The grid feeding and grid forming inverters are important candidates in grid connected and islanded modes (IMs) of microgrid system, respectively. The grid feeding inverter supplies the preset power during grid-connected mode and the grid forming inverter generates a reference voltage for other distributed generation (DG) interfacing inverters in IM. In such scenario, the proper control of these inverters is an utmost importance. Generally, a nested loop control strategy uses a conventional PI controller for the inner and outer loops of grid feeding and grid forming inverter, but it gives deteriorative performance under parameter uncertainty condition. This study proposes a robust nested loop control scheme with the mixed H ∞ /H 2 optimal controller in the outer voltage control loop and the robust linear quadratic regulator (LQR) state feedback controller in the inner current control loop for the smooth operation of the system in both modes. The simulation and experimental results of the DG unit with proposed control scheme demonstrate good stability and performance robustness under the parameter uncertainty. Also, superior transient and steady-state performance are confirmed over the conventional controller.

No abstract

No abstract

No abstract

No abstract

No abstract

This paper presents an output and state feedback robust LQR (OSRLQR ) optimal controller for the control of active (P) and reactive power (Q) in grid-connected mode, and voltage (V) and active power in islanded mode of photovoltaic (PV) distributed generation (DG) system. The OSRLQR scheme is comprising of an output and state feedback controllers, which are designed based on LMI-LQR optimization approach. The DG inverter along with proposed controller is configured to work as a current source in grid-connected mode and a voltage source in island mode using P-Q and P-V control scheme respectively. A seamless transition between the grid connected and island modes under the presence of the proposed controller is achieved using a passive island detection and synchronization algorithm along with load shedding. The entire control scheme of the DG system is modelled and analyzed using MATLAB/SIMULINK/Robust Tool-Box, and the practical feasibility of the proposed control scheme is verified using dSPACE. A superior trade-off robustness among the stability and performance is the final outcome of the DG system with proposed control scheme. Performance of the proposed control scheme is compared with conventional PI controller and the comparative results indicate the superior performance of proposed control scheme over the conventional control scheme.

No abstract