Partial shading in photovoltaic (PV) arrays renders conventional maximum power point tracking (MPPT) techniques ineffective. The reduced efficiency of shaded PV arrays is a significant obstacle in the rapid growth of the solar power systems. Thus, addressing the output power mismatch and partial shading effects is of paramount value. Extracting the maximum power of partially shaded PV arrays has been widely investigated in the literature. The proposed solutions can be categorized into four main groups. The first group includes modified MPPT techniques that properly detect the global MPP. They include power curve slope, load-line MPPT, dividing rectangles techniques, the power increment technique, instantaneous operating power optimization, Fibonacci search, neural networks, and particle swarm optimization. The second category includes different array configurations for interconnecting PV modules, namely series-parallel, total-cross-tie, and bridge-link configurations. The third category includes different PV system architectures, namely centralized architecture, series-connected microconverters, parallel-connected microconverters, and microinverters. The fourth category includes different converter topologies, namely multilevel converters, voltage injection circuits, generation control circuits, module-integrated converters, and multiple-input converters. This paper surveys the proposed approaches in each category and provides a brief discussion of their characteristics.

Control and Circuit Techniques to Mitigate Partial Shading Effects in Photovoltaic Arrays

Partial shading of PV arrays reduces the energy yield of PV systems and the arrays exhibit multiple peaks in the P-V characteristics. The losses due to partial shading are not proportional to the shaded area but depend on the shading pattern, array configuration and the physical location of shaded modules in the array. This paper presents a technique to configure the modules in the array so as to enhance the generated power from the array under partial shading conditions. In this approach, the physical location of the modules in a Total Cross Tied (TCT) connected PV array are arranged based on the Su Do Ku puzzle pattern so as to distribute the shading effect over the entire array. Further, this arrangement of modules is done without altering the electrical connection of the modules in the array. The Su Do Ku arrangement reduces the effect of shading of modules in any row thereby enhancing the generated PV power. The performance of the system is investigated for different shading patterns and the results show that positioning the modules of the array according to “Su Do Ku” puzzle pattern yields improved performance under partially shaded conditions.

Enhanced Power Generation From PV Array Under Partial Shading Conditions by Shade Dispersion Using Su Do Ku Configuration

A modified fuzzy-logic controller for maximum power point (MPP) tracking is proposed to increase photovoltaic (PV) system performance during partially shaded conditions. Instead of perturbing and observing the PV system MPP, the controller scans and stores the maximum power during the perturbing and observing procedures. The controller offers accurate convergence to the global maximum operating point under different partial shadowing conditions. A mathematical model of the PV system under partial shadowing conditions is derived. To validate the proposed modified fuzzy-logic-based controller, simulation and experimentation results are provided.

A Maximum Power Point Tracking Technique for Partially Shaded Photovoltaic Systems in Microgrids

In a photovoltaic (PV)- or fuel-cell-based grid-connected power system, a high step-up dc-dc converter is required to boost the low voltage of a PV or fuel cell to a relatively high bus voltage for the downstream dc-ac grid-connected inverter. To integrate the advantages of the high voltage gain of a switched-capacitor (SC) converter and excellent output regulation of a switching-mode dc-dc converter, a method of combining the two types of converters is proposed in this paper. The basic idea is that when the switch is turned on, the inductor is charged, and the capacitors are connected in series to supply the load, and when the switch is turned off, the inductor releases energy to charge multiple capacitors in parallel, whose voltages are controlled by a pulsewidth modulation technique. Thus, a high voltage gain of the dc-dc converter can be obtained with good regulation. Based on this principle, a series of new topologies are derived, and the operating principles and voltage gains of the proposed converters are analyzed. Finally, the design of the proposed converter is given, and the experiment results are provided to verify the theoretical analysis.

Nonisolated High Step-Up DC–DC Converters Adopting Switched-Capacitor Cell

Partial shading of a photovoltaic array is the condition under which different modules in the array experience different irradiance levels due to shading. This difference causes mismatch between the modules, leading to undesirable effects such as reduction in generated power and hot spots. The severity of these effects can be considerably reduced by photovoltaic array reconfiguration. This paper proposes a novel mathematical formulation for the optimal reconfiguration of photovoltaic arrays to minimize partial shading losses. The paper formulates the reconfiguration problem as a mixed integer quadratic programming problem and finds the optimal solution using a branch and bound algorithm. The proposed formulation can be used for an equal or nonequal number of modules per row. Moreover, it can be used for fully reconfigurable or partially reconfigurable arrays. The improvement resulting from the reconfiguration with respect to the existing photovoltaic interconnections is demonstrated by extensive simulation results.

Optimal Photovoltaic Array Reconfiguration to Reduce Partial Shading Losses

This paper applies a dynamical electrical array reconfiguration (EAR) strategy on the photovoltaic (PV) generator of a grid-connected PV system based on a plant-oriented configuration, in order to improve its energy production when the operating conditions of the solar panels are different. The EAR strategy is carried out by inserting a controllable switching matrix between the PV generator and the central inverter, which allows the electrical reconnection of the available PV modules. As a result, the PV system exhibits a self-capacity for real-time adaptation to the PV generator external operating conditions and improves the energy extraction of the system. Experimental results are provided to validate the proposed approach.

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Electrical PV Array Reconfiguration Strategy for Energy Extraction Improvement in Grid-Connected PV Systems

This paper presents the design and final realization of a transducer system for the measurement of high dc and ac currents. This transducer is based on the magnetic flux compensation technique, also called fluxgate principle. The transducer designed can measure currents of around 1 kA of peak value with a 170-kHz small-signal bandwidth. This functionality can be achieved with low power consumption if the designed system is compared with other fluxgate transducers available on the market and with similar functional specifications. Improvement in consumption was achieved by the inclusion in the design of a switching power supply (based on flyback topology) and a switched amplifier for generating magnetic flux compensation current (based on half-bridge inverter topology).

Design of a Low-Consumption Fluxgate Transducer for High-Current Measurement Applications

Community Microgrid offers effective energy harvesting from distributed energy resources and efficient energy consumption by employing an energy management system (EMS). Therefore, the collaborative microgrids are essentially required to apply an EMS, underlying an operative control strategy in order to provide an efficient system. An EMS is apt to optimize the operation of microgrids from several points of view. Optimal production planning, optimal demand-side management, fuel and emission constraints, the revenue of trading spinning and non-spinning reserve capacity can effectively be managed by EMS. Consequently, the importance of optimization is explicit in microgrid applications. In this paper, the most common control strategies in the microgrid community with potential pros and cons are analyzed. Moreover, a comprehensive review of single objective and multi-objective optimization methods is performed by considering the practical and technical constraints, uncertainty, and intermittency of renewable energies sources. The Pareto-optimal solution as the most popular multi-objective optimization approach is investigated for the advanced optimization algorithms. Eventually, feature selection and neural network-based clustering algorithms in order to analyze the Pareto-optimal set are introduced.

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A Comprehensive Review of Control Strategies and Optimization Methods for Individual and Community Microgrids

This paper compares two central dimmer system technologies used in street lighting. These dimmers are utilized in adaptive lighting systems based on high-intensity-discharge lamps and magnetic ballasts. The first technology is based on a multiple-tapped autotransformer which is commonly used for these types of installations. The second technology is based on a high-frequency switch converter (more specifically in a single-phase matrix converter topology) and represents a novelty for this type of application. Tests were conducted to determine the main features of both dimmer technologies, and the obtained results are presented.

Comparison of Central Dimmer Systems Based on Multiple-Tapped Autotransformer and High-Frequency Switching Converter

This work focuses on current sharing between punch-through insulated gate bipolar transistors (IGBTs) connected in parallel and evaluates the mechanisms that allow overall current balancing. Two different control strategies are presented. These strategies are based on the modification of transistor gate-emitter control voltage VGE by using an active gate driver circuit. The first strategy relies on the calculation of the average value of the current flowing through all parallel-connected IGBTs. The second strategy is proposed by the authors on the basis of a current cross reference control scheme. Finally, the simulation and experimental results of the application of the two current sharing control algorithms are presented.

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Guillermo Velasco-Quesada

Papers

Electrical PV Array Reconfiguration Strategy for Energy Extraction Improvement in Grid-Connected PV Systems

Design of a Low-Consumption Fluxgate Transducer for High-Current Measurement Applications

A Comprehensive Review of Control Strategies and Optimization Methods for Individual and Community Microgrids

Comparison of Central Dimmer Systems Based on Multiple-Tapped Autotransformer and High-Frequency Switching Converter

Current Sharing Control Strategy for IGBTs Connected in Parallel