Guest Editorial: Cyber Physical Power Systems: Advanced Intelligent Technologies and Applications

With the increased adoption of information and communication technologies (ICTs) and cyber and internet technologies, power systems are rapidly evolving into Cyber-Physical Power Systems (CPPS). CPPS are emerging technologies, with growing significant academic, industrial and societal impacts. Research into CPPS needs deep integration of smart electric power grid and new information systems, and consideration must be paid to the tight coupling between cyber, networking, communication and physical systems. To this end, the interdependency of the power system and its associated cyber properties should be investigated. Advanced intelligent technologies must be developed to deal with frontier challenges arising from multiple energy resources, multiple timescales, the presence of uncertainty, the existence of reliability concerns and the security issues related to modernised power systems. It is expected that these intelligent technologies can improve power system performance in terms of security, efficiency, reliability and, make a strong economic impact. Seven papers were accepted for this Special Issue and brief introductions of them are provided below. ‘Developing correlation indices to identify coordinated cyberattacks on power grids’, by Christian Moya and Jiankang Wang, studies coordinated cyber-attacks from the correlation indices on static control applications. The proposed indices improve attack identification, e.g., measurement attacks. Compared with existing approaches, the proposed method is deductive and able to detect sophisticated attacks without simulating a large number of attack events. A case study on the New England 39 bus system demonstrates the effectiveness of this method. ‘Electromagnetic torque analysis-based method for performance evaluation and optimisation of closed-loop CPS regarding small signal stability’, by Yibiao Sheng, Tao Lin, Rusi Chen, et al. presents a new method to explore the influence of wide-area damping control parameters and time delays for cyber-physical power system from a small signal stability viewpoint. An electromagnetic torque analysis (ETA) method is established to facilitate this stability study. The authors analyse the effectiveness and advantages of the proposed method using a two-area fourmachine system. ‘Market-based generator cost functions for power system test cases’, by Venkat Durvasulu and Timothy M. Hansen proposes a novel method to design generator cost functions to emulate existing market costs for power system test cases. This paper classifies real market generator offers from an independent system operator organised electricity market into generator types. By using the new market-based generator cost functions, power system simulation studies will better represent actual economic impacts. ‘Predictive control model to manage power flow on a hybrid wind-photovoltaic and diesel microgeneration power plant with additional storage capacity’ by António José Arsénio dos Santos Costa, Duarte Valério and Paulo José da Costa Branco is aimed at using model predictive control (MPC) approach for management of the power flow in a hybrid microgeneration power plant with additional storage capacity. The objectives of MPC are to maximise the use of power from renewable resources and to maximise the duration of lithium ion batteries. MPC is proven to be a suitable strategy for management of power flow dispatch on hybrid power generation plants with renewable resources. ‘Swarm-based automation of electrical power distribution and transmission system support’, by Stefan Dähling, Sonja Kolen, and Antonello Monti presents SwarmGrid-X, an agent-based control concept that considers the structure, demands and capabilities of components in the distribution system and the power requirements of the transmission system at the point of common coupling. The cooperative nature of SwarmGrid-X transforms the distribution system into a Cyber-Physical Power System. This paper also explains how SwarmGrid-X enables cyber-physical interactions of components to automate electrical power distribution and support the transmission system. ‘Game theory-based optimal deloading control of wind turbines under scalable structures of wind farm’ by Jianliang Zhang, Yujun Li, Zhao Xu, et al. addresses the problem of how to harvest as much kinetic energy as possible during deloading control of variable speed wind turbines (VSWTs) by distributedly adjusting rotor speeds under scalable wind farm topology. A game theorybased distributed control framework is investigated to enable the optimal rotor speed setting of VSWTs such that maximal kinetic energy can be stored in rotating masses of VSWTs for further system support, and meanwhile, the power dispatch objective for VSWTs can be fulfilled. Consequently, all of VSWTs within wind farm cooperatively achieve the objective of both system power balance and maximal kinetic energy harvesting. ‘Forecasting of commodities prices using a multi-factor PDE model and Kalman Filtering’, by Gerasimos Rigatos, Pierluigi Siano, Taniya Ghosh, et al. presents a method for forecasting commodities prices using Schwartz PDE and Kalman Filtering. The method is applicable to both the single-factor and the multifactor Schwartz PDE. By redesigning the Kalman Filter as a m-step ahead predictor it becomes possible to obtain accurate estimates of the future commodities’ price. The proposed method can contribute to maximising profits in commodities trading, including also the trading of electric power.


Introduction
With the increased adoption of information and communication technologies (ICTs) and cyber and internet technologies, power systems are rapidly evolving into Cyber-Physical Power Systems (CPPS). CPPS are emerging technologies, with growing significant academic, industrial and societal impacts. Research into CPPS needs deep integration of smart electric power grid and new information systems, and consideration must be paid to the tight coupling between cyber, networking, communication and physical systems.
To this end, the interdependency of the power system and its associated cyber properties should be investigated. Advanced intelligent technologies must be developed to deal with frontier challenges arising from multiple energy resources, multiple timescales, the presence of uncertainty, the existence of reliability concerns and the security issues related to modernised power systems. It is expected that these intelligent technologies can improve power system performance in terms of security, efficiency, reliability and, make a strong economic impact. Seven papers were accepted for this Special Issue and brief introductions of them are provided below.
'Developing correlation indices to identify coordinated cyberattacks on power grids', by Christian Moya and Jiankang Wang, studies coordinated cyber-attacks from the correlation indices on static control applications. The proposed indices improve attack identification, e.g., measurement attacks. Compared with existing approaches, the proposed method is deductive and able to detect sophisticated attacks without simulating a large number of attack events. A case study on the New England 39 bus system demonstrates the effectiveness of this method.
'Electromagnetic torque analysis-based method for performance evaluation and optimisation of closed-loop CPS regarding small signal stability', by Yibiao Sheng, Tao Lin, Rusi Chen, et al. presents a new method to explore the influence of wide-area damping control parameters and time delays for cyber-physical power system from a small signal stability viewpoint. An electromagnetic torque analysis (ETA) method is established to facilitate this stability study. The authors analyse the effectiveness and advantages of the proposed method using a two-area fourmachine system.
'Market-based generator cost functions for power system test cases', by Venkat Durvasulu and Timothy M. Hansen proposes a novel method to design generator cost functions to emulate existing market costs for power system test cases. This paper classifies real market generator offers from an independent system operator organised electricity market into generator types. By using the new market-based generator cost functions, power system simulation studies will better represent actual economic impacts. 'Predictive control model to manage power flow on a hybrid wind-photovoltaic and diesel microgeneration power plant with additional storage capacity' by António José Arsénio dos Santos Costa, Duarte Valério and Paulo José da Costa Branco is aimed at using model predictive control (MPC) approach for management of the power flow in a hybrid microgeneration power plant with additional storage capacity. The objectives of MPC are to maximise the use of power from renewable resources and to maximise the duration of lithium ion batteries. MPC is proven to be a suitable strategy for management of power flow dispatch on hybrid power generation plants with renewable resources.
'Swarm-based automation of electrical power distribution and transmission system support', by Stefan Dähling, Sonja Kolen, and Antonello Monti presents SwarmGrid-X, an agent-based control concept that considers the structure, demands and capabilities of components in the distribution system and the power requirements of the transmission system at the point of common coupling. The cooperative nature of SwarmGrid-X transforms the distribution system into a Cyber-Physical Power System. This paper also explains how SwarmGrid-X enables cyber-physical interactions of components to automate electrical power distribution and support the transmission system.
'Game theory-based optimal deloading control of wind turbines under scalable structures of wind farm' by Jianliang Zhang, Yujun Li, Zhao Xu, et al. addresses the problem of how to harvest as much kinetic energy as possible during deloading control of variable speed wind turbines (VSWTs) by distributedly adjusting rotor speeds under scalable wind farm topology. A game theorybased distributed control framework is investigated to enable the optimal rotor speed setting of VSWTs such that maximal kinetic energy can be stored in rotating masses of VSWTs for further system support, and meanwhile, the power dispatch objective for VSWTs can be fulfilled. Consequently, all of VSWTs within wind farm cooperatively achieve the objective of both system power balance and maximal kinetic energy harvesting.
'Forecasting of commodities prices using a multi-factor PDE model and Kalman Filtering', by Gerasimos Rigatos, Pierluigi Siano, Taniya Ghosh, et al. presents a method for forecasting commodities prices using Schwartz PDE and Kalman Filtering. The method is applicable to both the single-factor and the multifactor Schwartz PDE. By redesigning the Kalman Filter as a m-step ahead predictor it becomes possible to obtain accurate estimates of the future commodities' price. The proposed method can contribute to maximising profits in commodities trading, including also the trading of electric power.

Conclusion
The papers selected for this Special Issue present a large diversity of Cyber-Physical Power Systems (CPPS) that involve cyber, networking, communication and physical systems, where the interdependency of the power system and its associated cyber properties have been investigated. These papers have successfully demonstrated some of the notable approaches of cyber, stability, control, optimisation and modelling to meet the emerging challenges of CPPS.