Nonlinear dynamic modeling and analysis of self-oscillating H-bridge parallel resonant converter under zero current switching control: unveiling coexistence of attractors

This paper deals with the global dynamical analysis of an H-bridge parallel resonant converter under a zero current switching control. Due to the discontinuity of the vector field in this system, sliding dynamics may take place. Here, the sliding set is found to be an escaping region. Different tools are combined for studying the stability of oscillations of the system. The desired crossing limit cycles are computed by solving their initial value problem and their stability analysis is performed using Floquet theory. The resulting monodromy matrix reveals that these cycles are created according to a smooth cyclic-fold bifurcation. Under parameter variation, an unstable symmetric crossing limit cycle undergoes a crossing-sliding bifurcation leading to the creation of a symmetric unstable sliding limit cycle. Finally, this limit cycle undergoes a double homoclinic connection giving rise to two different unstable asymmetric sliding limit cycles. The analysis is performed using a piecewise-smooth dynamical model of a Filippov type. Sliding limit cycles divide the state plane in three basins of attraction, and hence, different steady-state solutions may coexist which may lead the system to start-up problems. Numerical simulations corroborate the theoretical predictions, which have been experimentally validated.Postprint (author's final draft

Studies on the Effect of Load Variations for Three-Phase AC-DC Current Injection Hybrid Resonant Converter

This paper presents an investigation on the effect of load variations for three-phase ac to dc current injection hybrid resonant converter. The performance of the converter was analyses with different values of output load resistor. The effect of load variations on the supply current waveforms, resonant current waveform and the output voltage waveform was observed and investigated. Apart of the waveforms, the performance of the converter was analyzed based on the total harmonics distortion (THD) level of the supply current waveform for both nominal output load operation and during increases the output load resistor. The circuit was simulated in MATLAB/Simulink environment. A 1-kW experimental test-rig was constructed to verify the output load variations studies for the three-phase ac-dc current injection hybrid resonant converter. Selected simulation and experimental results have been provided in the paper to validate the analysis

Stability analysis and control of DC-DC converters using nonlinear methodologies

PhD ThesisSwitched mode DC-DC converters exhibit a variety of complex behaviours in power electronics systems, such as sudden changes in operating region, bifurcation and chaotic operation. These unexpected random-like behaviours lead the converter to function outside of the normal periodic operation, increasing the potential to generate electromagnetic interference degrading conversion efficiency and in the worst-case scenario a loss of control leading to catastrophic failure. The rapidly growing market for switched mode power DC-DC converters demands more functionality at lower cost. In order to achieve this, DC-DC converters must operate reliably at all load conditions including boundary conditions. Over the last decade researchers have focused on these boundary conditions as well as nonlinear phenomena in power switching converters, leading to different theoretical and analytical approaches. However, the most interesting results are based on abstract mathematical forms, which cannot be directly applied to the design of practical systems for industrial applications. In this thesis, an analytic methodology for DC-DC converters is used to fully determine the inherent nonlinear dynamics. System stability can be indicated by the derived Monodromy matrix which includes comprehensive information concerning converter parameters and the control loop. This methodology can be applied in further stability analysis, such as of the influence of parasitic parameters or the effect of constant power load, and can furthermore be extended to interleaved operating converters to study the interaction effect of switching operations. From this analysis, advanced control algorithms are also developed to guarantee the satisfactory performance of the converter, avoiding nonlinear behaviours such as fast- and slowscale bifurcations. The numerical and analytical results validate the theoretical analysis, and experimental results with an interleaved boost converter verify the effectiveness of the proposed approach.Engineering and Physical Sciences Research Council (EPSRC), China Scholarship Council (CSC), and school of Electrical and Electronic Engineerin

Design Aspects of Inductive Power Transfer Systems for Electric Vehicle Charging

During the last decade the transition towards electric propelled vehicles has had an upswing and electric vehicle (EV) sales has increased steadily. This is much due to legislations on lowering emissions but also due to lower total cost of ownership. Eliminating tailpipe emissions is a major driver for the electrification of the transportation sector. In order to meet the goals on CO2 -emissions the shift towards EVs in the transportation sector needs to increase even faster. Two of the holdbacks for a more widespread penetration of EVs are the limited range and the frequent and slow recharging compared with internal combustion engine (ICE) vehicles. With technology advancements in energy storage and power electronics the energy storage and charging of EVs could instead become a strength for EVs.An emerging technology for recharging EVs is by inductive power transfer (IPT). Having no contact between the vehicle and the charger makes it inherently safe with respect to electrical shocks. Furthermore, with no moving parts the maintenance requirement becomes minimal. This technology is especially appealing in automated charging applications and opportunity charging. Charging can be initiated automatically for buses at bus stops, delivery trucks when loading or unloading goods, taxis at taxi ranks and at traffic light intersections. By charging more frequently the life time of the battery is increased. Alternatively, a smaller battery pack can be used. IPT can also be integrated seamlessly in public parking places without obscuring the view and without any risk of getting unplugged.The fundamental principle of IPT is based on power transfer by non-radiative electro-magnetic fields. Challenges with designing IPT systems involve trade-offs between efficiency, misalignment tolerance, gravimetric- and area related power density, and stray fields. In this thesis a thorough analysis of coil design is presented and the most common compensation topologies are evaluated. Two series-series compensated IPT chargers are designed and prototypes are developed and verified experimentally. Firstly, a home charger rated for 3.7 kW input power with an air gap of 210 mm is designed. The coil design is based on analytical results in combination with the finite element method. In this system, the current in the primary coil is constant, regardless of alignment and coupling between coils. At rated load with aligned coils, 94 % dc-to-dc efficiency is achieved. The second charger is a fast charger rated for 50 kW with an air gap of 180 mm. The dc-to-dc efficiency is above 95 %, down to 10 % of the rated load, including losses in the full-bridge inverter, transmitting- and receiving coil with compensation, and the output rectifier.By using SiC MOSFETs a high switching frequency (85 kHz) for power transfer and a more compact coil design can be utilized. The area related power density of the vehicle assemblies of the two chargers are 20 kW/m2 and 148 kW/m2 respectively. A limiting factor for the maximum achievable power transfer capability is the stray fields around and inside the vehicle. A simulation model of the stray field is developed and verified with measurements. With the home charger mounted on a plug-in hybrid electric vehicle (PHEV), measurements show that the magnetic flux density is less than 10 % of the allowed emission limits at the most severe locations

Surface micromachined MEMS variable capacitor with two-cavity for energy harvesting

In this research, a novel MEMS variable capacitor with two capacitive cavities for energy harvesting was developed that use the wasted energy associated with undesirable mechanical vibrations to power microelectronic sensors and actuators widely found in structures and systems surrounding us. The harvested power, though very small, can have a profound effect on the usage of microsensors. First, the self-powered sensors will no longer require regular battery maintenance. Second, the self-powered chip is a liberating technology. On a circuit board, it can simplify the connection. On a commercial jet, the sensors can greatly simplify cabling. The design, fabrication, modeling and complete set of characterization of MEMS variable capacitors with two-cavity are presented in details in this thesis. The MEMS variable capacitors are unique in its two-cavity design and use of electroplated nickel as the main structural material. The device consists of 2x2 mm² movable capacitive proof mass plates with a thickness of 30 [mu]m suspended between two fixed electrodes forming two vertical capacitors. When the capacitance increases for one cavity, it decreases for the other. This allows using both up and down directions to generate energy. The suspended movable plates are supported by four serpentine springs with a thickness of 3-5 [mu]m that are attached to the address lines on a silicon substrate only at the anchors' points which is made of electroplated nickel. The serpentine suspension beams are made with a width, thickness and total length (four serpentine turns) of 15 [mu]m, 5 [mu]m and 1485 [mu]m. Five gold stoppers with height of 2-4 [mu]m were electroplated on the fixed plates to prevent snap-down of the movable plates by overwhelming electrostatic force. SiO2 and Si3N4 thin layers were patterned on the fixed plates to insulate the stoppers and enhance the dielectric property of capacitive cavities. The MEMS variable capacitor with two-cavity has been designed and modeled using MEMS CAD tool and COMSOL Multi-PhysIncludes bibliographical references (pages 108-118)

DC-DC and AC-DC Converters Based on Three-Phase DC-DC Topologies

Power electronics is the field of electrical engineering that uses power semiconductor devices along with passive elements such as inductors, capacitor and transistors to convert electrical power that can be generated by a source to a form that is suitable for user loads. The main focus of this thesis is on the development of new DC-DC and AC-DC topologies that are based on three-phase DC-DC converters. Three-phase DC-DC converters take an input DC voltage, convert it into a high-frequency AC voltage that is then stepped up or down, then rectify and filter this voltage to produce an output DC voltage. They are implemented with a high-frequency three-phase transformer in their topology rather than a single-phase transformer. These converters are very attractive over other topologies that have a single-phase transformer in their topologies for several reasons. First, just one three-phase DC-DC converter can be used instead of using three DC-DC converters in parallel for particular applications; this advantage is especially attractive for higher power applications. In addition, by using three-phase DC-DC converters, the ripple of the source current is significantly reduced and that means less filtering is needed. Moreover, the components of the converter will have less current stress because current is split among three-phases. In this thesis, new DC-DC and AC-DC converters that are based on three-phase DC-DC topology are proposed. The proposed converters use fewer active switches than other previously proposed converters of similar type, thus resulting in lower cost and simpler operation. For each of the proposed converters, its steady-state characteristics are determined by mathematical analysis and procedure for the design of key converter components is developed. The feasibility of each proposed converter has been confirmed with results that have been obtained from experimental prototypes. For one of the proposed converters, a comparison between the operation of one of the proposed converters operating with traditional silicon devices (Si) and that with the converter operating with new silicon-carbide devices (SiC) was made to examine its performance with both types of devices

Vibration, Control and Stability of Dynamical Systems

From Preface: This is the fourteenth time when the conference “Dynamical Systems: Theory and Applications” gathers a numerous group of outstanding scientists and engineers, who deal with widely understood problems of theoretical and applied dynamics. Organization of the conference would not have been possible without a great effort of the staff of the Department of Automation, Biomechanics and Mechatronics. The patronage over the conference has been taken by the Committee of Mechanics of the Polish Academy of Sciences and Ministry of Science and Higher Education of Poland. It is a great pleasure that our invitation has been accepted by recording in the history of our conference number of people, including good colleagues and friends as well as a large group of researchers and scientists, who decided to participate in the conference for the first time. With proud and satisfaction we welcomed over 180 persons from 31 countries all over the world. They decided to share the results of their research and many years experiences in a discipline of dynamical systems by submitting many very interesting papers. This year, the DSTA Conference Proceedings were split into three volumes entitled “Dynamical Systems” with respective subtitles: Vibration, Control and Stability of Dynamical Systems; Mathematical and Numerical Aspects of Dynamical System Analysis and Engineering Dynamics and Life Sciences. Additionally, there will be also published two volumes of Springer Proceedings in Mathematics and Statistics entitled “Dynamical Systems in Theoretical Perspective” and “Dynamical Systems in Applications”

Network Synchronization and Control Based on Inverse Optimality : A Study of Inverter-Based Power Generation

This thesis dwells upon the synthesis of system-theoretical tools to understand and control the behavior of nonlinear networked systems. This work is at the crossroads of three topics: synchronization in coupled high-order oscillators, inverse optimal control and the application of inverter-based power systems. The control and stability of power systems leverages the theoretical results obtained for synchronization in coupled high-order oscillators and inverse optimal control.First, we study the dynamics of coupled high-order nonlinear oscillators. These are characterized by their rotational invariance, meaning that their dynamics remain unchanged following a static shift of their angles. We provide sufficient conditions for local frequency synchronization based on both direct, indirect Lyapunov methods and center manifold theory. Second, we study inverse optimal control problems, embedded in networked settings. In this framework, we depart from a given stabilizing control law, with an associated control Lyapunov function and reverse engineer the cost functional to guarantee the optimality of the controller. In this way, inverse optimal control generates a whole family of optimal controllers corresponding to different cost functions. This provides analytically explicit and numerically feasible solutions in closed-form. This approach circumvents the complexity of solving partial differential equations descending from dynamic programming and Bellman's principle of optimality. We show this to be the case also in the presence of disturbances in the dynamics and the cost. In networks, the controller obtained from inverse optimal control has a topological structure (e.g., it is distributed) and thus feasible for implementation. The tuning is analogous to that of linear quadratic regulators.Third, motivated by the pressing changes witnessed by the electrical grid toward renewable energy generation, we consider power system stability and control as the main application of this thesis. In particular, we apply our theoretical findings to study a network of power electronic inverters. We first propose a controller we term the matching controller, a control strategy that, based on DC voltage measurements, endows the inverters with an oscillatory behavior at a common desired frequency. In closed-loop with the matching control, inverters can be considered as nonlinear oscillators. Our study of the dynamics of nonlinear oscillator network provides feasible physical conditions that ask for damping on DC- and AC-side of each converter, that are sufficient for system-wide frequency synchronization.Furthermore, we showcase the usefulness of inverse optimal control for inverter-based generation at two different settings to synthesize robust angle controllers with respect to common disturbances in the grid and provable stability guarantees. All the controllers proposed in this thesis, provide the electrical grid with important services, namely power support whenever needed, as well as power sharing among all inverters

Wideband vibration energy harvesting using electromagnetic transduction for powering internet of things

The ‘Internet of Things-(IoT)’ envisions a world scattered with physical sensors that collect and transmit data about almost anything and thereby enabling intelligent decision-making for a smart environment. While technological advancements have reduced the power consumption of such devices significantly, the problem of perpetual energy supply beyond the limited capability of batteries is a bottleneck to this vision which is yet to be resolved. This issue has surged the research to investigate the prospect of harvesting the energy out of ambient mechanical vibrations. However, limited applications of conventional resonant devices under most practical environments involving frequency varying inputs, has gushed the research on wideband transducers recently. To facilitate multi-frequency operation at low-frequency regime, design innovations of the Silicon-onInsulator based MEMS suspension systems are performed through multi-modal activation. For continuous bandwidth widening, the benefits of using nonlinear stiffness in the system dynamics are investigated. By topologically varying the spring architectures, dramatically improved operational bandwidth with large power-density is obtained, which is benchmarked using a novel figure-of-merit. However, the fundamental phenomenon of multi-stability limits many nonlinear oscillator based applications including energy harvesting. To address this, an electrical control mechanism is introduced which dramatically improves the energy conversion efficiency over a wide bandwidth in a frequencyamplitude varying environment using only a small energy budget. The underlying effects are independent of the device-scale and the transduction methods, and are explained using a modified Duffing oscillator model. One of the key requirements for fully integrated electromagnetic transducers is the CMOS compatible batch-fabrication of permanent magnets with large energy-product. In the final module of the works, nano-structured CoPtP hard-magnetic material with large coercivity is developed at room-temperature using a current modulated electro-deposition technique. The demagnetization fields of the magnetic structures are minimized through optimized micro-patterns which enable the full integration of high performance electromagnetic energy harvesters

Measurements, Models, Systems and Design

531 s.