THE STUDY AND ANALYSIS OF MPPT CONTROLLER FOR SRBC

This work is about designing Maximum Power Point Tracker (MPPT) with Synchronous Rectifier Buck Converter (SRBC) circuit where the main purpose is to improve the performance and increase the output voltage and current. The MPPT controller controls the output current of the input (usually solar array) so that the output power converges on the maximum based on the linearity between the maximum output power and the optimal current. In this work, MPPT' s characteristics, performance, operation modes, advantages, and disadvantages are analyzed and observed. Then, combination ofMPPT and adaptive gate drive (AGD) will be applied to SRBC as the output circuit. PSPICE software is used in designing and simulating both circuits. The comparison is carried out based on the average output voltage and current, node voltage, output ripple voltage and current, gate-to-source voltage, and body diode conduction loss of the MPPT circuit and MPPT with AGD circuit. The details are discussed thoroughly that include limitations and advantages in the design of the controllers using I MHz switching frequency. It is found that by implementing MPPT controller with SRBC, the output voltage and output current have increased by approximately 12%- 13% for both CCM and DCM conditions. Besides that, it also reduces output voltage ripple and current around 70 % for CCM mode. However, in DCM condition, the output peak-to-peak ripple for both voltage and current have increased by 20 %

Real-time Modelling, Diagnostics and Optimised MPPT for Residential PV Systems

The work documented in the thesis has been focused into two main sections. The first part is centred around Maximum Power Point Tracking (MPPT) techniques for photovoltaic arrays, optimised for fast-changing environmental conditions, and is described in Chapter 2. The second part is dedicated to diagnostic functions as an additional tool to maximise the energy yield of photovoltaic arrays (Chapter 4). Furthermore, mathematical models of PV panels and arrays have been developed and built (detailed in Chapter 3) for testing MPPT algorithms, and for diagnostic purposes.In Chapter 2 an overview of the today’s most popular MPPT algorithms is given, and, considering their difficulty in tracking under variable conditions, a simple technique is proposed to overcome this drawback. The method separates the MPPT perturbation effects from environmental changes and provides correct information to the tracker, which is therefore not affected by the environmental fluctuations. The method has been implemented based on the Perturb and Observe (P&O), and the experimental results demonstrate that it preserves the advantages of the existing tracker in being highly efficient during stable conditions, having a simple and generic nature, and has the benefit of also being efficient in fast-changing conditions. Furthermore, the algorithm has been successfully implemented on a commercial PV inverter, currently on the market. In Chapter 3, an overview of the existing mathematical models used to describe the electrical behaviour of PV panels is given, followed by the parameter determination for the five-parameter single-exponential model based on datasheet values, which has been used for the implementation of a PV simulator taking in account the shape, size ant intensity of partial shadow in respect to bypass diodes.In order to eliminate the iterative calculations for parameter determinations, a simplified three-parameter model is used throughout Chapter 4, dedicated to diagnostic functions of PV panels. Simple analytic expressions for the model important parameters, which could reflect deviations from the normal (e.g. from datasheet or reference measurement) I −V characteristic, is proposed.A considerable part of the thesis is dedicated to the diagnostic functions of crystalline photovoltaic panels, aimed to detect failures related to increased series resistance and partial shadowing, the two major factors responsible for yield-reduction of residential photovoltaic systems.Combining the model calculations with measurements, a method to detect changes in the panels’ series resistance based on the slope of the I − V curve in the vicinity of open-circuit conditions and scaled to Standard Test Conditions (STC) , is proposed. The results confirm the benefits of the proposed method in terms of robustness to irradiance changes and to partial shadows.In order to detect partial shadows on PV panels, a method based on equivalent thermal voltage (Vt) monitoring is proposed. Vt is calculated using the simplified three-parameter model, based on experimental curve. The main advantages of the method are the simple expression for Vt, high sensitivity to even a relatively small area of partial shadow and very good robustness against changes in series resistance.Finally, in order to quantify power losses due to different failures, e.g. partial shadows or increased series resistance, a model based approach has been proposed to estimate the panel rated power (in STC). Although it is known that the single-exponential model has low approximation precision at low irradiation conditions, using the previously determined parameters it was possible to achieve relatively good accuracy. The main advantage of the method is that it relies on already determined parameters (Rsm, Vt) based on measurements, therefore reducing the errors introduced by the limitation of the single-exponential model especially at low irradiation conditions

Investigation to Improve the Control and Operation of a Three-phase Photovoltaic Grid-tie Inverter

Solar Energy or more precisely photovoltaic energy is one of the most promising sources of electricity for the future and it can be used as a distributed generator (DG) to play its role in ‘smart grids of the future’. Distributed PV (photovoltaic) generators can provide numerous potential benefits such as augmenting the capacity of distribution systems, deferring capital investments on distribution and transmission (T&D) systems and improving power quality and system reliability. The PV energy which possesses very special I-V and P-V characteristics has to be conditioned by a PV inverter before it can be consumed by an ac load and/or the grid. Technical improvements in maximum power point tracking (MPPT) and islanding detection are proposed for a three-phase photovoltaic grid tied inverter (GTI) keeping in mind the requirements of the international standards for connecting a DG to the utility grid. This PhD thesis will contain four major sections which are briefed below. A three phase GTI has been simulated using Matlab/Simulink to test the various control blocks and algorithms involved in the building of the power conditioning unit. A DS1104 dSpace DSP controlled, 5.625 kW three-phase GTI laboratory prototype has then been built. Various hardware components, including inverter switches, gate drivers, LCL filter, rectified dc source, boost circuit, transformer, 16A current protection circuit, additional sensing interface circuits and PWM level shifter have been designed and built within the laboratory. The software algorithm created in Simulink communicates directly with the built hardware via the graphical user interface that has been designed with dSPace Control Desk. Algorithms have been developed for the inverter in order to protect it from operating out of nominal frequency and voltage ranges. An algorithm has been developed iii to ensure the boost dc link voltage is controlled to 300V when dc voltage source varies between 150V and 265V. The Z-Source inverter (ZSI), with nine operating states that employs an extra shoot through (ST) state compared to the eight states (6 active and 2 zero states) in traditional VSI is one of the most recent boost topologies that has been proposed in the literature. A step by step design procedure of a ZSI has been developed. A topology comparison between Z-Source inverter and dc-dc boost with VSI is done using literature and simulations. Merits and demerits of the two topologies are summarised and the choice of the topology is justified. MPPT is a process by which maximum power from a PV panel or array is tracked and absorbed during a particular weather condition (insolation level and temperature). There are various MPPT techniques in the literature which are reviewed and a new MPPT approach based on the P&O (Perturb and Observe) method is proposed. The proposed technique is tested on the three phase GTI simulation, it is analysed and compared to the conventionally reviewed P&O MPPT approach. The issue of islanding of GTI’s has raised concerns of equipment and personal safety, for which reason the inverter has to detect and stop the inverter during loss of grid. Passive techniques can detect the grid failure quite well when there is a large power mismatch between the DG and the load but not when the mismatch is small. Active techniques can work well with lower levels of power mismatch but they degrade power quality by introducing disturbances into the power system. A novel wavelet based antiislanding technique is proposed and incorporated into the running hardware protection. This uses physical measurements to reduce the non-detection zone close to zero and keep the power quality of the inverter output unchanged. The developed algorithms have been validated in the laboratory prototype and yield very satisfactory performance

Analysis, design and implementation of grid connected PV inverter system

Solar power holds great potential for the future in the realm of renewable energy. The solar energy has room for improvement, due to the low efficiency of the solar panels. It can be implemented everywhere from calculators, buildings, cars, etc. Solar energy is a field that has to be studied and continually researched until the maximum efficiency is reached. This project can help for further developments in photovoltaic system components. This thesis focused on the implementation and design of the components of a photovoltaic system. These components are the MPP tracker, different topologies of DC-DC converters and inverters connected to the grid. More specifically, the implementation of an MPP tracker algorithm, and boost converter was carried out at the end of this thesis. For the algorithm of the maximum power point tracker, the Perturb and Observe algorithm has been used. It is one of the most used algorithms due to its simplicity of its implementation with analogue and digital circuits. After the MPP tracker, the boost converter has been designed in relation to the objective of this project of feeding electricity to the grid. The boost converter will increase the voltage of the solar panel so then it can be transformed from DC to AC, and transformed with different controls synchronized to the grid

Verification Of Non-Isolated Lcc Resonant Full Bridge Dc-Dc Converter For Solar Photovoltaic Systems

Awareness about global warming and fasting depleting fossil fuels has intensified researcher’s interest toward exploration of renewable energy resources. Among these renewable resources, photovoltaic (solar energy) is getting more attention because of its potential to be the greatest contributor of electrical energy generation. Generally DC-DC converters are used to interface solar panels with inverter which converters dc power to ac. The function of dc-dc converter is basically to step up the low dc voltage to desired higher output voltage level. Conventional switch mode dc-dc converters have problems of high switching loss and EMI. Resonant converters on the other hand have low switching loss and EMI when they operate under ZVS conditions. The aim of this research work is to explore the feasibility of a non-isolated series-parallel resonant dc-dc converter for application in PV systems. Accordingly, the working action, analysis and design procedure of series-parallel resonant full-bridge dc-dc converter is described in detail. To evaluate the performance of converter both simulation and experimental studies are carried out. First of all, converter is simulated using LT-Spice to evaluate the capability of converter to step-up dc voltage from 30V to 300V. It is shown that converter can provide desired voltage gain both for nominal and light loads with theoretical maximum efficiency up to 94%. Finally a low power laboratory prototype of the converter is built to test and evaluate the performance of the converter. The experimental results show promising performance of the converter up to 88% efficiency at 75 kHz resonance frequency. Therefore, this converter is suitable for application in PV systems where galvanic isolation is not necessary

Analysis And Simulation Tools For Solar Array Power Systems

This dissertation presents simulation tools developed specifically for the design of solar array power systems. Contributions are made in several aspects of the system design phases, including solar source modeling, system simulation, and controller verification. A tool to automate the study of solar array configurations using general purpose circuit simulators has been developed based on the modeling of individual solar cells. Hierarchical structure of solar cell elements, including semiconductor properties, allows simulation of electrical properties as well as the evaluation of the impact of environmental conditions. A second developed tool provides a co-simulation platform with the capability to verify the performance of an actual digital controller implemented in programmable hardware such as a DSP processor, while the entire solar array including the DC-DC power converter is modeled in software algorithms running on a computer. This virtual plant allows developing and debugging code for the digital controller, and also to improve the control algorithm. One important task in solar arrays is to track the maximum power point on the array in order to maximize the power that can be delivered. Digital controllers implemented with programmable processors are particularly attractive for this task because sophisticated tracking algorithms can be implemented and revised when needed to optimize their performance. The proposed co-simulation tools are thus very valuable in developing and optimizing the control algorithm, before the system is built. Examples that demonstrate the effectiveness of the proposed methodologies are presented. The proposed simulation tools are also valuable in the design of multi-channel arrays. In the specific system that we have designed and tested, the control algorithm is implemented on a single digital signal processor. In each of the channels the maximum power point is tracked individually. In the prototype we built, off-the-shelf commercial DC-DC converters were utilized. At the end, the overall performance of the entire system was evaluated using solar array simulators capable of simulating various I-V characteristics, and also by using an electronic load. Experimental results are presented

Maximum Power Point Tracking Charge Controller for Standalone PV System

The depletion of conventional energy sources and global warming has raised worldwide awareness on the usage of renewable energy sources particularly solar photovoltaic (PV). Renewable energy sources are non-polluting sources which can meet energy demands without causing any environmental issues. For standalone PV systems, a low conversion efficiency of the solar panel and high installation cost due to storage elements are the two primary constraints that limit the widespread use of this system. As the size of the system increases, the demand for a highly efficient tracking and charging system is very crucial. Direct charging of battery with PV module will results in loss of capacity or premature battery degradation. Furthermore, most of the available energy generated by the PV module or array will be wasted if proper tracking technique is not employed. As a result, more PV panels need to be installed to provide the same output power capacity. This paper presents selection, design and simulation of maximum power point tracker (MPPT) and battery charge controller for standalone Photovoltaic (PV) system. Contributions are made in several aspects of the whole system, including selection of suitable converter, converter design, system simulation, and MPPT algorithm. The proposed system utilizes direct duty cycle technique thus simplifying its control structure. MPPT algorithm based on scanning approach has been applied by sweeping the duty cycle throughout the I-V curve to ensure continuous tracking of the maximum power irrespective of any environmental circumstances. For energy storage, lead acid battery is employed in this work. MATLAB/Simulink® was utilized for simulation studies. Results show that the propose strategy can track the MPPs and charge the battery effectively

An improved maximum power point tracking for PV system

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.Working very far from maximum power point diminishes the created power from photovoltaic (PV) system. It is therefore vital, in order to ensure ideal operating conditions, to constantly track the Maximum Power Point (MPP) of the PV panel array. However, this is not easy to identify, due to considerable changes in external influences and the nonlinear relationship of the electrical attributes of PV panels. Therefore, Maximum Power Point Tracking (MPPT) methods can be used to uphold the PV panel operating at its MPP. To date, a number of MPPT methods have been developed, ranging from the simple to the more complex, depending on the weather conditions and the control strategies employed. This current study offers a novel approach to augment the MPPT method for the PV system, based on the Lagrange Interpolation (LI) formula and the Particle Swarm Optimisation (PSO) method. The LI method is used initially to determine the optimum value of the duty cycle in the case of the MPP, according to the operating point. Starting from that point, the PSO method can then be used to search for the true Global Peak (GP). The proposed MPPT controller essentially initialises the particles surrounding the MPP, thereby providing the initial swarm with information concerning the most effective position. This has the ability to improve PSO efficiency and lead to a more rapid convergence, with zero steady-state oscillations. Additionally, there is no need to restrict particle velocity, as the initial values are closer to MPP. Thus, the proposed technique aims to increase efficiency without adding additional complexity, thereby substantially enhancing potential tracking speeds, while also reducing the steady-state oscillation (i.e. to practically zero) once the MPP is located. This offers a number of significant improvements over the conventional PSO method, in which new operating points are at too great a distance from MPP, and thus require additional iterations. The algorithm put forward in this work is verified with an OPAL-RT real time simulator and Matlab Simulink tool. A number of simulations are undertaken and compared to: (1) the Perturb and Observe (P&O) method; (2) the Incremental Conductance (IncCond) method; and (3) the PSO based algorithm. The simulation results indicate that the proposed algorithm can effectively enhance stability and fast tracking capability under fast-changing non-uniform insolation conditions

Single-Inductor, Dual-Input CCM Boost Converter for Multi-Junction PV Energy Harvesting

abstract: This thesis presents a power harvesting system combining energy from sub-cells of multi-junction photovoltaic (MJ-PV) cells. A dual-input, inductor time-sharing boost converter in continuous conduction mode (CCM) is proposed. A hysteresis inductor current regulation in designed to reduce cross regulation caused by inductor-sharing in CCM. A modified hill-climbing algorithm is implemented to achieve maximum power point tracking (MPPT). A dual-path architecture is implemented to provide a regulated 1.8V output. A proposed lossless current sensor monitors transient inductor current and a time-based power monitor is proposed to monitor PV power. The PV input provides power of 65mW. Measured results show that the peak efficiency achieved is around 85%. The power switches and control circuits are implemented in standard 0.18um CMOS process.Dissertation/ThesisMasters Thesis Engineering 201

Doctor of Philosophy

dissertationThree major catastrophic failures in photovoltaic (PV) arrays are ground-faults, line-to-line faults, and arc faults. Although the number of such failures is few, recent fire events on April 5, 2009, in Bakersfield, California, and April 16, 2011, in Mount Holly, North Carolina suggest the need for improvements in present fault detection and mitigation techniques, as well as amendments to existing codes and standards to avoid such accidents. A fault prediction and detection technique for PV arrays based on spread spectrum time domain reflectometry (SSTDR) has been proposed and was successfully implemented. Unlike other conventional techniques, SSTDR does not depend on the amplitude of the fault-current. Therefore, SSTDR can be used in the absence of solar irradiation as well. However, wide variation in impedance throughout different materials and interconnections makes fault locating more challenging than prediction/detection of faults. Another application of SSTDR in PV systems is the measurement of characteristic impedance of power components for condition monitoring purposes. Any characteristic variations in one component will simultaneously alter the operating conditions of other components in a closed-loop system, resulting in a shift in overall reliability profile. This interdependence makes the reliability of a converter a complex function of time and operating conditions. Details of this failure mode, mechanism, and effect analysis (FMMEA) have been developed. By knowing the present state of health and the remaining useful life (RUL) of a power converter, it is possible to reduce the maintenance cost for expensive high-power converters by facilitating a reliability centered maintenance (RCM) scheme. This research is a step forward toward power converter reliability analysis since the cumulative effect of multiple degraded components has been considered here for the first time in order to estimate reliability of a power converter