# Design of the Converter Prototype for Powering the Hydrogen Electrolyzer
## 1 Introduction  
The demand for clean energy from alternative or renewable energy sources increases. Most of the world's energy production today is based on fossil fuels. Burning and producing them causes huge ecological problems, among which is the impossibility of recycling all waste produced during these processes. These days, commonly used alternative energy sources are water, solar, wind, and geothermal energy [1]. However, hydrogen is also an option for renewable energy sources. This demand opens comprehensive options for new power converter topology designs and an even bigger space for new control algorithm possibilities [2]. Conventional hydrogen production using electrolysis is based on direct current [3]. A reversible voltage calculated by the Nernst equation is necessary to decompose the water molecule. It is approximately 1.23 V in standard atmospheric conditions; practically, this is 1.5 V for water [4, 5]. Also, several ohmic overpotentials exist in electrodes, electrolytes, bubbles, etc. [6]. The resistance of each depends on the electrolyzer's parameter. Thus, the voltage that is needed to be applied to the electrolyzer's terminals is higher proportionally to the applied current. Various dynamic models can describe the electrolyzer's electrical response [7]. Figure 1 shows a general diagram of an electrolyzer that will be used in future experiments. An alkaline water solution is used during alkaline water electrolysis, although some applications also use acid solutions. Commonly used alkalines are sodium hydroxideand potassium hydroxide, which have low resistance for hydroxide anion OH- flow. In the cathode, ions are reduced, and oxygen gas is released. In the anode, ions oxidize while hydrogen is produced. Hydroxide OH- ions pass through the electrolyte from the cathode to the anode [8; 9]. In this method, a membrane that prevents gas mixing can be used. One of the points of interest is the pulse water electrolysis production [10]. This method reflects the electrolyzer's frequency dependence resulting from the double-layer behavior of polar water molecules [3]. By connecting the external voltage potential to the electrolyzer's electrodes, water molecules start orientating their potential toward the external electric potential. The change in the orientation of water molecules takes some time depending on electrolyzer parameters and input voltage/current parameters. The electrolyzer shows a capacitive character [11; 12]. That allows for increasing current density for a short period without exceeding internal voltage. [PERSON]'s first law of electrolysis claims that the amount of product is proportional to the local current density. Following earlier studies, using current pulses makes it possible to decrease the power consumption of the electrolyzer needed to produce one kilogram of hydrogen gas in contrast to only a direct current being used [4]. Theoretical electrotechnics knowledge indicates the possibility of using a wide range of different inverter topologies and control algorithms [13; 14]. Various topologies and algorithms have different effects on electrolyzers' properties. The following were considered during the design of the inverter: First, inverters with current and voltage outputs have different properties when used in electrolysis hydrogen production [10]. However, various sources diverge in these areas. Based on [PERSON]'s laws of electrolysis, the maximum possible efficiency of the electrolysis process occurs when the voltage applied to the electrolyzer's cell converges, ideally equally, to the reversible voltage of water [15]. The electrolyzer's equivalent circuit consists mainly of combinations of resistors and capacitors. Some of them are nonlinear [8; 16; 17]. According to this, the experimental measurements using both current and voltage pulses have been performed. The measured voltage and current curves were analyzed.