Continuous field control of series wound motors

A method for braking an operator controlled electric traction motor propelled vehicle of the type including, a power source, a time-ratio power regulator which is controlled to be conducting and non-conducting for connecting and disconnecting the motor to a direct-current power source in response to the relative position of an accelerator, a direction positioning means for controlling the direction of the vehicle, a signal processing means for controlling switching means, the switching means controlling the operation of the motor, a sensing means for providing signals representative of currents within field and armature windings of the motor, a braking means for providing signals representative of a brake position, said method comprising the steps of:

• (a) receiving data, the data including the position of the accelerator, the direction of motion of the vehicle, and the conducting and nonconducting time ratio interval;
• (b) setting the switching means in response to the position of the accelerator and the selected direction of motion of the vehicle;
• and
• (c) changing the switching means in response to release of the accelerator for implementing a first relatively low level of electrical braking of the vehicle distinct from a plug braking mode.

In a control system for a direct current traction motor having armature and field windings, the control system being of the type including a variable mark-space ratio power regulator, an accelerator and signal processing means responsive to accelerator position for supplying current command signals to the regulator, switching means for establishing connection of the motor in one of a series propulsion mode and a separately excited propulsion mode, the switching means being operated by the signal processing means in response to predetermined desired operating characteristics of the motor, and a power source, a method for switching between the series mode and separately excited mode comprising the steps of:

• (a) sensing the mark-space ratio of the regulator;
• (b) transitioning from a series mode to a separately excited mode when the mark-space ratio exceeds a predetermined value;
• (c) determining the magnitude of motor current just prior to transitioning;
• and
• (d) increasing the magnitude of field current above the determined magnitude of motor current immediately after transitioning whereby the magnitude of armature current is prevented from increasing above a determined magnitude at the time of transitioning.