This paper introduces a highly efficient bidirectional resonant dc/dc converter over wide range of battery voltages for vehicle-to-grid (V2G) capable electric vehicles (EVs). It operates as a pulse-width-modulation (PWM) full-bridge series-resonant converter in the forward direction and a half-bridge resonant boost converter in the backward direction. One advantage of the proposed converter is that it has wide voltage gain range in the backward operation. Also, it requires only six active switches. To achieve high efficiency, SiC MOSFETs are used for two bottom switches in the primary side, because only these switches suffer hard switching turn-off in both forward and backward directions. Since it operates with fixed-frequency and with PWM control, the magnetic components and passive filters can be optimally designed with respect to the volume and the loss. Thus, the proposed converter achieves low cost, high conversion ratio, and high efficiency over wide range of battery voltages. Detailed analysis of the converter operation is presented along with the design procedure. A 3.3 kW/400 V prototype of the proposed converter has been built to operate for 250-415 V primary source voltages and tested to demonstrate its circuit design.

This paper proposes a repetitive controller with phase-lead compensation for an unfolding-type Cuk continuous conduction mode (CCM) inverter operating in the CCM. The Cuk CCM inverter features medium power capacity, step up/down ability, and low input/output current ripples, so it is well suited to distributed power generation systems. To achieve accurate tracking of the reference output current, we make the use of the repetitive controller coupled with a conventional proportional-integral controller and a nominal duty ratio. In developing the proposed controller, we use the average model of the Cuk CCM inverter in the grid-connected case. The two right-half plane (RHP) zeros in the transfer function of the Cuk CCM inverter cause phase lag of the closed-loop system; to compensate for the phase lag, we implement a phase-lead compensation algorithm in the repetitive control scheme. We also provide detailed and practical design guidelines of the control parameters to develop a stable Cuk CCM inverter. Experimental tests using a 500-W Cuk CCM inverter demonstrate the desirable performance of the proposed control approach.

In this paper, we propose a high step-up resonant dc-dc converter with ripple-free input current for renewable energy systems. We use an input-current doubler and a switching mechanism employed at an output-voltage doubler to achieve high step-up voltage gain without having to use a transformer with high turns ratio. An active-clamp circuit installed on the primary side suppresses the surge voltage at the switch components and recycles the energy stored in the leakage inductance. A resonance that occurs at the secondary side of the converter is used to reduce the turn-off current and switching loss significantly, and to achieve high power conversion efficiency. The input-current ripple declines to zero theoretically because the duty cycle of the primary-side switches is always set to 0.5 regardless of the input voltages and load variations. The circuit operations, steady-state analysis, and design guideline of the proposed converter are also presented. A 600-W prototype converter has been fabricated to demonstrate the performance of the proposed converter.

This paper proposes a repetitive controller (RC) for a capacitor-less current-fed dual-half-bridge (CF-DHB) converter for a grid-connected fuel cell system. The pulsating power caused by the ac grid makes the dc-link voltage and input current fluctuate with twice the grid frequency. To achieve zero-voltage-switching (ZVS) for the capacitor-less CF-DHB converter and to increase the lifetime of the fuel cell, we need to suppress the low-frequency dc-link voltage ripple and the low-frequency input current ripple. We first make use of the duty cycle to regulate the dc-link voltage, and of the phase-shift angle to regulate the input current. Because the transfer function from the duty cycle to the dc-link voltage has a right-half plane (RHP) zero, the conventional proportional-integral controller cannot achieve satisfactory performance at the dc-link voltage. To compensate for the phase lag due to the existence of the RHP zero, we propose to use an RC with phase-lead compensation for dc-link voltage control. Because the transfer function from the phase-shift angle to the input current has one left-half plane zero, the conventional RC is used to control the input current. In developing the proposed controller, we first derive the dynamic model of the CF-DHB converter in the grid-connected environment, and then use the model to design an RC. We also provide a detailed and practical design guideline to select the control parameters of the capacitor-less CF-DHB converter that can meet the desired performance. The proposed RC can reduce the input current ripple significantly and suppress the dc-link voltage ripple within the predetermined range and thereby achieves ZVS. Experimental results demonstrate that the proposed control scheme achieves desirable performance.

This paper presents a dual-mode Cuk inverter for photovoltaic/thermoelectric power applications. A dual-mode Cuk inverter operates in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM), and has the advantages of low ripples of voltage and current at the input and output, medium power density, and step-up/step-down ability, but is difficult to control because DCM and CCM have distinct system dynamics. To overcome this control problem, we propose to use a repetitive controller (RC) with a multiple phase-lead compensator for the dual-mode Cuk inverter. If the RC is applied by itself, the distinct system dynamics may severely degrade its system performance. Thus, in the proposed RC, we mainly use a multiple phase-lead compensator to compensate for the different phase lags of the dual-mode Cuk inverter. To reduce the burden from the RC, we use the dual-mode nominal duty ratio as feedforward control input. We also analyze the boundary of operation modes in the dual-mode Cuk inverter, then provide detailed and practical guidelines to design the control parameters. Experimental results obtained on a 500-W digitally controlled module integrated converter prototype confirmed the effectiveness of the control approach.

Conventional current-fed resonant converter suffers from high turn-off loss over wide range of fuel-cell voltage. To alleviate this problem, we propose high voltage gain current-fed resonant converter that achieves almost ZVS turn-off over a wide range of voltage gain. By employing a bidirectional switch across center nodes of the voltage doubler and corresponding modulation, the presented converter achieved almost ZVS at the turn-off instant; this trait significantly increases the power conversion efficiency even under high frequency operation. The inherent boost function of the current doubler, an additional boosting operation using a bidirectional switch, and double boosting of the voltage doubler enable the presented converter to achieve high voltage gain without having to use a transformer that has a high turns-ratio. Moreover, 180 $^\circ$ phase interleaving reduces the input current ripple to zero. The steady-state operation is analyzed comprehensively, and design considerations of the proposed converter are given. Finally, a prototype with input of 48-72 V, output of 380 V, and rated power of 1 kW is developed to validate the effectiveness and feasibility of the proposed converter.