Abstract: Method and device for starting a motor (12) in weak grids, especially asynchronous motors, which motor after start-up is supplied by a supply grid (13). The device (11) includes a frequency converter (14), which is rated in relation to the size of the motor (12) and arranged to bring the motor (12) up in speed, arranged to synchronize output voltage with voltage from the supply grid (13), and arranged for connecting the motor (12) to the supply grid (13) after the voltage of the motor is synchronized with the voltage of the supply grid (13). The main object is to do this with as low costs as possible and in the most space-saving manner.

Abstract: Method and device for starting a motor (12) in weak grids, especially asynchronous motors, which motor after start-up is supplied by a supply grid (13). The device (11) includes a frequency converter (14), which is rated in relation to the size of the motor (12) and arranged to bring the motor (12) up in speed, arranged to synchronize output voltage with voltage from the supply grid (13), and arranged for connecting the motor (12) to the supply grid (13) after the voltage of the motor is synchronized with the voltage of the supply grid (13). The main object is to do this with as low costs as possible and in the most space-saving manner.

Abstract: Control device (30) and method for controlling an AC motor (18) by means of a motor control unit (19). The control device (30) includes an AFE unit (33) arranged in parallel with the rectifier unit (12), which AFE unit (33) is arranged for, under normal operation, to work as an active filter and inject super-harmonic current components opposite of the ones generated by the rectifier unit (12) to counteract the current distortion, seen from the grid side. When the motor control unit (19) is running regenerative, the AFE unit (33) will work as a 4-quadrant converter and supply energy back to the supply grid (13). Advantages of the invention are reduced physical size, lower cost and improved efficiency compared to existing solutions of motor drive with frequency converters in weak grids, where the motor drive must handle regenerative operation.