1,721,401 research outputs found
An investigation of electric spring technology for smart grid applications
No full textWith the increasing trend of renewable energy penetration in modern power systems, many nations in the world are establishing smart grids to tackle the uncertainty of renewable power inputs. Electric Spring (ES) technology is an emerging demand-side management (DSM) method which can provide the grid with some ancillary services (e.g., voltage regulation, frequency regulation, power quality improvement, etc.). ESs transfer some non-critical loads into smart loads (SLs) with adjustable power consumption.
In this thesis, the ES topology evolvement from ES-1, ES-2 to ES-B2B and hybrid ES are reviewed in the first section. The diverse control schemes for single ES as well as for ESs group and the system-level studies of massive distributed ESs in the power grid are also inclusively recapped. An in-depth investigation on the ES control and its valuable smart grid applications is then conducted, and progress have been made in the following three aspects:
1. In the ES control aspect, a uniform controller, on which three fixed-interior-angle control strategies can be executed, is proposed in chapter 3. The operating curves as well as the distinctive characteristics of the SLs under these three fixed-interior-angle control strategies are further analyzed. Experimental results show that the proposed uniform controller could be programmed to perform three fixed-interior-angle control strategies successfully, and the operating curves under these fixed-interior-angle control strategies are verified.
2. In the aspect of using ES for voltage regulation, an investigation into using the ESs for overvoltage prevention in distribution LV networks with high PV penetration is reported in chapter 4. It is revealed that due to the uncertainty of surplus PV generation and the corresponding reverse power flow, the overvoltage issues may happen at many nodes of the LV networks. The ES-B2Bs is combined with the storage-type electric water heater to form the smart thermal loads. The dynamic consensus protocol is used to coordinate different smart thermal loads units. A hierarchical collaboration model of using BESSs as a back-up is also established in chapter 3. The simulation results based on Hong Kong Sha Luo Bay LV network verifies the effectiveness of the proposed SL-plus-BESS system. The following comparison case study between the proposal and pure BESSs program shows the economic benefits of introducing ESs for overvoltage prevention.
3. In the aspect of using ES for frequency regulation, besides traditional primary frequency response service, the SLs are enabled to provide virtual inertia to the power system in this thesis. In chapter 5, the control scheme for ES-B2B to emulate inertia is presented and the mathematic expression of how much virtual inertia can be provided from SLs is derived. The case study in the CIGRE microgrid shows that significant virtual inertia could be obtained from SLs by only allowing the load voltages to fluctuate within 0.95~1.05 times the nominal value.
The proposed uniform controller in this thesis paves the way for the research of the ES with multiple switchable functions. The investigation also fills in the blanks of using ESs for overvoltage prevention and virtual inertia purpose. Future research can focus on the economic benefits of ES providing multiple services.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Some emerging aspects on wireless power transfer
No full textWireless power transfer (WPT) owns several benefits, which include elimination of various charging adapter types, avoidance of cord clutter, electric isolation, and easier maintenance. Its development has undergone significant progress in the past few decades due to the advancement in high frequency switching devices as well as growing application areas such as portable devices, medical implants, and electric vehicles. However, the rapid evolution of existing wireless charging standards and on-going studies of WPT show that there are uncovered areas and improvements to be made. Three emerging aspects of WPT are investigated in this thesis:
1. It is expected that there will be more applications in which power has to be transferred wirelessly with metal objects present in the future. One such emerging application is powering online monitoring systems on high voltage (HV) transmission towers with domino WPT systems in the form of insulation rods; a metal ring is present on the insulation rod to avoid corona discharge. Existing WPT studies focus primarily on foreign or unintended metallic objects. Owing to the lack of studies toward intended metal objects in WPT systems, a systematic evaluation of the behavior of WPT link with metal ring is carried out based on a reduced-order model. The conduction loss of the metal ring was found not to be the reason for efficiency or output power drop, but its alteration of the self- and mutual- inductances of the coils. Suggestions for minimizing the effects of metal ring were given and experimental results have proven them effective in enhancing the WPT link performance.
2. Different coupling structures have been studied recently for different purposes and applications such as increasing the coupling factor or achieving omnidirectional charging. A new ball-joint WPT structure aiming to achieve constant mutual coupling under a range of rotational angles for the application of movable mechanical parts is presented in this work. This structure is based on capacitive coupling and comprises four plates embedded in a rotatable ball-joint structure. Detailed design procedures and equivalent circuit model were presented. It is implemented and verified to possess constant coupling under different rotating angles.
3. One aspect of battery charging rarely studied by power electronic researchers is the thermal issue. The study of relationship between charging current profile and heat generation of battery is initiated in this work based on coupled electric and thermal models of a Li-ion battery. Through judging the average, RMS, and form factor of a charging current waveform, optimal charging methods with faster charging speed under the same heat constraints are established. These methods apply to both wired and wireless charging. A widely adopted guideline in industry proposed by Japan Electronics and Information Technology Industries Association (JEITA) for the prevention of extreme temperature charging is studied and found to charge batteries without optimal charging speed. Two new charging methods are therefore proposed to improve upon without violating this guideline. Experimental results have shown significant improvement in charging speed with the two new charging methods.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
An investigation into high efficiency, compact DC-DC power conversion systems
No full textThis thesis presents a study on high efficiency, compact DC-DC power conversion systems for several DC/DC converter applications in DC microgrids.
Firstly, a research study on high performance DC-DC power conversion systems in DC microgrids has been conducted. Specifically, design requirements and challenges have been highlighted based on different applications. It provides important design criteria for high performance DC-DC power conversion system design and guidance for further research directions.
Secondly, for automotive lighting system, the LED drivers require special design considerations, which include voltage step-up and –down function, high energy efficiency and fast current reference tracking capability. Unlike the conventional efficiency improvement methods, which are based on cumbersome circuit/component optimization and/or modification for a single operating point, a simple approach based on topology transition is proposed, which can achieve a high efficiency for a wide input voltage range. In particular, the topology of the LED driver can change between buck, boost and buck-boost converter according to the level of the input voltage. In addition, a novel current mode controller is proposed such that (i) compatibility to different topologies (ii) seamless topology transition and (iii) fast current reference tracking can be concurrently achieved. The feasibilities of the proposed topology transition method and its control have been experimentally verified through a four-switch buck-boost converter prototype. It is shown that there is more than 5% efficiency improvement as compared to the conventional four-switch buck-boost converter.
Then, for the renewable energy DC/DC power conversion, a new class of high-voltage-gain DC-DC converters for high efficiency and transformer-less DC-DC applications where large voltage step-up ratios are required, is presented in this thesis. It features high step-up voltage conversion ratio with a moderate duty cycle; non-pulsating input current; low voltage stress on all of the switches; easy implementation of control and driving circuits; and low cost due to reduced components via combination of a two-stage converter into a single-stage converter. A 300 W prototype of a 19-time converter achieving the peak efficiency of 96.1% is built. Both simulation and experimental results validating the theoretical analysis and operation of the converter are provided.
Finally, for the DC/DC power conversion in data center applications, a new class of high frequency high-voltage-gain DC-DC converters for high efficiency and transformer-less DC-DC applications where large voltage step-down ratios are required, is presented in this thesis. The converter is derived from the hybrid integration of a switched-capacitor converter and a buck converter. It features high step-down voltage conversion ratio with a moderate duty cycle; low voltage stress on all of the switches; scalability for high current high-power applications; and low cost. Full soft-charging operation and minimal device voltage stresses are achieved under all operating conditions. Steady-state operations of the converter are comprehensively analyzed. A 900 W prototype of a 20-time converter achieving the peak efficiency of 92.5% with 1MHz switching frequency is built. The theoretical analysis and operation of the converter have been experimentally verified.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Some control aspects of distributed power electronics equipment
No full textInstantaneous balance of electric “power generation” and “power demand” is a fundamental requirement for power system stability. In the emerging power grids with increasing penetration of distributed renewable energy generation of intermittent nature, the total power generation/supply becomes difficult to predict and control in real-time. This situation will be worse when the penetration of intermittent renewable energy becomes substantial. Under such a situation, the supply side management may be insufficient to tackle this new challenge. An alternative control paradigm called demand following generation (demand-side management) could be an effective supplement to the supply side management. Various demand response methods have been proposed, such as flexible pricing, direct load control, and load scheduling.
Electric spring (ES) has been proposed as a new demand response technology with fast dynamic. The previous research has explored the function of ES in voltage regulation, frequency recovery, power quality improvement, and power imbalance compensation. Most of the previous work focuses on the modeling and control of a single ES circuit. However, the future application scenario of ES may require accurate coordination among distributed ESs. There is a research gap in the control paradigm shift from individual control to group control.
Though droop control is proven to be effective in improving the performance of distributed ESs without communication network, accurate power sharing among ESs is not guaranteed. In the future smart grid, the development of communication technologies makes the information exchange between different power electronics units possible. There are new features that have not been explored by information-free control. Consensus control is a cooperative control method developed for ensuring a global agreement regarding a common quantity of interest through limited information exchange between neighbors. The communication links can be very sparse. Each agent has access to its local measurement and neighbors’ information only. Compared with centralized control, consensus control is robust against single-point failure because no global information is required.
In this thesis, the research line starts with the practical evaluation of the consensus control of distributed ESs. In chapter 2, a consensus control strategy is proposed to coordinate distributed ESs for voltage/frequency regulation and reactive/active power sharing purposes. Successful tests on the hardware platform serve as the basis for the future large scale simulation study. Chapter 3 is a comparison study between consensus control and droop control for ES. Droop control can serve as the last defense when communication network breaks down. Then in chapter 4, we expand the small scale test to a system-level study. An estimated dynamic model of ES is firstly constructed with order-reduce technology. This order-reduced model is suitable for system-level simulation with high accuracy and low computation cost. Based on the dynamic model of ES, a distributed optimized control for ES based domestic heating load is introduced. Every coin has two sides. The extra layer of communication exposes the system to potential cyber-attacks. In chapter 5, a general cyber-attack detection method is built based on the state observer. Case studies of both ES and DC microgrid are discussed in detail.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Partial inductance modeling and series integrated capacitance with optimization for thin and flexible planar transformers in LLC power converters
No full textThis thesis presents two novel devices: a novel integrated multilayer Flexible Printed Circuitry (FPC) transformer and a bendable transformer. Models of these transformers are established to analyze the characteristics of the proposed transformers. Furthermore, a multi-physics design and optimization method is suggested for the proposed transformer in high frequency LLC resonant converter.
The LLC resonant converter is popular but a discrete series resonant inductor and a capacitor in the resonant tank are needed, which increases the component count. In order to eliminate these two components, a novel multilayer FPC (Flexible Printed Circuitry) planar transformer is proposed in this thesis. The proposed transformer successfully integrates the resonant capacitor and the resonant inductor with the transformer such that one can reduce the amount of converter components. In order to study the characteristics of the transformer, a model is established to accurately predict the equivalent series resonant capacitance of the transformer, as verified by the experimental results. A 170 V to 5 V, 4 A output LLC converter prototype with the multilayer FPC planar transformer is built, which achieves 94% efficiency at full load.
In a typical LLC converter, ferrite-based transformers are commonly used but remain inflexible. This restricts applications that need physical flexibility such as wearable electronics. In this thesis, a bendable transformer with air core is presented for such applications. The winding of the bendable transformer is printed on a thin, bendable film, allowing the transformer to be wrapped around body limbs such as forearm. A model is developed to study the characteristics of this transformer based on the partial equivalent circuit theory (PEEC). A converter with 5 V, 500 mA output is included to confirm the usefulness of the transformer and the validity of the model.
An air core planar transformer is an attractive alternative to a typical ferrite core transformer, not only because of its physical flexibility, but also for its zero ferrite loss property while operating at high switching frequency. Although there are many design methods for LLC converters in literatures, most are based on traditional ferrite core transformers. There is a lack of effective methods to design air-core planar transformers for high frequency LLC converter. Therefore, an optimal design strategy that combines different modeling and optimization techniques is proposed for the high frequency air core LLC converter in this thesis. In this method, an accurate transformer model and loss model are built respectively for transformer design and efficiency evaluation. The bisection method and Bayesian optimization algorithm are both applied to accelerate the design process. An air core LLC converter with 2 MHz switching frequency is built to demonstrate the design method. Finally, the experimental results match well with the transformer models and loss model.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Electric spring applications in smart grids : from modeling to control
No full textIn the future smart grids, renewable sources, dominantly photovoltaic (PV) and wind generations, will be largely deployed to reduce the carbon emission and improve the energy availability. Such a dramatic change will bring new technical challenges due to intermittent nature of renewable energy. The traditional control paradigm of generation following demand has been proved to be insufficient in tackling the new challenges. A new control concept of demand following generation must be explored, as the penetration of wind and solar keeps increasing. In such a view of demand-side management, power system researchers and engineers have responded to the new challenge with various demand response methods.
Based on power electronics, electric springs (ES) have been proposed as a fast demand response technology to realize the demand-follow-generation control paradigm. An ES is typically connected with a noncritical load to form a smart load. Such a smart load is capable of adapting its own power consumption to enhance the stability of grid voltage or frequency. With various structures and control methods reported, ES technology has received increasing attention. However, some gaps once neglected in the rapid development of ES require to be addressed immediately. Specifically, a versatile but simple dynamic model of ES is imperative for complex analyses, as the previous ES model only suits for original ES with limited functions. Also, the power flow of ES and the smart load should be closely examined, as the existing works often ignore the energy limitation on the ES when utilizing its real power exchanging ability.
In this thesis, an in-depth investigation is conducted on these issues. Chapter 3 presents a modular ES model incorporating the dynamics of ES, controller design, and noncritical load characteristic. A second-order model of ES is simplified based on theoretical derivation and parametric estimation. The modular approach further allows the controller and the load modules to be designed independently but combined with the ES dynamic model in the d-q frame. Various demonstrations verified the accuracy and usability of the proposed model. In Chapter 4, a smart load with a novel configuration integrating ES and PV systems is proposed. To reduce supply-demand power imbalance, the possibility of adjusting the power consumption of this smart load while delivering maximum PV power is investigated, while battery storage is not a necessity in the proposed system. Validated by simulated comparisons and experimental test, the proposed system can be a solution better than energy storage and other ES-based ones. In Chapter 5, a coordinated battery management system (BMS) is proposed and tested on a Shunt ES. A hybrid battery model is extracted for state-of-charge (SOC) control. Verified both in simulation and experiment, this proposed BMS successfully coordinates the real power for frequency stabilization and SOC control by using variable weights. Such a BMS fills the vacancy of SOC control in existing ES technologies.
It can be concluded from the results in this thesis that the ES is further developed as a demand response technology for the emerging smart grids.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Constructing sustainable power grids : environment-friendly and resilient operation
No full textWith increased pressures and requirements introduced by the environment, economy and society, it becomes vitally important to construct sustainable power grids. While many issues have to be resolved to attain power grid sustainability, this thesis focuses on three critical topics, i.e. integration of renewable energy sources (RESs), emission control, and power grid resilience, so as to develop environment-friendly and resilient operation strategies.
To improve transmission-level RES integration, a robust optimization based methodology is established to accommodate uncertainties of RESs. Robust economic dispatch (ED) and unit commitment (UC) models are proposed, which are solved by algorithms based on Benders decomposition and column-and-constraint generation (C&CG), respectively. The models can generate ED and UC strategies with sufficient operational flexibilities for any scenario considered in uncertainty sets. Inadequate or excessive spinning reserve, which can undermine RESs’ effects in reducing emissions, is avoided. Thus power grid environmental sustainability is also enhanced.
To improve distributed RES integration in distribution systems (DSs), dynamic network reconfiguration is studied. As distribution system dynamic reconfiguration (DSDR) relies on real-time operations of remote-controlled switches (RCSs), this thesis addresses a research gap to identify critical switches that optimally enable DSDR to assist distributed RES integration. Considering the uncertainties of loads and renewable distributed generations (DGs), a robust critical switch identification model solved by the nested C&CG algorithm is constructed. Results show that, by a limited number of switching actions of only several critical switches, DSDR can significantly reduce DG curtailment.
As for emission control, this thesis explores a novel scheme considering air pollutant dispersion. Using the Gaussian plume model, each load center’s ground level air pollutant concentration (GLAPC) resulting from the generations’ emissions is estimated. The GLAPC estimation is added into the proposed robust ED and UC models as a constraint and cost, respectively. A production costing model with GLAPC limits is also formulated to select the coal type of each coal unit and decide purchase quantities of coals and gas, which determine partial operation conditions for ED and UC. Case studies verify this scheme’s effectiveness in air pollution control of power grid operations.
This thesis also investigates the problems of DS automation and mobile generation resource dispatch to enhance power grid resilience. In automating DSs, RCSs are allocated to enable prompt restoration of DSs. RCS allocation models for three different reliability objectives, i.e. minimizing customer interruption cost, minimizing system average interruption duration index, and maximizing the amount of loads that can be restored by the allocated RCSs, are proposed. Illustrative cases show that a small number of RCSs can substantially enhance restoration capacity of DSs. As for mobile generation resource dispatch, mobile emergency generators (MEGs) are concentrated on. A two-stage framework consisting of pre-positioning and real-time allocation is constructed to dispatch MEGs as DGs into DSs to restore critical loads by forming multiple microgrids. A scenario decomposition algorithm is developed to solve the stochastic mixed-integer linear programming pre-positioning problem. Case studies indicate that the proposed dispatch method provides resilient response strategies of MEGs to greatly reduce both outage scale and duration.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Advanced modeling and control of networked DC microgrid
No full textTo meet the requirements of decentralized energy supply and low-carbon concerns, the DC microgrid with high efficiency and low control complexity will be a key tool to provide the flexible power distribution for the energy prospect.
For the model and control of DC microgrid, this work will review the centralized secondary control and distributed secondary control with theoretical derivatives and results. Then, the improved adaptive virtual resistance control and event-triggering mechanism for secondary power and current allocation are proposed.
Many optimization problems in DC microgrids can be solved by using the convex optimization-based methods. The high distribution power loss of DERs is a prominent issue that can deteriorate efficient operations of DC microgrids. The distribution power loss may not only degrade power transfer efficiency but also increase the cooling system costs. After literature review and measurement, it is found that the line loss and converter loss are quadratic functions of the output currents of DERs. Hence, the distribution power loss of the multi-DERs in DC microgrid is proofed as a convex function of the output currents. Given supply-demand balance, the distribution loss model is further modelled as a convex function with equality and in-equality constraints. Then, a hierarchical control is designed for loss minimization: convex optimization strategy in the tertiary layer, an adaptive droop control in the secondary layer, and the local dual-loop control in the primary layer.
Generally, the distributed secondary control can eliminate the inherent drawbacks of the centralized counterparts, such as the high risk of facing single-point failure, high cost on data processing, and periodical updates on entire system models. However, it is also vulnerable to false data injection (FDI) attacks, which are considered to be the most frequent cyber-attacks in DC microgrids. Usually, the hackers are prone to falsify the variables of controllers to bring about incidents, such as bus voltage deviations, imbalanced power allocations, and even instability of the whole system. In practice, it is reasonable to assume that the dynamic response of primary control is much faster than that of higher control layer. By treating DERs as nodes, the DC microgrid can be modelled as a dynamic system. Thereby, the DC microgrid under FDI attack can be further written as a first-order equation with disturbance, which provides the theoretical basis for using observation method to solve the problem of FDI attack. Then, various extended state observers can be applied to estimate and compensate the attack signals. In this work, two observers, the distributed sliding mode observer (DSMO) and the distributed high-order differentiator (DHOD) are proposed with the convergence analysis. The results show that the dynamic response speed of the DHOD is better than that of the DSMO. However, the DHOD requires more computing resources of micro-processor.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Some aspects of magnetic designs in modern power electronics applications
No full textMagnetic design is an important part in modern power electronics. This thesis studies two aspects of magnetic designs: one is the optimal design of integrated magnetics for differential rectifiers and inverters, the other is the slim 3-D receiver coil structures for omnidirectional wireless power transfer applications.
For the first aspect, differential rectifiers/inverters are widely applied in power electronics applications, but they require two bulky low-frequency inductors. In this thesis, a low-frequency integrated inductor structure used for differential rectifiers/inverters is proposed. By eliminating the air gap in the central leg of the magnetic core, while still keeping the air gaps in the two outer legs, the two inductors integrated on the same core are magnetically decoupled, and can work the same as two discrete inductors. Besides, a novel numerical volume optimization method considering all the dimensions of the magnetic core to achieve a minimum core volume is proposed. Theoretical analysis shows that up to 54.0% of core volume reduction might be achieved with the proposed integrated inductor.
In this thesis, an integrated inductor with 34.9% volume reduction is designed and verified in the finite element analysis software Maxwell. Several integrated inductor prototypes with up to 30.9% volume reduction are also fabricated and examined experimentally in a differential rectifier circuit. Their performances including coupling coefficient, circuit efficiency, maximum switching frequency and steady-state temperature show that the optimized integrated inductor can operate normally in the differential rectifier, like two discrete inductors, while the power density of the system is significantly improved.
For the second aspect, omnidirectional wireless power transfer (WPT) becomes a popular technology in power electronics nowadays. In this thesis, two novel slim 3-D receiver coil structures for omnidirectional wireless power transfer applications are proposed. These two 3-D receivers are compatible with conventional 1-D planar transmitter coil, and their “slim” structures can be accommodated in many portable electronic products. Besides, as the two proposed receivers have multiple coils, two circuit topologies of the WPT system with a single-coil transmitter and a multi-coil receiver are proposed. One topology is that the outputs of the receiver coils are connected in parallel. The other is that the outputs are connected in series. Some theoretical analyses are conducted to compare the efficiencies of the two circuits.
In this thesis, the two slim 3-D receivers and a planar 1-D receiver used for reference are designed in the software Maxwell. The two circuit topologies are designed in the software Psim. The receiver prototypes and circuits are also constructed. The simulations and measurements of the coupling coefficients and circuit efficiencies under several positions and angular orientations are carried out. The results show that both two proposed 3-D receivers can achieve omnidirectional wireless power transfer with a 1-D planar transmitter as they have reasonably high coupling coefficients and circuit efficiencies. One particular design under investigation has a better performance as it is less sensitive to angular orientations and planar positioning, and uses less ferrite material. The parallel-outputs circuit topology is better as it has a higher averaged circuit efficiency.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
Single-inductor multiple-output (SIMO) DC-AC resonant inverters for multi-coil wireless power transfer
No full textMulti-coil wireless power transfer (MC-WPT) technology is highly conducive to simultaneous charging of multiple consumer electronic devices such as mobile phones, tablets, wearable devices, and implanted medical devices. Nowadays, one of the most popular inverter topologies used in a typical WPT system is the full-bridge (or half-bridge) inverter. In an MC-WPT system, each of the transmitting coils is powered separately by a dedicated bridge-type inverter. Therefore, the total number of inverters (and also that of power switches) is proportional to the targeted number of output channels, which renders the whole system bulky, costly and inefficient. In view of this, a new series of single-stage, low-cost single-inductor multiple-output (SIMO) resonant inverter is proposed and then thoroughly investigated in this thesis.
This research work begins with a complete review of the existing multiple outputs inverter topologies for practical WPT applications. To address their limitations, a SIMO-based boost DC-AC resonant inverter with cascaded blocking diode operating in the discontinuous conduction mode (DCM) of operation, which generates multiple independent AC outputs at the desired frequency from a single DC input, is proposed. Fundamentally, the proposed SIMO inverter is formulated through the proper integration of a conventional SIMO DC-DC converter and multiple parallel resonant blocks. By adding a resonant inductor in parallel with each output capacitor of the SIMO DC-DC converter, a single-stage, scalable and low-cost SIMO DC-AC resonant inverter can be realized. Also, with DCM operation, each output channel can be operated independently without cross-regulation, which makes precise and independent control feasible. An experimental prototype for a single-inductor three-output (SITO) inverter is built to demonstrate the effectiveness of the proposed circuit topology. It is experimentally verified that this SITO resonant inverter can achieve precise and independent peak voltage control across all three sinusoidal output with no noticeable cross-regulation.
In our subsequent investigations, we discovered that the blocking diode together with the MOSFET in series in the SIMO boost resonant inverter can actually be replaced by a back-to-back connected MOSFETs. This is advantageous because the overall voltage drop on the switches due to the turn-on resistance of the MOSFET, is much smaller than the forward voltage drop of the Schottky diode when operating at low power. This improves the overall efficiency. Since the proposed SIMO inverter is targeted for real MC-WPT applications, it is important to study its power distribution. A practical design approach of the SIMO inverter, which illustrates that this compact and cost-effective SIMO inverter can potentially be turned into a commercial product, is presented.
Wireless power transfer (WPT) is undoubtedly a highly promising technology. However, there exists more than one standard which govern the range of operating frequencies. In view of this, a SIMO-based boost inverter with different output frequencies, which benefits multi-band WPT applications by allowing interoperability of different WPT standards, is investigated. Various switching sequences are proposed to enable different output frequencies across the output channels. Also, due to the recent advances in the semiconductor technology, the hardware prototype of the SIMO boost inverter with multiple frequencies is implemented with the latest GaN transistor. Unlike its silicon counterpart, there is no parasitic body diode inside the GaN transistor. As a result, the cascaded blocking diodes (or back-to-back connected MOSFETs) are no longer needed, provided that an isolated driver is employed to prevent reverse conduction. Thus, a highly-compact and simplified circuit structure can be achieved.
To further increase the power rating of the SIMO-based inverter, a SIMO buck-boost resonant inverter is also proposed. Unlike the originally-proposed SIMO inverter operating in DCM, this inverter operates in pseudo-continuous conduction mode (PCCM). By maintaining a positive DC offset of the main inductor current, the input (or output) power can be increased, hence enabling the SIMO buck-boost inverter to operate in the medium power range of 15 W or above, as stated in the Extended Power Profile (EPP) of the Qi standard. This allows quick and simultaneous charging of a larger number of portable electronic devices.
In the previously-proposed SIMO inverter, no closed-loop control has been adopted and the relationship between the on-time duty ratio of the main switch and the output voltage magnitude is still unknown. In view of this, a new state partition method for the SIMO-based boost resonant inverter is introduced. A closed-form expression of the sinusoidal-like output voltage as a function of the duty ratio of the main switch is also analytically derived. Based upon the theoretical analysis, a closed-loop system is designed which enables the precise and independent regulation of the output voltage. A single-inductor three-output (SITO) inverter prototype with an analog-based controller is constructed for experimental verification. The experiment results show that the output voltage regulation can be achieved with very high accuracy while no cross-interference across the output channels is observed.published_or_final_versionElectrical and Electronic EngineeringDoctoralDoctor of Philosoph
- …
