الفهرس 
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Abstract
This thesis introduces a PV based dynamic voltage restorer (DVR) to
protect sensitive loads against voltage sags and/or swells. A standalone PV battery system is proposed to support the DVR with the required active and reactive power via a controlled DC- link. The DVR’s transient, steady-state, and dynamic responses are essential requirements for protecting sensitive
loads against upstream voltage disturbances via the DVR’s ride-through capabilities. Another inherent problem with the DVRs is the transient
oscillation occurrence on the load voltage at the instant of entering, and /or exiting by the DVR. So, an enhanced, optimized, and less complex DVR control system structure, which is capable of improving the transient,
steady-state, and dynamic responses as well as eliminating inherent transient
oscillations is presented in this study. The control system comprises a
closed-loop feedback control signal and feedforward upstream disturbance
detection signal. Incorporating the feedforward term helps, dramatically, in improving the system response and eliminating the transient oscillations in the load voltage. The error signals are adapted using a PI controller to make the load voltage faithfully track its predefined reference waveform. The
controller is implemented in the dq synchronous rotating reference frame.
The parameters of the PI controller are selected using modern populationbased optimization called the Harris Hawks Optimization (HHO) technique. The obtained results using the HHO technique are compared with the two other optimization algorithms, namely Particle Swarm Optimization (PSO) and Whale Optimization Algorithm (WOA). The results show that the HHO
gives the best system response. The system is simulated using MATLAB/Simulink and the validation via Typhoon HIL402 real-time emulator. Both HIL402 validation and simulation results show that the proposed control scheme recovers normal operation against voltage disturbance within approximately 1.2 milliseconds without overshoot with steady-state error near zero and significantly dampens the inherent voltage oscillation that occurs at the instant of DVR entrance and/or exit. Moreover, the DVR operation in the distorted grid is also covered in this study. The main problem with the DVR operation in the case of a distorted grid is voltage detection and synchronization with the point of common coupling (PCC) fundamental components. A comparison study between three-synchronization method has been applied in the DVR control system, stationary reference frame (αβ-PLL), decoupled stationary frame PLL(Dαβ-PLL), and sliding Fourier transform SFT-PLL. The SFT-PLL is superior in all estimations. It could estimate the fundamental voltage
magnitude, phase angle, and frequency without any oscillations and very
accurate even in highly distorted conditions. The proper estimation of the fundamental component, enable to separate the harmonics signal which
adding to the compensating voltage vector and led to a decrease in the THD of the load voltage.