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A Single-Source Photovoltaic Power Conditioning System using Asymmetric Cascaded Multilevel Inverter
Mohana Sundar Manoharan,Ashraf Ahm ed,Hyun-Woo Kim,Joung-Hu Park 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
This paper proposes a power conditioning system (PCS) for distributed photovoltaic (PV) applications using a hybrid asymmetric cascaded multilevel inverter with a single PV source. One of the main disadvantages of cascaded multilevel inverters in PV systems is the requirement of multiple isolated DC sources which leads to voltage unbalancing. The proposed PCS uses a single PV source with a flyback DC-DC converter to facilitate the reduction of the required DC sources and maintain voltage balance. The flyback converter is used to provide the input for low voltage H-bridge cell which processes only 20% of the total power. This helps to minimize the losses occurring in the proposed PCS. Furthermore, transient analysis and controller design for the proposed PCS in stand-alone mode of operation is presented. The feasibility of the proposed PCS has been tested using a 1kW hardware prototype and the obtained results are presented.
Mohana Sundar Manoharan,Ashraf Ahmed,Joung-Hu Park 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.5
In this paper, digital peak current mode control for single phase H-bridge inverters is developed and implemented. The digital peak current mode control is achieved by directly controlling the PWM signals by cycle-by-cycle current limitation. Unlike the DC-DC converter where the output voltage always remains in the positive region, the output of DC-AC inverter flips from positive to negative region continuously. Therefore, when the inverter operates in negative region, the control should be changed to valley current mode control. Thus, a novel control logic circuit is required for the function and need to be analyzed for the hardware to track the sinusoidal reference in both regions. The problem of sub-harmonic instability which is inherent with peak current mode control is also addressed, and then proposes the digital slope compensation in constant-sloped external ramp to suppress the oscillation. For unipolar PWM switching method, an adaptive slope compensation in digital manner is also proposed. In this paper, the operating principles and design guidelines of the proposed scheme are presented, along with the performance analysis and numerical simulation. Also, a 200W inverter hardware prototype has been implemented for experimental verification of the proposed controller scheme.
Continuous Oxygen Supply in Pump-less Micro-Bioreactor Based on Microfluidics
Mohana Marimuthu,김상효 한국바이오칩학회 2015 BioChip Journal Vol.9 No.1
This research aims a continuous and uniformoxygen tensions and oxygen gradients supply inmicrofluidic cell culture chip based micro-bioreactorwithout any external pumps by modifying the existingsiphon based perfusion strategy using conventionaltools to control constant hydrostatic pressure for constantfluid flow rate. In this study, the microfluidicbased micro-bioreactor is fabricated using a polydimethylsiloxane(PDMS) replication process. The micro-bioreactor chip is composed of simple oxygenperfusion setup connecting to capillary-like branchedmicrochannels and a cell culture and support loadingarea. The function of the new pump-less fluid perfusionin microfluidic cell culture chip and maintainsconstant oxygen supply in the cell culture area hasbeen experimentally evaluated. And the results demonstratethat this proposed microfluidic flow systemin a micro-bioreactor is proved to provide a linear distributionof oxygen throughout the cell culture areawithout any external and internal interference. Also,oxygen diffusion into the culture area through a microscalechannel has been successfully established bythe constant hydraulic pressure controlled by siphoningeffect. Such flow system was used in a PDMSbased microfluidic micro-bioreactor design to providethe high-throughput oxygen diffusion and perfusion,and the uniform oxygen/nutrient distribution continuouslysupplied for dermal fibroblast cell culture. Thiscould be a potential and effective model to be incorporatedinto tissue regeneration studies, drug screeningmodel, and in cancer tissue model studies for understandingangiogenesis, where oxygen tension andperfusion cultures play important roles.