Motor-driven compressor

A motor-driven compressor, comprising:

• an electric motor;
• a housing that accommodates the electric motor and includes a suction port into which a refrigerant is drawn;
• a compression portion configured to be driven by the electric motor and configured to draw in and compress the refrigerant in the housing;
• and
• an inverter device configured to drive the electric motor, wherein
• the inverter device includes
• an inverter circuit including switching elements included in upper arms and lower arms of u-, v-, w-phases, the inverter circuit being configured to convert direct-current voltage into alternating-current voltage when switching operation for the switching elements is performed and supply the alternating-current voltage to the electric motor,
• a current sensor configured to detect a value of current supplied to the electric motor,
• a coordinate converter configured to calculate a d-axis current value and a q-axis current value using a detected value of the current sensor,
• a speed controller configured to generate a d-axis current command value and a q-axis current command value using a difference between a rotation speed command value and a rotation speed estimated value for the electric motor,
• a current controller configured to calculate a d-axis voltage command value using a difference between the d-axis current command value and the d-axis current value and calculate a q-axis voltage command value using a difference between the q-axis current command value and the q-axis current value,
• a pulse-width-modulation controller configured to control the switching elements using the d-axis voltage command value and the q-axis voltage command value, and
• a rotation speed estimator configured to calculate the rotation speed estimated value using the d-axis current value, the q-axis current value, the d-axis voltage command value, and the q-axis voltage command value,
• the speed controller generates the d-axis current command value and the q-axis current command value such that necessary torque to drive the electric motor occurs,
• the inverter device includes a heat-generating current command section configured to increase a temperature of the electric motor by changing the d-axis current command value and the q-axis current command value, and
• the heat-generating current command section is configured to change the d-axis current command value and the q-axis current command value so as to shift the d-axis current command value and the q-axis current command value in a direction in which the d-axis current value increases along a constant torque curve in a d-q coordinate system.