A motor-driven compressor (20) comprising: an
electric motor (23); a housing (21) which accommodates the
electric motor (23) and contains a suction opening (21a) into which a
refrigerant is sucked; a compression section (22) configured to be driven by the
electric motor (23) and configured to suck in and compress the
refrigerant in the housing (21); and an
inverter device (31) configured to drive the electric motor (23), wherein the
inverter device (31) comprises an
inverter circuit (40) having switching elements (Q1-Q6) included in
upper arms and lower arms of the u, v, w phases, wherein the inverter circuit (40) is configured to convert
DC voltage into AC
voltage when a switching operation is performed for the switching elements (Q1-Q6) and supplies the AC
voltage to the electric motor (23), a
current sensor (41, 42) configured to detect a value of the current supplied to the electric motor (23), a coordinate converter (65) configured to calculate a d-axis current value and a q-axis current value using a detected value of the
current sensor (41, 42), a speed controller (61) configured to generate a d-axis current command and a q-axis current command using a difference between a speed command and a speed estimate for the electric motor (23), a current controller (64) 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 to 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 (71) configured to control the switching elements (Q1-Q6) using the d-axis voltage command value and the q-axis voltage command value, and a speed estimator (69) configured to calculate the speed estimate 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 (61) generates the d-axis current
setpoint and the q-axis current
setpoint in such a way that the required torque for driving the electric motor (23) is generated, the inverter device (31) has a heat-generating current command section (70) configured to increase a temperature of the electric motor (23) by changing the d-axis current command value and the q-axis current command value, and the heat-generating current command value section (70) is configured to change the d-axis current command value and the q-axis current command value such that the d-axis current command value and the q-axis current command value are shifted in a direction in which the d-axis current value increases along a
constant torque curve in a dq coordinate
system, and a
stress limit ellipse and the
constant torque curve intersect at a pair of intersection points on an enhanced field side and a weakened field side, the heat-generating current command section (70) is configured to generate the d-axis current command and the q-axis current command at the intersection point of the
voltage limit ellipse and the
constant torque curve on the boosted side in a dq coordinate
system, wherein the
voltage limit ellipse depends on an input voltage and a rotational speed, wherein the heat-generating current command section (70) is configured to define, in the dq coordinate
system, an upper current limit circle in a range not greater than a limit current value for a temperature of a component of the inverter circuit (40), and changes the d-axis current command value and the q-axis current command value such that the d-axis current command value and the q-axis current command value are shifted to an intersection point of the upper current limit circle and the constant torque curve, and a current limit circuit and the constant torque curve intersect at a pair of intersection points on a strengthened field side and a weakened field side, the intersection point on the strengthened field side is in a range where the d-axis current value and the q-axis current value are positive, and the intersection point on the strengthened field side is set as the
heat generation control
operating point.