A study of low-cost attitude and heading reference system under high magnetic interference

In an Attitude and Heading Reference System (AHRS), the heading estimation is generally achieved by measuring the Earth's magnetic field. However the Earth's magnetic field is easily distorted by magnetic interference from ferrous or magnetic objects. The traditional AHRS algorithm fuses the magnetic measurement into the estimation process of three attitude angles, acceleration and angular velocity with a Kalman filter. It may cause simultaneous misalignment of pitch, roll and yaw if the magnetic field is under high interference. In order to reduce the effect of the magnetic interference on orientation estimation, this paper proposed an adaptive Kalman filter algorithm, which alternates measurement equations in different magnetic conditions to achieve accurate and stable attitude and heading estimation. Quaternion is used to present the relation between body coordinate frame and navigation coordinate frame. To validate the algorithm, a prototype AHRS is designed. The experiments' results show that the prototype AHRS with the proposed algorithm could achieve both high accuracy and stability even under high magnetic interference.