Electrolysis plants powered from the grid must meet all grid standards and codes, such as achieving a unity PF and maintaining low harmonic distortion. Different power systems are required as green power sources are incorporated into the hydrogen separation process (Figure 3). Like the power grid, wind-based power sources are AC, and powering electrolysis cells from them requires a rectifier to convert the AC into DC. Solar energy and hybrid sources using batteries rely on DC/DC converters to control the DC levels driving the electrolysis cells. The electrolysis cell may also employ a local DC/ DC converter regardless of the
power source. The electrolysis cell represents a constant DC load. Due to aging considerations within the electrolyzer cell, the applied voltage needs to increase over the cell's lifetime, so the power conversion system (PCS) should be able to accommodate that process. PCSs, whether mated to an AC or a DC source, will have some common specifications. Their output voltage should be in the range of 400 VDC to 1,500 VDC). Alkaline cells have a maximum voltage range of approximately 800 V. PEM cells are not as limited and are moving toward the high end of the voltage range to lower losses and reduce
costs. The output power range can be 20 kilowatts (kW) to 30 megawatts (MW). The current ripple from the PCS should be less than 5%, a specification still being studied for its effect on the cell’s lifetime and efficiency. PCS rectifier designs for power grid sources, especially for higher power loads, must comply with power companies’ large load and PF requirements.
Power conversion for AC sources AC-powered hydrogen plants
require a rectifier that may drive an electrolysis cell directly or may drive a DC grid attached to multiple cells.
Figure 3: Electrolysis plants must convert power from the source into DC for the electrolysis cells. (Image source: Infineon Technologies)
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