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The cascaded delayed signal cancellation (CDSC) based PLL in dq rotate frame ( dq CDSC-PLL) can totally eliminate the disturbances of phase error. However, its open-loop bandwidth is significantly affected after incorporating CDSC into the PLL structure, so the transient response performance of three dq CDSC-PLLs are deteriorated. This paper proposes an improved dq CDSC-PLL by cascading a digital filter based phase-lead compensator into CDSC-based PLL to improve the dynamic response without sacrificing the stability. The filter shows flat gain in the passband, which can compensate the phase delay induced by CDSC and simultaneously maintain the attenuation of the notch point. The improved dq CDSC-PLLs significantly increases the open-loop bandwidth and enhances the dynamic performance. Besides, in order to further minimize the undesirable steady-state error, the frequency adaptive control was adopted without using any additional circuits. In order to verify the effectiveness of the proposed method, the simulation based on Matlab/Simulink is carried out for various conditions. Furthermore, experimental results for typical scenarios are provided, which highlight the advantage of the improved dq CDSC-PLL in terms of the dynamic performance. [ABSTRACT FROM AUTHOR]

In this article, a low complexity finite-control-set model predictive control (FCS-MPC) based on the discrete space vector modulation (DSVM) is proposed for T-type three-phase three-level (3P-3L) converters. Different from the conventional FCS-MPC, 48 virtual voltage vectors (VVs) of the converter are constructed by real VVs based on the DSVM. Thus, the performance of 3P-3L converters is significantly improved and the peak amplitude of high-order harmonics concentrates at the sampling frequency. Furthermore, two-stage FCS-MPC based on virtual VVs is proposed to reduce the computation burden. Its first stage selects one of six virtual VVs that minimizes the current tracking error. Then, these candidate VVs located in the same sector as the optimal virtual VV selected in the first stage are evaluated in the second-stage optimization. Thus, the computational efficiency has been greatly improved. To verify the validity of the proposed control method and show its superiority over the conventional FCS-MPC, experimental results are presented. [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]

This paper presents a novel model predictive control (MPC) for the T-type single-phase three-level inverters. The cumbersome procedure in tuning of weighting factors is eliminated so that the implementation of the proposed MPC becomes easy. The constant switching frequency is achieved during the control implementation in order to facilitate the filter design. In order to optimize the distribution of the output current harmonics, multiple voltage vectors are employed in each control cycle with their application times setting inversely proportion to the respective cost function. The redundant small voltage vectors are utilized to balance the neutral point voltage of the inverter by directly regulating the upper and lower dc-link capacitors voltages. Finally, the proposed MPC algorithm is experimentally evaluated and compared with other two unfixed switching frequency MPC algorithms in terms of the steady state, transient performance, and parameter sensitivity. [ABSTRACT FROM AUTHOR]

• The proposed method is suitable for more electric aircraft grids. • The proposed method has fast dynamics. • The structure of the proposed method is simple. Different from utility power systems, the grids of more electric aircraft (MEA) are frequency-variable, and the frequency change range is from 360 Hz to 800 Hz. Most grid synchronization methods are designed for constant-frequency grids whose frequency varies in a small range around 50 Hz or 60 Hz. Therefore, the dynamic performance of these methods decreases considerably in MEA grids. In addition, the frequency in MEA is higher than that in utility power systems. Grid voltage parameters are thus required to exhibit a fast dynamic response. To resolve this problem, this paper proposes an algebraic method to estimate the positive- and negative-sequence components (PNSC) of grid voltage accurately. By analyzing the relationship between grid voltage and its time delay signals, the linear regression model is established. Then, grid frequency, PNSC are obtained with an algebraic method. The proposed method relies on algebraic operations only and thus exhibits a fast dynamic response. Experiment results verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]