Position detection device for permanent magnetic machines
The invention indicates a correct one of multiple rotor positions. For example, the invention can determine, in a PM machine, which of two possible positions a rotor is in when the position is known only within ±π radians. If the actual rotor position is known to be one of ω and ω+π, for example as indicated by a resolver, the proposed invention can be used to determine whether the actual position is ω or ω+π.
1. A permanent magnet machine, comprising:
a motor with a stator having cores with windings thereon and a rotor, which is movable relative to the stator, having permanent magnets, the motor having an odd number of pole pairs;
a resolver configured to indicate an even number of pole pair positions, whereby upon start-up the resolver identifies a rotor position ambiguous by a predetermined value; and
a controller configured to receive a position signal from the resolver and generating a driving signal for moving the motor and wherein, upon start-up, the controller is configured to
(i) pulse a first voltage pattern to the windings in the form of the drive signal corresponding to a presumed rotor position and obtain a first measurement of current in the windings resulting from the application of the first voltage pattern,
(ii) pulse a second voltage pattern, opposite of the first voltage pattern, and obtain a second measurement of current in the windings resulting from the application of the second voltage pattern, and
(iii) compare the first and second current measurements to resolve said rotor position ambiguity.
2. A machine according to claim 1 , wherein the voltage pattern is applied at an amplitude sufficient to generate current that causes a saturation level in various stator cores to traverse a non-linear portion of their flux-density vs. applied magnetic intensity (B-H) curves as a result of the influence of the permanent magnets in the machine.
3. A machine according to claim 2 , wherein the first voltage pattern is applied repeatedly to obtain a series of current readings that are aggregated to yield the first current measurement and the second voltage pattern is applied repeatedly to obtain a series of current readings that are aggregated to yield the second current measurement.