Cascaded dc–dc converter is the main component of the dc distributed power system. It is valuable to establish the accurate model for studying the stability of cascaded dc–dc converters. However, the cascaded dc–dc system has many operating modes, such that the existing classic methods, e.g., state-space average model and discrete-mapping model, are difficult to explore to analyze cascaded dc–dc converter system, especially that with different switching frequencies. To overcome this drawback, this article promulgates a new modeling and stability analysis method for cascaded dc–dc converter. Small-step method, discretization method, and Euler method are exploited to modeling. All stages of the system are considered, therefore, accurate; and stability is divided into three categories according to the different definitions. Then, the cascaded systems with the same or different switching frequencies are studied using the presented method. As an example, two-stage peak current-mode controlled boost converter is scrutinized. Finally, simulations and experiments are manipulated to verify the correctness of the new method.

In order to obtain more realistic characteristics of the converter, a fractional-order inductor and capacitor are used in the modeling of power electronic converters. However, few researches focus on power electronic converters with a fractional-order mutual inductance. This paper introduces a fractional-order flyback converter with a fractional-order mutual inductance and a fractional-order capacitor. The equivalent circuit model of the fractional-order mutual inductance is derived. Then, the state-space average model of the fractional-order flyback converter in continuous conduction mode (CCM) are established. Moreover, direct current (DC) analysis and alternating current (AC) analysis are performed under the Caputo fractional definition. Theoretical analysis shows that the orders have an important influence on the ripple, the CCM operating condition and transfer functions. Finally, the results of circuit simulation and numerical calculation are compared to verify the correctness of the theoretical analysis and the validity of the model. The simulation results show that the fractional-order flyback converter exhibits smaller overshoot, shorter setting time and higher design freedom compared with the integer-order flyback converter.

A novel Cuk-based bridgeless rectifier is proposed for receiving side of wireless power transfer (WPT) system. The proposed converter can not only help improve overall efficiency but also is with features of wide power modulation range and very low output current ripple. In terms of the output current source characteristics of series-series-compensated WPT system, a bridgeless rectifier and a Cuk converter are combined and an input inductor of Cuk converter is cut down to form the proposed single-stage converter. Besides, a synchronization operation method is derived for the proposed converter to realize the optimal working point of transmission power and efficiency. Operation principles of the converter and its impact on performance of WPT system are analyzed. Also, design methods for system parameters are given. A prototype is built up to verify the feasibility of the proposed topology and the operation method. It is noted that the proposed converter can well adjust the output power of WPT system to realize the desired working point via adjusting the duty cycle at different transfer distances and loads.

This article presents a general method to obtain the improved common ground quasi-Z-source series dc–dc converters. Utilizing the negative output characteristic of the quasi-Z-source converter (QZSC), the output voltage of the improved converter is the sum of the input voltage and the output voltage of the original QZSC, which means that part of the energy is directly supplied by the input voltage source without passing through QZSC. Therefore, compared with the original QZSC, the proposed improved converter has advantages such as lower voltage stress, lower current stress, higher voltage gain, and higher efficiency. More importantly, all these improvements are obtained with no obvious drawback. No additional component is required, the input and output remain common ground, and if the input current of the original converter and the load current are continuous, the input current of the improved converter is also continuous. In order to prove the feasibility of the proposed method, first, the improved converters of three existing QZSCs are obtained. Then, the operation principle, parameter design, and comparison are introduced in sequence. Finally, the above analyses are verified by simulation and experiment results.

The stability issue of a single-phase two-stage grid-connected photovoltaic system is complicated due to the nonlinear v-i characteristic of the photovoltaic array as well as the interaction between power converters. Besides, even though linear system theory is widely used in stability analysis of balanced three-phase systems, the application of the same theory to single-phase systems meets serious challenges, since single-phase systems cannot be transformed into linear time-invariant systems simply using Park transformation as balanced three-phase systems. In this paper, (1) the integrated mathematical model of a single-phase two-stage grid-connected photovoltaic system is established, in which both DC-DC converter and DC-AC converter are included also the characteristic of the PV array is considered; (2) an observer-pattern modeling method is used to eliminate the time-varying variables; and (3) the stability of the system is studied using eigenvalue sensitivity and eigenvalue loci plots. Finally, simulation results are given to validate the proposed model and stability analysis.

As a basic structure of the distributed power systems, cascaded dc–dc converter systems have attracted a lot of attention. However, due to the interaction between the subconverters, classic methods for modeling cascaded systems are either not accurate enough, such as state-space averaging model, or not simple enough, such as discrete-time mapping model, especially the systems with different switching frequencies. To overcome this drawback, a simplified discrete-time mapping modeling method for cascaded dc–dc converter systems is proposed in this article. Based on the idea of state-space average, the original problem is simplified to modeling cascaded dc–dc converter systems with the same switching frequencies. The proposed method is able to predict the dynamic properties of the system at all stages, such as slow-scale and fast-scale instabilities. Then, two-stage cascaded boost converter with different switching frequencies under peak current double loop control is taken as an example to present the simplified discrete-time mapping model. Finally, the effectiveness of the proposed method is verified by simulations and experiments.