Motor control device, electric power steering device and inverter system failure detection method

A motor control device which controls driving of a motor having multiple-phase windings by using detection values of currents flowing in respective phases of the motor, the motor control device comprising:

• an inverter in which a plurality of circuits, each having switching elements respectively on an upper-side arm and a lower-side arm, are connected in parallel, and which supplies power to the motor;
• a motor control unit which controls driving of the motor by controlling the inverter;
• and
• a current detection unit which is connected to each of the switching elements on the lower-side arm and which detects the current in each of the phases,
• wherein the motor control unit has:
• a first drive mode in which switching control is carried out to switch on all of the switching elements on the lower-side arm, and to switch off all of the switching elements on the upper-side arm;
• and
• a second drive mode in which switching control is carried out to switch on all of the switching elements on the upper-side arm, and to switch off all of the switching elements on the lower-side arm, and
• the motor control unit:
• carries out a first failure determination for determining whether or not the sum of the currents of the respective phases detected as a first failure detection current by the current detection unit is within a previously established first threshold value range, when switching control is carried out in accordance with the first drive mode;
• carries out a second failure determination for determining whether or not each of the currents of the respective phases detected as a second failure detection current by the current detection unit is within a previously established second threshold value range, when switching control is carried out in accordance with the second drive mode;
• and
• detects an inverter system failure in accordance with the determination results of the first failure determination and the second failure determination.