In this paper, the input-parallel output-parallel (IPOP) three-level (TL) DC/DC converters associated with the interleaving control strategy are proposed for minimizing and balancing the capacitor ripple currents. The proposed converters consist of two four-switch half-bridge three-level (HBTL) DC/DC converters featuring with simple and compact circuit structures, which can reduce the current stresses of the components and increase the power rating of the converter. The combination of the proposed IPOP TL circuit structure and the interleaving control strategy can greatly reduce the ripple currents on the two input capacitor not only by doubling the frequencies of these ripple currents as the universal benefit of utilizing the interleaving control strategy but also by counteracting part of these ripple currents due to the operation principle of the proposed IPOP TL circuit structure. More importantly, the ripple current imbalance among the two input capacitors can be eliminated by combining the proposed IPOP TL converters and the interleaving control strategy, which can improve the reliability in balancing the thermal stresses and lifetimes of the two input capacitors. The theoretical analysis of the ripple currents on the two input capacitors is presented in detail. Finally, the simulation and experimental results are presented to verify the proposed converters with the interleaving control strategy. Index Terms Input-parallel output-parallel (IPOP), ripple currents on input capacitors, three-level (TL) DC/DC converter.
Unity grid power factor (GPF) is essential for the indirect matrix converter (IMC) applications to satisfy the grid-friendly requirement. The existing unity GPF control strategies usually consist of highcomplexity structures, resulting in difficult parameter adjustments and high-speed processor requirements. In this paper, a low-complexity input current control (LCICC) strategy is proposed for the IMC operating at the unity GPF. Unlike the conventional strategies designed in the d-q synchronous coordinate frame, the proposed LCICC strategy is set up in the α-β stationary coordinate frame. Then, the quasi-proportional resonant (QPR) controllers are utilized for a novel input current control manner, which is implemented to regulate the input currents based on the reconstructed grid voltage and current vectors. By this design, the proposed strategy can help to reduce the control complexity, with the advantages of the conventional closed-loop control strategies reserved. The steady-state and dynamic-state performance of the proposed strategy is validated by the experiments on a downscaled prototype. Besides, comparative experimental research with respect to an existing typical strategy indicates that the computational burden can be reduced 14.9% by the proposed strategy.INDEX TERMS Indirect matrix converter, grid power factor, quasi proportional resonant, control complexity reduction.
The traditional intelligent algorithms for the selected harmonic elimination pulse-width modulation (SHEPWM) of multilevel converters provide low convergent rate and low accuracy of solutions when solving quarter-wave symmetry nonlinear equations. To obviate this problem and obtain a better modulating performance, an improved imperialist competition algorithm is proposed. The proposed algorithm enhances the global search ability by using moving imperialists. Also, a novel type of particles, named independent countries, are proposed to help the algorithm jump out of the local optimum. These independent countries change their positions using swarm intelligence. Compared with the existing particle swarm algorithm and genetic algorithm, the proposed algorithm has significant advantages by improving the accuracy of solutions and the rate of convergence. Finally, the correctness and effectiveness of the proposed algorithm are verified and evaluated by simulation and experimental results.
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