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PhD defence by Zhen Xin on Advanced Control and Stability Enhancement of Grid-Connected Voltage-Source Inverter with LCL-Filter

Time

29.05.2017 kl. 13.00 - 16.00

Description

Zhen Xin, Department of Energy Technology, will defend the thesis "Advanced Control and Stability Enhancement of Grid-Connected Voltage-Source Inverter with LCL-Filter".

TITLE

Advanced Control and Stability Enhancement of Grid-Connected Voltage-Source Inverter with LCL-Filter

PHD DEFENDANT

Zhen Xin

SUPERVISOR

Professor Frede Blaabjerg

MODERATOR

Associate Professor Huai Wang 

OPPONENTS

Professor Remus Teodorescu, Dept. of Energy Technology, Aalborg University (Chairman)
Professor and co-director Josep Pou, the Electrical Power Systems Integration Lab at NTU, Singapore
Professor Vassilios Georgios Adelidis, DTU, Lyngby

ABSTRACT

Power converters have been widely used in renewable energy generation systems, whose high penetration into the grid is changing the characteristic of the traditional power system and imposing new challenges. Among different topologies of power converters, the LCL-filtered Voltage-Source Inverter (VSI) is the most commonly used interface between the renewable energy generation system and the power grid. However, the LCL-filtered VSI may introduce resonance into the system which reduces the power quality and more seriously, triggers system instability. Moreover, compared with the simple L-filtered VSI, the LCL-filtered VSI is sensitive to low-order harmonics due to its small impedance at low frequencies as seen from both the inverter-side and the grid-side.

On one hand, to enhance the system stability, the resonance of the LCL-filter must be damped properly using either active or passive damping techniques. Although the principle of the damping function is simple, its implementation may cause more losses, increased cost and design complexity of the system. Recent publications have researched the fundamental mechanism and the parameter design of active damping, but there is limited discussion about its practical implementation issues and stability enhancement techniques. On the other, to enhance the harmonic attenuation performance of the LCL-filtered VSI, diverse control methods have been developed. However, there is still not a cost-effective solution for harmonic suppression of the system with inverter-side current control in which the grid-current harmonics can freely flow into the capacitor without control. Moreover, most grid standards work on the premise of a harmonic-free grid, which is inconsistent with the real cases. It has been reported that an IEEE-1547-compliant PV inverter produces over 20 % total demand distortion under 3 % grid voltage distortion. Harmonic attenuation of the grid-connected inverters under distorted grid voltage is still an open research.

This thesis has developed corresponding solutions to cope with the aforementioned issues. The first contribution of this thesis lays on the development of two advanced digital differentiators which can ensure a cost-effective implementation of the active damping. Then, a robust damping gain is derived for the grid-current control system and a time-delay compensation technique is developed to further enhance the system stability. The knowledges obtained in the former are then used to develop a simple harmonic mitigation strategy for the LCL-filtered VSI with inverter-side current control. Finally, an improved Quadrature-Signal Generator (QSG) is proposed for grid synchronization, which inherits the simplicity of the second-order generalized integrator based QSG while still has an enhanced harmonic attenuation performance.

All the developments presented in this thesis have been validated by simulation and/or experimental results. These contributions have been published in 8 journal papers and 7 conference papers.

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PhD defence by Zhen Xin on Advanced Control and Stability Enhancement of Grid-Connected Voltage-Source Inverter with LCL-Filter

ALL ARE WELCOME. THE DEFENCE WILL BE IN ENGLISH.

AFTER THE DEFENCE THERE WILL BE AN INFORMAL RECEPTION AT PONTOPPIDANSTRAEDE 111 IN TNE COFFEE ROOM.

 

Host

Department of Energy Technology

Address

Pontoppidanstræde 111, auditorium

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