A heat pump device includes a compressor including a motor, a heat exchanger, an inverter, and an inverter control unit. The inverter control unit generates a drive signal for the inverter. When the compressor is heated, the inverter control unit applies, to the motor, a high-frequency voltage with which the motor cannot be rotationally driven; estimates a magnetic pole position indicating a stop position of a rotor of the motor; determines an amplitude and a phase of a voltage command based on an estimation result of the magnetic pole position and a necessary amount of heat, and generates a drive signal.

A pulse width modulation (PWM) based active harmonic filter (AHF) system including a controller configured to adjust a load on the system from a first to a second load, the first load being greater than the second load, wherein the controller is configured to adjust a frequency of the system from a first to a second frequency when the load is equal to the second load, and wherein the second frequency is greater than the first; a first harmonic compensator configured to filter a first order of harmonics of a load when the load is equal to the second load; and a second harmonic compensator configured to filter a second order of harmonics of the load in parallel with the first order of harmonics when the load is equal to the second load and frequency equals the second frequency, the second order of harmonics being greater than the first order.

In certain embodiments, a refrigeration system comprises an emergency electric power supply configured to supply power to at least one motor drive of the system. The system comprises a power switch coupled to the emergency electric power supply, a tank configured to store a refrigerant, a first compressor configured to compress the refrigerant of the tank, and a controller coupled to the power switch and first compressor. The controller may receive an indication from the power switch that the system is using the emergency electric power supply, and in response to receiving the indication from the power switch that the system is using the emergency electric power supply, operate the system in a first power outage mode. The controller may determine an amount of power to supply to the first compressor based on the first power outage mode and transmit a signal to instruct the first compressor to turn on.

A refrigerating system of the present invention includes a plurality of parallel type refrigerators each of which has a plurality of compressors, and a host control device having a compressor start/stop permission output unit which is configured to output a compressor activation permission or a compressor stop permission to one of the plurality of parallel type refrigerators which is activated according to a predetermined permission condition. Each of the parallel-type refrigerators has a compressor activation control unit which is configured to a stopped compressor included in a certain refrigerator when a load factor of the certain refrigerator is equal to or greater than a first specified value and the compressor activation permission is received, and a compressor stop control unit which is configured to stop an activated compressor included in a certain refrigerator when the load factor of the certain refrigerator is less than a second specified value and the compressor stop permission is received.

A method for controlling a linear compressor and a method for controlling a refrigerator are provided. The method for controlling a linear compressor may include measuring an ambient temperature, and when the measured ambient temperature is equal to or lower than a predetermined safety temperature, applying a safety current to a motor assembly for driving a piston. On the other hand, when the measured ambient temperature is higher than the predetermined safety temperature, a current lower than the safety current may be applied to the motor assembly.

A preheater for a compressor that is capable of heating a lubricant oil efficiently with smaller power is provided. A preheater for a compressor includes: a capacitive oil surface sensor that is provided at a compressor used in a refrigerating cycle, and detects an oil surface of a lubricant oil A in the compressor; and a power supply unit that applies high-frequency voltage to the oil surface sensor.

An air conditioning device has: a refrigerant circuit that includes a compressor, a switching valve, a cascade heat exchanger, an expansion valve and an outdoor heat exchanger connected to one another by a first pipe through which a refrigerant flows, and that performs a defrosting operation in which the refrigerant discharged from the compressor is introduced into the outdoor heat exchanger; a heat-transfer medium circuit that includes a pump, the cascade heat exchanger, and the indoor heat exchanger connected to one another by a second pipe through which a heat-transfer medium flows; and a control device that controls the compressor and the pump. When an amount of heat storage of the heat-transfer medium is less than a threshold, the control device reduces the heating capability of the indoor heat exchanger when the air conditioning device transitions from a heating operation to the defrosting operation.

A power converting apparatus includes: a rectifying unit configured to rectify an input AC power, a buck converter that is configured to step down a voltage of the rectified power and that is configured to output DC power having the step down voltage, a first inverter that is connected to an output terminal of the buck converter and that is configured to convert the DC power into AC power to drive a first motor, a second inverter that is connected to the output terminal of the buck converter, that is disposed in parallel to the first inverter, and that is configured to convert the DC power into AC power to drive a second motor, and a converter controller configured to control an output voltage of the DC power of the buck converter.

A chiller includes an evaporator, a compressor including a prime mover, a first pressure sensor that detects a first pressure in the evaporator, a second pressure sensor that detects a second pressure in a condenser, and a controller. The controller determines a predicted energy level of the compressor based on the first pressure and the second pressure, the predicted energy level associated with liquid droplet flow into the compressor, compares the predicted energy level to an operating energy level, and modifies the at least one of the input power and the input current to the prime mover based on the comparison satisfying a modification condition.

A motor drive device includes a reactor, a converter circuit, a capacitor, an inverter circuit, and overcurrent determination units. The converter circuit converts a first AC voltage output from an AC power supply into a DC voltage. The capacitor smooths a second voltage on the DC side of the converter circuit. The inverter circuit converts DC power stored in the capacitor into AC power. One of the overcurrent determination units determines overcurrent based on a detected value of the first AC current, flowing between the AC power supply and the converter circuit. Another overcurrent determination unit determines overcurrent based on a detected value of the second DC current, flowing between the converter circuit and the capacitor. The converter and inverter circuits stop operating when the determination result of one of the overcurrent determination units indicates an overcurrent.