Search

A high-efficiency bridgeless three-level power factor correction (PFC) rectifier is proposed. The circuit configuration of the proposed rectifier consists of four metal oxide semiconductor field-effect transistor (MOSFET) switches, and the reverse recovery problems of the switches are eliminated. Also, the proposed rectifier with three voltage levels reduces the power losses, harmonic components, voltage ratings, and electromagnetic interference. To control the grid current and the output voltage effectively, a feed-forward nominal voltage compensator with the mode selector is developed; by presetting the operating point of the grid voltage, this compensator improves the control environment. Thus, the proposed three-level PFC rectifier with developed control algorithm provides high power quality and high efficiency of 99.05%. Experimental results based on a 1-kW prototype are provided to evaluate its performance and verify the analysis. [ABSTRACT FROM AUTHOR]

This paper presents an electrolytic capacitor-less single-power-conversion on-board charger with high efficiency. The proposed on-board charger is composed of a step-up ac–dc converter which includes an active-clamp circuit and a series-resonant circuit. The active-clamp circuit provides a zero-voltage switching of switches and recycles the energy stored in the leakage inductance of the transformer. Also, this circuit clamps the surge voltage of switches. The series-resonant circuit reduces reverse-recovery problem of output diodes by providing a zero-current switching. Especially, the control algorithm is developed to achieve high power factor under the universal input voltage without the help of the any auxiliary circuit. Thus, due to these characteristics, the proposed charger can achieve high power efficiency and high power factor. In addition, the structure of single-power-conversion is very beneficial to the on-board charger that is installed in the vehicle. To confirm the theoretical analysis and validity of the proposed on-board charger, a 2-kW prototype is implemented under the universal input voltage. [ABSTRACT FROM AUTHOR]

This paper presents a bidirectional single power-conversion dc–ac converter with noncomplementary active-clamp circuits. The proposed converter comprises a bidirectional flyback converter and an unfolding bridge. In order to interface the grid with a low-voltage energy storage through only single power-conversion, the bidirectional flyback converter transforms the low voltage directly into the folded grid voltage and regulates the folded grid current. The proposed converter adopts noncomplementary operation strategy for the active-clamp circuits. By using this strategy, the bidirectional flyback converter not only avoids the voltage spike but also minimizes the power losses by the circulating energy. Thus, with single power-conversion and noncomplementary active-clamp circuits, the proposed converter obtains high power efficiency. To facilitate the bidirectional single power-conversion, a novel control algorithm is developed. With this control algorithm, the proposed converter ensures high grid power quality and seamless mode transition. The proposed bidirectional dc–ac converter is theoretically analyzed in detail. The experimental results based on a 250-W prototype are provided to evaluate its performance. [ABSTRACT FROM PUBLISHER]

This paper proposes a high-efficiency bidirectional dual-active-bridge (DAB) inverter using a novel hybrid modulation for a stand-alone power generating system with a low input voltage. The proposed DAB inverter consists of a DAB dc–dc converter and a synchronous rectifier (SR) for unfolding. The DAB dc–dc converter transforms the low dc voltage into a rectified sine wave that pulsates twice the grid frequency. The rectified sine wave unfolds into the grid voltage by SR. The proposed hybrid modulation combines a phase shift control and a variable frequency control. The variable frequency control converts the nonlinear function of the phase shift angle into a linear function and controls the output power. This leads to a simple closed-loop control for the sinusoidal current waveform, a low harmonic distortion, and a high-voltage conversion ratio without an increase of the transformer turn ratio. Since the proposed DAB inverter has only a single power conversion stage, it has a simple structure, high power density, and low cost. It also has a high efficiency of 94.2% by a zero-voltage switching (ZVS) turn on of the switches in two full bridges (FBs). The operation principle of the proposed DAB inverter using this hybrid modulation is analyzed and verified. Experimental results for a 1-kW prototype are obtained to show the performance. [ABSTRACT FROM AUTHOR]

This paper presents a highly efficient asymmetrical pulse-width modulated (APWM) full-bridge converter for renewable energy sources. The proposed converter adopts full-bridge topology and asymmetric control scheme to achieve the zero-voltage switching (ZVS) turn-on of the power switches of the primary side and to reduce the circulating current loss. Moreover, the resonant circuit composed of the leakage inductance of the transformer and the blocking capacitor provides the zero-current switching (ZCS) turn-off for the output diode without the help of any auxiliary circuits. Thus, the reverse recovery problem of the output diode is eliminated. In addition, voltage stresses of the power switches are clamped to the input voltage. Due to these characteristics, the proposed converter has the structure to minimize power losses. It is especially beneficial to the renewable energy conversion systems. To confirm the theoretical analysis and validity of the proposed converter, a 400 W prototype is implemented with the input voltage range from 40 to 80 V. [ABSTRACT FROM PUBLISHER]

This paper presents a control strategy of a flyback microinverter with hybrid operation mode for photovoltaic ac modules. The proposed control strategy consists of two components: the proportional-resonant (PR) controller with the harmonic compensator (HC) and the hybrid nominal duty ratio. Compared to the conventional control strategy using the proportional-integral controller, the PR controller with HC provides a higher system gain at the fundamental and harmonic frequencies of the grid without using a high proportional gain in both operation modes. Then, it enhances the tracking speed and disturbance rejection performances satisfying the desired stability. Moreover, by applying the hybrid nominal duty ratio yielded from the proposed operation mode selection, the disturbance rejection is achieved more effectively, and the control burden is reduced. Finally, the simulation and experimental results were shown to verify the tracking speed and disturbance rejection performances of the proposed control strategy. [ABSTRACT FROM PUBLISHER]

In this paper, a discrete-time repetitive controller (RC) is proposed for a flyback inverter operating in continuous conduction mode (CCM), which has a simple structure, low cost, and high efficiency. Conventional controller results in poor control performance due to the effect of the right-half-plane zero in CCM operation. To achieve accurate tracking performance and disturbance rejection, the RC is developed and applied to the flyback inverter in CCM operation. In the RC scheme, a low-pass filter is used to allow tracking and rejection of periodic signals within a specified frequency range. A phase lead compensator is also used to compensate for the effect of the closed-loop system dynamics. The stability of the closed-loop system is derived, and the zero tracking error is achieved. Numerical simulations validated the proposed control approach, and experimental tests using a 200-W digitally controlled module-integrated converter prototype confirmed its feasibility. [ABSTRACT FROM PUBLISHER]

This paper presents a novel microinverter for a single-phase grid-connected photovoltaic (PV) system. The proposed microinverter consists of a step-up dc–dc converter using an active-clamp circuit with a series-resonant voltage doubler and a high-efficiency inverter with single-switch-modulation step-down converters. The active-clamp circuit provides zero-voltage switching (ZVS) turn-on, recycles the energy stored in the leakage inductance of the transformer, and limits switch voltage stress. Moreover, to remove the reverse-recovery problem of the rectifier diodes, a series-resonant voltage doubler is used. Thus, this whole process provides high efficiency. To improve efficiency and reliability in the proposed inverter, only a single switch is modulated at the switching frequency without a shoot-through problem. A modified controller is also adopted to achieve fast output control. Thus, the proposed PV microinverter has the structure to minimize power losses. The experimental results show a maximum efficiency of 96.2% for a 400-W microinverter. [ABSTRACT FROM PUBLISHER]