Weichen Li

Interleaved High Step-Up ZVT Converter With Built-In Transformer Voltage Doubler Cell for Distributed PV Generation System

In this paper, the concept of built-in transformer voltage doubler cell is derived to generate an improved interleaved high step-up converter for distributed photovoltaic generation applications. The proposed built-in transformer voltage doubler cell is composed of three transformer windings, two voltage doubler diodes, and two voltage doubler capacitors. The voltage doubler capacitors are charged and discharged alternatively to double the voltage gain. The switch duty cycle and the transformer turns ratio can be employed as two controllable freedoms to lift the voltage ratio flexibly. The power device voltage stress can also be reduced to improve the circuit performance. Furthermore, the active clamp scheme is adopted to recycle the leakage energy, absorb the switch turn-off voltage spikes, and achieve zero-voltage switching (ZVS) operation for all active switches. Meanwhile, the diode reverse-recovery problem is alleviated by the leakage inductance of the built-in transformer. All these factors benefit the circuit performance improvements in the high step-up and large current applications. Finally, a 1-kW prototype with 40-380 V conversion is built and tested to demonstrate the effectiveness of the proposed converter.

General Derivation Law of Nonisolated High-Step-Up Interleaved Converters With Built-In Transformer

First, the limitations of the conventional interleaved boost converters in high-step-up and high-output-voltage applications are addressed in this paper. Then, a general derivation law of the nonisolated converters from their isolated counterparts is proposed and studied to give a universal solution for high-performance topology deduction. By employing the direct energy transfer concept, a family of nonisolated high-step-up interleaved boost converters is originated to make the turns ratio of a built-in transformer as another design freedom for the voltage gain extension. The derived converters have the advantages of large voltage conversion ratio, low power switch voltage stress, small input current ripple, and zero-voltage-switching soft-switching performance. The steady-state operation of the derived converter is analyzed, and the circuit performance is summarized to explore its advantages in the high-step-up, high-output-voltage, and large-current conversion systems. Finally, a 1-kW prototype with 40-V input and 380-V output voltages is implemented and tested to show the effectiveness of the derived converters. One of the main contributions of this paper is that a clear picture is made on the universal derivation law to generate high-step-up and high-performance dc/dc converters.

Single-Stage Single-Phase High-Step-Up ZVT Boost Converter for Fuel-Cell Microgrid System

In this paper, a voltage multiplier cell is inserted in the conventional boost converter operated in continuous conduction mode (CCM) to provide another design freedom for the voltage-gain extension. Thus, the voltage conversion ratio is enlarged and the narrow turn-OFF period is avoided in the high step-up applications. Furthermore, the voltage multiplier cell makes the voltage stress of all the power devices lower than the high output voltage. As a result, the low-voltage-rated power devices can be employed to reduce the conduction losses and to improve the power device reliability. Moreover, zero-voltage switching soft-switching operation is achieved for the power MOSFETs in the whole-switching transition. Zero-current switching turn-OFF condition is provided for the diodes. Therefore, the power device switching losses and the diode reverse-recovery losses are minimized greatly. In addition, the input current ripple is reduced due to the CCM operation compared with most of the published single-stage single-phase high step-up converters, which makes it more advantageous in the hybrid electric vehicles and the fuel-cell power conversion systems. Finally, the experimental results from a 500-W, 36-380-V prototype are provided to validate the effectiveness of the proposed converter.

High Step-Up Interleaved Converter With Built-In Transformer Voltage Multiplier Cells for Sustainable Energy Applications

In this paper, the built-in transformer voltage multiplier cell is inserted into each phase of the conventional interleaved boost converter to provide additional control freedom for the voltage gain extension without extreme duty cycle. The voltage multiplier cell is only composed of the built-in transformer windings, diodes and small capacitors. And additional active switches are not required to simplify the circuit configuration. Furthermore, the switch voltage stress and the diode peak current are also minimized due to the built-in transformer voltage multiplier cells to improve the conversion efficiency. Moreover, there is no reverse-recovery problem for the clamp diodes and the reverse-recovery current for the regenerative and output diodes are controlled by the leakage inductance of the built-in transformer to reduce the relative losses. In addition, the switch turn-off voltage spikes are suppressed effectively by the ingenious and inherent passive clamp scheme and zero current switch (ZCS) turn-on is realized for the switches, which can enhance the power device reliability. Finally, a 40 V-input 380 V-output 1 kW prototype is built to demonstrate the clear advantages of the proposed converter.

A smart and simple PV charger for portable applications

A smart and simple PV charger circuit is presented in this paper for the portable applications, which is only composed of several analog chips to simplify the system structure. A three-mode charging solution is employed to meet the demands of the PV array and the lithium battery, which includes the maximum power point tracking (MPPT) mode, the constant-voltage mode and the current-limited mode. Suitable charging mode can be achieved automatically by the smart switch to improve the utilization of the PV array and to protect the battery. The fractional open-circuit voltage method is employed to realize the MPPT performance due to its simple implementation performance. Furthermore, the proposed charger can be integrated into an IC chip to reduce the size and make it more attractive in the portable applications. At last, a 60W prototype is built and tested to verify the effectiveness of the proposed solution.

A non-isolated high step-up converter with built-in transformer derived from its isolated counterpart

In this paper, a non-isolated high step-up interleaved DC/DC converter is proposed for the photovoltaic and fuel cell grid-connected power applications. By employing the built-in transformer, the voltage gain is extended greatly without the extreme duty cycle and the voltage stress of the switches is reduced. The output diode reverse-recovery problem is alleviated by the leakage inductance of the built-in transformer, which reduces the reverse-recovery losses and the EMI noise. The active clamp scheme can suppress the surge voltage of the power switches and recycle the leakage energy. ZVS soft switching performance is realized for all the switches to reduce the switching losses. Finally, a 1 kW prototype with 40V input and 380V output is implemented and tested to show the performance of the presented converter.

An active clamp ZVT converter with input-parallel and output-series configuration

A novel converter is proposed in this paper to satisfy the high power, high step-up and isolated conversion requirements. In the proposed converter, the input-parallel configuration is adopted to share the large input current and reduce the conduction losses, while the output-series configuration is adopted to get a high voltage gain. Consequently, a transformer with a low turns ratio can be applied, which makes the transformer optimized easier. Moreover, the active clamp circuits are employed here to reduce the voltage stress of the switches and recycle the energy stored in the leakage inductance, and ZVT is achieved during the whole switching transition for all the active switches, so the switching losses can be reduced greatly. Furthermore, the diode reverse-recovery problem is partly solved due to the leakage inductance. Finally, a 40V-input 400V-output 1kW prototype is built to demonstrate the theoretical analysis, and the maximum efficiency of 94.9% and 93.3% at full load are achieved.