Non-isolated Converter Research Articles

Design and Implementation AC Fed Closed Loop Zeta Converter

DC-DC converters plays very important role in the field of power electronics. There are mainly classified as isolated and non-isolated dc-dc converters. The non-isolated converters are found to be advantageous over the isolated converters due to less size, higher power density, more efficient for higher rating and controlling is easier. The ZETA CONVERTER is non-isolated topology that provides regulated output voltage. Zeta converter produces output voltage, greater or lesser than input with non-inverted output. Zeta converter generates the lower output voltage ripple compared to SEPIC converter and it is easier to provide compensation. The objective of this paper is to design and implement zeta converter fed by diode bridge rectifier in closed loop method. The expressions of zeta converter operating in conduction mode is presented. For the pwm generation SG3525 ic is utilized. The hardware model is developed on pcb and results are analysed.

A High Voltage Gain Step-up Resonant DC-DC Converter Topology with Reduced Switch Count

The resonant converters have attracted a lot of attention because of their high efficiency and low switching losses. This paper presents the analysis of a high voltage gain non-isolated step-up DC-DC converter topology using resonant technology. The proposed converter configuration has reduced number of power semiconductor switches compared to the existing isolated converter topology having four semiconductor switches. The proposed topology employs capacitor-inductor-capacitor (C-L-C) resonant circuit configuration. The size of the proposed converter and the losses in the converter are greatly reduced. Both the converters with resonant components are simulated in Matlab/Simulink platform to validate their performance. The time-domain simulation results demonstrate that the proposed non-isolated converter gives improved voltage gain compared to the existing two-stage isolated resonant DC-DC converter.

Radiated Emission Due to Common Mode Current in Smps

The high frequency switching of semiconductor switches in Switched Mode Power Supplies (SMPS) cause high dV/dt and dI/dt resulting in differential mode (DM) and common mode (CM) conducted and radiated Electromagnetic Interference (EMI). The CM noise current circulating through the ground path is the major contributor for radiated EMI in the frequency range of 30 MHz to 1 GHz which will usually be above the stipulated international standards and are addressed here. The high dV/dt and dI/dt are major sources of EMI producing noise currents which will get coupled to ground through parasitic capacitances. The prominent parasitic capacitors are present in high frequency transformer and the semiconductor’s coupling to ground. They provide path for both DM and CM noise currents. The CM currents flowing in the different prominent parasitic capacitors are obtained by simulation for the four different topologies namely, non-isolated Buck, non-isolated Boost, Flyback and Forward converters. The radiated Emissions are calculated for each of the topologies and are presented. All the four converters are operated at same switching frequencies with same values of parasitic capacitances. The non-isolated Boost converter is found to generate higher radiated emissions due to CM current than the non-isolated buck converter and Forward converter has higher radiated emissions than Flyback converter. The results presented here can be used to decide on the topology of SMPS for a given application when EMI mitigation is a priority

Improved bidirectional DC/DC converter configuration with ZVS for energy storage system: analysis and implementation

This study proposes a novel design of soft-switching based bidirectional converter for the applications in energy storage systems. By implementing an additional auxiliary circuit to the conventional non-isolated converter, the proposed converter inherits better efficiency with minimised turn-on losses. Moreover, auxiliary switching devices are also soft-switched. This converter can be operated at high power outputs through ZVS turn-on operation. The operation principle, design analysis and experimental results are reported to validate its main features in the study. Furthermore, the performance of this converter is analysed on a 1 kW laboratory prototype for both boost and buck modes.

A new lossless snubber for DC-DC converters with energy transfer capability

In this paper, a new passive lossless snubber circuit with energy transfer capability is proposed. The proposed lossless snubber circuit provides Zero-Current Switching (ZCS) condition for turn-on instants and Zero-Voltage Switching (ZVS) condition for turn-off instants. In addition, its diodes operate under soft switching condition. Therefore, no significant switching losses occur in the converter. Since the energy of the snubber circuit is transferred to the output, there are no significant conduction losses. The proposed snubber circuit can be applied on isolated and non-isolated converters. To verify the operation of the snubber circuit, a boost converter using the proposed snubber is implemented at 70W. Also, the measured conducted Efficiency Electromagnetic Interference (EMI) of the proposed boost converter and conventional ones are presented which show the effects of proposed snubber on EMI reduction. The experimental results confirm the presented theoretical analysis.

A Combined Three-Port LLC Structure for Adaptive Power Flow Adjustment of PV Systems

This article proposes a scheme to achieve improved efficiencies for a standalone photovoltaic (PV) system. Specifically, a combined three-port LLC structure is utilized to adaptively regulate the power sharing between the PV and the energy storage battery. This is fulfilled by adjusting the equivalent resonant conditions of two phase-controlled resonant tanks through a shared resonant capacitor. Thus, the overall efficiency is improved by simultaneously reducing the power conversion stages and optimizing LLC converters with fixed-frequency operation. Because an extra power flow path is added to discharge the battery, the nonisolated converter used for battery charging does not need to be bidirectional. Also, since each resonant tank can share part of the load, the new circuit does not add any extra costs of power components. In addition to detailed theoretical analysis, experimental results verify the effectiveness of the proposed concept.

An Input-Series-Output-Parallel Converter System Exhibiting Natural Input-Voltage Sharing and Output-Current Sharing

Input-series-output-parallel (ISOP) converter system is suitable for high-input voltage applications owing to the reduced voltage stress of power switches. This article proposes an ISOP converter system with two-stage dc-dc converter as the basic module, which is composed by a non-isolated dc-dc converter and an isolated dc-dc converter. The isolated dc-dc converter functions as a dc transformer (DCX), and the non-isolated dc-dc converter serves as the pre- or post-regulator to regulate the output voltage. With this arrangement, a common duty ratio is applied to all the pre-or postregulators, and natural input-voltage sharing (IVS) and output-current sharing (OCS) can be achieved. The LLC resonant converter is adopted as the DCX, and the design considerations are given for achieving a nearly constant voltage gain even if there is parameters drift. Meanwhile, the non-isolated converter has simple topology and the parameters are easy to be identical. Thus, the proposed ISOP converter system realizes excellent IVS and OCS even the constituent modules are not well matched. Furthermore, the improved ISOP converter system employing boost+LLC resonant converter is proposed. Two 12-kW ISOP converter systems have been fabricated and tested in the lab, and the experimental results are provided to verify the natural voltage sharing of the proposed ISOP converter system.

A Non-Isolated Step-up DC-AC Converter With Reduced Leakage Current for Grid-Connected Photovoltaic Systems

In this paper, a non-isolated step-up single-phase dc-ac converter is proposed for distributed low voltage photovoltaic (PV) systems. The proposed converter has a common ground between the dc photovoltaic input and ac output voltage, which can reduce the leakage current to a very low level and thus improve the reliability and power generation efficiency. By analyzing and comparing the two modulation methods, a unified half cycle modulation is selected for the design of the proposed converter, in which only two switches are operated at high frequency in a line cycle. Therefore, the conduction and switching loss can be reduced greatly. In addition, due to the unified half cycle modulation for the active switches of the proposed inverter, the dc-link capacitor does not need to have a decoupling function. The capacitor can then be optimized to a small value for improving the reliability and power density. A theoretical analysis of the proposed converter is described, and an experimental prototype is implemented to verify the performance of the presented converter topology.

Hybrid Nonisolated Active Quasi-Switched DC-DC Converter for High Step-up Voltage Conversion Applications

This paper deals with a hybrid non-isolated active quasi-switched dc-dc converter with a high-boost voltage gain, which is applicable for the high step-up low power applications. By using fewer number of components in circuit topology, the proposed converter can provide higher-gain voltage with a small duty cycle, which can reduce the voltage stress and conduction loss on power switches. In addition, it draws continuous input current, has lower diode voltage stress and lower passive component voltage ratings. The operating principles and key waveforms in continuous conduction mode and discontinuous conduction mode are presented. Small-signal dynamic analysis, parameter design guideline, power loss calculation, and characteristics comparison with other non-isolated converters have been completed. Finally, a 250W hardware prototype is constructed and the experimental results are presented to verify the feasibility of the proposed converter.

Review and comparative analysis on dc-dc converters used in electric vehicle applications

This paper is reported with different kinds of DC-DC converters such as sepic, boost and bidirectional converters. Integrating the boost, sepic, bidirectional DC-DC converters enables to identify the suitable converter for renewable energy applications with accurate power rating. The performance of non-isolated converter is assessed on the basis of these review. The solar PV conversion efficiency is low, so the converter is used to step-up/step down the voltage levels. This paper attempts to perform by examing efficiency of DC-DC converters and the voltage and current stress on the switches. A detailed review is carried out on basic PV and fuel cell based electric vehicles.

Correction: C. Anuradha; C. Sakthivel; T. Venkatesan; N. Chellammal. Analysis of Non-Isolated Multi-Port Single Ended Primary Inductor Converter for Standalone Applications. Energies 2018, 11, 539

The authors wish to make the following corrections to their paper [...]

Design and Development of Dual Input DC–DC Converter for Hybrid Energy System

In hybridization of energy sources with distinct voltage–current characteristics, power electronic converter plays crucial role for efficient and reliable energy diversification. In this paper nonisolated dual input converter is proposed for integration and diversification of energy from two different sources with distinct voltage–current characteristics. The proposed dual input converter (DIC) is proficient for energy diversification from two sources individually and concurrently with series and parallel combination of connected sources. The proposed topology can be operated in buck, buck-boost and boost modes of operation. It offers compact design, higher degree of reliability in operation, simplicity in control and flexibility in selection of input source voltage magnitude. Comprehensive analysis of the proposed converter and detailed comparison with existing literature has also been presented. The proposed concept has been simulated in MATLAB SIMULINK and validated experimentally using dSPACE 1103 real time digital signal controller.

Soft-Switching Bidirectional DC/DC Converter With an LCLC Resonant Circuit

In this paper, a soft-switching bidirectional dc/dc converter with an LCLC resonant circuit is proposed. The proposed converter has the dual advantages of isolated converter and nonisolated converter. In boost mode, high efficiency can be achieved at high boost ratios. In buck mode, the circuit can also achieve automatic voltage equalization of half-bridge capacitors. In this paper, a detailed theoretical analysis of the LCLC structure is performed, and the specific operating modes of the circuit in buck and boost mode are given. The circuit modes of the soft-switching resonant process are quantitatively analyzed. The GSSA method was used to model and control the system. According to the obtained transfer function, the PID control circuit of the system is designed by using the zero-pole cancelation method, which enabled the system to obtain superior control performance. A prototype of 1000 W was made, and the experimental results are in a good agreement with the theoretical results.

Non‐isolated resonant link DC–DC converter for use with GaN devices

As new wide band-gap (WBG) devices are developed and improved, new topologies and control schemes are required to take advantage of the ultra-fast switching turn on/off speeds that are now available, without the limitations of switching losses and unacceptable EMI from fast switching transitions. This paper presents a non-isolated DC-DC resonant link converter that allows for soft switching over an extended load range that is particularly suited to GaN devices.

An Analysis of Non-Isolated DC-DC Converter Topologies with Energy Transfer Media

As miniaturized mobile devices with various functionalities are highly desired, the current requirement for loading blocks is gradually increasing. Accordingly, the efficiency of the power converter that supports the current to the loading bocks is a critical specification to prolong the battery time. Unfortunately, when using a small inductor for the miniaturization of mobile devices, the efficiency of the power converter is limited due to a large parasitic DC resistance (RDCR) of the inductor. To achieve high power efficiency, this paper proposes an energy transfer media (ETM) that can make a switched inductor capacitor (SIC) converter easier to design, maintaining the advantages of both a conventional switched capacitor (SC) converter and a switched inductive (SI) converter. This paper shows various examples of SIC converters as buck, boost, and buck-boost topologies by simply cascading the ETM with conventional non-isolated converter topologies without requiring a sophisticated controller. The topologies with the ETM offer a major advantage compared to the conventional topologies by reducing the inductor current, resulting in low conduction loss dissipated at RDCR. Additionally, the proposed topologies have a secondary benefit of a small output voltage ripple owing to the continuous current delivered to the load. Extensions to a multi-phase converter and single-inductor multiple-output converter are also discussed. Furthermore, a detailed theoretical analysis of the total conduction loss and the inductor current reduction is presented. Finally, the proposed topologies were simulated in PSIM, and the simulation results are discussed and compared with conventional non-isolated converter topologies.

On the Emerging Class of Non-Isolated Modular Multilevel DC–DC Converters for DC and Hybrid AC–DC Systems

Explosive levels of research into modular multilevel dc–dc converters (dc–dc MMCs) for dc and hybrid ac–dc systems are currently being witnessed. A new class of dc–dc MMCs has recently emerged that obviates the traditional intermediate ac link with galvanic isolation by internally circulating ac power among the converter switching cells. This novel power transfer mechanism opens the door to an array of new non-isolated converter structures with broad application in MVDC and HVDC systems. This paper gives a comprehensive overview of dc–dc MMCs that exploit the circulating ac power concept. Emergent topologies suitable for use in dc and hybrid ac–dc grids are identified and collated into the following categories: 1) two-terminal and multi-terminal dc–dc MMCs; 2) dc–dc MMCs with ac grid interface; 3) dc line power tapping devices; and 4) dc line power flow controllers. The survey provides researchers with an overall snapshot of technology development for this promising new class of converters in key areas relevant to smart grids.

Circulating Currents Suppression for IPOP Nonisolated DC/DC Converters Based on Modified Topologies

Nonisolated dc/dc converters are widely used in practice because of their low losses and high power density. To accommodate some high-power scenarios and modular applications, these nonisolated converters are usually connected in the input-parallel output-parallel (IPOP) structure. Because there is no galvanic isolation, the ac side and dc side are coupled together, which causes complicated circulating currents in the system. The great circulating currents will endanger the stable and reliable operation of the IPOP nonisolated dc/dc converters system. Focusing on this problem, this paper proposes a novel decentralized circulating currents suppression strategy for IPOP nonisolated dc/dc converters based on the modified topologies, which can still hold the main advantages of nonisolated solutions. First, the complicated circulating currents among the IPOP nonisolated dc/dc converters are analyzed in detail. It is found that various circulating currents exist in the system including the circulating currents within the single converter and the circulating currents among the multiple converters. Then, the limitations of the conventional dc/dc converter topologies are presented and it is proved that these topologies cannot eliminate all the circulating currents. Second, being inspired by the drawbacks of the conventional topologies, the modified topologies with two degrees of freedom modulation are designed. Based on the modified topologies, a corresponding suppression method consisting of two degrees of freedom control is proposed, which can eliminate the different types of circulating currents in a decoupling way. The first degree of freedom control mainly suppresses the circulating currents within the single converter, whereas the droop-based second degree of freedom control mainly suppresses the circulating currents among the multiple converters. Through the proposed solution, the IPOP nonisolated dc/dc converters can operate well with high reliability and scalability. The effectiveness of the proposed solution is validated by the real-time hardware-in-loop tests.

Design and Analysis of Non-Isolated Three-Port SEPIC Converter for Integrating Renewable Energy Sources

An efficient way of synthesizing a three port non-isolated converter from a single-ended primary inductor converter (SEPIC) is proposed in this paper. The primary SEPIC converter is split into a source cell and a load cell. Two such source cells are integrated through direct current (DC) link capacitors with a common load cell to generate a three-port SEPIC converter. The derived converter features single-stage power conversion with reduced structural complexity and bidirectional power flow capability. For bidirectional power flow, it incorporates a battery along with an auxiliary photovoltaic source. Mathematical analyses were carried out to describe the operating principles and design considerations. Experiments were performed on an in-house-built prototype three-port unidirectional converter, and the results are presented to validate the feasibility of the designed converter.

Examination of High <inline-formula> <tex-math notation="LaTeX">$Q$ </tex-math> </inline-formula> Factor Inductor With Vacant Space for a Non-Isolated DC–DC Converter

To miniaturize the non-isolated converter, the use of high driving frequencies is an effective means of downsizing inductors. However, the loss of inductors increases along with driving frequencies. In this paper, we considered means of reducing two types of loss in inductors, namely, iron loss using magnetic composite materials and copper loss using a vacant space. The Q factor can be effectively improved by providing vacant space that width of the vacant space is preferably slightly smaller than that of the copper plate above and below the copper plate. And the efficiency of the non-isolated dc–dc converter applied the inductor with vacant space is increased compared with that of the without vacant.

Modeling and Analysis of Circulating Currents Among Input-Parallel Output-Parallel Nonisolated Converters

Input-parallel output-parallel (IPOP) nonisolated converters, including dc/dc and dc/ac converters, are effective solutions to increase the power rating and to improve the reliability of the system. For the safe and steady operation of these IPOP nonisolated converters, the circulating currents are the main challenge, whose detailed mathematic model and corresponding characteristics are not well studied. This paper focuses on the modeling and analysis of circulating currents among these IPOP converters by deriving the detailed mathematic model. Through these models, the complicated characteristics of the circulating currents are presented, which shows that there are various types of circulating currents including circulating currents within the single converter and circulating currents among the multiple converters. It is first demonstrated that the circulating currents will cause port degradation of the converter, that is, the positive and negative currents of the converter are unequal, which makes some port-based control methods ineffective and influences the relay protection. Furthermore, the corresponding influence factors, including line resistances, filters, and so on, are analyzed in detail, especially the asymmetry of line resistances will cause large circulating currents even resulting in instability. It is also found that the traditional control methods cannot completely eliminate these circulating currents because of the strong coupling and complexity of IPOP nonisolated converters. All the theoretical analyses are verified by the real-time hardware-in-loop (HIL) tests.