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2008 IEEE Region 10 Colloquium and the Third International Conference on Industrial and Information Systems, Kharagpur, INDIA December 8 -10, 2008. 73

DVR with Sliding Mode Control to alleviate Voltage Sags on a Distribution System for Three Phase Short Circuit Fault
G.V.Nagesh Kumar
Associate Professor, Department of EEE Vignan’s Institute of Information Technology, Visakhapatnam, A.P,INDIA gundavarapu_kumar@yahoo.com
Abstract— Control of most of the industrial loads is mainly based on semiconductor devices, which causes such loads to be more sensitive against power system disturbances. Thus, the power quality problems have gained more interest recently. Voltage sags are mainly caused due to starting of large induction motors, switching of large inductive loads, short circuitfaults in transmission and distribution systems and energizing of large transformers. Therefore, different solutions are examined to compensate these sags and to avoid production losses at sensitive loads. Dynamic Voltage Restorer (DVR) is one of the solutions to realize this goal. For a successful compensation, the DVR must be able to detect the voltage sag and control the inverter to restore thevoltage. The Sliding mode control is used for the DVR. Using Sliding mode control to the DVR, additional sag detection method is eliminated. This improves the dynamic response of the DVR and also DVR is able to compensate for any variation in source voltage. In this paper, a DVR with sliding mode control strategy is used to alleviate the voltage sags caused due to faults occurring on the parallelfeeders in a Three-phase distribution system. The DVR along with the other parts of the distribution system are simulated using MATLAB/SIMULINK. Keywords- DVR, Sliding Mode Control, Voltage Sag, Power Quality

D.Deepak Chowdary
Associate Professor, Department of EEE Vignan’s Institute of Engineering for Women, Visakhapatnam, A.P, INDIA duvvada_27@yahoo.co.in • Practice of using current limitingreactors to decrease fault level values. • Choice of transformer impedances and connections. 3. System protection practices, this is further dependent on: • Inverse-time characteristics of the over current devices (fuses and relays). • Reclosing practices (number and reclosing operations allowed). Faults on feeders adjacent to one supplying an industrial facility will result in sags on thisfacility. During such sags, sensitive loads may be taken off-line due to either control action or operation of protective devices. Such loads may be critical to a process resulting in production losses and subsequent monetary costs. DVR is a custom power device for series connection into a distribution line. When connected in series between a source and a load, the DVR can control the voltage applied tothe load by injecting a voltage of arbitrary amplitude, phase and harmonic content into the line. This enables the voltage seen by the load to be compensated to a desired magnitude in the face of upstream disturbances. Conventional solutions for controller requirements are based on classical control theory or modern control theory [8]. Widely used classical control theory based design of PID familycontrollers requires precise linear mathematical models. The PID family of controllers does not perform satisfactorily under parameter variation, non-linearity, load disturbances, etc. Modern control theory based controllers are state feed back controllers, self tuning controllers, a model reference adaptive controllers, etc [9, 10]. These controllers also need mathematical models and aretherefore sensitive to parameter variation. To alleviate the need for accurate mathematical models, Sliding mode controllers (SMC’s) were introduced [11]-[13]. The SMC does not need accurate mathematical model but requires knowledge of parameter variation range to ensure stability and satisfy reaching conditions. As the power converters are highly variable structured, sliding mode control offers...