Background: In conventional radiation therapy, regarding normal tissue tolerance, the treatment of bulk tumors is one of the remaining challenges. grid Radiation Therapy (GRT) is a technique to deliver high doses, approximately 15–20 Gy per fraction, to several small volumes located in a large radiation field. This can be performed using a grid block. The current work has concentrated on the dosimetric characteristics of a designed mega-voltage grid, used for a unique treatment modality.Materials and Methods: All measurements performed using a Neptune linear accelerator (9 MV photon beam). A square 16×16 array grid block was designed and fabricated. Several dosimetric characteristics including: depth dose, Valley To Peak (VTP) ratio, and grid out-put factor were evaluated using a calibrated diode dosimeter for a range of radiation fields.Results: The percent depth dose curves, measured in the presence of grid block, lie within those measured for the corresponding open field and a narrow beam. At the Dmax, the VTP ratio was found to be within 17% - 28%, while these ranges between 23% - 35% at a depth of 10 cm. The grid out -put factor found to be 0.78 and it slightly decreases with increasing of radiation field size.Conclusion: The VTP ratio found to be dependent strongly on the grid design and manufacturing properties. However, other parameters such as radiation field size and the depth of measurement should also be addressed as important factors. The measured dosimetric characteristics of grid block indicate that the mega-voltage grid therapy can be applied as a possible clinical modality for palliative cases.

One of the critical components for the efficient operation of single-phase grid-connected converters is the synchronization unit. This paper presents a fast and adaptive phase-locked loop (PLL) structure that ameliorates the dynamic response of the estimated frequency and amplitude for grid-connected single-phase power systems. The second-order generalized integrator (SOGI) with a novel frequency-locked loop (FLL) is utilized which contains a DC offset rejection loop. The proposed method not only eliminates the transient response of the estimated frequency which is produced by FLL in grid voltage phase angle jumps, but also improves the PLL dynamic characteristics. The whole system has been simulated in MATLAB Simulink environment where a very small settling time for the estimated frequency of the FLL has been achieved. Therefore, it will improve the whole dynamic parameters of the system. Based on the simulation results, the settling time for the estimated frequency and amplitude are 22 ms and 10 ms, respectively.

In this paper, two control strategies are proposed for distributed generation inverter (DGI) to control 1) active power exchange with the grid, 2) load voltage and 3) grid current. The main goal in these strategies is supplying local load with a standard sinusoidal voltage in the presence of grid voltage distortions and load current nonlinearity. In conventional DGIs, the load is directly and without intermediate impedance connected to the grid; thus, the possibility of load feeding with appropriate voltage quality is hindered in the grid connected mode. In order to overcome this deficiency, DGI with an LC-L filter topology and two control strategies are presented in this paper to supply the local load with standard voltage and to exchang power with the grid, simultaneously. In the first control strategy, the local load is supplied with pure sinusoidal voltage and grid current quality is not important. In the second control strategy, load voltage waveform and grid current waveform are controlled by adding appropriate harmonics to load voltage. For the implementation of the mentioned control strategies, a cascade power-voltage-current control structure has been proposed. A new controller has been introduced in the stationary reference frame for the voltage loop which gives the opportunity for compensation and tracking of harmonics without the need for complex and vast calculations. Test results under nonlinear load and non-ideal grid conditions validate that the proposed method can supply the local load with a standard voltage, inject power to the grid, and also control the grid current.

This research presents a comprehensive analysis of the performance of direct power control (DPC) for doubly-fed induction generator (DFIG) under both balanced and unbalanced network voltages. voltage unbalance in three-phase systems results in the presence of positive and negative sequences in both voltages and currents. This unbalance leads to many issues, including active power ripple, reactive power ripple, and an increase in the Total Harmonic Distortion (THD) of the stator current. Therefore, it is crucial to have efficient control of the system to reduce power fluctuations. This research presents two solutions that aim to mitigate the fluctuations in both active and reactive power. The first strategy employs PI regulators within the controller system. A high selectivity filter (HSF) is employed to separate the fundamental component of stator phase currents from the harmonic components. The second option utilizes DPC (Direct Power Control) based on stator flux. The suggested method computes the active and reactive powers that correspond to positive sequence variables. Since grid unbalance has a smaller impact on stator flux compared to stator voltage, it can be demonstrated that the second suggested controller exhibits superior performance to the conventional DPC controller in unbalanced situations. To evaluate the effectiveness of the suggested techniques, a simulation is conducted on a 2MW Doubly-Fed Induction Generator (DFIG) system using the MATLAB/Simulink environment. The results demonstrate that both of the suggested DPC control approaches outperform the conventional DPC controller in terms of control system performance, even under unbalanced situations. Furthermore, these improvements are achieved without significantly increasing the complexity of the control system.

The voltage feedforward procedures at the point of common coupling (PCC) are utilized to remove current harmonics caused by grid voltage distortion in the grid-connected inverters. However, due to the time delay effect at the weak grid, the voltage feedforward at the point of common coupling can lead to instability of the grid-connected inverter. In this paper, an improved voltage feedforward procedure is presented to interconnect a photovoltaic power conditioning system to the weak grid. The stability of this system is investigated by impedance-based stability criterion in the presence of the voltage feedforward. Based on this analysis, it is suggested that the feedforward signal should be taken from the grid voltage instead of the PCC voltage. A method is introduced to extract the grid voltage from the measured PCC voltage to solve the challenge of direct detection of the grid voltage. To investigate the effectiveness of the proposed method, the photovoltaic power conditioning system based on the L filter connected to a single-phase weak grid has been simulated in Simulink MATLAB. The simulation results reveal the proper and better performance of the proposed grid voltage feedforward in attenuating the harmonics of the injected grid current, and the photovoltaic power conditioning system maintains its suitable stability in the weak grid condition.