Self tuning method and apparatus for permanent magnet sensorless control

1. A method of determining a plurality of parameters of a Permanent Magnet Synchronous Motor (PMSM) by a motor controller to differentiate between a plurality of PMSMs, the method comprising the steps of:

applying regulated DC motor currents at a commanded fixed rotor angle;

measuring a quadrature voltage v q after an initial transient has elapsed, the quadrature voltage being applied across the PMSM windings;

parking the PMSM at standstill, whereby the quadrature voltage is proportional to a stator resistance and to the applied park current I park ;

selecting an initial set of controller parameters;

applying the quadrature voltage equal to zero;

measuring a time constant T s corresponding to an exponential decay of a quadrature current i q ;

accelerating the PMSM with a constant torque up to a preset target speed;

measuring a total acceleration time t accelerate until the preset target speed ω target is reached;

regulating a stator current at 0 value, whereby the stator current is at 0 value when currents i q(ref) and i d(ref) are both at zero value;

measuring the quadrature voltage and a freewheeling motor speed ω freewheel immediately after applying the 0 stator current;

calculating an electrical constant K E of the PMSM based on the measured values of the applied quadrature voltage and the freewheeling motor speed;

calculating a load inertia J based on the previously measured total acceleration time; and

calculating a set of parameters for the controller based on the determined motor parameters.

2. The method of claim 1 , wherein the saliency of the PMSM is negligible and q and d axis inductances are equal to a PMSM inductance L and the regulated DC motor currents i q(ref) =I park and i d(ref) are equal to 0.

3. The method of claim 1 , wherein when stator current is regulated at 0, the applied quadrature voltage is equal to the Electro Motive Force (EMF).

4. The method of claim 3 , further comprising a step of calculating an electrical constant K E of the PMSM based on the measured values of the quadrature voltage and free motor speed as

k

E

=

V

q

ω

freewheel

.

5. The method of claim 4 , wherein the electrical constant of the PMSM is equal to (p·λ), where λ is an amplitude of a flux induced by the permanent magnets of the rotor in stator phases and p is a number of pole pairs.

6. The method of claim 5 , wherein the step of calculating of the load inertia is based on the measured total acceleration time as

J

=

1.5

·

p

·

λ

·

I

acc

·

t

accelerate

ω

target

.

7. The method of claim 1 , further comprising a step of filtering the applied quadrature voltage to attenuate noise.

8. The method of claim 1 , further comprising a step of waiting for a period of time after the regulated DC currents and applied before parking the PMSM.

9. The method of claim 1 , wherein the stator resistance R during the parking step is calculated as R=v q /I park based on the measured value of the quadrature voltage.

10. The method of claim 9 , the PMSM inductance is calculated based on the known time constant as T s ·R=L where R is the stator resistance.

11. The method of claim 1 , further comprising a step of estimating a friction coefficient F once a constant motor speed ω steady corresponding to a steady current i q =I steady is reached in the accelerating step.

12. The method of claim 11 , wherein the friction coefficient is calculated as

F

=

1.5

·

p

·

λ

·

I

steady

·

1

ω

steady

.

13. The method of claim 11 , further comprising a step of correcting the calculation of the friction coefficient given as

J

=

1.5

·

p

·

λ

·

I

acc

·

t

accelerate

ω

target

by a factor of

-

F

ω

target

accelerate

⁢

∫

ω

r

⁢

ⅆ

t

.

14. A method of measuring a plurality of parameters of a Permanent Magnet Synchronous Motor (PMSM) by a motor controller to differentiate between a plurality of PMSMs, the method comprising the steps of:

performing a first stage by

applying regulated DC motor currents at a commanded fixed rotor angle, parking the PMSM at standstill, whereby a quadrature voltage applied across the PMSM windings is proportional to a stator resistance and to an applied park current, and

selecting an initial set of controller parameters;

performing a second stage by

applying the quadrature voltage equal to zero,

accelerating the PMSM with a constant torque up to a preset target speed in accordance with a time constant corresponding to an exponential decay of a quadrature current, and

regulating a stator current at 0 value using a total acceleration time to the preset target speed, which the stator current is at 0 value when regulated DC motor currents are at zero value; and

performing a third stage by calculating

an electrical constant of the PMSM based on the values of the applied quadrature voltage and a free motor speed immediately after applying the 0 stator current,

a load inertia based on the previously measured total acceleration time, and

a set of parameters for the controller based on the determined motor parameters.

15. A controller for performing a Pulse Width Modulation (PWM) drive of a Permanent Magnet Synchronous Motor (PMSM) and for determining PMSM parameters to differentiate between a plurality of PMSMs, the controller comprising:

an outer speed loop for setting the desired speed of the PMSM;

a first inner current loop for regulating a quadrature component i q of the motor current;

a second inner current loop for regulating a direct component i d of the motor current, the motor current i d being the equivalent motor stator current projected onto a d-axis aligned with a rotor field, and the motor current i q being the equivalent motor stator current projected on a q-axis, which is perpendicular to the rotor field; and

a speed observer circuit having an input of voltages v α and v β and currents i α and i β and outputting an angular position of a rotor θ r and an observed rotor speed ω obs ,

wherein each of the loops includes a compensator, whose parameters can be adjusted based on measured motor parameters, further comprising a processor for measuring the motor parameters that implements the steps of

determining a plurality of parameters of a Permanent Magnet Synchronous Motor (PMSM) by a motor controller to differentiate between a plurality of PMSMs, the method comprising the steps of:

applying regulated DC motor currents at a commanded fixed rotor angle;

measuring a quadrature voltage v q after an initial transient has elapsed, the quadrature voltage being applied across the PMSM windings;

parking the PMSM at standstill, whereby the quadrature voltage is proportional to a stator resistance and to the applied park current I park ;

selecting an initial set of controller parameters;

applying the quadrature voltage equal to zero;

measuring a time constant T s corresponding to an exponential decay of a quadrature current i q ;

accelerating the PMSM with a constant torque up to a preset target speed;

measuring a total acceleration time t accelerate until the preset target speed ω target is reached;

regulating a stator current at 0 value, whereby the stator current is at 0 value when currents i q(ref) and i d(ref) are both at zero value;

measuring the quadrature voltage and a freewheeling motor speed ω freewheel immediately after applying the 0 stator current;

calculating an electrical constant K E of the PMSM based on the measured values of the applied quadrature voltage and the freewheeling motor speed;

calculating a load inertia J based on the previously measured total acceleration time; and

calculating a set of parameters for the controller based on the determined motor parameters.

16. The controller of claim 15 , wherein the controller operates on the Field Oriented Control (FOC) principle to regulate a speed of the PMSM.

17. The controller of claim 15 , wherein the inner current loops determine quadrature component i q of the motor current and the direct component i d of the motor current by

(a) receiving gate pulse signals from each switch and the DC bus voltage supply current,

(b) determining current values i a , i b and i c of PMSM windings,

(c) performing a Clarke transformation

[

i

α

i

β

]

=

[

1

0

0

0

1

3

-

1

3

]

⁡

[

i

A

i

B

i

C

]

 on the determined current values to determine current values i α and i β ,

(d) performing a Park transformation

[

i

d

i

q

]

=

[

cos

⁡

(

θ

r

)

sin

⁡

(

θ

r

)

-

sin

⁡

(

θ

r

)

cos

⁡

(

θ

r

)

]

⁡

[

i

α

i

β

]

 on the current values i α and i β , to determine current values i q and i d ,

(e) converting the current values i q and i d into corresponding voltage values v q and v d ,

(f) performing a reverse Park transformation

[

v

α

v

β

]

=

[

cos

⁡

(

θ

r

)

-

sin

⁡

(

θ

r

)

sin

⁡

(

θ

r

)

cos

⁡

(

θ

r

)

]

⁡

[

v

d

v

q

]

 on the voltage values v q and v d , to determine voltage values v α and v β , and

(g) performing the reverse Clarke transformation

[

v

A

v

B

v

C

]

=

[

1

0

-

0.5

3

2

-

0.5

-

3

2

]

⁡

[

v

α

v

β

]

 on the voltage values v α and v β , to determine voltages V a , V b , and V c required to drive the PMSM at the desired speed sets by the outer control loop.