In a control system it is important to reach a compromise between reference following and control effort. In power converters and drives, the control effort is related to the voltage or current variations, the switching frequency, or the switching losses. Using predictive control, it is possible to consider any measure of control effort in the cost function, in order to reduce it.
In a three-phase inverter, the control effort can be represented by the change in the voltage vector applied to the load. This can be implemented as an additional term in the cost function measuring the magnitude of the difference between the previously applied voltage vector v(k − 1) and the voltage vector to be applied v(k), resulting in
where x is the controlled variable and λ is a weighting factor that allows the level of compromise to be adjusted between reference following and control effort.
As an example, the predictive current control presented in Chapter 4 is considered, together with the constraint in the variation of the voltage vectors presented in (10.8). The resulting cost function is expressed as
By using this cost function, the control effort can be reduced by increasing the value of the weighting factor λ. Results for the current control of a three-phase ...