Differential Power Processing Systems Research Articles

Performance Quantization and Comparative Assessment of Voltage Equalizers in Mismatched Photovoltaic Differential Power Processing Systems

Performance Quantization and Comparative Assessment of Voltage Equalizers in Mismatched Photovoltaic Differential Power Processing Systems

Analysis and Design of Series Voltage Compensator for Differential Power Processing

Differential power processing (DPP) has been proven effective in many applications. This article explores a series voltage compensator (SVC) architecture for voltage regulation of DPP systems. An SVC is connected in series between the input dc bus and the DPP system to compensate for the voltage difference. It only processes a fraction of the overall power. The inclusion of an SVC changes the power flow of the DPP system and changes the loss distribution. We theoretically investigated the SVC power rating and the additional power conversion stress that SVC brings to the DPP converter. Accordingly, we identified the operation range where an SVC is more attractive than a conventional DPP pre-regulation converter that has to process the full power. Our analysis provides insights into system design and control strategy of SVC-DPP topologies. To validate the principles of SVC, a buck SVC is designed and applied to a ten-port DPP converter. The buck SVC can efficiently convert an input voltage ranging from 50 V to 65 V into a regulated 50 V for the DPP system. The size of the SVC is only 20% of the DPP converter, and the peak efficiency of the SVC-DPP system achieves 98.8%.

Power-Rating Balance Control and Reliability Enhancement in Mismatched Photovoltaic Differential Power Processing Systems

With the increase of the component number, the power stress distribution among differential power processing (DPP) converters, control implementation, system cost, and reliability become the most challenging issues for a practical photovoltaic (PV) DPP system. This article introduces an improved power-rating balance (IPRB) control for the PV-to-bus based DPP architecture that ensures each PV submodule operate at its true maximum power point (MPP) while achieving more balanced power stress distribution and higher reliability. Specifically, a submodule-level finite-state-machine-based MPP tracking is implemented to guarantee always maximum power yield, whereas a string-level power-rating balancing (PRB) control is adopted to balance the unit-maximum proceeded power by DPP converters based on the built power flow model with respect to the string current. A comprehensive comparison of advanced control strategies for PV-to-bus DPP architectures, including least power point tracking, voltage equalization (VE) based PRB control, and the proposed IPRB, has been carried out with the mission-profile-based reliability assessment under different partial shading scenarios. Component-failure-rate-based reliability analysis shows that the PV-to-bus DPP architecture with the proposed IPRB control can significantly improve the system reliability. Main simulation and experimental evaluations are carried out to verify the effectiveness of the proposed control.

Stochastic Power Loss Analysis of Differential Power Processing

This article presents stochastic power loss analysis for differential power processing (DPP). A stochastic model is developed to analyze power loss scaling in a DPP system based on probability distributions of loads or sources. Scaling factors are introduced to describe how losses change with DPP system size and load or source power variance. Expected power losses of representative DPP topologies are analyzed and compared to losses of a conventional dc–dc converter with the same total switch die area and magnetic volume. The results quantify performance trends of DPP architectures. Models and scaling factors are verified with SPICE simulations and experimental results. The analytical framework, scaling factors, and quantitative models provide useful guidelines for designing large-scale DPP systems. This article is accompanied by a video file demonstrating the modeling procedures and the experimental setup.

Segmented Differential Power Processing Converter Unit and Control Algorithm for Photovoltaic Systems

Differential power processing (DPP) for photovoltaic (PV) systems can achieve high system efficiency and maintain maximum power production even under mismatched conditions. However, DPP converters applied to large-scale systems have challenges of complicated installation and high voltage ratings. The segmented DPP structure is introduced as a modular approach that utilizes groups of bidirectional DPP flyback converters to maximize PV power generation while minimizing converter power loss. Groups of four DPP converters are combined into a segmented DPP unit with maximum power point tracking (MPPT) control to maximize output power of the unit. The segmented DPP system and control algorithm are verified through simulation and hardware experimentation. Simulation results verify the effectiveness of the control algorithm with multiple segmented DPP units interacting with a typical inverter employing MPPT. Experimental results verify that system efficiency of the segmented DPP unit reaches 96.4% in even lighting conditions, reaches 92.7% in severe partial shading conditions, and shows an increase of up to 14.8% in uneven lighting conditions compared to an equivalent series-connected PV system.

고효율 태양광 DC 발전을 위한 능동적인 최대전력추종 알고리즘 적용의 차동전력 DC/DC 컨버터

This paper is about differential power DC/DC converter (DPP) based on adaptive MPPT algorithm for high efficiency PV DC generation system. PV DC generation has a character that raising the irradiance causes the output power to increase and the lower temperature generates more production power. Therefore, PV system for maximum power generate is need method find the exact voltage point to generate the maximum power. It is called the maximum power point tracking(MPPT).BR In this study, we applied active MPPT algorithm for high efficiency maximum power point tracking control in the differential power processing system. Active MPPT algorithm proposed in this paper is easy to apply to DPP structure, and not only arrival time at the initial MPP zone is fast, but also obtain stable power with low ripple. Using the differential power DC/DC converter by active MPPT algorithm, we got the power production efficiency was 98.84 [%] which is the highest result.

Power rating analysis and protection for photovoltaic-isolated port based differential power processing systems

In a photovoltaic generation system (PGS), photovoltaic (PV) modules are often connected in series for increased string voltage. However, a significant reduction in the actual output power is observed due to the manufacturing tolerance, module aging and partial shaded. Compared with conventional methods such as bypass diodes and PV module reconfiguration, modular distributed architecture especially the differential power processing (DPP) is able to yield high output power even under partial shading conditions. Moreover, the system efficiency is improved since only the differential power is processed by the DPP converters. This paper mainly focuses on the power rating analysis and protection of PV-isolated Port (PV-IP) based DPP systems considering the significant power stress difference among DPP converters under different partial shading conditions. The voltage equalization (VE) control used in this work is able to provide up to 77% efficiency improvement through the simulation evaluation. The protection algorithm is proposed for the PV-IP DPP architecture to improve the system reliability even when some DPP converters are found failed. With the proposed protection strategy, not only the high output power yield can be maintained, but also the modular design of DPP converters with smaller power capacity can be achieved. Simulation and indoor experimental tests under various partial shading conditions were carried out to validate the effectiveness of the proposed power rating analysis and protection scheme.

Elimination of Photovoltaic Mismatching With Improved Submodule Differential Power Processing

Differential power processing (DPP) is a promising architecture to solve the issue caused by mismatches among photovoltaic (PV) submodules. To eliminate the mismatch power losses, this paper presents an optimized PV-to-bus DPP system with submodule-level individual maximum power point tracking (MPPT) and module-level minimum-power tracking (MPT) simultaneous implementation according to the built mathematical model of the power processed by DPP converters with respect to the string current. Furthermore, a flexible time-sharing algorithm is adopted to reduce the number of MPPT units. Compared with other solutions, such as PV optimizer, the proposed scheme can reduce the effects of mismatches to the minimum regardless of mismatch conditions. The system cost is reduced since only one adaptive MPPT controller is required. Besides, the system efficiency is improved due to the true MPPT implementation and MPT control. Both simulation and experimental tests are provided to validate the effectiveness of the proposed scheme.

Modularized Differential Power Processing Architecture Based on Switched Capacitor Converter to Virtually Unify Mismatched Photovoltaic Panel Characteristics

Photovoltaic (PV) strings consisting of multiple panels suffer from partial shading or characteristic mismatch issues, such as a significant reduction in power yield. Various kinds of differential power processing (DPP) converters have been developed to prevent the negative impacts of substring-level partial shading. For panel-level applications, however, conventional DPP converters face a variety of challenges, such as impaired extendibility and increased voltage stress of circuit elements. This paper proposes a switched capacitor converter (SCC)-based modular DPP architecture. Modules, each containing series-connected panels with a panel-level DPP converter, are connected through a switchless module-level DPP converter, and PV panel characteristics are unified at module- and panel-levels. The number of panels in each module is fixed, while the number of modules can be arbitrarily extended without redesigning DPP converters, hence offering good modularity. In addition, since voltage stresses of capacitors in the proposed architecture can be reduced lower than half the module voltages, the proposed DPP system realizes all-ceramic-capacitor SCC circuit by properly determining the module voltages. A prototype for eight panels, which were grouped into two modules, was built, and laboratory and field tests were performed. The experimental results demonstrated the enhanced power yield from the partially shaded PV string.

Review of Differential Power Processing Converter Techniques for Photovoltaic Applications

Differential power processing (DPP) converters are utilized in photovoltaic (PV) power systems to achieve high-efficiency power output, even under uneven lighting or mismatched PV cell situations. Since this DPP concept has been introduced for PV systems, various topologies and control algorithms have been proposed and validated, showing the benefits of DPP converters systems over existing series string and full power processing converter solutions. However, DPP systems are highly coupled and can be challenging to control. Various architectures, topologies, and control strategies for both series and parallel DPP architectures are reviewed and compared. Tradeoffs of different DPP converters and topologies are discussed. Also, the power curve for the PV connected to bus, PV to PV, and PV to independent port series DPP architectures are evaluated in terms of inverter interaction. To date, the PV to PV series DPP systems have been most widely implemented and robust system-level control for all architectures has been a major research focus. Furthermore, research and development is still needed, particularly for commercialization and parallel DPP approaches for emerging PV applications.

Unit-Minimum Least Power Point Tracking for the Optimization of Photovoltaic Differential Power Processing Systems

Recently, the module integrated converter and differential power processing (DPP) architecture were introduced to enable the photovoltaic (PV) power conditioning system to maintain the optimal operating condition of PV cells, such as maximum power point tracking (MPPT), even under partial shading conditions. However, the DPP architecture was found to have more room to optimize the performance of the systems, by the application of an extra extremum-seeking control, the so-called least power point tracking (LPPT) method that was introduced last year. The main idea is that most of the power from the PV modules is processed through the main-string high-efficiency nonisolation converter, and only a minimal fraction of the power that changes depending on the PV-string current is transferred through the low-efficiency bidirectional isolated DPP converters. This paper suggests a second version of the LPPT method, called unit-minimum power-distributing LPPT, which improves the first version of LPPT, called total-minimum centralized power-distributing LPPT. Instead of minimizing the total power of DPPs, the proposed LPPT minimizes the power of the DPP converter unit, which is the largest among them. Then, the system size and cost can be reduced by the proposed LPPT method, which enables the multiple DPP converters to have smaller power capacity and losses than those of the previous LPPT method. The real-time extremum-seeking algorithm employs a perturb-and-observe method, which comes from the conventional MPPT one, while the optimization process directs minimal extremity, not maximal. The peak system efficiency achieved with a 400-W prototype DPP system employing the LPPT algorithm is 96.7%.

Design Considerations for Parallel Differential Power Processing Converters in a Photovoltaic-Powered Wearable Application

Solar photovoltaic (PV) power is a widely used to supply power to the electric grid but can also be used in lower-power emerging applications, like in wearables or the internet of things. One fundamental challenge of using PV power in flexible wearable applications is that individual PV modules point at various angles, thus receiving different light intensities. Using a series configuration for the PV modules greatly decreases power utilization under uneven irradiance conditions. Parallel differential power processing (DPP) converters are employed to address this power reduction problem, while maintaining individual PV control and maximizing output power. Two parallel DPP configurations, with and without a front-end converter, are analyzed and compared for a target battery-charging application. The DPP system without a front-end converter shows consistently high performance and operates properly over a wider range of lighting conditions. Maximum power point tracking (MPPT) algorithms are also examined for parallel DPP systems. When the MPPT parameters are properly calibrated, simulation results indicate that voltage-offset resistive control is the most effective at maximizing PV power under unbalanced lighting conditions.

Least Power Point Tracking Method for Photovoltaic Differential Power Processing Systems

Differential power processing (DPP) systems are a promising architecture for future photovoltaic (PV) power systems that achieve high system efficiency through processing a faction of the full PV power, while achieving distributed local maximum power point tracking (MPPT). In the PV-to-bus DPP architecture, the power processed through the DPP converters depends on the string current, which must be controlled to minimize the power processed through the DPP converters. A real-time least power point tracking (LPPT) method is proposed to minimize power stress on PV DPP converters. Mathematical analysis shows the uniqueness of the least power point for the total power processed through the system. The perturb-and-observe LPPT method is presented that enables the DPP converters to maintain optimal operating conditions, while reducing the total power loss and converter stress. This work validates through simulation and experimentation that LPPT in the string-level converter successfully operates with MPPT in the DPP converters to maximize output power for the PV-to-bus architecture. Hardware prototypes were developed and tested at 140 and 300 W, and the LPPT control algorithm showed effective operation under steady-state operation and an irradiance step change. Peak system efficiency achieved with a 140-W prototype DPP system employing LPPT is 95.7%.

Magnetically-coupled boost-forward converter for high efficiency differential power processing systems

Magnetically-coupled boost-forward converter for high efficiency differential power processing systems

Bidirectional Power Conversion of Isolated Switched-Capacitor Topology for Photovoltaic Differential Power Processors

Differential power processing (DPP) systems are among the most effective architectures for photovoltaic (PV) power systems because they are highly efficient as a result of their distributed local maximum power point tracking ability, which allows the fractional processing of the total generated power. However, DPP systems require a high-efficiency, high step-up/down bidirectional converter with broad operating ranges and galvanic isolation. This study proposes a single, magnetic, high-efficiency, high step-up/down bidirectional DC-DC converter. The proposed converter is composed of a bidirectional flyback and a bidirectional isolated switched-capacitor cell, which are competitively cheap. The output terminals of the flyback converter and switched-capacitor cell are connected in series to obtain the voltage step-up. In the reverse power flow, the converter reciprocally operates with high efficiency across a broad operating range because it uses hard switching instead of soft switching. The proposed topology achieves a genuine on-off interleaved energy transfer at the transformer core and windings, thus providing an excellent utilization ratio. The dynamic characteristics of the converter are analyzed for the controller design. Finally, a 240 W hardware prototype is constructed to demonstrate the operation of the bidirectional converter under a current feedback control loop. To improve the efficiency of a PV system, the maximum power point tracking method is applied to the proposed converter.