Applying Directly Modified RDFT Method in Active Power Filter for the Power Quality Improvement of the Weak Power Grid

Rui Hou,Huihui Song,Dianguo Xu,Yanbin Qu,Jian Wu

doi:10.3390/en13184884

Abstract

The recursive discrete Fourier transformation (RDFT) method can be used for grid voltage phase-locking and harmonic current detection in a shunt active power filter (SAPF). However, in weak power grids such as microgrids, significant errors might occur in the amplitude and phase detection due to grid frequency deviation. In this study, to resolve this problem, a directly modified RDFT (DMRDFT) method is proposed for SAPF weak grid application. Through theoretical analysis, the errors of phase and amplitude detection were found to consist of fixed error and fluctuating error. The fixed error is only determined by frequency deviation, whereas the fluctuating error is also related to the recursive pointer and the initial phase. The DMRDFT algorithm can obtain the real grid frequency through the calculation of the phase angle difference for two consecutive periods. Then it can employ the grid frequency deviation and the recursive pointer value to directly correct the detection results gathered by the conventional RDFT algorithm. As a result, DMRDFT can yield accurate amplitude and phase information of the grid voltage or current with a simple calculation. Simulation results verify the high precision of the proposed DMRDFT method in both steady and dynamic situations. Experimental results show that the DMRDFT method can significantly increase the SAPF compensation performance when grid frequency shifts.

Highlights

The weak power grid, such as the microgrid, remote rural network, and poorly regulated network, is an integral part of current and future power systems [1,2]
Tointroduces overcome the error small caused by frequency deviation, the DMRDFTadvantage method proposed in this paper the error caused by frequency deviation, the method proposed in this paper introduces an
This paper has made the following conclusions based on previous studies: In a weak power grid, grid frequency often shifts, and large errors will occur for the amplitude and phase detection using the recursive discrete Fourier transformation (RDFT) algorithm

Summary

Introduction

The weak power grid, such as the microgrid, remote rural network, and poorly regulated network, is an integral part of current and future power systems [1,2]. Among the several power quality improvement measures, the shunt active power filter (SAPF), based on the principle of the controlled current source, provides a flexible and effective solution for the weak grid [6,7,8]. It can inject a compensation current characterized by the equal amplitude and the opposite phase compared with the load-side reactive and harmonic current to ensure the grid-side unity power factor and sinusoidal current. Due to merits such as having no need for load reform, good compensation

Methods

Findings

Discussion

Conclusion