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This paper proposes a method for minimizing the inductor current ripple of a DC–DC converter in a two-stage power conversion system consisting of a grid-connected PWM converter and an interleaved multiphase three-level DC–DC converter. To reduce the output voltage ripple, the three-level DC–DC converter is configured in parallel and operated interleaved. However, a circulating current generated by the interleaved operation increases the inductor current ripple of each DC–DC converter and causes system loss and inductor saturation. In this paper, the inductor and output current ripple of the interleaved three-phase three-level DC–DC converter is mathematically analyzed and the effect of the DC–DC converter's duty ratio and output voltage on each current ripple is described. Based on this analysis, a method is proposed for controlling the optimal DC link voltage through the PWM converter, so that the DC–DC converter is controlled with the duty ratio that minimizes the inductor current ripple. The simulation and experimental results under various operating conditions are presented to verify the feasibility of the proposed control method. [ABSTRACT FROM AUTHOR]

A decoupling controller of bridle rolls for steel mill drive system is introduced. With this type of controller, the tension of the steel trip is kept as a reference value and is unaffected by line speed changes. Likewise, the speed of the strip is kept stable even with tension variations. The use of a decoupling controller produces a torque reference of each roll driving motor based on the average roll speed and required tension.

A novel flux-weakening scheme for the interior permanent magnet synchronous motor (IPMSM) is proposed. This is implemented based on the output of the synchronous PI current regulator-reference voltage to the PWM inverter. The onset of flux weakening and the flux level are adjusted inherently by the outer voltage regulation loop to prevent saturation of the current regulator. Attractive features of this flux weakening scheme include no dependency on the machine parameters, the guarantee of current regulation at any operating condition, and smooth and fast transition into and out of the flux weakening mode. Experimental results at various operating conditions including the case of detuned parameters are presented to verify the feasibility of the proposed control scheme. Index Terms - Flux weakening, IPMSM, outer voltage regulation loop.

This paper proposes a pulsewidth modulation (PWM) control strategy for the efficient operation of the three-phase three-level neutral-point-clamped (NPC) inverters based on a bootstrap gate drive circuit. The bootstrap circuit used in the three-level NPC inverter has advantages in terms of the cost reduction and the compact circuit design. However, the bootstrap circuit has a drawback due to the low gate-emitter voltage during the low-frequency and variable load condition of the inverter system. This problem leads to lower efficiency and reliability of the inverter. Therefore, this paper analyzes the causes of the voltage decrease in bootstrap capacitors and proposes PWM control strategy to increase the voltage level of bootstrap capacitors for the efficient operation of the inverter. The proposed PWM control strategy provides efficient and stable operation of the inverter system by selecting the unipolar, dipolar, or partial-dipolar modulation methods according to the fundamental output frequency and load current of the inverter system. Furthermore, this paper proposes a design method of the size of bootstrap capacitors for the optimal circuit design. The effectiveness of the proposed PWM control strategy is verified using the experimental results. [ABSTRACT FROM AUTHOR]