# Enhanced Control Strategy for Three-Level T-Type Converters in Hybrid Power-to-X Systems
## 6 Conclusions  
This paper presents a dual-loop control system for three-level three-phase T-type converters in the hybrid operation of P2X systems. The proposed control strategy, incorporating both an inner current loop with a proportional-resonant controller and FF action to eliminate disturbances and an outer voltage loop with a proportional-resonant controller, has proven to be highly effective in managing the complexities and dynamics of P2X applications. In addition, a novel control strategy was added to the control loop to balance the DC side capacitors' voltages and maintain system stability. The identified control loops are discussed in detail in this paper, and comprehensive simulation and experimental results demonstrate that this control approach ensures precise regulation of converter output, which enhances the efficiency, stability, and overall effectiveness of P2X systems hybrid operation.  
Looking ahead, future research should explore the integration of machine learning-based controllers to enhance system adaptability and robustness, particularly in dynamic and uncertain grid conditions. Machine learning techniques can optimize controller parameters in real time, improving performance beyond traditional control methods. Additionally, hardware optimizations and other enhancement strategies should be investigated to improve system efficiency, reduce switching losses, and lower overall costs, with a focus on advanced semiconductor materials and optimized circuit topologies. Another important direction is the expansion of the proposed control strategy to smart grid applications, enabling seamless integration of P2X systems into future energy networks and addressing bidirectional energy flow, demand-side management, and grid interaction stability. Moreover, exploring advanced control techniques such as adaptive control, predictive control, and nonlinear control methods could further improve tracking accuracy, transient response, and overall system robustness. Finally, an important extension of this work is the development of a triple-loop control configuration incorporating FF action, which would build upon the current dual-loop approach to provide even greater disturbance rejection and enhanced control over system dynamics. By addressing these areas, future research can further optimize the proposed control system, enhance its efficiency, and ensure its successful deployment in large-scale, real-world P2X applications.  
Methodology, M.S.E.; Software, M.S.E.; Validation, M.S.E.; Investigation, M.S.E.; Writing--original draft, M.S.E.; Supervision, D.V. All authors have read and agreed to the published version of the manuscript.  
Figure 18: Comparison between experimental results of DC-link capacitors voltages (**top** and **bottom**), capacitor voltage of phase \(a\), and inverter current of phase \(b\) with PI controller.  
**Funding:** This research was supported in part by the Estonian Research Council grant PRG1086 and in part by the Estonian Centre of Excellence in Energy Efficiency, ENER (grant TK230) funded by the Estonian Ministry of Education and Research.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest.