Importance

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Abstract

An electric motor controller comprises a circuit for selecting between driving and braking an electric motor in accordance with the health or otherwise of a pair of main electric motor control switches (14 and 16). In a preferred embodiment the health of the switch is determined by the voltage (A) between the switches. The controller also comprises apparatus for detecting the sense of movement of the motor. In the event that the motor is moving in a sense opposite to that selected, the apparatus increase field current to reduce the armature current thereby increasing the braking effect of the motor. Also in the controller are apparatus for changing from armature to field current control and vice versa, in response to a given magnitude of control signal. In order to provide an unambiguous change-over, a lockout circuit is provided to inhibit change-over in a transition region. The lockout circuit maintains the mode of control to above/beneath the change-over level when changing from one level to another. The controller has a drive circuit which uses a flywheel inductor to provide an enhanced actuating signal for a transistor control switch for the motor. In a first state, the inductor is connected to by-pass the transistor to build-up a flywheel current. In a second state, the flywheel current is arranged to be applied to the transistor as a spike input.

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First Claim