Electrical Power and Energy Systems 141 (2022) 108039 Available online 15 March 2022 0142-0615/© 2022 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect International Journal of Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes Edge security in smart inverters: Physical invariants based approach Anusha Kumaresan a,∗,1,2 , Nandha Kumar Kandasamy b,2 , Robert E. Kooij c,d a Energy Research Institute at NTU (ERI@N), Interdisciplinary Graduate Programme, Nanyang Technological University, 639798, Singapore b Lite-On Singapore Pte. Ltd., 556741, Singapore c Delft University of Technology, Faculty of Electrical Engineering, Mathematics and Computer Science, Mekelweg 4, 2628 CD Delft, The Netherlands d TNO, Unit ICT, Anna van Buerenplein 1, 2595 DA, Den Haag, The Netherlands ARTICLE INFO Keywords: Cyber security Edge security Physical invariant Smart photovoltaic inverter Volt/VAR control ABSTRACT The endeavour towards making power distribution systems (PDSs) smarter has made the interdependence on communication network indispensable. Further, prospective high penetration of intermittent renewable energy sources in the form of distributed energy resources (DERs) has resulted in the necessity for smart controllers on such DERs. Inverters are employed for the purpose of DC to AC power conversion in the distribution network where the present standards require these inverters to be smart. In general, distributed energy resource management systems (DERMS) calculate and send set points/operating points to these smart inverters using protocols such as smart energy profile (SEP) 2.0. Given the nature of sites at which such DERs are installed i.e., home area networks with a pool of IoT(Internet-of-Things) devices, the opportunity for a malicious actor to sabotage the operation is typically higher than that for a transmission system. National Electric Sector Cyber-security Organization Resource (NESCOR) has described several failure scenarios and impact analyses in case of cyber attacks on DERs. One such failure scenario concerns attacks on real/reactive power control commands. In this paper, it is demonstrated that physical invariant based security on the edge devices, i.e. smart controllers deployed in DER inverters, is an effective approach to minimize the impact of cyber attacks targeting reactive power control in DER inverters. The proposed defense is generic and can also be extended to attacks on real-power control. The proposed defense is validated on a co-simulation platform (OpenDSS and MATLAB/SIMULINK). 1. Introduction While traditional power systems were centralized, the need for im- proved reliability and power/energy security initiated [1] the increase in deployment of distributed energy resources (DERs) [2]. Factors such as increasing energy demand, economic and environmental issues in using fossil fuel, and decreasing cost of renewable energy sources (RES) led to the growing attention towards their deployment [3]. Hence, RESs are extensively employed for DER applications, usually as a combination (hybrid) of two or more variants to tackle their inherent intermittent behaviour [4]. Solar energy is a promising source among the RESs owing to its pollution free nature, availability of unlimited energy from the sun, and above all, the drastically decreasing cost of solar photovoltaic (PV) panels [5,6], and hence, it is widely adopted. Irrespective of the advantages, solar PV power also depends on the intermittent solar irradiance level and module temperature [7,8]. As a result, high penetration of solar PV results in grid stabilization issues such as voltage sag/swell [9], voltage flickers and power quality ∗ Corresponding author. E-mail addresses: anusha010@e.ntu.edu.sg (A. Kumaresan), nandha001@e.ntu.edu.sg (N.K. Kandasamy), r.e.kooij@tudelft.nl (R.E. Kooij). 1 Department of Electrical and Electronics Engineering, National Institute of Technology Puducherry, Karaikal, UT of Puducherry, India 609609. 2 Singapore University of Technology and Design, 8 Somapah Rd, Singapore 487372. issues [10]. This in turn, might damage the electrical equipment present in the network. Hence, under these conditions, DERs are forced to disconnect from the system. The above process is called islanding [11] and is not preferable due to constraints such as restarting time and manual effort involved in restarting the DERs [12]. Further, islanding might lead to cascaded islanding of other DERs. Many plausible solutions that can be used to mitigate these grid connection complications such as Volt/VAR control [13,14], frequency/ watt control [15,16], Volt/watt [17], ramp rate control [18], etc., are available in the literature. DER inverters with such capabilities are usually referred to as smart inverters [19] and IEEE 1547 is a standard that provides regulatory limits for smooth integration and coordination of such smart inverters in power distribution systems (PDSs) [20]. The coordination of DERs is usually handled by a distributed energy resource management system (DERMS). DERMS calculates the optimal values of the parameters for the smooth operation of the system based on historic data and status of all the equipment in the system [21]. The https://doi.org/10.1016/j.ijepes.2022.108039 Received 28 May 2021; Received in revised form 24 December 2021; Accepted 5 February 2022