bidirectionalDC-DC converters in  , and  just need four semiconductors, the maximum voltage stress of the converter in  is that of the high voltage side, and the maximum voltage stress of the converter in  is higher than that of the high voltage side. The bidirectional converters in  , and  only require three semiconductors. But their voltage-gain ranges are still small. In addition, the low-voltage and high-voltage side grounds of these converter are connected by a power semiconductor or an inductor, which will also cause extra EMI problems. Finally, the high voltage-gainconverter in  needs more power components and fails to achieve bidirectional power flows. In addition, the balanced inductor currents just can be achieved when the number of the voltage multiplier stages is odd. The converter in  suffers from the huge current ripple in the low-voltage side.
ABSTRACT: In this paper, an interleavedswitched-capacitorbidirectionaldc-dcconverter with a high step-up/step- down voltagegain is proposed. The interleaved structure is adopted in the lowvoltage side of this converter to reduce the ripple of the current through the low-voltage side, and the series-connected structure is adopted in the high-voltage side to achieve the high step-up/stepdown voltagegain. In addition, the bidirectional synchronous rectification operations are carried out without requiring any extra hardware, and the efficiency of the converter is improved. Furthermore, the operating principles, voltage and current stresses, and current ripple characteristics of the converter are analyzed. Finally, a 1 kW prototype has been developed which verifies a widevoltagegainrange of this converter between the variable low-voltage side (50–120 V) and the constant high-voltage side (400 V). The maximum efficiency of the converter is 95.21% in the step-up mode and 95.30% in the step-down mode. The experimental results also validate the feasibility and the effectiveness of the proposed topology.
In some applications, dc-dc converters are required to achieve the galvanic isolation and the high voltagegain. Therefore, the Fly-back, forward or full bridge phase shifted dc-dc converters can often be used. When the galvanic isolation is not required, the traditional bidirectional buck/boost dc-dcconverter can be applied when power flows in both directions are required. Other standard bidirectionaldc-dc converters can also be applied in various energystoragesystems. Each converter has its own advantages and disadvantages in terms of the voltagegain, the component count and the voltage stress . By adding additional capacitors and power switches, the conventional buck/boost converter can be improved to the three level , four level  or multilevel converters  for a wider operation range of the higher voltagegain. However, the multilevel dc-dc converters need more power switches, additional hardware circuits and control strategies to maintain the balance of the voltage stresses across the power switches and capacitors. Other known dc-dc converters, such as Cuk/Sepic/Zeta converters, can also be modified into bidirectional topologies, but these unique structures may limit the efficiencies of the converters -.
A new non-isolated single capacitorbidirectionalDC-DCconverter is presented in . Although it has a widevoltagegainrange, the voltage stress on the power switches is relatively high. In , a switched-capacitor-based DC-DCconverter is proposed. Although the voltagegain is improved, more devices are used, and the converter does not have a common ground. A bidirectionalswitched-capacitorDC-DCconverter is presented in . This converter improves the efficiency, but the converter needs more power switches. A hybrid bidirectionalconverter with a switched-capacitor cell, which is suitable for a DC microgrid, is proposed in . It has a wider voltagegainrange and lower power voltage stress across the power switches, but the converter does not have an absolute common ground between the input and output sides, which produces an additional du/dt issue between the input and output grounds. Thus, its applications are limited. In , a novel coupled- inductor bidirectionalDC-DCconverter is proposed with increased voltagegain. However, the leakage inductance of the coupled inductor and the additional du/dt problems between the input and output grounds should be considered additionally, and the voltage stress on the power switches that are near the high voltage side is too high.
ABSTRACT: In this paper we describe about the utilization of braking energy during regenerative braking operation by using different cascaded multilevel topologies by interfacing of the super capacitor to dc bus in the regenerative applications. Energystorage plays an important role in the high power application. Super capacitors are chosen because they have high density, efficiency and long life cycles. The modular multilevel dc/dcconverter (MMC) is used to reduce voltage and increase frequency across the inductor in order to reduce the weight and size of the inductor with phase shifting modulation. The circuit is used as a bi-directional power source and converter. The super capacitors are used for voltage balancing for output current control. The proposed system is plays an important role in hybrid and electric vehicle applications
The PEM fuel cell presents a low-voltage output with widerange of variations -.As shown in fig. 1 a step-up dc-dcconverter is always necessary for providing a regulated high-voltage output to the post stage dc-ac inverter in high-power grid –tied applications. For PEM fuel cell system applications, the dc-dcconverter must be considered with following design criteria: large step-up ratio, low-input-current ripple and isolation-.Input choke with high inductance is needed at low voltage side because high ripple current may cause undesired hysteresis energy losses inside the fuel cell stacks-.Increased power loss and component size on input choke are significant to result in poor conversion efficiency and low power density for the step-up dc-dcconverter in high power PEM fuel-cell systems.
Power Generation by Non-renewable resources result in Pollution around the world. The Depletion of these resources prove to be a Major Concern for Future Generation. Thus the Need for Alternative Power Sources are Essential. Out of the available Renewable sources, solar Power Generation has a better Potential and Most Reliable among the others and they are also the Fast Developing Alternative Power Source in the Present Time. MPPT Controller helps in Improving and Utilizing the available Source in the Maximum Possible way. The conventional Boost Converters for High Voltage Step Gain have Higher Ripple Current and Voltage which are responsible for Losses. Further they are affected by the pulsating input current due to the switched operation of capacitors or inductors. For minimizing these Losses and also to improve the Overall Efficiency, the Interleaved Operation is suggested. This Converter setup makes use of the Multiplier circuits to improve the Output Voltage. The Coupled Transformer will reduce the Cost. The Leakage Inductance will be fed back to the Transformer. The Converter and the Coupled Inductors are present along with the Voltage Multiplier circuit are used for the operation. The Converter decreases the Inrush Current in the Inductor which improves the Performance and thereby reducing the Stress.
The BidirectionalDC-DC converters serves the purpose of stepping up or stepping down the voltage level between its input and output along with the capability of power flow in both the directions. BidirectionalDC-DC converters have attracted a great deal of applications in the area of energystoragesystems for Hybrid Vehicles, Renewable energystoragesystems, uninterruptable power supplies and fuel cell storagesystems. Traditionally they were used for the motor drives for the speed control and regenerative braking. The bidirectionalDC-DC converters are employed when the dc bus voltage regulation has to be obtained along with the power flow capability in both the direction . One such example is the power generation by wind or solar power systems, where there is a large fluctuation in the generated power because of the large variation and uncertainty of the energy supply to the conversion unit (wind turbines and PV panels) by the primary source. These systems cannot act as a standalone system for power supply because of these large fluctuations and therefore these systems are always backed up and supported by the auxiliary sources which are rechargeable such as battery units or super capacitors. These sources supplement the main system at the time of energy deficit to provide the power at regulated level and get recharged through main system at the time of surplus power generation or at their lower threshold level of discharge. Therefore a bidirectionalDC-DCconverter is needed to allow power flow in both directions at the regulated level. Principle of the switched-diode-capacitor cell is that: when the main switch S 1 is turned on, diodes D 1 , D 2 are turned off with capacitors C 1 , C 2 discharged in series and
This study uses a supercapacitor bank as the energystorage element, which is connected to the dc-link through a bidirectionaldc-dcconverter. Supercapacitors have the advantage of long life, high- power density, attractive temperature range, and high charge-discharge efficiency . The SCES is integrated into the OWC electrical power converter system to achieve smooth power delivery to the grid despite varying sea conditions. With the recent advancements of energystorage technologies, supercapacitors have become popular and commercially available for large power applications, such as WEC systems. The supercapacitor specification sheet in , confirms that the industrial 83 F or 165 F supercapacitor single modules with 48 Vdc can be connected in series and/or parallel configurations to gain the required voltage and capacity. Moreover, these modules provide up to 1,000,000 charge/discharge cycles. In this particular system, to attain the required voltage of the SCES (1000 V), a minimum 21 of 48 V modules are needed to connect in series, which results in the decrease of the total capacitance and increase of the internal resistance (𝑅 ) in each pole. Then, these high voltage modules can be connected in parallel to obtain the required total capacitance to gain the energystorage capacity that decreases 𝑅 . Considering 𝑅 , which represents only static losses, the stored energy and instantaneous voltage of the supercapacitor are given by the following :
Switched-capacitorconverter structures and control strategies are simple and easy to expand. They use different charging and discharging paths for the capacitors to transfer energy to either the low-voltage or the high-voltage side to achieve a high voltagegain. Thus, the switched-capacitorconverter is considered to be an effective solution to interface the super-capacitors with the high voltageDC bus. Single capacitorbidirectionalswitched-capacitor converters were proposed in , , but the converter’s efficiency is low. The efficiency of the converter in  has been improved through soft-switching technology, but it required many extra components.  proposed a multi-level bidirectionalconverter with very low voltage stress across the power semiconductors, but twelve semiconductors are needed, and the drawbacks of low voltagegain, complex control and structure limit its application. The high voltagegainbidirectionalDC-DC converters in ,  need only four semiconductors. However, the maximum voltage stress of the converter in  is that of the high voltage side, and the maximum voltage stress of the converter in  is higher than that of the high voltage side, which will increase switching losses and reduce the conversion efficiency of these converters. The bidirectionalconverter in  only requires three semiconductors, but its voltage-gainrange is still small. In addition, the low-voltage and high-voltage side grounds of this converter are connected by an inductor, which will also generate extra EMI problems. Finally, the converter in  has improved the conversion efficiency greatly, but it needs three inductors and a higher number of power semiconductors which increases the conduction losses and makes the design more challenging. Although exponential switched-capacitor converters have high step-up capabilities, they operate relatively poorly with respect
Abstract—In order to match voltages between the fuel cell stacks and the DC link bus of fuel cell vehicles, a single-switch Boost DC-DCconverter with diode-capacitor modules is proposed in this paper. The capacitors are charged in parallel and discharged in series. The widevoltage-gainrange can be obtained by using a simple structure. In addition, the basic operating principles, the extended stages, the fault tolerant operation, and steady-state characteristics of the converter are analyzed and presented in this paper, and the small-signal model is also derived. A 400V, 1.6kW experimental prototype is developed, and the widevoltage-gainrange (3.3~8) is demonstrated with a maximum efficiency at 97.25%. The experimental results validate the effectiveness and feasibility of the proposed converter and its suitability as a power interface for fuel cell vehicles.
The designed converter rated for 200Wwas simulated using MATLAB Software to verify the analysis, design and performance of the converter. The simulation result for two input voltages at peak power had been taken. Since PV modules have nonlinear V -I characteristics, its MPP varies dramatically with environmental factors such as solar irradiance and temperature. For a typical PV module, the MPP voltage ranges from 20 to 45 V at a power range of 100 to 300 W. The power generation has high variability that can drop by 80% due to shading and clouds. To achieve high efficiency, the power converter must show high performance for such varying conditions. The results have been taken for charging and discharging condition of battery.
efficiency includes the high frequency losses in the magnetics (detailed in section VI), the DC losses in the magnetics (DC resistances given in Table.V), semiconductor losses (calculated from the data sheet  of the semiconductor in the power circuit) and stand-by losses in the power circuit (like losses in the bleeder resistors). The round trip efficiency of ≥ 96% is obtained in the 40-100% of the power range. At full load, the percentage contribution of the various losses in the round-trip efficiency calculation of the DC-DCconverter is listed in Table. I.
A standalone photovoltaic (PV) system with energystorage requires a complex control architecture to take into account the various operating modes. This paper presents a flexible architecture of a PV power conditioning system with energystorage is executed. It consists of boost converter, a single-phase inverter, and bidirectionalDC/DCconverter connected to the PV side of the boost converter. The boost converter regulates the dc-link bus-voltage. The bidirectionalDC/DCconverter used for battery charge/discharge control and PV maximum power point tracking. The multi loop PI controller used to control the operation of DC to DCconverter. In this system there is no change in controller configuration when the storage disconnects.
In this case, combining renewable energy sources with energystorage system will be a better option. Battery is commonly used for storing energy. Battery has many advantages like long life span, low initial cost, high energy density. But has disadvantages such as slow dynamic response and low power density. So, can’t be operated at sudden load or power changes. Supercapacitor can operate at sudden load or power changes. Advantages of supercapacitor are fast charging or discharging time, has long life span and easy maintenance. Hence, hybrid energystorage system comprising battery together with supercapacitor is used for improving of system’s performance. Battery stores energy under steady state and supercapacitor stores energy during transient state (i.e) at sudden changes on load or power.
Renewable-energy-based micro-grids have appeared to be a better way of exploiting renewable energy and reducing the environmental risks of fossil fuels. In the view of the fact that most renewable energy sources (RES), such as photovoltaic (PV), fuel cell (FC) and variable speed wind power systems, generate either DC or variable frequency/ voltage AC power, a power–electronics interface is an indispensable element for the grid integration [1, 2]. In addition, modern electronic loads such as computers, plug-in hybrid electric vehicles and even traditional AC loads such as induction motors, when driven by a variable speed drive require DC power. The multilevel inverters have been considered as a key element in such grid-connected systems. Producing an acceptable sinusoidal voltage waveform at the output and boosting the output voltage are two challenging issues. Using a transformer in the boost multilevel inverter increases the size and cost and decreases the efficiency of the system due to its bulky inductors. Multilevel Inverters (MLI) began with the neutral point clamped inverter topology proposed by Nabae et al. .
ABSTRACT: This paper proposes a soft switching converter with high voltagegain for ac and dc photovoltaic applications. Day to day energy usage is snowballing significantly. Dc-Dc converters are the major consequence in renewable grid connected power applications because of the low voltage PV arrays. This shortcoming is overcome by using a novel soft switching dc-dcconverter. This proposed concept is used to change the power efficiency by boosting voltage and also reduces the switching losses and efficiency. This problem is handled by using a high gaininterleaveddc boost converter with capacitor and leakage inductor. A passive clamp network round the inductors affords the recapture of energy through leakage inductance leading to upgrading in the voltagegain and efficiency. The benefit of passive clamp network is that it condenses voltage stress on the switch. This proposed converter is designed and implemented by MATLAB/Simulation software and the results are results are validated.
circuit was studied in  and , and it can achieve flexible voltage regulation by combination with other DC-DC converters -. A Z source DC-DCconverter with a cascaded switched-capacitor has been presented in , which can improve the voltage-gain of the Z source Boost DC-DCconverter by using the voltage multiplier function of the switched-capacitor. However, compared with the quasi-Z source network, this converter may induce additional maintenance safety issues for fuel cell vehicles, due to the penalty of the discontinuous input current and non-common grounds between the input voltage source side and the load side. In this paper, a quasi-Z source Boost DC-DCconverter with a switched-capacitor is proposed for improving the voltage-gain and reducing the voltage stress across the components. This paper is organized as follows: In Section II, the configuration and operating principles of the proposed converter are analyzed in detail. The parameter design and dynamic modeling are presented in Section III . In Section IV, the detailed application of the proposed converter for fuel cell vehicles is addressed. In Section V, experimental results are presented to validate the features of the proposed converter.
which ought to be sinusoidal and in stage with the utility voltage. The dc–dc power converter supplies two free voltage sources with numerous connections and performs most extreme force point following (MPPT) so as to concentrate the greatest yield power from sun based cell array. A swell voltage with a recurrence that is twofold that of the utility shows up in the voltages of C 1 and C 2 , when the seven-level inverter encourages genuine force into the utility. The
The gate signals for the mosfet are driven by the PWM IC SG3524. The choice of selecting the capacitors is explained in . The totem pole switches and the buffer circuits are used to drive the P-channel mosfet since the gate signals have to be inverted and the optocoupler IC 3120 is used to drive the N-channel mosfet and the optocoupler is powered by the voltage across the transfer capacitor C T .