High-Voltage electrical system

Reading time: approx. 5 minutes – In this article, we compare the advantages of a high-voltage electrical system. We also discuss the associated challenges for electric vehicle manufacturers.

The much-discussed electrification of vehicles poses a major challenge for developers. So far, there are only a few well-founded empirical values and standards that they can fall back on. Regardless of whether the vehicle is designed as a hybrid or fully electric, an additional on-board power supply with a higher voltage is required. This is true even if a fuel cell is installed or only auxiliary units in commercial vehicles are operated electrically. This is in addition to the 12 VDC on-board power supply. There is a clear trend towards high-voltage electrical systems. These are defined for voltages between 60 VDC and 1500 VDC.

 The advantages of a high-voltage electrical system

The choice of voltage for this second vehicle electrical system has a fundamental impact on the respective vehicle concept. With the same available power, the required current increases indirectly in proportion to the voltage level. In order to minimise the line losses at currents and the resulting thermal problems, the line cross-sections must be increased disproportionately. This has a negative impact on both material costs and weight. Furthermore, it poses major design challenges with regard to the usually small installation space.

To summarise, increasing the voltage used in the vehicle electrical system results in advantages. These include better efficiency, thermal management, material costs, weight, and space requirements.

Energy storage in the high-voltage vehicle electrical system

 The centrepiece of every high-voltage vehicle electrical system is the energy storage unit. In the case of a battery as an energy storage device, this consists of a certain number of individual cells. This number depends on the capacity, which can have voltages of 1.75 VDC to 4 VDC depending on the cell chemistry and state of charge. The terminal voltage of the battery results solely from the parallel and serial connection of the individual cells. The capacity of a battery is therefore independent of the terminal voltage. It is only determined by the number of interconnected cells. If fuel cells with a hydrogen tank are used as energy storage, their output voltage is analogous to the terminal voltage of the battery. In order to achieve a desired output voltage, several fuel cells are connected to form a stack. This is usually with approx. 1 VDC.

 Challenges when using a high-voltage vehicle electrical system

In addition to the listed advantages of a high-voltage vehicle electrical system, it also presents vehicle developers with a number of challenges. Unlike the 12 VDC vehicle electrical system, they cannot rely on a broad and established product portfolio. Many components have to be developed specifically for the respective application. Sometimes, the application has to be adapted to the existing component.

Furthermore, various safety requirements regarding contact protection, electromagnetic compatibility and installation guidelines must be observed in high-voltage vehicle electrical systems.

The certification of the installed modules and the entire vehicles has also become more complex. It is increasingly presenting manufacturers with problems. In many cases, no standards have yet been defined, or these are not applicable to the application used.

However, the growing interest in alternative drives will lead to these challenges being overcome in the medium term. This is the case with all other innovative technologies as they enter the mass market. The advantages are obvious.