A transformer controller for a drive isolation transformer is provided. The transformer may include multiple sets of primary windings as an input, and the transformer controller may include multiple branches coupled between a power source and the transformer. Each branch may be coupled to its own primary winding on the transformer, and may include one or more components, such as an isolation switch, a fuse, contactor, or circuit breaker. One or more of the branches may include a pre-charge reactor to limit inrush or capacitor charging current occurring during startup, and may include a pre-charge contactor to remove the pre-charge reactor from the circuit when the startup process has reached a certain level (e.g., the charging or inrush current has dissipated, or a DC bus reaches a charged state).