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VOLTAGE ORIENTED CONTROL – SIMULATION

the dynamics are speeded up from L/R to L/(R+Ra). Active damping is also used when R and L value are not estimated precisely. This active damping is not implemented in this thesis.

REFERENCE VOLTAGE SATURATION

We have treated the current control loop as an ideal and linear system. In practice, this is not correct because the reference voltage is limited to an upper and lower value. For large step of the d current, the controller might demand a large voltage vector (outside the switching hexagon that defines the switching possibilities). This exceeds the realizable voltage modulus of a PWM converter ([4] [14] ).

The saturation is applied on the modulus of the complex value of the reference voltage

, that is,

.

The saturation value depends on the DC link voltage. The maximum value of reference voltage is Vmax = Vdc/2. The simplest method to create the saturation [Vdc/2 ; Vdc/2] in Simulink is to normalized the modulus of reference voltage by Vdc/2 before the saturation block. Then, the saturation block is the set to [1 ; 1] (it means a saturation between Vdc/2 and –Vdc/2). Finally, we multiply back the output

of the saturation block by Vdc/2.

Figure 3.11 : Reference voltage saturation – Simulink implementation

INTEGRATOR ANTI WINDUP

Principle

As we said in the previous section, for large step demand a too large voltage vector (outside the switching

of the d current, the controller might hexagon). This exceeds the realizable

voltage modulus of a PWM converter ([14] ).

We call

the reference voltage. The PI controller is :

Once

become limited (

), the integrator part of the PI controller can introduce a phenomenon

called integrator windup. An integrator windup generally manifest itself by an overshoot (to the step

response). In order to avoid windup, the integrator part

should not be updated with too large error

. We should feed the integrator with another error , so that

.

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