Predictive Control of Power Converters and Electrical Drives

11.3 Weighting Factors Adjustment

The weighting factor tuning procedure will vary depending on which types of terms are present in the cost function, as classified in the previous section.

11.3.1 For Cost Functions with Secondary Terms

This is the easiest case for weighting factor adjustment, since the system can be first controlled using only the primary control objective or term. This can be very simply achieved by neglecting the secondary terms forcing the weighting factor to zero (λ = 0). Hence the first step of the procedure is to convert the cost function with secondary terms into a cost function without weighting factors. This will set the starting point for the measurement of the behavior of the primary variable.

The second step is to establish measurements or figures of merit that will be used to evaluate the performance achieved by the weighting factor. For all the examples given in Table 11.2 a straightforward quantity should be one related to the primary variable, which is current error. Several error measures for current can be defined, such as the root mean square (RMS) value of the error at steady state, or the total harmonic distortion (THD). At least one additional measure is necessary to establish the trade-off with the secondary term. For the three cost functions of Table 11.2 the corresponding measures that can be selected are: the device average switching frequency f_sw, the RMS common-mode voltage, and the steady state input reactive power.

Once the measures ...