SENSORS
Current measurements in electric vehicles
Ralf Hickl, product sales manager ABU bei at Rutronik explores the options for sensors in automotive applications requiring measurement of high currents and voltages
A
s electro mobility increasingly becomes part of daily life, there is a growing demand for sensors that allow the bidirectional measurement of AC and DC currents in vehicles. They need to be effi cient, accurate, compact, and fl exible to use. A new current sensor meets all these demands. An increasing number of vehicle applications get their power from a battery, especially if the vehicle in question has an electric drive. At the same time, vehicle batteries and consumers are becoming increasingly powerful. This leads to higher voltages and currents in the vehicle’s electrical system. Other standards and safety regulations have emerged in response to higher voltages, such as galvanic isolation from the other voltage layers of the electrical system, as well as higher costs for protection against contact. The high currents lead to greater power loss in cables and anything with an ohmic resistance. So when it comes to current measurements, ultra-low ohmic shunt resistors that can dissipate high power loss are required. They are, however, relatively
30 MARCH 2022 | ELECTRONICS TODAY
large, which means many materials, weight, and costs.
To protect the battery and the electrical lines of the vehicle’s electrical system from overload, the currents must be measured, as a fi re in the wiring harness could quickly turn the vehicle into a write-off. This protective function used to be carried out by fuses. In the future, it will be the job of semiconductor switches to shut down the power supply in the event of overcurrent or a short circuit. A prerequisite for this procedure is accurate current measurement. Precise measurement of the current is also required, above all, by traction inverters to control the drive.
Magnetic fi eld sensors for galvanic isolation
As a result of various voltage levels of 12V, 48V, and high voltage in vehicles, the demands on galvanic isolation between these levels is increasing. Especially at high currents, sensors that measure the magnetic fi eld generated by the current and transmit it as an analogue signal offer great
Figure 1: A magnetic fi eld sensor with fl ux concentrator must be generously dimensioned to avoid permanent magnetization due to a short circuit and distortion of the system’s transfer characteristic
advantages: compared to a resistance- based current measurement using shunts, magnetic fi eld sensors offer signifi cantly lower power loss while at the same time providing galvanic isolation. These are particularly important features for high- voltage and high-current applications, since galvanic isolation ensures protection against contact, while the low power loss guarantees low self-heating.
To meet these challenges, Infi neon has now further developed its TLI4971 current sensor specifi cally for automotive applications: in the new TLE4972, the measurement current does not fl ow through the IC package as in the TLI4971 with an internal current path. Instead, the sensor is placed on the PCB or power rail close to the live line without contact.
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