Critical infrastructure (CI), such as energy and water distribution systems, is essential for the stability and well-being of the modern society. Industrial automation and control systems (IACSs) form the backbone of CIs and enable the operation of such systems in a safe and reliable manner. However, with the increasing use of industrial Ethernet communication protocols, such as Modbus-over-TCP (Modbus/TCP), once air-gapped IACSs are becoming vulnerable to potential cybersecurity threats. This paper presents a novel method for enhancing the cybersecurity of Modbus/TCP-based IACSs by implementing an authentication method based on message authentication codes (MACs). To provide partial protection of communication even when communicating with legacy Modbus/TCP peers, we propose a novel supervising device that analyzes exchanged messages and verifies the authenticity of the protected messages. To experimentally verify the protection method, a water-treatment cyber-physical system (CPS) was implemented as a digital twin in a programmable logic controller (PLC). The underlying MAC is the Chaskey-12, lightweight MAC defined in IEC 29192-6. It was implemented in the PLC program using the programming languages defined in IEC 61131-3. As an additional contribution, the presented implementation allows protection of communication between PLCs and other Modbus/TCP peers installed in existing IACSs without hardware or firmware modifications. The results show that the method provides protection against network attacks without significantly affecting performance, also demonstrating the feasibility of such protection in IACSs.

This paper proposes a dual-mode model predictive direct current control (MP-DCC) of a permanent magnet synchronous generator (PMSG). The proposed algorithm is capable of minimizing switching losses in a two-level synchronous generator side converter (SGSC). A new prediction model which takes the converter dead time into consideration when choosing the optimal switching state is introduced. The proposed prediction model provides a more accurate state prediction ensuring that the states of the system stay inside the control invariant set in the steady state even in the case of a significant converter dead time. To guarantee recursive feasibility and closed-loop stability a flexible control Lyapunov function (CLF) is employed as an optimization problem constraint which enables the minimization of switching losses both during transients and in the steady state. The influence of the converter dead time on the performance of the proposed algorithm is considered, and accordingly, a control invariant set is determined. Simulation results show that stator currents are kept within the control invariant set if dead time is taken into account in the prediction model. Furthermore, the proposed algorithm is implemented in a digital control system and experimentally verified on a 375 kW interior PMSG. Experimental results verify that the proposed control algorithm provides a successful flying start of the PMSG, and show that the application of the flexible CLF results in lower switching frequency, but also higher current ripple. By adjusting the upper bound of the control invariant set a desired trade-off between the low stator current ripple and the minimization of switching losses can be achieved.

In wind energy conversion systems of type 4, the critical operating point in permanent‐magnet generators (PMGs) is the moment of switching on the generator‐side converter (GSC). The induced back‐electromotive force (EMF) acting on PMG terminals can cause inrush currents if the synchronisation between PMG and GSC is not done well. The main condition for achieving a satisfying synchronisation is to know the rotor angle, rotating speed and induced back EMF before the GSC is switched on. This synchronisation together with the switching on of the GSC is called the flying start of a PMG. In this study, a novel sensorless PMG flying‐start method is proposed to ensure good synchronisation. The flying‐start method is based on an extended flux PMG model in a rotating reference frame with a discrete second‐order sliding‐mode observer and a phase‐locked loop controller during the discontinuous operating mode. This is based on discontinuous currents, which are induced because of the PMG rotation caused by wind energy. The proposed method ensures the operation of PMGs in the continuous operating mode as well. The effectiveness of the proposed method is verified on saturable models of low‐ and high‐power surface and interior PMGs through simulations in Simulink and Piecewise Linear Electrical Circuit Simulation (PLECS).

The paper investigates cyber threats and potential solutions for protecting industrial control systems (ICS). On the cyber threats side, different off-the-shelf offensive solutions, both hardware and software, are analysed and tested. The goal of the paper is to increase cyber threat awareness by showing how such off-the-shelf solutions, well known to IT security experts, can be utilised as (or inspire) attack vectors to gain access to generally unprotected industrial plants. After obtaining an accessing point, Man-in-the-Middle (MITM) and Legal-Client-to-Server (LCSA) types of attacks from reconnaissance, client-to-server and server-to-client categories are demonstrated. For this purpose, a Modbus communication protocol implemented in a real compressor station is used as basis. Regarding potential protection solutions, the paper proposes a simple-to-implement and cheap hardening methodology applicable inside almost any industrial plant. A novel, PLC-based ICS cyber security protection method, made of a signal validity monitoring mechanism and a control system integrity check mechanism is also discussed and demonstrated. Both penetration testing and hardening methodology are verified experimentally, using real PLC and HMI devices.

In this paper maximum torque per ampere and loss minimization control methods for an interior permanent magnet synchronous generator are compared. Permanent magnet synchronous generators have wide application in wind energy conversion systems due to high efficiency, high power density, high power factor and wide speed operating range. Maximum torque per ampere control method finds optimal d-and q-axis stator currents that produce desired electromagnetic torque while minimizing stator current magnitude. Loss minimization control method takes into account both copper and iron losses and finds optimal d- and q-axis stator currents that produce desired electromagnetic torque while minimizing total power loss. Characteristic curves for both control methods considering magnetic saturation are presented. Feed-forward torque control model developed in MATLAB/Simulink was used to verify described control methods.