Sudarshan Dahal

Investigation of small signal stability of a renewable energy based electricity distribution system

As the issues on market deregulation and renewable energy utilization are gaining significance, distributed generators are planned and installed in distribution systems to supply consumers directly. The distribution system is, therefore facing new challenges on its dynamic behavior with the addition of new dynamic devices. This paper investigates the small signal stability of renewable energy based distribution system. The distribution system is fed by synchronous, induction and static generators. The voltage controlled and power factor controlled operations of the synchronous generator are also considered. The results showed that wind generator dynamics are very significant in the system oscillations. The solar PV generator improves the small signal behavior of the system. The impact of penetration of renewable energy resources on a system is demonstrated through eigenvalue analyses. The eigenvalue results are corroborated with the help of time domain analysis.

Assessment and Enhancement of Small Signal Stability of a Renewable-Energy-Based Electricity Distribution System

Market deregulation and environmental concerns of the power sector have encouraged renewable energy integration in the form of distributed generation, mainly in distribution systems. With integration of different generators and controllers, distribution systems are facing different types of stability issues which were not a concern in the past. This paper examines the small signal stability performance of a renewable-energy-based distribution system. The system, which consists of static and dynamic loads, is supplied by synchronous, induction, and static generators. The existence and nature of oscillatory modes are systematically investigated. A control methodology of using existing capacitor banks to support small signal stability of a distribution system is proposed. A controllability-based index is used to identify the controllable capacitor bank. An observability index has been used to design the additional controller for damping control. The effectiveness of capacitor controller is illustrated by using both eigenvalue and time-domain analyses.

An approach to control a photovoltaic generator to damp low frequency oscillations in an emerging distribution system

Factors like diminishing fossil fuels and environmental concerns are driving the integration of locally available energy resources at a distribution level. As a result, a number of stability issues have become a concern for utilities at distribution systems. One of the important stability concerns is the small signal stability caused by electromechanical or other low frequency oscillations. The oscillations with lower values of frequency and damping may cause instabilities. In such cases, a suitable control methodology must be applied to ensure the stability of an emerging distribution system. In this paper, a methodology to control the power factor of photovoltaic generator (PV) is proposed for enhancement of system stability. The impact of PV power factor control on a low damped mode is assessed by using both eigenvalue sensitivity and time domain analysis. An appropriate signal for the proposed controller is identified by residue technique. The effectiveness of the controller is tested in IEEE 43 bus test distribution system with distributed generators. Results show that reactive power support from PV is better for damping of critical mode.

Enhancing small signal stability of an emerging distribution system by a coordinated controller

The structures of distribution systems are changing due to increasing penetration of distributed generations (DG units) as well as integration of advanced controllers and communication infrastructures. As a result, emerging distribution networks have a number of generators and controllers operating in a closer proximity. Such a proximity of dynamic devices results into modal interactions, which can deteriorate small signal stability of distribution systems. In such a case, a controller must be installed to ensure stability under different operating conditions. This paper presents a robust coordinated damping controller for distribution networks. The controller receives wide area control signal from network and sends supplementary control signals to the DG units. The advantage of the controller is that it can support small signal stability even if some DG units are out of operation. The effectiveness of the controller is tested in a 43-bus industrial distribution network.

Enhancing Damping Performance of Emerging Distribution Systems by Load Controller

Conventional distribution systems are transforming into smarter networks by accommodating renewable energy resources, communication infrastructure, and control devices. While the grids are transforming to be smart grids, issues relating to grid stability and control are emerging due to proximity and interactions among generator units and associated controllers. The existence of low damped oscillations could be harmful to power transfer capacity and generator stability. This paper presents small signal stability and control issue of emerging distribution systems. A robust control methodology for motor load current is proposed for stability enhancement. System loads are ranked based on their relative influence on small signal instability. The proposed methodology controls current of the selected motor load during system disturbances to improve overall small signal stability of the distribution system. The proposed methodology has been successfully implemented on a 16-bus distribution network.

Design of a robust controller for doubly fed induction generator to damp low frequency oscillations in emerging distribution systems

Abstract Emerging distribution systems accommodate a large number of dynamic devices such as distributed energy resources, their controllers and other smart devices. Complex interactions among these dynamic devices may result in a number of instability issues. One of the important instability concerns is the small signal instability caused by oscillatory modes with lower values of frequency and damping ratios. In such cases, a suitable control methodology must be applied to ensure the stability of an emerging distribution system. In this paper, a robust control methodology for a doubly fed induction generator (DFIG) is proposed for the enhancement of system stability. The impact of active and reactive power of the DFIG on a low damped mode is assessed. The effectiveness of the controller is tested in an IEEE 43 bus distribution system with distributed generation units. Results show that the proposed robust controller for the DFIG can support damping of critical modes.