Reduan H. Khan

Review Article: A comprehensive review of the application characteristics and traffic requirements of a smart grid communications network

A robust communication infrastructure is the touchstone of a smart grid that differentiates it from the conventional electrical grid by transforming it into an intelligent and adaptive energy delivery network. To cope with the rising penetration of renewable energy sources and expected widespread adoption of electric vehicles, the future smart grid needs to implement efficient monitoring and control technologies to improve its operational efficiency. However, the legacy communication infrastructures in the existing grid are quite insufficient, if not incapable of meeting the diverse communication requirements of the smart grid. Therefore, utilities from all over the world are now facing the key challenge of finding the most appropriate technology that can satisfy their future communication needs. In order to properly assess the vast landscape of available communication technologies, architectures and protocols, it is very important to acquire detailed knowledge about the current and prospective applications of the smart grid. With a view to addressing this critical issue, this paper offers an in depth review on the application characteristics and traffic requirements of several emerging smart grid applications and highlights some of the key research challenges present in this arena.

Multiterminal Hybrid Protection of Microgrids Over Wireless Communications Network

Communications network plays a key role in the next-generation microgrid protection schemes, as the protective relays need to communicate with each other to dynamically track their tripping currents due to the time-varying nature of the loads and the distributed generation (DG) outputs. Hence, communications cost and reliability are some of the key factors that need to be considered before deploying a microgrid protection scheme. In this paper, we introduce the concept of a hybrid microgrid protection system, which implements traditional differential protection scheme along with an adaptive microgrid protection scheme. While the differential scheme is more sensitive, yet relies on extensive communications, the adaptive scheme is less sensitive but has low communications load. The joint deployment of these two schemes has the potential to increase the accuracy and precision of the whole protection scheme, while reducing the overall communications cost. Moreover, we propose a preemptive switching algorithm for the microgrid relays, which ensures a seamless transition from differential protection to adaptive protection based on the bit error rate of the communications links. Some illustrative results are provided based on an IEEE 802.16/WiMAX network to justify the proposed hybrid protection scheme.

A heterogeneous WiMAX-WLAN network for AMI communications in the smart grid

The unique characteristics of advanced metering infrastructure (AMI) communications such as large number of devices, small data burst transmission, high reliability and variable propagation conditions require a robust communication network to serve them in an efficient and scalable manner. Being the two promising technologies of the next generation wireless networks, the synergic operation of WiMAX and WLAN can significantly improve the cost and efficiency of an AMI network by extending transmission range, improving link quality and allowing flexible data aggregation to reduce signalling and protocol overheads. In this paper, we provide some of our initial studies on a WiMAX-WLAN heterogeneous network (Hetnet) architecture for AMI communications in the smart grid. Using a basic numerical analysis and discrete event simulation models based on OPNET, we compare the behaviour and performance of a WiMAX-WLAN Hetnet with a standalone WiMAX network. The results indicate that the Hetnet provides a significant performance edge over the standalone network in terms of capacity, coverage and latency.

Wide area PMU communication over a WiMAX network in the smart grid

One of the key building blocks of the future smart grid is a wide area monitoring and control (WAMC) system that continuously monitors the health of the grid using the phasor measurement units (PMUs). Measurements from the PMUs are strictly delay-sensitive since they act as the triggering points for the underlying protection and control systems. This paper presents a detailed performance analysis of a wide area PMU communications system over a WiMAX/IEEE 802.16 network in the smart grid. It defines the basic application models and traffic requirements of a PMU communications system and maps them over the unsolicited grant service (UGS), real-time polling service (rtPS) and best-effort (BE) scheduling services of the IEEE 802.16 standard. Using a discrete event simulation model based on the OPNET simulation package, the paper evaluates the performance of these scheduling services in terms of delay, uplink data usage and signaling overheads. The results indicate that while the UGS performs best among the scheduling services, it consumes a significant amount of radio resources to achieve a tighter delay bound.

A predictive road traffic management system based on vehicular ad-hoc network

With an increasing number of vehicles on the road, demand for intelligent transportation systems is on the rise. In this paper, we present a predictive road traffic management system (PRTMS) based on the Vehicular Ad-hoc Network (VANET) architecture. The proposed PRTMS uses a novel communications scheme to estimate the future traffic intensities at different intersections based on a modified linear prediction algorithm. Based on the prediction, a central controller reduces the congestion level by re-routing the vehicles and adaptively changing the signaling cycles. An IEEE 802.11p based vehicle to-infrastructure communications system is used to collect trip information and transmit control signals to enforce multi-junction traffic flow control. Simulations are conducted using an integrated OPNET model comprised of road infrastructure, vehicular mobility management and communications networking to jointly examine the performances of the proposed PRTMS and the VANET. The results indicate that the proposed scheme provides a significant performance improvement in terms of total journey time and waiting time of the vehicles. In addition, the performance of the prediction algorithm is also investigated.

An adaptive RRM scheme for smart grid M2M applications over a WiMAX network

This paper presents an adaptive radio resource management (RRM) scheme to meet the diverse QoS requirements of bursty machine-to-machine (M2M) applications in the Smart Grid. The key features of the proposed RRM scheme include a differentiated random access scheme based on the virtual ranging channel (VRC) concept; a dynamic rangingcode allocation scheme to ensure an efficient utilization of the random access resources; and a prioritized grant allocation scheme to meet the delay bounds of the time critical data-packets. The performance of the proposed RRM scheme is demonstrated using an OPNET simulation model, and benchmarked against the conventional scheme.

Differential protection of microgrids over a WiMAX network

One of the widely used methods for protecting power system elements is the Line Current Differential Protection (LCDP) schemes that works by comparing the vector difference between the measured currents at two or more line-terminals. Communications network plays a vital role in such schemes since the local and the remote line-terminals must exchange their current elements to perform the differential calculation. This paper investigates the use of an IEEE 802.16/WiMAX based wide-area wireless communications network to support LCDP schemes in the smart microgrids. The possible use of the WiMAX network as a synchronization source to the differential relays is also proposed. Using theoretical capacity analysis, the paper examines the use of advanced WiMAX features such as persistent scheduling, robust header compression and grant synchronization to efficiently support such a scheme. In addition, simulations were conducted using an OPNET simulation model to analyze the communications performance of the scheme in terms of packet-loss and delay. The results indicate that a WiMAX network along with its advanced features is particularly well-suited to meet the challenging requirements of a differential protection scheme.

An enhanced random access mechanism for Smart Grid M2M communications in WiMAX networks

Random access is being considered as one of the key bottlenecks for supporting machine-to-machine (M2M) communications over an IEEE 802.16-based WiMAX network. Apart from handling massive access attempts from a large number of devices, the random access plane requires service differentiation capability to meet the diverse QoS requirements of various M2M applications. To address these issues, in this paper, we propose an enhanced random access scheme, where the fixed/low-mobility M2M devices pre-equalize their random access codes using the estimated frequency response of the slowly-varying wireless channel. Consequently, the base station is able to detect a large number of codes as their mutual orthogonality remains preserved. Moreover, a differentiated random access strategy is proposed to provide QoS-aware access service to various M2M devices. The performance of the proposed scheme is demonstrated under two different code matrices using both theoretical analysis and simulation results.

A network controlled load management scheme for domestic charging of electric vehicles

This paper proposes a end-to-end load management scheme for domestic charging of electric vehicles (EVs) based on the bidirectional communication capabilities of the smart grid. In particular, the paper considers the case of using EV fleets for night-time valley-filling of the daily load curve. The novel concept of discontinuous EV charging based on small energy bursts is introduced that utilizes the benefit of the statistical multiplexing to accommodate higher number of vehicles and to provide differentiated energy supply against a variable energy-budget within a pre-defined time. The paper also suggests two energy scheduling algorithms to ensure priority and/or fairness among the contending vehicles. A wide-area smart grid communications network based on WiMAX technology has been used as a proof of concept for this study. Simulations are conducted using an integrated OPNET model to jointly examine the performances of the energy scheduling algorithms and the communications network for a large-scale EV charging system. The results show that the proposed scheme can efficiently support the EV charging load in an equitable manner with a very low communications overhead.

A novel WiMAX ranging scheme for periodic M2M applications in smart grid

In a smart grid environment, a WiMAX network has to support a large number of machine-to-machine (M2M) applications with diverse bandwidth, latency and network entry requirements. While M2M devices like smart meters and time-triggered sensors will periodically perform network re-entry to send data, a large number of event driven sensors might initiate network entry procedures simultaneously after an event. Without mechanisms to handle such a large number of network access requests, the entire ranging channel could be congested degrading the performance of the whole network. In this paper a novel ranging scheme is proposed that can provide contention free network access to the periodic M2M applications in a smart grid. We first evaluate the performance of the existing WiMAX ranging channel in terms of random access success rate, access delay and access throughput using a discrete event simulation model based on OPNET Modeler v16.0. The results indicate that at high random access loads, the access success rate drops sharply and the mean access delay increases exponentially. We then simulate a smart grid event where the underlying WiMAX network faces a heavy random access load and show that the proposed scheme is able to provide better performance in comparison to that of the conventional ranging scheme.