Amit Patra

Swing-up and stabilization of a cart-pendulum system under restricted cart track length

This paper describes the swing-up and stabilization of a cart–pendulum system with a restricted cart track length and restricted control force using generalized energy control methods. Starting from a pendant position, the pendulum is swung up to the upright unstable equilibrium con5guration using energy control principles. An “energy well” is built within the cart track to prevent the cart from going outside the limited length. When su9cient energy is acquired by the pendulum, it goes into a “cruise” mode when the acquired energy is maintained. Finally, when the pendulum is close to the upright con5guration, a stabilizing controller is activated around a linear zone about the upright con5guration. The proposed scheme has worked well both in simulation and a practical setup and the conditions for stability have been derived using the multiple Lyapunov functions approach. c

New class of discrete-time models for continuous-time systems

Digital computing in estimation, control or signal processing for continuous-time systems requires the use of discrete-time models. While conventional difference equation or z-transfer function models are widely popular, a class of methods exists that uses discrete approximations of continuous signals and operators, retaining the continuous-time parameters. Some important advantages of this class have been demonstrated in the contexts of parameter estimation, adaptive control and controller design. This paper proposes a new class of discrete-time models that originates from the z transfer function but which is close to continuous-time models in structure and parameters, thereby retaining its advantageous features. The recently proposed ‘delta’ model is seen to be a member of this class. The interrelations among various digital model types are brought out. Better sensitivity properties over z transfer function models are established. Finite word length properties of these models vis-a-vis the z-transfer fu...

A Single-Inductor Multiple-Output Switcher With Simultaneous Buck, Boost, and Inverted Outputs

Portable applications require multiple supplies with different output levels and some applications also require negative outputs. Single-inductor multiple-output (SIMO) switchers are a good for existing parallel output configurations. This study presents an SIMO dc-dc converter capable of generating buck, boost, and inverted outputs simultaneously. The operation of this class of converter being driven by the ripple in the inductor current the conventional averaging method does not work well. An inductor current ripple-based modeling approach has been proposed to accurately model and analyze the converter. The control, cross-coupling, and cross-regulation transfer functions, generated through the model, accurately represent the performance of the converter. The proof of concept has been carried out with discrete components on an in-house built PCB and the experimental results validating the steady state and ac responses of the converter are presented.

ANN- and PSO-Based Synthesis of On-Chip Spiral Inductors for RF ICs

This paper presents an efficient layout-level synthesis approach for RF planar on-chip spiral inductors. A spiral inductor is modeled using artificial neural networks in which the layout design parameters, namely, spiral outer diameter, number of turns, width of metal traces, and metal spacing, are taken as input. Inductance, quality factor (Q), and self-resonance frequency (SRF) form the output of the neural model. Particle-swarm optimization is used to explore the layout space to achieve a given target inductance meeting the SRF and other constraints. Our synthesis approach provides multiple sets of layout parameters that help a designer in the tradeoff analysis between conflicting objectives, such as area, Q, and SRF for a target-inductance value. We present several synthesis results which show good accuracy with respect to full-wave electromagnetic (EM) simulations. Since the proposed procedure does not require an EM simulation in the synthesis loop, it substantially reduces the cycle time in RF-circuit design optimization.

A Current-Controlled Tristate Boost Converter With Improved Performance Through RHP Zero Elimination

A novel current mode control scheme for the tristate boost converter circuit is proposed, which eliminates the zero in the right-half plane (RHP), and improves the dynamic performance. The tristate boost converter contains an additional switch across the inductor. Within a clock cycle, the inductor current first rises during the on interval of the main switch, then falls during the off or capacitor charging interval, and finally, remains almost constant during the freewheeling interval when the additional switch is turned on. In the proposed controller, the peak value of the inductor current is controlled by peak current mode control using an outer voltage feedback loop, whereas the freewheeling current is controlled by the input voltage and the reference voltage feedforward path. Applying both feedback as well as feedforward control on the inductor current significantly improves the output voltage regulation, audio susceptibility, and transient responses. We show that the RHP zero is completely eliminated from the closed-loop control-to-output transfer function. This results in a very large bandwidth, and hence a superior dynamic performance. The latter is established by comparison with the voltage-mode- and current-mode-controlled classical boost converters that suffer from the RHP zero problem, as well as with other tristate boost converter control techniques like the constant charging interval and dual mode control, recently proposed in the literature. Significant superiority of the proposed scheme is established both through simulation and experimentation.

Identification of a class of nonlinear continuous-time systems using Hartley modulating functions

Most of the existing approaches to identification of nonlinear dynamic systems involve matching a given input-output behaviour with empirical discrete-time approximations such as artificial neural networks, Kolmogorov-Gabor polynomials, radial basis function networks, etc. Techniques for dealing with physically-based continuous-time models are either applicable to only a restricted class of systems or are computationally very demanding. In this paper a new methodology is presented that is applicable to a large class of nonlinear continuous-time systems, by defining a set of Hartley modulating functions for characterizing the continuous process signals. The advantages of this new class of modulating functions are that a set of algebraic equations with real coefficients results, the formulations are free from boundary conditions, and the computations can be made using fast algorithms for the discrete Hartley transformation. The resulting estimation scheme is applied to different categories of nonlinear syst...

Hybrid mode-switched control of DC-DC boost converter circuits

This paper has proposed a new switching scheme for controlling dc-dc boost converter circuits. The converter is represented as a hybrid system with three modes of operation. The switching among these modes is governed by the adjustable reference voltage and a reference current which are calculated by an energy balance principle. The scheme has been applied to a realistic converter circuit modeled with various parasitic components. All the specifications related to the ripple voltage, line and load regulation are shown to be achievable by relating them to the switching surfaces, namely a reference voltage and a reference current. The state trajectories have been shown to reach a hybrid limit cycle already proved to be super-stable from consideration of chaos. Numerical results clearly bring out the advantages of the proposed control scheme.

Discontinuous Map Analysis of a DC-DC Converter Governed by Pulse Skipping Modulation

This paper reports the bifurcation phenomena in a dc-dc converter governed by a pulse skipping modulation (PSM) scheme, which is normally used to improve efficiency under light load condition. It is shown that the discrete-time model of the system takes the form of a discontinuous map, where the discrete-time state space is piecewise smooth, divided into five regions, each with a different functional form and separated by four borderlines. One additional borderline is considered to identify an infeasible region during a PSM operation. For a restricted operating region, we show that the system is described by a one-dimensional discontinuous map; otherwise it is a combination 1-D and 2-D forms. We derive the conditions for the existence and stability of different periodic orbits. We observe a period-adding cascade in which the periodicity varies non-monotonically exhibiting abrupt changes in the spectral composition for a smooth parameter variation. The proposed method may be useful for modeling and analysis of other dc-dc converter topologies governed by a PSM operation.

Steady state and dynamic simulation of multi-stage flash desalination plants: A case study

A mathematical model and its solution procedure are developed to simulate the steady-state and dynamic behaviour of multistage flash desalination plants. The steady-state and dynamic models are based on the same set of equations and are of the same order. The solution procedure developed is numerically stable and easy to implement. The steady state model is used to predict the operating parameters of a particular plant. A close agreement between the predicted values and the measured data from the actual plant has been observed. The transient response of the plant for step changes in input variables has been obtained. The computed response of the plant is comparable to the operating records of a real plant.

Control Scheme for Reduced Cross-Regulation in Single-Inductor Multiple-Output DC–DC Converters

Single-inductor multiple-output (SIMO) dc-dc switching regulators are potentially very good replacement to multiple parallel converters in todays power management units for portable applications where multiple supplies are required. The outputs in these converters being coupled, cross-regulation among the outputs plays a major role in deciding the performance of the system. This paper proposes a control scheme that ensures good load and line regulation and stable system dynamics and reduces cross-regulation effect significantly. In designing a control scheme, proper analysis of the system is an important factor, and SIMO class of converters being driven by a ripple in the inductor current, conventional modeling does not hold good. Consequently, a ripple-based modeling approach that accurately judges the system performance is adopted. A cross-derivative state feedback control methodology has been proposed so as to completely decouple the outputs. Finally, a single-inductor dual-output SIMO converter has been built on a printed circuit board using discrete components, and the test results presented validate the modeling technique proposed. The simulation and experimental results show that the proposed control scheme significantly reduces cross-regulation at the outputs.