Abstract:In the research field of multilevel converters, three-level NPC (neutral-point-clamped) converters, which unfortunately may cause the deviation of the neutral-point voltage of DC-link capacitors, are widely discussed. Theoretically, virtual space vector modulation (VSVM) could guarantee the balance control of the neutral-point voltage. However, there still exist some uncontrollable space vector regions. Based on VSVM, this paper proposes a varied virtual space vector modulation (VVSVM) method for three-level NPC converters. Under complete modulation conditions, this method can control the balance of the neutral-point voltage of DC-link capacitors by adjusting the duty cycle of small vectors and regulating the current generated by virtual medium vectors. Compared with commonly used VSVM methods and mixed modulation strategies, this method is simpler and more practical. The effectiveness and validity of this method are verified by simulations and experiments.
Based on an innovative application of van der Pauw's theory, a system was developed for the absolute measurement of electrolytic conductivity in aqueous solutions. An electrolytic conductivity meter was designed that uses a four-electrode system with an axial–radial two-dimensional adjustment structure coupled to an ac voltage excitation source and signal collecting circuit. The measurement accuracy, resolution and repeatability of the measurement system were examined through a series of experiments. Moreover, the measurement system and a high-precision electrolytic conductivity meter were compared using some actual water samples.
A determination method for formaldehyde based on micro-fluidic chip was developed in this study. Formaldehyde samples with 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) and ammonium ferric sulfate were well mixed and reacted in a micro-fluidic chip, and signals in effluent were determined online. The correlation coefficient of calibration line was greater than 0.999, which indicated that signals of this device were highly positively correlated with formaldehyde concentration. The relative standard deviations (RSD) of same sample were less than 2% at different formaldehyde concentration levels, indicating perfect reproducibility of this method. Noteworthy, this method was affected significantly by temperature since the online signal was depended on the extent of reaction.
Cascaded multilevel inverters could realize high-voltage output based on a series connection of power cells which use standard low-voltage component configurations. This characteristic could achieve high-quality output voltage waveforms and input current waveforms. These merits are made for motor control, especially in the field of speed-sensorless vector control of induction motor based on the theory of MRAS. This paper constructs a simulation system with the help of MATLB/SIMULINK and a system combined cascaded H-bridge multilevel inverter with induction motor with the help of DSP and FPGA. The simulation and experiment results verified the superiority of cascaded multilevel inverter applied on the MRAS speed-sensorless vector control of induction motor.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.