Cemal Keles

Disturbance rejection performance analyses of closed loop control systems by reference to disturbance ratio.

This study investigates disturbance rejection capacity of closed loop control systems by means of reference to disturbance ratio (RDR). The RDR analysis calculates the ratio of reference signal energy to disturbance signal energy at the system output and provides a quantitative evaluation of disturbance rejection performance of control systems on the bases of communication channel limitations. Essentially, RDR provides a straightforward analytical method for the comparison and improvement of implicit disturbance rejection capacity of closed loop control systems. Theoretical analyses demonstrate us that RDR of the negative feedback closed loop control systems are determined by energy spectral density of controller transfer function. In this manner, authors derived design criteria for specifications of disturbance rejection performances of PID and fractional order PID (FOPID) controller structures. RDR spectra are calculated for investigation of frequency dependence of disturbance rejection capacity and spectral RDR analyses are carried out for PID and FOPID controllers. For the validation of theoretical results, simulation examples are presented.

Opportunities for energy efficiency in smart cities

Rapid migration from rural to urban areas leads to the emergence of urbanization and sustainability problems. Management and monitoring of resources and infrastructures are getting more important today in crowded cities. Energy consumption is increasing with the growing population and intensified in highly populated parts of cities. This increased energy consumption results in high energy demand as well as the production of more pollutants and heat in these city parts. The management of pollution and heat problems leads to an additional energy demand. Therefore, energy efficiency is becoming central challenge for urban life similar to energy efficient structuring of living organisms. Practically, all activities arranging city life require energy. For instance, job activities, transportation, security, climate, catering, entertainment, commerce etc. In this study, we review active and passive approaches, which can be utilized for improvement of energy efficiency and thus sustainability of urbanization in todays cities. We give a discussion to present a vision for future smart cities in term of improvement of energy utilization and efficiency, and relieve of environmental issues. These approaches can be helpful for future cities for relieving issues originating from population increase.

A note on demand side load management by maximum power limited load shedding algorithm for smart grids

Demand side load management (DSLM) applications improve grid flexibility and support intermittent renewable energy utilization. In this study, we discuss role of power limited load shedding algorithm for DSLM applications in domestic scales. By using this algorithm, domestic power consumption is limited with respect to dynamic electricity price signal and renewable energy generation level by switching off the low prior home electronics appliances (HEAs). The proposed load shedding scheme performs depending on power requirements of HEAs and their user priority presetting. In this study, power limited load shedding algorithm is improved to consider operation modes, which are grid mode, islanded mode and grid+renewable energy (RE) mode and effects of the proposed scheme on domestic consumption is discussed by using simulation results.

Multi-source energy mixing by time rate multiple PWM for microgrids

Smart grid applications aims to employ many optimization and artificial intelligence methods for optimal energy management. Results of these algorithms need to be implemented by power systems in practice. This study presents Time Rate Multiple Pulse Width Modulation (TRM-PWM) methods for multi-source energy mixing for DC microgrids, which is integrating several renewable energy resources. In the paper, we implement TRM-PWM multi-source energy mixer component for integration of energy flow coming from solar and wind energy systems, battery system and grid in MATLAB simulink. Simulation results show that proposed energy mixer component can adjust rate of energy mixing from different sources. By using this component, optimal energy mixing, which can be adjusted by optimization and artificial intelligence methods, can be realized in smart grid applications.

Frequency deviation indicators for estimation of energy balance state in smart AC grids

Due to increasing intermittent renewable energy utilization in smart grids, smart management of energy balance is becoming major concern of research studies. In the case of highly volatile generation and demand conditions, it is very important to estimate instant energy balance state of electricity grid to preserve energy balance automatically and avoid from the cases of generation deficiency and overloading. The utility frequency deviation is commonly used to restore power imbalance in AC grids. This study gives a discussion on the utilization of frequency deviation of AC power system as an indicator of energy balance state in smart grids. We consider two approaches to estimate instant AC frequency deviation of power systems under serious harmonic and noise conditions. The first one is based on frequency to amplitude conversion technique, which use band-pass ramp filtering of AC signal. The other method is based on the sinusoidal to pulse waveform conversion, and it uses measurement of pulse periods of the resulting square waveforms. We compare these two methods and discuss their advantages and disadvantages to generate a balance error signal for smart grid applications. A brief discussion on application of these signals for smart grid energy management is given.

Multi-source energy mixing for renewable energy microgrids by particle swarm optimization

Distributed intelligence is one of the prominent prospects of future smart grids besides distributed generation, distributed storage and demand side load management. This study illustrates utilization of particle swarm optimization (PSO) method for cost-efficient energy management in multi-source renewable energy microgrids. PSO algorithm is used to find out optimal energy mixing rates that can minimize daily energy cost of a renewable microgrids under energy balance and anti-islanding constraints. The optimal energy mixing rates can be used by multi-pulse width modulation (M-PWM) energy mixer units. In our numerical analyses, we consider a multi-source renewable energy grid scenario that includes solar energy system, wind energy system, battery system and utility grid connection. We assume that variable energy pricing is used in utility grid to control energy dispatches between microgrids. This numerical analysis shows that the proposed scheme can adjust energy mixing rates for M-PWM energy mixers to achieve the cost-efficient and energy balanced management of microgrid under varying generation, demand and price conditions. The proposed method illustrates an implementation of distributed intelligence in smart grids.

Communication opportunities in smart grids

The studies concentrate on the new generation electric power systems called smart grid for solution of energy management issues. An essential characteristic of the smart grid is the integration of efficient, reliable and secure communication networks to manage the complex power systems. In this paper, the communication architectures in the power systems, including the communication technologies, network requirements, advantages and application challenges are studied. This study summarizes the current state of the communication networks in the smart grid.

Towards energy webs: Hierarchical tree topology for future smart grids

Digital era of technology transforms communication and information systems in a revolutionarily way, which makes our applications more integrated, more connected and smarter. However, conventional energy systems do not adequately benefit from opportunities of digital revolution, yet. Interdisciplinary works in the scope of smart grids grow our expectations from electricity grids such as increase of domestic renewable energy utilization, application of active load management in residences. One of challenging tasks for the digital era of energy systems is the transforming traditional static consumer concept to the active user concept, namely prosumers, who exhibit renewable energy generation potential and share own generation by the energy webs. A major problem for the implementation of practical energy webs is the management of energy balance in grid due to the fact that prosumers lead to the high uncertainty and volatility in generation and demand. Authors suggest that hierarchical tree topology as grid architecture can facilitate energy balance management and energy dispatching mechanisms for future energy webs. Because, acyclic structure and scalability of hierarchical tree (HT) topology present advantages of defining family relationships on the node hierarchy of grids. This property can improve accessibility and controllability of the smart grid and facilitates energy dispatches on the grid. This study gives a discussion on advantages of HT topology for smart grid applications and projects for some opportunities on the way of future energy webs.

Design of fractional-order PI controllers for disturbance rejection using RDR measure

Parameter uncertainties and unpredictable environmental disturbances reduce control performance of real control systems. For a robust control performance, stability and disturbance rejection are two main concerns that should be addressed in practical controller design problems. This paper presents an analysis to deal with system stability and disturbance rejection control for fractional-order PI (FOPI) controllers. Stability Boundary Locus (SBL) is calculated for an example with FOPI control system and Reference to Disturbance Rate (RDR) performance is investigated for the chosen stable FOPI designs from the stability region obtained using SBL. MATLAB/Simulink simulation examples are used to demonstrate stable and Disturbance Rejection Control (DRC) of FOPI control systems and presents comparisons for various designs of FOPI controllers.