Dynamic modeling of pwm and single-switch single-stage power factor correction converters

The concept of averaging has been used extensively in the modeling of power electronic circuits to overcome their inherent time-variant nature. Among various methods, the PWM switch modeling approach is most widely accepted in the study of closed-loop stability and transient response because of its accuracy and simplicity. However, a non-ideal PWM switch model considering conduction losses is not available except for converters operating in continuous conduction mode (CCM) and under small ripple conditions. Modeling of conductor losses under large ripple conditions has not been reported in the open literature, especially when the converter operates in discontinuous conduction mode (DCM). In this dissertation, new models are developed to include conduction losses in the non-ideal PWM switch model under CCM and DCM conditions. The developed model is verified through two converter examples and the effect of conduction losses on the steady state and dynamic responses of the converter is also studied. Another major constraint of the PWM switch modeling approach is that it heavily relies on finding the three-terminal PWM switch. This requirement severely limits its application in modeling single-switch single-stage power factor correction (PFC) converters, where more complex topological structures and switching actions are often encountered. In this work, we developed a new modeling approach which extends the PWM switch concept by identifying the charging and discharging voltages applied to the inductors. The new method can be easily applied to derive large-signal models for a large group of PFC converters and the procedure is elaborated through a specific example. Finally, analytical results regarding harmonic contents and power factors of various PWM converters in PFC applications are also presented here

STUDY OF HIGH FREQUENCY RESONANT GATE DRIVER FOR ZERO VOLTAGE SWITCHED SYNCHRONOUS RECTIFIER BUCK CONVERTER (ZVS-SRBC) CIRCUIT

In this work, a new Synchronous Rectifier Buck Converter (SRBC) circuit is proposed that reduces low switching and conduction losses. Moreover, the Miller effect has also been reduced. The limitations of existing single-channel resonant gate driver (S-CRGD) is studied to determine the optimized parameter values in terms of duty cycle, dead time and resonant inductance. The findings result in designing the new SRBC circuit’s symmetrical dual-channel resonant gate drive (D-CRGD). The aim is to generate low switching and gate drive losses by operating in Zero Voltage Switching (ZVS) and lower on-state drain voltage conditions. It is found that the SRBC can operate effectively at 1 MHz compared to the conventional SRBC in solving the issues of dead time and effect of switching frequency. Experimental results are presented to validate the analysis of the proposed design procedure and to demonstrate the performance of the proposed approach. In addition, several gate drive control schemes such as Fixed Dead Time (FDT), Adaptive Gate Drive (AGD) and Predictive Gate Drive (PGD) have been simulated and the results show that FDT can operate SRBC correctly with shorter dead time and eventually reduce body diode conduction loss. Even though FDT is prone to cross-conduction effect, the design stage is simple. Apart from this, AGD and PGD control schemes have also shown high level of efficiency. However, AGD generates more losses which makes PGD preferable in achieving a highly efficient converter although there are advantages in FDT scheme

Low Voltage Regulator Modules and Single Stage Front-end Converters

Evolution in microprocessor technology poses new challenges for supplying power to these devices. To meet demands for faster and more efficient data processing, modem microprocessors are being designed with lower voltage implementations. More devices will be packed on a single processor chip and the processors will operate at higher frequencies, exceeding 1GHz. New high-performance microprocessors may require from 40 to 80 watts of power for the CPU alone. Load current must be supplied with up to 30A/µs slew rate while keeping the output voltage within tight regulation and response time tolerances. Therefore, special power supplies and Voltage Regulator Modules (VRMs) are needed to provide lower voltage with higher current and fast response. In the part one (chapter 2,3,4) of this dissertation, several low-voltage high-current VRM technologies are proposed for future generation microprocessors and ICs. The developed VRMs with these new technologies have advantages over conventional ones in terms of efficiency, transient response and cost. In most cases, the VRMs draw currents from DC bus for which front-end converters are used as a DC source. As the use of AC/DC frond-end converters continues to increase, more distorted mains current is drawn from the line, resulting in lower power factor and high total harmonic distortion. As a branch of active Power factor correction (PFC) techniques, the single-stage technique receives particular attention because of its low cost implementation. Moreover, with continuously demands for even higher power density, switching mode power supply operating at high-frequency is required because at high switching frequency, the size and weight of circuit components can be remarkably reduced. To boost the switching frequency, the soft-switching technique was introduced to alleviate the switching losses. The part two (chapter 5,6) of the dissertation presents several topologies for this front-end application. The design considerations, simulation results and experimental verification are discussed

Matlab

This book is a collection of 19 excellent works presenting different applications of several MATLAB tools that can be used for educational, scientific and engineering purposes. Chapters include tips and tricks for programming and developing Graphical User Interfaces (GUIs), power system analysis, control systems design, system modelling and simulations, parallel processing, optimization, signal and image processing, finite different solutions, geosciences and portfolio insurance. Thus, readers from a range of professional fields will benefit from its content

Application of Fuzzy Logic for Performance Enhancement of Drives

Fuzzy logic shows enormous potential for advancing power electronics technology. Its application to DC and AC drives control is discussed here. Initially, a phase-controlled bridge converter DC drive was considered. Analysis of converter performance at continuous and discontinuous conduction modes was first conducted. Fuzzy control was used to linearize the transfer characteristics of the converter in discontinuous conduction mode. It was then extended to current and speed loops, replacing the conventional proportional-integral controllers. The control algorithms were developed in detail, and verified by PC-SIMNON (developed by Lund Institute of Technology Sweden) digital simulation. Significant performance improvement was achieved over conventional control methods. Efficiency optimization of an indirect vector controlled induction motor drive was next considered. An accurate loss model of the converter induction machine system was first developed. Steady-state fundamental and harmonics loss characteristics, besides the dynamic of the machine were analyzed and incorporated in the model, resulting in a new synchronous frame dynamic De-Qe equivalent circuit. The converter system has been modeled accurately for conduction and switching losses. The lossy models were then used in the validation of the fuzzy logic based on-line efficiency optimization control. At steady-state, the fuzzy controller adaptively changes the excitation current on the basis of measured input power, until the maximum efficiency point is reached. The pulsating torque, due to flux reduction, has been compensated by an ingenious feedforward scheme. During transients, rated flux is established, to get the best transient response. After a comprehensive simulation study, an experimental 5 hp drive system was tested, with the proposed controller implemented on a Texas Instrument TMS320C25 digital signal processor, and the theoretical development was fully validated. Finally, fuzzy logic was applied in combination with model-reference adaptive control (MRAC) technique to slip gain tuning of an indirect vector controlled induction motor drive. The MRAC methods based on reactive power and D-axis voltage were combined through a weighting factor, generated by a fuzzy controller, that ensures the use of the best method for any point in the torque-speed plane. A second fuzzy controller tunes the slip gain based on combined detuning error and its slope. The drive performance was extensively investigated through simulations and experiments. The results confirmed the validity of the proposed method

Energy harvesting system design and optimization for wireless sensor networks

Wireless sensor networks (WSN) are becoming widely adopted for many applications including complicated tasks like building energy management. However, one major concern for WSN technologies is the short lifetime and high maintenance cost due to the limited battery energy. One of the solutions is to scavenge ambient energy, which is then rectified to power the WSN. The objective of this thesis was to investigate the feasibility of an ultra-low energy consumption power management system suitable for harvesting sub-mW photovoltaic and thermoelectric energy to power WSNs. To achieve this goal, energy harvesting system architectures have been analyzed. Detailed analysis of energy storage units (ESU) have led to an innovative ESU solution for the target applications. Battery-less, long-lifetime ESU and its associated power management circuitry, including fast-charge circuit, self-start circuit, output voltage regulation circuit and hybrid ESU, using a combination of super-capacitor and thin film battery, were developed to achieve continuous operation of energy harvester. Low start-up voltage DC/DC converters have been developed for 1mW level thermoelectric energy harvesting. The novel method of altering thermoelectric generator (TEG) configuration in order to match impedance has been verified in this work. Novel maximum power point tracking (MPPT) circuits, exploring the fractional open circuit voltage method, were particularly developed to suit the sub-1mW photovoltaic energy harvesting applications. The MPPT energy model has been developed and verified against both SPICE simulation and implemented prototypes. Both indoor light and thermoelectric energy harvesting methods proposed in this thesis have been implemented into prototype devices. The improved indoor light energy harvester prototype demonstrates 81% MPPT conversion efficiency with 0.5mW input power. This important improvement makes light energy harvesting from small energy sources (i.e. credit card size solar panel in 500lux indoor lighting conditions) a feasible approach. The 50mm × 54mm thermoelectric energy harvester prototype generates 0.95mW when placed on a 60oC heat source with 28% conversion efficiency. Both prototypes can be used to continuously power WSN for building energy management applications in typical office building environment. In addition to the hardware development, a comprehensive system energy model has been developed. This system energy model not only can be used to predict the available and consumed energy based on real-world ambient conditions, but also can be employed to optimize the system design and configuration. This energy model has been verified by indoor photovoltaic energy harvesting system prototypes in long-term deployed experiments

An improved maximum power point tracking for PV system

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University London.Working very far from maximum power point diminishes the created power from photovoltaic (PV) system. It is therefore vital, in order to ensure ideal operating conditions, to constantly track the Maximum Power Point (MPP) of the PV panel array. However, this is not easy to identify, due to considerable changes in external influences and the nonlinear relationship of the electrical attributes of PV panels. Therefore, Maximum Power Point Tracking (MPPT) methods can be used to uphold the PV panel operating at its MPP. To date, a number of MPPT methods have been developed, ranging from the simple to the more complex, depending on the weather conditions and the control strategies employed. This current study offers a novel approach to augment the MPPT method for the PV system, based on the Lagrange Interpolation (LI) formula and the Particle Swarm Optimisation (PSO) method. The LI method is used initially to determine the optimum value of the duty cycle in the case of the MPP, according to the operating point. Starting from that point, the PSO method can then be used to search for the true Global Peak (GP). The proposed MPPT controller essentially initialises the particles surrounding the MPP, thereby providing the initial swarm with information concerning the most effective position. This has the ability to improve PSO efficiency and lead to a more rapid convergence, with zero steady-state oscillations. Additionally, there is no need to restrict particle velocity, as the initial values are closer to MPP. Thus, the proposed technique aims to increase efficiency without adding additional complexity, thereby substantially enhancing potential tracking speeds, while also reducing the steady-state oscillation (i.e. to practically zero) once the MPP is located. This offers a number of significant improvements over the conventional PSO method, in which new operating points are at too great a distance from MPP, and thus require additional iterations. The algorithm put forward in this work is verified with an OPAL-RT real time simulator and Matlab Simulink tool. A number of simulations are undertaken and compared to: (1) the Perturb and Observe (P&O) method; (2) the Incremental Conductance (IncCond) method; and (3) the PSO based algorithm. The simulation results indicate that the proposed algorithm can effectively enhance stability and fast tracking capability under fast-changing non-uniform insolation conditions