Power systems are becoming increasingly dependent on flexible loads capable of supporting system operation as renewable resources penetration levels increase. In this context, hydrogen electrolyzers are not only large controllable loads, but also potential providers of ancillary services if their power electronic interface and control are properly designed. However, their low voltage and high current characteristics impose demanding requirements on the power electronic interface used to connect them to the AC grid.
Most reported grid-connected electrolyzer power chains are based on voltage-source rectifiers followed by one or more DC/DC stages. Although this architecture provides a high degree of controllability, the additional conversion stage increases the number of semiconductor devices, passive components and control loops. This becomes relevant for industrial scale hydrogen electrolyzers, where very high current operation, conversion stage reduction, reliability, and control simplicity are important design considerations. Current source rectifiers (CSRs) provide an alternative architecture due to their inherent buck characteristic, which is suitable for the low voltage and high current operating conditions to be obtained directly from the AC grid in a single conversion stage. Recent developments of parallel, interleaved, and multilevel current source converters for high power electrolyzers further highlight the industrial interest in this type of interface.
This work investigates a single stage CSR for directly supplying a PEM electrolyzer using an adaptive lead-lag current controller. The proposed controller extends and applies an adaptive methodology previously developed for a DC/DC buck converter to the higher order dynamics of the CSR. A complete averaged model in the synchronous dq frame is developed, including the AC-side LC filter and the operating point dependent electrolyzer load. The dominant low frequency current dynamics are identified from the complete model and used to obtain a reduced first-order representation for controller design. The controller coefficients are updated online according to the electrolyzer operating point and the desired transient response, while the complete sixth-order CSR model is used for validation.
The results demonstrate consistent current responses over a wide electrolyzer operating range and accurate tracking of variable current references. In addition, the system is evaluated under a severe 50% AC side voltage sag. Despite the resulting transient increase in the AC side current and temporary dip in the DC current, the CSR remains controllable and the electrolyzer current recovers to its pre-disturbance reference in approximately 50 ms.
Although voltage source converters remain the dominant industrial grid interface, these results show that a CSR can provide current regulation and voltage ride-through capabilities required from a grid connected electrolyzer interface.