Control Strategy in Parallel AC-DC Re-configurable Links System

Control Strategy in Parallel AC-DC Re-configurable Links System

Wu, Yang (TU Delft Electrical Engineering, Mathematics and Computer Science)

Soeiro, Thiago B. (mentor)
Bauer, P. (mentor)
Rueda, José L. (graduation committee)
Shekhar, A. (graduation committee)

Delft University of Technology

2019-08-21

Recent studies have shown that energy distribution systems based on hybrid (or parallel)point-to-point AC and DC links are interesting solutions for capacity enhancement andon-line improvement of energy efficiency under specific operating conditions, particularlyfor high power, medium to high voltage levels and long-enough distances, e.g.>5km.Additionally, due to the power controlability provided by the power electronic circuitswithin the DC links the parallel distribution system can be re-configured through GISdisconnectors operating with improved switching performance. In this work this featureis explored and strategies for the system re-configurations are proposed. These aim toprovide a nearly zero current switching for the GIS in order to prevent its deteriorationand to extend the number of maneuvers for the typical GIS lifetime.
In fact, the proposed re-configuration strategies rely on the DC bus voltage and powercontrols of a Back-to-Back (B2B) power electronic system constructed with Voltage SourceConverters (VSC). Herein, three-wire three-phase two-level VSCs with thrid-order AC har-monic filters (or LCL filter) are adopted in the B2B system. Moreover, Grid-side CurrentControls (GCC) for the inner/fast control loops of the front- and back-end circuits are im-plemented in order to enhance the system performance against grid disturbances. Herein,a notch filter-based GCC scheme with a harmonic rejection control is proposed. This isable to deliver attenuation to the LCL filter resonances while suppressing the harmonicsin the grid-side currents originated when the AC voltages are distorted. Interestingly,the parallel AC and DC links provides a low impedance path for the zero-sequence com-ponents which can be created by the power electronics, thus the implementation of aZero-sequence Circulating Current (ZSCC) controller becomes necessary for the properoperation of the system. Hence, ZSCC controllers for the VSCs are used, while bothfront- and back-end circuits are modulated with constant switching frequency using theconventional sinusoidal PWM strategy.
All in all, results are obtained in both, computational simulations carried out in MAT-LAB/SIMULINK and laboratory experiments performed in a5kVA VSC or a B2B circuit,are used to verify the study and to prove the superior performance of the investigatedand proposed technical concepts. Herein, more specifically for the re-configuration studyof the parallel AC and DC links, the standalone mode control of the receiving-end VSCin the full DC link configuration is investigated and the smooth transition between grid-connected and standalone modes are realized in both simulation and experimental tests.

Control of the Voltage Source Converter
parallel AC-DC system
re-configurable system

http://resolver.tudelft.nl/uuid:60e57237-f840-4b17-8be0-26e789f52f0a

2022-08-21

Student theses

master thesis

© 2019 Yang Wu