Application of frequency control in coal mine machinery has obvious energy-saving effect. With the wide application of frequency converter, the simovert masterdrives，as the central part of the frequency converter，is improving and perfecting．In the link of rectification, there is the fluctuating of power supply or absence of voltage, which may result in severe damage to rectifier modules. For the part of feedback, we need commutation operate smoothly, if inversion failed, the contravariant would overthrow and even causing serious damage. This paper ddsigned an automatic transmission test and control circuit to ensure the simovert masterdrives works smoothly. The design can meet the needs of most frequency conversion equipments.