Alessandro Costabeber

Parameter-Independent Time-Optimal Digital Control for Point-of-Load Converters

In this paper, a digital control approach is investigated for time-optimal load step response of DC-DC synchronous buck converters intended for point-of-load (PoL) applications and employing low-equivalent series resistance ceramic output capacitors. Unlike previously reported approaches, the proposed technique is insensitive to converter parametric variations and design uncertainties, as its operation does not rely on the knowledge of the output filter inductance or capacitance. The time-optimal response is achieved through a single on/off switching action undertaken as soon as a load transient is detected. In its most general formulation, the proposed technique automatically incorporates adaptive voltage positioning (AVP) regulation, according to the typical droop design guidelines for powering modern microprocessors. A simpler version, suitable for voltage-mode controlled PoL converters not requiring AVP positioning, is also presented. The technique employs an asynchronous A/D conversion scheme, which quantizes the converter state variables and triggers a nonlinear, event-based digital controller whenever a quantization level transition is detected. Additional sensing requirements are not needed, since the time-optimal transient is achieved through the measurement of the output voltage and, whenever AVP regulation is needed, of the phase currents. Effectiveness and properties of the proposed robust time-optimal approach are validated through both computer simulations and experimental tests on a synchronous buck converter prototype and a VHDL implementation of the control algorithm on an field programmable gate array device.

Time optimal, parameters-insensitive digital controller for DC-DC buck converters

In this paper a digital control approach is investigated for time-optimal load step response of DC-DC synchronous buck converters intended for point-of-load applications employing low-ESR ceramic output capacitors. Unlike previously reported approaches, the proposed technique is insensitive to the power stage parameters, as its operation does not rely on the knowledge of the output filter inductance or capacitance. The time-optimal response is achieved through a single on/off switching action undertaken as soon as a load transient is detected. An asynchronous A/D converter has been employed, realized in a standard 0.35 mum CMOS process. The A/D converter quantizes the output voltage and triggers a nonlinear, event-based digital controller whenever a quantization level transition is detected. Time-optimal response is based solely on output voltage measurements and on the knowledge of the steady-state duty cycle, a number easily available within the digital controller. Effectiveness and properties of the proposed robust time-optimal approach are validated through both computer simulations and experimental tests on a synchronous buck converter prototype and a VHDL implementation of the control algorithm on an FPGA device.

High Step-Up Ratio Flyback Converter With Active Clamp and Voltage Multiplier

In this paper, an isolated high step-up ratio dc-dc converter aimed to be used in interface systems between low-voltage renewable energy sources, such as photovoltaic panels and fuel cells and the utility grid, is presented. The converter is based on the active clamp flyback topology with a voltage multiplier at the transformer secondary side. Such configuration, while naturally clamping the rectifier diode voltages thus avoiding the use of dissipative snubber circuits, allows the reduction of the circulating current during the active clamp operation due to the resonance involving the transformer leakage inductances and the diode parasitic capacitances. Experimental results taken from a 300-W-rated prototype are reported, showing the absence of parasitic oscillations after diodes and switch transitions and high efficiency, in agreement with the theoretical expectations.

Distribution Loss Minimization by Token Ring Control of Power Electronic Interfaces in Residential Microgrids

Smart microgrids offer a new application domain for power electronics. In fact, every distributed energy resource includes an electronic power processor (EPP) to control the power exchange with the grid. If such distributed EPPs perform cooperatively, all the available energy sources and energy storage units can be fully exploited, resulting in reduced power consumption from the utility, high power quality, and increased hosting capability by the utility. This paper shows that, even in low-voltage meshed microgrids, where the electrical distribution pattern is complex and sources and loads may vary during daytime, such cooperative operation can be achieved by a proper selection of the local control algorithms and by allowing narrow-band communication capability among neighbor EPPs. In particular, this paper describes a token ring control approach which allows full exploitation of the microgrid capabilities with marginal investment in the information and communication technology infrastructure.

Distribution loss minimization by token ring control of power electronic interfaces in residential micro-grids

Smart grids offer a new application domain for power electronics. In fact, every Distributed Energy Resource (DER) includes an Electronic Power Processor (EPP) to govern the power exchange with the grid. Such distributed EPPs should perform cooperatively to take full advantage of smart grid potentiality (exploitation of renewable energy sources, power quality and transmission efficiency). In low-voltage residential micro-grids, where number and type of DERs and loads is unpredictable and may vary during daytime, cooperative operation can be achieved by simple cross-communication among neighbor EPPs, without centralized supervisor or additional control units. The paper describes the principles of such cooperative operation together with a communication and control architecture which allows exploitation of micro-grid capabilities without infrastructural investments.

Digital Time-Optimal Phase Shedding in Multiphase Buck Converters

This letter proposes a time-optimal digital controller for the phase shedding (PS) in multiphase buck converters. PS is an established technique to improve the efficiency of multiphase converters at light load by changing the active number of phases depending on the load-current level. In order to minimize the output-voltage deviation and the transient time during PS, a minimum time algorithm is investigated. The proposed technique is insensitive to the power stage parameters, as its operation relies only on a feedforward action, depending on the steady-state duty cycle and the number of phases to be turned on or turned off. The proposed approach is validated through experimental tests on a synchronous buck converter.

Time optimal, parameters-insensitive digital controller for VRM applications with Adaptive Voltage Positioning

A digital control approach is investigated for time-optimal load step response of Voltage Regulation Modules (VRM) equipped with low-ESR ceramic output capacitors. The proposed time-optimal technique is insensitive to the power stage parameters, as its operation does not rely on the knowledge of the output filter inductance or capacitance. The time-optimal response is achieved through a single on/off switching action undertaken as soon as a load transient is detected and automatically incorporates Adaptive Voltage Positioning (AVP) regulation. The proposed robust time-optimal approach is validated through both computer simulations and experimental tests on a synchronous buck converter prototype.

Improving power quality and distribution efficiency in micro-grids by cooperative control of Switching Power Interfaces

Smart grids offer a wide application domain for power electronics. In fact, every distributed energy resource (DER) includes an electronic power processor (Switching Power Interface, SPI) which controls the currents drawn from the grid and can be driven to optimize the power flow, improve voltage stability and increase distribution efficiency. For these aims, such distributed SPIs must perform cooperatively. This is true also in low-voltage residential micro-grids, where the number of active DERs and the generated power may vary during daytime, thus requiring dynamic adaptation of SPI operation. To achieve this goal different approaches can be adopted, depending on the available communication capability. This paper discusses various control solutions applicable in absence of supervisory control, e.g., in residential micro-grids, where communication is possible between neighbor units only (surround control) or is not available at all (plug & play control).

Digital Autotuning of DC–DC Converters Based on a Model Reference Impulse Response

This paper proposes a model reference-based autotuning technique for digitally controlled voltage-mode dc-dc converters. The proposed solution performs a comparison between the measured system impulse response and a reference derived from the desired dynamic performances, and minimizes the error function acting on the regulator parameters. Two different approaches are investigated to evaluate the impulse response: a deterministic tuning, injecting a duty-cycle impulse, and a statistical tuning, based on white noise injection in the control loop. Compared to existing approaches, this solution has the advantages of simplicity, small-signal processing, and on-line tuning capabilities. Experimental investigation is performed on a 20-A, 1.5-V digitally controlled synchronous buck converter, and both simulations and experimental results confirm the effectiveness of the proposed solution.

Effect of parasitic components in the integrated boost-flyback high step-up converter

The increasing interest for renewable energy sources like those based on photovoltaic panels and fuel-cells have driven the power electronics community toward the study and development of high step-up dc-dc converters, able to efficiently interface the low voltage side of such energy sources with the high-voltage dc link side of the grid connected inverter. Between the different investigated topologies, those based on the combination of a boost section and a flyback one are quite interesting, thanks to the possibility to boost the output voltage while keeping the switch voltage stress at a reasonable level. However, the analysis reported in literature always neglect the effect of parasitic components that strongly modify the converter behavior. In this paper, the analysis of the integrated boost-flyback converter with voltage multiplier is presented that includes the effect of the parasitic components. It is shown that a resonance occurs that helps to increase the converters voltage gain. Experimental results taken from a 300W rated prototype are included, showing a good agreement with the theoretical expectations.