Improved tuning methods for converter-modulators

The converter-modulator is a resonant power conditioning configuration that is optimized for a particular load impedance or parameter space. Although traction motor Insulated Gate Bipolar Transistors (IGBTs) are typically used for hard-switching application in the 1 kHz regime, the present use of high-power (10-15 MW) converter-modulators have used a 20 kHz resonant switching topology. This presents design challenges to maintain efficient and reliable switching characteristics for the IGBTs. Improved tuning methods and circuit topological changes now offer a significant reduction in IGBT switching losses as compared to those used on the spallation neutron source (SNS) design (perhaps by 10). These circuit and topology changes should also permit pulse width modulation (PWM) of the modulator output voltage to provide a regulated voltage without anomalous IGBT switching characteristics. This paper will review the results of this investigation based on models developed from the SNS converter-modulator operational data.