Download A nonlinear discrete-time model along with an optimal stabilizing

Modeling and Nonlinear Optimal Control of Weak/Islanded
Grids Using FACTS Device in a Game Theoretic Approach
Abstract:
A nonlinear discrete-time model along with an optimal stabilizing controller using a unified
power quality conditioner (UPQC) is proposed for weak/islanded grids in this paper. An
advanced stabilizing controller greatly benefits islanded medium-sized grid and microgrid due to
their relatively small stored energy levels, which adversely affect their stability, as opposed to
larger grids. In addition, a discrete-time grid model and controller are preferred for digital
implementation. Here, the discrete-time Hamilton-Jacobi-Isaacs optimal control method is
employed to design an optimal grid stabilizer. While UPQC is conventionally utilized for power
quality improvement in distribution systems in the presence of renewable energy, here, the
stabilizing control is added and applied to the UPQC series voltage in order to mitigate the grid's
oscillations besides UPQC's power conditioning tasks. Consequently, the UPQC can be
employed to stabilize a grid-tie inverter (GTI) or a synchronous generator (SG) with minimum
control effort. When controlling the GTI associated with renewable energy sources, a reduced
UPQC structure is proposed that only employs the series compensator. Next, a successive
approximation method along with neural networks is utilized to approximate a cost function of
the grid dynamical states, the UPQC control parameters, and disturbance, in a two-player zerosum game with the players being UPQC control and grid disturbances. Subsequently, the cost
function is used to obtain the nonlinear optimal controller that is applied to the UPQC.
Simulation results show effective damping behavior of the proposed nonlinear controller in
controlling both GTI and SG in weak and islanded grids.