Fuxin Liu

Synthesis of Multiple-Input DC/DC Converters

Hybrid power systems continuously deliver power to the load from several renewable energy sources. For such systems, the use of a multiple-input converter (MIC) has the advantage of simpler circuit structure and lower cost, compared to the use of several single-input converters. By decomposing converters into basic cells, namely, pulsating source cells and output filters, a set of basic rules for generating multiple-input converter topologies is proposed. Specifically, two families of multiple-input converters are systematically generated. In the first family of MICs, all the input sources can power the load simultaneously or individually. In the second family, only one power source is allowed to transfer energy to the load at a time. Furthermore, some isolated MICs are simplified for reducing the complexity of the circuit configuration.

Zero-Voltage and Zero-Current-Switching PWM Combined Three-Level DC/DC Converter

This paper proposes a zero-voltage and zero-current-switching (ZVZCS) PWM combined three-level (TL) dc/dc converter, which is a combination of a ZVZCS PWM TL converter with a ZVZCS PWM full-bridge converter. The proposed converter has the following advantages: all power switches suffer only half of the input voltage; the voltage across the output filter is very close to the output voltage, which can reduce the output filter inductance significantly; and the voltage stress of the rectifier diodes is reduced too, so that the converter is very suitable for high input voltage and wide input voltage range applications. The converter also can achieve zero-voltage-switching for the leading switches and ZCS for the lagging switches in a wide load range to achieve higher efficiency. The design considerations and procedures are presented in this paper. The operation principle and characteristics of the proposed converter are analyzed and verified on a 400-800-V input and 54-V/20-A output prototype.

An Improved ZVS PWM Three-Level Converter

This paper proposes an improved zero-voltage-switching pulse-width-modulation three-level converter (ZVS PWM TL converter), which is improved from the original ZVS PWM TL converter just by exchanging the position of the resonant inductor and the transformer, such that the transformer is connected with the lagging switches. The improved converter has several advantages over the original one, e.g., the clamping diodes conduct only once in a switching period, and the resonant inductor current is smaller in zero state, leading to a higher efficiency and reduced duty cycle loss. A blocking capacitor is usually introduced to the primary side to prevent the transformer from saturating, this paper analyzes the effects of the blocking capacitor in different positions, and a best scheme is determined. A 2.5-kW prototype converter verifies the effectiveness of the improved converter and the best scheme for the blocking capacitor

Three-Phase Three-Level DC/DC Converter for High Input Voltage and High Power Applications-Adopting Symmetrical Duty Cycle Control

Three-phase dc/dc converters have the superior characteristics including lower current rating of switches, the reduced output filter requirement, and effective utilization of transformers. To further reduce the voltage stress on switches, three-phase three-level (TPTL) dc/dc converters have been investigated recently; however, numerous active power switches result in a complicated configuration in the available topologies. Therefore, a novel TPTL dc/dc converter adopting a symmetrical duty cycle control is proposed in this paper. Compared with the available TPTL converters, the proposed converter has fewer switches and simpler configuration. The voltage stress on all switches can be reduced to the half of the input voltage. Meanwhile, the ripple frequency of output current can be increased significantly, resulting in a reduced filter requirement. Experimental results from a 540-660-V input and 48-V/20-A output are presented to verify the theoretical analysis and the performance of the proposed converter.

ZVS Combined Three-Level Converter—A Topology Suitable for High Input Voltage With Wide Range Applications

A novel zero-voltage-switching (ZVS) combined three-level (TL) converter is proposed in this paper. It is essentially a hybrid combination of a half-bridge TL section and a full-bridge section. The main advantages of the proposed converter are given as follows: the voltage stress of all the switches is ensured to be only half of the input voltage; the secondary rectified voltage is very close to the output voltage, so the high-frequency content is very low, leading to a reduced output filter requirement; the voltage stress of the rectifier diodes is also reduced; and the switches can achieve ZVS with the use of the leakage inductances of the transformers and the intrinsic capacitors of the switches. This paper describes the operating principles and design procedures for the proposed converter. Experimental results from a 1080 W prototype converter operating at 100 kHz are presented to validate the theoretical analysis and demonstrate the performance of the proposed converter

Multiple-input full bridge dc/dc converter

In the renewable power system with two or more sources, the application of multiple-input converter (MIC) instead of several single-input converters can simplify the circuit and reduce the cost. A novel multiple-input full bridge dc/dc converter is proposed in this paper. Taking the two inputs as the example, the operation principles and characteristics of the double-input full bridge dc/dc converter are presented. By applying the proposed double phase-shift control strategy, the soft-switching technology is accessible. Power management method of the new converter is also introduced. Finally, a 800W prototype is built to verify the theoretical analysis and the effectiveness of the control strategy.

Asymmetrical Half-Bridge Double-Input DC/DC Converters Adopting Pulsating Voltage Source Cells for Low Power Applications

In the renewable hybrid power system, multiple-input converters (MICs) serve as the interface of several sources with a load, and provide the energy to the load simultaneously or individually, which can optimize the utilization of sources, simplify the system configuration, and reduce the overall cost. In the applications with isolated requirement, available MICs usually have complex configuration and numerous transformer windings. In this paper, a family of asymmetrical half-bridge double-input converters (DICs) adopting pulsating voltage source cells (PVSCs) for low power applications is proposed. Compared with available isolated DICs, the proposed converters have advantages of simple architecture, soft-switching realization, and high conversion efficiency. In this paper, the derivation and feasible control strategy for the proposed converters are illustrated. Specifically, the operation principle of DIC composed of two buck PVSCs is analyzed. Finally, theoretical analysis is validated by the experimental results from a 240 W prototype.

Modeling, analysis and design for hybrid power systems with dual-input DC/DC converter

Hybrid power systems derive power simultaneously from several renewable energy sources and deliver power continuously to the load. For such systems, the use of a multiple-input converter (MIC) has the advantage of simpler circuit design and lower cost, compared to the conventional use of several single-input converters. Taking dual-input Buck converter as the example in this paper, a new power management strategy is first proposed and the multiple operation modes of the system are analyzed. Based on the small signal modeling, a new approach for designing the closed-loop system can be proposed. The system with the designed regulators can operate stably in each operation mode and switch smoothly among the multiple operation modes.

Multi-phase multi-level LLC resonant converter with low voltage stress on the primary-side switches

To satisfy the requirement for high voltage and high power applications, a multi-phase multi-level LLC resonant converter with modular structure was proposed in this paper. The voltage stress on the primary switch is only one-nth of the input voltage due to its multi-level structure, the current rating of power devices can be reduced by introducing the proposed multi-phase structure. Using the variable frequency control strategy, the primary switches can operate with zero-voltage-switching (ZVS) and the rectifier diodes can operate with zero-current-switching (ZCS) in a wide input voltage and load range. Take the topology with three modules for example, the operation principle of the converter under variable frequency control method was analyzed, the equivalent model and voltage gain of the converter were derived according to fundamental harmonic analysis. The parameters were designed under the condition that the switching frequency is higher or lower than the resonant frequency. To validate the feasibility of the proposed converter, a prototype with 540V~660V input and 400V/5A output has been built and tested in the lab and the experimental results can be agree with the theoretical analysis.

Isolated Multiple-Input DC/DC Converter Using Alternative Pulsating Source as Building Cells

Multiple-input dc/dc converters (MICs) serving as the interface of several sources with a load provide the energy to the load simultaneously or individually, which can optimize the utilization of sources, simplify the system structure and reduce the overall cost, so they are attractive for the hybrid renewable power system. In this paper, a novel method using the alternative pulsating sources as the building cells to generate the isolated MICs is proposed. The basic isolated MICs are deduced, and the control strategy is proposed to realize the maximum power transfer, leading to further simplification of the basic isolated MICs. Taking the double-input converter incorporating a half-bridge three-level cell and a full-bridge cell as the example, the operation principles and characteristics of the converter are presented and the power management strategy is introduced. Finally, the theoretical analysis is validated by the simulation and experimental results from a 1000 W prototype.