The motor-driven compressor includes an electric motor, a housing, a compression portion, and an inverter device. The inverter device includes an inverter circuit, a current sensor, a coordinate converter, a speed controller, a current controller, a PWM controller, and a rotation angle estimator. The speed controller generates a d-axis current command value and a q-axis current command value such that a necessary torque to drive the electric motor occurs. The inverter device includes a heat-generating current command section that increases a temperature of the electric motor by changing the d-axis current command value and the q-axis current command value. The heat-generating current command section changes the d-axis current command value and the q-axis current command value so as to shift them in a direction in which a d-axis current value increases along a constant torque curve in a d-q coordinate system.

A HVAC system refrigeration circuit is provided. Embodiments of the present disclosure relate to a refrigeration circuit configured to balance the oil carryover between multiple compressors using a single refrigeration circuit. Embodiments of the present disclosure allow for the use of one or more inverter compressors and one or more fixed speed compressors. Embodiments of the present disclosure utilize capillary tubes or other flow control methods to balance the oil carryover between multiple compressors.

A heat transport system includes: a refrigerant circuit that seals therein a fluid including HFC-32 and/or HFO refrigerant as a refrigerant and that includes a refrigerant booster that boosts the refrigerant, an outdoor air heat exchanger that exchanges heat between the refrigerant and outdoor air, a medium heat exchanger that exchanges heat between the refrigerant and a heat transfer medium, and a refrigerant flow path switch that switches between a refrigerant radiation state and a refrigerant evaporation state; and a medium circuit that seals carbon dioxide therein as the heat transfer medium.

A refrigerator includes a controller that is configured to perform operations including driving a refrigerator compartment compressor, determining whether a sensed temperature in the refrigerator compartment satisfies a first temperature, driving, based on the sensed temperature in the refrigerator compartment satisfying the first temperature, a freezer compartment compressor, stopping the refrigerator compartment compressor, maintaining, after stopping the refrigerator compartment compressor, operation of the freezer compartment compressor, restarting the refrigerator compartment compressor, and varying a driving frequency of the refrigerator compartment compressor.

To reduce the possibility that temperature of refrigerant discharged from a compressor of a refrigeration apparatus becomes excessively high by controlling torque of a motor built into the compressor, the compressor includes the motor having rotation thereof controlled by inverter control. An inverter controller controls torque of the motor using inverter control when operation frequency of the compressor is at least one value within a range of from 10 Hz to 40 Hz. When at least the operation frequency is within the range of from 10 Hz to 40 Hz, torque of the motor is controlled, and under a predetermined condition in which temperature of refrigerant discharged from the compressor easily becomes excessively high, a device controller controls devices provided in a refrigerant circuit such that refrigerant sucked into the compressor is placed in a wet vapor state.

An air-conditioning apparatus includes: a heat source unit that generates a heating energy or a cooling energy that is transferred to refrigerant; a heat-use unit that causes the refrigerant to transfer the heating energy or the cooling energy to a heat load through heat exchange between the refrigerant and the heat load; a plurality of return pipes arranged parallel to each other and connecting the heat source unit and the heat-use unit to allow the refrigerant to flow therein from the heat-use unit to the heat source unit; an opening and closing device provided at at least one of the return pipes to control a flow rate of refrigerant; and a controller that opens the opening and closing device in a cooling operation, and closes the opening and closing device in a heating operation.

A compressor and a refrigeration device are provided. The compressor has a crankshaft, a connecting structure, and an avoidance part arranged on the connecting structure and/or the crankshaft. The avoidance part is located at a position where the connecting structure is matched with the crankshaft. The avoidance part is configured to be suitable for avoiding at least one of the connecting structure and the crankshaft. A gap between the crankshaft and the connecting structure is increased through the arrangement of the avoidance part, so that the avoidance part can avoid the crankshaft when the crankshaft is obliquely deformed.

A heat transport system includes: a refrigerant circuit that seals therein a fluid including HFC-32 and/or HFO refrigerant as a refrigerant and that includes: a refrigerant booster that boosts the refrigerant; an outdoor air heat exchanger that exchanges heat between the refrigerant and outdoor air; a medium heat exchanger that exchanges heat between the refrigerant and a heat transfer medium; and a refrigerant flow path switch that switches between a refrigerant radiation state and a refrigerant evaporation state; and a medium circuit that seals carbon dioxide therein as the heat transfer medium.

A driving apparatus includes: an inverter unit generating a three-phase alternating-current voltage from a direct-current voltage in accordance with a drive signal based on a voltage command and outputting the three-phase alternating-current voltage to a permanent-magnet motor, the permanent-magnet motor including a permanent magnet; a current detection unit detecting a motor current flowing through the permanent-magnet motor; and a control unit generating the voltage command to control an operation of the inverter unit and estimating a temperature of the permanent magnet to perform a protection operation on the inverter unit on the basis of the motor current and an overcurrent protection threshold. The control unit sets the overcurrent protection threshold on the basis of a magnet temperature estimated value of the permanent magnet and any one of a control computation period of the control unit, an output voltage frequency of the inverter unit, and a carrier frequency based on the output voltage frequency of the inverter unit.

An inverter for driving a motor that has a switchable connection of windings and drives a load element having a periodically varying load torque is provided. The inverter is controlled so that an output torque of the motor follows the periodic variation of the load torque. The inverter is controlled so that a current flowing through the motor is zero during a period including a minimum torque phase at which the load torque is at or near a minimum value. The connection is switched while the current flowing through the motor is zero. It is possible to switch the connection of the windings while the motor is rotating, and avoid an increase in apparatus size.