Xiangjun Quan

A Concise Discrete Adaptive Filter for Frequency Estimation Under Distorted Three-Phase Voltage

To improve the control performance for grid-tied power converters, the fundamental frequency and harmonics of the grid voltage should be quickly and accurately estimated even under distorted voltage condition. This paper introduces a straightforward discrete adaptive filter to observe fundamental and harmonic sequence components of the grid voltage. The proposed filter possesses a simple and straightforward implementation. Based on the newly developed filter, frequency error transmission was analyzed when the frequency of the input voltage was unequal to the center frequency of the filter. Consequently, a frequency estimation loop was designed to adapt to the frequency variation for the filter. Compared to previous algorithms, the proposed algorithm has a better dynamic performance rating for frequency estimation, robust stability, and a simpler implementation. The effectiveness of the algorithm is verified by simulations and laboratory experiments.

Self-synchronized voltage control algorithm for microgrid inverter

The wide application of distributed generations (DGs) and microgrids (MGs) infuses new vitality into the voltage control of the inverter, which represents a traditional power electronic research area. In this paper, a self-synchronized resonance voltage control algorithm is proposed to satisfy the requirement of an inverters seamless switching from grid-connected (GC) mode to stand-alone (SA) mode, limiting switching over-voltage and improving switching dynamic performance. Meanwhile, a frequency closed-loop control method is proposed to get rid of the frequency static errors introduced by the self-synchronized feedback voltage control. The effectiveness of the proposed algorithm was confirmed by an experimental MG system.

Discrete time optimal design for voltage prefilter in grid synchronization system from control perspective

The grid synchronization system, which plays an important role in the control of grid-connected power converters, often needs to manipulate the grid voltage to extract the fundamental and harmonic sequence components. Generally a prefilter can achieve this function. In this paper, a systematic and general approach to design the multiple block based prefilter is introduced. First a complex variable discrete resonantor is adopted in the prefilter. Furthermore, the multiple coefficients of the prefilter are tuned by means of minimum energy method with variance constraint from control perspective. The proposed approach is described as an optimal solution in form of linear matrix inequality (LMI). Moreover, the approach is allowed to customize the settling time of the prefilter by designer. In addition, the prefilter yielded from the approach also performs good dynamic performance such as the fast settling time and smooth transient waveforms. The effectiveness and superiority of the proposed approach is verified by the numerical results.