How to get 99% inverter efficiency

Base drive methods are proposed to realize high efficiency Darlington transistor inverters. High efficiency is achieved by reducing the on-state drop of the Darlington transistors to that of simple ones, thus significantly cutting the resultant on-state losses. Two practical drive circuits are presented. First, the circuit for directly driving the output transistor of a Darlington transistor is discussed and some experimental results are included when applied to a 100 kVA three-phase bridge inverter. In the second drive circuit, the on-state drop of a Darlington transistor is reduced by compensating the drop of the driver transistor with a current transformer; thus reducing the on-state losses while keeping the advantages of the Darlington transistor. A 10 kVA three-phase bridge inverter using Darlington transistors intended for electric vehicle applications was built to test the CT compensated base drive method. Typical experimental results are included, which showed high efficiency of 99.3% at a 10 kW resistive load. An energy recovery snubber for reducing the switching losses is also presented