A hybrid powertrain system includes an electric motor/generator unit having a multiphase asynchronous AC machine electrically connected to a multiphase bridge inverter. A high-voltage capacitor is electrically connected between positive and negative sides of a high-voltage DC power bus. High-voltage DC bus pre-charge circuits are electrically connected between gate drive bias power supplies and the multiphase bridge inverter. A low-voltage battery electrically charges the high-voltage DC link capacitor via the gate drive bias power supplies and the high-voltage DC bus pre-charge circuits when the high-voltage energy storage system is disconnected from the high-voltage DC power bus.