Electromagnetic Compatibility of CAN And CAN FD in New Energy Vehicles

I.Background of New Energy Vehicle Communication Network

With the rapid development of new energy vehicles, the intelligence and automation of vehicles are constantly improving, which makes the communication between the electronic control units (ECUs) in the vehicle more and more critical. The communication network is like the "nervous system" of new energy vehicles, responsible for transmitting various control instructions and data information to ensure the coordinated work of various vehicle systems.

In new energy vehicles, the battery management system (BMS) needs to communicate in real time with the motor controller (MCU), vehicle control unit (VCU), etc. to achieve accurate monitoring of the battery status and efficient control of the motor, thereby ensuring the vehicle's range and power performance.

II.Introduction to CAN and CAN FD

1、CAN definition and development

CAN, or Controller Area Network, is one of the most widely used fieldbuses in the world. It was originally developed by Bosch of Germany for automotive electronic control systems. Since its release, CAN has gradually become the standard bus for automotive computer control systems and embedded industrial control LANs due to its high reliability, real-time performance, and strong anti-interference capabilities. In early cars, the CAN bus was mainly used to connect some basic electronic control modules, such as engine control units, transmission control units, etc., to achieve data interaction and collaborative work between these modules.

2、CAN FD Definition and Development

CAN FD (CAN with Flexible Data - Rate) means CAN with variable rate, which is an enhanced version of CAN bus. It started protocol development in 2011 and was included in ISO11898 - 1 standard in 2015. CAN FD optimizes and expands the data transmission rate and data frame format while retaining the basic characteristics of CAN.

With the development of automobile intelligence and networking, the requirements for in-vehicle communication networks are getting higher and higher. CAN FD came into being to meet the needs of emerging applications such as advanced driver assistance systems (ADAS) and vehicle-to-everything (V2X) for high-speed and large data transmission.

III(1). Comparison Core Advantages

III(2).Contrast Deficiencies

IV. Application Scenario Comparison

V. Selection Suggestions

(1) When choosing between CAN and CAN FD, you need to consider the specific application requirements and system constraints.

(2) For some traditional automotive electronic systems that are cost-sensitive and have low data transmission requirements, CAN is still an economical and practical choice.

(3) For emerging smart car applications that have strict requirements on data transmission rate and data volume, CAN FD can better meet their development needs.

(4) Based on different functional modules and communication requirements, CAN and CAN FD can be used simultaneously in the same vehicle to build an efficient and flexible communication network.

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VI(1). Common hardware problems of CAN interface

Category	Phenomenon and description
Hardware Issues	Bus short circuit: Abnormal connection between CAN_H and CAN_L leads to signal distortion or loss. This may be caused by line wear, insulation damage, etc., which causes the lines to contact each other, or external objects squeezing or puncturing the lines.
	Terminal resistance problem:120 ohm terminal resistance must be installed at both ends of the CAN bus to ensure signal integrity. The resistor is damaged, not installed or installed improperly.
	Connector failure: Poor contact, corrosion or damage to the connector will cause unstable or interrupted signal transmission. Wear and tear after long-term use, looseness caused by vibration, corrosion caused by humid environment, etc. are common causes.
	Grounding problem: Poor grounding can introduce electromagnetic interference, affect signal transmission quality, and cause data errors or loss.
	Power supply problem: unstable power supply, insufficient voltage or excessive voltage fluctuation, affecting the normal operation of CAN bus devices.

VI(2). Common communication and protocol issues of CAN interface

Category	Phenomenon and description
Communication and protocol issues	Signal attenuation: If the bus length is too long and exceeds the standard (usually 40 meters), or the line quality is poor and there are too many branches, the signal will be attenuated, resulting in data transmission errors or instability.
	Data conflict: There are too many nodes on the bus, and conflicts are likely to occur when multiple nodes send data at the same time, resulting in data transmission failure or error.
	Different communication baud rates: Different nodes use different communication baud rates, which will lead to communication failure or data transmission errors.
	Protocol error: The data sent by the node does not comply with the CAN protocol specification, such as frame format error, data length error, etc., which will cause the data packet to be discarded or misinterpreted.

VI(3). Common environmental issues related to CAN interface

Category	Phenomenon and description
Environmental issues	Electromagnetic interference: External electromagnetic fields, such as interference from nearby motors, transformers, radio equipment, etc., may cause unstable signal transmission, data errors or loss.
	Temperature effects: Excessively high or low temperatures may cause electronic components to degrade in performance and change parameters, resulting in unstable equipment operation and affecting CAN bus communication.
	Humidity and vibration: Excessive humidity may cause equipment corrosion and short circuits; vibration may loosen connectors and break lines, leading to communication failures.

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VII.CAN bus solution

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