The battery voltage of the shuttle bus is 24 V, and the battery voltage of the car is 12 V, while, stable constant voltages 12 V and 5 V are required by VEPSS. Thus, the battery voltage is converted to a stable CP voltage (typically 12 V and 5 V) by using two voltage regulators. The CP ground is connected with the LP ground only within the CP portion of the system, so that CP voltage quality is not polluted by LP. Both ec and es are switch controllable, which makes it possible to cut them off when over-current is detected