This thesis is organized as follows.
• Chapter 2: This chapter starts with a brief introduction on the backstepping control method and its application to the problem of DC-DC buck converter. The adaptive backstepping con- troller is designed next for DC-DC buck converter fed resistive load and PMDC-motor load. The proposed control method is simulated and verified via experimental validation on a laboratory prototype.
1.7 Organization of the Thesis
• Chapter 3: In this chapter, a Chebyshev neural network (CNN) with adaptive learning is proposed for estimation of the unknown load. A backstepping controller is integrated with the CNN to achieve the desired output tracking in the presence of unanticipated load and input disturbances. The developed control scheme has also been applied to the problem of angular velocity tracking in a DC-DC buck converter fed PMDC motor load and the simulation and experimental results obtained are quite promising. A Hermite neural network (HNN) based backstepping control law to enable a faster estimation of the unknown load is proposed next.
• Chapter 4: In the previous chapters, the load estimation error is bounded or at the most asymptotically stable to the origin. Further, there is no design freedom on the time of esti- mation convergence. Therefore, to increase the degrees of freedom in control design and to exactly estimate the parametric uncertainties within a stipulated time, a finite time disturbance observer based backstepping controller is proposed. A rigorous stability analysis follows the proposed control design. Both simulation and experimental studies are conducted to investigate the efficacy of the proposed control scheme.
• Chapter 5: This chapter proposes a current sensorless adaptive backstepping controller for DC-DC buck converters. A finite time current observer is used in the adaptive backstepping control, wherein the unknown current is treated as a disturbance term in the voltage tracking error dynamics. Such a control scheme alleviates the drawbacks of measurement noise and delay in the control loop inherent in the sensor, which otherwise adversely affect the tracking performance. The proposed controller promises a better output voltage regulation besides being robust to uncertainties. This novel design methodology ia validated experimentally.
• Chapter 6: In this chapter, conclusions from the research work are drawn and the scope for future research is outlined.
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Adaptive Backstepping Control of DC-DC Buck Converters
Contents
2.1 Introduction . . . . 15 2.2 Adaptive Backstepping Control Design . . . . 16 2.3 DC-DC Buck Converter with Resistive Load . . . . 21 2.4 DC-DC Buck Converter Driven PMDC Motor . . . . 33 2.5 Summary . . . . 43
2.1 Introduction
2.1 Introduction
The merits of backstepping control method motivated active research for developing it as an adequate adaptive control strategy [52–56]. However, very few works related to DC-DC buck con- verter [57–63] can be found in the literature in this regard. In 1995, H. Sira-Ramirez et al. first presented the preliminary results on adaptive backstepping control of DC-DC converters [64]. In 2003, H. El Fadil et al. [62] demonstrated on simulation platform, the effectiveness of adaptation in the controller, by framing adaptive laws to estimate unknown converter parameters. In 2007, Li-kui Yi et al. [60] proposed adaptive backstepping in combination with sliding mode control to operate DC-DC buck converters. Their work was examined with numerical results. Nevertheless, the con- troller response with wide range of load uncertainty has not been investigated there. Fan Liping et al. [59] proposed an integrated control algorithm by combining adaptive backstepping and terminal sliding mode control (TSMC), where a fast settlement of initial transients was achieved. However, the influence of the proposed control on the dynamic behavior of the inductor current during start-up and disturbances has not been investigated there. In addition, the efficacy of the suggested method has not been validated through experiments on wide range of converter operating points. In 2011, Salimi M. et al. [57] designed backstepping control by taking into account the effect of parasitic elements and equivalent series resistance of filter inductance along with a precise modeling of power semicon- ductor switches. Multiple adaptive laws were framed here for estimating the varying values of load and filter components of the converter. However, the results exhibited a poor transient performance featuring significant overshoots in the output voltage and inductor current during load disturbances.
This method was evaluated through simulation studies only. Later in 2013, McIntyre M. L. et al. [58]
presented an adaptive backstepping control of DC-DC buck converters in presence of unknown and slowly varying load resistance. In the above design propositions, very few results pertaining to real time implementation have been reported. However, it must be noted that in reality the load change occurs abruptly and hence the assumption of slowly varying load does not always hold good. Besides, the above results mostly exhibit a slow start-up response with substantial overshoot and undershoot during the load disturbance, making the control design unsuitable for practical use.
To the best of author’s knowledge, extensive and rigorous investigations into physical realization of DC-DC buck converter control through adaptive backstepping scheme have not been explored yet.
Therefore, adaptive backstepping control for DC-DC buck converters (i) feeding a resistive load and (ii) driving a PMDC-motor load is investigated through extensive simulation and experimentation.
Further, in this chapter the controller response for the output alongwith all other system states is studied under widely varying operating points.
This chapter is organized as follows. Firstly, the basic control strategy involving the procedure for adaptive backstepping control (ABSC) design is explained. Thereafter, the adaptive backstepping controller design for DC-DC buck converters feeding a resistive load is presented and evaluated the- oretically by conducting simulation studies. A laboratory prototype is constructed for the same and its details are explained, followed by experimentation. This ABSC method is further extended for angular velocity control of a PMDC-motor using the DC-DC buck regulator. Design, analysis and ex- perimental studies regarding the DC-DC buck converter fed PMDC-motor control using the proposed
ABSC method are described.