Marcos Pascual

Robust average current-mode control of multimodule parallel DC-DC PWM converter systems with improved dynamic response

This paper presents a novel average current-mode control (ACC) strategy for the control of multimodule parallel pulsewidth modulation DC-DC converters, which represents a drastic improvement over conventional ACC. This new method consists of the addition of an auxiliary controller into the control loop, besides the current and voltage regulators. The reference-model-based auxiliary controller improves the robustness of the ACC dynamics in buck-derived distributed power systems, preserving loop gain crossover frequency and stability margins over significant changes of the number of connected modules, the load and the line voltage. Moreover, this control scheme shows much better disturbance rejection properties, i.e., closed-loop output impedance and audiosusceptibility, than conventional ACC. From a control theory point of view robust performance is achieved, preserving stability. A multimodule buck prototype has been experimentally tested with different numbers of modules on stream, line, and load conditions, including discontinuous conduction mode. Measurements of the small-signal frequency response of the converter have been carried out, showing the improvement achieved by the proposed control scheme. The empirical large-signal response of the converter under load steps is also shown in order to validate the concept.

Robust control of power-factor-correction rectifiers with fast dynamic response

This paper proposes a new robust control technique for single-phase boost high-power-factor rectifiers. The proposed circuit significantly improves the dynamic response of the converter to load steps without the need of a high crossover frequency of the voltage loop, so that a low distortion of the input current is easily achieved. A 250-W power-factor-correction rectifier with the proposed control scheme has been designed and implemented, validating the concept both analytically and experimentally.

Measurement of the Loop Gain Frequency Response of Digitally Controlled Power Converters

The study of the loop gain frequency response in a power converter is a powerful tool commonly used for the design of the controllers used in the control stage. As the control of medium- and high-power electronic converters is usually performed digitally, it is useful to find a method to measure the digital loop gains. The purpose of this paper is to present a method for properly measuring the loop gain frequency response of digitally controlled power converters by means of an analog frequency response analyzer (FRA). An analog sinusoidal reference signal generated by the FRA is injected through an analog-to-digital converter into the digital controller, and added to the discrete feedback signal. To obtain the frequency response of the open-loop gain, both feedback and disturbed feedback signals are sent back to the FRA by using the pulsewidth modulation peripherals of the controller.

A new current controller applied to four-branch inverter shunt active filters with UPF control method

The purpose of this paper is to present a new current controller applied to a four-branch inverter shunt active filter in unbalanced and nonsinusoidal conditions. It is based on a space vector generalization using Scotts transformation that is able to decrease the relationship between do and ac voltage. For controlling the active filter the UPF control method based on the time domain analysis is used.

Robust average current mode control of DC-DC PWM converters based on a three controller scheme

The purpose of this paper is to present a drastic improvement in the conventional ACC (average current mode control) of switching DC-DC power converters, consisting of the addition of an auxiliary controller in the control loop, besides the current and voltage regulators. The model-based auxiliary controller preserves the closed loop small-signal bandwidth (including loop gain crossover frequency and stability margins) of buck derived converters over a large range of variation of the power stage passive elements, the load and the line voltage. Moreover, this control scheme shows much better perturbation rejection properties (closed loop impedance and audiosusceptibility) than conventional ACC. From a control theory point of view, robust performance is achieved preserving stability. A 5 V-5 A, 50 kHz buck prototype operating from an input voltage ranging from 30 V to 15 V has been experimentally tested with different LC output filters, line and load conditions, including discontinuous conduction mode. Measurements of the small signal frequency response of the converter (loop gain, closed loop audiosusceptibility and output impedance) have been carried out, showing the improvement achieved by the proposed control scheme. The empirical large signal response of the converter, under load steps, is also shown in this paper in order to validate the concept.

Design and evaluation of a power factor correction rectifier with robust control and fast dynamic response

This work presents a new robust control technique for boost based high power factor rectifiers. The proposed control scheme improves significantly the dynamic response of the converter without the need of high crossover frequencies in the voltage loop. Therefore, the harmonic distortion components of the input current are easily reduced. Experimental measurements on a 250 W low harmonic rectifier have been carried out to validate the concept.

Comparative analysis of ACC control loops of DC-DC converters by means of robust parametric control theory

Robust parametric control theory is a powerful tool for the research of linear control systems robustness against simultaneous changes in the parameters that define the plant and controller transfer functions. The purpose of this paper is to show how those techniques can be applied to the comparative performance study of conventional average current mode control (ACC) of DC-DC converters and an advanced three-controller robust ACC loop developed by the authors. In the analysis carried out in this work the sensitivity of both ACC loops with respect to simultaneous variations (or tolerances) of all the parameters defining the power stage is studied: line voltage, load and passive elements of the power stage (L, C, Rc etc.). theoretical Bode and Nyquist envelopes of both ACC control loops have been easily obtained by means of MATLAB/sup TM/ software.