taking advantage of the preheating resistive element typically found in most microturbine systems the new topology achieves a PWM-free starting current regulation. Also the proposed topology uses the preheating resistor element as a load dump to prevent any unacceptable over speed conditions due to loss of load. To achieve sensorless commutation during starting, the terminal voltages of the machine are sensed and processed. With PWM-free regulation, switching losses are reduced significantly, consequently lower rating power switching devices can be used. Also PWM-free regulation eliminates the need for any external inductors typically used to reduce the PM machine heating due to the high current ripple resulting from the switching and the machine low inductance. Finally, with PWM-free operation the cost and the weight of the EMI filter are drastically reduced. As a result more reliable, lower cost and higher power density electronic package is realized. The new topology was verified experimentally.