Present renewable portfolio standards are changing power systems by replacing conventional generation with alternate energy resources such as photovoltaic (PV) systems. With the increase in penetration of PV resources, power systems are expected to experience a change in dynamic and operational characteristics. This paper studies the impact of increased penetration of PV systems on static performance as well as transient stability of a large power system, in particular the transmission system. Utility scale and residential rooftop PVs are added to the aforementioned system to replace a portion of conventional generation resources. While steady state voltages are observed under various PV penetration levels, the impact of reduced inertia on transient stability performance is also examined. The studied system is a large test system representing a portion of the Western U.S. interconnection. The simulation results obtained effectively identify both detrimental and beneficial impacts of increased PV penetration both for steady state stability and transient stability performance.

Impact of increased penetration of photovoltaic generation on power systems

Photovoltaic (PV) systems are presently allowed to inject into the grid all the power they can generate. However, in the near future, utilities are expected to impose additional regulations and restrictions on the power being injected by large centralized PV systems because of their possible adverse impacts. One of the main issues associated with large PV systems is the fluctuation of their output power. These fluctuations can negatively impact the performance of the electric networks to which these systems are connected, especially if the penetration levels of these systems are high. Moreover, the fluctuations in the power of PV systems make it difficult to predict their output, and thus, to consider them when scheduling the generating units in the network. The main objective of this paper is to investigate some methods that can be used to reduce the fluctuations in the power generated from a large customer-owned PV system, in the order of megawatts. This paper focuses on three methods: 1) the use of battery storage systems; 2) the use of dump loads; and 3) curtailment of the generated power by operating the power-conditioning unit of the PV system below the maximum power point. The emphasis in the analysis presented in this paper is on investigating the impacts of implementing these methods on the economical benefits that the PV system owner gains. To estimate the maximum revenues gained by the system owner, an linear programming optimization problem is formulated and solved. Moreover, the effect of varying different parameters of the problem is investigated through sensitivity analysis.

Investigation of Methods for Reduction of Power Fluctuations Generated From Large Grid-Connected Photovoltaic Systems

This paper proposes a control strategy for a single-stage, three-phase, photovoltaic (PV) system that is connected to a distribution network. The control is based on an inner current-control loop and an outer DC-link voltage regulator. The current-control mechanism decouples the PV system dynamics from those of the network and the loads. The DC-link voltage-control scheme enables control and maximization of the real power output. Proper feedforward actions are proposed for the current-control loop to make its dynamics independent of those of the rest of the system. Further, a feedforward compensation mechanism is proposed for the DC-link voltage-control loop, to make the PV system dynamics immune to the PV array nonlinear characteristic. This, in turn, permits the design and optimization of the PV system controllers for a wide range of operating conditions. A modal/sensitivity analysis is also conducted on a linearized model of the overall system, to characterize dynamic properties of the system, to evaluate robustness of the controllers, and to identify the nature of interactions between the PV system and the network/loads. The results of the modal analysis confirm that under the proposed control strategy, dynamics of the PV system are decoupled from those of the distribution network and, therefore, the PV system does not destabilize the distribution network. It is also shown that the PV system dynamics are not influenced by those of the network (i.e., 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).

A Control Methodology and Characterization of Dynamics for a Photovoltaic (PV) System Interfaced With a Distribution Network

In terms of the improvement of reliability and efficiency, integration of distributed generation (DG) into distribution network has gained significant interest in recent years. However, existing distribution systems were not designed considering large-scale penetration of DG. Due to the increasing penetration of DG, several technical challenges may arise which include voltage control, power quality and protection issues, etc. Therefore, additional components need to be modelled together with conventional distribution system components in order to study the impact of DG on the distribution system. The first objective of this paper is to review the required models of system components, the impacts of DG on system operation, mitigation of challenges, associated standards and regulations for the successful operation of distribution systems. A number of commercial and open source tools are available for modelling and analysis of distribution systems. An ideal computational tool should include necessary functionalities to study the impacts of increased DG penetration as well as various options to overcome possible operational problems. Based on the first objective, the second objective is to make a summary of characteristics and features that an ideal computational tool should have to study increased DG penetration. A comparison study of two commonly used computational tools is also carried out in this paper.

Large-scale integration of distributed generation into distribution networks: Study objectives, review of models and computational tools

Optimal sizing and location of SPV (solar photovoltaic) based MLDG (multiple location distributed generator) in distribution system for loss reduction, voltage profile improvement with economical benefits

The grid-connected photovoltaic (PV) power generation system is expected to be more widespread in distribution systems due to increasing fossil-fuel cost. Recent advances in PV technology and great demand has led to cost reductions. This paper presents the effects of PV system installation location on the power quality of the distribution system. A measurement setup is prepared for a PV grid-contected system. The system consists of a PV array and a grid-connected inverter. The measured data are used to investigate the effects of a PV system. A feeder line with PV system is simulated in Matlab. This study focuses on both radial and loop operated distribution system. The distribution system's power quality, in terms of voltage, active power, total losses, and power factor of the network are presented. The simulation results show that implementation of the PV grid-connected system could improve the power quality of a distribution feeder.

N. Srisaen

Papers

Effects of PV Grid-Connected System Location on a Distribution System