Shujun Xin

Emission-Concerned Wind-EV Coordination on the Transmission Grid Side With Network Constraints: Concept and Case Study

This paper presents a study of emission-concerned wind-electric vehicle (EV) coordination on the transmission grid side. An aggregator model representing a cluster of controllable EVs is proposed, and is coordinated with large-scale wind power on the transmission side. Using these EV aggregators, a conceptual framework is developed for wind-EV coordination, based on a three-level hierarchy. At the top level, the control center determines the optimal plant outputs and EV charging strategies from the proposed wind-EV dispatch model, where emission costs, thermal plant generation, controllable EVs, and CO2 capture power plants are taken into account and set as multi-objectives. The time-varying number of EV connections, plant ramp rate limits, and network constraints, including interface and branch transmission capacities, are also considered in the model. The model is used to verify the benefits of wind-EV coordination in an IEEE 14-bus system. Compared with uncoordinated charging, wind curtailment, emissions, total optimized cost, and EV charging fees are all greatly reduced by coordination. Moreover, interface transmission capacity and discharging price are found to be important factors in coordination, and the impacts are investigated.

Cyber-Physical Modeling and Cyber-Contingency Assessment of Hierarchical Control Systems

Online closed-loop hierarchical control systems (HCSs) are widely used in power-system operation. Like typical cyber-physical systems, the contingencies on the cyber side of an HCS may lead to inappropriate control commands, which will influence the physical power system. To evaluate the degree to which these inappropriate control commands influence the power system, we propose a cyber-physical equivalent model for HCSs. In this model, the HCS cyber network is abstracted to a directed graph consisting of data nodes and directed branches, and connectivity is described by using a node-branch incidence matrix. Using this strategy, we can describe the general information flow in an HCS using mathematical equations on the basis of which quantitative evaluation can be carried out. Furthermore, by using existing operation records, several kinds of typical cyber-contingencies are also modeled on the basis of which cyber-contingency assessment (cyber-CA) can be implemented by using a model-based approach. Considering the computational efficiency, such an approach keeps only key characteristics of the information flow rather than all features of the cyber network. In the case study, a coordinated secondary-voltage control system is studied as an example. The physical impacts of various cyber-contingencies on different data transmission and processing modules are compared. The results show that the model-based method provides improved efficiency compared with conventional simulation-based methods while maintaining accuracy.

A New Real-Time Smart-Charging Method Considering Expected Electric Vehicle Fleet Connections

This letter presents a real-time electric vehicle (EV) smart-charging method (N-RT), that not only considers currently connected EVs, but also uses a prediction of the EVs that are expected to plug in in the future. Numerical tests show that the N-RT method improves valley-filling under various levels of prediction accuracy.

Information-Energy Flow Computation and Cyber-Physical Sensitivity Analysis for Power Systems

Power systems are the typical cyber-physical systems in which the closed-loop hierarchical control systems (HCSs) are widely used to ensure their stable and safe operation. To describe the coupling operation mechanism of an HCS and power grid by expanding current steady-state power flow analysis theory, we propose an information-energy flow model and develop a matrix-based computational approach. With the help of the methods, we can directly calculate the mutual influence of the cyber and physical parts. Since the mechanism of power flow computation is mature, we focus on the cyber side, proposing an information-flow-oriented network model as well as a matrix-based computation method for its information flow. In particular, we develop a minimum-cut-set-based partition and equivalence method to address a complex cyber network with non-linearity issues associated with data processing. Subsequently, we discuss cyber-physical sensitivity and vulnerability issues. In the case study, we calculate the information-energy flow of an IEEE 14-node system with real time-voltage stability monitoring and control application and compare the results with simulation results. The similarity of the results between the two methods verifies the effectiveness of our approach.

Information Masking Theory for Data Protection in Future Cloud-based Energy Management

Implementation of advanced information and communication technologies upgrades energy management systems (EMSs) by allowing more participants and improving the control ability, in which cloud-based service plays an essential role. However, its information exchange also raises concern about information safety and privacy. To overcome this challenge, we propose the mechanism of information masking (IM), which helps to hide the original information by transforming it to another form. In the main body, we first review the basic theory of IM. Then, we introduce three typical scenarios for cloud-based EMSs [i.e., home/building EMS (for end users), aggregated load/generation management (for aggregated loads), and coordinated dispatch (for multi-regional power systems)], then analyze and compare their IM requirements. After discussing the IM design rules for two general requirements, we discuss IM algorithms for the three scenarios and study three typical cases to verify the feasibility and effectiveness of the IM approaches. The results show that the proposed IM approaches successfully hide all the targeted information while leading to only minor increases in computation cost and matrix sparsity.

Cyber-physical assessment and comparison between centralized and distributed control mode in coordinated substation voltage control

The smart grid is a typical cyber-physical system (CPS) utilizing more advanced information and communication technologies (ICTs), in which hierarchical control system (HCS) plays an essential role. However, it should be noted that for the same control function, HCSs could have multiple modes for making control decisions. They may have different cyber structures and information flows, which could lead to different levels of system reliability under cyber contingency conditions. In this paper, we describe and compare two control modes of coordinated substation voltage control (CSVC), the centralized-control and distributed-execute (CCDE) mode and the distributed mode of centralized-coordinate and distributed-control (CCDC). We first introduce CSVCs control theory, as well as its two application modes. After generating quantitative node-branch cyber-physical models for each, we perform a cyber contingency assessment and compare the results. The computation result shows that distributed mode CCDC is more reliable against cyber contingencies. By comparing their cyber networks, we identify three possible reasons for their differences and propose a simple improvement plan for CCDC, which has proved to be helpful by cyber contingency assessment results.

A V2G prototype system: Design, field test and discussion

To better apply the researches on V2G technology, this paper designs a V2G prototype system in a client/server architecture, which includes an energy management server and smart charging pole. The server consists of a data processing module, a database, and a Man-Machine interface. The smart charging pole is composed of charging device and charging pole control system (CPCS), where a P-Q controlling method is developed for accurately adjusting charging power. Afterwards, a field-test as well as four aspects of the results are described and analyzed, which verifies that V2G system can respond to charging/discharging requirements quickly and accurately.