| Abstract |
The recent development of the new power transistor generation has led to the realization of High Voltage/High Current IGBTs, which allow the electric power management with higher commutation speed. Therefore, IGBTs have been progressively replacing GTO devices in low and medium voltage inverters used in trams or regional trains and now they are also becoming attractive for modern locomotives. Nevertheless the maximum voltage supported by the actually available IGBTs doesn’t yet permit the employment of two-level VSI in high-speed or heavy traction drives applications; so, to take advantage of IGBTs characteristics, Neutral Point Clamped inverters must be used. The paper analyzes the peculiarities of the previously developed hysteresis modulation techniques for NPC inverters and suggests a suitable improvement. The proposed technique keeps the advantages of simplest hysteresis controls, i.e. fast response, good accuracy, no need to know load parameters; in addition, the modulator can be easily implemented if the microcontroller performs the error zone computation and a Programmable Logic Device provides the inverter control signals. |
