Current and voltage measurement in and around hybrid and electric drives

No matter if you're designing a hybrid, electric or fuel cell powered application - a new development's sustainability always depends on the reliability in every-day use and therefore on controlling its energy flow and consumption permanently. Not every method for measuring current and voltage is able to fulfill each of the difficult requirements. Isabellenhütte has developed the current and voltage measuring module IVT for DC applications in alternative drive concepts based on its experience in the area of car battery management.

Storing energy
Many electric drive solutions have been introduced already. The similarity between all these applications, is that 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 applications is concerned.

Continuous measurement
Each stage of the supply chain, such as energy transformation, transport, charging stations, mobile voltage transformers (DC/DC transformers) and even the electrical drive 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 known 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. 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 IVT-MOD
The IVT-MOD is a high precision current and voltage measurement system, designed for DC applications. The product is based on a modular design and provides flexibility for fast adaptations to meet customer requirements in the automotive and the industrial area. The continuous current measurement has a range of ±2,500 A and the voltage channels include a range of ±800 V, and it is approved for continuous operation. At higher currents (i. e. peaks) the measurement range will extend automatically. The shunt-based measurement method uses a 16-bit analog-digital converter to transform the voltage drop into a digital signal. All used components are automotive qualified. The communication is based on a CAN bus interface. A CAN description file (CAN-dbc) is available and supports a fast system integration.

Main Advantages

• High precision current and voltage measurement
• Operating range up to 2500A continuous current
• Overcurrent detection
• Accuracy: 0.1 %
• Interfaces: CAN, SPI
• Up to 3 voltage channels (up to 600V)

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