Digital-controlled Power Converter Research Articles

Accurate Modeling and Elimination of Double Vertical Crossing in Multi-Sampled Digital-Controlled Buck Converters

The multi-sampling method is an effective approach to reduce delay in digital controlled power converters. However, this method may deteriorate the dynamic performance of converters due to double vertical crossing (DVC) of modulation signal and carrier signal, which makes the closed-loop regulation lost. This phenomenon is influenced by the operating point, parameters of power stage and control system. Therefore, it is significant to predict and eliminate the DVC for avoiding its negative influences. This paper proposes an accurate model of DVC in multi-sampled digital-controlled buck converters, where the output capacitance and the sampling delay is taken into account. Then a carrier phase adjusting algorithm is proposed to eliminate DVC. The proposed method features better dynamic performance than existing methods, and it is easier to realize since it keeps switching frequency constant. Finally, the theoretical analysis is validated by the simulation and the experimental results.

Undershoot-Less Open-Loop Soft-Start Strategy for Digital-Controlled Power Converters Based on an Error-ADC and Initial Duty Ratio Estimator

In digital control, an error-analog-to-digital converter (EADC) is used to increase the effective resolution of analog-to-digital converter and achieve stability. However, digital control with EADC involves challenges in achieving soft-start without an output voltage undershoot or using a complex circuit, which increases the circuit cost and power loss. To overcome the aforementioned problems, this brief proposes an open-loop soft-start strategy without undershoot for a digital-controlled power converter based on an EADC. The proposed strategy does not require a digital-to-analog converter and accurate wide-range analog front-end circuit. A duty ratio estimator and design considerations were established to achieve a seamless open-loop/closed-loop transition for avoiding a large output voltage undershoot. The proposed control can be applied to various types of power converters. It was verified through simulations with a buck converter. Finally, a buck converter experiment was performed to verify the proposed strategy, in which the output voltage was within a ${V} _{{o}}$ dynamic range of ± 5% after start-up.

Investigation in the PV Converter Smoothing Circuit Size Reduction vs. Loss in Energy Capturing

The Photovoltaic (PV) cell which can convert directly sunlight into electricity has a nonlinear power vs. voltage curve, and a digital controlled power converter is required to implement the Maximum Power Point Tracker (MPPT) function. This paper aims to investigate the influence of current ripple amplitude which results from the operation of power converter on the efficiency of capturing the available solar energy. By simulation, a tradeoff between the filter size, the current ripple amplitude and the solar energy capture efficiency is found.