How to Manage the Increased Numbers of Electrical Consumers in Vehicles?
The energy consumption of different ECUs in a vehicle is associated with an increased need for electrical energy (peak power) in various driving situations. In general, the electrical power consumption in vehicles has more than doubled. This was caused by the gradual decoupling of more and more vehicle systems that were traditionally consumers of the internal combustion engine, for example the steering system or coolant compressors. These have been directly replaced by electrical systems in electric vehicles. In addition, numerous new or greatly enhanced electrical consumers such as complex infotainment systems are installed in vehicles to increase comfort and safety.
Challenges for the Management of the Electrical System
To make things even more difficult, the on-board electrical system structure has moved to a two-battery architecture in electrical vehicles. This architecture has two voltage levels, which are coupled via a DC/DC converter, and must also incorporate a feed of high recuperation energies when braking. Therefore, complex energy management systems are necessary to manage these requirements and to ensure the safety and full functionality of a vehicle even in the case of a prolonged passive parking period. Stable behaviour of the on-board electrical system must be maintained through a variety of disturbance variables such as driving cycles, load scenarios or external temperatures.
Testing the Vehicle Prototype
For this reason, the energy management system of a vehicle is already simulated in the prototype phase of the vehicle development and the accuracy of the simulation models is verified in later development phases by means of measurements. For these measurements, all electrical consumers of a vehicle type are assembled on so-called "breadboards", which remain in existence and available throughout the entire development and production time.
This allows, for example, errors in components and software updates to be reproduced. Up to 100 current channels must be monitored in these test stands to fully assess the energy management system and capture the resulting data.
Measuring load currents in vehicle electrical systems, especially when dealing with a wide range of current levels, presents several challenges. These challenges arise from the need to accurately and safely measure both very large and very small currents simultaneously. Here are some of the key challenges:
- Wide Current Range: Vehicle electrical systems typically have a wide range of current levels, from very small currents, nanoamps, in electronic control units (ECUs) to very large currents, tens of amps, in power-hungry components like motors and headlights. Measuring this wide range with a single device can be challenging.
- Accuracy and Precision: Maintaining high accuracy and precision across the entire current range is essential. Inaccurate measurements can lead to improper diagnosis and maintenance, affecting vehicle performance and safety.
- Shunt Resistance: To measure current, shunt resistors are often used. However, selecting an appropriate shunt resistor that can handle high current without overheating while still providing good resolution for small currents is a challenge.
- Voltage Drop: Large current measurements across shunt resistors can result in significant voltage drops. This can impact the performance of sensitive electronics or devices with low supply voltage thresholds. Mitigating this voltage drop is crucial.
- Heat Dissipation: Large currents produce heat, which can affect the accuracy of measurements and potentially damage components. Effective heat dissipation solutions must be employed to avoid these issues.
- Electrical Noise: The presence of both high and low current signals in the same system can introduce electrical noise. This noise can affect the accuracy of measurements and may require the use of additional shielding or filtering.
- Safety: Safety is a paramount concern when dealing with high currents. Adequate protection mechanisms, such as fuses or circuit breakers, must be in place to protect against overcurrent conditions. Ensuring safety while making accurate measurements is a balancing act but must always fall on the side of safety for the person taking the measurements.
- Sensor Calibration: Calibrating a current sensor to be accurate over a wide range can be challenging. Calibrating for small currents may require different techniques and equipment than for large currents.
- Cost: Developing a sensor or measurement system that can handle a wide current range while maintaining accuracy can be costly, which is a concern for both manufacturers and consumers.
- Size and Packaging: Creating a measurement device that can fit into the often limited space within a vehicle's electrical system can be challenging, especially when dealing with both very small and very large currents.
To address these challenges, automotive engineers and manufacturers may employ various strategies, such as using multiple sensors for different current ranges, using auto-ranging instruments, employing advanced calibration techniques, and integrating temperature and voltage compensation mechanisms. Ultimately, it's crucial to strike a balance between accuracy, safety, and cost when designing measurement systems for vehicle electrical loads.
