A new transformerless buck-boost converter with simple structure is proposed in this study. Compared with the traditional buck-boost converter, the proposed buck-boost converter's voltage gain is squared times of the former's and its output voltage polarity is positive. These advantages enable it to work in a wider range of positive output. The two power switches of the proposed buck-boost converter operate synchronously. In the continuous conduction mode (CCM), two inductors are magnetized and two capacitors are discharged during the switch-on period, while two inductors are demagnetized and two capacitors are charged during the switch-off period. The operating principles, the steady-state analyses, and the small-signal model for the proposed buck-boost converter operating in CCM are presented in detail. The power electronics simulator (PSIM) and the circuit experiments are provided to validate the effectiveness of the proposed buck-boost converter.

In this paper, a new negative output (N/O) buck-boost converter, which can be applied for applications that need wide range of inverse voltage, is proposed. The steady-state, small-signal model and power losses of the proposed converter operating in a continuous conduction mode are analyzed. Comparisons among the traditional buck-boost converter, N/O hybrid buck-boost converter and N/O self-lift Luo converter are presented, and it is found that the proposed converter possesses a widest voltage conversion ratio in these four converters. Finally, a prototype is built, and the simulated waveforms from the PSIM software and the experimental results are presented for validation.

The bridgeless buck power factor correction (PFC) converters feature the merits of low output voltage and high efficiency while their inherent dead angles in the input current will deteriorate the input current harmonics and power factor (PF). Aiming to reduce the dead angles, a new bridgeless buck PFC converter is proposed in this paper. Through integrating the main buck circuit and the auxiliary flyback circuit with one magnetic core, the dead angles in the input current of the proposed bridgeless buck PFC converter is eliminated so that the PF and input current harmonics are improved. The proposed bridgeless buck PFC converter is designed to operate in discontinuous conduction mode (DCM) with the merits of simple controller and nature current shaping ability. A new logic control circuit is provided. The detailed theoretical derivations and design consideration are presented. The experimental comparison among the proposed bridgeless buck PFC converter, the conventional buck PFC converter, and the conventional bridgeless buck PFC converter is displayed to validate the effectiveness of the new converter.

In this paper, the slow-scale instability in a boost PFC converter under average current mode control is studied via the harmonic balance method and floquet theory. Systematic and general numerical algorithm of the technique is developed. The objective is to identify instability of the system. If instability exists, the type of bifurcation and the boundaries of slow-scale instability in the parameter space of the system can be found for facilitating the design of such converters. Firstly, based on the fact that the current compensator is designed very well and what we considered is the slow-scale instability, the simplified model of a boost PFC converter under average current mode control is derived. And then, the solution of the simplified model is calculated by using the harmonic balance method. Subsequently, both the stability of the circuit system and the type of bifurcation are identified via floquet theory. Meanwhile, the critical conditions of the stable operation in the parameter space of the system are given accurately. Finally, experimental results are presented for the verification of the analytical results.