PROJECT TITLE: Medium Voltage AC-AC Modular Multilevel Converter Solution Applied to Pumped Hydro Storage Systems and Wind Turbines
PhD period: 2019.09.01 - 2022.08.31.
Section: Power Electronic Systems
Research Programme: Modern Power Transmission Systems
Supervisor: Remus Teodorescu
Co-Supervisor: Tamas Kerekes
Collaborator: To be announced later.
Funding: To be announced later.
The development of the modern industry has led to a worldwide increase of the energy demand. Nonetheless, environmental issues have led to a need of change of the energy consumption paradigm, consisting in the reduction of the use of fossil-fuel-based energy sources. Thus, in the last few years, the world’s power systems have been facing a high insertion of renewable sources of energy. The high penetration of wind and solar photovoltaic power plants to the electrical systems leads to energy storage requirements due to their intermittent characteristic. One of the most proven forms of energy storage for high-power applications are the pumped hydro storage systems. Meanwhile, in order to fulfill the world’s increasing energy demand, an upscaling process has been occurring, which consists in the increase of the power ratings of generating sources such as wind and hydro turbines. Both upscaled wind turbines and hydro power plants must deal with a considerably high amount of power and, thus, devices capable of handling such power levels are required.
The advances in power electronics have improved the flexibility of modern electrical systems. Power electronics devices can be used to integrate renewable sources of energy to the electrical grid. However, until recent years, the electronic converters presented limitations in their power ratings, which jeopardized the upscaling possibility. This problem was solved with the invention of the modular multilevel converter that can operate as a voltage source and can reach high power ratings using low-voltage semiconductor devices, currently available in the industry.
Modular multilevel converters could be suitable to drive high-power medium-voltage machines used in large wind turbines and in hydroelectric power plants in the pumped hydro storage configuration. However, both applications operate with a wide range of frequency variation and one of the drawbacks of the modular multilevel converter is the problem dealing with critical voltage ripples in the submodules’ capacitors when a low-frequency output voltage is required. Besides, this converter presents high control and structural complexity.
The aim of this work is to develop a new modular multilevel converter solution suitable for AC-AC medium voltage applications such as pumped hydro storage systems and large wind turbines. The proposed converter should be able to synthesize a low-frequency output voltage with better performance in comparison to conventional modular multilevel converters, which would lead to reduced size of submodules’ capacitors and, thus, reduced costs. The reduction of the control and structural complexity is another objective to be reached, in such a way that DC-side faults and circulating currents are not issues to deal with.
Publications in journals and conference papers may be found at VBN.