Mitigation of DC Components Using Adaptive BP-PID Control in Transformless Three-Phase Grid-Connected Inverters

Long Bo,Yufei Dai,Kil To Chong,Youliang Lu,Lijun Huang

doi:10.3390/en11082047

Abstract

Transformerless grid-connected inverters, due to their advantages of high efficiency, small volume and light weight, have been the subject of more research and interest in recent years. Due to the asymmetrical driving signal in pulse width modulation (PWM) caused by time-delay, zero-drift of the current sensors and imparities of the power transistors, output of the grid current contains dc component. As a result, power quality of the grid is degraded. In this paper, a dc (direct current) component suppression scheme with adaptive back-propagation (BP) neural network proportional-integral-differential (PID) control is proposed for dc component minimization. Moreover, sliding-window-double-iteration-method (SWDIM) is utilized for fast dc component extraction. Compared with the conventional method, the proposed scheme shows better performance, and the dc component can be attenuated to be within 0.5% of the rated current.

Highlights

Grid-connected inverter systems are the key facilities for wind turbine generation (WTG), photovoltaic, and fuel cell power generation systems
The THD has been reduced from (7.68%, 6.81%, and 8.13%) to (6.52%, 6.38%, and 5.87%), respectively. These results have shown the effectiveness of the proposed dc component minimization control strategy
The factors that influence dc components are analyzed in detail

Summary

Introduction

Grid-connected inverter systems are the key facilities for wind turbine generation (WTG), photovoltaic, and fuel cell power generation systems. Since the inherent equivalent resistance of a voltage-source grid-connected inverter is very small, this will cause the saturation of distribution transformers in the grid and result in poor power quality, higher loss, line-frequency power ripple, dc-link voltage ripple and overheating issues in the power system [8,9]. Power quality of the grid is degraded, as a result, other equipment sharing the same grid may not work properly, and dc component injection to the grid should be strictly inhibited.

Methods

Results

Conclusion