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Title:	Dynamic voltage restorer for voltage sag mitigation using two-vector control
Authors:	Ali Omar Ahmed Al-Mathnani (P33979)
Supervisor:	Mohd Alauddin Mohd Ali, Prof. Dr.
Keywords:	Electric power system stability Electric power systems -- Control Energy storage Electric controllers Power resources Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia
Issue Date:	20-Sep-2012
Description:	Voltage sag is one of the very severe power quality (PQ) problems encountered by the customers and utilities because of its adverse financial impact. In recent years, custom power devices have been developed to improve the quality of power. Dynamic voltage restorer (DVR) is one of the devices that compensate PQ problems of the sensitive loads against sags, swells, outage voltage sag, voltage flicker and harmonic interference. Therefore, the objective of the research is to develop a more efficient DVR for power quality improvement. Firstly, the developed DVR consists of two 6-switch inverters connected in shunt and connected to the DC-link. The inverters are also connected to a filter circuit to improve the DVR efficiency and eliminate the high frequency inverter switching harmonics. The second unique feature of the proposed DVR is the control system. Basically, it employs two fast continuous vector and proportional controllers to track the injected voltage and compensate for the voltage loop across the LC-filter. A photovoltaic (PV) source is included to keep the DC voltage level constant at the energy storage capacitor during deep voltage sag using energy balance concept. In the DVR controller, new in-phase compensation is used to improve the efficiency of the DVR. It also uses symmetrical components to simplify analysis of unbalanced three phase power system and feedback control loop to achieve stable characteristic for control of 12 switch of DVR. Moreover, dq0 model and phase locked loop with a proportional integral controller is incorporated in order to obtain the phase and frequency information of the grid voltage and tracking the sag time. This novel design and control can compensate the voltage sags, over voltage, outage voltage and harmonics. It also improves the transient, steady-state responses, dynamic response, and active power of the system. The design increases the DVR efficiency and eliminates the zero sequence. The new work is compared to the 6-switch, 6-pulse inverter connected to the 3-step down transformer, 12-switch, 12-pulse inverter connected to the 6-step down transformer, and 24-switch, 24-pulse inverter connected to the 12-step down transformer. Fuzzy logic controller is modeled by MATLAB/Simulink to regulate the voltage compensation. Simulation was carried out using the PSCAD/EMTDC electromagnetic transient program to validate the capabilities of the 11/0.4 kV DVR in performing voltage sag compensation. The test results show that the new design and controller can recover load voltage from 0.001 to 0.99 p.u. within 1 ms response for sudden sags. The measured total harmonic distortion was 0.02%, which is much lower than the IEEE standard of 5%. The results also show that there is no transient voltage during recovery moment and the amount of active power is optimized to 0.1 kW for power factor 99%. The test result shows that the continuous two vector control for the 12-switch and 6-pulse inverter with PV source is better than that of the conventional controller. The new controller can detect and compensate the system within fast response time under various operating conditions including with non-linear loads.,Certification of Master's / Doctoral Thesis" is not available
Pages:	122
Call Number:	TK1007.M347 2012 3 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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