Wide speed range six-step mode operation of IPMSM drives with adjustable dc-link voltage

Driving a synchronous machine in overmodulation region and six-step mode is a common way to reduce switching losses in the inverter and fully utilize inverter output voltage. Main issues concerning this operating area in combination with state of the art field oriented control are saturation of the current controller and reduced torque dynamics. This paper presents a strategy that is based on a voltage angle control in order to improve dynamics and overcome stability problems of the PI-controller. An additional dc-link voltage control loop for drive trains including a dc/dc converter gives the designer a new degree of freedom to improve the drives overall efficiency. Precise control of both dc-link and inverter output voltages creates the possibility to shift six-step mode to an arbitrary operating region including base speed.