Design of Bus-Side RCD Snubber Circuit for Three-Phase High-Power Inverters

To protect the transistors operating in high-power converters, the simple and low-cost RCD snubber circuits are widely used. This paper presents operation and design principles of RCD snubbers that can be effectively used in many industrial applications. The typical RCD snubbers can be classified as: 1) the switchside snubber (if the snubbers are connected at the collector-emitter terminals of the transistor switch) and 2) the bus-side snubber (if the snubbers are connected at the dc bus). These two classes of snubbers are compared in terms of energy losses and operation under variable duty cycle theoretically. The latter snubber topology is chosen in this work as a more advantageous approach. The paper further proposes the design methodology for the bus-side snubbers. The proposed snubber methodology and its functionality are verified using the detailed simulation as well as the experimental prototype of a three-phase converter feeding 60-hp induction motor.