Optimization And Design Of Photovoltaic Micro-inverter

To relieve energy shortage and environmental pollution issues, renewable energy, especially PV energy has developed rapidly in the last decade. The micro-inverter systems, with advantages in dedicated PV power harvest, flexible system size, simple installation, and enhanced safety characteristics are the future development trend of the PV power generation systems. The double-stage structure which can realize high efficiency with nice regulated sinusoidal waveforms is the mainstream for the micro-inverter. This thesis studied a double stage micro-inverter system. Considering the intermittent nature of PV power, a PFC was analyzed to provide additional electrical power to the system. When the solar power is less than the load required, PFC can drag power from the utility grid. In the double stage micro-inverter, the DC/DC stage was realized by a LLC converter, which could realize soft switching automatically under frequency modulation. However it has a complicated relationship between voltage gain and load. Thus conventional variable step P&O MPPT techniques for PWM converter were no longer suitable for the LLC converter. To solve this problem, a novel MPPT was proposed to track MPP efficiently. Simulation and experimental results verified the effectiveness of the proposed MPPT. The DC/AC stage of the micro-inverter was realized by a BCM inverter. With duty cycle and frequency modulation, ZVS was achieved through controlling the inductor current bi-directional in every switching cycle. This technique required no additional resonant components and could be employed for low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes were derived from the basic theory of the proposed technique. They were referred to as Boundary Current Mode (BCM), Variable Hysteresis Current Mode (VHCM), and Constant Hysteresis Current Mode (CHCM) individually in this paper with their advantages and disadvantages analyzed in detail. Simulation and experimental iv results demonstrated the feasibilities of the proposed soft-switching technique with the digital control schemes. The PFC converter was applied by a single stage Biflyback topology, which combined the advantages of single stage PFC and flyback topology together, with further advantages in low intermediate bus voltage and current stresses. A digital controller without current sampling requirement was proposed based on the specific topology. To reduce the voltage spike caused by the leakage inductor, a novel snubber cell combining soft switching technique with snubber technique together was proposed. Simulation and experimental waveforms illustrated the same as characteristics as the theoretical analysis. In summary, the dissertation analyzed each power stage of photovoltaic micro-inverter system from efficiency and effectiveness optimization perspectives. Moreover their advantages were compared carefully with existed topologies and control techniques. Simulation and experiment results were provided to support the theoretical analysis

Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

A Novel Induction Heating System Using Multilevel Neutral Point Clamped Inverter

Contribution to Knowledge: The main knowledge contribution of the dissertation can be summarized as follows: 1-A new design of induction heating power supply configuration with two categories of LLC topologies: A Novel induction heating power supply topology using multilevel neutral point clamped inverter (MNPCI) is investigated and verified. The proposed converter topology decreases the switching losses by decreasing the DC link voltage to half its DC rail voltage value with the aid of operation under soft switching mode condition. Depending on the modified LLC optimum design being introduced, it shares the advantage features of both voltage fed and current fed inverters with the capability to absorb the undesired parasitic components in the design. The new design involves adding new circuit parameter that helps in controlling the power transfer from the MNPCI to the resonant load tank. All the analytical analysis made and the corresponding experimental work verifies the prototype configuration. This contribution was presented by the author and published in: {B.M. Flayyih; M.Z. Ahmed; M. Ambroze, ''A Novel Hybrid Voltage-Current Fed Induction Heating Power Supply System Using Multilevel Neutral Point Clamped Inverter '', Energycon 2014 IEEE International Energy Conference, Dubrovnik-Croatia. From 13th - 16th May 2014}. 2-An optimum power control of induction heating system by reducing harmonic distortion content: The development of IH system has become a pressing need to improve the power transfer from power supply to the IH load of the application required, and due to variable characteristic of IH load workpiece during the heating cycle, it is necessary to develop an IH system that operates using resonant inverters with switching frequency that changes according to changing load conditions during the IH application process, in order to keep tuning with natural resonant frequency of the system and keep working under optimal operational point. A novel super frequency induction heating power supply using MNPCI with optimum control algorithm is introduced. The control strategy is to keep phase shift angle between voltage and current approximately zero at all load conditions to ensure maximum power transfer whatever the load parameters changes, that is necessary to reduce the switching losses and increase the efficiency. The load topology being used consists of variable LLC resonant tank with values chosen carefully to coincide with the design. Afterword, an Optimum Harmonic Control of a proposed induction heating power supply with MNPCI is also introduced in this research. The proposed system achieves the soft switching mode for both current and voltage with low harmonic distortion and the capability to maximize the heating power by controlling the harmonics. The modulation strategy depends on changing the ON switching time of the prototype to an optimized value that achieves natural switching with lowest possible harmonic distortion and thus, gaining highest heating power efficiency. This contribution was also presented by the author and published in {B.M. Flayyih; M.Z. Ahmed; S. MacVeigh, ''A Comprehensive Power Analysis of Induction Heating Power Supply System Using Multilevel Neutral Point Clamped Inverter With Optimum Control Algorithm '', 2015 IEEE 11th International Conference on Power Electronics and Drive Systems (PEDS), From 9th - 12th June 2015, Sydney, Australia}. This contribution is also presented by the author in: {B.M. Flayyih; M.Z. Ahmed; M. Ambroze, ''An Optimum Harmonic Control of Induction Heating Power Supply System Using Multilevel Neutral Point Clamped Inverter'', The IEEE Transportation Electrification Conference and Expo Asia-Pacific (ITEC2016), Busan, Korea on 1st - 4th June, 2016}.This thesis investigates a novel DC/AC resonant inverter of Induction Heating (IH) system presenting a Multilevel Neutral Point Clamped (MNPCI) topology, as a new part of power supply design. The main function of the prototype is to provide a maximum and steady state power transfer from converter to the resonant load tank, by achieving zero current switching (ZCS) with selecting the best design of load tank topology, and utilizing the advantage aspects of both the Voltage Fed Inverter (VFI) and Current Fed Inverter (CFI) kinds, therefore it can considered as a hybrid-inverter (HVCFI) category . The new design benefits from series resonant inverter design through using two bulk voltage source capacitors to feed a constant voltage delivery to the MNPCI inverter with half the DC rail voltage to decrease the switching losses and mitigate the over voltage surge occurred in inverter switches during operation which may cause damage when dealing with high power systems. Besides, the design profits from the resonant load topology of parallel resonant inverter, through using the LLC resonant load tank. The design gives the advantage of having an output current gain value of about Quality Factor (Q) times the inverter current and absorbs the parasitic components. On the contrary, decreasing inverter current means decreasing the switching frequency and thus, decreasing the switching losses of the system. This aspect increases the output power, which increases the heating efficiency. In order for the proposed system to be more reliable and matches the characteristics of IH process , the prototype is modelled with a variable LLC topology instead of fixed load parameters with achieving soft switching mode of ZCS and zero voltage switching (ZVS) at all load conditions and a tiny phase shift angle between output current and voltage, which might be neglected. To achieve the goal of reducing harmonic distortion, a new harmonic control modulation is introduced, by controlling the ON switching time to obtain minimum Total Harmonic Distortion (THD) content accompanied with optimum power for heating energy.Iraqi Ministry of Higher Education and Scientific Research.Al Shuhadaa Establishment of Iraq

Bidirectional High Current DC/DC Converters for Capacitive Deionisation Water Treatment

This thesis proposes three new DC/DC topologies and related technologies to control salt removal from water sources using the capacitive deionisation (CDI) technique. These technologies are critical in improving energy utilization, higher product yield and water recovery, and simpler design. A lossless bidirectional current sensing circuit is proposed. The proposed circuit avoids the use of conventional current shunt and extracts the current information from the winding resistance of the inductor (DCR) without introducing excessive conduction loss. Moreover, this improved DCR current sensing circuit has a high bandwidth and a low error over the entire range, even near the zero-crossing. A successful application of the proposed circuit is demonstrated in a 5-phase interleaved Buck/Boost bidirectional converter. The same converter has been used for CDI cell characterization. A time-domain analysis of the three-phase interleaved LLC topology is presented. The proposed analysis method reveals various facts that cannot be explained with the conventional Fundamental Harmonic Analysis (FHA) methods, including the number of resonant frequencies. The theory also gives a more accurate prediction of the gain-frequency-power relationship and the soft-switching conditions. Extensive simulations and experiments validate the correctness of the theory. Two new switch-capacitor two-phase interleaved flyback converters are proposed, which can invert the polarity of the input voltage and efficiently supply a high current while inheriting all the advantages of the Buck and Boost counterparts, such as the intrinsic current sharing, high conversion ratio, lower current ripple, and reduced switching loss. The operating principle, key waveform, simulation, and experimental results are presented. Finally, a new two-phase interleaved bipolar four-quadrant converter is proposed. Without sacrificing efficiency, it enables high-current discharge at extremely low cell voltage and features seamless transition. The proposed converter combines the switch-capacitor flyback converter with the switched-capacitor Buck converter in a creative manner so that the input and the output share a common ground reference while featuring a bipolar output, which can simplify the wiring when connecting more units in parallel. A switching pattern is proposed to enable a seamless transition between different operation modes. An auxiliary switching network is introduced to correct the loss of natural inductor current balancing in the transition mode

GaN-Based High Efficiency Transmitter for Multiple-Receiver Wireless Power Transfer

Wireless power transfer (WPT) has attracted great attention from industry and academia due to high charging flexibility. However, the efficiency of WPT is lower and the cost is higher than the wired power transfer approaches. Efforts including converter optimization, power delivery architecture improvement, and coils have been made to increase system efficiency.In this thesis, new power delivery architectures in the WPT of consumer electronics have been proposed to improve the overall system efficiency and increase the power density.First, a two-stage transmitter architecture is designed for a 100 W WPT system. After comparing with other topologies, the front-end ac-dc power factor correction (PFC) rectifier employs a totem-pole rectifier. A full bridge 6.78 MHz resonant inverter is designed for the subsequent stage. An impedance matching network provides constant transmitter coil current. The experimental results verify the high efficiency, high PF, and low total harmonic distortion (THD).Then, a single-stage transmitter is derived based on the verified two-stage structure. By integration of the PFC rectifier and full bridge inverter, two GaN FETs are saved and high efficiency is maintained. The integrated DCM operated PFC rectifier provides high PF and low THD. By adopting a control scheme, the transmitter coil current and power are regulated. A simple auxiliary circuit is employed to improve the light load efficiency. The experimental results verify the achievement of high efficiency.A closed-loop control scheme is implemented in the single-stage transmitter to supply multiple receivers simultaneously. With a controlled constant transmitter current, the system provides a smooth transition during dynamically load change. ZVS detection circuit is proposed to protect the transmitter from continuous hard switching operation. The control scheme is verified in the experiments.The multiple-reciever WPT system with the single-stage transmitter is investigated. The system operating range is discussed. The method of tracking optimum system efficiency is studied. The system control scheme and control procedure, targeting at providing a wide system operating range, robust operation and capability of tracking the optimized system efficiency, are proposed. Experiment results demonstrate the WPT system operation

Design and Control of Power Converters for High Power-Quality Interface with Utility and Aviation Grids

Power electronics as a subject integrating power devices, electric and electronic circuits, control, and thermal and mechanic design, requires not only knowledge and engineering insight for each subarea, but also understanding of interface issues when incorporating these different areas into high performance converter design.Addressing these fundamental questions, the dissertation studies design and control issues in three types of power converters applied in low-frequency high-power transmission, medium-frequency converter emulated grid, and high-frequency high-density aviation grid, respectively, with the focus on discovering, understanding, and mitigating interface issues to improve power quality and converter performance, and to reduce the noise emission.For hybrid ac/dc power transmission,• Analyze the interface transformer saturation issue between ac and dc power flow under line unbalances.• Proposed both passive transformer design and active hybrid-line-impedance-conditioner to suppress this issue.For transmission line emulator,• Propose general transmission line emulation schemes with extension capability.• Analyze and actively suppress the effects of sensing/sampling bias and PWM ripple on emulation considering interfaced grid impedance.• Analyze the stability issue caused by interaction of the emulator and its interfaced impedance. A criterion that determines the stability and impedance boundary of the emulator is proposed.For aircraft battery charger,• Investigate architectures for dual-input and dual-output battery charger, and a three-level integrated topology using GaN devices is proposed to achieve high density.• Identify and analyze the mechanisms and impacts of high switching frequency, di/dt, dv/dt on sensing and power quality control; mitigate solutions are proposed.• Model and compensate the distortion due to charging transition of device junction capacitances in three-level converters.• Find the previously overlooked device junction capacitance of the nonactive devices in three-level converters, and analyze the impacts on switching loss, device stress, and current distortion. A loss calculation method is proposed using the data from the conventional double pulse tester.• Establish fundamental knowledge on performance degradation of EMI filters. The impacts and mechanisms of both inductive and capacitive coupling on different filter structures are understood. Characterization methodology including measuring, modeling, and prediction of filter insertion loss is proposed. Mitigation solutions are proposed to reduce inter-component coupling and self-parasitics