Novel soft swithcing space vector PWM inverters using parallel resonant DC link topologies

Abstract

In this dissertation, four kinds of novel soft switching PWM inverters using parallel resonant DC link topologies are proposed to resolve both the high voltage stresses and restricted PWM capability of the conventional soft switching inverters with various resonant DC link topologies simultaneously. These have the minimum voltage stresses (1.0 p.u.) for all of the switching devices and highly improved PWM capability due to not only variable link pulse width but also variable pulse position. At first, a novel soft switching inverter is proposed by using a modified parallel resonant DC-link (PRDCL). This topology has most of the advantages of the conventional RDCL inverter such as high switching frequency, low switching loss, reduced acoustic noise and EMI and so forth. As it has also the above mentioned distinctive merits, the proposed PRDCL inverter can be applied to high power application. Furthermore, the design and control of the PRDCL circuit are fairly simple. Operational principle, detailed analysis and design procedures are described. A 7.5kVA prototype PRDCL inverter is implemented and tested with 20kHz switching frequency using power transistor modules. Experimental results verifying the principle of operation are presented. Another approach for a soft switching PWM inverter with low voltage stress and improved PWM capability is presented having only one additional switch. This circuit needs no snubber circuit owing to either ZVS or ZCS at switching instant and can operate at relatively high switching frequency by introducing new shoot-through pole concept. It has also simple structure and flexible PWM capability due to the convenient choices of switching conditions. Based on the operational principle, analyses and design procedures are described and verified by simulations. A soft switching quasi-parallel resonant DC link (QPRDCL) inverter with enhanced PWM capability is suggested using two additional switches. As mentioned earlier, it has also mi...