Main Power Devices Research Articles

Eliminating Harmonics in a Five Level Inverter by Optimized Both Switching Angles and Dc Link Voltage

This paper presents design and analysis of a single phase multilevel inverter by optimizing both switching angles and DC link voltage of a cascaded inverter. The switching angles and dc link voltage are chosen such that to minimize the total harmonic distortion of the output voltage. The main power devices are switched only once per cycle , so that to overcome the switching loss problem, as well as electromagnetic interference (EMI) problem, a method is given to determine the optimum value of the switching angles and the value of the dc link voltage. Theoretical analysis and simulation of a single phase 5-level cascaded inverter are introduced with a wide range of modulation index.

Zero-Current and Zero-Voltage Soft-Transition Commutation Cell for PWM Inverters

This paper presents a universal auxiliary commutation cell for pulse-width modulated (PWM) inverters termed zero current and zero voltage transition (ZCZVT) commutation cell. It provides zero current and zero voltage commutation, simultaneously, during main power devices turn-on and turn-off, with controlled di/dt and dv/dt. As a result, commutations of the main power devices occur without any losses. This unique characteristic is not achieved by any other soft-switching commutation cell for inverters hitherto presented in the literature, making it a strong candidate for use in low-power (MOSFET), medium-power (IGBT) or high-power applications (GTO, thyristor). Furthermore, reverse recovery losses of main diodes are minimized and auxiliary switches commutate at zero current. To demonstrate the operation of the proposed universal auxiliary commutation cell, a ZCZVT PWM full-bridge inverter is analyzed. To evaluate the operation of the auxiliary circuit in different conditions, prototypes with both IGBTs and MOSFETs for different output powers levels were implemented and their performances compared. Experimental results confirm that there is no overlap between main switch current and voltage, and that waveform ringing is practically eliminated.

A non-linear turn-off snubber for power electronic switches

A novel suggestion for a non-linear turn-off snubber is simulated experimentally with linear capacitors and an auxiliary power electronic switch. Thus the principle and advantages of this concept is partly illustrated, particularly concerning the important reduction of reactive stored energy for the same switching dissipation in the main power device. The full advantages of the concept will be realised when a snubber capacitor with non-linear, voltage dependent dielectric is used. The work on this part of the solution is being continued.