Design and experimental validation of robust PID control for a power converter in a DC microgrid application

In a DC microgrid, power electronic DC-DC converters are interfaced with DC loads that pose a stringent requirement of maintaining constant DC output voltage across the load terminals. In particular, the problem of controlling the load voltage of nonminimum phase (NMP) DC-DC boost converter with the measured load voltage under voltage mode control (VMC) is addressed. This control problem is challenging due to NMP dynamics and restricts the achievable bandwidth in the closed-loop operation. To improve the closed-loop performance of NMP boost-type converter against the disturbances (external) and uncertainty in DC microgrid environment, the Quantitative feedback theory (QFT) is used to synthesize a robust PID controller systematically. The merits of the proposed robust PID design procedure using QFT are as follows: (i) it does not require any tuning of the PID values unlike in the conventional PID design which heavily depends on the ad-hoc tuning, (ii) the dynamics of the disturbance (load current and input voltage variations) are accounted in the synthesis stage that further improves the disturbance effect minimization on the load voltage response, and (iii) the simple, straight forward design of the right half plane zero of boost-type DC-DC converter with the bandwidth limitations. The proposed design is illustrated extensively using the simulation with the external disturbances and demonstrated its advantages over a conventional PID. Finally, under various regulatory scenarios, experiments are performed to validate the simulation of the proposed PID design without retuning the controller parameters. The superior dynamic performance of the proposed PID is delineated in experimental results and provides more robustness in different scenarios as compared to the conventional PID.