Alireza Maheri

A Multivariable Optimal Energy Management Strategy for Standalone DC Microgrids

Due to substantial generation and demand fluctuations in standalone green microgrids, energy management strategies are becoming essential for the power sharing and voltage regulation purposes. The classical energy management strategies employ the maximum power point tracking (MPPT) algorithms and rely on batteries in case of possible excess or deficit of energy. However, in order to realize constant current-constant voltage (IU) charging regime and increase the life span of batteries, energy management strategies require being more flexible with the power curtailment feature. In this paper, a coordinated and multivariable energy management strategy is proposed that employs a wind turbine and a photovoltaic array of a standalone DC microgrid as controllable generators by adjusting the pitch angle and the switching duty cycles. The proposed strategy is developed as an online nonlinear model predictive control (NMPC) algorithm. Applying to a sample standalone dc microgrid, the developed controller realizes the IU regime for charging the battery bank. The variable load demands are also shared accurately between generators in proportion to their ratings. Moreover, the DC bus voltage is regulated within a predefined range, as a design parameter.

A critical evaluation of deterministic methods in size optimisation of reliable and cost effective standalone hybrid renewable energy systems

Abstract Reliability of a hybrid renewable energy system (HRES) strongly depends on various uncertainties affecting the amount of power produced by the system. In the design of systems subject to uncertainties, both deterministic and nondeterministic design approaches can be adopted. In a deterministic design approach, the designer considers the presence of uncertainties and incorporates them indirectly into the design by applying safety factors. It is assumed that, by employing suitable safety factors and considering worst-case-scenarios, reliable systems can be designed. In fact, the multi-objective optimisation problem with two objectives of reliability and cost is reduced to a single-objective optimisation problem with the objective of cost only. In this paper the competence of deterministic design methods in size optimisation of reliable standalone wind–PV–battery, wind–PV–diesel and wind–PV–battery–diesel configurations is examined. For each configuration, first, using different values of safety factors, the optimal size of the system components which minimises the system cost is found deterministically. Then, for each case, using a Monte Carlo simulation, the effect of safety factors on the reliability and the cost are investigated. In performing reliability analysis, several reliability measures, namely, unmet load, blackout durations (total, maximum and average) and mean time between failures are considered. It is shown that the traditional methods of considering the effect of uncertainties in deterministic designs such as design for an autonomy period and employing safety factors have either little or unpredictable impact on the actual reliability of the designed wind–PV–battery configuration. In the case of wind–PV–diesel and wind–PV–battery–diesel configurations it is shown that, while using a high-enough margin of safety in sizing diesel generator leads to reliable systems, the optimum value for this margin of safety leading to a cost-effective system cannot be quantified without employing probabilistic methods of analysis. It is also shown that deterministic cost analysis yields inaccurate results for all of the investigated configurations.

Wind Speed and Solar Irradiance Variation Simulation Using ARMA Models in Design of Hybrid Wind-PV- Battery System

The financial support by Synchron Technology Ltd. through co-funding of this project is gratefully acknowledged.

Acausal Modelling and Dynamic Simulation of the Standalone Wind-Solar Plant Using Modelica

In order to design model-based controllers applicable to hybrid renewable energy systems (HRES), it is essential to model the HRES mathematically. In this study, a standalone HRES, consisting of a photovoltaic (PV) array, a lead-acid battery bank, a pitch-controlled wind turbine, and a three-phase permanent magnet synchronous generator (PMSG), supplies a variable DC load demand through two boost- and buck-type DC-DC converters. It is shown that the mathematical model of the HRES can be represented by a system of nonlinear hybrid differential algebraic equations (hybrid DAEs). The developed model in this paper employs the Modelica language that allows object-oriented and acausal modelling of the multimode systems. The OpenModelica environment is utilised to compile the model and simulate the system. It is shown that the simulation provides a sufficiently accurate prediction of all the differential and algebraic states including mode transitions. The results of the simulation show a good match with the information available in the components datasheet.

An assessment of solar irradiance stochastic model for the UK

Hybrid Renewable Energy System (HRES) can effectively supply sustainable electrical energy in standalone remote areas. However, in order to design a reliable site and a robust controller, uncertainties in sustainable energy resources need to be modeled properly. This paper proposed a stochastic model of hourly solar irradiance for four locations across the UK. The goodness-of-fit of the proposed model has been evaluated using the Kolmogorov-Smirnov (K-S) test. The proposed model has been employed to simulate the amount of hourly solar irradiance for a location in the UK.

Performances of AC induction motors with different number of poles in urban electric cars

This paper presents the results of a study on the effect of the number of poles of AC induction motors (IM) on their performance in both propulsion and regenerative brake modes in eco-urban electric cars (EC). Since changing the number of poles affects the maximum motor speed, different transmission ratios are considered in modelling of the powertrain system. Two speed profiles, namely, normal and aggressive, are used in this study. Both profiles are based on the field data of a route in Kayseri-Turkey. For each configuration the total consumed energy of the EC is found. Results show that IM with 4 poles performs better than other configurations with respect to the cost and energy efficiency.

MODELLING AND SIMULATION OF STANDALONE SOLAR POWER SYSTEMS

In the design of the controllers of hybrid renewable energy system (HRES), the system dynamics and constraints need to be modelled and simulated in conjunction with the controller itself. This paper presents mathematical and equivalent electrical models taking into consideration all system dynamics and constraints for the solar branch of HRES. This branch consists of photovoltaic (PV) array, load and battery connected through a boost-type DC–DC converter. The probabilistic behaviour of the solar irradiance, which intrinsically includes the effect of cloud shading, and the dynamics of the battery are also modelled. The platform developed for dynamic simulation of the solar branch of HRES can be employed for design of DC–DC converter controllers as well as design of energy management systems.

Design of a single-DOF kinematic chain using hybrid GA-pattern search and sequential GA

With the aim of obtaining an optimal design for a single-DoF kinematic chain with the function of morphing aerofoils, two search methods are developed. The assessment criteria arethe length of the linkage and the accuracy of mapping. While the former is taken as the objective of optimization, the latter is treated as a constraint. The accuracy in mapping is measured by the aerodynamic performance deviation, a parameter defined by combining the geometric deviation and a weighting function based on the distribution of pressure coefficient. The first search method is based on a genetic algorithm (GA) with an embedded pattern search algorithm. The aim of the pattern search is to reduce the number of failed attempts in generating feasible solutions for the initial population of the GA as well as repairing infeasible individuals produced by reproduction operators. In the second search method, the set of design variables is determined in two consecutive steps by employing a sequential GA. Results of five runs of each search method reveal that while the best solution was produced by the sequential GA search method, hybrid GA-pattern search yielded more consistent results with shorter lengths and better mapping precision in average.

Effect of laminate configuration and shell-thickness variation on the inducted twist distribution in wind turbine adaptive blades

This paper presents an analytical model for predicting the dynamic characteristics of composite wind turbine blades. In this model, the governing equations of motion are derived using Hamiltions principle and are solved by using extended Galerkins method. This model is capable of predicting natural frequencies of composite beams with arbitrary single-cell cross sections. For various layup configurations, the results obtained by the developed analytical model are compared with the results of the finite element analysis. It is shown that the analytical model provides reasonable accuracy in predicting natural frequency of unbalanced layup configurations with ply angles of up to 40 degrees.

A comparative study of the performance of DC permanent magnet and AC induction motors in urban electric cars

This paper presents a comparative study of the performance of two types of electric motors used in eco-urban electric cars (EC). The power transmission system of an EC is modelled once with a DC permanent magnet (PM) and once with an AC induction motor (IM). In both cases the electric motors can operate in two modes: propulsion mode (motor) and regenerative brake mode (generator). Two standard velocity history profiles SFUDS and ECE-15 are used to model the dynamic of the car. It is shown that IM performs more effective than PM.