Digital control of IGBTs for module shutdown in input-series and output-parallel connected modular DC-DC converter

In an input-series and output-parallel (ISOP) connected modular DC-DC converter, the input voltage range can be significantly increased by shutting down the respective modules. Additionally, the converter's efficiency at certain input voltage can be increased by utilising the most optimum number of operating modules. The shutdown of non-essential modules is implemented with the available IGBTs in the input bridge of the modules. Due to the large amount of energy stored in the input bus capacitors especially at high input voltages, the IGBTs have to be controlled to limit the initial discharge current from the input capacitors. Digital control is hence employed here to accurately control the IGBTs in their active region during module shutdown to ensure operation within their safe operation region. A complex programmable logic device (CPLD) is used here to generate the required gate voltage based on current and voltage feedback from the IGBTs. Upon completion of shutdown, the algorithm enables the IGBTs to fully turn on and operate in their saturation region to create a low resistance current bypass path. The details of the digital control as well as its implementation are discussed here. Results of the module shutdown and module reactivation with the implemented digital control are subsequently experimentally verified.