Innovative solutions for e-drive validation
By Mario Propst, Application Manager at AVL List GmbH in Graz
Using the latest technology, the experts from AVL List GmbH are simulating, developing and testing single electric components and complete electrified powertrains. Whoever wishes to develop the perfect e-drive system, consisting of electric motor and inverter, is faced with a whole series of tasks. On the one hand, it needs to harmonize with the electrical components such as the battery regarding communication, state of charge, temperature, DC voltage ripple and recuperation. On the other hand, the mechanical aspects need to be optimized. For example, synchronous motors display a certain torque ripple. This can negatively influence the driveability during vehicle pull-away or produce noise and vibration in conjunction with the e-axle and resonant frequencies can even damage the powertrain. This torque ripple needs to be eliminated as much as possible.
E-motors are designed for different configurations: P0 (starter-motor), P1 (integrated starter generator, or ISG after the combustion engine), P2 (ISG in front of the transmission), P3 (ISG after the transmission) and P4 (axle motor). This results in huge differences in construction; even speeds, torque and power can vary depending on the vehicle type. Nowadays, speeds between 15,000 and 20,000 rpm are standard. In the future, these speeds could increase to 30,000 rpm and higher. High Speeds have the advantage that the e-motor can be constructed smaller. This reduces weight, material used and costs; at the same time, there is the danger of introducing noise and Vibration (NVH).
AVL’s modern e-drive test systems are therefore built to validate e-motors with different designs, Speeds and torques as well as voltage and current levels. In the design phase, e-Motors are often optimized in several loops. The more precise the measurements can be performed by the development team on a test system, the greater and more valuable is the input. This enables the improvement of mechanics, electromagnetic performance, control or thermal behavior. This high level of data quality, together with precise measurement and control capability, is essential to be able to develop an e-drive system within a short time.
An e-drive test system mainly consists of the following components:
- Automation system – for automation, control and data storage(e.g. AVL PUMA Open 2™)
- Battery emulator – for battery emulation or constant HV voltage supply (e.g. AVL E-STORAGE BE™)
Power measurement System (e.g. AVL X-ion™)
Base measurement system
Cooling conditioning for Inverter and e-motor
- Climatic chamber
AVL differentiates between three types of e-drive test system: They are used for research and development, or for endurance testing, or end-of-line testing.
This article mainly deals with R&D test systems. In research and development, a prerequisite is a load machine with excellent speed control, which is required, for example, to be able to measure the torque ripple of synchronous drives at low and high speeds. The Instrumentation (in particular the power measurement device) also plays a decisive role. The power measurement system AVL X-ion™ measures AC and DC voltages and currents and uses the values to calculate the power of the e-motor and inverter.
In order to optimize an e-drive system, it is necessary to measure the harmonic oscillations of current and torque as well as the power to be able to calculate their contribution. They usually not only contribute to useful power but also cause losses in the form of heat. They are also partially esponsible for vibrations and noise. These harmonics need to be specifically detected. Only then can the simulated and measured effects be compared, and the efficiency of the e-drive system be optimized, for example by slightly modifying the design.
A huge advantage can be gained by recording the raw data for later analysis. This Permits the Analysis and development of remedies to combat phenomena such as DC voltage ripple, AC voltage peaks and currents, the effect of inverter switching on operating behavior, torque ripple, losses and the excitation of vibrations.
A well-optimized e-drive systemrequires less cooling, consumes less energy from the battery and thus increases vehicle range.
OEM&Supplier, Edition 2/2018