## 4 Performance Comparison  
This work obtains the power factor and current total harmonic distortion (THDi) among 12-TR, 12-DRMC, and 12-TRASPF through simulation. Figures 8 and 9 exhibit the simulated power factor and THDi of the three topology candidates, respectively. It can be seen from Figure 8 that the 12-TRASPF features superior power factor values (\(\geq\)0.99) since the ASPF module can also compensate for reactive power. The 12-DRMC also performs satisfactorily in terms of power factor, i.e., between 0.96 and 0.98, which is relatively flat according to the output variation. For 12-TR based systems, the power factor becomes unsatisfactory under small output current conditions due to their large firing angles. Therefore, depending on their operating range of output current, the 12-TR requires external power factor correction measures (e.g., a static VAR compensator, static synchronous compensator, or ASPF module) to compensate for their reactive power. Furthermore, it can be seen from Figure 8 that the power factor of the 12-TR system increases as the electrolyzer becomes more aged, given the identical amount of output current. This can be explained by the increase in electrolyzer resistance alongside its aging process (see Figure 3), leading to the increased portion of active power fed into the electrolyzer, given the identical amount of current.  
mentioned in Sections 3.1 and 3.2. On the other hand, using the ASPF can also be a promising solution to handle the power quality issue, as the THDi values of 12-TRASPF are regulated well, to be lower than 5%. On the contrary, the AFE rectifier does not seem to have power quality issues, as both the phase-lag angle and the input current waveform can be controlled well by IGBT-based B6 converters. The power quality rating of the four aforementioned topologies is summarized in Table 2.  
Regarding the efficiency performance, the 12-DRMC system exhibits more losses than the 12-TR system. The excessive dissipation of 12-DRMC comes from IGBT's conduction and switching losses. The percentage of IGBT's switching loss is dependent on its switching frequency and gate driver parameters. The 12-TRASPF system is also less efficient than the 12-TRASPF, considering the extra losses dissipated in the active power filter. From a reliability viewpoint, the 12-TR system exhibits the best performance. The thyristors are considered as reliable components as they have demonstrated their maturity in utility-scale applications. The 12-DRMC is considered less reliable as multiple Si IGBTs are used as the output stage. Nevertheless, the industry is gradually gaining confidence in terms of the reliability of 12-DRMC, as more projects using 12-DRMC are being carried out [20,21]. It is noted that the reliability performance investigated in this work is a system-level concept. For the 12-TRASPF system, a single failure from either the ASPF or 12-TR is regarded as a failure from the system perspective. Although the 12-TR is reliable, the 12-TRASPF system is regarded as neutral in terms of reliability being comparable with the AFE rectifier, because commercial ASPFs use the IGBT-based B6 topology, which is identical with the AFE rectifier presented in this work. The principles of their control and driver systems are also of the comparable level of complexity.