Ground fault detection device for motor driving circuit

A ground-fault detection device for a motor driving circuit comprising:

• an inverter circuit comprising upper switching devices and lower switching devices which are connected in a bridge and are connected at output sides to respective phases of a motor;
• electric-current detection resistances connected between respective lower switching devices in the inverter circuit and ground;
• a switching control circuit which repeatedly causes
• a first powering time interval during which an electric current flows from a power supply through an upper switching device in the inverter circuit, the motor, and a lower switching device for powering the motor,
• a first regenerative time interval during which lower switching devices, electric-current detection resistances and the motor constitute a closed circuit and a regenerated electric current flows through the circuit,
• a second powering time interval during which an electric current flows from the power supply through an upper switching device in the inverter circuit, the motor, and a lower switching device for powering the motor and
• a second regenerative time interval during which upper switching devices and the motor constitute a closed circuit and a regenerated electric current flows through the circuit and, performs switching control for switching among respective time intervals;
• and
• electric-current detection circuits for detecting values of the electric currents flowing through the electric-current detection resistances during the switching control,
• wherein, in an event that an electric current value detected by the electric-current detection circuits during the first regenerative time interval becomes equal to or greater than a predetermined electric current value by a ground-fault electric current based on a ground-fault electric energy that is accumulated in an inductance component between the inverter circuit and the motor, a ground-fault is determined to have occurred in connection lines between the inverter circuit and the motor.