Method and apparatus for control of switched reluctance motors

Abstract

A method of controlling a switched reluctance motor is disclosed herein. The motor composes a stator carrying a plurality of phase windings and a rotor. The method comprises activating the phase windings in a sequence selected to apply torque to the rotor. Wherein during a cycle of rotation of the rotor the phase windings switch between an active state in which current in the phase winding applies torque to the rotor and an inactive state, applying a voltage to a selected phase winding whilst the selected phase winding is in the inactive state to provide a flux in the selected phase winding: determining the current in the selected phase winding; determining the rotor angle based on the current and the flux, and controlling said activating based on the rotor angle.

1 . A method of controlling a switched reluctance motor, the motor comprising a stator carrying a plurality of phase windings and a rotor, the method comprising:
 activating the phase windings in a sequence selected to apply torque to the rotor, wherein during a cycle of rotation of the rotor the phase windings switch between an active state in which current in the phase winding applies torque to the rotor and an inactive state;   applying a voltage to a selected phase winding whilst the selected phase winding is in the inactive state to provide a flux in the selected phase winding;   determining the current in the selected phase winding;   determining the rotor angle based on the current and the flux; and   controlling said activating based on the rotor angle.   
     
     
         2 . The method of  claim 1  comprising determining the flux by integrating the voltage as a function of time. 
     
     
         3 . The method of  claim 1  wherein determining the rotor angle comprises applying a flux mapping to the current and the flux. 
     
     
         4 . The method of  claim 3  wherein the flux mapping is selected based on the rotor speed and a torque demand signal. 
     
     
         5 . The method of  claim 3  wherein the flux mapping comprises an association between rotor angle, phase winding flux, and phase winding current. 
     
     
         6 . The method of  claim 5  wherein the association is provided by a plurality of stored data values, for example wherein the stored data values are arranged to provide a look-up-table functionality. 
     
     
         7 . The method of  claim 6  wherein the look-up-table comprises a two-dimensional look-up-table to allow rotor angle to be determined based on phase winding flux and phase winding current, and for example further comprising selecting between a plurality of said look up tables based on a speed of the rotor. 
     
     
         8 . The method of  claim 1  wherein the rotor angle is determined based on the current and flux in a first one of the plurality of phase windings, and the controlling comprises selecting the flux to be applied by a second one of the plurality of phase windings. 
     
     
         9 . A method of controlling a switched reluctance motor, the method comprising:
 controlling flux in stator windings of the motor in a sequence selected to apply torque to its rotor during periods of rotation of the rotor, wherein the flux is selected based on the rotor angle and the rotor angle is determined by an iterative method comprising:   obtaining previous flux data indicating the flux in a stator winding at a preceding time;   incrementing the previous flux data by a flux increment to determine present flux data, wherein the flux increment is based on integrating a voltage applied to the stator winding since the preceding time;   obtaining present current data indicating the present current in the stator winding; and   estimating the present rotor angle based on the present flux data and the present current data; and   modifying the estimate of present rotor angle based on (a) the present flux data, and (b) an estimate of the flux error, wherein the estimate of flux error is based on the current in the winding and an angle error characteristic, dθ/dΨ defining the differential of angle with respect to flux.   
     
     
         10 . The method of  claim 9  in which the estimate of flux error is obtained by subtracting, from the present estimate of flux, an expected flux obtained using the present current data from a flux characteristic which defines flux as a function of stator phase current. 
     
     
         11 . The method of  claim 9  in which the angle error characteristic, dθ/dΨ, defines the differential of rotor angle with respect to flux as a function of phase current. 
     
     
         12 . An apparatus for controlling a switched reluctance motor, the motor comprising a stator carrying a plurality of phase windings and a rotor, the apparatus comprising a controller arranged to control a source of electrical energy adapted for activation of the phase windings, and to obtain current signals indicating the current in said phase windings, wherein the controller is configured to perform a method of controlling the switched reluctance motor, the method comprising:
 controlling flux in stator windings of the motor in a sequence selected to apply torque to its rotor during periods of rotation of the rotor, wherein the flux is selected based on the rotor angle and the rotor angle is determined by an iterative method comprising:   obtaining previous flux data indicating the flux in a stator winding at a preceding time;   incrementing the previous flux data by a flux increment to determine present flux data, wherein the flux increment is based on integrating a voltage applied to the stator winding since the preceding time;   obtaining present current data indicating the present current in the stator winding; and   determining the present rotor angle based on the present flux data and the present current data;   wherein obtaining previous flux data comprises obtaining reset data selected based on the rotor angle and the current in the stator winding.   
     
     
         13 . The apparatus of  claim 12 , wherein the controller is configured to operate on polling driven input/output. 
     
     
         14 . The apparatus of  claim 13  wherein the controller comprises a DSP.