High step-up dc–dc converters are widely used in new energy applications such as photovoltaic cell, fuel cell, dc microgrid, etc. Active switched-inductor (ASL) converter has simple operation and low stress on switches. To further increase the voltage gain, some SC (switched-capacitor)/ASL step-up converters have been proposed recently. However, these SC/ASL step-up converters have voltage oscillation on switches, which leads to the voltage stress on switches is higher than the theoretical value. In this article, a novel high step-up SC/ASL converter is proposed. Compared with other SC/ASL step-up converters, the proposed converter has lower voltage stress on the switches, output diodes, and output filter capacitors, and the efficiency is higher. In addition, the proposed converter can achieve self-voltage balancing on switches. This article analyzes the proposed converter from operation principle, continuous conduction mode (CCM) analysis, CCM operation with unbalanced inductors, input current ripple analysis, discontinuous conduction mode and boundary conduction mode analysis, switches self-voltage balancing characteristic, voltage stress, current stress, comparison analysis, and design considerations. Finally, a 200 W, 25–45 V/380 V, 50 kHz experimental prototype has been established in the laboratory to evaluate the proposed converter, which reached a peak efficiency of 97.3%.

Under the unbalanced condition of grid voltages, the second-order harmonic voltage ripple will appear on the DC bus of the three-phase PWM rectifier due to the existence of the negative sequence voltages. In addition, the total harmonic distortion (THD) of the grid currents will increase correspondingly. In this paper, the coupling mechanism between the DC bus voltage ripple and the grid harmonic currents is revealed. Based on the situation above, a grid harmonic current suppression method is proposed. Compared with existing methods, the proposed method has the advantages in the following three aspects. Firstly, the proposed method does not require either the extraction of positive/negative sequence or the positive/negative sequence current control, which can highly reduce the complexity of the system. Secondly, the grid current harmonics can be reduced by an improved proportional quasi resonant (IPQR) controller. Thirdly, the IPQR controller has little effect on the parameter design of the control system, which facilitates the control design. Finally, the experiments show the accuracy of the theoretical analysis and the effectiveness of the proposed method.

This study presents a grid‐tied photovoltaic (PV) system based on the series Z‐source inverter. The grid‐tied current control strategy, the dc‐link voltage control, as well as the maximum power point tracking scheme is realised in the single‐stage system. The current control strategy is performed based on dq rotating frame. Indirect dc‐link control is adopted to achieve constant peak dc‐link voltage and thus can simplify the controller design in inversion stage. The overall control strategy is given and analysed in detail. Simulation and experimental results demonstrate that the proposed system can be applied in PV system with a wide input voltage range, which verify the correctness and validity of the analysis.

A high step-up integrated coupled inductor-capacitor DC-DC converter for renewable energy applications has been proposed in this paper. Because of relative low output voltage of renewable energy systems, a high step-up converter is necessary. In this paper, a new configuration has been given by integrating coupled inductor-capacitor to get the desire voltage gain. The voltage gain dramatically boosted up by using a coupled inductor to charge a capacitor and the voltage across the switch are clamped inherently. The proposed converter possesses of only six components, which makes it uncomplicated and more efficient. The derivation of the steady state operation’s principles has been analyzed in detail, this paper. Prototype hardware is implemented in the laboratory and the experimental results are given to verify the theoretical analysis.

Carrier-based discontinuous pulse width modulation (CB-DPWM) is widely used in three-level AC/DC converters due to its features of higher efficiency and simpler implementation. However, the problems of switching losses, current distortion around zero-crossing points, and neutral point (NP) voltage fluctuation are mutually coupled for the Vienna rectifier. Therefore, this article proposes a modified carrier-based discontinuous pulse width modulation (MCB-DPWM) scheme for the Vienna rectifier with improved zero-sequence voltage injection. The clamping range and clamping mode that suppress zero-crossing distortion are adjusted. Compared to continuous PWM and conventional discontinuous PWM (DPWM), the proposed MCB-DPWM could effectively eliminate zero-crossing distortion and reduce the NP voltage fluctuation and switching loss, which means higher input current quality and efficiency. Moreover, it features a simpler implementation and less computational burden than space-vector-based PWM. Therefore, it is more suitable for high frequency applications. Finally, the simulation and experiment results demonstrate the proposed MCB-DPWM could reduce switching loss and current distortion with lower NP voltage fluctuation under different modulation indices.

A phase-shifted full-bridge (PSFB) converter is widely used in various applications due to its soft-switching characteristics. However, one of the recognized shortcomings of the PSFB converter is that it cannot simultaneously have a wide soft switching range and a small secondary-side duty cycle loss. The shortcoming hinders the high frequency and high efficiency of the converter. In this article, the change of the energy demand of the converter on the external series inductor with input voltage and load is analyzed. On this basis, a variable saturation inductor with controllable energy is proposed to meet the energy demand and solve the problem of core heating. The controllable change characteristics of the inductor energy are studied directly instead of the controllable change of the inductance value. By adjusting the inductor energy, the PSFB can not only achieve soft switching under light loads, but also reduce duty cycle loss under heavy loads. Theoretical analysis and experimental verification are carried out on the soft switching and duty cycle loss of the converter. Since the transformer ratio can be increased due to thesmaller duty cycle loss. The efficiency of the converter can be further improved.