Study on medium-frequency transformer isolated substation

Abstract

In this paper study on solid-state medium-frequency transformer isolated substation is modeled in detail. The substation is formed by AC/DC rectifier, six-pulse DC/AC inverter, high-frequency transformer, DC/AC six-diode rectifier and DC/AC inverter. Both AC/DC rectifier at high AC grid-1 side and DC/AC inverter at lower grid-2 side are controlled by proportional resonant controller and are interfaced with the grids through LCL filters. LCL filters interfaced with both grids are optimized and the controller parameters are also optimized using differential evolution algorithm. It is found by adding passive filter between six-pulse inverter and medium-frequency transformer, it is possible to remove most harmonic voltage components and ensure that the voltage applied across medium- frequency transformer can be quite close to sinusoidal waveform. By doing so, the core losses could be effectively contained, thereby leading to higher frequency and efficiency operation.