Theoretical analysis of DC link capacitor current ripple reduction in the HEV DC-DC converter and inverter system using a carrier modulation method

This paper presents theoretical analysis of the dc link capacitor current ripple reduction in the HEV dc-dc converter and inverter system by using a proposed carrier modulation method. This carrier modulation method introduces a modified triangle carrier, with a switching frequency that is twice as much as the inverter´s, for the dc-dc converter to synchronize this dc-dc converter output current with the SPWM inverter input current. Resulting from this synchronization, the current ripple flowing into the dc link capacitor is greatly reduced by 50%, compared to the unsynchronized traditional triangle carrier method, whose switching frequency is the same as the inverter´s. Experimental results are obtained from a 30 kW boost converter and inverter prototype. Theoretical equations are derived to demonstrate the effectiveness for all situations, considering different load power factors and dc-dc converter duty cycles.