Monitoring conditions of an electric motor using stator current and voltage signals from power supplied to the motor is disclosed herein. The stator voltage and current signals may be used to calculate instantaneous power values which may be used to calculate slip. The slip may be used to monitor for a locked rotor condition during startup of the motor. The slip value may be used to provide thermal protection to the electric motor.

A method for starting an induction machine without residual flux includes: scanning a state of the induction machine with different stator frequencies by controlling a supply voltage applied to the induction machine; determining whether a slip value, being a difference between a rotor frequency and a stator frequency, is within a slip interval; and, when it has been determined that the slip value is in the slip interval, regulating the slip value towards zero and magnetising the machine to the required level.

A method for starting an induction machine without residual flux includes: scanning a state of the induction machine with different stator frequencies by controlling a supply voltage applied to the induction machine; determining whether a slip value, being a difference between a rotor frequency and a stator frequency, is within a slip interval; and, when it has been determined that the slip value is in the slip interval, regulating the slip value towards zero and magnetising the machine to the required level.

A controller for a drive motor (60) of a product conveyor belt at a checkout has a phase-start cutting and/or phase-end cutting controller (50) that controls the drive motor (60) in such a manner that the product conveyor belt is accelerated with reduced torque from a non-driven state. A start controller controls the drive motor (60) in such a manner that the drive motor (60) initially drives with a non-reduced torque when accelerating the product conveyor belt from the non-driven state before the phase-start cutting and/or phase-end cutting controller (50) further accelerates the product conveyor belt with reduced torque.

A controller for a drive motor (60) of a product conveyor belt at a checkout has a phase-start cutting and/or phase-end cutting controller (50) that controls the drive motor (60) in such a manner that the product conveyor belt is accelerated with reduced torque from a non-driven state. A start controller controls the drive motor (60) in such a manner that the drive motor (60) initially drives with a non-reduced torque when accelerating the product conveyor belt from the non-driven state before the phase-start cutting and/or phase-end cutting controller (50) further accelerates the product conveyor belt with reduced torque.

A hybrid air-gap/solid-state device protection device (PD) for use in an electrical power distribution system includes an air-gap disconnect unit connected in series with a solid-state device, a sense and drive circuit, and a microcontroller. Upon the sense and drive circuit detecting an impending fault or exceedingly high and unacceptable overvoltage condition in the PD's load circuit, the sense and drive circuit generates a gating signal that quickly switches the solid-state device OFF. Meanwhile, the microcontroller generates a disconnect pulse for the air-gap disconnect unit, which responds by forming an air gap in the load circuit. Together, the switched-OFF solid-state device and air gap protect the load and associated load circuit from being damaged. They also serve to electrically and physically isolate the source of the fault or overload condition from the remainder of the electrical power distribution system.

A hybrid air-gap/solid-state device protection device (PD) for use in an electrical power distribution system includes an air-gap disconnect unit connected in series with a solid-state device, a sense and drive circuit, and a microcontroller. Upon the sense and drive circuit detecting an impending fault or exceedingly high and unacceptable overvoltage condition in the PD's load circuit, the sense and drive circuit generates a gating signal that quickly switches the solid-state device OFF. Meanwhile, the microcontroller generates a disconnect pulse for the air-gap disconnect unit, which responds by forming an air gap in the load circuit. Together, the switched-OFF solid-state device and air gap protect the load and associated load circuit from being damaged. They also serve to electrically and physically isolate the source of the fault or overload condition from the remainder of the electrical power distribution system.

A system for driving one or more motors includes: a controller having an instruction output; one or more motor drivers, each of the motor drivers are coupled to the instruction output of the controller and each of the motor drivers having a unique address; and wherein each motor driver is only operable to receive instruction from the controller when its unique address is provided by the controller at the instruction output.

A system for driving one or more motors includes: a controller having an instruction output; one or more motor drivers, each of the motor drivers are coupled to the instruction output of the controller and each of the motor drivers having a unique address; and wherein each motor driver is only operable to receive instruction from the controller when its unique address is provided by the controller at the instruction output.

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.