In a motor driving apparatus having an inverter which can drive n (n being an integer not smaller than 2) motors each having a permanent magnet in its rotor, and a connection switching device for switching the connection state of the n motors, the connection switching device is operated to change the number of the motors connected to the inverter thereby to change the impedance as seen from the inverter towards the motors. When i (i being any of 2 to n) motors among the n motors are concurrently driven by the inverter, the voltage outputted by the inverter may be controlled such that the inductance values of the i motors are identical. It is possible to prevent hunting and step-out due to the phase difference between the motors driven by the inverter.

An electric motor system is described. The electric motor system includes a drive circuit including an inverter configured to supply variable frequency current and a contactor configured to supply line frequency current. The electric motor system also includes an electric motor coupled to the drive circuit wherein the electric motor is communicatively coupled to a controller. The controller is configured to control the inverter to supply variable frequency current to the electric motor, thereby operating the electric motor at a motor speed, and determine, based upon at least one input parameter, a maximum potential motor speed the inverter can achieve. The controller is also configured to receive a command to operate the electric motor at line frequency current and control the drive circuit to transition from supplying variable frequency current to supplying line frequency current before the maximum potential motor speed the inverter can achieve is reached.

A method of operating a transport refrigeration system having a plurality of inverters configured to power a refrigeration unit includes placing a first inverter of the plurality of inverters in an active state; monitoring a load on the first inverter; comparing the load on the first inverter to an upper threshold; placing a second inverter of the plurality of inverters in an active state upon the load on the first inverter being greater than the upper threshold.

In an air conditioner that uses a refrigerant mixture containing at least 1,2-difluoroethylene, high efficiency is achieved. In the air conditioner (1), a compressor (100, 200) can be driven without interposing a power conversion device between an AC power source (90, 190) and a motor (70, 170). Thus, it is possible to provide the air conditioner (1) that is environmentally friendly and has a relatively inexpensive configuration.

A liquid level detector includes: a vertically-mounted accumulator configured to store refrigerant; a heater configured to heat the accumulator; a temperature detector configured to detect a surface temperature of the accumulator; a pressure detector configured to detect a pressure of the refrigerant in the accumulator; and a controller configured to detect a position of a liquid surface of the refrigerant in the accumulator based on a surface temperature of the accumulator detected by the temperature detector when the accumulator is heated by the heater, and a pressure of the refrigerant in the accumulator detected by the pressure detector.

A variable speed drive comprises a voltage filter and voltage polarity protection unit including 1) a voltage filter circuit configured for low-pass filtering a voltage of an associated DC voltage source, and 2) a voltage polarity protection circuit configured to prevent incorrect polarity parring between the variable speed drive and the associated DC voltage source; a DC power supply unit being operatively connected to the voltage filter and voltage polarity protection unit via at least a positive polarity connection; an inverter unit being operatively connected to the DC power supply unit, a controllable load dump inserted in series with the positive polarity connection between the voltage filter and voltage polarity protection unit and the DC power supply unit, and a control unit configured to control at least the DC power supply unit, the inverter unit and the controllable load dump.

A control device for a compressor includes an operation stop control unit that stops the compressor in a procedure different from a normal stop request signal when a signal different from the normal stop request signal that requests the compressor to stop in a predetermined procedure and a forced stop request signal from a device including the compressor is detected. The operation stop control unit stops the compressor in the different procedure according to a speed of the compressor when the forced stop request signal is detected.

An air-conditioning apparatus includes an indoor unit and an outdoor unit including a compressor that compresses a refrigerant and a motor drive system that drives the compressor. The motor drive system includes an inverter that converts a DC voltage into an AC voltage, and an electric motor including three stator windings with both ends open. The electric motor operates based on the AC voltage obtained by the inverter. The motor drive system further includes a connection state switching unit that has a function to change the connection state of the three stator windings included in the electric motor, and sets the connection state to a star connection at the start of operation of the air-conditioning apparatus.

The present disclosure relates to a motor operated compressor, including a housing, a compressor provided in the housing, a motor connected to the compressor to drive the compressor, an inverter coupled to one side of the housing, and connected to the motor unit in an electrically conductive manner. The motor operated compressor includes a hermetic terminal assembly, one side of which extends into the inverter unit, and an opposite side of which extends into the housing. A plurality of busbars have one end of each busbar connected to the opposite side of the hermetic terminal assembly, and the other end of each busbar connected to the motor unit. A first insulating cover portion encloses and seals the hermetic terminal assembly and the plurality of busbars inside the housing, such that a conductive body connecting the motor unit and the inverter unit in the main housing is sealed from refrigerant.

A motor driver for driving a motor including three-phase windings includes: an inverter that applies a desired voltage to the motor; and an inverter controller that controls an operation of the inverter. The inverter includes: a current detector that detects a direct current in a first connecting line among three-phase connecting lines connecting the respective three-phase windings and the inverter; and a current detector that detects an alternating current in a second connecting line among the three-phase connecting lines, and a maximum direct current is caused to flow to the first connecting line in a first control mode for positioning a rotor of the motor.