During the last decades, the development of increasingly sensitive magnetic sensors led to numerous applications of magnetic field measurements in neuro-science, medical diagnostics, brain-computer interfaces, metrology or for experiments testing the fundamental laws of nature. Especially the development of small, lightweight, rather mobile and easy to handle optically pumped magnetometers allows for more advanced and dynamic studies of e.g. the brain. The limitation for the quality of such magnetic signals are gradients and drifts in the measuring environment. Our presented work combines the result of many years of work, resulting in calculations to quantitatively predict the areas with ultra-low magnetic fields inside passive magnetic shields, as well as the experimental confirmation. The calculation shows that a conventional three-layer chamber with an improved degaussing system will already provide environmental conditions never reached before. In the most recent implementation an unprecedented residual field of < 130 pT was repeatedly achieved over 0.5 m x 0.5 m x 0.5 m inside an easily accessible space, consistent with the numerical modeling.

This paper proposes an enhanced system-delay-tolerant signal processing method for high-frequency (HF) signal injection based position sensorless interior permanent magnet machine (IPMSM) drives. To reduce the acoustic noises induced by the HF response current using the conventional fixed-frequency sinusoidal injection based method, the pseudo-random-frequency sinusoidal injection strategy is proposed and comparatively evaluated in terms of the power spectral density of the phase current. Furthermore, the position estimation degradation caused by the system delay effects due to the pulse-width modulation (PWM) update delay and the hardware delay using the common signal processing method, especially with the injection frequency increasing, is analyzed. On this basis, an enhanced system-delay-tolerant signal processing strategy is proposed. Through the normalization process for the HF response current and coordinate transform, the terms related to plant parameters and system delays can be cancelled. Therefore, the reliable saliency based method with higher injection frequency can be achieved. The comparative evaluation on a 2.2-kW position sensorless IPMSM drive is carried out, which verifies the effectiveness of the proposed scheme.

This paper presents a two-degree-of-freedom (2-DOF) H speed control structure for permanent magnet synchronous motors (PMSMs). This structure consists of three parts: an H disturbance observer (DOB), an H feedback and an H feedforward controller. Firstly, the H problem and the feedback controller design method for PMSM are presented. The stability and solution are introduced. Secondly, the disturbance observer (DOB) is designed as an H disturbance tracking problem to estimate the external load torque and increase the robustness. The speed controller is adjusted and regards the estimated torque as one of the input. Finally, based on the 2-DOF structure, an H feedforward controller is designed, taking the closed loop performance into account. The proposed method has a better dynamic and stronger robustness against external disturbance and parameter variation. Several simulations and experiments of conventional PI controller, standard H speed controller and proposed method are operated in a PMSM system and compared to validate the accuracy of the disturbance observation and the effectiveness of the proposed method

This paper presents an analytical model of magnetic field of a permanent magnet synchronous motor (PMSM) with a trapezoidal Halbach permanent magnet array (THPMA). Compared with conventional Halbach array, the shape of each magnet in THPMA is transformed from rectangle to trapezium in polar coordinates. The THPMA is delaminated indefinitely radially and each layer is approximately considered to be a conventional Halbach array. The air-gap magnetic field of each layer is analyzed with the scalar magnetic potential. Then, the air-gap magnetic field of the THPMA is obtained by superposing magnetic fields of all layers. The validity of the analytical model is verified by a finite-element model (FEM). The air-gap flux density is optimized by adjusting the center angle coefficients of the THPMA, and a no-load phase back electromotive force (EMF) with the harmonic distortion rate (THD) of 0.75% is obtained by FEM. The back EMF is basically consistent with the measured result of a prototype motor.

The triaxial fluxgate magnetometers (TFM) are widely used in space exploration, positioning and navigation, geological exploration, etc. As a high-precision vector magnetometer, the measurement accuracy will directly determine the accuracy of the obtained magnetic field data. The TFM has three kinds of own errors in measurement: zero offset error, proportional coefficient error and non-orthogonal error. These three kinds of errors will cause the TFM to deviate from the actual magnetic field value, and the fluxgate magnetometer needs to be calibrated. At present, the accuracy of the calibration method adopted by the fluxgate magnetometer depends on the stability of the natural environment magnetic field and the triaxial turntable (there is an uncontrollable residual magnetic interference), which limits the further improvement of the calibration accuracy. And due to the wide application of electromagnetic equipment, the natural electromagnetic environment is further damaged, and the calibration accuracy is subject to deterioration. In this paper, a magnetic shielded room (MSR) is used to provide a near-zero magnetic environment, and a triaxial uniform magnetic field coil (TUMC) is installed inside the MSR to construct a controllable arbitrary vector direction magnetic field, which solves the magnetic field disturbance problem of the original method. The TUMC and TFM error models were built and the MSR magnetic ambient noise model was added. The emphasis is on the degree of distortion of the magnetic field generated by the MSR as a ferromagnetic boundary condition and the influence of the deviation of the center point of TUMC on the calibration accuracy. Then, based on the above error model and magnetic environmental conditions, the calibration accuracy of the calibration magnetic field distribution is analyzed. Finally, the calibration experiment of the TFM is carried out by using the existing MSR, which proves the feasibility and effectiveness of the calibration method, and the method can greatly improve the calibration efficiency.