This paper presents a modular grid-connected single-phase system based on series-connected current-source module integrated converters (MICs). The modular configuration improves the reliability, redundancy and scalability of photovoltaic (PV) distributed generators. In this system, each PV panel is connected to a dc/ac inverter to permit individual Maximum Power Point Tracking (MPPT) operation for each panel. Thus, the harvested power from the PV system will increase significantly. There are four different inverter topologies suitable to be used as MICs with different performances in terms of filtering elements size, power losses, efficiency, output voltage range, and high frequency transformers' size. For the MPPT control, the oscillating even order harmonic components should be eliminated from the inverter's input side otherwise the maximum power cannot be extracted. The proposed modulation scheme in this paper will ease the control of inverter's input and output sides. Therefore, the 2 nd order harmonic in the input current can be eliminated without adding new active semiconductor switches. A repetitive controller coupled with proportional-resonant controllers are employed to achieve accurate tracking for grid side as well as input side currents. Comparisons and performance evaluations for the proposed MICs are presented and validated with 1 kVA prototype controlled by TMS320F29335 DSP.
The use of photovoltaic (PV) systems as the energy source of electrical distributed generators (DG) is gaining popularity, due to the progress of power electronics devices and technologies. Large-scale solar PV power plants are becoming the preferable solution to meet the fast growth of electrical energy demand, as they can be installed in less than one year, as compared to around four years in the case of conventional power plants. Modular multilevel inverters (MMIs) are the best solution to connect these large-scale PV plants to the medium-voltage (MV) grid, due to their numerous merits, such as providing better power quality, having higher efficiency, providing better reliability, and their scalability. However, MMIs are still progressing and need some improvement before they can be implemented safely in the industrial, medium, and high voltage networks. The main purpose of this paper is to review the present MMIs topologies when used in PV applications. The review aims to present a comprehensive study of the various recent submodule circuits associated with MMI topologies. Maximum power point tracking (MPPT) control schemes for PV inverters will be explored extensively. Then, the different control strategies of PV MMIs will be presented and compared to give a holistic overview of the submodules balancing techniques, ranges, and capabilities under balanced and unbalanced grid conditions. In addition, the paper will discuss the future of PV MMIs systems in electricity networks.
The paper presents a new four-quadrant converter based on dual-winding isolated Cuk converters. The proposed converter can operate as a DC/DC converter, DC/AC inverter or AC/DC rectifier. The new converter offers important merits such as losses reduction, voltage boosting, flexible output voltage range, passive element reduction and galvanic isolation with small-size highfrequency transformers. If the proposed converter output is applied to a DC motor, providing the possibility of motoring, braking and regenerative braking if required. In addition, the converter offers the possibility to generate AC voltages and currents if it is employed in renewable energy systems as a DC/AC inverter. The paper presents the description of the converter with the associated mathematical analysis. Simulation results are obtained using MATLAB/SIMULINK software while experimental results are obtained using a scaled down prototype, controlled by TMS320F28335DSP.
A new modular dc/ac inverter based on a dual-winding isolated SEPIC/Cuk converter for medium and high power Photovoltaic (PV) applications is introduced. In this system, several current-source submodules (SMs) are connected in series to allow for additional voltage boosting. Each SM is designed as a combination of SEPIC/CUK converter to offer a flexible output range and continuous currents with small ripple at input and output sides. Furthermore, the SMs structure can generate different output voltage polarities. The main purpose of employing small-size highfrequency transformers are to (1) provide galvanic isolation, (2) eliminate PV grounding problems, (3) achieve minimum electromagnetic interference (EMI). The paper presents a description of the proposed topology and investigate its reliability performance in a PV grid-tied system using MATLAB simulations. An experimental prototype has been used and controlled by TMS32028335 DSP, as a proof of concept.
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