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Measurement errors are inevitable in the current sensors, which cause speed ripple including one and twice the stator electrical frequency. For the undesired harmonics, the adaptive selected harmonic elimination (ASHE) algorithm outputs the sum of the sinusoidal signals multiplied by the adaptive weights. In order to solve the current measurement error (CME) issue, this article adopts the ASHE algorithm. According to the deterministic functional relationship of the surface-mounted permanent magnet synchronous motor (SPMSM), the adopted algorithm extracts the harmonics of the steady state speed error, and outputs the q-axis current compensation. However, there is no explicit connection between speed and d-axis current, so their relationship is uncertain. The remaining d-axis CMEs result in poor current performance. Therefore, this article proposes an improved ASHE algorithm, which compensates the dq-axis CMEs simultaneously depending on their mutual deterministic connection. The proposed method does not need motor parameters, additional sensors, or complex calculation process. Finally, the effectiveness of the method is verified by the SPMSM platform. Experimental results also show that the proposed method reduces speed ripple and suppresses the negative effects of CMEs. [ABSTRACT FROM AUTHOR]

The presence of dc offsets results in fundamental frequency oscillations in the frequency estimation and it is a challenging problem in single-phase grids. In this article, a four consecutive samples (4CSs) based method is proposed to estimate grid frequency with strong dc offset rejection capability. In details, a 4CS model is established based on the relationship among the fundamental grid voltage, dc offsets, and their consecutive sample signals. Different from the traditional 3CS model, the proposed 4CS model can reject the negative effects of dc offsets completely. Based on the obtained model, a frequency estimation is proposed and stability analysis is provided according to the adaptive control theory. Unlike the traditional 3CSs relying on prefilters, the proposed method is filter-free and it still has strong suppression capability against dc offsets. The theoretical sound and experimental results indicate that the proposed method achieves accurate frequency estimation with good dc offset rejection capability. [ABSTRACT FROM AUTHOR]

In aircraft grids, the voltage frequency is much higher than that in utility power systems and it challenges the dynamics of frequency estimations. In this letter, a fast and robust frequency estimation method is proposed for aircraft grids even when the grid voltage is distorted. In detail, a mathematical model is established based on the relationship among the fundamental grid voltage, harmonics and their time-delay signals. Accordingly, a robust parameter identification method is proposed to achieve grid frequency estimation and harmonic immunity. Compared with the frequency estimations for utility power systems, the proposed method, so-called robust frequency estimation (RFE), has faster dynamics and stronger harmonic suppression capability. Hence, it takes advantages in the applications of aircraft grids. Experimental results also indicate that the proposed RFE has good performance in terms of fast dynamics and strong robustness. [ABSTRACT FROM AUTHOR]