Control method for a novel converter topology for permanent magnet drives

The paper describes a new converter concept for permanent magnet drives and its control. It is called multilevel integrated step-up (MIS) converter, because the new topology enables output voltages higher than the DC link voltage and a multilevel-like output voltage waveform, too. DC/DC converters to stabilize and increase the DC link voltage are not necessary, since DC-link voltage variations can be compensated by control of the MIS converter. The converter comprises internal switched ¿boost-capacitors¿. The machine inductance is used to generate a step-up conversion for the internal capacitor voltage. These points lead to additional degrees of freedom for controlling the system and optimization of important parameters e.g. current ripple or switching frequency. In comparison to standard flying capacitor topologies no upper limit exists for the internal capacitor voltage. This is a unique feature of the MIS converter. The extended operating range is explained with respect to different machine characteristics with a low and high short circuit current ratio. The control scheme shows different ways to control the internal capacitor voltage in relation to machine´s power and speed. Additionally, design considerations for the size of the internal boost capacitor are presented.