Synchronization of Heterogeneous Vehicle Platoon Using Distributed PI Controller Designed Based on Cooperative Observer Agung Prayitno * , Veronica Indrawati , Yohanes Gunawan Yusuf Department of Electrical Engineering, University of Surabaya, Surabaya 60293, Indonesia Corresponding Author Email: prayitno_agung@staff.ubaya.ac.id Copyright: ©2024 The authors. This article is published by IIETA and is licensed under the CC BY 4.0 license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.18280/mmep.110616 ABSTRACT Received: 22 January 2024 Revised: 11 April 2024 Accepted: 22 April 2024 Available online: 22 June 2024 The challenge in designing distributed controllers for vehicle platoon synchronization arises when full-state information for control algorithm calculations cannot be obtained from the entire vehicle. Therefore, this paper presents a control scheme using a cooperative observer to estimate full-state information, enabling its use in calculating control signals. Instead of relying solely on a control signal proportional to the cooperative tracking error, the proposed control signal includes an additional integral form of the cooperative tracking error. This addition is expected to mitigate the effects of disturbances experienced by follower vehicles. Distributed control generally comprises two major components: The proportional-integral (PI) controller and the cooperative observer. The paper provides conditions for choosing control parameter values to guarantee the stability of the vehicle platoon. A numerical simulation of a vehicle platoon comprising one leader and ten followers is presented to demonstrate performance and validate the research results. Simulation results indicate that the controller performs effectively when followers experience constant disturbances, demonstrating the continuous achievement of vehicle platoon synchronization. Keywords: cooperative observer, distributed proportional- integral controller, limited output information, vehicle platoon 1. INTRODUCTION The intelligent transportation system of the future will be increasingly implemented with the rapid development of sensor, actuator, computing, communication, and information system technology. As this field advances, it becomes possible to exchange information among road users, infrastructure, vehicles, transportation platforms, and existing public facilities. Therefore, the keyword 'collaboration' will emerge as a trend in future transportation systems. Notably, collaboration between vehicles can provide solutions to various existing problems. One such collaboration involves vehicles traveling in groups, commonly known as vehicle platoons. A vehicle platoon comprises a group of autonomous vehicles that travel in a parallel formation, resembling a series of train cars. The potential benefits of this platoon formation are substantial, as it can optimize road capacity, save fuel, reduce congestion and air pollution, and increase economic productivity [1, 2]. With this significant potential, it is not surprising that research into vehicle platoon development is extensive and actively conducted by researchers worldwide. To form a platoon configuration, the leading vehicle acts as the leader, providing a reference for other vehicles, which function as followers. The leader is responsible for broadcasting information to some or all of its followers. Similarly, each follower is equipped with the ability to send and receive information from its neighbors. The flow of information from source to receiver depends on an agreed- upon topology. In general, there are six topologies used in vehicle platoons, namely: Predecessor Following (PF), Two Predecessor Following (TPF), Predecessor Following Leader (PFL), Two Predecessor Following Leader (TPFL), Bidirectional (BD), and Bidirectional Leader (BDL) [3]. The first four topologies are classified as directed topologies [4], while the last two are undirected topologies [5]. The characteristics of each topology in the platoon have been extensively reviewed in various studies and can be found at references [3, 6, 7]. Apart from topology, another important component that needs consideration in vehicle platooning is an agreement regarding the distance between vehicle and the one in front of it when moving in a convoy (spacing policy). The distance between vehicles can always be constant, or change over time depending on speed. The first option is usually known as constant spacing policy (CSP) as used by Qiang et al. [8] and Li et al. [9], while the second option can be implemented with the concept of constant time heading (CTH) as used by Gaagai and Horn [10]. These two spacing policies are the most commonly used in vehicle platoon development research, although several other spacing policies also exist, such as the non-linear spacing policy [11] and the delay-based spacing policy [12]. Another component in the vehicle platoon is the distributed controller, which is implemented on each follower. For clarity, a vehicle platoon serves as an application example of the leader-follower multi-agent system (MAS) concept. This implies that the distributed controller developed from the leader-follower MAS concept can generally be implemented for vehicle platoons. An example of this is the concept of Mathematical Modelling of Engineering Problems Vol. 11, No. 6, June, 2024, pp. 1558-1566 Journal homepage: http://iieta.org/journals/mmep 1558