A New Control Scheme and System Configuration for Dynamic Voltage Restorer (DVR)

  • Abdul Mannan Rauf

Student thesis: Master's Thesis

Abstract

Proliferation of renewable energy based generation at transmission and distribution level has imposed new challenges to the modern power system. Likewise, the upsurge in the integration of sensitive industrial loads and critical equipment to the grid has put stringent limits on gird voltage variation rendering it as a major power quality concern. The disturbances in grid voltage may occur due to the system faults, load rejection, switching operation, and most recently by the intermittent nature of the renewable energy systems. The well-known disturbances include sags, swells, flicker notching, transients/phase jumps etc. and are not always possible to avoid because of the finite clearing time of protection relays resulting in industrial process disruption and substantial production loss. To protect loads from these disturbances, flexible AC transmission systems (FACTS) devices have gained widespread acceptance among which, the dynamic voltage restorer (DVR) has emerged as the most effective and comprehensive solution The vital aspect for the success of the DVR lies in its control. Since the last decade, numerous control strategies have been reported in literature. The emphasis is on either reducing the VA rating of DVR using inphase injection or minimizing the dc storage capacity by using reactive compensation/energy optimized injection. However the tradeoff which comes in the form of transient distortion/ phase jump in load voltage is mostly overlooked. The first part of this thesis aims to provide detailed understanding of DVR modeling and existing control methods. It then goes on to explain the proposed compensation strategy which mitigates voltage sag as well as phase jump while achieving the minimum active power operation. In the proposed method, the DVR restores the load voltage magnitude and phase to presag values and then through a controlled transition settles into minimum active power mode. A set of analytical comparisons demonstrate that the proposed method significantly increases the sag support time compared with current transient compensation methods. This extended compensation time will lead to considerable reduction in dc link capacitor size for the new installation and thus, reducing the cost and size of the DVR system. The performance of the proposed method is evaluated using simulation studies and verified experimentally on a scaled lab prototype. Furthermore, to achieve a better dynamic performance of DVR, a new configuration is presented in the final part of this thesis, where photovoltaic (PV) system is integrated with DVR using a six port converter. The proposed configuration exhibits all the functionalities of existing PV and DVR system (operating through independent converters) each, as well as overcomes the DVR limitation for compensating deep voltage sags due to dc link loss. It allows DVR to utilize active power of PV plant and therefore improves the system robustness against various grid faults. The performance of the proposed structure is validated through extensive simulations in MATLAB/Simulink
Date of Award2014
Original languageAmerican English
SupervisorVinod Khadkikar (Supervisor)

Keywords

  • Dynamic Voltage Restorer (DVR); Voltage Sag; photovoltaic (PV) system.

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