Arif I. Sarwat

Determination of the minimum-variance unbiased estimator for DC power-flow estimation

One of the most important features of the Smart Grid (SG) is real-time self-assessment which may threat that target power system stability. In order to improve robustness of power systems against such attacks, accurate estimation of the power system operation is required and conventional power flow methods should be upgraded. In this paper, we derive minimum variance unbiased estimators (MVUEs) for active power based on the voltage phase at each node of the power system. The state variables are the voltage phases and the received measurement signals are active power measurements. The proposed method is implemented on a four-bus test system. Three scenarios are defined to investigate the effect of covariance matrix topology on the estimation accuracy. The results shows that lower correlation between the noise vector elements leads to a more accurate estimation of power system operation.

A survey on security assessment of metering infrastructure in Smart Grid systems

Effective integration of renewable energy resources, energy management and better usage of the high voltage transmission system are major motivating forces for an improved electric grid regularly called the Smart Grid. Along with the soundless features of the Smart Grid, cyber security appears to be a serious issue because many electronic devices are connected via communication networks throughout critical power services, which has a direct impact on the reliability of such a common infrastructure. An assessment of cyber security topics in the Smart Grid is presented in this paper especially, security necessities of AMI, network vulnerabilities, attack countermeasures, secure communication protocols and architectures in the Smart Grid. Cyber-attacks against the power grid may aim to disrupt operations modifying or inserting messages. For example, malicious entities might change the set points at outstation devices, by pretending to be a master device at a control center, and cause instability in the grid. Satisfactory protection contains authenticating both the devices and control commands.

Artificial neural network based Duty Cycle estimation for maximum Power Point tracking in Photovoltaic systems

According to a nonlinear current-voltage characteristic of Photovoltaics (PV) we need to track maximum power output of PV generation units instantly. The aim of this paper is to introduce a non-complicated method for tracking the maximum Power Point without any previous knowledge of the physical parameters linked with a Grid-Connected photovoltaic (PV) system using artificial neural networks (ANN) modelling. The ANN is trained in various conditions of PV Output Voltage and PV Output Current to forecast the Duty Cycle of DC-DC boost converter as the MPPT device. The proposed technique is implemented in Matlab/Simulink and compared with the conventional method of incremental conductance. Simulation results show a good performance of the ANN based MPPT controller. MPPT techniques that properly detect the global MPP has been widely investigated in the literature. They include hill climbing (HC), incremental conductance (IncCond), perturb-and-observe (P&O), and fuzzy logic controller (FLC). As the best of our knowledge estimation of the duty cycle of the DC-DC boost converter by Artificial Neural Network and using it in place of the whole MPPT controller and using Voltage and current has not been done so far in the literature.

A New Topology of Higher Order Power Filter for Single-Phase Grid-Tied Voltage-Source Inverters

In order to reduce the influence of the grid harmonic currents and voltages, harmonic compensation is regularly implemented for a grid-tied inverter. In this study, a new topology of a higher order power filter for single-phase grid-tied voltage-source inverters, named L(LCL)2, is presented. The subscript is added to the name to prevent confusion with the LLCL filter. In the proposed design, the inverter side inductance is divided into three parts, and the grid side inductor is removed. Also, an additional resonant branch at the double of the switching frequency is added to the traditional LLCL filter to attenuate high-frequency harmonics. The overall inductance of the recommended filter is smaller than the LLCL filter. A comparative study and discussions on the subject of the traditional LLCL filter and the proposed L(LCL)2 filter have been conducted and assessed through an experimental hardware implementation on a 700 W, 120 V/60 Hz single-phase grid-tied inverter. Furthermore, a straightforward engineering design benchmark is suggested to discover parameters of the L(LCL)2 filter. Moreover, stability analysis, loss analysis and an optimization of the L(LCL)2 filter parameters have been conducted in this study. The analysis shows that in comparison with the LLCL filter, the L(LCL)2 filter not only has lower voltage drop and less total inductor size, but also has improved performance in decreasing high-order current harmonics.

Single-Stage Three-Phase AC–AC Matrix Converter for Inductive Power Transfer Systems

A direct three-phase ac-ac matrix converter for inductive power transfer (IPT) systems with soft-switching operation is introduced. The proposed topology is expected to have a high reliability and extended lifetime due to the soft-switching operation and elimination of short-life electrolytic capacitors. The soft-switching operation will also reduce switching stress, switching loss, and electromagnetic interference of the converter. A variable-frequency control strategy based on the energy-injection and free-oscillation technique is used to regulate the resonant current, the resonant voltage, and the output power. With the use of reverse-blocking switches, the proposed converter can be built with a reduced number of switches (only seven), which will consequently increase the reliability and efficiency and reduce the cost of the converter. The converter operates in eight modes, which are described in detail. With the use of the proposed converter as the primary converter, simulation analysis and experimental implementations on a case study IPT system show that the current regulation control method can fully regulate the output current and output power around user-defined reference values, thus making it suitable for dynamic IPT applications, where the system has inherent variations.

Frequency band for HAN and NAN communication in Smart Grid

Smart Grid metering and control applications require fast and secured two-way communication. IEEE 802.15.4 based ZigBee is one of the leading communication protocols for Advanced Metering Infrastructure (AMI). In North America, ZigBee supports two distinguished frequency bands - 915 MHz and 2.4 GHz. In Home Area Network (HAN) of AMI, home appliances communicate with smart meters whereas the communication among neighboring meters is termed as Neighborhood Area Network (NAN). In this study, optimum frequency bands for NAN and HAN communication have been proposed based on the throughput, reliability and scalability. We evaluated and compared the performance of bands 868/915 MHz and 2.4 GHz for AMI context. The solution also meets the requirements for Smart Grid communication standards as recommended by the US Department of Energy (DOE).

RSS based loop-free compass routing protocol for data communication in advanced metering infrastructure (AMI) of Smart Grid

Communication is the heart of the Smart Grid. Smart Grid metering and control applications require fast, reliable and secured two-way communication network. In this study, random signal strength (RSS) based localization of smart meters of Advanced Metering Infrastructure (AMI) has been proposed using the location information of meters whose position are known. Based on the location information, a loop free routing protocol has been developed. As a consequence, loop freedom, local routing decision and limited flooding, faster and reliable data transmission can be achieved.

Defending mechanisms for protecting power systems against intelligent attacks

The power system forms the backbone of a modern society, and its security is of paramount importance to nations economy. However, the power system is vulnerable to intelligent attacks by attackers who have enough knowledge of how the power system is operated, monitored and controlled. This paper proposes a game theoretic approach to explore and evaluate strategies for the defender to protect the power systems against such intelligent attacks. First, a risk assessment is presented to quantify the physical impacts inflicted by attacks. Based upon the results of the risk assessment, this paper represents the interactions between the attacker and the defender by extending the current zero-sum game model to more generalized game models for diverse assumptions concerning the attackers motivation. The attacker and defenders equilibrium strategies are attained by solving these game models. In addition, a numerical illustration is demonstrated to warrant the theoretical outcomes.

LAA-based LTE and ZigBee coexistence for unlicensed-band smart grid communications

The advent of smart grid introduces abundant number of smart meters which require bidirectional reliable communication. The deployment of advanced metering infrastructure (AMI) in smart grid networks will be auspicious if the existing infrastructure of LTE networks can be utilized. On the other hand, use of LTE infrastructure and spectrum by AMIs will further load the already congested broadband wireless networks. Recently, use of the unlicensed spectrum by the LTE technology is seen as a promising approach to offload the existing traffic from the licensed spectrum. In our study, we investigate the coexistence of LTE and ZigBee networks at the unlicensed frequency band of 2.4 GHz. We consider a time division duplexing (TDD)-LTE system accompanied by ZigBee network with FTP traffic model for system level simulations. The simulation results demonstrate that the simultaneous operation of LTE and ZigBee on the 2.4 GHz band reduces ZigBees performance, but still meets the data communication requirements for AMI as prescribed by Department of Energy (DoE).

Active/Reactive Power Control of Three Phase Grid Connected Current Source Boost Inverter Using Particle Swarm Optimization

PID control is the most common and simplest control method used for system control. However, selecting PID control coefficients for an optimal performance in power system applications is a central problem that few have addressed. Here, we propose the use of the particle swarm optimization (PSO) method to search for the optimal parameters of a PI controller. We applied this method to design an optimal PI controller for active and reactive power in a three phase grid connected current source boot inverter (CSBI). Simulation results show that our PSO-PI parameters selection method leads to better performance.