A control method is used with a control system to control a screw pump. The control system includes an electric motor and a motor drive. The control method includes following steps. Firstly, a DC bus voltage is monitored. If the DC bus voltage is smaller than a first threshold value, a potential energy stored in the pump screw and released by a backspin action is converted into a regenerative electrical energy so as to maintain a normal operation of the motor drive. Then, the motor drive drives the electric motor to control the backspin action of the screw pump according to a backspin torque limit strategy. If the electrical power from the power source is not restored and the level of a reverse regenerative torque is smaller than a preset torque value, the backspin action of the screw pump is stopped freely.

A device for compressing a gaseous fluid, in particular a refrigerant in a refrigerant circuit, specifically of an air-conditioning system of a motor vehicle. The device has a housing, a compression mechanism for compressing the gaseous fluid, and an electric motor for driving the compression mechanism. The housing is formed with a suction-pressure chamber and a high-pressure chamber.

A motor-driven compressor is provided with a motor including a rotor, a housing including an inlet through which low-pressure refrigerant serving as a low-pressure fluid is drawn in, a compression unit that compresses the low-pressure refrigerant and discharges compressed high-pressure fluid, an inverter that drives the motor, and a controller that controls the inverter. If the rotor is activating in a reverse direction that is opposite to a forward direction when activating the motor, the controller obtains a position of a d-axis of the rotor and controls the inverter so that current flows to the obtained d-axis and so that frequency of current flowing to the motor decreases as time elapses.

The present invention corresponds to a check valve with an inertial mass that is installed in the bottom of the production tubing and above the progressive cavity pump (PCP) of an oil well, which prevents that the hydrostatic column that is inside of the production tubing go down in the moment where the artificial lift of the column stops for the detention of the PCP pump. If we prevent that this phenomenon to happen, the PCP pump will not rotate in the opposite direction of its normal operation and it will not be clogged by any particulate material that is contained in it.

A motor-driven compressor includes a three-phase motor including a rotor, a housing, a compression unit, a drive circuit, and a controller. The drive circuit includes u-phase upper and lower arm switching elements, v-phase upper and lower arm switching elements, and w-phase upper and lower arm switching elements. The controller performs a deceleration control in response to the rotor being rotating in a direction opposite to the forward direction. The controller controls the drive circuit in a switching control mode that includes a first mode, in which one or more switching elements of the upper and lower arm switching elements of the three phases are activated while the remaining switching elements are deactivated, and a second mode, which differs from the first mode in a combination of the activated and deactivated switching elements.

A motor-driven compressor includes an electric motor including a rotor, a housing, a compression unit, a drive circuit, and a controller. The controller includes a deceleration controller that performs a deceleration control, which decelerates the rotor, during a first period in response to the rotor being rotating in a direction opposite to the forward direction, and a continuation controller that performs a continuation control, which continues the rotation of the rotor, during a second period that is longer than the first period after the deceleration control is performed. A fluctuation difference of a rotational frequency of the rotor during the continuation control is less than a deceleration rotational frequency difference.

There is provided an oil-free air compressor that prevents oil from entering a compressor body by preventing a reverse rotation of the compressor body when the compressor is in shutdown, while improving the rust prevention effect, and that has improved reliability. An oil-free air compressor 100 includes an oil-free compressor body 1 that compresses air, and that outputs the compressed air; a cooler 5 that is connected to the compressor body, and that cools the compressed high-temperature air; a dry air supply mechanism for supplying dry air to an output side of the compressor body; and a mechanism for preventing a reverse rotation of the compressor body during a shutdown of the compressor.

A device for compressing a gaseous fluid, in particular a refrigerant in a refrigerant circuit, specifically of an air-conditioning system of a motor vehicle. The device has a housing, a compression mechanism for compressing the gaseous fluid, and an electric motor for driving the compression mechanism. The housing is formed with a suction-pressure chamber and a high-pressure chamber.

A scroll compressor including a casing forming the exterior; a driving unit installed in the casing and generates a drive power; a rotary shaft installed in the driving unit to be rotatable; a compression portion including an orbiting scroll installed on the rotary shaft to be capable of orbiting, and a fixed scroll which is coupled to be engaged with the orbiting scroll so as to form a compression chamber between the orbiting scroll and the fixed scroll; and a check valve including a valve portion which is arranged so that one side thereof faces the compression chamber and guides suction of a refrigerant when being opened and is closed when the driving of the compressor is stopped so as to prevent the refrigerant from flowing backward, and a valve fixing portion which is installed on the side surface provided in the suction port of the fixed scroll.

Provided is a scroll-type electric compressor capable of promptly decreasing pressure inside a scroll compression mechanism to smoothly and efficiently prevent reverse rotation and reduce noise when a motor is stopped. A control device 62 executes deceleration control of switching switching elements to decrease the rotation speed of a motor 2 after having received an instruction to stop the motor 2, and brake control of stopping a rotor 29 of the motor 2 at an angle at which a back pressure hole of a movable scroll is not closed or an angle at which a discharge hole of a fixed scroll is not closed after the rotation speed of the motor 2 has been decreased by the deceleration control and switching the switching elements 66A to 66F to fix the rotor at the angle.