Finite Control Set Model Predictive Control (FCS-MPC) can improve the control performance of Five-level Active NPC (5L-ANPC) inverter effectively. However, with the increasing of the levels of inverter, the traditional FCS-MPC method has many problems, such as large amount of rolling optimization calculation and difficulty in weight coefficient design. In order to solve those problems, an Optimal Model Predictive Control (O-MPC) method is proposed. First, an optimal control method based on level jump limitation is proposed to reduce the number of switch states. Second, in order to solve the conflict problem of multiple control objectives and reduce the design difficulty of weight factors, a satisfactory optimal control method based on hierarchy is proposed. After the optimization, the calculation time of the controller is greatly reduced and the control performance of the multi-objective control system will be significantly improved. At last, the effectiveness and feasibility of the proposed O-MPC are validated by the experimental results.

The three-level active-neutral-point-clamped (ANPC) grid-connected inverter is a promising alternative for photovoltaic (PV) power generation, thanks to its capability of balancing the losses of power devices. This paper proposes a multi-objective optimal model predictive control (MO2-MPC) algorithm for three-level ANPC grid-connected inverter, and thus the number of rolling optimizations of the model can be reduced by eliminating the switching states of the three-level output that violate the unit level jump principle. The power loss of each switch was calculated in real time by the linear fitting of the turn-on and turn-off losses of the switches, and the imbalanced losses were added to the target cost function to minimize imbalance losses. Finally, the proposed control method was proved correct and effective through an experiments prototype.

The five-level active neutral-point-clamped (5L-ANPC) converter has a great application potential in high power variable-frequency drives (VFDs) with high and medium voltage. However, the traditional method for capacitor voltage buildup is not applicable to the capacitors inside the back-to-back (B2B) 5L-ANPC converter. To solve the problem, the topological features of the B2B-5L-ANPC converter are fully analyzed, and a capacitor voltage pre-charge strategy for this converter is also proposed. With this strategy, all the capacitors in the converter can be charged by controlling the on and off states of switch tubes in the bridge arm, no additional hardware is needed. Moreover, the structural features of the voltage booster circuit were examined in four stages, and used to derive the capacitor voltage buildup formula in each stage. In addition, the relationship between voltage buildup rate, equivalent pre-charge resistor and capacity of capacitor is identified. Finally, Simulation results from a B2B-5L-ANPC simulation model which is constructed according to the actual system parameters and experimental results from a scaled-down prototype are provided to support the proposed control strategy.

The five-level active neutral-point clamped (5L-ANPC) converter has been a subject that has attracted more research and development for medium/high-power energy conversion systems in industrial application due to the advantages of high quality of voltages and currents, low voltage stresses, etc. In this paper, a review of the research and development achieved in recent years on the 5L-ANPC converter is discussed about the challenges and proposed solutions for this power converter. Introducing typical 5L-ANPC converter topology and operation principles, this paper focused on photovoltaic (PV) system and motor drive to summarize the derived topologies of the 5L-ANPC. Then the analysis and theoretical research on the unbalanced capacitor voltage of the 5L-ANPC converter is carried out. On this basis, various voltage equalization methods based on different modulation strategies and model predictive control (MPC) are fully explained and analyzed. Furthermore, additional key issues, such as the capacitor voltage pre-charge process and the compensation of the dead-time effect, are also identified. This indicates that the 5L-ANPC converter has a promising future in next-generation high-voltage high-power conversion systems.

Three‐phase AC–DC converter based on integrated transformer is a novel converter which is capable of handling high power levels and can realise power factor correction function. Owing to different parameter tolerances of the primary windings, grid current could be unbalanced, which usually could not be solved through traditional control methods. To handle this problem, a current balancing method is adopted in this study to improve former current control loop. Meanwhile, based on the principle of instantaneous power balance, a dual loop control strategy with an outer voltage loop and an inner current loop is designed. Besides, load current feedforward control is introduced to enhance the dynamic response. Moreover, phase‐shift control is employed as the modulation method, in which duty ratios change along with sinusoidal signals. Simulation and experimental results show that the control strategy could make the three‐phase current of the converter sinusoidal and balanced.

The Modular Multilevel Converter-Battery Energy Storage System (MMC-BESS) is a converter system with the potential to enhance grid reliability. However, the implementation of model predictive control (MPC) in MMC-BESS is confronted with challenges such as substantial computational demands, suboptimal quality of output current, and challenges in selecting weighting factors. To address these challenges, this paper puts forward an extended-level MPC approach, which involves the direct calculation of the output voltage reference value in the load MPC stage, followed by the optimization of the output level through a step-by-step optimization method. Additionally, it employs a cost function that optimizes the current area to further reduce the total harmonic distortion (THD). Notably, this process ensures a computational complexity of 5 for each control cycle, independent of the number of sub-modules. Two control strategies are employed to optimize the circulating current control depending on the number of inserted sub-modules. The use of independent cost functions for output current and circulating current eliminates the need for weighting factors, while the circulating current feedback for balancing the state-of-charge (SOC) is incorporated into the circulating current reference to achieve inter-phase and bridge arm SOC balancing control. The effectiveness of the proposed method is validated by simulation and experimental results.