Understanding current sensing in HEV/EV batteries

By Sandeep Tallada, Texas Instruments

Texas Instruments

When I was six years old, I got a remote-control car as a present from my dad. With just a click of a button, I was able to control the car and it was running all around my home. One day, my brother and I suddenly got into a fight and broke the remote-control car into pieces. I was curious to look inside and see how it worked. I learned that remote-control cars used batteries as their main source of energy. I went to my father and asked, “Do all cars operate with batteries?” My father laughed and said, “No, it is impossible to power a car with a battery; only toy cars can operate with batteries. Cars on the road operate with fuel.”

Whenever I remember this story I am quite amazed, because now I work on systems for electric vehicles (EVs), and I know that it’s 100% possible to power a car with batteries. The main source of energy for hybrid EVs (HEVs) and EVs is the battery; efficient control of the battery implies an efficient battery-monitoring system.

The battery-monitoring system is mainly used to estimate state of health (SOH) and state of charge (SOC). In order to obtain detailed information about SOH and SOC, integrating accurate sensors into the battery-monitoring system is important. For a typical battery, current, voltage and temperature sensors measure the following parameters, while also protecting the battery from damage:

  • The current flowing into (when charging) or out of (when discharging) the battery.
  • The pack voltage.
  • The individual cell voltages.
  • The temperature of the cells.

Figure 1 shows the location of current sensors in a block diagram of a battery-control unit.

Figure 1

Figure 1: Current-sensor location in battery-control unit

When the battery is the main source of energy for systems in HEVs/EVs, it is essential to have information about its charging and discharging cycles. Current sensors are the main source of information for charging and discharging cycle information by reporting the status of battery SOH to the battery management system. They may be located onboard or externally. With the increase of battery capacities in HEVs/EVs, the requirements on higher current ranges are…


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