Quasi optimum PI controller tuning rules for a grid-connected three phase AC to DC PWM rectifier

Abstract

Controller tuning is deemed to be critical when dealing with the voltage oriented control (VOC) as it ultimately defines the system performance. This paper contributes to the tuning issue associated with VOC in three key points. Firstly, an algebraic solution (i.e. PI-parameters) based on the first-order-plus-time-delay (FOPTD) approximations of the plant dynamics is developed, along with approximating relationships and methodology. Secondly, a non-linear multi-criteria optimization algorithm, with PI-controller parameters being the decision variables, is developed in order to achieve the optimum disturbance rejection. The cost function employs a weighted-sum criterion to account for two sources of disturbances: grid voltage sag/dip and load current disturbances, which affect the regulated dc voltage. Simulation results suggest a quasi-optimum system performance, in terms of minimum integral time absolute of the error (ITAE) performance index of the dc-bus voltage, using the FOPTD tuning parameters. Hence, the developed FOPTD approximations demonstrate an accurate linear approximation. Thirdly and consequently, analytic tuning rules for the PI-controllers are proposed. The proposed rules provide quasi-optimum PI-parameters by direct substitution of system parameters in the tuning formulae, rather than solving complex algebraic equations as in the FOPTD tuning approach. The obtained results are verified experimentally.