# Design of the Converter Prototype for Powering the Hydrogen Electrolyzer
## 2 Constant Current Source  
Due to the nature of the load, it is necessary to ensure that the converter has sufficient dynamics. At the same time, when no current is supplied to the electrolyzer, it is essential to ensure the conductive path of the output of the constant current source. The interleaved topology of the buck converter with peak current control was chosen for the best possible dynamics and the lowest ripple of the output [18]. Each phase of the inverter is mounted on  
Figure 2: Converter’s block diagram. a separate PCB. The outputs are connected in parallel. Controlling is ensured by the central control unit fitted with a microcontroller. The constant current source output voltage for experimental electrolyzer measurement was established at a maximum value of 9 V. The supply voltage was based on a value of 15 V. The output current of one phase is a maximum of 10 A with a ripple of 20%. The total maximum current of both phases is, therefore, 20 A. The switching frequency was set to a value of 400 kHz. The inductance value \(L\) was derived from these parameters [19]; see Equations (1) and (2). \[D=\frac{V_{out}}{V_{in}}=\frac{9\,\mathrm{V}}{15\,\mathrm{V}}=0.6 \tag{1}\]  
\[L=(V_{out}-V_{in})\frac{D}{0.2I_{out}.f_{sw}}=(15\,\mathrm{V}-9\,\mathrm{V}) \frac{0.6}{0.2\cdot 10\,\mathrm{A}\cdot 400\,\mathrm{kHz}}=4.5\,\mathrm{\mu H} \tag{2}\]  
From the available choke types with the required \(I_{R}\) > 10 A, \(I_{SAT30\%}\) > 15 A, \(f_{res}\) > 10 MHz, and \(L\) > 4.5 \(\mathrm{\mu H}\), the inductance SMD WE-HCI 10 \(\mathrm{\mu H}\) was chosen; see parameters in Table 1.  
The power loss on the inductance can only be calculated for the DC loss of the winding \(P_{LDC}\) according to Equation (3), where \(R_{L}\) is winding resistance. The core losses and losses due to the skin effect and proximity effect at specified operating conditions are 178 mW according to the manufacturer's calculation tool. The total power loss on the choke is 518 mW. The manufacturer also states that the expected heating of the choke is at 11.6 \({}^{\circ}\)C when the recommended installation regulations are met. \[P_{LDC}=(I_{L})^{2}\cdot R_{L}=(10\,\mathrm{A})^{2}\cdot 3.4\,\mathrm{m} \Omega=340\,\mathrm{mW} \tag{3}\]  
The current measurement method for achieving the maximum possible dynamic range and enabling peak current control of the converter was chosen using shunt current measurement in the upper branch of the converter [9]. This approach requires an operational amplifier with a sufficiently wide unity gain bandwidth with a maximum common mode input voltage exceeding 9 V.  
Using simulation and empirical methods, two parallel shunts with a value of \(R_{sh}\) = 40 m\(\Omega\) were chosen. The total power loss at one shunt at a current of 10 A is \(P_{sh}\) = 1 W.  
Because the input voltage range of the ADC is 0-2.048 V, the voltage drop on the shunt needs to be amplified by factor A = 6.8 using a differential operational amplifier setup. The required parameters are met by the LT1632 \"Rail-to-Rail\" operational amplifier. This amplification matches the converter current to 0-15.0568 A, which means the possibility of measuring 5 A overcurrent in peak. The low-pass filter on the ADC input composed of R29 and D6 diodes' barrier capacitance, so as to attenuate high-frequency components, was tuned [18] according to Equation (4). The current measurement constant K\({}_{CCS}\) for ADC