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Line current distortion is an important issue to a high-power current source rectifier(CSR) system. There are two main challenges related to this issue. First, the CSR input LC resonance can be affected by the variation of the source inductance from the power system and the effects of the CSR DC side circuit, which may lead to a line current distortion higher than expected. Another challenge is that the traditional high-power CSR using Selective Harmonic Elimination (SHE) pulse-width modulation (PWM) technique attempts to eliminate certain harmonics in the PWM current, which limits its ability for line current harmonic control. To control the CSR line current harmonics, this thesis focuses on two aspects: 1) the analysis and design of CSR input filter to avoid unexpected input LC resonance, and 2) the development of a new PWM scheme that can compensate the effects of the grid voltage harmonics and DC link current ripples. The thesis work has been validated by simulations and on an experimental CSR prototype. / Power Engineering and Power Electronics

Among the different multiphase ac drive solutions, one of the most widely reported in the literature is the six-phase machine. The machines can be realised into two different configurations, symmetrical and asymmetrical. For the symmetrical configuration, the stator winding consists of two sets of three-phase windings that are spatially shifted by 60 degrees where spatial displacement between any two consecutive phases is the same and equal to 60 degrees. For the asymmetrical configuration, the two sets of three-phase windings are spatially shifted by 30 degrees. As a result, the spatial shift between consecutive phases becomes non-equidistant. In this thesis, modulation techniques for both symmetrical and asymmetrical six-phase machines are investigated. The machines are configured in open-end winding configuration where both ends of the stator winding are connected to separate isolated inverters in a topology known as dual-inverter supply. Compared to conventional single-sided supply topology where one end of the winding is connected to an inverter while the other side is star-connected, some additional benefits are offered by the dual-inverter supply topology. First, fault tolerance of the drive is improved, since the supply is realised with two independent inverters. In case one of the inverters is faulted, the other can continue to provide power to the machine. Second, the same phase voltages can be achieved with half the dc-link voltages on the two inverter inputs compared to the single-sided supply, which can be useful in applications such as electric and hybrid electric vehicles and medium sized ships, where the dc voltage levels are limited. Further, due to the nature of the topology, additional diodes and capacitors like in the Neutral Point Clamped (NPC) and Flying Capacitor (FC) VSIs are not required. The latter results in a further advantage - capacitor voltage balancing techniques are not required. Two pulse width modulation (PWM) techniques for control of the dual-inverter supplied six-phase drives are proposed in this thesis. The first is a reference sharing algorithm where the inverters are modulated using reference voltage that is shared equally and unequally between the two modulators. For both symmetrical and asymmetrical six-phase drives, a better performance, in term of total harmonic distortion (THD) of phase voltage is obtained when the reference is shared unequally between the two modulators. The second technique is carrier-based modulation where the modulation of the two inverters is determined by the disposition of the carrier signals. Three variations of carrier signals disposition are investigated namely; the phase disposition (PD-PWM), alternate phase opposition disposition (APOD-PWM) and phase-shifted PWM (PS-PWM). For the symmetrical six-phase drive, the best phase voltage and current THDs are obtained using APOD-PWM while for asymmetrical six-phase drive, the APOD-PWM produces the worst current THD despite having the best voltage THD among the three methods. All the developed modulation techniques are analysed using simulations and experiments undertaken using a laboratory prototypes. The waveforms and spectra of phase voltage and load current obtained from the simulation and experimental works are presented in this thesis together with the THD of both the voltage and current over entire linear modulation range.

A two-wire, low component count soil temperature sensor was developed. The sensor uses one wire for ground and the other wire is used for both power and communication. Pulse width modulation is used to send temperature measurements to the master, where the duty cycle is proportional to the temperature. The sensor parasitically powers itself from the bidirectional data line. In order to reduce the number of components necessary, a microcontroller with an internal temperature sensor is used. Finally, the sensor can receive data from the master on the bidirectional communication line, which is used for calibrating the sensor.

This thesis deals with design of devices for control and regulation of LEDs. The document summarizes basic information about light, its origin and variety. This work discusses the effects of light on humans. There are also discussed the possibilities of lighting control with LEDs. The work includes a diagram that describes a device for controlling and controlling light for daylight and night light.

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Compared to other instruments for chemical analyses, electrochemical analyzers are relatively simple, inexpensive, easy to miniaturize and require little-to-no maintenance. However, like all commercially available instruments, commercial electrochemical analyzers like potentiostats primarily operate as black boxes with manufacturers providing little or no information about internal circuitry and programming. This practice can limit a researcher’s ability to develop new techniques or adapt an instrument for applications outside its typical use. In contrast, creators of open-source instruments release all the necessary information for reproduction of the hardware and software – minimizing such barriers to innovation in chemical analyses. Here, we report a low-cost, compact potentiostat based on an open-source Arduino microcontroller capable of performing electrochemical analyses such as cyclic and linear sweep voltammetry with an operating range of ± 208 𝜇A and ± 2.5 V. Performance of the potentiostat is investigated with low-cost pencil graphite electrodes and compared to a commercial potentiostat.

Catfish aquaculture is the largest cultured food fish industry in the United States, accounting for approximately $375 million in sales annually, with Mississippi leading the industry with 36,200 surface acres of production. However, infectious diseases such as enteric septicemia of catfish (ESC) are decreasing production efficiencies, creating losses of $40-60 million annually. Live-attenuated oral ESC vaccines are effective in preventing ESC infections, but have not been widely adopted by the catfish industry due to the lack of a system to administer the oral vaccine at the scale seen in commercial catfish production systems. An automated system was developed to administer a dosage of 220.5 ml of a live-attenuated ESC vaccine per kg of catfish feed, adapting commercial catfish feeder design to include a screw conveyor for mixing vaccine and feed in a continuous process, pulse-width modulated spray nozzle control for precise vaccine application, and a programmable automation controller to regulate and monitor system performance. Initial performance evaluations demonstrated system operation within the desired design specifications. System feed rates were determined to be a function of the rotational speed (RPM) of the screw conveyor and to be linear across the operational range. Feed rates were observed to decrease by 45% over dry feed when applying liquid vaccine to the feed stream at the 220.5 ml/kg (100 ml/lb) rate, resulting in a feed rate range of 6.80-34.02 kg/min (15-75 lb/min) (95% CI). Uniform pellet-level vaccine distribution is crucial to efficacy as pellet consumption is directly correlated with fish size, with more criticality in smaller fish fed at low rates. Pellet vaccine concentrations at 6.80, 20.41, and 34.02 ml/kg were highly variable and vaccine application at all rates were observed to be statistically different (less) than the target 220.5ml/kg rate (95% CI), pointing to potential issues with vaccine delivery system configuration or inadequacies in sampling methodology. Further evaluation at the pellet level with live-attenuated vaccine to obtain viable cell counts within individual pellets would provide data necessary to address uniformity of coverage questions more fully and to develop operational protocols that maximize system capabilities and vaccine efficacy.

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