Life diagnosis method for power storage device

A life diagnosis method for a power storage device included in a power storage apparatus connected to a direct-current bus in parallel to an inverter circuit in a motor control apparatus including a converter circuit that converts an alternating-current power supply into a direct-current power supply, and the inverter circuit that converts direct-current power output to the direct-current bus by the converter circuit and generates alternating-current power for controlling to drive a motor, the power storage apparatus including the power storage device, a step-up/down chopper circuit provided between the power storage device and the direct-current bus, and a control unit that performs discharging control for causing the step-up/down chopper circuit to perform a step-up operation and causing the power storage device to supply, to the direct-current bus, the direct-current power for supplementing the direct-current power output to the direct-current bus by the converter circuit and charging control for causing the step-up/down chopper circuit to perform a step-down operation and causing the power storage device to store regenerative power generated by the motor and output from the inverter circuit to the direct-current bus,

• wherein the life diagnosis for the power storage device carried out by the control unit during initial charging for forming a predetermined bus voltage in the direct-current bus performed in the converter circuit when power is supplied to the motor control apparatus comprises:
• a step of causing a step-down switching element to perform ON/OFF operations a predetermined times in the step-up/down chopper circuit to step down the predetermined bus voltage formed in the direct-current bus by the converter circuit, and applying the initial charging to the power storage device;
• a step of calculating total energy given to the power storage device in a period in which the ON/OFF operations are performed the predetermined times;
• a step of calculating actual capacitance of the power storage device from the calculated total energy and a charging voltage indicated by the power storage device;
• and
• a step of estimating a deterioration degree of the power storage device and diagnosing the life of the power storage device on the basis of a comparison of the calculated actual capacitance and initial capacitance of the power storage device.