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Angle compensation

IP.com Disclosure Number: IPCOM000132140D
Publication Date: 2005-Dec-02
Document File: 3 page(s) / 119K

Publishing Venue

The IP.com Prior Art Database

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Page 1 of 3

1 Overview of the control algorithm

The control is shown in the figure below (Figure 1.1). To the reference speed f s

ω Re is added the

damping signal obtained from a DC filtering of the active power act

P . The result is

Comp

ωsRef and by using

an integrator, the transformation angle Transf

θ for the current can be obtained. The reference angle sRef

θ

equals with transformation angle Transf

θ but leading with 2

π .

isu,v,w ωsRefComp

i i i

3 isx,y

x,y

isy

Pact

Active Power Computation

isx Reference Computation

isxRef

isx PI

UsRef

isx,y

UsComp

isx

Test

Test

ωsRef

Comp

  Voltage Computation and Limiting

isx,y

UsRef

Figure 1.1. The control scheme chosen

The phase currents are transformed to voltage vector reference frame (x-y). The active current

sy

U for computing the active power act

                                                 P . Furthermore the active power and both currents are utilized in calculation of the reference reactive current sxRef

i is used together with the reference voltage sRef

i for

aligning d-axis current sd

              i in the motor. The error between the reference and real reactive current is applied to the PI controller, which will compute the necessary voltage for compensation sComp

U .

    Based on the xy currents, compensated reference speed and the compensation voltage, the Voltage Computation block is estimating the necessary reference voltage for the PWM generation.

1.1 Detailed block description

In the following the background and the functionality of each block is described.

1.1.1 Current transformation

    In order to transform the 3-phase motor currents to the xy-system used internal in the control core is used so called "Park transformation". The transformation is done in two steps: First the stationary axis current components are calculated (1.1) and afterwards the transformation angle ρ is used to rotate the currents to x-y reference frame (1.2).

i

   - =

 2 3

 2 1

i

( )

i

+

i

(1.1)

     su s

α

    sw sv

s

i

=


()

i

-

i

β

    sw sv

i

sx

α

=

i

  θ cos

( ) ( )

        Transf s

+

i

  θ sin

        Transf s

β

i

sy

=

i

  θ cos


() ()

(1.2)

-

i

  θ sin

        Transf s

β

        Transf s

α

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Page 2 of 3

1.1.2 Active Power Computation

The active power necessary for damping and reference reactive current ( sxRef

i ) computation is

calculated as shown in equation (1.3).

=sRef (1.3)

It has to be mentioned here that the reference voltage sRef

U is coming from the previous sample.

   U P

sy

i

3

act

1.1.3 isxRef Computation

The reference reactive current sxRef

i is needed for the voltage compensation in order to align the

d-axis current sd

         i in the motor. In this way is ensured that the total flux in the motor equals with the flux of the permanent magnet, so energy optimized functioning of the motor. The estimation of sxRef

i is

done after the algorithm presented in the figure below (Figure 1.1).

e

i

sy

P...