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ABSTRACTThis article proposes an enhanced non-isolated high-gain DC-DC converter for interfacing renewable energy sources (RESs). This converter utilizes active switched-inductor (ASL) and switched-capacitor (SC) networks in which the ASL network increases the voltage gain. Furthermore, using the SC network as a multiplier cell helps to reach a high voltage conversion ratio with a proper duty cycle. The main advantages of the proposed converter are the high voltage gain, continuous input current, and low voltage stress on the semiconductor switch and the passive component. Since the voltage stress of the semiconductor element is low, a low ON-state resistance switch is used, which leads to reduced conduction losses. Comprehensive analysis of the steady-state operation in continuous conduction mode (CCM), inductor and capacitor design, and a comparison considering other similar topologies are presented in this article. Also, the parasitic elements are assumed to calculate the DC-Voltage gain and the efficiency of the converter. Finally, simulation results are presented in the PSIM environment to validate the feasibility of the proposed converter.

A multi-input-multi-output (MIMO) sliding mode controller has been proposed in this paper in order to control a grid-connected photovoltaic (PV) power conditioning system with an LCL filter. In the proposed control approach, nonlinear-control method is used and simultaneous control of both the AC and DC inverter sides is done. Therefore, all the state variables are controlled simultaneously. The proposed sliding mode control (SMC) method provides several advantages, including zero grid current error, easy implementation, and robustness against parameter uncertainties of the investigated system. Hence, the resonance in the inverter output resulting from the LCL filter can be eliminated using SMC with no need for active damping techniques. Applying this approach can bring about maximum power point tracking (MPPT), control of the DC side, and injection of high-quality current into the grid at the AC side of the inverter. Various simulations have been conducted in MATLAB/Simulink for the proposed system.

ABSTRACTThe 2/3-level hybrid inverters are a combination of three-level Neutral Point Clamped (NPC) inverter and conventional two-level inverter, which has the advantage of both two-level and three-level structures with fewer switches than the NPC inverter. In this paper, a new structure of 2/3 hybrid inverter based on dual-Z-‏source network is proposed. The proposed structure improves the performance of the 2/3-level inverter and increases its independent DC input voltages. The output voltage gain can be obtained by selecting the shoot-through interval appropriately in dual Z-source networks. In addition, shoot-through intervals in Z-source networks allow the inverter to run without dead time, thus increasing the output voltage quality. A modified switching method is presented for the proposed inverter, and the necessary calculations are performed. The proposed structure can be used to connect different distributed generation sources to the load separately from the grid or to the low-pressure network. The performed simulations show the accuracy of the proposed structure.

The current-controlled grid-connected inverter with LCL filter is widely utilized in the distributed power generation systems at remote places with weak grids. Oscillations in weak grids have raised the stability issue in grid-tied inverter systems, and the quality of the injected power into the grid is highly affected by the variations of grid-side inductance. In this study, a multi-loop control has been applied in the LCL-type grid-connected inverter based on capacitor current feedback control method. Computational delays in the control unit can remarkably influence the damping capability of this method. The accuracy of the modeling has been increased by considering the computational delays of the capacitor current active damping inner loop as well as the grid current outer loop. The impact of the computational delay is eliminated by the proposed approach, and the performance of the control system has been remarkably enhanced. The harmonic attenuation of the grid voltage has been improved by utilizing virtual series and parallel impedances, which leads to strong stability-robustness and high harmonic-rejection-ability even in severe variations of the grid-side inductance. Simulation results verify the credibility of the proposed approach, and the quality of the injected power is proved to be improved in a weak and harmonically distorted grid.

Design of a power conditioning system is a matter of concern in LCL-type grid-connected systems. The governing standard on power delivery has limited the total harmonic distortion (THD) of the injected power into the grid. Both stability of the system and the power quality should be considered in the control of grid-tied systems. In this study, a grid-connected system consists of photovoltaic arrays, inverter, and LCL filter has been considered for investigation. The proportional resonant (PR) controller is applied in the control system. A systematic procedure has been proposed for tuning the PR controller in converter side current control (CSCC) of the grid-tied inverter. The proposed control scheme for PV-based power conditioning system aims at suppressing contents of injected current harmonics, enhancing the power quality, and ensuring the system stability. Besides, the robustness of the proposed power conditioning system against grid voltage and grid impedance variation is investigated. Simulations are carried out in MATLAB/Simulink environment to verify the credibility of the proposed approach.