System for controlling operation of a switched reluctance motor between multi-phase operating mode and a reduced phase operating mode

An apparatus for controlling a switched reluctance machine to change operating modes between a multi-phase operating mode and a reduced phase operating mode wherein the machine includes a rotatable rotor, a stator, and a plurality of stator windings defining a corresponding plurality of machine phases, comprising:

• a speed sensing circuit for sensing a speed of the rotor and generating a speed signal in response thereto;
• a comparator circuit responsive to said speed signal for changing the operating mode of the machine from the multi-phase mode, wherein a first number of machine phases are energized according to a predetermined operating strategy, to the reduced phase operating mode, wherein a second number less than said first number of machine phases are energized according to said strategy, when said rotor speed reaches a first predetermined level, and for changing the operating mode of the machine from the reduced phase mode to the multi-phase mode when said rotor speed reaches a second predetermined level that is less than said first predetermined level to thereby define a hysteresis operating band to prevent undesirable oscillation between the reduced phase mode and the multi-phase mode, said apparatus further comprising a multi-phase reference circuit responsive to said speed signal for generating a multi-phase current reference signal having a magnitude corresponding to a desired multi-phase current level through each one of the first number of machine phases, and a reduced phase reference circuit responsive to said speed signal for generating a reduced phase current reference signal having a magnitude corresponding to a desired reduced phase current level through each one of the second number of machine phases, said apparatus further comprising an analog switch having an output and a pair of inputs coupled to said multi-phase reference circuit and said reduced phase reference circuit, respectively, said analog switch being operative for selecting and outputting on said switch output one of said multi-phase and reduced phase current reference signals in accordance with said mode signal.

An electric motor comprising:

• a stator including a plurality of stator poles having stator windings provided thereon defining a plurality of motor phases;
• a rotor supported for rotation relative to said stator, and including a plurality of rotor poles;
• a speed sensing circuit for sensing a speed of said rotor and generating a speed signal in response thereto;
• a multiple-phase reference circuit responsive to said speed signal for generating a multi-phase current reference signal;
• a reduced phase reference circuit responsive to said speed signal for generating a reduced phase current reference signal;
• a comparator circuit responsive to said speed signal for generating a mode signal having a first state indicative of the multi-phase mode of operation, wherein a first number of machine phases are energized, and a second state indicative of the reduced phase mode of operation, wherein a second number less than said first number of machine phases are energized, said mode signal transitioning from said first state to said second state when said rotor speed reaches a first predetermined level, said mode signal transitioning from said second state to said first state when said rotor speed reaches a second predetermined level that is less than said first predetermined level to thereby define a hysteresis operating band to prevent undesirable oscillation between the single-phase mode and the multi-phase mode;
• an analog switch having an output for selecting and outputting on said switch output one of said multi-phase current reference signal and said reduced phase current reference signal in accordance with the state of said mode signal;
• a plurality of phase drive circuits for energizing said plurality of machine phases, said analog switch output being connected to at least one of said phase drive circuits for varying a current level through the machine phase connected thereto according to one of said multi-phase current reference and said reduced phase current reference signals.