A system for controlling an AC motor is provided. The system comprises an electrical connection path for connecting an electrical input of the AC motor to a first phase of alternating current from an electric power supply. The system also comprises two or more motor controllers, each motor controller is located on the electrical connection path between the electric power supply and the AC motor and is operable to regulate current of the first phase passing through it. Each motor controller is connected in parallel, relative to the other motor controllers, to the electrical connection path. At least one processor is configured to control the motor controllers to repeatedly change which of the motor controllers current of the first phase passes through, such that at any given time current of the first phase only passes through one of the motor controllers. A corresponding method is also provided.

An embodiment relates to a method for operating a three-phase machine including a rotor and a stator connected to a three-phase network. The stator is connected to the three-phase network via a first semiconductor circuit arrangement for forming a first rotational field rotating in a first direction of rotation in the stator and via a second semiconductor circuit arrangement for forming a second rotational field rotating in a direction of rotation opposite to the first direction of rotation in the stator. The three-phase machine further includes a controller. The method includes controlling, via the controller, semiconductors of the first and second semiconductor circuit arrangement to accelerate the rotor by current pulses of both the first rotational field and second rotational field in the first direction of rotation.

In a control device for discharging a DC link capacitor by means of a discharging device including a load resistor and a switch element connected in series with the load resistor, the control device includes a generator unit, which is configured to generate a pulse width-modulated actuation signal for the switch element with an ascertained duty cycle, and a control unit, which is configured to ascertain the duty cycle in such a way that, in the time average, a desired discharge current flows through the load resistor.

A controller for a motor determines a voltage limit circle based on a velocity of the motor, a DC bus voltage of an inverter, calculates a q axis current limit value based on the voltage limit circle and a predetermined current limit circle, determines, as a q axis current command value, a value obtained through a limit process which is applied using the q axis current limit value to a q axis current value calculated in accordance with a torque command value, and determines a corresponding d axis current value based on the q axis current command value.

A control method for verifying the compatibility between an input filter and a variable speed drive. The method includes applying a plurality of successive commands so as to define a plurality of operating points of the electric motor, for each operating point, measuring the DC voltage of the bus, comparing the maximum variation in the amplitude of the DC voltage measured for the operating point with a threshold value, defining a new operating point as long as the maximum variation in the amplitude of the DC voltage is lower than the threshold value, determining an operating range including all of the operating points for which the maximum variation in the amplitude of the DC voltage is lower than the threshold value.

A control method for verifying the compatibility between an input filter and a variable speed drive. The method includes applying a plurality of successive commands so as to define a plurality of operating points of the electric motor, for each operating point, measuring the DC voltage of the bus, comparing the maximum variation in the amplitude of the DC voltage measured for the operating point with a threshold value, defining a new operating point as long as the maximum variation in the amplitude of the DC voltage is lower than the threshold value, determining an operating range including all of the operating points for which the maximum variation in the amplitude of the DC voltage is lower than the threshold value.

Systems and methods for soft starting a motor (40) using solid-state switching devices are disclosed. The system (10) includes a soft starting switch (53) that is made of a plurality of solid-state switches (62, 63). The system (10) also includes a controller (86) that is programmed to regulate currents and voltages delivered to the motor (40) during a start-up operation of the motor by cycling the solid-state switches (62, 63) ON and OFF during the start-up operation.

The apparatus according to the present invention comprises a command voltage determination circuit section configured to determine a predetermined first compensation voltage as a command voltage upon initial startup and provide the command voltage to an inverter; a conversion circuit section configured to convert an output current of the inverter into a q-axis current on a synchronous reference frame; and a compensation voltage determination circuit section configured to determine a second compensation voltage based upon the q-axis current and to provide the second compensation voltage to the command voltage determination circuit section.

The apparatus according to the present invention comprises a command voltage determination circuit section configured to determine a predetermined first compensation voltage as a command voltage upon initial startup and provide the command voltage to an inverter; a conversion circuit section configured to convert an output current of the inverter into a q-axis current on a synchronous reference frame; and a compensation voltage determination circuit section configured to determine a second compensation voltage based upon the q-axis current and to provide the second compensation voltage to the command voltage determination circuit section.

In a method for actuating a motor for starting up a mill containing material to be ground, the motor for triggering sedimentation of the material to be ground in the mill is initially fed by a first inverter. The motor is subsequently disconnected from the first inverter, and in a further step the motor is connected to a first supply which has a first supply voltage. The maximum output voltage of the first inverter is lower than the first supply voltage.