Active and Reactive Power Compensation Control Strategy for VSC-HVDC Systems under Unbalanced Grid Conditions

Weiming Liu,Shihong Miao,Da Wang,Zhihua Fan,Yilong Kang,Ziwen Liu,Tingting Zheng,Mingming Zhang

doi:10.3390/en11113140

Abstract

This paper presents a power compensation strategy to suppress the double frequency power ripples of Voltage source converter high-voltage direct current (VSC-HVDC) systems under unbalanced grid voltage conditions. The mathematical control equations of the double frequency ripple power of VSC under unbalanced operating conditions are firstly derived and established, where the dynamic behaviors of the double frequency ripples in active and reactive power are regarded as being driven by current-relevant components and voltage-relevant components, respectively. Based on the equations, a power compensation control strategy of VSC-HVDC is proposed via the passivity-based control with disturbance observer to suppress both the current-relevant and voltage-relevant components in the power ripples. With this control strategy, the double frequency ripples in active and reactive power are suppressed simultaneously and system performance is significantly enhanced with the implementation of the disturbance observer in the passivity-based control. Theoretical stability analysis and simulation cases show the effectiveness and superiority of the proposed strategy.

Highlights

The voltage source converter based high voltage direct current (VSC-HVDC) is widely used in dc transmission, renewable energy generation, island network supply and other fields [1,2,3,4].In general control scheme of VSC-HVDC, the three-phase AC grid voltage is usually assumed to be balanced
When the unbalanced grid conditions occur, the VSC converter operates in abnormal condition and the negative sequence electrical components is adverse for the system normal operation
The main contribution of this paper is that with this proposed control strategy, the double frequency ripples in active and reactive power of VSC-HVDC under unbalanced grid conditions can be suppressed simultaneously and system performance is significantly enhanced with the implementation of the disturbance observer in the passivity-based control

Summary

Introduction

The voltage source converter based high voltage direct current (VSC-HVDC) is widely used in dc transmission, renewable energy generation, island network supply and other fields [1,2,3,4]. In general control scheme of VSC-HVDC, the three-phase AC grid voltage is usually assumed to be balanced. If no compensation measures are adopted, the double frequency ripples will appear in the output power of VSC, which affects output quality of the converter [5,6,7] and may even make the converter malfunction. How to suppress the double frequency ripples under unbalanced grid conditions becomes a hot topic in the research of VSC-HVDC control.

Results

Discussion

Conclusion