Current and voltage measurement in and around hybrid and electric vehicles

Developing hybrid and electric vehicles is now a high priority worldwide, and fuel-efficient vehicles are promising to become the automobile sector's major future business.

Many electric drive solutions have been introduced already. Here it is important to differentiate between a fully electric drive and various hybrid drives in integrated, serial or parallel versions. Fuel cells are also very promising candidates in this field. No matter which of these solutions is implemented, there must be a storage device for electric power which can be charged internally or externally to provide the stored energy to the respective consumers when required.

However, the question of the best way of storing energy has not yet been answered. One of the competing solutions is using Ultra Caps, which are essentially capacitors with a high storage capacity, and others include various battery types, such as nickel metal hybrid, high-temperature and Li-ion batteries. Conditions that must be met by suitable energy storage include the cell's chemical properties, the availability of its contents, its behavior under various temperatures, safety, charging and de-charging behavior and, most of all, energy density in relation to weight, or power-to-energy ratio. In this respect, Li-ion cells are currently the favorite as far as use in electrically powered vehicles is concerned.

Each stage of the supply chain, such as energy transformation, transport, charging stations, mobile voltage transformers (DC/DC transformers) and even the electrical drive in the vehicle requires the physical properties of current and voltage to be determined, and in many cases also temperature for technical and commercial reasons. These properties must be measured as accurately as possible. Isabellenhütte offers a suitable measuring module for each of these areas of application.

Charging current balance and the exact battery voltage must be determined both for billing purposes and to determine the battery's state of charge (SOC). In order to use an electric drive in an optimum way, the available energy must also be used efficiently. Hybrid or electric vehicles will only be accepted by consumers if we can guarantee safe and reliable operation and if the driver is able to continuously monitor the vehicle's status. Both of these requirements can only be fulfilled with substantial technical effort. Energy flow regulation must be a controlled process under any operating condition, which also requires a continuous measurement of current and voltage. The voltage range may be up to 800 V, depending on type of battery and number of cells. The current range reaches from extremely low currents of some 10 mAmp to permanent high currents of up to 600 Amps and peak currents of up to 1.5 kAmps, which have to be measured with a precision of 0.1 and 0.5 % respectively (1.5 kAmps range). Better resistances against over-current and over-voltage are also required, meaning that the dynamic range to be displayed is extremely high.