Showing papers on "Flyback converter published in 2015"

Survey on non-isolated high-voltage step-up dc–dc topologies based on the boost converter

Abstract: The major consideration in dc-dc conversion is often associated with high efficiency, reduced stresses involving semiconductors, low cost, simplicity and robustness of the involved topologies. In the last few years, high-step-up non-isolated dc-dc converters have become quite popular because of its wide applicability, especially considering that dc-ac converters must be typically supplied with high dc voltages. The conventional non-isolated boost converter is the most popular topology for this purpose, although the conversion efficiency is limited at high duty cycle values. In order to overcome such limitation and improve the conversion ratio, derived topologies can be found in numerous publications as possible solutions for the aforementioned applications. Within this context, this work intends to classify and review some of the most important non-isolated boost-based dc-dc converters. While many structures exist, they can be basically classified as converters with and without wide conversion ratio. Some of the main advantages and drawbacks regarding the existing approaches are also discussed. Finally, a proper comparison is established among the most significant converters regarding the voltage stress across the semiconductor elements, number of components and static gain.

Comparison of the Modular Multilevel DC Converter and the Dual-Active Bridge Converter for Power Conversion in HVDC and MVDC Grids

Abstract: It is expected that in the near future the use of high-voltage dc (HVDC) transmission and medium-voltage dc (MVDC) distribution technology will expand. This development is driven by the growing share of electrical power generation by renewable energy sources that are located far from load centers and the increased use of distributed power generators in the distribution grid. Power converters that transfer the electric energy between voltage levels and control the power flow in dc grids will be key components in these systems. The recently presented modular multilevel dc converter (M2DC) and the three-phase dual-active bridge converter (DAB) are benchmarked for this task. Three scenarios are examined: a 15 MW converter for power conversion from an HVDC grid to an MVDC grid of a university campus, a gigawatt converter for feeding the energy from an MVDC collector grid of a wind farm into the HVDC grid, and a converter that acts as a power controller between two HVDC grids with the same nominal voltage level. The operation and degrees of freedom of the M2DC are investigated in detail aiming for an optimal design of this converter. The M2DC and the DAB converter are thoroughly compared for the given scenarios in terms of efficiency, amount of semiconductor devices, and expense on capacitive storage and magnetic components.

A Novel High Step-up DC/DC Converter Based on Integrating Coupled Inductor and Switched-Capacitor Techniques for Renewable Energy Applications

Abstract: In this paper, a novel high step-up dc/dc converter is presented for renewable energy applications. The suggested structure consists of a coupled inductor and two voltage multiplier cells, in order to obtain high step-up voltage gain. In addition, two capacitors are charged during the switch-off period, using the energy stored in the coupled inductor which increases the voltage transfer gain. The energy stored in the leakage inductance is recycled with the use of a passive clamp circuit. The voltage stress on the main power switch is also reduced in the proposed topology. Therefore, a main power switch with low resistance $R_{{\rm DS} ({\rm ON})}$ can be used to reduce the conduction losses. The operation principle and the steady-state analyses are discussed thoroughly. To verify the performance of the presented converter, a 300-W laboratory prototype circuit is implemented. The results validate the theoretical analyses and the practicability of the presented high step-up converter.

Quasi Two-Level Operation of Modular Multilevel Converter for Use in a High-Power DC Transformer With DC Fault Isolation Capability

Abstract: DC fault protection is one challenge impeding the development of multi-terminal DC grids. The absence of manufacturing and operational standards has led to many point-to-point HVDC links built at different voltage levels, which creates another challenge. Therefore, the issues of voltage matching and DC fault isolation are undergoing extensive research and are addressed in this paper. A quasi two-level operating mode of the modular multilevel converter is proposed, where the converter generates a square wave with controllable dv/dt by employing the cell voltages to create transient intermediate voltage levels. Cell capacitance requirements diminish and the footprint of the converter is reduced. The common-mode DC component in the arm currents is not present in the proposed operating mode. The converter is proposed as the core of a DC to DC transformer where two converters operating in the proposed mode are coupled by an AC transformer for voltage matching and galvanic isolation. The proposed DC transformer is shown to be suitable for high-voltage high-power applications due to the low switching frequency, high efficiency, modularity, and reliability. The DC transformer facilitates DC voltage regulation and near instant isolation of DC faults within its protection zone. Analysis and simulations confirm these capabilities in a system-oriented approach.

Isolated DC/DC Structure Based on Modular Multilevel Converter

Abstract: In the future, new aspects from decentralized generation using different dc voltage levels are expected to influence the general concept of power exchange. Converter are needed to adapt the voltage between low voltage (LV), medium voltage (MV), and high voltage (HV). In this paper, a galvanic isolated bidirectional dc/dc converter based on the modular multilevel converter is studied, with a large potential for secure and flexible dc power flow control. The use of medium frequency transformation allows savings in copper and iron. A fundamental frequency modulation method is introduced for the presented converter, that enables variable stepup or step-down between primary and secondary dc voltage in discrete steps. The balancing mechanism of the internal power storage components is explained and verified by simulation and experiment.

A Nonisolated Multiinput Multioutput DC–DC Boost Converter for Electric Vehicle Applications

Abstract: A new nonisolated multiinput multioutput dc-dc boost converter is proposed in this paper. This converter is applicable in hybridizing alternative energy sources in electric vehicles. In fact, by hybridization of energy sources, advantages of different sources are achievable. In this converter, the loads power can be flexibly distributed between input sources. Also, charging or discharging of energy storages by other input sources can be controlled properly. The proposed converter has several outputs with different voltage levels which makes it suitable for interfacing to multilevel inverters. Using of a multilevel inverter leads to reduction of voltage harmonics which, consequently, reduces torque ripple of electric motor in electric vehicles. Also, electric vehicles which using dc motor have at least two different dc voltage levels, one for ventilation system and cabin lightening and other for supplying electric motor. The proposed converter has just one inductor. Depending on charging and discharging states of the energy storage system (ESS), two different power operation modes are defined for the converter. In order to design the converter control system, small-signal model for each operation mode is extracted. The validity of the proposed converter and its control performance are verified by simulation and experimental results for different operation conditions.

Electric Vehicle Charging Station Using a Neutral Point Clamped Converter With Bipolar DC Bus

Abstract: This paper proposes a novel architecture for plug-in electric vehicles (PEVs) dc charging station at the megawatt level, through the use of a grid-tied neutral point clamped (NPC) converter. The proposed bipolar dc structure reduces the step-down effort on the dc–dc fast chargers. In addition, this paper proposes a balancing mechanism that allows handling any difference on the dc loads while keeping the midpoint voltage accurately regulated. By formally defining the unbalance operation limit, the proposed control scheme is able to provide complementary balancing capabilities by the use of an additional NPC leg acting as a bidirectional dc–dc stage, simulating the minimal load condition and allowing the modulator to keep the control on the dc voltages under any load scenario. The proposed solution enables fast charging for PEVs concentrating several charging units into a central grid-tied converter. In this paper, simulation and experimental results are presented to validate the proposed charging station architecture.

A Modular Multilevel DC/DC Converter With Fault Blocking Capability for HVDC Interconnects

Abstract: This paper introduces a modular multilevel dc/dc converter, termed the DC-MMC, that can be deployed to interconnect HVDC networks of different or similar voltage levels. Its key features include: 1) bidirectional power flow; 2) step-up and step-down operation; and 3) bidirectional fault blocking similar to a dc circuit breaker. The kernel of the DC-MMC is a new class of bidirectional single-stage dc/dc converters utilizing interleaved strings of cascaded submodules. The DC-MMC operation is analyzed and an open loop voltage control strategy that ensures power balance of each submodule capacitor via circulating ac currents is proposed. Simulations performed in PLECS validate the DC-MMC's principle of operation and the proposed control strategy. Experimental results for a 4-kW laboratory prototype illustrate the single-stage dc/dc conversion process for both step-down and step-up operating modes.

A High Gain Input-Parallel Output-Series DC/DC Converter With Dual Coupled Inductors

Abstract: High voltage gain dc-dc converters are required in many industrial applications such as photovoltaic and fuel cell energy systems, high-intensity discharge lamp (HID), dc back-up energy systems, and electric vehicles. This paper presents a novel input-parallel output-series boost converter with dual coupled inductors and a voltage multiplier module. On the one hand, the primary windings of two coupled inductors are connected in parallel to share the input current and reduce the current ripple at the input. On the other hand, the proposed converter inherits the merits of interleaved series-connected output capacitors for high voltage gain, low output voltage ripple, and low switch voltage stress. Moreover, the secondary sides of two coupled inductors are connected in series to a regenerative capacitor by a diode for extending the voltage gain and balancing the primary-parallel currents. In addition, the active switches are turned on at zero current and the reverse recovery problem of diodes is alleviated by reasonable leakage inductances of the coupled inductors. Besides, the energy of leakage inductances can be recycled. A prototype circuit rated 500-W output power is implemented in the laboratory, and the experimental results shows satisfactory agreement with the theoretical analysis.

High Step-Up Converter With Three-Winding Coupled Inductor for Fuel Cell Energy Source Applications

Abstract: This paper presents a high step-up converter for fuel cell energy source applications. The proposed high step-up dc-dc converter is devised for boosting the voltage generated from fuel cell to be a 400-V dc-bus voltage. Through the three-winding coupled inductor and voltage doubler circuit, the proposed converter achieve high step-up voltage gain without large duty cycle. The passive lossless clamped technology not only recycles leakage energy to improve efficiency but also alleviates large voltage spike to limit the voltage stress. Finally, the fuel cell as input voltage source 60-90 V integrated into a 2-kW prototype converter was implemented for performance verification. Under output voltage 400-V operation, the highest efficiency is up to 96.81%, and the full-load efficiency is 91.32%.

Robust sliding-mode control of dc/dc boost converter feeding a constant power load

Abstract: Tightly regulated power electronic converters show negative impedance characteristics and behave as a constant power load (CPL) which sink constant power from their input bus. This incremental negative impedance characteristics of tightly regulated point-of-load converters in multi-converter power systems have a destabilising effect on source converters and may destabilise the whole system. Similar phenomena also occur in many situations like dc microgrid, vehicular power system. Here, the authors present a robust pulse-width modulation-based sliding-mode controller for a dc/dc boost converter feeding the CPL in a typical dc microgrid scenario. A non-linear surface is proposed which ensures constant power to be delivered to the load. The existence of sliding mode and stability of the sliding surface are proved. The proposed controller is implemented using OPAL-RT real-time digital simulator on a laboratory prototype of dc/dc boost converter system. The effectiveness of the proposed sliding-mode controller is validated through simulation and experimental results under different operating conditions.

DC/DC Buck Power Converter as a Smooth Starter for a DC Motor Based on a Hierarchical Control

Abstract: In this paper a smooth starter, based on a dc/dc Buck power converter, for the angular velocity trajectory tracking task of a dc permanent magnet motor is presented. To this end, a hierarchical controller is designed, which is integrated by a control associated with the dc motor based on differential flatness at the high level, and a control related with the dc/dc Buck converter based on a cascade control scheme at the low level. The control at the high level allows the dc motor angular velocity to track a desired trajectory and also provides the desired voltage profile that must be tracked by the output voltage of the dc/dc Buck power converter. In order to assure the latter, a cascade control at the low level is designed, considering a sliding mode control for the inner current loop and a proportional-integral control for the outer voltage loop. The hierarchical controller is tested through experiments using MATLAB-Simulink and the DS1104 board from dSPACE. The obtained results show that the desired angular velocity trajectory is well tracked under abrupt variations in the system parameters and that the controller is robust in such operation conditions, confirming the validity of the proposed controller.

Improving the Stability of Cascaded DC/DC Converter Systems via Shaping the Input Impedance of the Load Converter With a Parallel or Series Virtual Impedance

Abstract: Interactions between individually designed power subsystems in a cascaded system may cause instability. This paper proposes an approach, which connects a virtual impedance in parallel or series with the input impedance of the load converter so that the magnitude or phase of the load converter's input impedance is modified in a small range of frequency, to solve the instability problem of a cascaded system. The requirements on the parallel virtual impedance (PVI) and series virtual impedance (SVI) are derived, and the control strategies to implement the PVI and SVI are proposed. The comparison and general design procedure of the PVI and SVI control strategies are also discussed. Finally, considering the worst stability problem that often occurs at the system whose source converter is an $LC$ filter, two cascaded systems consisting of a source converter with an $LC$ input filter and a load converter, which is either a buck converter or a boost converter, are fabricated and tested to validate the effectiveness of the proposed control methods.

Effective Test Bed of 380-V DC Distribution System Using Isolated Power Converters

Abstract: This paper proposes an effective test bed for a 380-V dc distribution system using isolated power converters. The proposed test-bed system is composed of a grid-interactive ac–dc converter for regulating the dc-bus voltage, a bidirectional converter for the battery power interface, a renewable energy simulator, dc home appliances modified from conventional ac components, a dc distribution panel board, and its monitoring system. This paper discusses three isolated power converters, i.e., a bidirectional ac–dc converter, a bidirectional dc–dc converter, and a unidirectional dc–dc converter for the effective power interface of a dc bus. These isolated power converters are designed using a dual-active-bridge converter and the resonant topologies of $CLLC$ and $LLC$ . The proposed test-bed system was implemented using a 5-kW bidirectional ac–dc prototype converter, a 3-kW bidirectional dc–dc prototype converter, and a 3-kW unidirectional dc–dc prototype converter. Finally, the performance of the test-bed system has been verified using practical experiments of load variations and bidirectional power flow, employing the prototype converters.

Comparative Analysis of Bidirectional Three-Level DC–DC Converter for Automotive Applications

Abstract: In battery/ultracapacitor electric vehicles, a bidirectional dc/dc converter is employed to process the power according to the power references obtained from the energy management controller. The selection of this converter is of critical importance for the overall system efficiency and size. This study proposes using a three-level dc/dc converter and provides a comprehensive comparison with the conventional two-level and interleaved bidirectional buck/boost converters in terms of magnetic component size/weight and overall efficiency. Unlike the comparative studies presented in the literature, where the efficiency comparison of converters is conducted based on given fixed input and output parameters, power references obtained from a wavelet-transform-based energy management strategy with varying energy source voltages and traction power are considered in this paper. The results of the analyses show that a three-level converter exhibits higher overall efficiency and has smaller size inductor. A 1-kW bidirectional three-level dc/dc converter is designed as a proof of concept, which exhibits 93.2% peak efficiency at 200-kHz switching frequency.

Multicell Switched-Inductor/Switched-Capacitor Combined Active-Network Converters

Abstract: High step-up voltage gain dc/dc converters are widely used in renewable energy power generation, uninterruptible power system, etc. In order to avoid the influence of leakage inductor in coupled inductors based converters, switched-inductor boost converter (SL-boost), switched-capacitor boost converter (SC-boost) and active-network converter (ANC) have been developed. With the transition in series and parallel connection of the inductors and capacitors, high step-up voltage conversion ratio can be achieved. This paper discusses the characteristics of the switched inductor and switched-capacitor cell; makes some comparisons between the ANC and boost converter. Based on the aforementioned analysis, this paper proposed the multicell switched-inductor/ switched-capacitor combined active network converters (MSL/SC-ANC). The proposed converters combine the advantages of SL/SC unit and active-network structure. Compared with previous high step-up converters, the novel converter provides a higher voltage conversion ratio with a lower voltage/current stress on the power devices, moreover, the structure of proposed SL/SC-ANC is very flexible, which means the quantity of SL and SC cells can be adjusted according to required voltage gain. A 20 times gain prototype is designed as an example to show the design procedure. Theoretical analysis and experimental results are presented to demonstrate the feature of the proposed converter.

Novel Modular Multiple-Input Bidirectional DC–DC Power Converter (MIPC) for HEV/FCV Application

Abstract: This paper proposes a novel multiple-input bidirectional dc–dc power converter to interface more than two dc sources of different voltage levels. This finds applications in hybrid electric/fuel cell vehicles (FCVs), where different dc sources of unequal voltage levels need to be connected with bidirectional power flow capability. The converter can be used to operate in both the buck and boost modes with bidirectional power control. It is also possible to independently control power flow between any two sources when more than two sources are actively transferring power in either directions. The operation, analysis, and design of the converter are presented with different modes of power transfer. The proposed converter is demonstrated for FCV application using real-time hardware-in-the-loop system. Experimental results for a 5-kW system are presented, validating the theoretical analysis.

Integrated Dual-Output Converter

Abstract: This paper presents a family of single-input–multiple-output (SIMO) dc–dc converter topologies, which can provide one step-up and multiple step-down outputs. These topologies are synthesized by replacing the control switch of a boost converter topology with series-connected switches and using the additional switch nodes to generate step-down dc outputs. Compared with separate converters, these topologies utilize a lower number of switches and are more reliable due to their inherent shoot-through protection. Analysis shows that the topologies exhibit similar dynamic behavior as individual buck and boost converters. Hence, the control system methodology is the same as that of separate converters, with each output being precisely regulated. The behavior of these converters has been illustrated in this paper using the integrated dual-output converter (IDOC), which has a step-up and a step-down output. The steady-state characteristics and dynamic behavior of the converter have been studied. An analog closed-loop control system for the converter has been described for regulation of both the outputs. The operating principles have been experimentally validated using a 120-W prototype. Results show that the proposed converter has very good cross-regulation to step load change as well as dynamic reference change in either output. The measured efficiencies of the IDOC prototype are around 90%.

An Isolated Three-Port Bidirectional DC–DC Converter for Photovoltaic Systems With Energy Storage

Abstract: This paper proposes a new isolated three-port bidirectional dc–dc converter for simultaneous power management of multiple energy sources. The proposed converter has the advantage of using the least number of switches and soft switching for the main switch, which is realized by using an inductor–capacitor–inductor ( $LCL$ ) -resonant circuit. The converter is capable of interfacing sources of different voltage–current characteristics with a load and/or a dc microgrid. The proposed converter is constructed for simultaneous power management of a photovoltaic (PV) panel, a rechargeable battery, and a load. Simulation and experimental results show that the proposed converter is capable of maximum power point tracking control for the PV panel, when there is solar radiation, and controlling the charge and discharge of the battery, when there is surplus energy and power deficiency with respect to the load, respectively.

An Interleaved High-Power Flyback Inverter for Photovoltaic Applications

Abstract: This paper presents analysis, design, and implementation of an isolated grid-connected inverter for photovoltaic (PV) applications based on interleaved flyback converter topology operating in discontinuous current mode In today's PV inverter technology, the simple and the low-cost advantage of the flyback topology is promoted only at very low power as microinverter Therefore, the primary objective of this study is to design the flyback converter at high power and demonstrate its practicality with good performance as a central-type PV inverter For this purpose, an inverter system rated at 2 kW is developed by interleaving of only three flyback cells with added benefit of reduced size of passive filtering elements A simulation model is developed in the piecewise linear electrical circuit simulator Then, the design is verified and optimized for the best performance based on the simulation results Finally, a prototype at rated power is built and evaluated under the realistic conditions The efficiency of the inverter, the total harmonic distortion of the grid current, and the power factor are measured as 9016%, 442%, and 0998, respectively Consequently, it is demonstrated that the performance of the proposed system is comparable to the commercial isolated PV inverters in the market, but it may have some cost advantage

Soft-Switching DC–DC Converter for Distributed Energy Sources With High Step-Up Voltage Capability

Abstract: This paper presents high step-up dc-to-dc converter for low voltage sources such as solar photovoltaics, fuel cells, and battery banks. To achieve high voltage gain without large duty cycle operation, combination of coupled inductor and switched capacitor voltage doubler cells are used. By incorporating active clamp circuit, voltage spike due to the leakage inductance of the coupled inductor is alleviated and zero-voltage switching turn on of the main and auxiliary switch is obtained. Due to the use of MOSFETs of low voltage rating and soft turn on of the switches, conduction loss and switching losses are reduced. This improves the efficiency and power density of the converter. The proposed converter can achieve high voltage gain with reduced voltage stress on MOSFET switches and output diodes. Design and analysis of the proposed converter is carried out, and finally, a 500-W experimental prototype is built to verify theoretical analysis.

A Novel Switched-Coupled-Inductor DC–DC Step-Up Converter and Its Derivatives

Abstract: This paper presents a novel dc–dc converter configuration, which successfully integrates two technologies, including a switched capacitor and a switched coupled inductor, into one converter. By adopting a coupled inductor to charge a switched capacitor, the voltage gain can be effectively increased, and the turns ratio of the coupled inductor can be also reduced. Not only lower conduction losses but also higher power conversion efficiency is benefited from a lower part count and lower turns ratios. The proposed converter is simply composed of six components, which can be further derived to varied converters for different purposes, such as a bidirectional converter. The operating principle and steady-state analysis are discussed in this paper. A 250-W laboratory hardware prototype is completed and verified. The voltage gain is up to 11. The highest efficiency is 97.2%, and the full-load efficiency is kept at 93.6%.

Y-Source Boost DC/DC Converter for Distributed Generation

Abstract: This paper introduces a versatile Y-source boost dc/dc converter intended for distributed power generation, where high gain is often demanded. The proposed converter uses a Y-source impedance network realized with a tightly coupled three-winding inductor for high voltage boosting that is presently unmatched by existing impedance networks. The proposed converter also has more variables for tuning the required gain and, hence, more degrees of freedom for meeting design constraints. These capabilities have been demonstrated by mathematical derivation and experimental testing. For the experiments, a 300-W prototype has been built in the laboratory using silicon carbide devices for better efficiency. The prototype has been tested with a regulated power supply, before operating it with a high-temperature proton-exchange-membrane fuel cell. Results obtained confirm the practicality and performance of the proposed converter.

Finite Control-Set Model Predictive Control (FCS-MPC) of Nested Neutral Point-Clamped (NNPC) Converter

Abstract: This paper proposes a model predictive control (MPC) strategy for a nested neutral point-clamped (NNPC) converter to control output currents and voltages of flying capacitors. The NNPC converter is a four-level converter topology for medium-voltage applications with interesting properties such as operating over a wide range of voltages (2.4–7.2 KV) without the need for connecting power semiconductor in series, high quality output voltage, less number of components compared to other classical four-level topologies. A discrete-time model of the converter is presented and all the control objectives are formulated in terms of the switching states. During each sampling interval, the predicted variables are assessed by the cost function and the best switching state which gives minimum value for the cost function is selected and applied to the converter gating terminals. The performances of the NNPC converter and predictive control scheme are verified through MATLAB/Simulink simulations and their feasibility is evaluated experimentally.

A Hybrid Modular Multilevel Converter With Novel Three-Level Cells for DC Fault Blocking Capability

Abstract: A novel hybrid, modular multilevel converter is presented that utilizes a combination of half-bridge and novel three-level cells where the three-level cells utilize a clamp circuit which, under dc side faults, is capable of blocking fault current thereby avoiding overcurrents in the freewheel diodes. This dc fault blocking capability is demonstrated through simulation and is shown to be as good as the modular multilevel converter which utilizes full-bridge cells but with the added benefits of: lower conduction losses; fewer diode and semiconductor switching devices, and; fewer shoot-through modes. The semiconductor count and conduction loss of the proposed converter are reduced to around 66.5% and 72% of that of modular multilevel converter based on the full-bridge cells respectively, yielding lower semiconductor cost and improved efficiency. Dc fault ride-through operation is realized without exposing the semiconductors to significant fault currents and overvoltages due to the full dc fault blocking capability of the converter.

Novel High Step-Up DC–DC Converter With an Active Coupled-Inductor Network for a Sustainable Energy System

Abstract: In this letter, a novel high step-up dc–dc converter with an active coupled-inductor network is presented for a sustainable energy system. The proposed converter contains two coupled inductors which can be integrated into one magnetic core and two switches. The primary sides of coupled inductors are charged in parallel by the input source, and both the coupled inductors are discharged in series with the input source to achieve the high step-up voltage gain with appropriate duty ratio, respectively. In addition, the passive lossless clamped circuit not only recycles leakage energies of the coupled inductor to improve efficiency but also alleviates large voltage spike to limit the voltage stresses of the main switches. The reverse-recovery problem of the output diode is also alleviated by the leakage inductor and the lower part count is needed; therefore, the power conversion efficiency can be further upgraded. This letter shows the key waveforms of the proposed converter and the detailed derivation of the steady-state operation principle. The voltage conversion ratio, the effect of the leakage inductance and the parasitic parameters on the voltage gain are discussed. The voltage stress and current stress on the power devices are illustrated and the comparisons between the proposed converter and other converters are given. Finally, a prototype circuit rated 200-W output power is implemented in the laboratory, and the experimental results show the satisfactory agreement with the theoretical analysis.

A Family of Multiport Buck–Boost Converters Based on DC-Link-Inductors (DLIs)

Abstract: A systematic method for derivation of a multiport converter (MPC) based on the dc-link inductor (DLI) concept is proposed in this paper. The MPC is generated by interconnecting multiple pulsating voltage cells (PVCs) through the DLIs. The PVCs can be input type, output type, and bidirectional type, and bidirectional MPC topologies can be harvested if all the PVCs are bidirectional type. As a result, a family of novel MPCs, including multiinput converters, multioutput converters, and bidirectional MPCs, are derived. With the proposed MPCs, step-up and step-down voltage conversion between any two of the ports can be implemented. As an example, the three-port bidirectional buck-boost (TP-B 3 ) converter is analyzed and applied to a stand-alone renewable power system for interconnection of three dc subsystems. The operation principles, pulse width modulation, and feed-back control strategies are presented and analyzed in depth. The analysis indicates that, compared to the traditional common dc-bus-based solution, bulky dc-link capacitor is eliminated and single-stage conversion between any two of the three dc-buses are achieved with the TP-B 3 converter, which is beneficial for higher efficiency, power density, and reliability. Experimental results are given to verify the feasibility and effectiveness of the developed TP-B 3 converter.

High step-up DC–DC converter based on the switched-coupled-inductor boost converter and diode-capacitor multiplier: steady state and dynamics

Abstract: In this study a new scheme of a step-up converter with very high voltage gain is proposed. The scheme is based on a natural combination of the switched-coupled-inductor boost converter and the diode-capacitor multiplier. The study proposes a special scheme of their mutual use for attaining very high voltage gain. An important advantage of the proposed circuit is the avoidance of the current spikes through the transistor and diodes because of the leakage inductance of the coupled inductors. The scheme provides soft commutation of the switch and the diodes. The study analyses the modes of operation and obtains the basic fundamental relations in steady state; an expression for voltage stress across the switch is derived. A new method for dynamic analysis is proposed. The corresponding analytical expressions and curves of the transient behaviour are also obtained. Modelling of the proposed structure and the experimental results are in full agreement regarding the expected efficiency and correctness of the theoretical analysis. A 100 W laboratory prototype was built and verified.

High-Gain Resonant Switched-Capacitor Cell-Based DC/DC Converter for Offshore Wind Energy Systems

Abstract: With the increasing integration of renewable energy generation into high-power grids, transmission at the dc level is becoming increasingly more useful than ac transmission. In this regard, emerging applications, such as offshore wind farms, require a high voltage gain dc/dc conversion system to interface with high-power transmission networks. This paper presents a new high-voltage gain resonant switched-capacitor dc/dc converter for high-power offshore wind energy systems. The proposed dc/dc converter is characterized by the resonant switching transitions to achieve minimal switching losses and maximum system efficiency. Therefore, a higher switching frequency is conceivable to attain a higher power density. The double stage output voltage of the proposed converter operates at seven times as high as the input voltage with a small device count. The output capacitors are charged and discharged continuously by a 180° phase shift with respect to each other to eliminate the output voltage ripples with the low capacitance requirements. The proposed series-modular and cascade configurations show the intrinsic advantage of being readily applicable to multistage power switching converters. The developed topology has been implemented on a 5-kW prototype converter to test its feasibility.

Integration of Wind Power and Wave Power Generation Systems Using a DC Microgrid

Abstract: In order to study the uncertainty and intermittent characteristics of wind power and wave power, this paper proposes an integrated wind and wave power generation system fed to an ac power grid or connected with an isolated load using a dc microgrid. The proposed dc microgrid connects with a wind power generator through a voltage-source converter (VSC), a wave power generator through a VSC, an energy storage battery through a bidirectional dc/dc converter, a resistive dc load through a load dc/dc converter, and an ac power grid through a bidirectional grid-tied inverter. The studied integrated wind and wave system joined with the dc microgrid is modeled and simulated using the written program based on MATLAB/Simulink. Root-loci plots of the studied system under various speeds of the wave generator are analyzed. To examine the fundamental operating characteristics of the studied integrated system joined with the dc microgrid, a laboratory-scale platform is also established. Comparative simulation and experimental results reveal that the studied integrated system can maintain stable operation to supply power under different operating conditions using the proposed dc microgrid.