A method of operating an HVAC system including a motor having five taps, and an HVAC controller communicatively connected to a plurality of the five taps the motor includes storing, by a processor of the HVAC controller, selected speeds associated with a plurality of operating conditions in a memory of the HVAC control. The processor controls the motor according to the selected speeds and their associated operating conditions using a group of taps of the plurality of taps of the motor to which the HVAC controller is communicatively connected. Data is communicated between the motor and the HVAC controller using one of the plurality of taps of the motor to which the HVAC controller is communicatively connected.

An electronic control unit includes a first calculator and a second calculator. When the first calculator has an abnormality, even if a start switch of a vehicle is switched OFF by a driver of the vehicle, the second calculator is configured to maintain system main relays on a positive terminal side and a negative terminal side in a conductive state in case that a certain travel continuation condition is fulfilled. Therefore, even when the driver has erroneously switched OFF the start switch, an electric power is suppliable to an inverter via the system main relays kept in the conductive state, thereby the vehicle is travelable by using a vehicle travel-power motor.

An electronic control unit includes a first calculator and a second calculator. When the first calculator has an abnormality, even if a start switch of a vehicle is switched OFF by a driver of the vehicle, the second calculator is configured to maintain system main relays on a positive terminal side and a negative terminal side in a conductive state in case that a certain travel continuation condition is fulfilled. Therefore, even when the driver has erroneously switched OFF the start switch, an electric power is suppliable to an inverter via the system main relays kept in the conductive state, thereby the vehicle is travelable by using a vehicle travel-power motor.

A power conversion device includes a first inverter connected to first ends of the first coil group, a second inverter connected to first ends of the second coil group, a separation relay circuit connected to second ends of the first coil group and second ends of the second coil group to switch between connection and disconnection of the first and second coil groups, a first neutral point relay circuit connected to the second ends of the first coil group to switch between connection and disconnection of the second ends of the first coil group, and a second neutral point relay circuit connected to the second ends of the second coil group to switch between connection and disconnection of the second ends of the second coil group.

A motor driver includes an inverter, a multiphase pre-driver circuit, a controller and motor relays. The inverter includes pairs of an upper-arm switching element and a lower-arm switching element being connected in series between a ground line and a power supply line, and supplies power to a multiphase motor by converting direct current power of a battery. The multiphase pre-driver circuit drives the upper-arm and lower-arm switching elements. The controller commands the multiphase pre-driver circuit to drive the switching elements, and controls electrical conduction from the inverter to the multiphase motor. The motor relays interrupt a current flowing from the multiphase motor to the inverter during an off state. The multiphase pre-driver circuit includes a charge pump. The motor relays are turned on by an output voltage of the charge pump during an operation of the charge pump in a situation apart from that the controller provides an instruction.