High voltage adjustable speed drive systems offer significant advantages in many applications such as a fan, pump, or blower. In these applications, the adjustable speed drive systems achieves a higher level of system efficiency.Usually, low voltage inverters with output transformer were used for a high voltage induction motor drive system. Recently, direct drive inverter system without output transformer has proposed and investigated. This inverter system is composed of single phase unit inverters and outputs multilevel voltages.In this paper, pulse width modulation (PWM) technique suitable for high voltage direct drive inverter systems are discussed. At first, conventional multi-level PWM techniques based on the sub-harmonic method are shown and evaluated using time domain simulation.Next, new PWM method is proposed. This method has advantages that a modulation principle is very simple, distortion of the output voltage is very low, and well balanced switching losses among the unit inverters are achieved. Finally, simulation andexperimental result are shown to illustrate the effectiveness of this method.
Functional crystalline materials are applicable to various fields because of their unique physical and (photo)chemical properties. Flux crystal growth is a versatile liquid-phase method that enables efficient crystal growth below the melting points of the solutes. Although tremendous effort focuses on the design growth conditions and synthesis of crystalline materials with target physicochemical properties, it is difficult to completely clarify relationships between experimental conditions and physicochemical properties. Therefore, much trial and error is necessary to obtain target crystalline materials. In this study, machine learning (ML) and Bayesian optimization (BO) improve the efficiency of the synthesis of crystalline layered lithium titanate Li 2 TiO 3 (LTO) with a target particle size and morphology. An experimental data set that centers on the flux crystal growth of LTO verifies our proposed method. Coupling flux growth experiments with ML and BO methods can achieve a high preparation efficiency of LTO crystals with a desired particle size and morphology.
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