Angle control system for a switched reluctance drive utilizing a high frequency clock

Claim 2

A control system as claimed in claim 1 in which the frequency multiplier comprises: an increment detector arranged to receive the first output signals, the increment detector being operable to generate a series of clock pulses, each clock pulse being defined by a change in state of the output signals of the first output signals; a counter having a reset input arranged to receive the series of clock pulses, the counter being resettable in response to each clock pulse generated by the increment detector, the counter having a clock input coupled to a system clock, the counter being operable to provide an output that varies in proportion to the frequency of the series of clock pulses from the increment detector; and a programmable divider coupled to receive the output of the counter and the system clock, the programmable divider being operable to provide at its output the high frequency clock signal, the high frequency clock signal having a frequency that is a fraction of the frequency of the system clock, wherein the relationship of the frequency of the high frequency clock signal to the frequency of the system clock is controlled by the output of the counter.

Claim 3

A control system as claimed in claim 2 in which the increment detector comprises an exclusive OR gate.

Claim 4

A control system as claimed in claim 2 or 3 in which the frequency of the high frequency clock signal is equal to the frequency of the system clock divided by the output of the counter.

Claim 5

A control system as claimed in any of claims 1 to 5 in which the angle control means comprises: a counter having a clock input and a reset input, the clock input being coupled to receive the high frequency clock signal, the reset input being coupled to receive the first output signals, the counter being operable to provide a counter output representative of the number of pulses applied to the counter clock input following the application of a pulse to the counter reset input; a first comparator coupled to receive the counter output and a turn-on signal having a value corresponding to a rotor position at which the phase winding should be energised, the first comparator providing an output signal at a first logic level when the value of the counter output exceeds the value of the turn-on signal; a second comparator coupled to receive the counter output and a turn-off signal having a value corresponding to a rotor position at which the phase windings should be de-energised, the second comparator providing an output signal at a predefined logic level when the counter output exceeds the value of the turn-off signal; and logic means responsive to the output signals from the first and second comparators to generate a firing signal to energise the phase winding when the output signals from the comparators indicate that the counter output is greater than the value of the turn-on signal but less than the value of the turn-off signal.

Claim 6

A control system as claimed in claim 5 in which the first logic level is a logic low level, the predefined logic level is a logic low level, and in which the logic means responsive to the output signals from the first and second comparators comprise an inverter coupled to the output of the first comparator for inverting the output of the first comparator and an AND gate having a first input coupled to receive the output of the inverter and a second input coupled to receive the output of the second comparator.

Claim 7

A control system as claimed in any of the preceding claims in which the first output signals are at a first resolution corresponding to the absolute position of the rotor, the second output signals are at a second resolution corresponding to the incremental position of the rotor, the second resolution being greater than the first resolution.

Claim 8

A control system as claimed in claim 7 in which the rotor position encoder comprises a member including a first set of features and a second set of features, a first set of sensors arranged to produce output signals indicative of movement of the member past the first set of sensors, and a second set of sensors arranged to produce output signals indicative of the movement of the member past the second set of sensors, wherein the output signals from the first set of sensors comprise the first output signals and the outputs from the second set of sensors comprise the second output signals.

Claim 9

A control system as claimed in any of claims 1 to 6 in which the rotor position encoder comprises a member including a set of features, a set of sensors operable to produce the output signals indicative of the movement of the member past the sensors, the first and second output signals being the same signals.

Claim 10

A control system as claimed in claim 8 or 9 in which the features define light blocking and light transmissive regions and wherein the sensors that comprise the sets of sensors are optical sensors.

Claim 11

A control system as claimed in claim 10 in which the light blocking and light transmissive regions define an angular extent and wherein the angular extent of the light transmissive and light blocking regions defined by the features in the first set of features are substantially equal.