Control strategy for a high power DC transformer with soft switching scheme for mining applications

This paper proposes a new concept to control a bidirectional LCL converter which is suitable for applications in mobile mining equipment. This converter employs two DC/AC insulated-gate bipolar transistor-based (IGBT) converters and a passive LCL which replaces the more common high frequency transformer and plays the most important role in energy conversion. Compared to the previously known control schemes, the proposed scheme uses p-q theory resulting in simpler and more robust control design. In order to apply p-q theory to a single phase circuit, a pseudo orthogonal signal is generated from one phase by using a second order generalized integrator (SOGI). The definitions of instantaneous active and reactive powers are adjusted accordingly. Performance of the proposed control scheme under steady state, during load and reference voltage step changes, and under a DC fault is studied via a detailed EMTP-RV simulation of a full size 20-MW 24kV/1.2kV converter. The simulation results are experimentally validated on a laboratory 200-W 100V/20V prototype converter.