A Compact Three-Port DC-DC Converter for Integrated PV-Battery System

© 2018 IEEE. In this paper, a new non-isolated three-port DC-DC converter (NITPC) to integrate a battery storage with a PV module is proposed. The intermittency of renewable energy and the unpredictable load demand are eliminated by firming a backup battery with the PV module to supply extra power when it is required. The proposed converter is reconfigurable and able to operate as a conventional boost converter, a buck-boost converter or a forward converter in different modes to support several power flow combinations and achieve power conditioning and regulation among the PV module, battery and an output port simultaneously. Nevertheless, the converter only consists of two switches, one coupled inductor, one diode and two capacitors. Thus, the system size and number of components are reduced compared with the traditional DC-DC converters. High output regulated voltage is achieved by using a coupled inductor and by combining the PV module and the battery in series. Simulation and experiment are carried out to verify the proposed circuit

Simple and Fast Dynamic Photovoltaic Emulator based on a Physical Equivalent PV‐cell Model

Photovoltaic emulators are a specific type of power electronics system to mimic the behaviour of a photovoltaic (PV) panel or array and facilitate the testing of energy systems. Existing solutions usually require sophisticated hardware design and fast computing. This paper presents a simple, reliable, and effective circuit-based photovoltaic (PV) emulator based on the equivalent PV stacked cells. The PV emulator can be used for solar system testing and analysis, such as maximum power point tracking (MPPT) and partial shading effect. The – and – characteristic curves of the emulator have been generated by using an LTspice simulator. It is experimentally investigated and compared with a real PV panel and existing emulator products. The experiment results show good agreement with the mimicked actual PV panel. The proposed PV emulator shows a better dynamic response and shorter settling time than several benchmarked commercial products. The enhancement in the time response is due to the simplicity of the emulator, where a few power diodes and some resisters are used. In addition to simplicity, the PV emulator is very cost-effective

Efficiency Improvement Scheme for PV Emulator Based on a Physical Equivalent PV-Cell Model

Recently, a photovoltaic (PV) emulator is proposed which is based on a combination of a constant current source and a one-diode photovoltaic model. Its superior dynamic performance is compatible with that of a real PV system. Although it is power efficient at the maximum power point (MPP), it suffers from high power loss around and at the open-circuit voltage (OCV) operation condition. The PV emulator can be used for PV system analysis and testing, such as maximum power point tracking (MPPT). This paper presents a new switching circuit which is placed in parallel with the diode string to minimize the power loss. The switching circuit consists of a two-switch non-inverting buck-boost DC/DC converter. When the operating point of the PV emulator moves from the current source region to the voltage source region, the converter, which is more efficient, switches in to replace the diode string seamlessly to maintain the circuit operation of the emulator. Experimental results show that in the worst case scenario, i.e. OCV condition, the efficiency and temperature of the proposed solution reach 81.47% and 30.1 °C respectively, as compared with 2.8% and 94.2 °C respectively for the diode string only case. In terms of dynamic response, the proposed PV emulator lags the real PV panel by only 3.5 ms as compared with 120 ms by a commercial emulator under the 30% to 60% insolation change test

An Analog BJT-Tuned Maximum Power Point Tracking Technique for PV Systems

© 2004-2012 IEEE. In this brief, an analog, bipolar junction transistor (BJT)-tuned voltage reference maximum power point tracking (MPPT) method for photovoltaic modules is proposed. The conventional fixed voltage reference method is the simplest method for tracking, but it does not obtain good MPPT efficiency because the maximum power point (MPP) voltage changes at different insolation levels. In reality, an approximately linear slope is formed when connecting the MPPs measured from the highest insolation level to the lowest. Utilizing this characteristic, a BJT, which has a similar electrical property, is used to implement a variable voltage reference that improves the accuracy of the MPP voltage when the insolation changes. The proposed circuit is simple and easy to implement, and it can track the MPP very quickly without the need for a digital controller or PID controller. Hence, the circuits cost and complexity are reduced. Experimental results are given to verify the feasibility of the proposed MPPT method

Experimental study of static and dynamic behaviours of cracked PV panels

© The Institution of Engineering and Technology 2019. Solar cell power performance is greatly affected by two critical factors ageing and crack. In order to mitigate their negative effects on the solar system, these cells are to be substituted by new cells, thus, replacing the panels. This study presents an active crack detection method that detects the cracked cells within a solar string by using AC parameter characterisation without a need to have a physical inspection. The mathematical module of the solar cell shows that it constitutes of series and parallel resistors in addition to a parallel capacitor and that their values change by ageing and crack. In addition to studying the effects of the crack on the solar cell, it is verified by the experiment that the solar cells behave as a capacitive circuit, and their capacitance increases when the cell gets cracked, getting higher as the crack becomes more serious. The experiment is extended to investigate the effect of series and parallel PV strings, which are affected by cracked and partially shaded cells to evaluate their criticality levels. By monitoring the AC parameter of the solar cell and the change of the capacitance, it is easy to detect the crack when it occurs

Fast Photovoltaic Emulator Based on PV-cell Equivalent Circuit Model

Photovoltaic (PV) emulator is a specific type of power electronic device used to simulate and produce the nonlinear characteristic curves for actual solar panel or array. It usually requires fast computing and power converters with a wide output range. However, the emulator response time is restricted by the controller bandwidth, and it must stabilize the converter for many different operating points. Hence pure power converter based solutions generally have a slower response time when compared with the real PV system. This paper presents a PV emulator based on a PV cell equivalent circuit model. It consists of a constant current source converter (CCSC) and a string of diodes to mimic the nonlinearity of any PV source. The CCSC simplifies the converter and controller designs as it operates at a fixed point for each insolation level, as compared with a converter-based solution which requires a voltage-source converter with wide output operating ranges. This study focuses on two aspects of the PV emulator design. Firstly, a detailed parametric design from model equations to the extraction of practical real PV parameters is explained to estimate the electrical performance of the PV simulator. Secondly, the CCSC and controller designs are explained. An experimental prototype is designed to validate the PV simulator. In addition to steady-state operation, the dynamic response of series connected cells is also emulated to verify the effectiveness of the proposed platform. Both simulations and experimental results are conducted. The response time of the proposed emulator system is comparable to both a benchmarked commercial product and a real PV system

Performance investigation of a PV emulator using current source and diode string

© 2018 IEEE. Energy emulator is a specific t ype o f p ower electronic system to mimic the electrical behavior of an energy source and facilitate the testing of energy system. This paper presents a study of a photovoltaic (PV) emulator which is formed by a current source, a diode string and some resistors. It is constructed according to the one-diode photovoltaic model. Unlike the previous study, this paper focuses on using the model equations to design the circuit parameters of the emulator to mimic a selected PV panel and evaluate the circuit performance from both electrical and thermal perspectives. A laboratory experimental setup is built and tested to verify the design. The emulator is power efficient a t t he m aximum p ower p oint. The highest power dissipation of the circuit occurs at the open-circuit voltage operating point

Experimental study of PV strings affected by cracks

Crack is one critical factor that degrades the performance of photovoltaic (PV) panels. To gain a better understanding of the impacts of cracks appeared on PVs and also to mitigate it, its failure mechanism, detrimental effects, criticality, and potential risks on independent PV panels are firstly reviewed in this study. An experimental study which investigates the degree of series connected and parallel connected PV strings which are affected by cracked cells are presented. A comparison of impacts of the partially shaded PV panel string and cracked cells happened to the PV panel string is given to evaluate their criticality levels. The experimental results show that the series connected PV panel string is strongly affected once the cell is seriously cracked, as the current generation capability is clamped. Partial shading, however, shows better performance. In addition, though the overall power the parallel connected PV string is reduced, it is less affected by the cracked cells compared to the series connected one. Lastly, a bypass diode is added to a series connected PV panel string with cracked cells, and the experimental results show that it can be an effective way to minimise the negative impacts of cracks

A Novel High Step-up Three-Port Bidirectional DC/DC Converter for PV-Battery Integrated System

In this paper, a new high step-up non-isolated three- port DC-DC converter (HS-NITPC) is proposed. The converter is designed to integrate a solar panel with battery storage in order to boost its voltage, reduce the effect of solar energy intermittency and enhance solar power performance under unpredictable load demand. The converter combines three converters to form one integrated converter by sharing some components. Thus, the converter has high power density and fewer components compared to the traditional DC-DC converters. The coupled inductor is used to achieve a high output regulated voltage, transfer energy among the ports and facilitate maximum power point tracking for the solar panel. A hardware prototype was built and tested to verify the proposed circuit for 180 W input power. The proposed converter is suitable for stand-alone or grid- connected solar system. Moreover, it could be used in the electric vehicle where the regenerative braking is used