This paper provides an automated design to provide robust PIDs with fixed control gains, suitable to be applied in power converters whose parameters belong to real intervals. Differently from conventional PIDs which use only a nominal model to obtain the fixed control gains and, a posteriori, verify robustness, the proposed approach ensures, a priori (i.e. during the design stage), robust performance for a set of plant parameters. To illustratethe proposed procedure, two conventional PID controllers are given, to achieve phase margin and crossover frequency for a nominal model of a buck converter. An objective function based on frequency domain specifications is proposed. A particle swarm optimization algorithm is then used to find PIDs, in a large search space that include stable and unstable controllers, allowing to optimize this function for all cases of combinations of plant parameters. A case study for the buck converter illustrates the improvements of performance with the proposed method when compared to the conventional PID controllers. Additionally, the design is used in a more challenging application, for a buck-boost converter suitable for small satellites application, becoming a simple alternative for benchmarks for robust control of power converters.

This paper provides a new design procedure for robust current controllers applied to LCL-filtered grid-tied inverters suitable for the integration of renewable energy sources. The design takes into account the digital implementation delay, multiple resonant controllers and operation under uncertain grid impedance. The procedure is based on the optimization of an objective function that allows to get a good trade-off between the settling of transient responses and rejection of disturbances. A particle swarm algorithm is used to find the optimal control gains and, differently from other works, here the robust stability of the closed-loop system under uncertain parameters is theoretically certified by means of linear matrix inequalities. Experimental results are shown, confirming that the closed-loop system with gains obtained by the proposed procedure presents a good tradeoff between robustness and performance, with suitable transients and grid currents with low harmonic content, complying with requirements from IEEE 1547 Standard, becoming a useful robust control design alternative for power converters in the distributed generation scenario.

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