A novel converter topology for permanent magnet drive systems

A new converter concept for electric drives is presented. It is especially suitable for permanent magnet (PM) machines with a high power density and a low inductance. An additional switched capacitor in each converter arm is introduced in order to supply the reactive power of the machine and to avoid a field-weakening current. A multilevel waveform and output voltages above the DC link can be applied in a well controlled manner. The new topology offers additional degrees of freedom for control of the system leading to minimization of certain factors e.g. current ripple or torque ripple. It produces fewer losses compared to conventional converter designs. Additionally, the pulse frequency of the semiconductor devices can be lower for a given fundamental, because of the additional switching states in the converter. For PM machines the novel converter is able to operate and stop safely at high speeds. No undesired energy is fed into the DC link and no undesired braking occurs. The concept can be applied to different phase numbers and enables generator and motor operation. Full bridge or half bridge concepts configurations are possible. The paper describes the new concept and gives a calculation example that compares the new topology with conventional converter designs with respect to total system losses.