Improved Large DC Gain Converters with Low Voltage Stress on Switches Based on Coupled-Inductor and Voltage Multiplier for Renewable Energy Applications

Starting from a common principle, two new coupled-inductor-based DC-DC converters with large DC gains are proposed. Both of them present a low voltage stress on the power switch with their leakage inductance energy recuperated to the load. The first coupled-inductor-based converter employs two diode-capacitor voltage multipliers (VMs) inserted in an innovative way to give it many advantages. Specifically, the first VM is placed near the switch to serve as both a multiplier and a switch-voltage clamp cell, while the second one is inserted into the output circuit. The two VMs working in harmony then provide a very large DC gain. Conduction losses are also reduced as power switches with low on-state resistance can be selected due to the clamping role of the first VM. Moreover, the availability of capacitors of both VMs in the output diode loop results in low voltage stress on all semiconductor devices. The choice of a lower voltage-rating output diode with a lower parasitic capacitance can then alleviate oscillations between the leakage inductance and diode capacitance at its turn-off. The second converter uses a three-winding coupled inductor and a single VM, forming a new hybrid VM cell. Its component count is reduced without affecting the practical dc gain. Its advantage is the elimination of the output diode recovery problem and thus, does not result in spikes at its turn-off. Operational principles and DC steady-state analyses of the two converters are discussed, followed by comparison with available converters. Experimental results from two prototypes built for supplying a 400V grid are given for validating feasibility and theoretical analyses of the proposed converters.