Search

Traditionally, standalone closed-loop drain–source sensed synchronous rectification (SR) implementation has been limited by the voltage limits of commercial IC controllers. Commercially available SR controllers have low maximum voltage limits, necessitating a high-voltage blocking mechanism for use in higher voltage rectifiers. Therefore, in this article, a board-level blocking method to protect drain–source voltage sensed SR controllers from high voltage and currents at the board level is presented. This method allows for the high-voltage operation of drain–source SR controllers. This method is self-biasing and allows for SR controller operation far beyond the datasheet voltage limits (kV+). The mechanisms of operation are analyzed, and design criteria created for selecting an optimal clamp is proposed. The proposed solution is simple and low in cost and component count, making closed-loop, cyclically adaptive SR a practical solution for high-voltage rectifiers. The blocking circuit is presented, analyzed, and tested for use with commercially available drain–source SR controller integrated circuits (ICs). Hardware SR testing is completed on two LLC-DCX (dc-transformer) modules with 300 V, and over 1-kV output voltages to demonstrate the voltage blocking capabilities.

In a magnetic bearing system, the levitation coils or electromagnets must be driven by an amplifier in order to control their currents for levitation stability. This amplifier typically drives every coil individually with hard-switching H-bridges. However, the inherent high dv/dt of hard-switching in conjunction with the large parasitic capacitance of magnetic bearing coils typically results in high current spikes and severe ringing in the switching process, which may interfere with position sensors and system communication. Furthermore, driving each coil individually requires a large number of switches. In this brief, a switch sharing zero-voltage-switching (ZVS) multichannel switching amplifier topology is proposed, which not only reduces the number of switches needed when driving multiple coils, but also eliminates current spikes and reduces the switching loss of the magnetic bearing amplifier. The proposed topology is experimentally tested to validate expected benefits.

In photovoltaic applications, many previous research works have focused on pulsewidth modulation (PWM) resonant converters in order to achieve a high efficiency with a wide input voltage range. Conventional approaches utilized symmetric boosting modulation at the secondary side rectifier to obtain a symmetric operation, and they utilized two boosting modes in a switching period. Among various rectifier structures, the voltage doubler structure has a strong advantage due to a small number of components. However, it suffers from serious hard switching losses in the secondary side rectifier. In this paper, a new converter with a novel asymmetrical modulation is proposed and verified. The strong point of the proposed converter is that it eliminates hard switching turn- on losses from the rectifier, while maintaining the minimized number of components. Although the proposed converter adopts an asymmetric modulation, the offset current on the transformer becomes zero inherently. Furthermore, a “forced half resonance” operation of the proposed converter keeps rms current stresses at the same level as conventional converter although it has a higher peak current. Accordingly, the proposed converter achieves a superior efficiency with the minimum number of components at 35–25 V input and 380 V/300 W output specification.

The increasing usage of LLC-type dc-dc converters in utility, automotive, and power distribution applications has led to a push for a further increase in the converter's operating load range and efficiency. The secondary-side rectifier remains one of the lossiest areas in the converter, alluring designers to synchronous rectification (SR). One method is drain-source SR for cyclically adaptive, closed loop SR. However, when utilized, a severe current oscillation can be observed. An increase in SR duty cycle results in an increase in conduction time of the SR channel over the body diode. This issue becomes increasingly prevalent due to the usage of wide band-gap MOSFETs with high reverse drops and low sensed signal strength. This results in a current oscillation effect, leading to inconsistent SR operation, output ripple, and high EMI. In this paper, the issue is root caused analyzed. A method of improving drain-source SR for light-load SR operation is proposed. The method is prototyped on an FPGA to alleviate the issue on a $600\text{-}V_{in}/ 340\text{-}V_{out}$ 2.5-kW LLC-DCX (DC transformer) power converter.

A conventional asymmetrical half-bridge (AHB) converter is one of the most promising topologies in low-power applications because of the zero-voltage switching (ZVS) of all switches and the small number of components. However, when it operates with an asymmetrical duty ratio, it has a large dc-offset current in the transformer, which increases the size and core loss of the transformer. Moreover, because the dc-offset current decreases ZVS energy for one of the half-bridge switches, it has low efficiency in a light load condition. In addition, because most of the output current is concentrated in high-voltage-rating diodes that have large forward voltage drops, large conduction loss occurs in the secondary rectifier. To solve these problems, a new AHB converter with a coupled inductor rectifier (CIR) is proposed in this paper. By adopting the CIR structure in the AHB converter, the proposed converter not only eliminates the dc-offset current in the transformer, but it also has equalized current stress in the rectifier diodes. As a result, the proposed converter achieves high efficiency in entire load condition, compared to an AHB converter with a full-bridge rectifier. The effectiveness and feasibility are verified with a 250–400 V input and 100 V/200 W output prototype.

The inverter that requires isolation typically consists of an isolated dc-dc and a pulse-width-modulated dc-ac stages. However, the component counts, control complexity, efficiency and power density tend to be suffered with such a two-stage configuration. In this paper, a single-stage soft-switching isolated inverter based on MHz LLC converter is introduced with a novel hybrid modulation method, which operates under full-bridge and half-bridge variable frequency conditions for high- and low-line outputs, respectively. A rectified sine wave can be generated at the output of LLC converter and isolated through a high-frequency transformer for additional voltage gains. A lossless line frequency unfolder circuit is added afterwards to convert the rectified sine wave to ac sine output. The optimization method for the resonant tank is also proposed to achieve even lower voltage gains at high frequency to improve the output ac waveform quality. Compared to the traditional two-stage method, this single-stage solution makes the circuit simpler, and the bulky dc bus capacitor can be saved. To verify the circuit design and the proposed hybrid modulation method, a GaN based 380 V dc – 600 V ac , 1.2 kW prototype is built and tested. Under the full load condition, the measured total harmonic distortion of output voltage is 2.67% with 98.30% efficiency for the overall inverter.

LLC resonant converter is widely used for isolated dc-dc power conversion applications due to its soft switching characteristics and simple structure. With the help of wide bandgap (WBG) devices, the switching frequency can be pushed to MHz range and the transformer loss becomes a more critical factor for the efficiency of the whole LLC converter. The high frequency effects, such as skin effect, proximity effect and fringing effect, make the transformer design even more challenging. Many research have been performed to evaluate core loss and copper loss from calculation, simulation or direct measurement in specific tester circuits. However, they are different from real circuit conditions. In this paper, the design principles and optimization considerations for the transformer in MHz LLC converter are presented. An accurate test-based method for core loss and copper loss estimation is proposed. Based on the proposed method, several optimization considerations are provided. To verify the optimized transformer design and its loss prediction method, a GaN based 1 MHz/2.8 kW LLC converter prototype is built, which can achieve 99.04% peak efficiency.

A single-inductor dual-supply dc–dc converter with bidirectional energy flow is proposed for the Internet-of-Things applications. This paper combines two dc–dc converters into one by sharing a single inductor, and it is capable of storing energy and powering output load by using the bidirectional inductor current. Besides, the voltage of the energy storage element is continuously monitored in the proposed converter, which eliminates the possibility of overcharging. Furthermore, the variations on the output voltage are typically negligible when the input voltage changes. In addition, a novel two-step startup procedure that does not require any on-chip/off-chip startup auxiliary circuit is proposed, which can significantly reduce the chip area. The proposed converter is fabricated by a 0.18- $\mu \text{m}$ CMOS mixed-signal process. The voltage range of the storing element is 1.2–1.4 V, and the maximal output power of the proposed converter is 18 mW with its output voltage setting at 1.8 V.

In this paper, a highly efficient isolated resonant converter with a novel modulation method is proposed for delivering power from photovoltaic (PV) modules to the dc microgrid. The proposed modulation method allows the converter to boost low input voltages and regulate a wide input voltage range. The converter design is based on a series resonant converter (SRC) that operates at the resonant frequency to achieve highest efficiency under nominal input voltage condition. Under shadowed or low irradiance conditions of PV panels, the converter will operate with the proposed “double-pulse duty cycle” modulation method to step up the voltage for the dc microgrid connection. With the proposed modulation method, the output switches serve for both synchronous rectification and voltage boost function. This method enables a higher voltage boost ratio than the SRC without adding additional switches while operating at the resonant frequency. A 300-W hardware prototype with gallium-nitride devices is built to verify the performance of the proposed converter and modulation method. The converter achieved a peak efficiency of 98.9% and a California Energy Commission weighted efficiency of 98.7% under nominal input voltage condition.

With the availability of wide bandgap devices, the power converters can now potentially operate at megahertz (MHz) or higher frequencies while achieving ultrahigh efficiency. Such a high-frequency switching is particularly important for isolated converters to reduce the size of the passive components, achieve high power-density, and reduce costs. However, unlike the conventional kilohertz switching, in MHz switching, the parasitic components will significantly affect the circuit operation. These effects are compounded by high-ratio step-up or step-down isolated converters because the parasitic capacitances/inductances are squared times the turns’ ratio of the transformer when reflecting from high-voltage (HV) to low-voltage (LV) side to LV/HV side. In this paper, a high-step-up series resonant converter is used as a design example to explore the effects of parasitic inductances induced from the LV side and parasitic capacitances induced from the HV side on the circuit operation under MHz switching conditions. Afterward, the printed circuit board (PCB) layout and the planar transformer are optimized through the finite-element method to minimize the parasitic effects. Finally, a 1-MHz, 38-V/380-V, 300-W resonant converter prototypes are built and compared to verify the design optimization.

LLC resonant converter is one of the promising converter topologies due to its simple structure and high efficiency. However, when LLC resonant converter is designed considering a hold-up time requirement, it has definite drawbacks such as large conduction and turn-off losses due to large circulating current. To solve this problem, various resonant converters with boost capability have been investigated. Although these methods improved overall performance, they still suffer from a large number of switching components. In this paper, a new LLC resonant converter with boost capability is introduced and verified. The advantage of the proposed converter is a small number of components while achieving the hold-up time capability. Furthermore, it achieves zero average transformer current despite its asymmetric operation. A prototype has been built and tested with 400–250-V input and 200-V/200-W output specification.

LLC resonant converter is popular for dc-dc converter designs due to its simple topology, galvanic isolation and soft switching capability. Therefore, lots of researches have been performed for LLC converter design and optimization to pursue high efficiency and high power density with high switching frequency. However, relevant research about the analysis and ZVS model for LLC converter with light load condition under MHz switching is scarce. In this paper, detailed analysis for MHz GaN based LLC converter is provided with light load. Moreover, a simple and accurate ZVS model is proposed, which can help determine fully ZVS condition for primary side devices. To verify the analysis and the proposed ZVS model, a 1 MHz/300 W (10% load) GaN based LLC converter prototype is built and tested.

Since the last decade day by day, there is a revolution in an existing power grid network due to an increase in demand for the convenient electric power supply required for the smart component in the power grid network. So this is a time for the power grid to become smart in accordance with all components which are actively participated in his network which is nothing but Smart Grid network. A different component in a Smart grid network required variable AC/DC power supply at the different amplitudes and different frequencies. Power electronics converters are required to meet all these requirements. Solid State Transformer (SST) is one of the key components in a smart grid network. This paper presents the Bidirectional Soft Switched Solid-State Transformer for a Smart Grid Network. A proposed circuit presents in this paper used a LCLC type resonant network to achieved soft switching action. An analysis of the resonant network and it's effect on the performance indices are presents in this paper. A front end bidirectional boost rectifier is used in a proposed circuit to achieved bidirectional power flow feature and desired voltage gain at the output. A proposed circuit is designed for power level 10KW and is simulated in a PSIM/Simulink co-environment. The results were obtained at an input voltage of Three-phase 440V, 50 Hz, and provide the output of 800V, 12.5A and is verified for desired features in the proposed converter.

Gallium Nitride (GaN) devices have shown greater potential in high switching frequency operation due to its much lower switching loss compared to Silicon devices. However, the faster switching speed makes it more difficult for device dynamic characterization because it is more sensitive to the parasitic components in the circuit and it requires better testing equipment. Double Pulse Test (DPT) is commonly used to characterize device dynamic performance and proper device drain current probing method is a must for accurate switching loss measurement. However, for GaN devices designed to have loop inductance within sub-nH range, any coaxial shunt to measure drain current will insert enough parasitic inductance to influence switching performance and impact measurement results. In this paper, a novel and simple method is proposed to accurately evaluate switching loss without shunt resistor in series with GaN device in a half bridge configuration, which is a common building block in power electronics circuits. A 130 W GaN based buck converter prototype is built to verify the proposed method.

The series resonant dc-dc converters are mature technology used mostly in applications requiring constant dc voltage gain. They were recently enhanced by the application of the boost rectifiers. This approach showed new opportunities for input voltage regulation range extension. The given paper summarizes known operating modes and shows a way of significant input voltage range extension through the utilization of hybrid full-bridge switching cell. Two converter topologies are introduced in this paper. Possible operating modes are identified and summarized.

High frequency PCB windings magnetic is one of the key components in high power density and high efficiency MHz power converter. High frequency PCB windings magnetic losses are the main limitation for the whole converter efficiency and power density, while the PCB windings losses are the main part of the magnetic losses. Currently, the Dowell’s model is used for the layout of PCB windings. However, the Dowell’s model has its restrictions, namely, magnetic field is assumed to be distributed evenly in one direction. But the magnetic field around the windings are three-dimensional and unevenly. Therefore, further arrangement of PCB windings is proposed to minimize the PCB windings losses. Besides, the magnetic circuit is analogous to electrical circuit, and the magnetic core structure shape the footprint of the PCB winding, so different magnetic core structure can be proposed for the trade-off design among the high power density, high efficiency, and low temperature stress. Therefore, both PCB winding layout and magnetic core structure design are important for the optimization of high frequency magnetic components.

Due to high efficiency and simple structure, LLC resonant converter is a promising topology for developing solid-state transformers. The heart of an LLC converter is the high frequency transformer that provides necessary insulation and step-up/down between primary and secondary sides. In addition, the efficiency of the transformer is a critical factor as it processes the entire power. This becomes even more challenging when circuit switching frequency is raised for shrinking passive component sizes, as skin effect and other non-ideal effects start to kick in. In solid-state transformer applications, size, efficiency and insulation have stringent specifications and meeting all requirements at once is not a simple task. Therefore, this paper presents multiple perspectives in terms of transformer design in an LLC converter and demonstrates with a 3-kW transformer capable of more than 15 kV insulation. Testing results show peak converter efficiency of 98.9% with transformer power density of 480 W/in3.

A novel auxiliary resonant snubber is introduced. The design and operation are carried out, in which this snubber circuitry enables main Gallium Nitride (GaN) switches operating under zero voltage switching (ZVS) condition, and auxiliary Silicon Carbide (SiC) diodes switching under zero current switching (ZCS) condition. Besides, the auxiliary snubber circuitry gating algorithm is also optimized which allows reducing the switching and conduction loss in auxiliary GaN switches to obtain higher system efficiency and better thermal performance. This proposed inverter can be applied to wide range of potential applications, such as string solar inverter, renewable energy combined distributed generation, dc-ac part of bi-directional electrical vehicle (EV) on-board charger, and uninterruptible power supply (UPS), etc.

This paper proposes a hybrid-mode Cuk inverter with low-voltage ride-through (LVRT) capability under grid-faults. It operates as an unfolding-type inverter during normal grid condition and two-stage inverter during abnormal grid condition. Thus, it normally transfers the energy to the utility grid highly efficiently, and also has the LVRT ability under grid-faults. Moreover, two types of inverters share the full-bridge circuit on the grid-side and so the proposed circuit can be developed with low cost and reduced size. This paper outlines operation principles and control methods for the proposed inverter. The prototype of the proposed converter was implemented and experimental tests were carried out to demonstrate its practical feasibility.

The LLC series resonant converter is widely used in many applications due to its high power density and efficiency. However, under applications with relatively small magnetizing current and resonant inductance such as DC transformer (DCX) for telecom power systems and PV optimizers, the resonance between the leakage inductance and the secondary parasitic capacitance during dead-time is unneglectable. It will affect the zero-voltage switching (ZVS) transition and the resonant current during the power delivery period. Therefore, in this paper, two different scenarios of the ZVS condition for an LLC series resonant converter with secondary parasitic capacitance considered will be presented. Moreover, the impact of the resonant to steady state operation under different ZVS timing will be discussed. Experimental results of a 140kHz prototype are provided for verification.

Nowadays, high power density is one of main pursuits for power converters. High switching frequency can greatly reduce the size of passive components. With the availability of wide bandgap devices, the converters have opportunities to operate at megahertz switching frequency with higher efficiency and power density. However, unlike the conventional kilohertz switching, parasitic inductances induced from the printed circuit board (PCB) could significantly affect the circuit operation under megahertz switching. In particularly, the parasitic effects will be enlarged for high step-up or step-down isolated converters, since the parasitic inductances are square times the turns ratio of the transformer when reflecting from low voltage side to high voltage side. This paper takes LLC converter as an example to discuss the optimization of PCB layout to reduce the parasitic effects with finite element method. In the experiments, a couple of 1-MHz 38V/380V 300-W LLC resonant converters are built and compared to verify the design optimization.

A high step-up constant frequency resonant converter with PWM controlled active boost quadrupler rectifier (ABQR) is proposed in this paper. The proposed converter operates at the resonant frequency throughout the whole operation region to achieve the highest efficiency. Under low input voltage conditions, the quadrupler based active boost rectifier will operate with the proposed PWM modulation scheme to step up the voltage. With the proposed ABQR, the output switches serve both for synchronous rectification and voltage boost function. It enables a higher voltage boost ratio than series resonant converter. Moreover, the voltage stress on secondary power devices are reduced to half of the high output voltage and the transformer turns ratio can be lower. A 300-W hardware prototype with gallium-nitride devices is built to verify the performance of the proposed converter and modulation method. It can achieve a peak efficiency of 98.9% and a California Energy Commission weighted efficiency of 98.7% under nominal input voltage condition.

High power density is the primary design consideration for power converters in more electric aircraft (MEA) to meet both space and weight requirements. Therefore, wide bandgap (WBG) semiconductor switching devices, such as SiC, have been chosen to push the switching frequency of the power converter further for size and weight reduction. To meet power quality and conducted emission requirements, a LCL filter is necessary between the converter output and the power grid. With the power switching devices operating at higher frequency, the parasitic effects of various key circuits of the converter cannot be ignored and must be accounted for in the simulation model. This paper describes a complete equivalent circuit model that includes these effects of DC bus-bar, power semiconductor device, gate driver and LCL filter. With the comprehensive model, common-mode (CM) conducted emissions can be predicted and evaluated during the design phase for performance optimization purpose. National Research Foundation (NRF) Accepted version This research work was conducted in the Rolls-Royce@NTU Corporate Lab with funding support from the National Research Foundation (NRF), Rolls-Royce and Nanyang Technological University, under the Corp Lab@University Scheme.

In this paper, the low voltage stress of switches, high voltage gain DC-DC converter is proposed. The operating principle of the converter is similar to that of the conventional buck converter. Therefore, the proposed converter can be operated in the discontinuous conduction mode, continuous conduction mode, depending on the design. Moreover, the controller is also similar to that of the traditional buck converter, results in the simple controller. Furthermore, the voltage stress of every switch is reduced significantly compared with the conventional converter. Therefore, the use of the low voltage rating switches reduces the losses significantly. A 200W converter prototype is successfully built and tested to verify the feasibility of the proposed converter.

High switching frequency (HF) operation of solid-state transformers (SSTs) reduces the weight and volume of magnetic parts. Yet in medium-voltage (MV) SSTs, electrical insulation becomes a great concern and demands extra spacing. To resolve the issue, resistive shielding technique is considered in this paper to mitigate the threat of partial discharge. In addition, geometric shaping is applied to alleviate local electrical field. On top of the insulation and size requirements, HF transformer design should also consider skin effect and other effects induced by ac electromagnetic field. This paper is meant to develop a planar transformer for a MV SST, taking all critical factors into account. 2-d finite element analysis is adopted as main research and conceptual verification method.

Non-isolated step-down converters are widely used as auxiliary power supplies. Active and passive components, excluding large magnetic components, are usually integrated in a single chip in the industry. High power density and high efficiency are always the most important requirements. High switching frequency, such as megahertz (MHz), can highly shrink the volume of passive components compared with kilohertz frequency, however, it will cause huge switching loss for hard switching converters. Zero-voltage-switching (ZVS) is able to highly reduce switching loss, especially under high switching frequency. In this paper, three ZVS buck-type converters operating at MHz frequency, including conventional buck, tapped-inductor buck and hybrid resonant buck converter, are compared. Finally, three hardware prototypes using gallium-nitride (GaN) devices with 24–48 V input and 3-A/5-V output are demonstrated and compared in terms of efficiency, size and thermal performance.

A conventional asymmetrical half-bridge (AHB) converter is a good candidate for low power applications such as TV and LED driver. It has small number of components and all switching devices have soft swtiching capability. However, when the AHB converter is designed with wide input voltage range, it has a large offset current in transformer which increases size of the transformer and core loss. Also, DC-offset current worsens ZVS condition of one of the half-bridge switches resulting in low efficiency in light load condition. To overcome above problems, a new asymmetrical half-bridge converter with coupled inductor rectifier (CIR) is proposed in this paper. Since two capacitors of the new rectifier equalize an average current flowing through secondary rectifier, the proposed converter doesn’t have DC-offset current. Therefore, the proposed converter reduces size of the transformer and can increase efficiency. Experiment is implemented with a 250V-400V input voltage variation and 50V/200W output specifications.

This paper discusses the details of the control scheme and EMI filter design for a modular front-end solid-state transformer (SST). The multi-cell configuration is achieved by connecting the active-front-end (AFE) cells in series, with the voltage from the MV evenly distributed among the cells. The isolated outputs of the dc-dc converters are tied in parallel. The EMI filter is designed to reduce line impedance and switching noise. Simulations showed the EMI filter reduced noise below FCC Class A standards. The SST controller consists of a voltage controller, current controller, and a phase lock loop (PLL) with an ideal duty feedforward. The implementation of these subsystems is explained and its integration in the system is shown. The results show that at low voltage level, the input current waveform is nearly sinusoidal.

Synchronous rectification technique can reduce secondary-side conduction loss of the LLC resonant converter. Typically, the control of synchronous rectifier (SR) relies on either voltage or current information; however, the detection circuit is sensitive to parasitic effects and high frequency noises. Since reliability is among top priorities in solid-state transformer application, open-loop controlled scheme becomes advantageous. Unfortunately, secondary-side current of LLC converter reaches zero-crossing-point (ZCP) earlier at light-load condition and the SR signal could turn off after ZCP. In that case, high circulating current appears in the secondary side and dramatically deteriorate efficiency. Therefore, a tuning method utilizing external primary-side output capacitor and dead-time extension is proposed to avoid late turn-off issue of open-loop controlled scheme. In this paper, the cause of ZCP shifting and late turn-off issue are explained first. Then a model for dead-time transient of LLC converter is derived as the theoretical basis of proposed tuning method. Finally, hardware testing results of a 4-kW LLC converter module are presented. With the proposed tuning method, the open-loop controlled synchronous rectification can improve the efficiency of the LLC converter module even at light-load condition.

In this paper, a detailed design procedure is presented for a bidirectional CLLLC-type resonant converter for a battery charging application. This converter is similar to an LLC-type resonant converter with an extra inductor and capacitor in the secondary side. Soft-switching can be ensured in all switches without additional snubber or clamp circuitry. Because of soft-switching in all switches, very high-frequency operation is possible; thus, the size of the magnetics and the filter capacitors can be made small. To reduce the size and cost of the converter, a CLLC-type resonant network is derived from the original CLLLC-type resonant network. First, in this paper, an equivalent model for the bidirectional converter is derived for the steady-state analysis. Then, the design methodology is presented for the CLLLC-type resonant converter. Design of this converter includes determining the transformer turns ratio, design of the magnetizing inductance based on ZVS condition, design of the resonant inductances and capacitances. Then, the CLLC-type resonant network is derived from the CLLLC-type resonant network. To validate the design procedure, a 3.5-kW converter was designed following the guidelines in the proposed methodology. A prototype was built and tested in the laboratory. Experimental results verified the design procedure presented.

This paper presents a nonisolated, high boost ratio dc-dc converter with the application for photovoltaic (PV) modules. The proposed converter utilizes a hybrid transformer to incorporate the resonant operation mode into a traditional high boost ratio active-clamp coupled-inductor pulse-width-modulation dc-dc converter, achieving zero-voltage-switching (ZVS) turn-on of active switches and zero-current-switching turn-off of diodes. As a result of the inductive and capacitive energy being transferred simultaneously within the whole switching period, power device utilization (PDU) is improved and magnetic utilization (MU) is optimized. The improved PDU allows reduction of the silicon area required to realize the power devices of the converter. The optimized MU reduces the dc-bias of magnetizing current in the magnetic core, leading to smaller sized magnetics. Since the magnetizing current has low dc-bias, the ripple magnetizing current can be utilized to assist ZVS of main switch, while maintaining low root-mean-square (RMS) conduction loss. The voltage stresses on the active switches and diodes are maintained at a low level and are independent of the wide changing PV voltages as a result of the resonant capacitor in series in the energy transfer loop. The experimental results based on 250 W prototype circuit show 97.7% peak efficiency and system CEC efficiencies greater than 96.7% over 20 to 45 V input voltages. Due to the high efficiency over wide power range, the ability to operate with a wide variable input voltage and compact size, the proposed converter is an attractive design for PV module applications.

In this paper, a contactless charging system for an electric vehicle (EV) battery is proposed. The system consists of three parts: 1) a high-frequency power supply from a full-bridge inverter with frequency modulation; 2) a loosely coupled transformer that utilizes series resonant capacitors for both the primary and secondary windings; and 3) a rectification output circuit that uses a full-bridge diode rectifier. With carefully selected compensation network parameters, zero-voltage switching can be ensured for all the primary switches within the full range of an EV battery charging procedure, which allows the use of low ON-state resistance power MOSFETs to achieve high-frequency operation and system efficiency. The design of loosely coupled transformer is simulated and verified by finite element analysis software. For a 4-kW hardware prototype, the peak dc–dc efficiency reaches 98% and 96.6% under 4- and 8-cm air gap conditions, respectively. The prototype was tested with an electronic load and a home-modified EV to verify the performance of constant current and constant voltage control and their transitions.

Flyback type converters are widely used in various applications including small power LED drivers. However, they suffer from the losses from the snubber circuit. To beat this problem, previous studies investigated the lossless snubbers. However, they still have a limitation due to the additional components resulting in a high cost and low power density. In this paper, a new converter topology for two-channel LED driving with the reduced number of components. The proposed converter is based on the isolated forward-flyback converter with the blocking capacitors for two-channel output structure. The proposed converter delivers the energy stored in the leakage inductor to the output side directly, whereas conventional approaches store the energy in the additional components. Therefore, the proposed converter can remove the additional snubber components, and it also can achieve a high efficiency. The effectiveness of the proposed converter has been verified with 3.3V input and 11.55W output prototype.

This paper discloses the development of modular front-end medium-voltage solid-state transformer (SST) to show system level design, circuit topology, and prototype test results. Each multilevel front-end module consists of two stages: (1) ac to dc boost converter with power factor correction dc and (2) isolated dc-dc LLC converter. The proposed system has been designed, simulated, and fabricated with the rating of 7.2-kV input, 400-V output, and 25-kW power capability. With the adoption of silicon carbide devices, the peak efficiency of the entire front-end converter from high-voltage ac to low-voltage dc achieves 98.2% efficiency. The individual switch is switched at 10 kHz. With complementary switching for the 3-level boost converter, the equivalent switching frequency is 20 kHz for the individual module and 200 kHz for the combined ten-module power stage. The full-voltage, full-power testing with a near ideal source shows a clean input current waveform.

In this paper, a tapped-inductor (TI) buck converter using planar coupled inductor is presented for low power applications. The duty cycle of TI buck is much wider compared with traditional buck converter under same voltage conversion ratio conditions. Therefore, it is suitable for high step-down applications. With synchronous conduction mode (SCM), TI buck converter obtains zero voltage switching (ZVS) of both switches and thus be able to operate at high switching frequency. Besides, compared with other three-switch buck-type topologies, its simplicity in circuit topology leads to less gate driver and other auxiliary power loss, which is beneficial for low power applications. In this paper, converter operating principle and design for a compact coupled inductor are presented. Finally, experimental results of a 15-W prototype are given. Under switching frequency of 2 MHz, the peak efficiency of power stage reaches to 89 % with magnetic component size less than 150 mm3.

This paper proposed a new topology that can achieve high-step-down conversion compared with traditional buck converter. A coupled inductor is employed to extend duty cycle which is for high-step-down applications. Soft-switching of all switches can be achieved. A prototype with 24 V input 5 V/2 A output is given to verify the circuit operation. Switching frequency is up to 1.3 MHz to minimize magnetics size. The peak efficiency can reach to 87 %.

This paper presents a hybrid switch that parallels a power MOSFET and an insulated-gate bipolar transistor (IGBT) as the main switch of a zero-voltage switching (ZVS) inverter. The combination features the MOSFET conducting in the low-current region and the IGBT conducting in the high-current region, and the soft switching avoids the reverse recovery problem during the device turn-on. A custom hybrid switch module has been developed for a variable-timing-controlled coupled-magnetic-type ZVS inverter with a nominal input voltage of 325 V and the continuous output power of 30 kW for a traction motor drive. Experimental results of the hybrid-switch-based inverter with the total loss projected by temperature indicate that the inverter achieves 99% efficiency at the nominal condition and demonstrate ultrahigh-efficiency operation over a wide load range. At 375-V input, the maximum measured efficiency through temperature projection and loss separation analysis is 99.3%.

This paper presents a high-reliability single-phase transformerless grid-connected inverter that utilizes superjunction MOSFETs to achieve high efficiency for photovoltaic applications. The proposed converter utilizes two split ac-coupled inductors that operate separately for positive and negative half grid cycles. This eliminates the shoot-through issue that is encountered by traditional voltage source inverters, leading to enhanced system reliability. Dead time is not required at both the high-frequency pulsewidth modulation switching commutation and the grid zero-crossing instants, improving the quality of the output ac-current and increasing the converter efficiency. The split structure of the proposed inverter does not lead itself to the reverse-recovery issues for the main power switches and as such superjunction MOSFETs can be utilized without any reliability or efficiency penalties. Since MOSFETs are utilized in the proposed converter high efficiency can be achieved even at light load operations achieving a high California energy commission (CEC) or European union efficiency of the converter system. It also has the ability to operate at higher switching frequencies while maintaining high efficiency. The higher operating frequencies with high efficiency enables reduced cooling requirements and results in system cost savings by shrinking passive components. With two additional ac-side switches conducting the currents during the freewheeling phases, the photovoltaic array is decoupled from the grid. This reduces the high-frequency common-mode voltage leading to minimized ground loop leakage current. The operation principle, common-mode characteristic and design considerations of the proposed transformerless inverter are illustrated. The total losses of the power semiconductor devices of several existing transformerless inverters which utilize MOSFETs as main switches are evaluated and compared. The experimental results with a 5 kW prototype circuit show 99.0% CEC efficiency and 99.3% peak efficiency with a 20 kHz switching frequency. The high reliability and efficiency of the proposed converter makes it very attractive for single-phase transformerless photovoltaic inverter applications.

This paper presents a nonisolated, high boost ratio hybrid transformer dc–dc converter with applications for low-voltage renewable energy sources. The proposed converter utilizes a hybrid transformer to transfer the inductive and capacitive energy simultaneously, achieving a high boost ratio with a smaller sized magnetic component. As a result of incorporating the resonant operation mode into the traditional high boost ratio pulsewidth modulation converter, the turn-off loss of the switch is reduced, increasing the efficiency of the converter under all load conditions. The input current ripple and conduction losses are also reduced because of the hybrid linear-sinusoidal input current waveforms. The voltage stresses on the active switch and diodes are maintained at a low level and are independent of the changing input voltage over a wide range as a result of the resonant capacitor transferring energy to the output of the converter. The effectiveness of the proposed converter was experimentally verified using a 220-W prototype circuit. Utilizing an input voltage ranging from 20 to 45 V and a load range of 30–220 W, the experimental results show system of efficiencies greater than 96% with a peak efficiency of 97.4% at 35-V input, 160-W output. Due to the high system efficiency and the ability to operate with a wide variable input voltage, the proposed converter is an attractive design for alternative low dc voltage energy sources, such as solar photovoltaic modules and fuel cells.

Effective photovoltaic power conditioning requires efficient power conversion and accurate maximum power point tracking to counteract the effects of panel mismatch, shading, and general variance in power output during a daily cycle. In this paper, the authors propose an integrated boost resonant converter with low component count, galvanic isolation, simple control, as well as high efficiency across a wide input and load range. Provided is a discussion of the converter synthesis, key operational features, converter design procedure, and loss analysis, as well as experimental verification by way of a 250-W prototype with a California Energy Commission efficiency of 96.8%.

This paper first presents a hybrid-switching step-down dc-dc converter, and then, by introducing transformer isolation, a novel hybrid-switching phase-shift full-bridge dc-dc converter is derived for electric vehicle battery chargers. The proposed converter provides wide zero-voltage-switching range in the leading-leg switches, achieves zero-current-switching for lagging-leg switches, and uses a hybrid-switching method to avoid freewheeling circulating losses in the primary side. Because the resonant capacitor voltage of the hybrid-switching circuit is applied between the bridge rectifier and the output inductor for the duration of the freewheeling intervals, a smaller sized output inductor can be utilized. With the current rectifier diode of the hybrid-switching circuit providing a clamping path, the voltage overshoots that arise during the turn-off of the rectifier diodes are eliminated and the voltage stress of bridge rectifier is clamped to the minimal achievable value, which is equal to secondary-reflected input voltage of the transformer. The inductive energy stored in the output inductor and the capacitive energy stored in the resonant capacitor of the hybrid-switching circuit are transferred to the output simultaneously during the freewheeling intervals with only one diode in series in the current path, achieving more effective and efficient energy transfer. The effectiveness of the proposed converter was experimentally verified using a 3.6-kW prototype circuit designed for electric vehicle onboard chargers. Experimental results of the hardware prototype show that the converter achieves a peak efficiency of 98.1% and high system efficiencies over wide output voltage and power ranges.

Phase-shift transformers have been widely used for harmonic cancellation in a large-scale three-phase motor drive system. For a shipboard with multiple sources and loads, a shunt-connected phase-shift transformer can serve as harmonic path to conduct certain harmonic contents. This paper shows how the harmonics can be cancelled in a dual drivetrain system of a shipbboard. A laboratory scale of two 7.5-kW systems was set up for experimental verification of harmonic trapping. Both simulation and experimental results verify the harmonic trapping principle through square-wave analysis. With experimental the same harmonic cancellation performance, the kVA capacity of the shunt-connected phase-shift transformers will be compared to that of the conventional series connected Δ-Δ and Δ-Y transformer pair to show significant advantage of using this recently proposed system in a dual or multiple drivetrain system.

This paper discloses the development of 15-kV class intelligent universal transformer (IUT) to show system level design, circuit topology, and prototype test results. The complete system is split into two stages: (1) high-voltage ac to low-voltage dc and (2) low-voltage dc to low-voltage ac. With the adoption of silicon carbide (SiC) devices, the high-voltage front-end ac to low voltage dc conversion stage achieves 98.4% efficiency, and the complete power stage can be naturally cooled. With the adoption of auxiliary resonant soft-switching inverter, the second stage achieves 99.2% efficiency. Overall the system has been demonstrated at 97.5% efficiency without forced-air cooling. Extended 8-hour testing was conducted to ensure long-term operation reliability. Overall efficiency and voltage regulation were compared with that of a conventional transformer for justification of IUT adoption.

The high-brightness white-light-emitting diode (LED) has attracted a lot of attention for its high efficacy, simple to drive, environmentally friendly, long lifespan, and compact size. The power supply for LED also requires long life, while maintaining high efficiency, high power factor, and low cost. However, a typical power supply design employs an electrolytic capacitor as the storage capacitor, which is not only bulky, but also with a short lifespan, thus hampering performance improvement of the entire LED lighting system. In this paper, a novel power factor correction (PFC) topology is proposed by inserting the valley-fill circuit in the single-ended primary inductance converter (SEPIC)-derived converter, which can reduce the voltage stress of the storage capacitor and output diode under the same power factor condition. This valley-fill SEPIC-derived topology is, then, proposed for LED lighting applications. By allowing a relatively large voltage ripple in the PFC design and operating in the discontinuous conduction mode (DCM), the proposed PFC topology is able to eliminate the electrolytic capacitor, while maintaining high power factor and high efficiency. Under the electrolytic capacitor-less condition, the proposed PFC circuit can reduce the capacitance of the storage capacitor to half for the same power factor and output voltage ripple as comparing to its original circuit. To further increase the efficiency of LED driver proposal, a twin-bus buck converter is introduced and employed as the second-stage current regulator with the PWM dimming function. The basic operating principle and analysis will be described in detail. A 50-W prototype has been built and tested in the laboratory, and the experimental results under universal input-voltage operation are presented to verify the effectiveness and advantages of the proposal.

This paper presents a 55-kW three-phase inverter based on soft-switching modules for hybrid electric vehicle drives at high-temperature conditions. The main switch of the module is composed of the hybrid switch, which is composed of parallel IGBT and MOSFET. Highly integrated soft-switching modules have been employed to achieve switching loss as well as conduction loss reduction. The operation principle of the proposed inverter is analyzed in detail. Experimental evaluations of the inverter have been conducted through both inductive load and motor-dynamometer load at coolant temperatures ranging from 25°C to 90°C. Efficiency measurement using power meter showed that the peak efficiency is around 99%, and it drops slightly at lower speed and higher temperature conditions. To ensure measurement fidelity, a double-chamber differential calorimeter system was designed and calibrated for the inverter testing. Through long-hour testing, the measured efficiencies consistently showed 99% and higher. The soft-switching inverter has been operated reliably and demonstrated high efficiency at different temperature and test conditions.

A novel, high-efficiency inverter using MOSFETs for all active switches is presented for photovoltaic, nonisolated, ac-module applications. The proposed H6-type configuration features high efficiency over a wide load range, low ground leakage current, no need for split capacitors, and low-output ac-current distortion. The detailed power stage operating principles, pulsewidth modulation scheme, associated multilevel bootstrap power supply, and integrated gate drivers for the proposed inverter are described. Experimental results of a 300 W hardware prototype show that not only are MOSFET body diode reverse-recovery and ground leakage current issues alleviated in the proposed inverter, but also that 98.3% maximum efficiency and 98.1% European Union efficiency of the dc-ac power train and the associated driver circuit are achieved.

Lithium-ion-based battery energy storage system has started to become the most popular form of energy storage system for its high charge and discharge efficiency and high energy density. This paper proposes a high-efficiency grid-tie lithium-ion-battery-based energy storage system, which consists of a LiFePO4-battery-based energy storage and a high-efficiency bidirectional ac-dc converter. The battery management system estimates the state of charge and state of health of each battery cell and applies active charge equalization to balance the charge of all the cells in the pack. The bidirectional ac-dc converter works as the interface between the battery pack and the ac grid. A highly efficient opposed-current half-bridge-type inverter along with an admittance-compensated quasi-proportional resonant controller is adopted to ensure high power quality and precision power flow control. A 1-kW prototype has been designed and implemented to validate the proposed architecture and system performance.

This paper presents a high-efficiency grid-connected photovoltaic (PV) module integrated converter (MIC) system with reduced PV current variation. The proposed PV MIC system consists of a high-efficiency step-up DC–DC converter and a single-phase full-bridge DC–AC inverter. An active-clamping flyback converter with a voltage-doubler rectifier is proposed for the step-up DC–DC converter. The proposed step-up DC–DC converter reduces the switching losses by eliminating the reverse-recovery current of the output rectifying diodes. To reduce the PV current variation introduced by the grid-connected inverter, a PV current variation reduction method is also suggested. The suggested PV current variation reduction method reduces the PV current variation without any additional components. Moreover, for centralized power control of distributed PV MIC systems, a PV power control scheme with both a central control level and a local control level is presented. The central PV power control level controls the whole power production by sending out reference power signals to each individual PV MIC system. The proposed step-up DC–DC converter achieves a high-efficiency of 97.5% at 260 W output power to generate the DC-link voltage of 350 V from the PV voltage of 36.1 V. The PV MIC system including the DC–DC converter and the DC–AC inverter achieves a high-efficiency of 95% with the PV current ripple less than 3% variation of the rated PV current.

This paper first introduces the design of an ultrahigh efficiency 50-kW bidirectional dc-dc converter at zero-voltage-switching operation, and then, a high-precision efficiency measurement method using a regenerative approach. The ultrahigh efficiency bidirectional dc-dc converter is achieved with 1) the use of CoolMOS as the main switch under zero-voltage soft switching condition; 2) multiple-phase legs for current sharing to reduce the conduction loss; and 3) coupling inductors between each two-phase legs to reduce the core loss. Two identical hardware prototypes were designed, fabricated, and tested for performance evaluation. In order to precisely measure the converter efficiency, the two identical bidirectional dc-dc converters are tested with one as the device under test and the other as the regenerative unit. With the use of ± 0.5% current shunt and regenerative measurement, the relative efficiency error stays below ±0.025%. Measured efficiency with load from 20% to 100% consistently shows above 97.50%. At the 50 kW full-load condition, the efficiency is 99.05% with ±0.01% efficiency relative error.