Modular multilevel converters (MMCs) are favoured in high voltage direct current (HVDC) systems because of huge energy transmission capacity and few harmonics. However, the complicated control and the intricate communication network introduce cyber delay that affects the system dynamics. The communication structure is discussed and delay components are studied. The authors derive the MMC-HVDC system model considering the cyber delay effect. Padé approximation is utilised to transform the transcendental characteristic equation of the delay model into an algebraic equation so that the dynamics can be observed through the eigenvalues. The comparison between the established model and the simulation in Simulink validates the proposed model's accuracy. The exact delay margin and the root cause of losing the stability are also discussed. The results show that the model is able to obtain the delay margin with a tiny error caused by the omitted high-order harmonics and the cyber delay destabilises the system by lowering the controller performances. | INTRODUCTION | Motivation and incitementModular multilevel converters (MMCs) are widely applied in medium or high-voltage industrial applications (HVDC) [1]. In the MMC-HVDC system, hundreds of sub-modules (SMs) are combined as a strong, flexible equivalent voltage source. The large transmission capacity of MMC-HVDC system enables the power grid to integrate other forms of energy more efficiently. In other words, the MMC-HVDC energy interconnected system is an important element of energy integration. However, it also brings a challenge for the design of control and communication [2,3] and induces serious delay issue, which jeopardises the whole system's dynamics and stability [4,5].Further, to ensure that the control system offers the appropriate control signals of the converters in time, the communication network is designed meticulously.Besides, an appropriate MMC-HVDC system model is required to analyse the system dynamics and stability under the control and cyber delay's effect. | Literature reviewBecause of the practicability and reliability, [6-10] utilised the ring topology in their communication networks. A lot of communication protocols like EtherCAT (Ethernet for Control Automation Technology) [6][7][8][9][10][11][12], CAN [13], PROFINET IRT [7] are applied, among which EtherCAT has the best performance [6,8] and is suitable for the ring topology. Distributed control [2,3,13] is a good idea to lighten the computation burden and reduce the information shared inside the system. In the distributed modulation situation, the controller is only in charge of calculating and outputting reference signals. The local control units (LCUs) of SMs thenThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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With the popularity of MicroMouse project growing up, more and more people have participated in this activity. However, it is not efficient to develop and debug a MicroMouse in a real environment, and it is difficult to observe the details of the robot’s motion state. This paper proposes a development-oriented IEEE MicroMouse simulation system that can accurately simulate the decision-making, control algorithm, and sensor information collection of real MicroMouse on embedded device, so that the development of mobile robots can free from the restricted of real environment.

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