Increasing Energy Capture From Partially Shaded PV String Using Differential Power Processing

Fault-tolerant strategy without redundant switches for PV systems based on differential power processing converters

A novel population based maximum point tracking algorithm to overcome partial shading issues in solar photovoltaic technology

A novel control strategy for mode seamless switching of PV converter in DC microgrid based on double integral sliding mode control

Photovoltaic (PV) modules subject to partial shading (PS) or inhomogeneous irradiation drastically decrease the PV string power output. An algorithm composed of maximum voltage point tracking (MVPT) and maximum power point (MPP) tracking (MPPT) is presented to restore part of the power loss caused by PS. The MVPT can simultaneously drive the operating point of series PV modules toward their respective MPPs and guarantee power peak uniqueness. The MVPT is performed by means of a controllable current transformer (CCT) disposed at the terminal of each PV module permitting a compatible current in the series path of a PV string. The CCT output current can be regulated using a dependent current source according to the MPPT algorithm. An appropriate CCT current determined by the MPPT algorithm can avert undue CCT activation and consequently reduces the switching and copper losses of the converter circuit. Experimental results validate that the proposed strategy can balance the PV modules' output current subject to PS and facilitate convergence to the theoretical global MPP.

A hybrid maximum power point tracking for partially shaded photovoltaic systems in the tropics

Energy crises and the growth of the energy demand have increased the interest in utilizing unconventional power sources. Thus, renewable energy sources have become a topic of interest to mitigate rising energy concerns and cope with increased electricity demand. With remarkable merits including cleanness and abundance, photovoltaic (PV) solar energy systems are a key to solving these issues. The employed inverters should effectively utilize the maximum available power from the PV solar system and transfer this power to the utility grid without posing any further limitations. However, the unequal power generation of different PV systems caused by partial shading (PS) and other PV panel degradation factors leads to a reduction in generation capacity. One of the relatively new solutions to mitigate the mismatch concerns between the PV modules and sub-modules is to extract the maximum power of each sub-module individually. The main objective of this paper is to present a comprehensive review of such PV grid-connected inverters topologies associated with sub-module connection and control. It will classify the PV grid-tied inverters in accordance with the level where the maximum power point tracking (MPPT) system is implemented. A special focus has been placed on sub-module microinverters (MI) in terms of circuit topologies, conversion efficiency, and controller design. This paper provides a comprehensive analysis of employing the distributed MPPT (DMPPT) approach to maximize the power generation of PV systems by mitigating the mismatch issues inside the PV module. The circuit topology, PV system configuration, and MPPT algorithms used for applying DMPPT solutions in PV SMs are discussed in detail in this study.

Submodule mismatch has become the major cause of losses in the photovoltaic (PV) power generation system, which has been an important factor restricting the development of PV technology. Differential power processing (DPP) architecture is increasingly employed in PV distributed MPPT (DMPPT) due to its low processed power. In order to improve the PV utilization efficiency, minimize the power loss and reduce the system cost, a novel scheme based on DPP is introduced in this article. The proposed DPP converter is composed of multiple buck-boost choppers, and a multidimensional perturb and observe (MPO) algorithm is proposed to achieve true DMPPT through correcting the voltage of each submodule to its voltage at the maximum power point by using a single current sensor. A prototype with multiple buck-boost choppers for 36 V/200 W PV module is designed and built to verify the operating principle and evaluate the performance of the proposed DPP converter and DMPPT strategy, and the experimental results show that the prototype is low-cost and effectively improves system efficiency.

Energy assessment of enhanced fixed low concentration photovoltaic systems

This work describes a distributed maximum power point tracking (MPPT) control scheme that requires no perturb and observe (P&O) synchronization and little communication among power converters. Design and benefits of this architecture with respect to control, communication, and converter efficiency are analyzed. Isolated dc-dc converter prototypes are constructed and employed within a string of series-connected photovoltaic sub-modules to experimentally validate the proposed control method. An experimental extraction efficiency of 98.47% is achieved for a 3 sub-module connection with approximately 30% mismatch- a 9.66% improvement from the conventional, non-DPP architecture.

A maximum power point tracking (MPPT) controller was used to make the photovoltaic (PV) module operate at its maximum power point (MPP) under changing temperature and sunlight irradiance. Under partially shaded conditions, the characteristic power–voltage (P–V) curve of the PV modules will have more than one maximum power point, at least one local maximum power point and a global maximum power point. Conventional MPPT controllers may control the PV module array at the local maximum power point rather than the global maximum power point. MPPT control can be also implemented by using soft computing methods (SCM), which can handle the partial shade problem. However, to improve the robustness and speed of the MPPT controller, a hybrid MPPT controller has been proposed that combines two SCMs, the Genetic Algorithm (GA) and Ant Colony Optimization (ACO). Matlab was used in a simulation of a GA-ACO MPPT controller where four SunPower SPR-305NE-WHT-D PV modules with a maximum power of 305.226 W connected in series were used under conditions of partial shade to investigate the performance of the proposed MPPT controller. The results obtained were analyzed and compared with others obtained under perturb and observe (P&O) MPPT and conventional ACO MPPT controllers were observed.

Photovoltaic (PV) module mismatching and non-uniform insolation conditions are the major drawbacks of the PV systems. The distributed maximum power point tracking (DMPPT) method is an effective solution to mitigate these drawbacks but, the DMPPT with conventional algorithms requires more sensors to implement. A single output voltage sensor based DMPPT algorithm with parallel configuration is presented in this paper. The operating point of each PV module is regulated independently through a single microcontroller. The output voltage sensor based DMPPT is developed based on the output voltage characteristics with respect to the converter duty cycle and its mathematical validation is presented in this paper. The proposed DMPPT algorithm is validated through experimentation by using the developed prototype with two designed SEPIC (single ended primary inductance converter) converters, two PV modules and a microcontroller.

This paper reviews the existing models, connection schemes and maximum power point tracking (MPPT) methods of PV arrays. The partial shading causes significant power losses. It is very difficult to maintain uniform irradiance over the entire PV array, especially for rooftop or building-integrated PV systems. The aspects such as connection scheme of PV array, shading pattern and maximum power point tracking (MPPT) techniques, etc., decide the power generated by the PV array. The conventional MPPT methods are only capable of reaching maximum power point (MPP) in identical insolation situations. Hence, conventional MPP tracking becomes inept due to the existence of several peaks in the P-V characteristics. There are different global maximum power point (GMPP) tracking techniques available in the literature that operate in partial shading scenarios. The reconfiguration of the PV array reduces the number of multiple peaks. This reduction in several peaks makes conventional MPP tracking techniques competent even under partial shading conditions with low implementation complexity and higher tracking speed. This paper can assist scientists in choosing a precise objective-based PV module model, connection schemes and MPP tracking methods out of numerous schemes available in the literature.

Conventional microinverter or module-integrated converter (MIC)-based photovoltaic (PV) systems are prone to be complex and costly because each MIC requires not only a boost converter to bridge a huge voltage gap between a PV panel and grid but also desirably a differential power processing (DPP) converter to preclude partial shading issues. This paper proposes a novel MIC based on cascaded quasi-Z-source inverters (qZSIs) with DPP capability. A traditional qZSI and voltage multiplier (VM)-based DPP converter are integrated into a single unit with sharing active switches and magnetic components, achieving system- and circuit-level simplifications. In addition, a novel control strategy utilizing two control freedoms of shoot-through duty cycle $d_{st}$ and modulation index M to simultaneously perform maximum power point tracking (MPPT) and DPP function, respectively, is also presented. A 150 W prototype for a standard PV panel consisting of three substrings is built, and experimental tests are performed emulating partial shading conditions. The results demonstrate that the proposed integrated qZSI could perform MPPT with satisfactory preventing partial shading issues while generating ac voltage at the inverter output.

An isolated modular boost converter (IMBC) consisting of plural phase-shifted full bridge converters is proposed as a solution for an automotive photovoltaic system. The IMBC not only controls multiple photovoltaic (PV) modules around their maximum power points individually, but also supplies distributed power from each PV module to the high voltage battery used for propelling the vehicle through boosting by the cascaded structure. This paper shows that 4M-IMBC prototype consisting of four boost modules can operate with distributed maximum power point tracking control under both a solar irradiance imbalance and partial shade transitions. In addition, 12M-IMBC prototype consisting of twelve boost modules charged power by actual photovoltaic modules to the high voltage battery. The average measured power conversion efficiency during sunny weather was 84.8%, which is similar to the efficiency of a single boost module.

The partial shading on parallel-connected photovoltaic (PV) modules introduces severe mismatch issues in PV systems, which significantly affects the overall output power. Distributed maximum power point tracking (DMPPT) is considered as an effective solution to the resultant mismatch in parallel-connected PV sub-modules. In this context, this paper proposes a sub-module level switched-inductor (SL) based differential power processing (DPP) technique for parallel connections to alleviate the mismatch effect. The technique can achieve the maximum output power under mismatch by equalizing the sub-module voltages. The proposed technique is analyzed and compared through simulations with a traditional (Schottky diode) bypassing technique.