Chee Wei Tan

A study of maximum power point tracking algorithms for stand-alone Photovoltaic Systems

The Photovoltaic (PV) energy is one of the renewable energies that attracts attention of researchers in the recent decades. Since the conversion efficiency of PV arrays is very low, it requires maximum power point tracking (MPPT) control techniques to extract the maximum available power from PV arrays. In this paper, two categories of MPPT algorithms, namely indirect and direct methods are discussed. In addition to that, the advantages and disadvantages of each MPPT algorithm are reviewed. Simulations of PV modules were also performed using Perturb and Observe algorithm and Fuzzy Logic controller. The simulation results produced by the two algorithms are compared with the expected results generated by Solarex MSX60 PV modules. Besides that, the P-V characteristics of PV arrays under partial shaded conditions are discussed in the last section.

A study of maximum power point tracking algorithms for wind energy system

This paper reviews and studies the state-of the-art of available maximum power point tracking (MPPT) algorithms. Due to the nature of the wind that is instantaneously changing, hence, there is only one optimal generator speed is desirable at one time that ensures the maximum energy is harvested from the available wind. Therefore, it is essential to include a controller that is able to track the maximum peak regardless of any wind speed. The available maximum power point tracking (MPPT) algorithms can be classified according to the control variable, namely with and without sensor, and also the technique used to locate the maximum peak. A comparison has been made on the performance of the selected MPPT algorithms on the basis of various speed responses and the ability to achieve the maximum energy yield. The tracking performance is performed by simulating wind energy system using MATLAB/Simulink simulation package. Besides that, a brief and critical discussion is made on the differences of available MPPT algorithms for wind energy system. Finally, a conclusion is drawn.

An Improved Maximum Power Point Tracking Algorithm with Current-Mode Control for Photovoltaic Applications

An improved perturb-and-observe maximum power point tracking algorithm is presented that incorporates a current compensated converter. In order to achieve fast response and accurate holding of the maximum photovoltaic (PV) power under changing environmental conditions, a variable perturbation step size is adopted. In addition, a control parameter alpha, is introduced to enhance the tracking sensitivity during abrupt changes of environmental conditions. Instead of directly perturbing the switch duty-cycle, the system operates on the current reference of an inner controller that regulates the PV current. The effects of different values of fixed and variable step sizes are assessed through simulation and the results described. The performance of the new MPPT controller was simulated using the PLECS extension to Simulink

Analysis of perturb and observe maximum power point tracking algorithm for photovoltaic applications

This paper highlights the compromises between good steady-state accuracy and the speed of convergence in Perturb and Observe (P&O) maximum power point tracking (MPPT) algorithm. Three fixed step-sizes and a variable step-size have been defined as the perturbation step-sizes and the effect of applying different step-sizes for P&O algorithm are discussed. The perturbation step-sizes have been simulated using Matlab/Simulink and the maximum power tracking efficiency for each step-size is analysed. These step-sizes have been experimentally tested using a PV illumination test rig to emulate rapid changes in shadow effect on a PV panel. The fixed step-sizes are tested using a direct duty-cycle control boost converter while the variable step-size is examined by applying current-mode controlled boost converter. It is concluded that the application of fixed perturbation step-size has a limitation in performing MPPT while a variable step-size is necessary to balance the competing aims of speed and accuracy.

A review of recent development in smart grid and micro-grid laboratories

In recent decades, smart grid have become increasingly attractive to both energy producers and consumers. Amongst the main challenges for the successful realization of smart grid includes the integration of renewable energy resources, real time demand response and management of intermittent energy resources. Apart from smart grid, the development of micro-grids should take into consideration of issues such as the system performance, modeling, monitoring and controlling of the micro-grids. In particular, the recent advancements in information and communication technologies (ICTs) could facilitate the effective development of the future micro-grid system. This paper presents an overview of smart grids features and highlights the recent development of micro-grid laboratories in Europe, US and Japan.

A current-mode controlled maximum power point tracking converter for building integrated photovoltaics

This paper presents a current-mode controlled maximum power point tracking (MPPT) converter and BIPV design considerations covering the photovoltaic orientation and tilt angle. An MPPT algorithm featuring rapid convergence and steady-state accuracy is described. The power tracking performance of the proposed MPPT converter has been experimentally verified. The experimental test rig consists of a 65 W multi-crystalline PV panel with controllable illumination to emulate the changes of solar irradiance. The test rig is fitted with a FPGA-DSP controlled rapid prototyping platform for power conditioning. The current-mode control method provides better transient performance than directly perturb the duty-cycle of the converter. A step-size varies in response to the former approach and previous error ensures rapid accurate tracking following shadow effects of clouds or obstructions. The experimental results show that the proposed MPPT converter is capable of reaching the steady-state condition quickly during a transient with negligible oscillations and tracking under dynamic changes of solar irradiance efficiently.

A Stochastic Simulation of Battery Sizing for Demand Shifting and Uninterruptible Power Supply Facility

This paper presents a stochastic simulation using Monte Carlo technique to size a battery to meet dual objectives of demand shift at peak tariff times and outage protection (an uninterruptible power supply function) for commercial buildings. Both functions require battery storage and the sizing of battery using numerical optimization is popularly used. However, outage and demand peaks are not of deterministic nature or location. A given battery size can only offer a particular probability of surviving an outage or completing a demand shift, this offers an opportunity to battery sizing using stochastic methods. In this work, the Monte Carlo method takes into account the historical outage statistics and building load profiles. Further, it describes the life-cycle cost of the system and the ratio of saving and investment for ten cases of demand shifting. It also reports on the customer outage costs which were calculated based on a weekday load profile for different outage durations. By considering the statistics of both problems together, customers can assess the risk of not being able to survive in an outage and the success rate of meeting the demand shift capability based on the results of the proposed method.

Control of a bidirectional converter to interface ultracapacitor with renewable energy sources

This paper highlights the controller of a bidirectional converter to interface an ultracapacitor as storage device to renewable energy systems. Ultracapacitors are typically used in renewable energy systems to improve the systems reliability and energy conversion efficiency. The controller of the converter system has been designed and simulated based on the integration of both Current Mode Control and Linear Quadratic Regulator methods. The controller performance is tested under different modes of operating conditions in bidirectional converter using MATLAB/Simulink simulation package. The simulation results show that a good DC bus voltage regulation is achieved in the tested conditions. In addition to that, the controller ensures smooth transition between the buck and boost modes of the bidirectional converter operation.

A review of power and energy management strategies in electric vehicles

This paper reviews state-of-art on power and energy management strategies in hybrid electric vehicle and fully electric vehicle. Generally, there are two layer control strategies, namely the low level component control and the high level supervisory control. Management and control strategy of electric vehicles require careful design considerations because it involves multiple energy sources and storage. This would ensure that the energy storage system is managed and used at the optimum level which would ultimately contribute to system cost reduction. The overall electric vehicle performance and fuel efficiency is typically controlled by high level supervisory control algorithm that consists of event-based or time-based conditions. In short, the management of sources and control strategies used in electric vehicles should also take into account other associated factors, such as the vehicle size, purpose, operation area of vehicle, environment and weather.

Techno-economic analysis of hybrid photovoltaic/diesel/battery off-grid system in northern Nigeria

The rate of dependence on stand-alone diesel generator for individual electricity generation among households in Nigeria is geometrically increasing and has thus led to significant increase of the environment pollution. This is due to the inability of the utility company to meet the energy demand of its yearning consumers due to ageing and limitations in power infrastructures. This has led to about 40% of the countrys population been cut off from the national grid. In view of these hazardous effects posed from the usage of these individual diesel-powered generations, this paper reports on the assessment of techno-economic viability of a hybrid photovoltaic diesel/battery off-grid system as an alternative solution to these threats. For that purpose, a remote area located far in the northern part of Nigeria was taken as the case study in which an international institution with peak demand of 90 kW was considered. The HOMER optimization software is used to evaluate both the technical and economic viability of the proposed energy system by taking into account the variations of both the solar radiation and diesel prices, as experienced in most part of Nigeria. The study reveals the potential capability of the hybrid photovoltaic/diesel energy system with battery backup as a good alternative energy source for individual household replacement for diesel-powered generator. In addition, the proposed system is of high energy potential as well as low carbon emission at affordable cost of electricity.