Battery management system (BMS) of a electric vehicle (EV) in the different architectures needs a set of reliable set of sensors for current, voltage and temperature measurement to achieve a good control and monitoring. Those sensors are mounted in the battery pack to monitor different parameters like cell voltage, current through the cells, temperature of cells and pack, leakage, Insulation, Impedance, state-of-charge (SOC), state-of-health (SOH), and finally the state of Function like an estimation according to the SOC, SOH and the environment.

Fluxgate Transducers for Battery Monitoring System in Electric Vehicles

Fluxgate Current Transducer for Battery Monitoring System in Electric Vehicles (EV)The basic operating principle of Fluxgate Current Transducers is based on the detection of the saturation state of a magnetic circuit. The usually-called “standard” fluxgate transducer uses a toroidal magnetic circuit which includes an air gap with the element for magnetic field measurement. This sensing element is also called “saturable inductor”. The current sensor proposed by PREMO is based on a variation of the “standard” fluxgate transducer structure, and it operates in closed-loop conditions. This kind of transducer uses its own ring core as a magnetic field detector and includes no gap on the magnetic path. Reliable current transducers for Battery Management Systems have to be designed taking into account many parameters related with:

  • DC and AC current measurement capability
  • Temperature response characteristics 
  • Low aging, measurement stability over time
  • High accuracy and linearity
  • Automotive AECQ compliant
  • Automotive communication interface

After a deep analysis of current transducers capabilities and characteristics the best option chosen by Premo group is a current transducer based on fluxgate principle. Finally, the main characteristics of the designed fluxgate current transducer are summarized below:

  • Nominal primary current: up to 700A
  • Maximum peak primary current: 1kA
  • Conversion ratio: 1000:1
  • Small-signal bandwidth (1% of nominal primary current): 170kHz
  • Supply voltage: from 10 to 30 VDC
  • Standby power consumption (IP = 0): 3.1W.
  • High Accuracy and linearity.

One important drawback of this structure is the possibility of noise injection from the excitation winding circuit into the primary current circuit. This noise can be coupled into the primary current circuit due to the transformer effect present in the magnetic core of the transducer. The solution usually adopted, in order to avoid this negative influence, is the use of a second core with a new auxiliary winding (or new excitation winding). Under ideal conditions, these two cores and their winding must be identical.

In order to obtain a more detailed characterization of the designed current transducer, reference DCT-700A can be consulted on the general datasheet of PREMO Group. This datasheet is available online at: www.grupopremo.com. Some parts of the presented transducers are protected by PREMO Patents.