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Master of Science Thesis in Electric Power Engineering - page 48 / 114

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VOLTAGE ORIENTED CONTROL – SIMULATION

3.5.6 Controller improvements FILTERS

Figure 3.26 : Decoupled controller with filter

Êdq represent the line voltage (grid, or

) and Vdq the converter voltage. We received a

piece of advice regarding the feed forward term Êdq in the controller Figure 3.26. This feed forward could turn the system unstable if some high frequency oscillations appear on Êdq. To remove any high frequency oscillations, we decided to add a filter for each feed forward. We chose a first order discrete filter with a bandwidth a decade lower than the current control

bandwidth :

10

(3.37)

If the grid is stiff enough, the bandwidth of the filter can be equal to the current controller bandwidth.

INTEGRATORS

We can see in the previous scheme that two integrator are in cascade, an integrator in the voltage controller and one in the current controller. The current controller integrator can probably be removed (then, the anti windup also).

LOAD COMPENSATION

In the papers [11] , a load compensation has been proposed to minimized the influence of rapid changes of the converter load. The feed forward information (see schematic on Figure 3.27) about the actual converter load has also contributed to improve the transient response of the DC link voltage. This compensation is not implemented in this report.

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