In this article, a model-based sensorless control method which incorporates the orthogonal master-slave adaptive notch filter (ANF) for surface mounted permanent magnet synchronous motor is proposed. Since the rotor position estimation is seriously affected by the harmonics of estimated back-electromotive force (EMF), the orthogonal master-slave ANF is designed to deal with this problem. The orthogonal master-slave ANF is developed based on the ANF with frequency adaptation. The theoretical analysis indicates that the orthogonal master-slave ANF can accurately track the specific harmonics and the fundamental wave of back-EMF. Both the satisfactory harmonics elimination and the fast response speed of filter can also be achieved at the same time. Besides, the proposed frequency adaptation algorithm overcomes the dependence of frequency convergence on the signal amplitude and the problem of “double-frequency oscillation” in the estimated frequency. And since the use of frequency adaptation, the phase-locked loop is unnecessary, which simplifies the system and enhances the reliability. The corresponding experimental results under different conditions demonstrate the effectiveness and the superiority of the proposed method.

The analysis of the dynamic process of winding destabilization under sudden short-circuit conditions is of great importance to accurately assess the short-circuit resistance of power transformers. Based on magneto-solid coupling, an axisymmetric model of the transformer and a 3D multilayer model of the transformer considering the support components are established, respectively, and the short-circuit electromagnetic force (EF) is simulated by using the finite element method. It is concluded that the middle layer of the winding is subjected to the larger radial EF, while the axial EF has a greater effect on the layers at both ends. Moreover, the impression of the preload force, aging temperatures, and the area share of spacers on the vibration and deformation of windings are studied under short-circuit conditions. The overall distribution of plastic strain and residual stress in the winding is symmetrical, and the maximum values occur in the lower region of the middle of the winding. Finally, considering the material properties of disks and insulating components, the cumulative effect of plastic deformation under multiple successive short-circuit shocks is calculated. Compared with the traditional axisymmetric model of transformer, the three-dimensional multilayer model of the transformer established in this paper is more suitable for the actual winding structure and the obtained results are more accurate.

In this study, a novel sensorless control of the surface‐mounted permanent‐magnet synchronous motor (PMSM) is proposed. Firstly, by taking the derivative of the back electromotive force (EMF), the high‐order voltage equations of PMSM, in which the dominant time‐changing parts of back‐EMF are separated and modelled, are deduced. Then a generalised extended state observer, which possesses the preferable tracking ability for time‐varying states, is designed to estimate the back‐EMF. Also, since the difference between the measured stator resistance and its real value, which changes with temperature, will lead to position errors, a resistance estimation scheme is proposed. Compared with the conventional sensorless method of PMSM, the proposed method can provide a more accurate and smooth position and speed estimation under resistance uncertainty without extra filter and compensator. Furthermore, since the effects of speed and current change rate are taken into consideration, the application of the proposed scheme is broadened. The effectiveness of the proposed method is verified by the experiments in different cases.

As a common interface circuit for renewable energy integrated into the power grid, the inverter is prone to work under a three-phase unbalanced weak grid. In this paper, the instability of grid-connected inverters under the unbalanced grid condition is investigated. First, a dual second-order generalized integrator phase-locked loop (DSOGI-PLL)-based inverter under balanced and unbalanced conditions is modeled. A fourth-order impedance model is established to describe its impedance characteristics under the unbalanced grid condition. To analyze this multi-input multi-output system, a simplified stability analysis method based on the generalized Nyquist stability criterion and matrix theory is proposed. Then, the influences of circuit and control parameters on the stability of the grid-connected inverter system under the unbalanced grid condition are investigated. Finally, the accuracy of the derived frequency-coupled impedance model is verified via simulations, and the effectiveness of the proposed simplified stability analysis method on the system stability analysis is verified via both simulations and hardware experiments.