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Solar energy is one of the most promising energy types, but photovoltaic (PV) mismatches have several negative effects. Finding an efficient and low-cost method to reduce or eliminate the power loss caused by the mismatch in PV power generation systems is necessary. In this paper, we propose a PV submodule-distributed maximum power point tracking (DMPPT) scheme based on a multi-port DC converter. In-depth analysis and research are performed on the PV model and mismatch characteristics, the PV module voltage equalization (VE) strategy, and implementation with the multi-port buck–boost converter. We discuss the trade-off between true DMPPT and VE on control overhead and tracking accuracy, and a detailed derivation is created to illustrate the differences between them. The VE can reduce the cost and complexity of the system at the expense of a small PV energy capture. The proposed implementation reduces the number of semiconductor components and current sensors, which is conducive to the integrated design of the hardware. A prototype based on a multi-port buck–boost converter for a 36 V/200 W PV module was designed and built. The feasibility and progress of the proposed scheme were verified through experiments.

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.

Microgrid (MG) technologies facilitate reliable, efficient, and economic operation of distributed resources such as photovoltaic and battery storage systems. The well-known droop method controls different sources in an MG to properly share power supply. However, utilizing the droop method poses two major challenges. First, while the droop method can prevent converter overloading, it cannot protect them from overstressing, thus deteriorating system reliability. Second, operating a 100% renewable-based MG requires a supervisory unit to monitor and control energy flow for load-generation balance. However, the supervisory unit relies on communication systems which impacts overall system reliability by being exposed to single-point failures and cyberattacks. This article proposes a decentralized power sharing approach that restricts thermal damage of converter components to avoid over-stressing converters. The main goal is to improve overall system performance and reliability by appropriately sharing active and reactive power among different sources without using communication systems. The simulations and numerical analysis show that the proposed decentralized strategy will properly control the power and energy flow among different sources. Moreover, it prevents over-stressing converters, consequently enhancing the overall reliability of the MG. An experiment is also presented to demonstrate the effectiveness of the proposed decentralized control approach.

Distributed maximum power point tracking (DMPPT) is an effective method to address the problem of photovoltaic (PV) mismatch and improve the utilization of PV elements. Differential power processing (DPP) is considered a very satisfactory power processing method for submodule level DMPPT. This paper introduces two power processing methods, FPP and DPP, analyses the three DMPPT power transmission architectures based on DPP, PV-PV, PV-bus and PV-IP, and compares the implementation complexity, converter volume, control difficulty, and hardware cost of various typical implementation topologies, and finally analyses the two most common control methods of DMPPT, voltage equalization (VE) and true MPPT.

This paper proposes a single-stage three-phase grid-connected inverter with the center-tapped energy storage inductor, which is suitable for low-voltage and high-current conditions. By adding the center-tapped inductor, the circuit has two controllable boost parameters, i.e. energy storage switch duty ratio and center-tapped inductor turn ratio, to ensure that the circuit has a larger step-up ratio. Moreover, the active-clamped branch in the circuit can effectively suppress the drain-source voltage spike of the energy storage switch to ensure the efficient and stable operation of the system. According to the proposed improved dual-loop interval sinusoidal pulse width modulation (SPWM) control strategy, the circuit can stably provide high-quality grid-connected current in any working intervals. The feasibility and effectiveness of the proposed circuit and control strategy are verified by the experiments on the 3kW 96VDC/380V50HzAC prototype.

As the demand for power reliability keeps rising in modern society, the integration of energy storage systems into power networks increases at an unprecedented rate. Meanwhile, reliability analysis and enhancement of a power network attracts more and more attention. This paper explores the impact of four different energy management strategies (EMSs) on the reliability of microgrids, which play an important role in future distribution networks. The reliability performance is analysed on different levels, including converter interfaces and battery storage units on device level as well as power supply reliability on system level. The numerical analysis has shown that the employed EMS can remarkably affect the reliability indices of the system. The battery lifetime can be increased by more than 50% and annual energy loss can be reduced by up to 92%. Since the economic decision-making depends on the components lifetime and overall system performance, this paper provides deep insights for power engineers to properly design, plan and control future microgrids.

An accurate reactive power sharing scheme aiming to prioritize renewable sources is proposed and implemented under modified droop control in islanded microgrids. In order to improve reactive power sharing accuracy, an interfacing inductor and grid voltage estimation strategy is used. Simulation and experimental results show the efficacy of the approach.

Aiming at shortcomings of single new energy power generation, such as unstable power supply, discontinuity and changing with climate conditions, a quasi-single-stage isolated Buck-Boost mode multi-input inverter and master-slave power management SPWM control strategy with smooth and seamless switching in different power supply modes are proposed. The circuit topology, characteristic of steady principle and power management strategy are fully investigated. The circuit topology is composed of a bidirectional isolated Buck-Boost DC converter with a multi-input selector switch in series, and a polarity inversion bridge. The master-slave power management strategy is consisted of n-1 input voltage control loops, n power distribution circuits and instantaneous output voltage control loop with independent power control, it can realize smooth and seamless switching in different power supply modes. Designed and implemented 500VA 80-110VDC/220V50HzAC prototype has excellent performances such as high conversion efficiency, high quality of output waveforms, strong load adaptability, smooth and seamless switching in different power supply modes, etc.

In power converter, the system model has a significant meaning of the design of the controller and the dynamic characteristics. In this paper, the switching network average method is used to set up the small signal model of flyback circuit, which is operating in discontinuous current mode(DCM). A controller with single zero and single pole is designed based on the small signal model which is set up in this paper. Moreover, the analysis of system stability and dynamic response is proposed. Finally, the system is simulated and verified by a flyback LED constant current drive circuit (220AC input, 0.7A/16W output).

Microgrids provide an effective way to increase renewable energy (RE) penetration level in the power network. The cooperation of renewable microsources, energy storage systems (ESSs) and conventional dispatchable microsources is an important issue in the operation of an islanded microgrid. In this paper, the designed power sharing scheme aims to maximize renewable penetration level by giving RE the priority of power supply. This requires RE to be able to regulate grid voltage rather than only operating under power control mode (PCM) in the conventional way. Droop control strategy is modified to support a microsource operating under both voltage control mode (VCM) and PCM, and switching between both modes automatically. It also enables “peer to peer” and “plug and play” operation of a microgrid. Meanwhile, the characteristics of power sources (photovoltaic and batteries) are considered. DC/DC converter controller is proposed correspondingly with the aim of keeping the system stable. Simulations have been conducted to verify its effectiveness.

To integrate more renewable energy (RE) into the power grid, an effective control strategy for photovoltaic (PV) sources in an islanded microgrid is investigated. A power sharing scheme is designed to give PV sources the priority of power supply. Based on the scheme, adjusted droop control strategy is employed for voltage source inverters (VSI). Considering PV power characteristics, a DC/DC converter controller is also designed for PV panels. There are two operating modes of PV sources: maximum power point tracking (MPPT) mode and power curtailment (PC) mode. MPPT mode is supported by MPPT technique combining with a frequency increment on the VSI droop controller. The traditional droop controller and DC bus voltage tracking loop support PC mode. Stability analysis is conducted. Simulation results show the control strategy can share power demand effectively among different kinds of power sources even under varying weather conditions.

Microgrids provide an effective way to integrate distributed energy sources, particularly renewable energy sources, into the power system. Renewable energy sources differ from traditional microsources as their generation is variable depending on weather conditions. To achieve the highest renewable energy utilisation, photovoltaic (PV) panels tend to be operated at their maximum power point which also forms the boundary for stable operation. In this arrangement the DC bus voltage can collapse should the PV panels be overloaded. In an islanded microgrid, a droop controller is adopted to limit reactive power as well as distribute real power demand amongst the microsources. This paper proposes a modification to the droop controller to ensure a PV source remains within its maximum power limit. Simulation results are presented to demonstrate the controller's effectiveness.

Even though most universities in China have successively introduced digital resources, traditional paper-based resources still share major percentage in the whole library resources. In the current library management schemes, the information of the resource requirement and usage record is not utilized effectively either in resource purchase decision or in resource allocation plan. Furthermore, there is no efficient approach proposed to utilize the advanced information technologies in library management. In this paper, we firstly analyze the patterns of the current library services in Chinese universities and points out some problems existing in the current resource management systems. We then propose several approaches attempting to improve user satisfactory and resource utilization by considering customer behavior and requirement information.