Survey Paper: A survey on the communication architectures in smart grid

A smart grid is a new form of electricity network with high fidelity power-flow control, self-healing, and energy reliability and energy security using digital communications and control technology. To upgrade an existing power grid into a smart grid, it requires significant dependence on intelligent and secure communication infrastructures. It requires security frameworks for distributed communications, pervasive computing and sensing technologies in smart grid. However, as many of the communication technologies currently recommended to use by a smart grid is vulnerable in cyber security, it could lead to unreliable system operations, causing unnecessary expenditure, even consequential disaster to both utilities and consumers. In this paper, we summarize the cyber security requirements and the possible vulnerabilities in smart grid communications and survey the current solutions on cyber security for smart grid communications.

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A Survey on Cyber Security for Smart Grid Communications

A system for dynamically managing and controlling distributed energy resources in a transmission/distribution power grid is disclosed. A plurality of regions within a transmission/distribution power grid is autonomously managed using regional control modules. Each regional control module oversees the management and control of the transmission/distribution power grid and is further associated with a plurality of local control modules that interface with distributed energy resources within a region. Power production and power consumption are monitored and analyzed by the enterprise control module which, upon determining that power consumption within a region does not match power producing capability, dynamically reallocates distributed energy resources throughout the grid keeping the system balance. Power flow at key nodes within the network are monitored and analyzed by the local control modules, regional control modules, and enterprise control modules with compensating actions taken in the event that system parameter risks violating safety, stability, or operational thresholds.

Dynamic Distributed Power Grid Control System

The concept of microgrid hierarchical control is presented recently. In this paper, a hierarchical scheme is proposed which includes primary and secondary control levels. The primary level comprises distributed generators (DGs) local controllers. The local controllers mainly consist of power, voltage and current controllers, and virtual impedance control loop. The central secondary controller is designed to manage the compensation of voltage unbalance at the point of common coupling (PCC) in an islanded microgrid. Unbalance compensation is achieved by sending proper control signals to the DGs local controllers. The design procedure of the control system is discussed in detail and the simulation results are presented. The results show the effectiveness of the proposed control structure in compensating the voltage unbalance.

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Secondary Control Scheme for Voltage Unbalance Compensation in an Islanded Droop-Controlled Microgrid

The paper describes the solution of an optimal power flow (OPF) problem in rectangular form by an interior-point method (IPM) for nonlinear programming. Some OPF variants when formulated in rectangular form have quadratic objective and quadratic constraints. Such quadratic features allow for ease of matrix setup, and inexpensive incorporation of higher-order information in a predictor-corrector procedure that generally improves IPM performance. The mathematical development of the IPM in the paper is based on a general nonlinear programming problem. Issues in implementation to solve the rectangular OPF are discussed. Computational tests apply the IPM to both the rectangular and polar OPF versions. Test results show that both algorithms perform extremely well.

An interior-point method for nonlinear optimal power flow using voltage rectangular coordinates

Existing and forthcoming devices at the residential level have the ability to provide reactive power support. Inverters which connect distributed generation such as solar panels and pluggable hybrid electric vehicles (PHEVs) to the grid are an example. Such devices are not currently utilized by the power system. We investigate the integration of these end-user reactive-power-capable devices to provide voltage support to the grid via a secure communications infrastructure. We determine effective locations in the transmission system and show how reactive power resources connected at those buses can be controlled. Buses belong to reactive support groups which parallel the regions of the secure communications architecture that is presented. Ultimately, our goal is to present how the smart grid can enable the utilization of available end-user devices as a resource to mitigate power system problems such as voltage collapse.

An Authenticated Control Framework for Distributed Voltage Support on the Smart Grid

The introduction of remotely controlled network devices is transforming the way the power system is operated and studied. The ability to provide real and reactive power support can be achieved at the end-user level. In this paper, a framework and algorithm to coordinate this type of end-user control is presented. The algorithm is based on a layered architecture that would follow a chain of command from the top layer (transmission grid) to the bottom layer (distribution grid). At the distribution grid layer, certain local problems can be solved without the intervention of the top layers. A reactive load control optimization algorithm to improve the voltage profile in distribution grid is presented. The framework presented in this paper integrates agent-based technologies to manage the data and control actions required to operate this type of architecture.

A Control Framework for the Smart Grid for Voltage Support Using Agent-Based Technologies

This paper develops a method for reliably determining the set of low-voltage solutions which are closest to the operable power flow solution These solutions are often used in conjunction with techniques such as energy methods and the voltage instability proximity index for assessing power system voltage stability This paper presents an algorithm which provides good initial guesses for these solutions The results are demonstrated on a small power system and on larger power systems with up to 2000 buses

Effective calculation of power system low-voltage solutions

The size and complexity of the intercon- nected power grid pose significant challenges to system operators. The requirement of rapid response under di- verse conditions in a highly complex environment under- scores the need for tools that can help operators detect potential problems and identify solutions quickly and accurately. This paper discusses the design, development, and deployment of a software application that attempts to address this need. The software illustrates system condi- tions on a geographic map of the interconnection using a variety of innovative visualization techniques that help the application convey the current state of the system in a clear, unambiguous, and engaging way. This paper dis- cusses the architecture of the application, the benefits, design, and implementation of each of its visualization tools, guidelines for designing displays that take maximum advantage of the platform's strengths, and planned future enhancements. It also emphasizes a key ingredient to the success of the application: seeking and responding to the ideas and needs of the operators who depend on the plat- form for the information they require to operate the power system. Several figures are included that demon- strate the types of displays currently being shown in the control room.

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An advanced visualization platform for real-time power system operations

By reporting time-synchronized phasor magnitudes and phase angles at rates at or above the system frequency, phasor measurement units promise to dramatically increase our ability to understand both historical and real-time power system conditions. This new information does not come without a cost, however, and one potential barrier to the effective utilization of this new data source is the increased amount of information transmission and storage capability these devices require. One way to mitigate the increased storage requirements of synchrophasor data is to compress the data, although this compression should not come at the cost of reduced accuracy. This paper proposes a new method for the lossless compression of voltage magnitude and phase data in which known characteristics of the power system are used to improve upon common, off-the-shelf compression techniques. The method is evaluated with real and simulated PMU data to show its effectiveness.

R.P. Klump

Papers

An Authenticated Control Framework for Distributed Voltage Support on the Smart Grid

A Control Framework for the Smart Grid for Voltage Support Using Agent-Based Technologies

Effective calculation of power system low-voltage solutions

An advanced visualization platform for real-time power system operations

Lossless compression of synchronized phasor measurements