Indirect Current Control Method Based on Reference Current Compensation of an LCL-Type Grid-Connected Inverter

Zheng Li,Daliang Yang,Dashuai Shao,Zuwen Peng,Linhang Yang,Jinbao Liu

doi:10.3390/en15030965

Abstract

NPC (neutral point clamped converter) is widely used in medium- and high-voltage grid connection because of its small power devices, simple overall structure, and easy control. This paper presents an improved indirect current control strategy for an LCL-type NPC. Firstly, the reference current is compensated to suppress the resonant peak of the LCL filter and improve the tracking accuracy of the output current. Then, with the relationship between state variables, the control structure is optimized by introducing the non-PLL control method, so that the sensors are reduced to only two sets. Finally, the traditional differential operator is improved to compensate the calculation delay in digital control. The experimental results show that the amplitude of thee grid-connected current is consistent with the reference value, the phase deviation is reduced from 7° to about 1°, and the transient response time is shortened to 1/3 of that of the traditional method.

Highlights

Reference Current Compensation ofWith the social demand for energy increasing, the energy crisis is becoming increasingly prominent
The grid-connected inverter, as the interface that connects to the power grid, has a huge demand [1,2]
To achieve the technical requirements of grid-connected inverters, it is necessary to install filters on the grid-connected side of the inverter, usually with L-type, LC-type, LCL-type, or other more complex structures

Summary

Introduction

Reference Current Compensation ofWith the social demand for energy increasing, the energy crisis is becoming increasingly prominent. The grid-connected inverter, as the interface that connects to the power grid, has a huge demand [1,2]. To achieve the technical requirements of grid-connected inverters (e.g., the harmonic content in the grid-connected current cannot be more than 5%), it is necessary to install filters on the grid-connected side of the inverter, usually with L-type, LC-type, LCL-type, or other more complex structures. The LCL-type filter has been applied increasingly more in grid-connected inverters due to its advantages of a small volume, strong attenuation of high-frequency harmonics, higher quality of grid-connected current control, etc. Studies on LCL-type grid-connected inverters have mainly focused on the stability problems caused by LCL resonant peak [6,7,8] and digital control delay [9,10]

Methods

Results

Conclusion