Distributed control scheme for parallel connected soft-switching high-power high-frequency inverters

Inductive heating applications, such as pipe welding or steel-tape annealing, require electrical power ratings of several MWs at frequencies up to 100 kHz and higher. To realize this high power frequency product, several inverters or several power semiconductor devices have to be connected in parallel, because the maximum rating of a single inverter unit is often far below the required rated power. In this paper, a control strategy for parallel connected soft-switching (ZVS and near ZCS) high-frequency voltage-source IGBT- or MOSFET-inverters is presented. The proposed distributed control system, where one control unit is dedicated to each inverter, ensures synchronous switching without any communication between individual control units. Distinctive features include high reliability, flexible configurations, reduction of long communication lines and good monitoring properties.