Jorge Alberto Morales-Saldaña

A design criteria for the current gain in current-programmed regulators

The design of the inner loop for current-programmed regulators is discussed in this paper. The effect that current gain has on the quality factor Q of the LC filter is shown. A methodology is derived to reduce this value that, in most cases, can be very high. A high quality factor can produce drastic changes with undesirable effects on regulator stability. A low quality factor will produce two real poles with a consequent reduction in the current response. After the proper selection of the current gain is done, the design procedure for the proportional integral controller of the outer loop can be continued. The design-oriented analysis is applicable to the three basic switch-mode pulsewidth modulation converters, i.e. buck, boost and buck-boost. At the end, the procedure is applied to a 280 W boost regulator that shows the simplicity of this approach.

Robust stability analysis for current-programmed regulators

Uncertainty models for the three basic switch-mode converters: buck, boost, and buck-boost are given in this paper. The resulting models are represented by linear fractional transformations with structured dynamic uncertainties. Uncertainties are assumed for the load resistance R=R/sub O/(1+/spl delta//sub R/), inductance L=L/sub O/(1+/spl delta//sub L/), and capacitance C=C/sub O/(1+/spl delta//sub C/). The interest in these models is clearly motivated by the need to have models for switch-mode DC-DC converters that are compatible with robust control analysis, which require a model structure consisting of a nominal model and a norm-bounded modeling uncertainty. Therefore, robust stability analysis can be realized using standard /spl mu/-tools. At the end of the paper, an illustrative example is given which shows the simplicity of the procedure.

Uncertainty models for switch-mode DC-DC converters

Uncertainty models for the three basic switch-mode converters, buck, boost, and buck-boost, are given in this paper. The resulting models are represented by linear fractional transformations (LFTs) with structured dynamic uncertainties. Uncertainties are assumed for the load resistance R=R/sub o/(1+/spl delta//sub R/), inductance L=L/sub o/(1+/spl delta//sub L/), and capacitance C=C/sub o/(1+/spl delta//sub C/), The interest in these models is clearly motivated by the need to have models for switch-mode DC-DC converters that are compatible with robust control design, which require a model structure consisting of a nominal model, and a norm-bounded modeling uncertainty. Therefore, a robust controller design under parameter uncertainties can be obtained instead of the deterministic approach widely used.

Modeling and Control of a Cascaded Boost Converter with a Single Switch

In this paper, a controller design methodology is given for a cascaded boost converter with a single switch using current-mode control. Nonlinear and linear models are presented, the later exhibits fourth-order characteristic dynamics with right-half side zeros. The proposed control scheme is based on sensing the current of the switch and using it for feedback purposes. When the current loop is introduced, the fourth-order dynamics of the converter is changed to a dominant first-order, which simplifies substantially the controller design of the outer loop. For this loop, a conventional controller is designed. The design-oriented analytic results allow the designer to easily pinpoint the control circuit parameters that optimize the converters performance. At the end, experimental results are given for a 23 W current-mode regulator

Analysis of Quadratic Step-Down DC-DC Converters Based on Noncascading Structures

In the technical literature has been reported the array of dc-dc basic switching converters to increase power handling capabilities on dc-dc applications. In this paper, switching step-down dc-dc converters based in the principle of reduced redundant power processing (R2P2) are presented. This principle states that the non-cascading connection of dc-dc basic converters increases the efficiency on array of converters, from the theoretical point of view. The resulting converters are formed by a pair of L-C networks and a pair of active switches. Also, they have wide conversion ratios and quadratic dependence with respect to the duty ratio. Voltage conversion ratios and steady-state operating conditions are derived. Simulations and experimental results are given to verify the converter characteristics.

Design methodology for quadratic step-down dc-dc converters based on non-cascading structures

This paper deals about a design methodology of a family of quadratic step - down converters based on the reduced redundant power processing principle (R2P2). Here, it is included the expressions for the selection of passive elements, as well as, the expressions of average and maximum values of voltage and current useful to select properly the semiconductor elements. The aim of this paper is to develop a methodology for R2P2 converters under an operation in Continuous Conduction Mode. Simulations in PSpice verifies the results.

Robust stability analysis for a power system stabilizer

This contribution presents the robust stability tests for a Power System Stabilizer (PSS) of the type PSS1A under two different modeling of uncertainties. The PSS is a supplementary excitation controller used to damp electromechanical oscillations that appear in a synchronous generator. Using an unstructured uncertainty modeling the limits of stability of the PSS1A are found. The proposed tests are explained and validated through simulation.

Dynamical modeling for a fuel-cell based power generation system

Fuel-cell stacks are an attractive and efficiently way for power generation; however, its low and unregulated DC output voltage demands a DC-DC conversion stage to step-up the voltage to suitable levels. In this way, a transformerless boost converter with high step-up conversion ratios is proposed in this work to process the energy from a fuel-cell stack. This configuration is formed by two inductors, two active switches, one diode and one output capacitor. Both inductors are charged (simultaneously) in parallel via the active switches, and discharged in series across the diode. The dynamical behavior of the fuel-cell stack connected to the transformerless boost power converter is captured in terms of Kirchhoff voltage and current laws. As a result, a set of mathematical representations for feedback purposes is detailed. Experimental results are shown for a 250 W laboratory prototype to verify the validity of the proposed models.

Uncertainty modeling of a PSS3B Power System Stabilizer

Power systems are dynamic systems subject to disturbances, which can lead to unstable system operating conditions. For that, the Power System Stabilizer (PSS), which it is a complementary excitation controller, is used for damping electromechanical oscillations present in the power system, ensuring stability. In this paper, a robust stability test is proposed for the PSS3B stabilizer using an unstructured modeling. The limits of stability of the PSS3B stabilizer are found using additive uncertainty for a Single-Input Multiple-Output (SIMO) model. The proposed test is explained and is validated through simulations.

Optimized design of a quadratic boost converter based on the R 2 P 2 principle

In this paper is presented the optimal design of a switching boost converter based on the reduced redundant power processing (R2P2) principle. Using the NSGA-II optimization method is found a set of optimal combinations for the converter parameters (inductors and capacitors), such that the open loop performance of the converter is improved. The constraints associated to current/voltage ripples and zero-pole locations are used to improve the design. Simulation results show that the optimized converter can be easily controlled with only one control loop.