A new three-input dc-dc boost converter is proposed in this paper. The proposed converter interfaces two unidirectional input power ports and a bidirectional port for a storage element in a unified structure. This converter is interesting for hybridizing alternative energy sources such as photovoltaic (PV) source, fuel cell (FC) source, and battery. Supplying the output load, charging or discharging the battery can be made by the PV and the FC power sources individually or simultaneously. The proposed structure utilizes only four power switches that are independently controlled with four different duty ratios. Utilizing these duty ratios, tracking the maximum power of the PV source, setting the FC power, controlling the battery power, and regulating the output voltage are provided. Depending on utilization state of the battery, three different power operation modes are defined for the converter. In order to design the converter control system, small-signal model is obtained in each operation mode. Due to interactions of converter control loops, decoupling network is used to design separate closed-loop controllers. The validity of the proposed converter and its control performance are verified by simulation and experimental results for different operation conditions.

Modeling and Control of a New Three-Input DC–DC Boost Converter for Hybrid PV/FC/Battery Power System

This paper presents a quantitative method to evaluate dc microgrids availability by identifying and calculating minimum cut sets occurrence probability for different microgrid architectures and converter topologies. Hence, it provides planners with an essential tool to evaluate downtime costs and decide technology deployments based on quantitative risk assessments by allowing to compare the effect that converter topologies and microgrid architecture choices have on availability. Conventional architectures with single-input converters and alternative configurations with multiple-input converters (MICs) are considered. Calculations yield that all microgrid configurations except those utilizing center converters achieve similar availability of 6-nines. Three converter topologies are used as representatives of many other circuits. These three benchmark circuits are the boost, the isolated SEPIC (ISEPIC), and the current-source half-bridge. Marginal availability differences are observed for different circuit topology choices, although architectures with MICs are more sensitive to this choice. MICs and, in particular, the ISEPIC, are identified as good compromise options for dc microgrids source interfaces. The analysis also models availability influence of local energy storage, both in batteries and generators' fuel. These models provide a quantitative way of comparing dc microgrids with conventional backup energy systems. Calculations based on widely accepted data in industry supports the analysis.

https://users.ece.utexas.edu/~kwasinski/05677476%20published.pdf

Quantitative Evaluation of DC Microgrids Availability: Effects of System Architecture and Converter Topology Design Choices

A systematic approach is proposed for the derivation of nonisolated three-port converter (TPC) topologies based on dual-input converters (DIC) and dual-output converters (DOC), which serves as an interface for a renewable source, a storage battery, and a load simultaneously. The power flow in a TPC is analyzed and compared with that in a DIC or a DOC, respectively. Beginning with building the power flow paths of a TPC from a DIC or a DOC, the general principles and detailed procedures for the generation and optimization of TPC topologies are presented. Based on these works, a family of nonisolated TPC topologies is developed. The derived TPCs feature single-stage power conversion between any two of the three ports, and result in high integration and high efficiency. One of the proposed TPCs, named Boost-TPC, is taken as an example for verifying the performance of its circuit topology with related operational methods. Pulsewidth modulation and power management methods, used in this circuit, are analyzed in detail. Experiments have been carried out on a 1-kW prototype of the Boost-TPC, which demonstrate the feasibility and effectiveness of the proposed topology derivation method.

Topology Derivation of Nonisolated Three-Port DC–DC Converters From DIC and DOC

This paper presents a dynamic modeling and control strategy for a sustainable microgrid primarily powered by wind and solar energy. A current-source-interface multiple-input dc-dc converter is used to integrate the renewable energy sources to the main dc bus. Potential suitable applications range from a communication site or a residential area. A direct-driven permanent magnet synchronous wind generator is used with a variable speed control method whose strategy is to capture the maximum wind energy below the rated wind speed. This study considers both wind energy and solar irradiance changes in combination with load power variations. As a case study a 30-kW wind/solar hybrid power system dynamic model is explored. The examined dynamics shows that the proposed power system is a feasible option for a sustainable microgrid application.

Dynamic Modeling and Operation Strategy for a Microgrid With Wind and Photovoltaic Resources

The input-series-output-parallel (ISOP) converter, which consists of multiple dc-dc converter modules connected in series at the input and in parallel at the output, is an attractive solution for high input voltage and high power applications. This paper reveals the relationship between input voltage sharing (IVS) and output current sharing of the constituent modules of the ISOP converter. A novel IVS control strategy, which is decoupled with the output voltage regulation, is proposed. This control allows IVS and output voltage regulation to be designed independently. An ISOP converter, which uses the phase-shifted full-bridge (PS-FB) converter as the basic module, is considered. Based on the proposed control strategy, this ISOP converter together with the control circuit can be decoupled from several independent single-input and single-output systems. An ISOP converter consisting of three PS-FB modules is used to illustrate the design procedure, and a 3-kW experimental prototype is fabricated and tested.

Control Strategy for Input-Series–Output-Parallel 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.

Synthesis of Multiple-Input DC/DC Converters

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.

/pdf/zero-voltage-and-zero-current-switching-pwm-combined-three-alzatyymt1.pdf

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

Phase-shifted ZVS PWM full-bridge converter realizes ZVS and eliminates the voltage oscillation caused by the reverse recovery of the rectifier diodes by introducing a resonant inductance and two clamping diodes. This paper improves the converter just by exchanging the position of the resonant inductance and the transformer such that the transformer is connected with the lagging leg. The improved converter has several advantages over the original counterpart, e.g., the clamping diodes conduct only once in a switching cycle, and the resonant inductance 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 2850 W prototype converter is built to verify the effectiveness of the improved converter and the best scheme for the blocking capacitor.

An improved ZVS PWM full-bridge converter with clamping diodes

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

An Improved ZVS PWM Three-Level Converter

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.

Fuxin Liu

Papers

Synthesis of Multiple-Input DC/DC Converters

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

An improved ZVS PWM full-bridge converter with clamping diodes

An Improved ZVS PWM Three-Level Converter

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