Solve ECU validation issues with EMC simulation

Thomas Edison would be happy, but for automotive product development groups, the growing electrification of automotive platforms presents all sorts of new EMC validation challenges. Driven by the growing number of electrical functions such as drive systems for hybrid vehicles or pure electrical drives, driver assistance systems, and advancements in consumer electronics, electrification of automotive platforms means teams have to validate each systems for electromagnetic compatibility (EMC) across the complete operating range to ensure full compliance with the required quality and safety criteria. In particular the noise emission of dedicated components or embedded control units (ECU) may adversely impact the vehicle's network or other components.

EMC specifications determined by EU framework directive 2007/46/EC or according to rule ECE-R10 require careful verification.^{1, 2} Verification tests span frequency ranges up to 2GHz or higher. To complicate matters, vehicle manufacturers often impose additional EMC constraints on the system designs. Identifying and resolving design malfunctions caused by EMC issues can consume significant resources and add cost intensive design iterations. Often, ECU implementation-specific problems are encountered that require answers to the following questions. Whether a lead frame has to be used or an ordinary circuit board? Which HF filter types are being deployed? What about the control unit construction and the positioning of the components within the ECU? Should the emission be analysed as narrowband or broadband?

In extreme cases, it may be necessary to change the physical design, the ECU architecture, or filter elements. Implementing these changes may be costly and require additional development time adding risk to platforms that are otherwise ready for production. Substantial changes may even delay the product launch. In order to minimise the risk associated with these issues, early detection is crucial. To achieve this goal, designers are employing simulation tools to develop virtual solutions. Simulation-based methodologies enable engineers to perform EMC analyses of the control unit early in the development process, even before the ECU is available for EMC testing.³

Typically, applying the EMC tests to automotive ECUs in actual hardware is time consuming. In addition, it's difficult to precisely reproduce the exact measurement conditions such as temperature or device parameter drift. Owing to the persistent miniaturisation of automotive electronic components, direct measurements might not even be possible to perform. In such scenarios, simulation presents the only path to validate EMC performance.

Combining 3D field simulation and system simulation with discrete components
Creating a simulation model is critical for the success of simulation-based approaches. Understanding the advantages and limitations of the available modelling and simulation approach plays an important role. Partitioning of the simulation model provides a possibility to study the EMC behaviour of a complex automotive ECU system. First, the ECU system is decomposed into smaller components such as the circuit board, plug connectors, and cables. By means of 3D field simulation, these parts can be analysed separately to determine their individual electromagnetic performance. Afterwards, the EM field simulation data can be used to extract discrete models of the components, which are connected in a system simulator at the second stage.

In a 3D field simulation, Maxwell's equations are solved within a given volume by applying numerical methods. The user provides the geometry to be analysed, such as the lead frame of the ECU power electronics, and defines stimulus ports. Typical outputs from the field simulator include scattering parameters (s-parameters) and geometric distributions of currents and fields. In particular the ability to visualise the EM fields or the current distribution can be helpful because it provides insight that typically cannot be obtained by a measurement. Moreover, the field data provides information that can be used to identify potential coupling paths within the ECU physical structure. Typical applications include calculation of return current distribution on the reference layer of a circuit board, coupling of fields from mounted inductors, resonance generation in enclosures, or transmission behaviour of connectors.

If the system components are spatially separated from each other and don't interact through radiated emission—like a sensor wired to an ECU—it doesn't pay to model and simulate the complete system within a 3D field solver. In this case, the computational effort and required simulation time would increase significantly and swamp the benefits associated with minimal accuracy improvements. Combining the complementary advantages of system simulation and 3D field simulation provides a good approach for this problem. Precise EMC models of the individual control device components can be generated using a 3D field simulation within the CST Studio Suite and ported to discrete models that are used by a system simulator like Saber. This approach produces a holistic system model for EMC simulation of the ECU without requiring a 3D simulation of the complete ECU system. The design partitioning approach combines the strengths of both simulation models, preserving the accuracy of the EMC component models and the efficiency and coverage of a system model. In addition, working at the system level enables the use of other behavioural models to simulate the effects of logic, regulation, and control algorithms required for pulse-width modulation (PWM). These sub-systems can be modelled using VHDL-AMS or other description languages. In this way, the electromagnetic emission behaviour of the ECU system can be analysed precisely.