Series Connection of Insulated Gate Bipolar Transistors (IGBTs)

High-voltage switches required in present power electronics applications are realized by connecting existing devices in series. Unequal sharing of voltage across series-connected devices can be minimized by using active gate control techniques, snubber circuits, and active clamping circuits. The primary objectives of this paper are to discuss existing voltage-balancing techniques, to present a novel hybrid voltage-balancing technique, and to optimize the number of insulated gate bipolar transistors (IGBTs) in a series string in terms of power losses. The novel voltage-balancing technique can achieve good voltage balancing with a minimum number of components and minimum total losses (i.e., IGBT losses and balancing circuit losses). This technique was validated by both simulation and experimental work. The power loss of a high-voltage switch depends on the voltage-balancing circuit and the number of IGBTs in series and switching frequency. For a given application, the optimum number of IGBTs, in terms of power losses, depends on device characteristics and switching frequency.