Current source IGBT-inverter for low inductive synchronous machines

Synchronous machines with air-gap permanent magnet excitation are advantageous in many modern applications. As a result of the construction principle the stator inductivities are often very low. Therefore, common voltage source inverters with sinusoidal output currents are not automatically the best supply solution for these machines. Either load reactors have to be used to smooth the output current or the high du/dt-rates of faster switches produce EMI problems and overvoltages at the machine windings. Investigations have shown that sine-wave machine currents are not the most effective way to feed these drives. This paper presents a novel way to overcome these problems by using a current source IGBT-inverter. The investigated system consists of a pulse-rectifier, a DC-current-link and an inverter with an output capacitor bank to decouple the stator currents from the DC-link. A simple, modular inverter construction is proposed. It makes no use of snubbers and is scalable over a wide power range. Practical experiments to prove the feasibility have been carried out with positive results.