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

Development of a Strategy for the Management and Control of Multiple Energy Sources within Series Hybrid Electric Vehicles

The battery in an EV is designed according to a power to energy ratio and is a trade-off in the design of the pack. It also suffers from effects such as rate capacity effect, ripple effects and inefficiency under charging. These effects result in losses through which the capacity and life span of the batteries are compromised affecting range and drivability. In this thesis a novel development path resulting in a novel Power and Energy Management Strategy (PEMS) is presented. The effects of (dis)charging a battery are researched and converted to an energy optimisation formula and result in reduced power demand for the converter which reduces weight. The resulting Power Management Strategy (PMS) aims to recover energy more efficiently into UC while responding fast to a change in demand. The effects of converters on the battery current ripple are researched and discussed, resulting in an optimal topology layout, improved battery life and reduced losses. Through the use of Markov Chain analysis and a newly derived Bias function a predictive Energy Management Strategy (EMS) is developed which is practical to use in EVs. This resulted in a PEMS which because of the fast PMS results in a fast response time. The use of Markov Chain results in predictive EMS and improves the efficiency of the energy sources and allows the design to be reduced in size. Through the design methodology used the parallel topology (the battery converter parallel to the UC Module) was rated preferred choice over battery only and battery with UC Module. The rating was based on capacity, ripple control, weight, 10 year cost, potential for motor controller efficiency improvement, range and efficiency. v The combination of method and PEMS resulted in an improved life expectancy of the pack to over 10 year (up from 7) while increasing range and without sacrificing drivability

Foldings and grazings of tori in current controlled interleaved boost converters

Δημοσιεύσεις μελών--ΣΤΕΦ--Τμήμα Αυτοματισμού, 2014Interleaved boost converters (IBCs) are used when energy conversion is required at high current levels. Such converter systems may undergo various nonlinear phenomena which can affect their performance adversely. In this paper, we study an IBC and demonstrate the first instability through a Neimark–Sacker bifurcation, resulting in a torus. An analysis based on the calculation of the monodromy matrix reveals that the torus has a rather strange form as the complex Floquet multipliers that became unstable have a real value close to 1. We show that further variation in a parameter can result in novel nonlinear phenomena where the torus itself folds and grazes a switching manifold, resulting in a ‘wobbling’ of the closed loop that represents the torus in discrete time. Numerical and analytical results validate our work. Copyright © 2013 John Wiley & Sons, Ltd