Analysis and Design of PI Plus Repetitive Control for Grid-Side Converters of Direct-Drive Wind Power Systems Considering the Effect of Hardware Sampling Circuits

Mingcheng Lyu,Wu Liao,Xin Long,Shoudao Huang,Gongping Wu,Yelun Peng,Qianming Xu,Lerong Hong

doi:10.1109/access.2020.2993041

Abstract

In inverters based on a single proportional-integral (PI) or deadbeat (DB) controller, an inherent resonance peak may emerge near their current loop cut-off frequency, which results in harmonic amplification or even resonance. Additionally, inappropriate filter circuits implemented in sampling circuits may result in the expansion of the resonance peak. Thus, this paper further investigates the influence of the sampling circuits on a PI- or DB-based control loop. Then, the RC filter in the sampling circuit is designed to reduce the inherent resonance peak. Moreover, a compound control strategy based on an improved repetitive controller (IRC) plus a PI controller is adopted for the grid-side converter of a direct-drive wind system. This strategy enhances the harmonic and reactive compensation performance by reconstructing the internal model of the classic repetitive controller (CRC) and limiting the bandwidth of the PI-based loop to a low level. The parameters of the presented IRC-plus-PI control are designed for the purpose of resonance peak elimination and system stability. Furthermore, the non-integer delay problem is solved with an inserted fraction compensator (FC), which plays the role of a low-pass filter in the IRC. Finally, the feasibility and effectiveness of the presented control method is verified by the experimental results.

Highlights

Distributed wind power generation has been widely adopted to meet the increasing demand for electrical power due to its clean and renewable characteristics
It is found that inappropriate filter design may result in the expansion of the inherent resonance peak, and it is difficult to achieve a satisfactory trade-off between system bandwidth and compensation performance when depending only on a single PI or DB controller
IMPACT MECHANISM OF THE HARDWARE SAMPLING CIRCUIT As shown in Fig. 4, when only a DB or PI controller is implemented in the current control loop, an inherent resonance peak emerges near the cut-off frequency of the closed-loop transfer function even though H (s) is considered to be 1

Summary

INTRODUCTION

Distributed wind power generation has been widely adopted to meet the increasing demand for electrical power due to its clean and renewable characteristics. B. IMPACT MECHANISM OF THE HARDWARE SAMPLING CIRCUIT when only a DB or PI controller is implemented in the current control loop, an inherent resonance peak emerges near the cut-off frequency of the closed-loop transfer function even though H (s) is considered to be 1. For the grid-side converter with the function of harmonic suppression and a wider control bandwidth, the single controller structure (i.e., DB or PI) cannot ensure satisfactory performance in the high frequency range due to the inherent resonance peak. As highlighted by the red curve, the PI loop bandwidth is limited to a low level for resonance suppression, it plays the important role of tracking the low frequency signals and improving the dynamic response, which makes it a good addition to the IRC

EXPERIMENTAL VERIFICATION

Findings

CONCLUSIONS