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High conversion ratio switching converters are used whenever there is a need to step-up dc source voltage level to a much higher output dc voltage level such as in photovoltaic systems, telecommunications and in some medical applications. A simple solution for achieving this high conversion ratio is by cascading different stages of dc-dc boost converters. The individual converters in such a cascaded system are usually designed separately applying classical design criteria. However these criteria may not be applicable for the complete cascaded system . This paper first presents a glimpse on the bifurcation behavior that a cascade connection of two boost converters can exhibit. It is shown that the desired periodic orbit can undergo period doubling leading to subharmonic oscillations and chaotic regimes. Then, in order to simplify the analysis the second stage is considered as constant current sink and design-oriented analysis is carried out to obtain stability boundaries in the parameter space by taking into account slope interactions between the state variables in the two-different stages.

Summary: This paper presents a unified and exact nonaveraged approach to derive a frequency‐domain control‐oriented model for accurate prediction of the fast timescale dynamics and performances of switching converters with fixed frequency naturally sampled pulse width modulation and integrating feedback loop. Because the approach avoids averaging and approximations related to this process, a very good accuracy of the derived model is obtained. The main difference between the presented approach and the existing methodology for accurately predicting the behavior of switching converters is that, here, we break the feedback loop and we focus on analyzing the open‐loop gain and the effect of the system parameters on relative stability. This results in an approach much similar to control systems techniques rather than nonlinear dynamical system approaches. Consequently, the relative stability is tackled easily in the frequency domain. In particular, by treating the modulator as a gain depending on the operating point, the new model is formulated in such a way that standard control‐oriented tools such as Bode diagrams and root‐loci can be easily used. Therefore, the proposed approach gives some important issues like gain and phase margins that are highly useful in controller design. It is noticed that the crossover frequency, gain, and phase margins predicted by using the averaged model may deviate significantly from the actual values given by the proposed approach. The paper points out the sources of discrepancies and the theoretical results are validated by simulations using a circuit‐level switched model. [ABSTRACT FROM AUTHOR]

This paper proposes a new methodology for designing robust affine state-feedback control laws, so that wide-range safe and efficient operation of switched-mode DC–DC boost converters is guaranteed. Several undesirable nonlinear phenomena such as unstable attractors and subharmonic oscillations are avoided through bifurcation analysis based on the bilinear averaged model of the converter. The control design procedure also relies on constrained stabilization principles and the generation of safety domains using piecewise linear Lyapunov functions, so that robustness to supply voltage and output load variations is ensured, while input saturation is avoided and additional state constraints are also respected. The technique has been numerically and experimentally validated. [ABSTRACT FROM AUTHOR]

A new self‐compensation technique is proposed for eliminating subharmonic oscillation and chaotic regimes in dc–dc switching converters under peak current mode control. The proposed method extracts a control signal from the error between the inductor current and a suitable reference and does not require an external signal generator as in the conventional ramp compensation scheme. The analytical expressions of the control domain using Filippov method are obtained. Simulation results show that the proposed technique can be implemented using standard analogue devices and can effectively eliminate subharmonic and chaotic oscillations and can ensure a stable operation for a wide range of the duty ratio. [ABSTRACT FROM AUTHOR]

Abstract: The design of the speed controller greatly affects the performance of an electric drive. A common strategy to control an induction machine is to use direct torque control combined with a PI speed controller. These schemes require proper and continuous tuning and therefore adaptive controllers are proposed to replace conventional PI controllers to improve the drive''s performance. This paper presents a comparison between four different speed controller design strategies based on artificial intelligence techniques; two are based on tuning of conventional PI controllers, the third makes use of a fuzzy logic controller and the last is based on hybrid fuzzy sliding mode control theory. To provide a numerical comparison between different controllers, a performance index based on speed error is assigned. All methods are applied to the direct torque control scheme and each control strategy has been tested for its robustness and disturbance rejection ability. [Copyright &y& Elsevier]

Abstract: One common problem in drives applications is the presence of noise that corrupts the useful information in measurements such as of current, due to sensor imperfections. Digital low pass filters are a solution to the problem but they cannot cope when the useful information has time varying high frequency characteristics. In this paper, wavelet analysis, seldom used as yet in electric drives, is analysed and compared to classical methods. The key points of wavelet analysis are presented in a way that is appropriate for drives. Application of this new method to a typical practical current signal demonstrates the advantages and limitations of these methods over more conventional techniques. The true power of the wavelet transform is revealed when it is applied to a speed estimation problem where the rotor speed of a permanent magnet machine is modulated and coupled with high frequency components. [Copyright &y& Elsevier]

High frequency signal injection is considered a parameter independent sensorless speed and position estimation technique which operates efficiently at low and zero speed. That is due to the saliency presence in the machine, which gives information about the rotor speed and position. Therefore the high frequency signal injected into the motor is modulated by the rotor speed and position information. Conventionally, to extract the useful information from the spectrum of the resultant signal, Phase-Locked Loop structure based demodulation schemes have been used. However, the PLL dynamics can be affected by the variation of inductances, PI parameters, and filter characteristics. In addition the error between the actual and estimated angle has to be small at the beginning of the estimation process. These restrictions are essential to maintain stability and to track the rotor speed and position accurately. However, such conditions are not always satisfied and are dependent on the operating conditions of the machine. Recently the concept of instantaneous frequency has become useful in many engineering applications where it is used to describe time varying signals. In this paper an instantaneous frequency estimation scheme based on the short time Fourier Transform ridges algorithm is proposed to detect the rotor speed and position. Theoretical and simulation aspects of the conventional and proposed methods are discussed and the obtained results are compared. [ABSTRACT FROM AUTHOR]