Electrolysis

According to the current state of knowledge, electrolysis to produce hydrogen is an essential part of the energy transition.

In the case of high system outputs in particular, the electrical energy is taken from transformers at the medium-voltage level and made available to the rectifiers connected on the secondary side in the low-voltage range. The rectifiers supply the electrolyser with the required direct current.

Our rectifier portfolio covers the entire power range up to the parallel connection of modules to achieve any high power.

Rectifiers for electrolysis applications are designed using different technologies:

• Thyristor technology: Thristors have low on state losses and a high ampacity. However, thyristor rectifiers cause system perturbations that should not be neglected, which entail further expenditure. In order to reduce the mains feedback, the system power is often divided between two rectifiers whose phase angle is shifted against each other. A transformer with two secondary windings designed for converter operation is required. Filter circuits that are tuned to individual harmonics are also used. Depending on the design, the power is controlled via phase angle control of the rectifiers.
• Transistor technology: IGBT (Insulated Gate Bipolar Transistor) modules are used as semiconductors. In direct comparison to thyristors, these modules show higher on-state losses and less ampacity. On the other hand, current is drawn from the mains supply with almost no system perturbation, so that the transformer does not have to be designed for converter operation and makes do with one secondary winding. The IGBT rectifiers work independently of power with a constantly low, adjustable phase angle on the mains.
• Combination of thyristor- and transistor technology: This variant combines the advantages of both technologies. Thyristors take over most of the current and thus take advantage of their low on state losses. Transistors connected in parallel correct the current drawn from the mains in the direction of an optimal sinusoidal shape and reduce the phase angle. It is not necessary to design the input transformer for converter operation.

Our latest development to increase system efficiency is the application of SiC (Silicon Carbide) technology to our transistor rectifiers. The SiC version enables the construction of very powerful rectifiers with the advantages of the transistor technology described above and significantly reduced conduction losses compared to the IGBT versions.
Our rectifiers have very low residual ripples on the DC side. Optionally, this residual ripple can be set in both directions.