Power Electronics

EMC Poses Challenge for Automotive Electronics

Ensuring safe and trouble-free transportation requires thorough EMC (electromagnetic compatibility) testing of automotive electronics hardware and software.

With respect to the number of units in service, automotive electronic systems are now the most pervasive of today's electronic applications. And, continuing demand for new automotive functionality is leading to the addition of even more electronic systems. Also, there is a trend to replace automotive mechanical and hydraulic systems with “by-wire” configurations of sensors, actuators and microprocessors. This leads to the conclusion that today's automobiles are now merely distributed, embedded computer environments on wheels. Compared with an embedded computer in a stationary, environmentally protected area, today's automobiles have to survive a wide temperature range, humidity, bumpy roads, and an external environment that can generate broadband electrical noise. There is one similarity: software is a major ingredient in all embedded computers, although automotive software requires more fail-safe functions.

Software and electronics now make up more than 30 percent of the cost of a typical modern car. The vehicle's software controls its engine, maps its transmission shift points, and interacts with the components of the powertrain, climate control, infotainment systems, anti-lock braking, engine control, active suspensions, and vehicle dynamics. So much so that some modern cars now total up to 100 million lines of software code running on dozens of microprocessors. In many cases, that amount of code could possibly represent an investment of millions of dollars for a new car design. As an example, the GPS navigation system alone can employ a million lines of code. And, as more electronic systems are added the total lines of code could double or triple in a few years.

Although automobiles employ many different types of microprocessors, virtually all use the basic stored-program (Von Neumann) architecture shown in Fig. 1. These microprocessors store their programmed lines of software code instructions, as well as data, in read-write, random access memory (RAM). The microprocessor may have some internal RAM, as well as external RAM. In a typical simplified sequence, the microprocessor fetches an instruction from RAM and decodes it. If necessary, it fetches data from RAM, executes the instruction, and stores the results in RAM. Then, the process repeats itself with the next instruction. Program execution involves continuous interaction between instructions and data stored in RAM and typical internal microprocessor units that include:

  • Program counter that indicates where the computer is in its instruction sequence.

  • Instruction Decoder that interprets and implements the instruction.

    Internal registers that hold values of internal operations, such as the address of the instruction being executed and the data being processed.

  • ALU (arithmetic and logic unit) that performs arithmetic and logic operations.

  • Data I/O (input/output) going into and out of the microprocessor.

This movement of instructions and data must move flawlessly through the microprocessor units, RAM and external sources. Any unintended interruption can upset software control of the microprocessor and may affect automobile operation.

There can be cases where the internal microprocessor units and external RAM are subjected to sudden, random noise pulses that cause software to misbehave and affect automotive functions. This could be a one-time occurrence that goes away. If the affected software controls climate control or infotainment, the result would probably be inconsequential. However, if an affected microprocessor subsystem impacts software that controls operation of the car, then the results could be damaging to the car and its occupants. These one-event problems are very difficult to troubleshoot and cure.

These issues mean that EMC (electromagnetic compatibility) tests are an essential element of automotive electronics design. Designers must consider EMC issues at all stages of the process, from designing printed circuit boards, implementing modules, and final car layout.

Therefore, measures must be taken to:

  • Protect against unwanted electromagnetic emissions by other on-board electronic systems, such as high-speed microprocessors.
  • Protect on-board electronics from the automotive environment that can cause transients or interference from the switching of heavy or inductive loads, such as lamps and motors.
  • Protect or harden on-board electronics against EMI produced by sources external to the automobile.

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RADIATED NOISE

Among the present-day EMI concerns are problems caused by external electromagnetic fields, including:

  • Mobile phones
  • Power lines
  • Radar transmitters
  • Radio transmitters

You could bombard the automobile with external RF radiation at high power and various frequencies in a test chamber to see how the automobile reacts to external EMI. If this test fails, it could mean that some electronic circuits might have to be hardened, that is, redesigned for greater protection against EMI. However, this would not catch problems caused by interactions between devices internal to the automobile.

Internal interactions of electronic systems can affect automobile performance. This situation has been exacerbated by the rapid increase in number and complexity of electronic systems across vehicles of all types, including:

  • Anti-lock Braking Systems (ABS)
  • Electronic Stability Program (ESP)/Traction control
  • Adaptive Cruise Control/Automatic Distance Regulation
  • Automatic rain sensors
  • Headlamp leveling
  • Automatic headlamp controls
  • Parking aids
  • RKE (Remote Keyless Entry)
  • Tiptronic gearshift mechanisms
  • Navigation systems
  • Automatic speed control systems
  • Night vision systems
  • Electric park brake and automatic roll braking systems

The increasingly tight time constraints of today's vehicle programs means there is too much risk involved in leaving EMC testing to be done at the vehicle level. Vehicle manufacturers must ensure that their systems have passed stringent test schedules prior to integration into the vehicle.

TESTING

Automotive testing requires knowledge of every electronic function now deployed in cars. Taiwan's Automotive Research & Testing Center (ARTC) established in 1990 is one of the worldwide companies that provide this expertise. It is responsible for the integration of research resources and the upgrading of industrial technology throughout Taiwan. It has a complete series of laboratories, proving ground, testing technologies, experience in analysis, innovation capability in key components and systems. In addition, it combines joint efforts of the industrial, academic and research circles.

ARTC's Electromagnetic Compatibility (EMC) Lab, established in 2003, focuses on complete EMC service, testing and design improvement, for automotive component suppliers and vehicle manufacturers. It's the second lab in Asia accredited for A2LA AEMCLAP program and OEM GM, Ford and Chrysler.

A2LA is the American Association for Laboratory Accreditation. AEMCLAP is an accreditation program that evaluates a suite of 13 EMC and electrical test methods common to automotive testing. It includes on-site assessment by A2LA auditors of the lab's test and calibration process, equipment, and personnel. It also includes proficiency testing that correlates measured test results with those of the automotive manufacturerís reference laboratories.

An anechoic chamber is a specially shielded room intended to attenuate electromagnetic energy. Among ARTC's EMC facilities are an anechoic chamber for conducted emission, conducted immunity, conducted transient and ESD testing of automotive components. Fig. 2(top) shows a model of an anechoic chamber used for automotive testing. Fig. 2 (bottom) is a closer look at testing a car in an anechoic chamber. Another anechoic chamber is intended for EMC testing of cars and motorcycles (Fig. 3). Fig. 4 is a shielded room used to test automotive components. There is a debug working area equipped with PCB scan analyzer, near field measurement system, broadband/RF circuit simulator and debug devices. Monitoring systems include a fiber optical system, auto recording system, system bus testers as well as an audio and video analyzer.

Specific EMC services include:

  • Testing of automotive components for conducted emission, radiated emission, ALSE (Aviation Life Support Equipment, free field) immunity, TEM (Transverse Electromagnetic) cell immunity, BCI (bulk current injection) immunity, stripline immunity, direct RF power injection immunity, magnetic field immunity, extended audio frequency immunity, conducted transient emission/immunity, and ESD (electrostatic discharge).
  • Testing of whole vehicles including radiated emission, radiated immunity, and ESD testing.
  • Improving design of automotive components using a PCB scan analyzer, near field measurement system, broadband / RF circuit simulator and debug devices.
  • Automotive EMC integrated projects including product co-design with customers, test plan writing, technical transferring, education training and EMC design, testing & debug integrated projects.

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ARTC's CAE (Computer-Aided Engineering) Center assists customers in evaluating vehicle field product performance, including structural strength, fatigue and durability, vibration, impact and thermal reduction by using CAE techniques. ARTC CAE provides services for manufacturers on product verification, trouble shooting, design change modifications, customized CAE training courses and transfer of technology based on the operational demands of its clients. Fig. 5 shows the results of structural and mechanical analysis software.

The Component Testing Lab performs durability tests of vehicle components, including vehicle wheels, safety belts, brake components, child restraint systems and flammability of interior materials. Fig. 6 shows a test performed on an automotive component. It is accredited by BSMI, (Bureau of Standards, Metrology and Inspection), for alloy wheels and child restraint systems, VSCC, (Vehicle Safety Certification Center), for safety belts and flammability of interior materials, and TUV SUD Automotive and AMECA, (Automotive Manufacturers Equipment Compliance Agency), for vehicle wheels. Besides, the lab has abundant testing experience and cooperates with CAE to provide comprehensive analysis and improvement service of above products.

In addition, ARTC has facilities for road testing vehicles, as shown in Fig. 7. ARTC's Proving Ground facilities assist manufacturers at every crucial step in the process of developing vehicles and for any specified critical system. It can carry out subjective testing and assessment of braking and turning capability, suspension and braking systems, including total vehicle durability and quality.

HARDWARE/SOFTWARE TESTING

Another reason for testing automotive electronics is the need to verify that a hardware and software combination is actually trouble-free. There can be a myriad of possible fault conditions that can cause a problem. And, there is no systematic approach for ensuring the quality of all integrated hardware and software. To be safe, each specific hardware/software combination requires its own unique test to ensure that it is trouble-free. That test would have to exercise every possible fault condition, which can sometimes be difficult to identify.

Of particular importance is a software and hardware combination with the potential for placing the car and its occupants in peril. As a minimum, this software/hardware must be fail-safe, or have a safe backup in case either the hardware or software encounters a fault that could lead to a life-threatening result. As a minimum, there should be graceful degradation that protects the car's occupants. In addition, software/hardware must be tested to ensure that it functions properly under failure conditions.

Although the automotive software developers may try to adopt solutions from non-automotive systems, the specific requirements of the automotive industry are so unique that this knowledge may not be directly transferable. As in many new applications, there is a learning curve in solving unique problems. There is also a learning curve in unique test strategies and procedures. Unfortunately, there may be little margin for error in both the actual design and testing of automotive electronic systems.

Compared with embedded stationary systems, automotive systems have greater software/hardware design and test complexity. For example, automotive embedded systems:

  • Receive inputs come from many event-gathering sources, such as sensors and timers rather than a single interactive user, or storage device for the stationary computer.
  • Usually produce computer outputs associated with specific time constraints, rather than ASAP in a stationary computer.
  • Must be able to work continuously without supervision, whereas stationary systems do not have that limitation; they can employ operator assistance.
  • Must allow each node in a distributed automotive system to tolerate failures of all other nodes in a controlled way, without jeopardizing the safety of the car's occupants.

Another automotive complexity is that each embedded computer must not interfere with operation of the other on-board computers. Ideally, this means that software/hardware testing should be accomplished while other embedded computers are operating. However, this may not be practical in all cases.

FUTURE AUTOMOTIVE ELECTRONICS

The ability to successfully solve automotive electronics problems has become more challenging as vehicle electronic content has grown. Besides potential problems with software code, there could be hardware issues with sensors that operate with low signal levels, where EMI can cause worrisome consequences.

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In addition, today's automotive systems have ICs, RAM, and microprocessors with operating voltages below 3.3V and as low as 1V. This makes them more susceptible to noise on their power lines. Lower operating voltages also require tighter voltage regulation for ICs, RAM and microprocessors, which means input power must be stable. Now, these embedded computer systems are moving to higher clock frequencies and pipelining to provide faster throughput. If automotive electronic systems follow these trends, protecting against EMI will become even more challenging than it is today.

EMC STANDARDS

Several international standards cover EMC testing of automobiles. Standards include the International Standards Office (ISO), and SAE (Society of Automotive Engineers). In addition, major car companies have their own standards. Described below are some of the standard tests.

ISO 11452-1:2005 specifies general conditions, defines terms, gives practical guidelines and establishes the basic principles of the component tests used in the other parts of ISO 11452 for determining the immunity of electronic components of passenger cars and commercial vehicles to electrical disturbances from narrowband radiated electromagnetic energy, regardless of the vehicle propulsion system (e.g. spark-ignition engine, diesel engine, electric motor). The electromagnetic disturbances are limited to continuous narrowband electromagnetic fields. A wide frequency range (0.01 MHz to 18 000 MHz) is allowed for the immunity testing of the components in this and the other parts of ISO 11452.

ISO 11452-2:2004 specifies an absorber-lined shielded enclosure method for testing the immunity (off-vehicle radiation source) of electronic components for passenger cars and commercial vehicles regardless of the propulsion system (e.g. spark-ignition engine, diesel engine, electric motor). The device under test (DUT), together with the wiring harness (prototype or standard test harness) is subjected to an electromagnetic disturbance generated inside an absorber-lined shielded enclosure, with peripheral devices either inside or outside the enclosure. It is applicable only to disturbances from continuous narrowband electromagnetic fields. See ISO 11452-1 for general test conditions.

ISO 11452-7:2003 specifies a direct RF power injection test for determining the immunity of electronic components of passenger cars and commercial vehicles to electrical disturbances from narrowband electromagnetic energy, regardless of the propulsion system. The test method provides differential mode excitation to the DUT (device under test) and is applicable to all DUT leads, except RF Ground. Applicable over the frequency range 0.25 MHz to 500 MHz, the method can be used to predict the compatibility in the vehicle environment with respect to radiated and conducted RF energy, including transient RF energy, and is useful as a means to isolate the susceptible circuits within a DUT and evaluating potential solutions.

Electrical Interference by Conduction and Coupling - Capacitive and Inductive Coupling via Lines Other than Supply Lines, August 2006. This SAE Standard establishes a common basis for the evaluation of devices and equipment in vehicles against transient transmission by coupling via lines other than the power supply lines. The test demonstrates the immunity of the instrument, device, or equipment to coupled fast transient disturbances, such as those caused by switching of inductive loads, relay contact bouncing, etc. Four test methods are presented - Capacitive Coupling Clamp, Chattering Relay, Direct Capacitor Coupling, and Inductive Coupling Clamp.

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