## 1 Introduction  
Nowadays, hydrogen is widely used for industry-scale ammonia production for fertilizers and fossil fuel processing (e.g., hydrocracking). The global demand for pure hydrogen has been rising over recent decades, accounting for 74 million tonnes produced in 2018 [1]. Due to the global ambition to achieve net zero carbon emissions and the transition toward using hydrogen-based e-fuels instead of fossil fuels, the future demand for hydrogen is expected to increase by a factor of more than ten in 2050 [2]. However, the mainstream of global hydrogen production is based on steam reforming of natural gas, and this fossil hydrogen production generates CO\({}_{2}\) emission of approximate 830 million tonnes per year [1]. One of the other methods for hydrogen production is water electrolysis, where water is split into hydrogen and oxygen by using electric power [3]. It accounts for 2% of the global hydrogen supply [4]. The water electrolyzer typically consumes 50 kWh electricity power for producing 1 kg of hydrogen. Therefore, the CO\({}_{2}\) emission of hydrogen from water electrolysis is highly dependent on methods of electricity generation. Using coal-based electricity will lead to heavy carbon emissions, whereas renewable power, e.g., wind turbines and photovoltaics, involves no carbon emissions. Hence, this renewable hydrogen production via water electrolysis is promising in fulfilling the increasing worldwide hydrogen demand and in the goal of achieving net zero carbon emissions by 2050 [5]. On the other hand, the global warming crisis also led to booming interests and investments in renewable energy over recent decades. As such, a large number of wind farms and photovoltaic power plants are being built worldwide [6]. However, the high penetration level of renewable energies brings a fluctuating nature to the power grid and causes instability issues, as their electricity productions are highly dependent on climate conditions [7]. Power-to-hydrogen (P2H) facilities can act as energy storage units by transforming the excessive energy delivered by renewable sources to hydrogen when low electrical demands are present. Hydrogen storage can be converted back to electricity via fuel cell convertersduring high electricity demand periods. In both ways, the intermittent nature of renewable power can be balanced to match the demand profile of power grids well [8; 9; 10]. Moreover, the generated hydrogen can be utilized as green fuel for mobility as well as raw material in the chemistry industry. Due to the emission and grid support features of the renewable hydrogen system, in recent years, a booming number of demonstration and commercial plants are being built worldwide [11; 12; 13]. Figure 1 demonstrates the general architecture of the renewable hydrogen system [14]. Renewable energies typically come from wind turbines and photovoltaic power plants, which are connected to medium-voltage (MV) or high-voltage (HV) ac power grids via an ac/dc/ac frequency converter and a dc/ac inverter, respectively. The generated renewable electricity then transmits through the power grid to the hydrogen production site. The P2H converter plays a crucial role in this renewable hydrogen plant, as it converts the MV ac electricity from the grid to a controlled, high-current dc power flow, which is fed into the water electrolyzer for large-scale hydrogen production. The produced hydrogen can be directly used or further converted to methane and methanol, which are widely used in various industries, such as oil refining, mobility, and electricity generation. The power quality, efficiency, cost, and reliability are several of the P2H system's critical performance metrics, which can be significantly affected by the topology of P2H converters. Thyristor-based ac/dc power converters have been dominating solutions in high-power ac/dc applications due to their high robustness, high efficiency, and low cost [15; 16; 17; 18; 19; 20; 21; 22].