Coexisting fast-scale and slow-scale instability in current-mode controlled DC/DC converters : analysis, simulation and experimental results

Author name used in this publication: Chi K. Tse2008-2009 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

Study of intermittent bifurcations and chaos in buck-boost converters with input regulators

Author name used in this publication: C. D. XuAuthor name used in this publication: K. W. E. ChengAuthor name used in this publication: X. K. MaAuthor name used in this publication: K. DingRefereed conference paper2006-2007 > Academic research: refereed > Refereed conference paperVersion of RecordPublishe

Nonlinear Analysis and Control of Interleaved Boost Converter Using Real-Time Cycle to Cycle Variable Slope Compensation

Switched-mode power converters are inherently nonlinear and piecewise smooth systems that may exhibit a series of undesirable operations that can greatly reduce the converter's efficiency and lifetime. This paper presents a nonlinear analysis technique to investigate the influence of system parameters on the stability of interleaved boost converters. In this approach, Monodromy matrix that contains all the comprehensive information of converter parameters and control loop can be employed to fully reveal and understand the inherent nonlinear dynamics of interleaved boost converters, including the interaction effect of switching operation. Thereby not only the boundary conditions but also the relationship between stability margin and the parameters given can be intuitively studied by the eigenvalues of this matrix. Furthermore, by employing the knowledge gained from this analysis, a real-Time cycle to cycle variable slope compensation method is proposed to guarantee a satisfactory performance of the converter with an extended range of stable operation. Outcomes show that systems can regain stability by applying the proposed method within a few time periods of switching cycles. The numerical and analytical results validate the theoretical analysis, and experimental results verify the effectiveness of the proposed approach

High-feedback Operation of Power Electronic Converters

electronic

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

Nonlinear dynamics of DC-DC converters

Power electronic converters are time-varying, nonlinear dynamical systems. They exhibit a wide range of steady-state responses. The desired behaviour is a stable periodic motion around a predefined value with a frequency that is equal to that of the external clock. However, as parameters vary the operation can lose stability and go from one regime to another. Such phenomena are termed bifurcations and can degrade the output performance of the converter. Hence, it is of practical importance to know the conditions that cause such bifurcations to occur and to design the system so that it operates in the desired region. In the past, engineers have typically analysed the stability of power electronic systems by linearising the model about a fixed point. This captures the low-frequency properties while ignoring the detailed dynamics occurring at frequencies higher than the external clock. However, the demand for better functionality, reliability and performance means an in-depth analysis into the complex behaviour exhibited by dc-dc converters is required. Traditionally, dc-dc converters are employed with analog controllers whose function is to regulate the circuit. With advances in technology, digital control has become a potentially advantageous alternative to analog control. One of the main advantages of digital control is the ability to design more sophisticated design strategies to enable high performance dc-dc converters e.g. digital state-feedback control. Unfortunately, little work exists in the area of the effect of noise on digital control. This is a field that requires intensive study as to completely understand the nonlinear dynamics so as to enable accurate and economic designs. The aim of this thesis is to address these issues through the application of advanced nonlinear mathematics. The stability of power electronic systems is assessed with a view to developing design guidelines in order to ensure stable operation over a wide operating region

Analysis and control of nonlinear phenomena in electrical drives

PhD ThesisElectrical motors are key to the growth of any modern society. In order to ensure optimal utilisation of the motors, the shaft speed and armature current must be controlled. Currently, the most efficient way of achieving both speed and current control in electrical motors is through power electronic switching, thus making the system both nonlinear and time varying. The combination of electric motors and control electronics is referred to as electric drives. Due to the inherent nonlinear nature of electrical drives, the system is prone to complex dynamical phenomena including bifurcations, chaos, co-existing attractors and fractal basin boundaries. The types of nonlinear phenomena that occur in some of the more common electrical drive systems, namely permanent magnet dc (PMDC) drives, series connected dc (SCDC) drives and switched reluctance motor (SRM) drives, are considered for analysis in this project. The nominal steady state behaviour of these drives is a periodic orbit with a mean value close to the reference value. But as some system parameters are being varied, the nominal orbit of the system referred to as the period-1 orbit, may lose its stability leading to the birth of new attracting orbit that is periodic, quasi-periodic or chaotic in nature. The most common technique for performing stability analysis of a periodic orbit is the Poincaré map approach, which has been successfully applied in DC-DC converters. This method involves reducing the continuous time dynamical system into a discrete time nonlinear iterative map and the periodic orbit into a fixed point. The stability of the periodic orbit then depends on the eigenvalue of the Jacobian matrix of the map evaluated at the fixed point. However, for some power electronic based system the nonlinear map cannot be derived in closed form due to the transcendental nature of the equation involved. In this project, the recently introduced Monodromy matrix approach is employed for the stability analysis of the periodic orbit in electrical drives. This method is based on Filippov’s method of differential inclusion and has been successfully applied in the stability analysis of periodic orbits in both low order and higher order DC-DC converters. This represents the first application of the technique in electrical drives. The Monodromy matrix approach involves computing the State Transition Matrix (STM) of the system around the nominal orbit including the STM at the switching manifold (sometimes referred to as the Saltation matrix). Also, by manipulating some of the parameters in the Saltation matrix, it is possible to control the instabilities and thus extend the system parameter range for nominal period-1 operation. The experimental validation of the nonlinear phenomena in a proportional integral (PI) controlled PMDC drive, which is absent in literature, is presented in this thesis. The system was implemented using dsPIC30F3010 which is a low cost and high performance digital signal controller.Petroleum Technology Development Fund (PTDF) of Nigeri