This work introduces a six-level flying capacitor-based converter (6L-FCB) tailored for three-phase systems operating from a single DC source. The proposed structure overcomes key drawbacks of traditional multilevel designs, including dependence on multiple isolated sources, auxiliary voltage-balancing hardware, and excessive device counts. Each phase incorporates four flying capacitors, with voltage balance maintained through an optimized switching-state selection scheme that operates without additional circuitry. The control employs a level-shifted carrier PWM method combined with a priority index mechanism that exploits phase current polarity to regulate capacitor voltages. This strategy enables straightforward implementation while delivering high-quality output voltages with low harmonic distortion. Comparative analysis against existing six-level alternatives highlights the performance and hardware advantages of the proposed design. Simulation studies confirm the robustness of the modulation and balancing methods across various load and modulation index conditions.

Among multilevel topologies, flying capacitor (FC)-based converters stand out for their modularity, self-voltage balancing features, and fault-tolerant operation. However, conventional FC converters require multiple capacitors per phase, increasing hardware complexity and control effort. To address this, a four-level single flying capacitor (4L-SFC) converter is proposed in literature, which reduces the number of capacitors to one per phase without sacrificing output quality. The major challenge of this simplified topology lies in the absence of redundant switching states, which restricts voltage balancing flexibility. To overcome this, a Virtual Space Vector Modulation (V-SVM) technique is developed. By synthesizing virtual vectors through weighted combinations of space vectors, the method ensures zero-average capacitor current over each sampling period, enabling effective voltage balancing. The V-SVM algorithm divides each space vector sector into triangular regions and maps reference vectors to optimized switching sequences, ensuring stable flying capacitor voltages, improved switching loss distribution, and low voltage ripple.

The four-level single flying capacitor converter (4L-SFC) is an efficient topology for medium-voltage applications, offering a reduced component count over traditional four-level flying capacitor converters. However, maintaining balanced capacitor voltages is a key challenge in this topology, which is critical for stable and reliable operation. In this paper, an active voltage balancing method for 4L-SFC converters is presented, using a straightforward algorithm to adjust voltage levels in response to real-time measurements of capacitor voltages and phase currents. As a result of the proposed method, capacitor voltages remain balanced across a wide range of modulation indexes and operating conditions without significantly increasing switching frequency. Simulation results have demonstrated the effectiveness of the proposed approach, demonstrating that it is capable of maintaining stable capacitor voltages.

This paper presents an Multi-Input Multi-Output (MIMO) control strategy for a soft-switched AC-DC bidirectional power converter, optimally designed using an extended linear quadratic regulator (LQR) method. The proposed method is comprehensively compared with conventional approaches across three distinct scenarios: normal operation, harmonic mitigation, and grid imbalance conditions. Through detailed analysis and performance evaluation, our study demonstrates the superiority of the proposed control strategy in all three scenarios. Specifically, significant improvements are observed in harmonic mitigation and grid imbalance situations, where the proposed method exhibits exceptional effectiveness in reducing phase current total harmonic distortion (THD) and enhancing system robustness compared to conventional technique. These results emphasize the flexibility and effectiveness of the proposed control strategy in various operating conditions, indicating its capacity to improve the performance and reliability of AC-DC bidirectional converters in real-world applications.

One of the main challenges of the NPC topology in high-power applications is to balance the power losses of the switching devices. This paper proposes a modulation method for loss balancing among main switching devices of the NPC converter. The concept of the proposed modulation scheme is based on reconstructing the middle voltage level of each phase by a linear combination of other voltage levels. By applying the proposed modulation scheme, the power losses of switching devices are balanced. However, an added feature of the reconstructed voltage levels is that its implementation results in lower neutral point current over one sampling period. The proposed scheme retains the merits of NPC topology such as the dv/dt of output voltage and dynamic voltage sharing of the switches. In addition, due to reduced rms current of the dc capacitors in the proposed scheme, the use of bulky and large capacitors is avoided. Simulations and experiments are presented to demonstrate the effectiveness of the proposed modulation method.

A two-stage AC/DC converters, generally, consist of an input Power Factor Correction (PFC) in order to improve the quality of the current drawn from the grid, and a DC/DC converter in order to provide galvanic isolation. Since there is a low frequency ripple (2nd Harmonic of the input ac line frequency) in the output voltage of the PFC AC/DC Boost converter due to the power ripple, the voltage loop in the conventional control system should have a very low band-width in order to avoid distortions in the input current waveform. This leads to a very sluggish transient response for the PFC against load variations. This paper presents a new control approach, based on the Control-Lyapunov Function (CLF), which is able to significantly improve the transient response of the PFC stage. Since the dynamics of the PFC stage is highly nonlinear, the optimal controller is derived by solving the Hamilton-Jacobi- Bellman equation. Experimental results from a 3KW AC/DC converter validate the performance of the proposed control method compared to the conventional control technique.