Development of high bandwidth current sensors based on the magnetoresistive effect

New control techniques for electric drives pose new problems for the manufacturers of current sensors. In particular the sensorless control of permanent magnet synchronous machines places new demands on the current sensors used to measure the motor phase currents. The latest control techniques to determine the rotor position from the inductive signature of the electric machine require best performance characteristics for phase current sensing in terms of dynamic range and bandwidth. Oversampling of the motor current allows a low noise calculation of the rate of change of current (di/dt), which improves the measurement resolution and allows smooth operation down to zero speed without negative side-effects, such as acoustic noise. The magnetoresistive (MR) effect offers a unique combination of high bandwidth, high resolution, miniaturization and robustness, and is particularly well-suited for the development of compact, fast and accurate current sensors. The power losses are significantly lower than for shunt resistors and the response time is almost an order of magnitude faster than for hall-effect based current sensors. Furthermore, MR-based current sensors have an extremely high bandwidth, in the range of several MHz, which allows the full exploitation of new wide bandgap power electronic technologies, such as Silicon Carbide switches and diodes.