Extended-speed low-ripple torque control of switched reluctance motor drives
Various embodiments are described herein for an extended-speed low-ripple torque control of a switched reluctance motor (SRM) using online torque sharing function (TSF). Two operational modes of an online TSF are defined during the commutation: In Mode I, absolute value of rate of change of flux linkage (ARCFL) of incoming phase is higher than outgoing phase; in Mode II, ARCFL of outgoing phase is higher than incoming phase. To compensate the torque error produced by imperfect tracking of phase current, a proportional and integral compensator with torque error is added to the torque reference of outgoing phase in Mode I and incoming phase in Mode II. Therefore, the total torque is determined by the phase with lower ARCFL rather than the phase with higher ARCFL as in conventional TSFs.
1. A method for controlling an overall torque response of a switched reluctance motor, the method comprising:
receiving a torque reference T e _ ref ;
receiving a first total torque response T e of the switched reluctance motor via a feedback system;
determining an incoming phase torque reference and an outgoing phase torque reference; and
outputting the incoming phase torque reference and the outgoing phase torque reference to the switched reluctance motor;
wherein:
i) during a first range of rotor positions:
the incoming phase torque reference T e _ ref(k) is generated by a torque sharing function controller using a torque sharing function for the torque reference T e _ ref and a present rotor position θ for the switched reluctance motor, and
the outgoing phase torque reference is an adjusted outgoing phase torque reference T e _ ref(k-1) new comprising a sum of an initial outgoing phase torque reference T e _ ref(k-1) generated by the torque sharing function controller using the torque sharing function for the torque reference T e _ ref and the present rotor position θ, and a compensation signal received from a compensator, the compensation signal being based on a difference between the torque reference T e _ ref and the first total torque response T e ; and
ii) during a second range of rotor positions:
the outgoing phase torque reference T e _ ref(k-1) is generated by the torque sharing function controller using the torque sharing function for the torque reference T e _ ref and the present rotor position θ; and
the incoming phase torque reference is an adjusted incoming phase torque reference T e _ ref(k) new comprising a sum of an initial incoming phase torque reference T e _ ref(k) generated by the torque sharing function controller using the torque sharing function for the torque reference T e _ ref and the present rotor position θ, and the compensation signal.
2. The method of claim 1 , wherein the first range of rotor positions corresponds to a start of commutation, and the second range of rotor positions corresponds to an end of commutation.
3. The method of claim 1 , wherein, during the first range of rotor positions, a maximum absolute value of rate of change of flux linkage (ARCFL) for an outgoing phase is lower than a maximum ARCFL for an incoming phase.
4. The method of claim 1 , wherein, during the second range of rotor positions, a maximum absolute value of rate of change of flux linkage (ARCFL) for an incoming phase is lower than a maximum ARCFL for an outgoing phase.
5. The method of claim 3 , wherein, during the second range of rotor positions, a maximum absolute value of rate of change of flux linkage (ARCFL) for an incoming phase is lower than a maximum ARCFL for an outgoing phase.
6. The method of claim 1 , wherein the compensation signal comprises a product of the difference between the torque reference T e _ ref and the first total torque response T e and a proportional and integral (PI) compensation factor.
7. The method of claim 6 , wherein, during the first range of rotor positions, the PI compensation factor is of a general form G (k-1) (s), and during the second range of rotor positions, the PI compensation factor is of a general form G (k) (s).
8. The method of claim 7 , wherein G (k-1) (s)=G (k) (s)=10+10/s.
9. The method of claim 1 , wherein, during the first range of rotor positions, outputting the incoming phase torque reference and the outgoing phase torque reference to the switched reluctance motor further comprises:
determining an incoming phase current reference i e _ ref(k) using the incoming phase torque reference T e _ ref(k) , the present rotor position θ, and a set of torque-current-rotor position characteristics, determining an incoming phase current i k using the determined incoming phase current reference i e _ ref(k) and a transfer function of a general form H (k) (s), and
outputting the determined incoming phase current i k to the switched reluctance motor, and
determining an outgoing phase current reference i e _ ref(k-1) using the adjusted outgoing phase torque reference T e _ ref(k-1) new , the present rotor position θ, and the set of torque-current-rotor position characteristics,
determining an outgoing phase current i k-1 using the determined outgoing phase current reference i e _ ref(k-1) and a transfer function of a general form H (k-1) (s), and
outputting the determined outgoing phase current i k-1 to the switched reluctance motor.
10. The method of claim 9 , wherein, during the second range of rotor positions, outputting the incoming phase torque reference and the outgoing phase torque reference to the switched reluctance motor further comprises:
determining the outgoing phase current reference i e _ ref(k-1) using the outgoing phase torque reference T e _ ref(k-1) , the present rotor position θ, and the set of torque-current-rotor position characteristics,
determining the outgoing phase current i k-1 using the determined outgoing phase current reference i e _ ref(k-1) and the transfer function of a general form H (k-1) (s), and
outputting the determined outgoing phase current i k-1 to the switched reluctance motor; and
determining the incoming phase current reference i e _ ref(k) using the adjusted incoming phase torque reference T e _ ref(k) new , the present rotor position θ, and the set of torque-current-rotor position characteristics,
determining the incoming phase current i k using the determined incoming phase current reference i e _ ref(k) and the transfer function of a general form H (k) (s), and
outputting the determined incoming phase current i k to the switched reluctance motor.
11. The method of claim 1 , wherein, during the second range of rotor positions, outputting the incoming phase torque reference and the outgoing phase torque reference to the switched reluctance motor further comprises:
determining an outgoing phase current reference i e _ ref(k-1) using the outgoing phase torque reference T e _ ref(k-1) , the present rotor position θ, and a set of torque-current-rotor position characteristics,
determining an outgoing phase current i k-1 using the determined outgoing phase current reference i e _ ref (k-1) and a transfer function of a general form H (k-1) (s), and
outputting the determined outgoing phase current i k-1 to the switched reluctance motor; and
determining an incoming phase current reference i e _ ref(k) using the adjusted incoming phase torque reference T e _ ref(k) new , the present rotor position θ, and the set of torque-current-rotor position characteristics,
determining an incoming phase current i k using the determined incoming phase current reference i e _ ref(k) and a transfer function of a general form H (k) (s), and
outputting the determined incoming phase current i k to the switched reluctance motor.