Analysis of different PWM schemes for 3-level boost converter to reduce current stress in DC link capacitors of single phase NPC inverter

Reliability of the grid feeding or stand-alone inverter system is a concern. Apart from the power electronic switching devices, DC link capacitors have an impact on reliability of the whole system. Two different PWM switching schemes are analysed for a 3-level DC-DC converter connected to a single phase NPC inverter. To reduce the current stress on DC link capacitors, it is suggested to use inverter Output Coordinated PWM (OCP) for DC-DC converter. Analytical study and simulation is carried out to derive the current stress on DC link capacitors. It is shown that the capacitor I²R loss is reduced to half in the proposed scheme, which improves the capacitor operational life time. With the reduction in current stress, the required number of parallel DC link capacitors can be reduced. The study and conclusion drawn can be extended to other half-bridge type single phase inverter topologies.