All About EMI in Electric Vehicles

Key Takeaways

• The EMI in electric vehicles creates a hostile environment for the external electronic devices or gadgets to function normally inside an electric automobile.

• The conducted emissions in electric vehicles are characterized by high spectral content within a frequency band starting from the fundamental switching frequency.

• The common-mode currents in the vehicle chassis induce radiated EMI. 

Electric vehicles are the future of transportation. Traditional internal combustion engine (ICE) powered automobiles are being replaced by electric vehicles due to their long-term mobility. Electric vehicles offer a noticeably better driving experience, with excellent torque, power, speed, and acceleration compared to traditional vehicles. Electric vehicles offer other advantages over ICE-powered vehicles such as zero fuel consumption, eco-friendliness, low maintenance, efficiency, and reliability.

The key reason behind these advantages is that the mechanical motion in electric vehicles results from the conversion of electrical energy. The combination of batteries, chargers, and motors make electric vehicles a reality. As high voltages are involved in the electrical and electronic architecture of electric vehicles, they are vulnerable to electromagnetic interference (EMI). The EMI in electric vehicles is detrimental to the electrical and electronic systems present in them, and it is critical to shield electric vehicles from EMI. 

EMI in Electric Vehicles 

Electric vehicles are open to the revolutionary application of information-communication technology (ICT). The ICT applications in electric vehicles include energy control, navigation services, info-mobility, road safety, traffic congestion forecast, connectivity, etc. Various electronic devices are installed in electric vehicles to support the use of intelligent technologies. Even though the benefits of electronic systems increase the comfort of driving these vehicles, they also increase the susceptibility to EMI. Electronic systems act as both source and target of electromagnetic emissions. The co-existence of signal systems and power systems in a relatively small area of electric vehicles makes the scenario even worse, with increased emissions and susceptibility. The EMI in electric vehicles creates a hostile environment for external electronic devices or gadgets to function normally inside an electric automobile.

Let’s discuss the two types of EMI in electric vehicles.

Conducted EMI in Electric Vehicles

The conducted EMI in electric vehicles can be linked to inverters. The DC-AC converter or inverter in electric vehicles usually uses insulated gate bipolar transistors (IGBT) or metal-oxide-semiconductor field-effect transistors (MOSFETs) as switching devices. These devices are switched on and off at high frequencies. High-frequency switching is employed for reducing the size of the magnetics (associated elements such as transformers, inductors, filters, etc.), current ripples, and acoustic noises. However, this fast switching causes sudden changes in voltages (dVdt) and currents (dIdt), which result in the generation of conducted EMI.

The conducted emissions in electric vehicles are characterized by high spectral content within a frequency band starting from the fundamental switching frequency. Conducted EMI in electric vehicles can be summarized as any electromagnetic disturbance that is transferred to the target from the source via conducting path. A conducting path can be the DC power bus, AC power bus, cables, wires, or traces. In the case of conducted emissions generated from inverters, the EMI spreads through the DC power bus.

The DC power bus is the conducting path connecting the electrochemical battery at the rear end of the vehicle to the inverter placed at the front end. The EMI from inverters reaches the electric motors via the AC power bus. The AC power bus connects the inverter to the motor, and is typically of a length ranging to tens of centimeters. The AC power bus is normally shorter than the DC power bus. The shorter the cable length, the lesser the effect of EMI. Therefore, the EMI in an AC power bus is weaker than the EMI in a DC power bus. 

Radiated EMI in Electric Vehicles

The voltage fluctuations in an electric vehicle during the fast switching of power electronic devices in the inverters produces conducted emissions. Usually, conducted EMI causes common-mode currents in the vehicle’s metallic chassis. The common-mode currents in the chassis induce radiated EMI. From the vehicle chassis, the EMI radiates to interfere with the internal system as well as external vehicles and electronic equipment.

As aforementioned, conducted emissions from the inverters propagate through DC power bus cables and AC power bus cables to the battery and motor, respectively. This conducted EMI couples with electronic circuits in the form of crosstalk and interferes with signal interconnects. The digital signal systems utilized in vehicular electronics architecture typically use isolation between high and low voltage domains. The high impedance path offered by the isolation hinders conducted EMI from reaching the secondary side, and currents are made to travel back to the source. These currents cover large loop areas and initiate the generation of radiated EMI affecting signal electronics.

Irrespective of the type, EMI in electric vehicles impairs the normal functioning of the electronic systems in them. The most common malfunctions are experienced in audio systems, engine control units, GPS navigation systems, antilock braking systems, air-bag controls, car alarms, collision warnings, and avoidance controls. As the strength of the EMI field in electric vehicles increases, the severity of the electromagnetic compatibility issues also increases. Cadence software can help you implement EMI mitigation techniques and EMI shielding methods in your electric vehicle design. 

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