US 4,250,435 A · Clock rate control of electronically commutated motor rotational velocity

Abstract

A speed control system for an electrically commutated motor which is readily adaptable to digital velocity control input and which provides highly efficient and accurate control in a relatively inexpensive manner. Desired motor rotational velocity is commanded by an input clock rate, which may be variable, rather than by a voltage or current signal. A sensor is provided for determining actual rotor position, and actual rotor position is periodically compared with instantaneous desired motor position as indicated by the time of occurance of one of the input clock signals or pulses. Depending upon the results of this periodic comparison, a dynamically established active current limit is modified. Specifically, if motor rotor actual position leads desired position, the current limit is reduced. If, on the other hand, actual motor position is lagging, the current limit is increased. If the rotor is at the correct position, or within a predetermined deadband, the current limit is unchanged. This control action occurs simultaneously with conventional winding commutation taking place under the control of a, commutation sequencer periodically advanced in conventional fashion as the rotor reaches each of a plurality of predetermined positions.

Claims12

Dependent claims

A speed control system for an electronically commutated motor having a rotor and a plurality of stator windings operable to produce magnetic fields in response to selective winding energization, said system comprising:

a commutation sequencer operable to selectively energize the motor windings in a sequence appropriate for effecting motor rotor rotation, said commutation sequencer operable to advance step-by-step through the sequence as the rotor reaches each of a plurality of predetermined positions;
a storage device for storing a changeable representation of an established limit for motor winding current;
a controller responsive to said representation for limiting current through motor windings energized by said sequencer to the established limit;
a sensor for determining actual rotor position;
a source of periodic signals representative of desired rotor position and occurring at a rate proportional to desired rotational velocity, the time of occurrence of each individual one of the periodic signals representative of a particular instantaneous desired rotor position;
and
and adjustment element responsive to said sensor and to said periodic signal source, said adjustment element operable to periodically compare actual rotor position to desired rotor position and to decrease the established limit for motor winding current in the event actual rotor position leads desired rotor position by at least a predetermined amount, and to increase the established limit for motor winding current in the event actual rotor position lags desired rotor position by at least a predetermined amount.

4 more elements

A method for controlling the rotational velocity of an electronically commutated motor having a rotor and a plurality of stator windings selectively energized in a step-by-step sequence for effecting motor rotor rotation, stepping through the sequence occurring as the rotor reaches each of a plurality of predetermined angular positions, said method comprising:

providing a series of periodic signals representative of desired rotational velocity, the periodic signals occurring at a rate proportional to desired rotational velocity with each of the periodic signals representative of a particular instantaneous desired rotor position;
sensing rotor position;
providing a changeable stored current limit;
limiting current through energized motor windings to an established limit;
said
periodically comparing sensed rotor position to desired rotor position and, in the event actual rotor position leads desired rotor position by at least a predetermined amount, decreasing the established current limit, and, in the event actual rotor position lags desired rotor position by at least a predetermined amount, increasing the established current limit.

3 more elements

Dependencies are inferred from the claim text.

Clock rate control of electronically commutated motor rotational velocity

Life of this patent

Clock rate control of electronically commutated motor rotational velocity

Life of this patent

Abstract

Claims12