# Model-Based Analysis and Improvement of Vehicle Radiation Emissions at Low Frequency
## 1 Introduction  
Electrification and intelligence are the main technical trends of vehicle industry because of their contributions on traffic safety, energy conservation and emission reduction of air pollutant [1, 2]. From the viewpoint of electromagnetic compatibility (EMC), the electromagnetic environment inside vehicles deteriorates substantially due to the high voltage/current of electrical drivetrains, dense radio systems and onboard electronics with high frequency/speed [3]. Meanwhile the increase of potential interference sources, sensitive equipment and coupling paths poses great challenges on the design efficiency of vehicle-level EMC [4]. Simulation is an effective way to analyze EMC, which can be adopted throughout the whole vehicle product development process. However, when using the simulation method, its effectiveness depends heavily on the model accuracy. The key of the EMC modelling is to characterize the equivalent interference sources and sensitive equipment [5], and map the propagation paths of interferences among them [6]. The modeling method normally is selected according to the electrical size. Electrically small parts, whose structure is much less than the wavelength of the considered signals, can be regarded as a circuit and the propagation of electromagnetic waves in its physical-space can be ignored. For example, [PERSON] et al. extracted the electrical characteristics of a drive inverter to create an equivalent lumped circuit and a good simulation accuracy was achieved [7]. Otherwise, the propagation of electromagnetic wave in electrical large parts, such as cables, should be considered in detail. Some approximation methods have been proposed for such structures, which are integrated in the numerical solving software for 3 Delectromagnetic fields. For instance, to acquire a reliable model of large electrical cables for the prediction of the radiated emission at high frequency, the distributed parameters of automotive cables were converted into the lump parameters by the partial element equivalent circuit method [8]. Moreover, the transfer function was also used to describe the propagation characteristic of the radiated coupling path [9]. This approach is concise and explicit, but the transfer function varies with its port impedance. To overcome this limitation, [PERSON] et al. adopted the multi-port network with Z-parameter to describe the electromagnetic propagation path of the high voltage components in an electric vehicle (EV) [10]. The coupling of the high and low power systems in the power distribution unit (PDU) is further considered in [11]. To reduce the scale of the model, electromagnetic topology is an effective way, which decomposes a large and complex system into multiple subsystems according to the electromagnetic shielding level [12; 13]. This method has been successfully applied to evaluate the EMC of Boeing 707 airplanes [14]. With the help of simulation models, the comparative analysis of the improvement of EMC between different methods becomes feasible. For example, [PERSON] et al. compared by simulation the reduction effect of interferences when using different MOSFET and IGBT switches [15]. Unfortunately, we require the candidate solutions beforehand when using this approach. This depends greatly on the engineer's experience. For systems as complex as the vehicle-level radiation emissions, the key coupling paths, interference sources and sensitive equipment are hard to determine directly, let alone the possible solutions. Moreover, the vehicle radiation emission is a systematic problem. Reducing the source interference and weakening the transfer path both are beneficial to the vehicle radiation emission. Furthermore, how to make a balance between these technical factors, the application difficulty and costs systematically is still a problem too [16]. To overcome the design challenge of vehicle-level radiation emissions and improve the development efficiency, a model based analysis and improvement strategy is proposed.