- A DESIGN-TO-COST ALTERNATIVE TO CONVENTIONAL VARIABLE RELUCTANCE RESOLVERS FOR THE ELECTRIC DRIVES CONTROL -

Many synchronous electric motors require a very accurate position sensor compatible with a sinusoidal control. The purpose of such a control is to enable an efficient and smooth operation enhancing the comfort by limiting vibrations. In some cases related to mechanical constraints, we have to deal with through-shaft design. One can quote for examples power drives for Electric or Hybrid Electric Vehicles as well as for Electric Power Steering motor. More generally, these sensors need to keep a simple and robust design and a restricted number of parts as they are submitted to high vibration levels, a wide temperature range and speeds of several krpm. In order to meet such requirements, MMT has developed a magnetic sensor principle offering a competitive alternative to the conventional inductive resolver type sensors. The basics of this solution is a through shaft angular position sensor using one or two Hall-effect probes. These Hall IC measure the angle of the magnetic field generated by a ring or a disc magnet. The magnetic field angle is shaped in order to meet very demanding accuracy requirements (+/-1° of electric error). The use of two probes allows enhancing even more the accuracy and provides as well the design with an intrinsic robustness against external magnetic perturbations coming from the motor coils. The paper deals with this sensor principle showing that the challenge to meet less than +/-1° of electric error on rotary position sensors with motor mechanical shaft diameters up to 100 mm was taken up. The need for sensor accuracy of less than +/-1° electric to control electric machines required from us to develop new sensor topology as an alternative to inductive resolver type sensor (1;2). The key point was to keep the sensor architecture as simple as possible to be compatible with mass production process required in automotive field. Thus the rotary sensor is made of one magnet and two Hall IC. Starting with an analysis of the standard sensor topology using Hall-effect principle based on traditional magnetization, we will illustrate, in the first part of the paper, the reason why a new sensor topology was considered. The key features of this patented sensor architecture called MM126 (3) are the use of a specific magnetization and the use of 2 Hall probes, 90° electric shifted (i.e. the second probe is at a quarter period of the first probe). After explaining the theory of these features, the sensor robustness versus mechanical defaults, effects of the rotor speed and temperature thanks to prototype results will be illustrated.