Publication Date: 2005-Dec-02
The IP.com Prior Art Database
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
ωsRef and by using
an integrator, the transformation angle Transf
θ for the current can be obtained. The reference angle sRef
equals with transformation angle Transf
θ but leading with 2
i i i
Active Power Computation
isx Reference Computation
Voltage Computation and Limiting
Figure 1.1. The control scheme chosen
The phase currents are transformed to voltage vector reference frame (x-y). The active current
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
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
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).
⋅( ) ( )
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).
It has to be mentioned here that the reference voltage sRef
U is coming from the previous sample.
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
done after the algorithm presented in the figure below (Figure 1.1).