Multipulse Rectifiers for Large Scale Water-Electrolysis - Reactive Power and Harmonics

In order to decarbonize the industry, energy and transport sectors, emission free produced hydrogen is a crucial component. In the future water electrolysis plants will require a significant share of global electricity generation. To expand electrolysis installations, high efficient, low cost and high power density solutions are required in the two and three MW digit scale. Presently two fundamental converter concepts compete on the market - conventional grid commutated converters based on thyristors or diodes and self commutated converters with IGBTs. Grid commutated converters have the advantages of low costs, high efficiency and high power density if grid filters are not considered. However, the limitation of fundamental reactive power and current harmonics by existing electrical grid standards cause bulky and expensive grid filters. This paper considers two attractive topologies of grid commutated converters regarding fundamental reactive power and current harmonics. Both characteristics are essential for the grid filter which is an important part of the converter. To quantify these properties a simulative case study is set up for a 25 MW electrolysis plant. The results show that the two investigated topologies have an substantial reactive power demand ranging from 50% to 80% of the active power. The injected current harmonics are heavily mitigated by the 24-Pulse solution but the design of filters is not straightforward due to possible asymmetries of the 24-Pulse transformer.