Speed Sensorless Vector Control Induction Motor Drives Fed by Cascaded Neutral Point Clamped Inverter

An effective control solution for speed sensorless vector control of induction motor fed by a cascaded neutral point clamped (NPC) inverter is proposed, where the novel SPWM pulse rotation control approach provides a simple way to implement vector control for induction motor when the cascaded NPC inverter is employed. The single carrier is used in the novel pulse control, instead of the multi-carriers, which makes the voltage modulation simpler and the hardware burden decrease. It is of great benefits to the cascaded NPC inverter, i.e., the output voltages and powers of all inverter modules, and two series-capacitor dc voltages of each inverter module are perfectly balanced, and a low switch frequency of all inverter modules provides a synthesized high frequency PWM phase voltage. A rotor flux-oriented vector control is combined with back EMF-based MRAS speed estimation, which results in a speed closed-loop control. The voltage sensors together with the filters of changeable parameters ensure the precision of speed estimation for the whole frequency range. The proposed scheme is applied to control an 800kW 4160V induction motor fed by the 1MVA 6000V 17-level cascaded NPC inverter, where the controller mainly consists of one DSP and one CPLD. The experimental results verify the proposed scheme.