Michal Sztykiel

Overview of power converter designs feasible for high voltage transformer-less wind turbine

Many leading wind turbine manufacturers are pushing forward in variable-speed wind turbines, often exceeding 5 MW. Therefore, novel designs and concepts for optimal high power wind turbines appeared. One of the most promising concepts is the high voltage (10–35 kV) transformer-less topology. High voltage design enables low power losses and elimination of bulky step-up transformer from the wind turbine system. However, new challenges appear for such topology, which have to be properly identified and successfully overcome. This paper presents possible concept for transformer-less wind turbine topology along with an overview of most promising candidates for optimal full-scale power converter design. Study is carried with proposed and justified high voltage wind turbine application along with selection of existing and most promising multilevel power converter topologies, which could be successfully proposed for transformer-less wind turbines.

Modular multilevel converter modelling, control and analysis under grid frequency deviations

A tool for component sizing for MMCs has been developed and tested through simulations in PLECS. The steady-state behaviour under grid frequency deviations - interesting for offshore wind farm connections - has been analysed, providing insights in MMC characteristics and further testing the proposed tool.

Development of modulation strategies for NPC converter addressing DC link voltage balancing and CMV reduction

3L-NPC inverters are more popular due to their superior performance compared with two level inverters. One of the most optimal applications for multilevel inverter is the Adjustable Speed Drives (ASD). The industry reported numerous ASD failures due to high frequency PWM. Those failures consist in insulation breakdown and bearing failures. By the use of this type of converters, both Electromagnetic Interference (EMI) and harmonic distortions are improved. This paper proposes two modulation strategies for Three Level Neutral Point Clamped Converter (3L-NPC). The main focus of these modulation strategies is to reduce the Common Mode Voltage (CMV) and balance the DC Link Voltage.

Grounding system studies for transformer-less collector feeder of full-scale power converters

Following work examines current and voltage distribution during ground faults in cables of the transformer-less feeder system consisting of interconnected voltage source converters. Analysis is performed with regard to converter block operation, fault-ride-through requirements, cable design and different grounding schemes. Analysis show, that systems with effective grounded generators neutral in general provide best ground current and voltage distribution across cables.