DC chopper with energy recovery transformer

Abstract

In DC choppers and inverters transformers are employed to recover the trapped energy in the commutating inductors in order to reduce the overvoltage of the commutating capacitors. It is known that the leakage factor of real transformers keeps the overvoltage substantially high. The present work shows that a finite Q-factor of real transformers significantly reduces the overvoltages, resulting in lowering of voltage and current ratings of the components. The proposed modification in the connection of the transformer leads to additional recovery of the trapped energy, resulting in further reduction of overvoltage and commutation loss. This energy recovery process must be completed in the OFF-interval to avoid spikes in the output voltage. Graphs for overvoltages, peak currents, per-unit loss and maximum permissible frequency factor have been plotted for the original and the modified scheme of the DC chopper. Experimental results justify the theoretical analysis.