## 1 Introduction  
The active safety of the semi-trailer is significantly affected by the reliability of the vehicle's electronically controlled pneumatic braking system (ECPBS). To realize coordination between the two braking units of the tractor and trailer in ECPBS, lots of preliminary testing should be carried out to verify control strategies [1]. Currently, the braking performance verification of ECPBS [2] is mostly implemented through Model-In-Loop (MIL), Hardware-In-Loop (HIL) and Vehicle-In-Loop (VIL) testing methods. Although MIL and HIL have the virtues of universality and expandability, the confidence of testing results depends on the accuracy of the simulation model [3]. Moreover, the adoption of the vehicle model cannot truly reflect the dynamic characteristics of the actual vehicle. The problem can be better solved by VIL, but it requires specialized testing sites and has a high risk factor. It has been proven to be unsuitable for a large number of concept validation tests where the technology is not yet mature. Therefore, it has become a trend to adopt scaled-down test vehicles with similar dynamic characteristics to replace the actual vehicles in the concept validation stage [4]. [PERSON] et al. [5] built a scaled-down testing platform to solve the problem that autonomous self-driving vehicles are difficult to test under harsh conditions and verified the effectiveness of the platform through a simplified vehicle dynamics model and trajectory tracking algorithm. [PERSON] et al. [6] verified lane keeping and static obstacle avoidance algorithms using a proportional scaling model vehicle based on Ackermann steering. The results showed that the proportional scaling model vehicle could effectively verify the autonomous driving algorithm, and it could overcome the problems of high experimental costs and insufficient simulation confidence. [PERSON] et al. [7] analyzedthe feasibility of using scaled vehicle models to measure the characteristics and dynamics of actual vehicles and verified the effectiveness of using proportional model vehicles in boundary conditions that cannot be achieved in actual vehicle testing, such as vehicle instability or overturning. [PERSON] et al. (2018) used the Hardware-In-Loop (HIL) model of electric vehicle traction systems to simulate electric vehicles and analyzed the impact of different scaling ratios of electric drive models on vehicle energy consumption using [PERSON]'s \(\pi\) theorem. They proposed a method for simulating different electric traction systems and efficiency without changing the HIL setting. A scaled-down semi-trailer twin test vehicle based on [PERSON]'s \(\pi\) theorem was adopted in the experiment to reduce the dependence of the simulation process on the vehicle simulation model. Due to the long distance between the ECPB hardware test bench of the semi-trailer vehicle and the twin test vehicle, a real-time and reliable communication architecture should be adopted. Regarding the communication interconnection between different simulation systems, [PERSON] et al. (2019) adopted a distributed real-time simulation method to connect an automotive suspension HIL in Spain and the complete vehicle model in Germany in real time and verified the feasibility of the simulation method through experiments. [PERSON] et al. (2019) coupled the HIL simulation platform of electric vehicles, engines and batteries through cloud servers, enabling electric vehicles without hybrid power to simulate the output of hybrid power systems. The feasibility and reliability of the system were verified through urban road tests. [PERSON] et al. (2019) developed a method to simulate ADAS vehicles, introduced virtual environments in real-world testing and successfully verified the control strategy of the ADAS controller. [PERSON] et al. (2019) proposed a communication delay compensation method based on a long short-term memory network and model predictive control and verified that this method can reduce the impact of delay on system stability in the presence of communication delay.