A plug-and-play ripple mitigation approach for DC-links in hybrid systems

© 2016 IEEE.In this paper, a plug-and-play ripple mitigation technique is proposed. It requires only the sensing of the DC-link voltage and can operate fully independently to remove the low-frequency voltage ripple. The proposed technique is nonintrusive to the existing hardware and enables hot-swap operation without disrupting the normal functionality of the existing power system. It is user-friendly, modular and suitable for plug-and-play operation. The experimental results demonstrate the effectiveness of the ripple-mitigation capability of the proposed device. The DC-link voltage ripple in a 110 W miniature hybrid system comprising an AC/DC converter and two resistive loads is shown to be significantly reduced from 61 V to only 3.3 V. Moreover, it is shown that with the proposed device, the system reliability has been improved by alleviating the components' thermal stresses

MODELING AND TOPOLOGY EVALUATION FOR RECTIFIER CIRCUITS IN MEDIUM VOLTAGE DIRECT CURRENT SYSTEM

Naval ship propulsion design is evolving from the traditional structure with a main engine driving a shaft through a reduction gear, to a new architecture that uses electric drives powered from a direct current (DC) power distribution system. The goal of this thesis is to compare different medium voltage rectifiers interfacing an alternate current (AC) generator to a DC bus which can power the ship propulsion system. Power quality and efficiency of the power converters are the parameters used to compare four different rectifier circuit topologies: 2-level converter, 3-level converter, modular multi-level converter, and modular multi-level rectifier. Converter operating principles, design trade-offs, modeling characteristics, performance, and naval shipboard applicability are discussed in detail. Using a power electronics simulation platform, the four power rectifier circuits and their controls are connected between a 6.6kV AC generator and a regulated DC bus that represents the shipboard platform. Inside each rectifier circuit, thermal properties of the chosen semiconductor switching devices and diodes are built in and losses are captured and analyzed in steady state operation. This study shows that the modular multi-level rectifier circuit is the most efficient, easiest to maintain, and the recommended topology for Naval shipboard applications.Lieutenant, United States NavyApproved for public release. Distribution is unlimited

Modeling and Control of a 7-Level Switched Capacitor Rectifier for Wireless Power Transfer Systems

Wireless power continues to increase in popularity for consumer device charging. Rectifier characteristics like efficiency, compactness, impedance tunability, and harmonic content make the multi-level switched capacitor rectifier (MSC) an exceptional candidate for modern WPT systems. The MSC shares the voltage conversion characteristics of a post-rectification buck-boost topology, reduces waveform distortion via its multi-level modulation scheme, demonstrates tank tunability via the phase control inherent to actively switched rectifiers, and accomplishes all this without a bulky filter inductor. In this work, the MSC WPT system operation is explained, and a loss model is constructed. A prototype system is used to validate the models, showing exceptional agreement with the predicted efficiencies. The modeled MSC efficiencies are between 96.1% and 98.0% over the experimental power range up to 20.0 W. Two significant control loops are required for the MSC to be implemented in a real system. First, the output power is regulated using the modulation of the rectifier\u27s input voltage. Second, the switching frequency of the rectifier must exactly match the WPT carrier frequency set by the inverter on the primary side. Here, a small signal discrete time model is used to construct four transfer functions relating to the output voltage. Then, four novel time-to-time transfer functions are built on top of the discrete time model to inform the frequency synchronization feedback loop. Both loops are tested and validated in isolation. Finally, the dual-loop control problem is defined, closed form equations that include loop interactions are derived, and stable wide-range dual-loop operation is demonstrated experimentally

Dc Line-Interactive Uninterruptible Power Supply (UPS) with Load Leveling for Constant Power and Pulse Loads

Uninterruptable Power Supply (UPS) systems are usually considered as a backup power for electrical systems, providing emergency power when the main power source fails. UPS systems ensure an uninterruptible, reliable and high quality electrical power for systems with critical loads in which a continuous and reliable power supply is a vital requirement. A novel UPS system topology, DC line-interactive UPS, has been introduced. The new proposed UPS system is based on the DC concept where the power flow in the system has DC characteristic. The new DC UPS system has several advantageous with respect to the on-line 3-phase UPS which is extensively used in industry, such as lower size, cost and weight due to replacing the three-phase dual converter in the on-line UPS system with a single stage single phase DC/DC converter and thus higher efficiency is expected. The proposed system will also provide load leveling feature for the main AC/DC rectifier which has not been offered by conventional AC UPS systems. It applies load power smoothing to reduce the rating of the incoming AC line and consequently reduce the installation cost and time. Moreover, the new UPS technology improves the medical imaging system up-time, reliability, efficiency, and cost, and is applicable to several imaging modalities such as CT, MR and X-ray as well. A comprehensive investigation on different energy storage systems was conducted and couple of most promising Li-ion cell chemistries, LFP and NCA types, were chosen for further aggressive tests. A battery pack based on the LFP cells with monitoring system was developed to be used with the DC UPS testbed. The performance of the DC UPS has also been investigated. The mathematical models of the system are extracted while loaded with constant power load (CPL) and constant voltage load (CVL) during all four modes of operation. Transfer functions of required outputs versus inputs were extracted and their related stability region based on the Routh-Hurwitz stability criteria were found. The AC/DC rectifier was controlled independently due to the system configuration. Two different control techniques were proposed to control the DC/DC converter. A linear dual-loop control (DLC) scheme and a nonlinear robust control, a constant frequency sliding mode control (CFSMC) were investigated. The DLC performance was convincing, however the controller has a limited stability region due to the linearization process and negative incremental impedance characteristics of the CPL which challenges the stability of the system. A constant switching frequency SMC was also developed based on the DC UPS system and the performance of the system were presented during different operational modes. Transients during mode transfers were simulated and results were depicted. The controller performances met the control goals of the system. The voltage drop during mode transitions, was less than 2% of the rated output voltage. Finally, the experimental results were presented. The high current discharge tests on each selected Li-ion cell were performed and results presented. A testbed was developed to verify the DC UPS system concept. The test results were presented and verified the proposed concept

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

Wireless Information and Power Transfer: Architecture Design and Rate-Energy Tradeoff

Simultaneous information and power transfer over the wireless channels potentially offers great convenience to mobile users. Yet practical receiver designs impose technical constraints on its hardware realization, as practical circuits for harvesting energy from radio signals are not yet able to decode the carried information directly. To make theoretical progress, we propose a general receiver operation, namely, dynamic power splitting (DPS), which splits the received signal with adjustable power ratio for energy harvesting and information decoding, separately. Three special cases of DPS, namely, time switching (TS), static power splitting (SPS) and on-off power splitting (OPS) are investigated. The TS and SPS schemes can be treated as special cases of OPS. Moreover, we propose two types of practical receiver architectures, namely, separated versus integrated information and energy receivers. The integrated receiver integrates the front-end components of the separated receiver, thus achieving a smaller form factor. The rate-energy tradeoff for the two architectures are characterized by a so-called rate-energy (R-E) region. The optimal transmission strategy is derived to achieve different rate-energy tradeoffs. With receiver circuit power consumption taken into account, it is shown that the OPS scheme is optimal for both receivers. For the ideal case when the receiver circuit does not consume power, the SPS scheme is optimal for both receivers. In addition, we study the performance for the two types of receivers under a realistic system setup that employs practical modulation. Our results provide useful insights to the optimal practical receiver design for simultaneous wireless information and power transfer (SWIPT).Comment: to appear in IEEE Transactions on Communication

Housing equilibrium price framework for Malaysian middle Class group in affordable housing market

Failure in getting housing equilibrium price for affordable housing market has become a hot topic that is often discussed in the press due to the imbalance between housing demanded and supplied. The basic purpose of the research was to investigate the relationship between macroeconomic housing demand and supply detenninant factors and affordable housing needs in Malaysia, and to dete1111ine the equilibrium house price for middle-class income in the affordable housing market. The research involved the development of theoretical framework by synthesising the models and framework developed by past researchers on the housing equilibrium price framework. It also uses time series analysis together with regression analysis to collect and analyse data. As initial, 371 respondents from household's side and 32 respondents from developer's side in Melaka Tengah were selected as samples as case study in Melaka. During data analysed, around 200 questionnaires from households and 32 questionnaires from developers can be used. The data was analysed using SPSS software to investigate the relationship between macroeconomic housing demand and supply determinant factors towards the needs f and supply of afordable housing market. From the investigation, current house price, monetary status and population changes are the most critical factors that lead to the needs of affordable housing supplies. Meanwhile, developers put the interest rate, government interventions and population changes as the catalyst to develop the affordable housing projects. On the other hand, the empirical data of housing prices are collected from NAPIC from 2006 to 2015. The equilibrium price calculated from the sales perfonnance within four quarter reported by NAPIC is examined using linear regression method. Based on these themes, the research contended that the housing equilibrium price can be achieved using empirical data from demand and supply with supported from current house price, monetary status and population changes the interest rate, government interventions and population changes. Hence, government is the key player and be a pulling effect in controlling the housing price by using the housing demand and supply determinant factor to create a win-win situation between middle-class income and housing developers

Modeling and Simulation of Parallel D-STATCOMs with Full-Wave Rectifiers

In recent years, both a significant increase in electrical demand and a large influx of intermittent renewable energy sources have put a considerable stress on the nation’s electrical grid. Conventional power flow control techniques such as capacitor banks and tap-changing transformers are incapable of adequately handling the rapid fluctuations in power supply and demand that today’s grid experiences. Flexible AC Transmission System (FACTS) controllers are a practical way to compensate for such rapid power fluctuations. One type of shunt FACTS controller is the Static Synchronous Compensator (STATCOM), which uses fully controllable switches to source or sink reactive power to a point on the grid, thus reducing voltage fluctuations due to load changes. The purpose of this thesis is to model and simulate the operation of two Distribution STATCOMs (D-STATCOMs) operating on the same point on the grid. These D-STATCOMs also utilize parallel full-wave rectifiers that directly connect the ac grid to the dc capacitor of the D-STATCOMs. Parameters such as power loss, reaction time, stability, and THD are measured for several test scenarios. Results from this thesis show that two D-STATCOMs operating on the same point can be stable and effective under a wide range of conditions. This thesis also concludes that the inclusion of parallel rectifiers with the D-STATCOMs results in no performance improvement of the D-STATCOMs