Power system stabilizer for power sharing control of parallel inverters in a grid-connected micro-grid system.

摘要

This work considers the power sharing stability of a grid connected Micro-grid (MG) system with multiple Distributed Generation (DG) units via Power System Stabilizer (PSS). One of the objectives of this work is to rectify the MG system stability condition by implementing a controller that shifts the system unstable modes to the stable region of the complex s-plane. The controller will be constructed in PSS structure where the inverter output voltage angular frequency variations is used as an input to the PSS. The PSS will be designed in five generic structures which are: Proportional, Proportional -- Integral, Lead, Lag and Lead -- lag. The PSS should be able to stabilize the system and various DG penetration levels. The inverter output active are reactive power response should be characterized by fast transient response, minimal overshoot and zero steady state error. Small signal model was used to model the system by linearzing system's differential equations. The overall MG system matrix was developed and the PSS was incorporated in the system matrix in order to select the PSS parameters to stabilize the system. Particle Swarm Optimization (PSO) was used to optimally tune the controller parameters. The optimal controller's parameters where found by minimizing an objective function that moved the unstable eigenvalues to the left-hand side of the complex s-plane. The PSO based PSS is designed for low and medium loading of the MG. The system performance was tested by varying the frequency set---point and the output active power was monitored. The results proved the effectiveness of the PSO tuned PSS in stabilizing the power system for the selected operating points. The Proportional and Lead controllers produced the best results that matched the design objectives. It was recommended to avoid direct connection of DG units to load buses in case the DG rating is lower than the load rating and that the problem is of lead type. So other control schemes to be applied in future should possess lead property.