Shungang Xu’s research while affiliated with Southwest Jiaotong University and other places

This article proposes a two-mode active balancing circuit for series-connected cell strings. The proposed balancing circuit has two operation modes: any cell to any cell (AC2AC) and direct cell to cell (DC2C) modes. In AC2AC mode, the balancing circuit can be equivalent to an improved switched-capacitor (SC) balancing circuit, and the energy is transferred among all imbalanced cells, implementing the higher balancing speed when the voltage gap between cells and the number of imbalanced cells are large. In DC2C mode, the proposed balancing circuit can be equivalent to a balancing circuit based on three-resonant-state LC unit, and the energy is transferred from the highest voltage cell to the lowest voltage one, achieving the higher balancing efficiency and speed as well as accuracy when the voltage gap between cells is small. The operation state, balancing power, and balancing efficiency of each mode are analyzed in detail. The control strategy and design considerations of the balancing circuit are introduced to obtain the optimal balancing performance. Experimental results are provided to verify the validity of the proposed balancing circuit. The results show that the proposed balancing circuit achieves high balancing accuracy and efficiency as well as balancing speed.

In this paper, a modified maximum power trapezium (M-MPT) method for global maximum power point tracking (GMPPT) of photovoltaic (PV) systems under partially shaded conditions (PSCs) is proposed. Compared with the traditional maximum power trapezium (MPT) method, the proposed method introduces a variable current range lower bound by utilizing monotonic output characteristics of the PV array. Moreover, considering the influence of the initial operating point of the PV array on the scanning path under dynamic PSCs, a judgement mechanism for the initial voltage is added in the modified method. The proposed method guarantees that the global maximum power point is tracked accurately with a smaller voltage scanning range and shorter tracking time under all conditions. Furthermore, the excellent performance of the proposed method has been verified by both simulation and experimental results.

In order to eliminate the voltage imbalance among battery cells when they are connected in series, the paper proposes a double-layer E-structure (DLE) equalizer based on bidirectional buck–boost converters, which has the advantage of quick equalization speed and can be applied to arbitrary number batteries. Furthermore, a novel two-stage equalization control strategy is proposed for the DLE equalizer to decrease maximum voltage gap between the maximum and minimum voltage cells. The paper analyses the working principle of proposed equalizer in detail and describes the detailed design of the control strategy and implement process. Simulation and experiment results show that the proposed equalizer can improve equalization performance of battery cells compared with adjacent cell-to-cell (AC2C) equalizer.

Through analysing the operating principle of current mode controlled (CMC) tri-state dc-dc converters, the inductor current borders are obtained and a unified discrete-map model of CMC tri-state dc-dc converters with ramp compensation is established. According to this model, the dynamical behaviour of the tri-state dc-dc converters is analysed by utilising bifurcation diagram. In addition, the boundary equation of tri-state dc-dc converters from stable pseudo-continuous conduction mode (PCCM) period-1 state to unstable state is derived. The expressions of the minimum slope of ramp compensation for the converter shifting from unstable state to stable PCCM period-1 state are also obtained. Meanwhile, the operating regions are divided effectively by the boundary equation. The research results indicate that border collision bifurcation could occur when the circuit parameters vary, including a bifurcation from one periodic orbit to another periodic orbit, such as period-1 to period-2 or period-2 to period-4 and so on, or a bifurcation from a period orbit to chaotic orbit. By using ramp compensation, the stable working range of the CMC tri-state dc-dc converter could be broadened. Finally, an experimental circuit is built and the experiment results verify the theoretical analysis.

Current-mode controlled single-inductor dual-output (SIDO) switching converters have three borders in wide-range parameter variations. Based on the slopes of inductor current during the power switches being turn-on or turn-off, a unified discrete-mapping model of current-mode controlled SIDO switching converters with ramp compensation is established in this study, which can be applied to three basic SIDO switching converters, i.e. buck type, boost type, and buck-boost type. Only six parameters appear in this model after non-dimensional analysis, from which the dynamical behaviours of SIDO switching converters in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) can be effectively illustrated. The effect of ramp compensation is analysed in detail. By utilising the proposed unified model, two transition conditions and boundary equations of the converter are derived, where its operation state transits from stable period-1 to instability and operation mode shifts from CCM to DCM. The operation region with varied circuit parameters can be estimated and divided by the parameter-space map, which is significant for the design of circuit parameters and stability. Finally, taking a current-mode controlled SIDO boost converter as an example, its experimental results are carried out to validate the theoretic analysis and the non-dimensional unified model.

Buck type, boost type and buck-boost type are basic topologies of single-inductor dual-output (SIDO) DC-DC converters. Current-mode controlled SIDO DC-DC converters have three current borders in wide-range parameter variations. According to the change of inductor current which presents five trends of “up-down-down”, “up-up-down”, “up-down-up”, “down-up-down”, and “up-down”, the corresponding current borders are defined. On this basis, a unified discrete-mapping model of five inductor current trends is established and the boundary equations of system stability and mode shifting are derived in the meantime. The dynamic behaviors with the variations of circuit parameters in different inductor current trends are analyzed in detail by numerical simulation, and theoretical analysis of period-doubling bifurcation and tangent bifurcation are presented to validate the simulation results. The research results indicate that the SIDO DC-DC converter has different bifurcation sequences with the same circuit parameter varying for different inductor current trends. Operating regions of the converter are given in this paper, which provides theoretical guidance in designing current-mode controlled SIDO DC-DC converters. Experimental results are presented to verify the correctness of theoretical analysis and unified discrete-mapping model. IEEE

Considering that the state equations of peak current-mode (PCM) controlled buck light-emitting diode (LED) driver with proportion-integration (PI) compensator are third-order singular matrices with maximum rank 2, it is not invertible and may lead to non-convergent problem under certain circuit parameters. Therefore, an improved discrete-time modeling is performed by substituting state variables of power stage circuit for PI compensator equivalently in this paper. Based on this modeling, the stability of PCM controlled buck LED driver is investigated by analyzing bifurcation diagram and the maximum Lyapunov exponent spectrum, while the conduction-mode boundary and stability boundary are deduced which indicate the operation regions of the system intuitively, providing design guidelines for LED driver. Experimental results are further presented to verify the theoretical analysis.