EMC - EV

CAN bus (for controller area network) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer. CAN bus is a message-based protocol, designed specifically for automotive applications but now also used in other areas such as aerospace, maritime, industrial automation and medical equipment. 

CAN bus is one of five protocols used in the OBD-II vehicle diagnostics standard. The OBD-II standard has been mandatory for all cars and light trucks sold in the United States since 1996, and the EOBD standard has been mandatory for all petrol vehicles sold in the European Union since 2001 and all diesel vehicles since 2004. 

Automotive Applications

A modern automobile may have as many as 70 electronic control units (ECU) for various subsystems. Typically the biggest processor is the engine control unit (also engine control module/ECM or Powertrain Control Module/PCM in automobiles); others are used for transmission, airbags, antilock braking/ABS, cruise control, electric power steering/EPS, audio systems, windows, doors, mirror adjustment, battery and recharging systems for hybrid/electric cars, etc. Some of these form independent subsystems, but communications among others are essential. A subsystem may need to control actuators or receive feedback from sensors. The CAN standard was devised to fill this need.

The CAN bus may be used in vehicles to connect the engine control unit and transmission, or (on a different bus) to connect the door locks, climate control, seat control, etc.

Today the CAN bus is also used as a fieldbus in general automation environments, primarily due to the low cost of some CAN controllers and processors.

Bosch holds patents on the technology, and manufacturers of CAN-compatible microprocessors pay license fees to Bosch, which are normally passed on to the customer in the price of the chip. Manufacturers of products with custom ASICs or FPGAs containing CAN-compatible modules may need to pay a fee for the CAN Protocol License.

Technology

CAN is a multi-master broadcast serial bus standard for connecting electronic control units (ECUs). Each node is able to send and receive messages, but not simultaneously. A message consists primarily of an ID (identifier), which represents the priority of the message, and up to eight data bytes. The improved CAN (CAN FD) extends the length of the data section to up to 64 bytes per frame. It is transmitted serially onto the bus. This signal pattern is encoded in non-return-to-zero (NRZ) and is sensed by all nodes.  

The devices that are connected by a CAN network are typically sensors, actuators, and other control devices. These devices are not connected directly to the bus, but through a host processor and a CAN controller. If the bus is idle which is represented by recessive level (TTL=5V), any node may begin to transmit. If two or more nodes begin sending messages at the same time, the message with the more dominant ID (which has more dominant bits, i.e., zeroes) will overwrite other nodes' less dominant IDs, so that eventually (after this arbitration on the ID) only the dominant message remains and is received by all nodes. This mechanism is referred to as priority based bus arbitration. Messages with numerically smaller values of IDs have higher priority and are transmitted first.

Each node requires:

Host processor

• The host processor decides what received messages mean and which messages it wants to transmit itself.

• Sensors, actuators and control devices can be connected to the host processor.

CAN controller (hardware with a synchronous clock).

• Receiving: the CAN controller stores received bits serially from the bus until an entire message is available, which can then be fetched by the host processor (usually after the CAN controller has triggered an interrupt).

• Sending: the host processor stores it’s transmit messages to a CAN controller, which transmits the bits serially onto the bus.

Transceiver

• Receiving: it adapts signal levels from the bus to levels that the CAN controller expects and has protective circuitry that protects the CAN controller.

• Transmitting: it converts the transmit-bit signal received from the CAN controller into a signal that is sent onto the bus.

Bit rates up to 1 Mbit/s are possible at network lengths below 40 m. Decreasing the bit rate allows longer network distances (e.g., 500 m at 125 kbit/s). The improved CAN (CAN FD) extends the speed of the data section by a factor of up to 8 of the arbitration bit rate.

The CAN data link layer protocol is standardized in ISO 11898-1. This standard describes mainly the data link layer (composed of the logical link control (LLC) sublayer and the media access control (MAC) sublayer) and some aspects of the physical layer of the OSI reference model.  All the other protocol layers are the network designer's choice.

Sources: Bosch

Christian Rosu

See Movie

1) Check mirrors
2) Signal before changing lanes
3) Shoulder check
4) Check mirror again then change lanes

Types of Electromagnetic Coupling: Conducted, Radiation, Magnetic Field, Electric Filed

Electric Field Coupling

The EF lines start on positive charge and end on negative charge from higher voltage conductors to lower voltage conductors. Any two conductors at different potentials (voltages) have electric field lines between them. EF shields are connected to “ground” to maximize their effectiveness.

     The electric field lines are passing through ungrounded metallic planes. 

Grounding a copper enclosure does not increase or decrease its shielding property but it reduces the crosstalk within the product itself. The ungrounded shield allows coupling signals from circuits within the shielded enclosure. If the device is connected via external cable to another module the ungrounded shield can serve to capacitively couple signals from outside the enclosure. 

Stand by and Wake up

The supply device is woken up by a signal from the EV.

Compatibility check

Compatibility of the primary and the secondary devices is checked with the information exchanged at the initialization phase: power classes, operating frequency, magnetic coupling, circuit topology, tuning.

Initial Alignment check

The MF-WPT system will determine that the primary and secondary devices are properly well positioned relative to each other.

Start Power Transfer

The MF-WPT system is capable to transfer the power from the primary device to the secondary device upon the request from the vehicle. The MF-WPT system does not perform power transfer until the command and control communication is properly established and the primary device and secondary device are properly positioned.

Time Scheduled Power Transfer

Perform Power Transfer

MF-WPT system transfers the power from the primary device to the secondary device in accordance with the power demand of the EV. The maximum transferring power of the off-board MF-WPT system must not be exceeded. The vehicle can change the requested transfer power.

Stop Power Transfer

MF-WPT system is able to stop transfer the power from the primary device to the secondary device in accordance with the demand of the EV. The vehicle can requested stop power transfer.

User initiated Stop Power Transfer

MF-WPT system allows the user to terminate of power supply. (e.g. pushing stop button).

Safety monitoring & diagnostics

continuous monitoring of power transfer conditions

continuous monitoring of command & control communication

continuous monitoring of safety conditions

Power Transfer Monitoring: The supply device provide means to verify that the actual output power does not differ from the expected output power by a certain limit; if the limit is exceeded, it shall stop power transfer.

Thermal Monitoring: WPT systems is capable to detect metallic objects and to stop the power transfer.

Live Object Protection: WPT systems provide life object protection by design or may provide means to detect live objects and to stop power transfer.

Failure Conditions: The supply device stops the transfer in case of of power short-circuit, earth leakage, excess temperature, insulation failure, overcurrent, overload conditions.

Ventilation: Verify that the ventilation system of the area is functioning and active.

EV require higher power for the electric drive components and higher voltage (900 V) in the high voltage bus. The HV Bus is built as a completely insulated power supply network with cables most often shielded.

The main components of the automotive electric drive are:

• electric motor (the connection between converter and motor must be very short)
• power converter (the main source of EMI due to high speed switching devices with changing pulse patterns)
• power supply (traction battery providing power to the converter is a main part of the path for EMI)
• lines connecting the above components

Each of these components acts as a path for electromagnetic emissions:

• RF noise emissions due to the ratio between the size of the power converter and the frequency of the EMI.
• The high-voltage system is insulated and does not use the car body as return conductor like the low-voltage supply system. However, the high-voltage and the low voltage cables are arranged closely to each other, one important coupling path being the crosstalk between the different lines.
• The drive system can be either noise source or part of the coupling path within EV electrical system.