Position-sensorless control of interior permanent magnet machines

1. A method of controlling an IPM machine having a rotor and a stator, said method comprising:

measuring a stator terminal signal to obtain a measured signal;

rotating the measured signal to obtain a synchronous reference frame current signal;

estimating a rotor position based on an impedance generated using the rotor and included in the current signal; and

using the estimated rotor position to control the machine.

2. The method of claim 1 further comprising:

vector-rotating a synchronous reference frame command voltage signal to obtain a stationary voltage;

injecting a high-frequency signal into the stationary voltage; and

pulse-width modulating the stationary voltage to obtain the stator terminal signal.

3. The method of claim 2 wherein estimating a rotor position comprises:

filtering the synchronous reference frame current signal to obtain a signal having an imaginary component in the q-axis;

multiplying the imaginary component by a signal having a frequency the same as a frequency of the injected high-frequency signal to obtain a DC value; and

applying a gain to the DC value.

4. The method of claim 3 wherein said gain comprises:

-

2

⁢

ω

inj

⁢

L

d

⁢

L

q

V

inj

⁡

(

L

d

-

L

q

)

where ω inj represents a frequency of the injected signal, L d and L q represent inductance in d- and q-axes, and V inj represents a voltage of the injected signal.

5. The method of claim 1 wherein estimating a rotor position comprises:

using a synchronous reference frame command voltage signal to estimate a synchronous stator current; and

using the estimated synchronous stator current to estimate the rotor position.

6. The method of claim 5 wherein using the synchronous reference frame command voltage signal comprises:

applying an error signal to the synchronous reference frame command voltage signal in accordance with V=jω e LI to obtain a corrected voltage; and

processing the corrected voltage in accordance with

I

=

V

Ls

+

R

to obtain the estimated synchronous stator current,

where I represents stator current, V represents stator voltage, L represents stator inductance and R represents stator resistance.

7. The method of claim 6 wherein using the estimated synchronous stator current comprises:

filtering the synchronous reference frame current signal to remove the high frequency signal;

summing the filtered current signal with the estimated synchronous stator current to obtain a summed current signal; and

controlling the summed current signal using a proportional-integral controller to estimate the rotor position.

8. The method of claim 1 wherein said estimating is performed without using a rotor position sensor.

9. The method of claim 1 further comprising placing a plurality of magnets into the rotor in a plurality of slots and leaving several of the slots empty to generate the impedance.

10. A method of providing cranking torque and power generation for an engine-powered vehicle using an alternator-starter system, said method comprising:

measuring and vector-rotating a stator terminal signal of an IPM machine of the alternator-starter system to obtain a synchronous reference frame current signal;

capturing in said current signal an impedance generated by a rotor of the IPM machine;

estimating a position of the rotor based on said impedance; and

controlling the IPM machine based on said estimated rotor position;

said impedance captured at a low speed of the machine using a high-frequency signal injected into the stator.

11. The method of claim 10 further comprising:

distributing a plurality of magnets in a plurality of slots in the rotor to form barriers; and

leaving several of the slots empty.

12. The method of claim 10 further comprising:

capturing said impedance at a high speed of the machine in accordance with

I

=

V

Ls

+

R

to obtain an estimated synchronous stator current,

where I represents stator current, V represents stator voltage, L represents stator inductance and R represents stator resistance; and

processing said estimated synchronous stator current using a proportional-integral controller to estimate the rotor position.

13. The method of claim 12 further comprising merging a low-speed estimate of rotor position with a high-speed estimate of rotor position, said merging based on a speed of the machine.

14. An alternator/starter system for an engine-powered vehicle, said system comprising:

an interior permanent magnet (IPM) machine having a stator and a salient rotor; and

a controller that:

measures and vector-rotates a stator terminal signal to obtain a synchronous reference frame current signal;

captures an impedance generated by said rotor in the current signal;

estimates a position of said rotor based on the impedance; and

controls said machine based on the estimated rotor position.

15. The alternator/starter system of claim 14 wherein said controller:

captures a low-speed impedance using a first algorithm and a high-speed impedance using a second algorithm; and

merges outputs of the algorithms based on a speed of said machine to estimate said rotor position.

16. The alternator/starter system of claim 15 wherein said controller uses a high-frequency signal injected into said stator to capture the low-speed impedance and a synchronous reference frame command voltage signal to capture the high-speed impedance.

17. The alternator/starter system of claim 14 wherein said rotor comprises a plurality of barriers formed by a plurality of magnets in slots, and wherein several slots are left empty.

18. The alternator/starter system of claim 14 wherein said magnets comprise injection molded magnets.