Date of Award


Degree Type


Degree Name

Master of Engineering Science


Electrical and Computer Engineering


Prof. Amirnaser Yazdani


In recent years, there has been significant interest in utilization of PhotoVoltaic (PV) solar systems of single- and double-digit MW power ratings, at sub-transmission and distribution voltage levels of the power system, under the umbrella of Distributed Generation (DG). Despite this interest, however, inadequate investigation has been dedicated to the connection of PV systems to distribution networks, and there is little experience regarding the operation of such PV systems. The study reported in this thesis attempts to address this gap. This thesis proposes a control strategy and provides stability analysis for a typical singlestage, three-phase, PV system that is connected to a (residential/commercial) distribution network. The control is based on an inner current-control loop and an outer DC-link voltage regulator. The current-control strategy decouples the dynamics of the PV system from those of the network and the loads. The DC-link voltage control scheme enables the control and maximization of the output real power of the PV system. Further, a feed-forward control strategy is employed for the DC-link voltage regulation scheme, to enhance the stability of the PV system. The feed-forward compensation scheme makes the PV system dynamics independent of the nonlinear characteristic of the PV panels. This, in turn, permits the design and optimization of the PV system controllers for a wide range of operating conditions. In this thesis, a mathematical model and a control design methodology are presented for the PV system, and it is shown that, under proposed control, the PV system fulfills the operational requirements for a grid-connected PV system. The effectiveness of the proposed control strategy and the most important transients of the PV system are evaluated through simulation studies conducted on a detailed switched model of the PV system, in the PSCAD∕EMTDC software environment. Based on the developed mathematical model, a modal/sensitivity analysis is conducted in this thesis on a linearized model of the overall system, i.e. the PV system, the distribution network, and the local loads, to characterize the dynamic properties, to evaluate the robustness of the controllers, and to identify the nature of interactions between the PV system and the network/loads. The modal analysis confirms that, under the proposed control strategy, dynamics of the PV system are decoupled from those of the distribution network/loads. This, alternatively, means that, if its controllers are designed based on the proposed structure and methodology, the PV system iii does not destabilize the distribution network. It is also shown that the PV system dynamics are not influenced by those of the network. Thus, the PV system maintains its stability and dynamic properties despite major variations in the line length, line X/R ratio, load type, and load distance from the PV system.



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