Liu Jiaxi

Rotor Position Estimation for PMSM Based on Sliding Mode Observer

Most methods to estimate the rotor position of permanent magnetic synchronous motor (PMSM) suffer from the motor parameters, which are difficult to be applied due to the complicated algorithm. This paper presents a sliding mode observer (SMO) to estimate the rotor position of PMSM. The SMO makes use of the error between the estimated current and measured current. And the phase lag, which is caused by the low pass filter, is compensated in a proper way. The convergence of the SMO is guaranteed. A novel estimated speed is used to improve the systematic stability. High performance sensorless drive of the PMSM based on SMO is established and the whole system is simulated by matlab. Simulations show the effect of variation of the torque and speed on the estimated rotor angle. From these experiments, it is found that this method is more robust and easier to be applied.

An Approach to Analyzing Magnetically Shielded Room Comprising Discontinuous Layers Considering Permeability in Low Magnetic Field

To enable the realization of weak magnetic field at the level of several nanotesla, a magnetically shielded room (MSR) is required to create a space with residual magnetic field below 1 nT. Since the magnetic field shielded by inner shielding shells is very low, the permeability of shielding materials in this range is measured. As the gaps between ferromagnetic material strips in shielding wall lead to considerable reduction of shielding factor, a new numerical model to evaluate the equivalent permeability of discontinuous shielding layers is proposed and demonstrated experimentally. Based on the equivalent magnetic property in lower and normal magnetic field range, the improved approach to predicting the performance of MSR is obtained.