Analysis, Design, Modeling and Control of an Interleaved-Boost Full-Bridge Three-Port Converter for Hybrid Renewable Energy Systems
Abstract
This paper presents the design, modelling and control of a three-port (TPC) isolated dc-dc converter based on interleaved-boost-full-bridge with pulse-width-modulation and phase-shift control for hybrid renewable energy systems. In the proposed topology, the switches are driven by phase-shifted PWM signals, where both phase angle and duty cycle are controlled variables. The power flow between the two inputs is controlled through the duty cycle, whereas the output voltage can be regulated effectively through the phase-shift. The primary side MOSFETs can achieve zero-voltage switching (ZVS) operation without additional circuitry. Additionally, due to the ac output inductor, the secondary side diodes can operate under zerocurrent switching (ZCS) conditions. In this work, the operation principles of the converter are analyzed and the critical design considerations are discussed. The dynamic behavior of the proposed ac inductor based TPC is investigated by performing state-space modelling. Moreover, the derived mathematical models are validated by simulation and measurements. In order to verify the validity of the theoretical analysis, design and power decoupling control scheme, a prototype is constructed and tested under the various modes, depending on the availability of the renewable energy source and the load consumption. The experimental results show that the two decoupled control variables achieve effective regulation of the power flow a the three ports.
EXISTING SYSTEM:
In order to fulfil different system requirements, various hybrid system configurations and converter topologies have been proposed and investigated as reviewed. In applications where galvanic isolation is required, there are basically two categories classified as: multiple-converter conversion and multiple-port conversion. In the multiple converter configurations, power converters are connected in parallel or in series in order to couple the energy sources and loads. By contrast, multiple-port power conversion systems can have high power density and low cost, due to the fact that some components and circuits in various power ports, such as transformers, rectifiers and output filters, can be shared as a common part along the power conversion path. Therefore, multiple-port converters have been receiving increased attention in recent years. A general solution to obtain an isolated multiple-port converter is to adopt the magnetic coupling method, where various input power sources can be coupled with transformer windings or independent transformers. In this solution, the multiport converter can be constructed from the basic high frequency switching cells, including the half-bridge (HB), full-bridge (FB), boost-half-bridge (BHB) and their combinations, according to the system constraints imposed by the features of the input power sources. Based upon this principle, a number of three-port (TPC) bidirectional dc-dc converters, which can fully isolate the various power ports and control the power flows into/out of each port, were reported. However, a large number of power switches have to be employed in those converters, resulting in increased cost and size. Besides the fully isolated multi-port topologies, partially isolated multiple-input converters, i.e. only some of the input/output ports are fully isolated, have been attracting more attention due to simple structure, less components and easy control.
PROPOSED SYSTEM:
The goal of this work is to propose, analyse and design a TPC topology for hybrid renewable energy systems. The proposed topology, as illustrated in Fig. 1, is derived from a ZVS HB inductive dc-dc converter with an active clamped circuit. By replacing the clamp capacitor in the ZVS circuit with the second voltage source, an additional input port can be obtained. Compared to the topologies , the rectifier diodes achieve zero-current switching (ZCS) at turn-off avoiding reverse recovery losses. Additionally, the voltage across the diodes is inherently clamped by the output capacitor C , therefore, voltage rings caused by the stray inductance can be eliminated. Furthermore, the secondary freewheeling current is limited due to the absence of a dc output inductor. Moreover, this converter is superior to its LLC counterparts due to lower complexity of the modulation and control. Compared to previous research on TPC topologies, modelling and analysis of dynamic performance with multiple control parameters are seldom reported. The major contribution of this paper is to analyse the relation between the two control variables, phase-shift and duty cycle, and the system dynamics based on the converter small-signal model. The derived mathematical model is verified by simulations as well as experimental measurements. Based on the small-signal model, the power flow control is designed and the converter is tested under various operation modes, i.e. dual input (DI) mode, dual output (DO) mode and single input single output (SISO) mode.
CONCLUSION
In this paper, an isolated soft-switched TPC to interface with hybrid renewable energy systems is presented. Its operating principle and design considerations are discussed and verified by simulation and experimental results. In order to control the power flow between the different ports, a duty cycle and phase-shift control scheme is adopted. The duty cycle is used to control the power flow between the two independent sources, whereas the phase-shift angle is employed to regulate the output voltage. The state-space modelling and control of the proposed TPC operating in completely demagnetized and fully magnetized mode is presented. The mathematical model is validated by simulation as well as experimental measurements of the plant and line-tooutput transfer functions. The advantage of the proposed topology is that it can be dynamically modelled as individual converters, which makes it possible to design a control strategy with totally uncoupled control variables. This fact makes this topology a very interesting solution in renewable energy applications where an energy storage element is required, since full reutilization of the converter primary side switches is achieved, without having a negative impact in the controllability of the converter. By selecting the renewable source and the energy storage voltages, V 1 and V , to require a duty cycle approximately to 0.5 the phase-shift value range 2 V O (50 V/div) 1 2 1 I O (200 mA/div) . Transition between different operating modes due to variations of the output port load demand. Time scale: 50 ms/div. can be fully utilized. Experimental results demonstrate that the proposed energy/power management solution achieves effective control of the power flow a the input, bidirectional and output ports.
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