Full-load Efficiency Research Articles

Nonisolated Three-Phase Current DC-Link Buck–Boost EV Charger With Virtual Output Midpoint Grounding and Ground Current Control

Non-isolated three-phase AC/DC converter concepts facilitate more compact and more efficient realizations of future EV chargers. However, without the galvanic isolation and/or high common-mode (CM) impedance provided by an isolation transformer, non-isolated chargers must employ other means to suppress CM leakage currents to ground sufficiently and to prevent nuisance tripping of mandatory residual current devices (RCDs). Typically, the required EMI filters reduce high-frequency (HF) CM leakage currents to uncritical values. However, low-frequency CM voltages, e.g., generated by third-harmonic injection, may drive significant LF CM currents through the parasitic capacitances of the DC output (including the battery pack) to protective earth (PE). Therefore, considering a non-isolated three-phase buck-boost current DC-link PFC rectifier system that consists of a buck-type current-source rectifier (CSR) stage and a three-level boost-type DC/DC-stage, this paper first proposes a virtual grounding control (VGC) of the DC output voltage midpoint. VGC employs the DC/DC-stage to compensate the LF (third-harmonic) CM voltage inherently generated by the CSR-stage, and thus controls the LF CM voltage between the DC output midpoint and PE to zero. This enables further a direct connection of the DC output midpoint to PE, where an additionally proposed ground current control (GCC) ensures near-zero LF CM leakage current. The proposed concepts are verified with a 10kW hardware demonstrator (power density of 6.4 kW/dm3 or 107.5 W/in3, full-load peak efficiency of 98.5%) considering TT (Terra-Terra) and TN (Terra-Neutral) grounding systems. With a direct connection of the DC output midpoint to PE, GCC limits the LF CM leakage current to < 6mA RMS, i.e., significantly below typical RCD trip levels, and, using the human-body impedance model according to UL 2202, achieves a test voltage of 110mV that is clearly below the most stringent limit (250 mV) of the standard.

A 380 V High Efficiency and High Power Density Switched-Capacitor Power Converter using Wide Band Gap Semiconductors

State-of-the-art switched-capacitor DC-DC power converters mainly focus on low voltage and/or high power applications. However, at high voltage and low power levels, new designs are anticipated to emerge and a power converter that has both high efficiency and high power density is highly desirable. This paper presents such a high voltage low power switched-capacitor DC-DC converter with an input voltage up to 380 V (compatible with rectified European mains) and an output power experimentally validated up to 21.3 W. The wide band gap semiconductor devices of GaN switches and SiC diodes are combined to compose the proposed power stage. Their switching and loss characteristics are analyzed with transient waveforms and thermal images. Different isolated driving circuits are compared and a compact isolated half bridge driving circuit is proposed. The full-load efficiencies of 98.3% and 97.6% are achieved for the power stage and the complete power converter, without heatsink or airflow. The corresponding power densities are 7.9 W/cm3 and 2.7 W/cm3, based on boxed volumes, respectively.

An industrial design of 400 V – 48 V, 98.2% peak efficient charger usingE‐mode GaNtechnology with wide operating ranges for xEV applications

AbstractThis paper offers a wide‐operating range electric vehicle charger design by employing an interleaved inductor–inductor–capacitor iL2C DC–DC converter. It uses two parallel L2C converters with 8‐GaN switches on the primary side and a shared rectifier circuit on the secondary side, which it also enhances the circulating current, conduction losses, and current sharing. For iL2C converter, a constant voltage charging mode of operation is designed, also it proposes a hybrid control scheme of variable frequency + phase shift modulation (VFPSM). The entire concept is designed, simulated, and validated with a rated input voltage and load voltage of three different load conditions with converter line and load regulations are analyzed. To evaluate controller and converter performance, the idea is proven experimentally for variable load condition of full load, half load, light load with a rated input and output voltage of 400Vin–48V0. In addition, line regulation is also performed and validated for wide input voltage application of 300Vin–500 Vinwith an output voltage of 48V0at full load and peak efficiency of 98.2% is determined. Further, to provide the system effectiveness converter efficiencies are presented at various load operations from 3.3 kW to 330 W.

Dual switch ultra-high gain DC–DC converter with low voltage stress

DC microgrids have gained prominence by successfully incorporating renewable energy sources like photovoltaics, fuel cells, etc. through power electronic interfaces. To incorporate renewable energy sources to the DC microgrid, the utilization of DC–DC converters becomes necessary. This requirement arises from the lower voltage levels associated with these energy sources. This paper introduces a new dual switch, ultra-high gain, non-isolated dc–dc converter with low voltage stress. A modified switched inductor(SI) cell is combined with a switched capacitor(SC) cell to obtain a significant gain in voltage for this proposed converter. A second switch is incorporated in lieu of the diode of the SI cell to reduce the voltage stress on the active switches to less than 25% of the output voltage. The reduced voltage stress further contributes to enhancing efficiency while lowering the rating and cost of the components. The experimental findings from a prototype converter rated at 380[V] and 200[W] corroborate the credibility of the proposed methodology. The results also show that the converter has a full-load efficiency of 95.53% and uses its components better.

A novel two‐stage solution for low‐power 48‐V voltage regulator module (VRM) using high step‐down hybrid LLC with integrated planar transformer

SummaryIn this paper, a novel two‐stage solution based on a 1‐MHz high step‐down hybrid LLC converter is proposed for low‐power 48 V voltage regulator modules (VRM). Since the hybrid LLC DCX converter with high step‐down ability is employed as the first‐stage, lower bus voltage can be obtained with the same transformer turns, which contributes to enhancing the duty cycle and efficiency of the second‐stage multi‐phase buck converter. Thus, an overall efficiency improvement can be achieved in the proposed two‐stage system, especially in low‐power applications. To further improve efficiency and power density, a novel integrated planar transformer is adopted for the double resonant tanks of the hybrid LLC converter. To validate the analysis, a 150‐W hardware prototype of the hybrid LLC converter is constructed in the laboratory. To ensure a fair comparison with existing LLC DCX designs, the output voltage is set at 6 V. The measured efficiency results of the first‐stage demonstrate an efficiency advantage at low power output levels compared to the similar full bridge LLC designs, especially at an output of around 100 W. Under the nominal 48‐V input, the first‐stage achieves a peak efficiency of 98.5% and a full load efficiency of 94.62%. Furthermore, a 4‐phase buck converter with nominal 6‐V input and 1.6‐V output is constructed to evaluate the efficiency performance of the overall system. When the second stage operates at 500 kHz, the proposed two‐stage system achieves a peak efficiency of 93.2% at 40A load, while maintaining an efficiency of 91.2% at 65A output. The calculated efficiency of the proposed two‐stage solution exhibits higher performance compared to the majority of single‐stage schemes.

Geometrical State-Plane Analysis of Resonant Switched-Capacitor Converters: Demonstration on the Cascaded Multiresonant Converter

To realize high efficiency and high power density for resonant switched capacitor (ReSC) converters, it is critical to have a thorough understanding of the soft-switching mechanism and design the converter appropriately. However, this can be challenging as the soft-switching operation depends on multiple variables and its design difficulty increases quickly with respect to the topology complexity. This paper demonstrates a framework of using geometrical state-plane analysis to facilitate ReSC converter design. The methodology is first applied to a basic 2-to-1 ReSC converter, and then extended to a new 4-to-1 ReSC converter topology we proposed, herein named cascaded multi-resonant converter. This topology has reduced component count thanks to a new “switching bus” architecture. However, it comes at a cost as the converter has multiple resonances within each switching cycle, complicating the soft-switching design. Despite the high circuit complexity, the state-plane analysis neatly provides analytical equations of all state parameters, which are verified by simulations and experiments. Our hardware prototype achieves 6000 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> power density at 48-to-12 V conversion and 80 A continuous output. Its peak efficiency reaches 99.02%, and full-load efficiency reaches 97.67%, including gate drive loss. Both the power density and efficiency are superior to the state-of-the-art 48-to-12 V solutions.

An ultrahigh synchronous drive step-up converter for PEMFC and its explicit model predictive control: A neural network fitting strategy

This paper proposes an ultrahigh synchronous drive step-up dc-dc converter to improve the low voltage generated by proton exchange membrane fuel cell (PEMFC) with proper duty cycle. Coupled inductor and voltage multiplier technologies are utilized to obtain high voltage gain in the converter. The energy stored in leakage inductor can be recycled by the clamp circuit, reducing the voltage stresses on switches, and improving the efficiency significantly. The operating principles and steady-state analyses in continuous conduction mode are provided in detail. Compared with relevant converters, the proposed converter performs lower voltage stresses on power switches and higher voltage gain. Moreover, to improve the dynamic performance and interference immunity of the proposed converter, the offline fitting strategy using the explicit model predictive control (MPC) laws of neural networks is used. The tracking accuracy of the output voltage is improved, disturbances caused by variable loads are reduced, and superior dynamic response can be achieved. Finally, to verify the feasibility and validate the theoretical analyses, a 200 W laboratory prototype with input voltage 20 V and output voltage 400 V is implemented. The maximum efficiency of the proposed converter is 97.21% and the full load efficiency is 91.67%.

Part-Load Energy Performance Assessment of a Pumped Thermal Energy Storage System for an Energy Community

Research on pumped thermal energy storage (PTES) has gained considerable attention from the scientific community. Its better suitability for specific applications and the increasing need for the development of innovative energy storage technologies are among the main reasons for that interest. The name Carnot Battery (CB) has been used in the literature to refer to PTES systems. The present paper aims to develop an energy analysis of a CB comprising a high-temperature two-stage heat pump (2sHP), an intermediate thermal storage (latent heat), and an organic Rankine cycle (ORC). From a broad perspective, the CB is modeled considering two types of heat inputs for the HP: a cold reservoir in the ground (at a constant temperature of 12 °C throughout the entire year) and a heat storage at 80 °C (thermally-integrated PTES—TI-PTES). The first part defines simple models for the HP and ORC, where only the cycles’ efficiencies are considered. On this basis, the storage temperature and the kind of fluids are identified. Then, the expected power-to-power (round-trip) efficiency is calculated, considering a more realistic model, the constant size of the heat exchangers, and the off-design operation of expanders and compressors. The model is simulated using Engineering Equation Solver (EES) software (Academic Professional V10.998-3D) for several working fluids and different temperature levels for the intermediate CB heat storage. The results demonstrate that the scenario based on TI-PTES operation mode (toluene as the HP working fluid) achieved the highest round-trip efficiency of 80.2% at full load and 50.6% round-trip efficiency with the CB operating at part-load (25% of its full load). Furthermore, when the HP working fluid was changed (under the same scenario) to R1336mzz(Z), the round-trip full-load and part-load efficiencies dropped to 72.4% and 46.2%, respectively. The findings of this study provide the HP and ORC characteristic curves that could be linearized and used in a thermo-economic optimization model based on a Mixed-Integer Linear Programming (MILP) algorithm.

Analysis and design of synchronous‐rectified LLC DC–DC converter for LDC of electric vehicles

AbstractIn electric vehicles (EVs), the low voltage dc‐dc converter (LDC) with synchronous rectifier switches (SRs) can be used to reduce conduction loss caused by the high load current and improve the efficiency. Therefore, it is important to design a proper turn‐on time of SRs. As a popular driving strategy for the SRs, the drain–source voltage across the SRs is sensed to generate the gate driving signal. However, when LLC dc–dc converter operates at O mode, there will be a voltage ringing across the SRs. If the ringing voltage reaches to the threshold voltage −Vth,on, it would make SRs turn‐on early and results in abnormally working of the converter. The novelty and contribution of this paper lie in: (1) elaborating on the voltage ringing across the SRs, (2) the accurate ringing model is established during O mode, and (3) a simple, lossless, and low‐cost filter circuit is used to solve the negative effect of the ringing voltage for LLC converter at high load current. A 1.26 kW experimental prototype with ≈250–430 V wide input voltage and ≈9–16 V wide output voltage is implemented, 96.7% peak efficiency and 96% full load efficiency are achieved with a 3.12 kW/L power density. The theoretical analysis has been validated by the simulated and experimental results, and the SR LLC dc–dc converter with the SR works efficiently and reliably with the proposed solution at a high load current.

Integrated Fractional-Turn Planar Transformer for MHz and High-Current Applications

In MHz and high current applications, planar transformers face problems such as significant winding loss and limited winding current-carrying capacity, which seriously restrict converter's efficiency and power density improvement. This paper proposes a fractional-turn planar transformer structure and embeds key power devices into the transformer. The proposed method can significantly shorten the winding length, thus reducing winding losses. At the same time, the high integration of the transformer and key power devices can effectively reduce the overall volume of the converter and eliminate terminal losses. The analysis and optimization of the proposed integrated fractional-turn transformer are presented in detail. Finally, a 380V-12V 1kW unregulated LLC is built with the proposed integrated transformer. The full-load efficiency is 97.7%, and the power density is 99W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , both of which are the highest among the state-of-the-art prototypes with similar specifications.

A high step‐up DC–DC converter with switched‐capacitor and switched‐inductor using one coupled inductor

AbstractThis paper proposes a high step‐up DC–DC converter which integrates switched‐inductor and switched‐capacitor techniques with a four‐winding coupled‐inductor. With switched‐inductor technique, two primary windings of the coupled‐inductor are charged in parallel and discharged in series to obtain high voltage gain. Moreover, by adding two sets of diode‐capacitor circuits on both primary side windings, not only can recycle the energy causing the voltage spike on the power switches, but can also lift the conversion ratio. Then, the power switches with lower voltage stress are used to improve the efficiency of the proposed converter. The operating principle, steady state analyses, and key parameters design of the proposed converter are discussed and provided. Finally, a 400 W laboratory prototype with 24 V input voltage and 480 V output voltage is constructed and tested to validate the performance. The highest and full load efficiencies are 95.8% and 94.8%, respectively.

A Novel LCL Resonant Converter With Inherent CC-CV Output for On-Board Chargers of Plug-In Electric Vehicles

The <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> Resonant converter is widely used in on-board charger applications for its high efficiency. However, conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter with pulse-frequency-modulation suffers from a wide switching frequency range for realizing constant current (CC) and constant voltage (CV) charges. To address this problem, different from the traditional solution, a novel <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> resonant converter operating at a fixed resonant frequency with inherent CC and CV output characteristics is proposed in this letter. In the proposed concept, the CC and CV charges are accomplished by the special <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> tank. With the increasing of battery voltage during charging process, the resonant tank of the proposed converter is equal to the conventional <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> tank and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> tank for CC mode and CV mode, respectively. Thus, the sensing and control circuits are canceled while the wide zero-voltage-switching operation for primary switches and zero-current-switching for secondary diodes still be maintained. Therefore, the fixed resonant frequency operation, high efficiency, high reliability, and low cost are key features of the proposed converter. A 1-kW prototype with 400 V input and 250–400 V output is built and tested. The full load efficiency of 96.7% and higher than 96% for the CC mode were both achieved. The experimental results demonstrate the advance and validity of the proposed converter.

Star Power Factor Correction Architecture

Conventional two-stage power factor correction (PFC) architecture based on a boost PFC front end and an isolated dc–dc back end is increasingly challenged by the recent trend toward higher power density and efficiency. One key reason for the challenge is the difficulty of increasing the operating frequency of the boost PFC stage. This article presents a new star PFC architecture that allows the boost PFC stage to operate efficiently at a higher frequency while maintaining the performance of the second dc–dc stage, leading to a high-power-density and high-efficiency ac–dc converter design across a universal input. The high performance of star architecture is enabled by realizing: 1) continuous-conduction-mode (CCM) operation of the boost PFC stage; and 2) full-range zero-voltage-switching (ZVS) of all active switches. In addition, the star architecture can: 1) operate at a constant frequency via a proper selection of the circuit topology and modulation method; and 2) be controlled based on simple and low-cost analog circuits. A 300-kHz, 240-W, 48-V-output, and universal-input prototype is built to verify the performance of the star architecture, showcasing high power factor, constant output voltage, 97.1 % full-load efficiency, 55.6 W/in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> power density by box volume.

Operational characterization of tokamak and stellarator type fusion power plants from an energy system perspective

Fusion power plants are not yet considered specifically in European long-term energy system studies. In order to include them in such studies a corresponding and valid parametrization of their operating performance has to be established despite the fact that fusion reactor design is still an ongoing effort.The goal of the present paper is to specify and energetically represent the prospect of feasible operation and dynamics of tokamak and stellarator type fusion power plants from an energy system perspective. Special focus is given on time and operation mode dependent self-consumption. The basis of the parametrization is a one GWel power output plant. As a result, we propose the representation of fusion power plants as a system with three main components (fusion reactor, thermal energy storage (TES) and power conversion system), followed by a set of parameters for both tokamak and stellarator type devices. Five different operating states are defined for a fusion plant, depending on the required and active auxiliary subsystems. The comparison between operational dynamics of conventional and fusion power plants showed no tremendous differences due to the TES utilization. However, fusion plants had a lower full-load operation efficiency due to higher self-consumption as well as extensive pre-production losses.

Design and analysis of isolated high step-up Y-source DC/DC resonant converter for photovoltaic applications

ABSTRACT This paper presents the design and analysis of an isolated high step-up Y-source DC/DC converter for photovoltaic systems. At high switching frequencies, the conventional impedance source converter (ISC) experiences higher switching losses. To mitigate this, a high gain soft-switched frequency-modulated Y-source DC/DC converter is proposed. Here, soft switching is implemented on the Y-source impedance converter by creating quasi-resonance during a shoot-through instant. Thus, quasi-resonance occurs by an LC resonant tank, and it is formed using a resonant capacitor and leakage inductance of a transformer. It ensures that all the active switches are turned off with zero current switching (ZCS) and the voltage stress on each switch is much lower than the output voltage with lower turn-off voltage spikes. Thus, it eliminates the need for a snubber circuit. The output voltage is regulated by frequency modulation with the ON period of all four active switches kept constant. The converter can also deliver a continuous input current (CIC) and high voltage gain with a small shoot-through duty ratio . The galvanic isolation of the converter helps to eliminate the leakage current issues and safety hazards faced by the non-isolated counterparts. The proposed topology has all the inherent characteristics of a typical impedance source DC/DC converter with higher conversion efficiency over a wide range of output loads. The proposed converter achieves 96.46% of full load efficiency. Finally, a 200W prototype is built and tested in the laboratory to verify the converter design and performance.

A reduced‐switch‐count two‐phase interleaved switch‐control‐capacitor LLC converter with accurate current balancing

AbstractIn this paper, a reduced‐switch‐count two‐phase interleaved LLC converter with precise current balancing is proposed by using switching‐control‐capacitor (SCC) technology. Compared with the conventional SCC‐LLC converter, the proposed two‐phase SCC‐LLC converter reduces the switch count with the SCC circuits, and achieves excellent current sharing under all the tolerance conditions between the two‐phase resonant elements. In the proposed converter, the SCC circuit is only used in the first phase. The design of the SCC circuit parameters is analyzed to reduce the voltage stress of the SCC circuit and to ensure that two‐phase currents are balancing with large tolerance of resonant elements. A 2.16‐kW GaN‐based two‐phase interleaved SCC‐LLC converter prototype is established for data center application, and the experimental results show that the 98.1% peak efficiency, the 97.6% full load efficiency, and higher than 96% efficiency at the wide range from 3‐A to 40‐A load current are achieved. The precise current sharing lower than 1% is achieved by using a cheap ceramic capacitor with high tolerance, which validates the performance of the converter.

Single-Phase GaN-Based T-Type Totem-Pole Rectifier With Full-Range ZVS Control and Reactive Power Regulation

This article proposes a high-efficiency single-phase GaN-based rectifier with reactive power transfer for use in front-end power supplies as an efficient alternative to centralized reactive power compensation. A full-range zero-voltage switching (ZVS) modulation for both unity power factor (PF) operation and nonunity PF operation is proposed for the GaN-based rectifier in critical conduction mode (CRM) operation. A frequency limitation method is also developed to limit the peak frequency during the ac current zero-crossing. Also, a GaN-based T-type totem-pole rectifier is proposed to overcome the control challenge in CRM during the ac voltage zero-crossing. Meanwhile, a digital-based control scheme is developed to implement ZVS operation and reactive power regulation. The proposed rectifier and ZVS control have the advantages of simple topology, high efficiency, straightforward control implementation, and capability of flexible reactive power regulation. A 1.6-kVA prototype of the GaN-based CRM T-type totem-pole rectifier is built and demonstrated with full-range ZVS operation, 98.9% full-load efficiency, and flexible reactive power regulation with smooth dynamic response.

Design Procedure for Reduced Filter Size in a Buck Converter Using a Fourth-Order Resonance Filter

This article presents a novel design procedure for fourth order and fourth-order resonance (4thRes) output filters, for given buck converter specifications, making components selection a straightforward process. An accurate filter analysis is provided to predict the filter component currents and voltages in both frequency and time domains. Application of the analysis in a design study of a 20 MHz, 5.4 W buck converter shows that the 4thRes filter has the potential to reduce the output passive components for a wide duty cycle range. As compared with a second-order filter at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IN</sub> = 6.6 V to <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OUT</sub> = 1.8 V, total inductance, inductor energy, capacitance, and capacitor energy are 58%, 35%, 45%, and 31% lower, respectively. Air-core printed circuit board (PCB) integrated solenoid inductors are considered for implementation and testing within a prototype converter to show the impact of these filters on the converter performance. The 4thRes filter achieved 3.7% and 3.6% higher full-load efficiency than the second- and fourth-order filters, respectively, and a better load transient performance.

A Novel Analytical Formulation of SiC-MOSFET Losses to Size High-Efficiency Three-Phase Inverters

This paper presents a novel analytical loss formulation to predict the efficiency of three-phase inverters using silicon carbide (SiC) metal—oxide—semiconductor field-effect transistors (MOSFETs). The proposed analytical formulation accounts for the influence of the output current harmonic distortion on the conduction losses as well as the impact of the output parasitic capacitances and the deadtime on the switching losses. The losses are formulated in balanced conditions to select suitable SiC MOFETs for the desired target efficiency. To validate the proposed methodology, a 3-phase inverter is designed to present full load efficiency in excess of 99% when built using SiC MOSFETs antiparalleled with SiC Schottky diodes selected for the specified full load efficiency. Experimental assessment of the designed inverter efficiency is compared with the expected values from the proposed analytical formulation and shown to match or exceed the predicted results for loads ranging from 40% to 100% of full load.

Modified Two-Channel LLC Resonant Converter With Optimal Efficiency for Wide Input Voltage Applications

A modified two-channel LLC resonant converter with optimal efficiency for wide input voltage applications. The converter has the same voltage gain and power handing ability as conventional full-bridge (FB) resonant converter, but the hardware cost is lower than conventional FB resonant converter, and the operational frequency range is narrower than conventional resonant converter for the same working condition. It has the characteristics of low input impedance at low input voltage, which is used to provide high voltage gain, and high input impedance at high input voltage, which is used to provide low voltage gain, the above characteristics are analyzed and optimized to improve the efficiency for photovoltaic applications where wide voltage gain is require. A 1 kW prototype is developed, the input voltage ranges from 80 V to 200 V, the output voltage and output power are 400 V and 1 kW, the experimental result shows that the full-load efficiency can reach 96.5% over the entire input voltage range, and the peak efficiency can reach 96.9% at full-load state.