System and method for controlling a permanent magnet electric motor

1. A system for controlling a permanent magnet electric motor ( 12 ), comprising:

a motor controller ( 16 ), said motor controller ( 16 ) using phase currents of the permanent magnet electric motor ( 12 ) at a preset speed ω to generate voltage-controlling signals used to obtain changes in torque T of the permanent magnet electric motor ( 12 ); and

a power stage ( 14 ), said power stage ( 14 ) receiving the voltage-controlling signals from the motor controller ( 16 ) and feeding them back to the permanent magnet electric motor ( 12 ), wherein said motor controller ( 16 ) is a park vector rotator unit that generates continuously rotating angles.

2. The system for controlling a permanent magnet electric motor according to claim 1 , said system continuously responding to changes of the preset speed and torque of the permanent magnet electric motor ( 12 ) as well as to changes in ambient conditions.

3. A method for controlling a permanent magnet electric motor ( 12 ) comprising:

determining a current of each phase of the permanent magnet electric motor ( 12 ) at a preset speed ω;

obtaining voltage controlling signals at the preset speed ω in relation to changes in torque of the permanent magnet electric motor ( 12 ); and

feeding the voltage controlling signal back to the permanent magnet electric motor ( 12 ); computing a current torque T of the permanent magnet electric motor ( 12 );

wherein said computing a current torque T comprises rotating the currents of each phase of the permanent magnet electric motor by an angle −θ n to output two currents I d and I q , according to the following relations on a d-q axis fixed on a rotor axis of the permanent magnet electric motor ( 12 ):

I d =⅔ ×[i a ×cos(θ n )+ i b ×cos(θ n +120°)+ i c ×cos(θ n −120°)] and

I q =⅔ ×[i a ×sin(θ n )+ i b ×sin(θ n +120°)+ i c ×sin(θ n −120°)]

4. A method for controlling a permanent magnet electric motor ( 12 ) comprising:

determining a current of each phase of the permanent magnet electric motor ( 12 ) at a preset speed ω;

obtaining voltage controlling signals at the preset speed ω in relation to changes in torque of the permanent magnet electric motor ( 12 ); and

feeding the voltage controlling signal back to the permanent magnet electric motor ( 12 ), wherein said determining a current of each phase of the permanent magnet electric motor ( 12 ) comprising measuring a current of two phases thereof and calculating a current of a third phase using the relation:

∑

three

⁢

⁢

phases

⁢

i

=

0.

(

4

)

wherein said obtaining voltage controlling signals comprises:

computing a current rotating angle θ n+1;

computing two voltage outputs V q and V d ; and

rotating the voltage outputs V q and V d by the angle θ n+1 .

5. The method for controlling a permanent magnet electric motor according to claim 4 , wherein said computing a current rotating angle θ n+1 is done using a current torque T and a preset speed ω of the permanent magnet electric motor ( 12 ) with the formula θ n+1 =θ n +k 1 ×ω+k 2 ×T where k 1 and k 2 are constants.

6. The method for controlling a permanent magnet electric motor according to claim 5 , wherein said computing two voltage outputs V q and V d comprises:

computing the voltage output V q on a d-q axis fixed on a rotor axis: V q =PI(I*−I d )+k 3 ×I q where k 3 is a constant, “PI”referring to a proportional and integral operator, defined as follows: PI(x)=ax+b∫x dt where a and b are constants and integration is over time; and

computing the voltage output V d , according to the following equation on the d-q axis fixed on the rotor axis: V d =k 5 ×I d +k 4 ×I q ×ω where k 4 and k 5 are constants.

7. The method for controlling a permanent magnet electric motor according to claim 5 , wherein said obtaining voltage controlling signals comprises obtaining three voltage controlling signals V a , V b and V c according to the following equations:

V a =V d ×cos(θ n+1 )+ V q ×sin (θ n+1 ), V b =V d ×cos(θ n+1 +120°)+ V q ×sin(θ n+1 120°) and V c =V d ×cos(θ n+1 −120°) + V q ×sin(θ n+1 −120°).

8. A circuit for controlling a permanent magnet three-phases electric motor provided with a rotor and a stator, comprising:

a rotator allowing rotation of current signals of the phases of the permanent magnet electric motor ( 12 ) from a stationary frame to two decoupled current components in a rotor synchronous frame along a direct axis (I d ) and a quadrature axis (I q ) respectively;

a proportional and integral operator for deriving a voltage (V q ) along the quadrature axis and a voltage (V d ) along the direct axis;

a rotator allowing rotating the voltages V q and V d back from the rotor synchronous frame to the stationary frame to yield terminal voltages V a , V b and V c of the permanent magnet electric motor;

wherein a current rotating angle θ n+1 is computed using a current torque T and a preset speed ω of the permanent magnet electric motor with a formula as follows: θ n+1 =θ n +k 1 ×ω+k 2 ×T where k 1 and k 2 are constants.

9. A method for controlling a permanent magnet three-phases electric motor provided with a rotor and a stator, comprising:

rotating current signals of the phases of the permanent magnet electric motor ( 12 ) from a stationary frame to two decoupled current components in a rotor synchronous frame along a direct axis (I d ) and a quadrature axis (I q ) respectively;

deriving a voltage (V q ) along the quadrature axis therefrom;

deriving a voltage (V d ) along the direct axis;

rotating the voltages V q and V d back from the rotor synchronous frame to the stationary frame to yield terminal voltages V a , V b and V c of the permanent magnet electric motor;

wherein a current rotating angle θ n+1 is computed using a current torque T and a preset speed ω of the permanent magnet electric motor ( 12 ) with a formula as follows: θ n+1 =θ n +k 1 ×ω+k 2 ×T where k 1 and k 2 are constants.

10. A method for controlling a permanent magnet electric motor having three-phases each supporting a current i a , i b and i c respectively, comprising:

determining the currents i a , i b and i c ;

rotating the currents i a , i b and i c by an angle −θ n to yield currents I d and I q ;

computing a current torque of the permanent magnet electric motor ( 12 );

computing a current rotating angle θ n+1 ;

computing a voltage output V q ;

computing a voltage output V d ;

rotating the voltages V q and V d by the rotating angle θn+1 to yield three voltage controlling signals V a , V b and V c ; and

applying the voltage controlling signals V a , V b and V c to the permanent magnet electric motor;

wherein a current rotating angle θ n+1 is computed using the current torque T and a preset speed ω of the permanent magnet electric motor ( 12 ) with a formula as follows: θ n+1 =θ n +k 1 ×ω+k 2 ×T where k 1 and k 2 are constants.