DC-DC Converter Load Research Articles

Analysis, Modeling, and Simulation of Adaptive Control Based on Dynamic Conductance Estimation of Photovoltaic Generator Interfaced Current-Mode Buck Converter

In this paper, a novel adaptive control method is presented, aimed at robustifying the terminal voltage of the photovoltaic generator, interfaced by the current-mode-controlled buck DC-DC converter load, and based on conductance estimation. The photovoltaic generator, which is integrated into the buck converter and a battery storage unit, is continuously affected by the operating point of the system and environmental variables, thus presenting a nonlinear behavior. Furthermore, the development of small-signal equations reveals a potentially unstable condition when the system is used as a micro-grid with a battery storage unit. This study shows that when the nonlinear behavior of the photovoltaic generator is combined with a typical nominal controller, designed for a single nominal operating point and due to the possibility of an unstable condition, it forces the controller to operate mostly outside the nominal operating point. These conditions result in significantly varied closed-loop performance. In contrast, an almost perfect loop gain performance can be achieved when implementing an adaptive controller based on an online conductance estimation method. Applying estimator results and injecting its value in real-time into the inverse-based plant controller results in an adaptive controller. Therefore, the closed-loop performance of the system integrated with an adaptive controller achieves an almost nominal response throughout the operating range.

Low-Frequency Input Current Ripple Reduction Based on Load Current Feedforward in a Two-Stage Single-Phase Inverter

A large amount of ripple at twice the output frequency will emerge in the input current due to the pulsating output power in a two-stage single-phase inverter. To reduce the low-frequency input current ripple, a control strategy is presented in this paper based on the front-end dc-dc converter load current feedforward. It intends to control the dc bus voltage to swing properly at twice the output frequency, making the dc bus capacitor supply nearly all the pulsating power. The implementation method is illustrated, and the operation performance analysis as well as the key parameter design principle is provided. Introducing the proposed feedforward path is able to significantly suppress the input current ripple with little impacts on the original system stability, steady-state tracking accuracy, and dynamic response. Finally, experimental results performed on a buck-type stand-alone two-stage single-phase inverter prototype verify the validity of proposed method and the correctness of analysis.

Capacitor Ripple Current in an Interleaved PFC Converter

To achieve high-power density in power supplies, it is desirable to minimize the physical size of the energy storage capacitor. The capacitance is determined by the energy storage requirement for line outage ride-through and also the ripple current handling capability of the capacitor. Interleaving is well known as an effective method to reduce the capacitor ripple current and in cases where ripple current considerations dominate, it could reduce capacitor size. This paper presents a methodology to calculate the ripple current, both for single phase and for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</i> interleaved phases of power factor correction converters operating with constant load or a DC-DC converter load. Experimental results from a commercial power supply yielded a small error when compared to the calculations, showing that the proposed methodology has enough accuracy to be used as a design tool.

Predictive Efficiency Optimization for DC–DC Converters With Highly Dynamic Digital Loads

This paper presents a novel technique and system for increasing the efficiency of dc-dc converters that supply dynamic electronic loads, such as modern audio and video equipment and other devices whose power consumption largely depends on the digital data they process. The optimization does not require a current-measurement circuit and is well-suited to portable applications. It is based on a real-time prediction of the dc-dc converter output current from easily accessible digital data streams present in the targeted loads. The result of the prediction is used for dynamic adjustment of the power-stage transistor size and/or for switching into pulse-frequency-mode of output voltage regulation, in order to maximize the instantaneous converter efficiency on-the-fly. The use of a segmented power-stage allows the effective power-transistor size to be changed on-the-fly, and the tradeoff between the gate-drive and rms conduction losses is continuously optimized over the full range of operation. The effectiveness of the optimization is demonstrated on an experimental system, including a 1-W digitally controlled 4-MHz, 3.6 V-1.8 V buck converter with an integrated segmented power-stage and a digital high-fidelity class-D audio amplifier acting as the digital load. The results show a good agreement between the digitally predicted and actual dc-dc converter load current, as well as a reduction in total energy consumption of up to 38%.