Search

A family of inductorless forward-flyback converters utilizing dual constant on-time modulation is proposed, in order to maintain high efficiency over a wide load and input range. The main switch is turned on for the constant half resonant period to achieve zero-current-switching for the forward diode and to minimize the deadtime between the two output diodes. The auxiliary active switch is in the on-state with a very short constant interval to realize zero-voltage-switching for the main active switch, even if the magnetizing inductor operates in the continuous current mode. Experimental results for a 250 W hardware prototype verifies soft-switching operation from zero to full load over 25 to 45 V input range and the CEC weighted efficiency reaches 97%. The proposed converter is attractive for the tree-type PV system applications.

This paper presents a hybrid switch that parallels a power MOSFET and an IGBT as the main switch of a zero-voltage switching 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 an analysis of losses that occur during dead time in an active-clamp flyback converter utilizing Gallium Nitride based MOSFETs. This analysis is used to optimize the length of the dead-time period in order to minimize losses in the switching devices. When compared to silicon-based MOSFETs, GaN-based MOSFETs have lower switching losses and much higher reverse conduction losses, so it is not desirable to design for zero-voltage switching (ZVS) over a wide load range. The analysis presented in this paper finds an optimal trade-off between partial ZVS and reverse conduction losses, minimizing overall device switching losses and therefore increasing converter efficiency over the desired load range. A 15-W, four-output active-clamp flyback converter utilizing GaN devices at 1 MHz is designed and implemented using the recommended optimization. The experimental results confirm this analysis and result in a minimization of switching losses and an increase in converter efficiency.

This paper presents a new three-phase four-leg inverter based on dual-buck power cell. Compared to traditional standard three-phase four-leg inverters with two IGBT switches in one leg, the proposed inverter incorporates dual-buck power cell, which results in several benefits. First, the dual-buck power cell allows the use of power MOSFETs for higher switching speed and efficiency improvement. Second, with the help of unique operation of dual-buck power cell, the inverter reliability is enhanced because no dead time is needed for all four legs and shoot-through concerns are totally eliminated. A unified pulse width modulation (PWM) is introduced for the proposed inverter to reduce computational burden of real-time implementation by digital signal processor (DSP). Space vector PWM (SVPWM) and discontinuous space vector PWM (DSVPWM) are analyzed under the unified PWM scheme. A prototype of the proposed inverter is designed and tested with three-phase unbalanced load under different dc bus voltage and modulation index conditions to verify the feasibility and effectiveness of the topology and the unified PWM scheme.

A fuzzy logic controlled (FLC) MPPT controller based on the perturb-and-observe (P&O) algorithm presents in the paper. It can effectively reduce power waste and attain the high rates voltage conversion by using the proposed converter with the FLC MPPT. A stand-alone PV inverter system is proposed that contains a high conversion ratio converter with the FLC and a dc/ac inverter with phase-lock loop design. The simulation and experimental results for the PV inverter with the FLC MPPT control to verify the effectiveness of the proposed method.

Modeling of a complete photovoltaic (PV) inverter system poses a significant challenge because it involves different time-scaled dynamics including filter elements, fast current loop, voltage loop, maximum power point tracking (MPPT) loop, and response of the energy source. This paper intends to utilize the state-space modeling approach for stability analysis for a grid-tie PV inverter system by eigenvalue evaluation with different irradiation levels, PV output voltages, voltage-loop gains and current-loop gains. The stability analysis can not only show more insight of the two-loop interaction with current-loop gain variation, but also show the stability trend due to the change of both the source voltage and the source impedance with the input PV voltage change, which are quite difficult to detect with conventional single-variable transfer function analysis. The controller based on state-space modeling and analysis has been designed and implemented. Experimental results are used to verify the stability trend predicted in the model.

Photovoltaic (PV) inverter is the most important part for energy conversion, and the current research focus for PV inverter is high efficiency, high reliability, and low-output ac-current distortion. With considerable grid-connected PV installation in last few years, high penetration PV system is desired, which requires integrating PV inverter into grid regulation. New code in Germany already requires PV inverter providing system regulation and service for low voltage distribution system. One of obvious impact on PV inverter is reactive power generation requirement. Most state-of-the-art high-efficiency PV inverters that adopt single-stage topology only allow unity power generation but none of them are able to generate reactive power. This paper proposes a high-efficiency dual-buck full-bridge PV inverter for a wide range power factor operation. Additionally, a novel hybrid bipolar PWM method is proposed to achieve low ground leakage current and low output current distortion in the PV system. At last, simulation and experiment demonstrate that the proposed PV inverter system can provide a wide-range power factor operation with high efficiency, low ground leakage current, and low output current distortion.

This paper presents a non-isolated, 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 size magnetic component. As a result of incorporating the resonant operation mode into the traditional high boost ratio PWM converter, the turn off loss of the switch is reduced, increasing the efficiency of the converter under all load conditions. The input current ripple is also reduced because of the linear-sinusoidal hybrid 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. The effectiveness of the proposed converter was experimentally verified using a 220 W prototype circuit. Utilizing an input voltage ranging from 20V to 45V and a load range of 30W to 220W, the experimental results show system of efficiencies greater than 96% with a peak efficiency of 97.4% at 35V input, 160W output. Because of high efficiency over wide output power range 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 (PV) modules.

In this paper a new methodology is presented to calculate the average power quickly and accurately for the single-phase paralleled inverters intended to be applied in a droop-control microgrid system. Most existing droop control systems utilize a simple first-order filter to calculate the active and reactive power. The added filter can smooth the calculated results but it tends to hurt the system dynamic response due to a low cut-off frequency that is intended to get enough ripple attenuation. This low frequency pole in the low-pass filter could also introduce system instability under certain load conditions. A new filter calculation methodology is thus proposed to achieve better ripple attenuation with faster response by combining a low-pass filter, a delay, and summation blocks. Both simulation and experiment are used to verify the effectiveness of the proposed power calculation methodology.

This paper presents a new type of cascade inverter, named cascade dual-buck full-bridge inverter. Compared to cascade H-bridge inverter, the proposed inverter has several advantages. First, it eliminates the possibility of shoot-through problems, which is the major failure of traditional voltage source inverters. Second, it does not need dead time, which fully utilizes the pulse width modulated voltage and transfers total desired energy to the load. In addition, it can use high-voltage power MOSFETs without the complexity of soft-switching assisting circuits to improve the system efficiency. In this paper, several PWM techniques are analyzed and compared, including bipolar PWM, unipolar PWM and phase-shifted PWM, when applied to the proposed inverter. It has been found out that a hybrid PWM technique with the combination of the two out of the three PWMs mentioned above leads to better performance of the cascade dual-buck full-bridge inverter in terms of less output current ripple and harmonics, no zero-crossing distortion, and higher efficiency. A prototype of the proposed inverter has been built and tested to verify the feasibility and effectiveness of the topology and the hybrid PWM technique.

High brightness white LED has attracted a lot of attention for its high efficacy, simple to drive, environmentally friendly, long lifespan and small size. The power supply for LED also requires long life while maintaining high efficiency, high power factor and low cost. However, a typical design employs electrolytic capacitor as storage capacitor, which is not only bulky, but also with short lifespan, thus hampering the entire LED lighting system. In this paper, a novel PFC topology is proposed by inserting the valley fill circuit in the SEPIC-derived converter, which can reduce the voltage stress of storage capacitor and output diode to half under the same power factor condition. This valley fill SEPIC-derived PFC topology is then proposed for LED lighting application. By allowing a relatively large voltage ripple allowable in a PFC design and operating in DCM, the proposal is able to eliminate the electrolytic capacitor while maintaining high power factor. The basic operating principle and analysis will be described in detail. A 50-W prototype has been built to verify the proposed approach.

For a single-phase grid-connected power system, output power is pulsated instantaneously with a double-fundamental frequency. Accordingly, the current drawn from renewable energy sources tends to be pulsated and contains low frequency ripple components, which causes several issues including a power harvesting deterioration and energy source's life shortening. This paper proposes a novel power pulsation decoupling scheme to reduce low frequency ripple current with a fast voltage loop. Proper control design based the small-signal model of two-stage dc-dc-ac converter is presented in a frequency domain analysis, and its experimental waveforms are provided to verify the effectiveness.

In this paper, a novel control scheme of an induction machine for 48V- battery based traction drive system is presented. The main features of the proposed control scheme are the capability to boost the maximum torque capability over the entire speed range by an optimized over-modulation strategy and smoothly transition the maximum torque-per-ampere to field weakening region despite significant variations of the source voltage and machine parameters. The nonlinear saturation effect of the mutual inductance is taken into account to produce the limitation curves thus to reach the actual maximum torque over the whole speed range. Experimental results show that the proposed control scheme is most suitable for low-voltage 48V- battery traction drive systems.

High brightness white LED has attracted a lot of attention for its high efficacy, simple to drive, environmentally friendly, long lifespan and small size. The power supply for LED lighting also requires long life while maintaining high efficiency, high power factor and low cost. However, a typical design employs electrolytic capacitor as storage capacitor, which is not only bulky, but also with short lifespan, thus hampering the entire LED lighting system. To prolong the lifespan of power supply, it has to use film capacitor with small capacitance to replace electrolytic capacitor. In this paper, a universal input high efficiency, high power factor LED driver is proposed based on the modified SEPIC converter. Along with a relatively large voltage ripple allowable in a PFC design, the proposal of LED lamp driver is able to eliminate the electrolytic capacitor while maintaining high power factor. To increase the efficiency of LED driver, the presented SEPIC-derived converter is modified further as the twin-bus output stage for matching ultra-high efficiency twin-bus LED current regulator. The operation principle and related analysis is described in detail. A 50-W prototype has been built and tested to verify the proposed LED Driver.

In this paper, a novel single-switch three-level (TL) boost converter for PWM dimming LED lighting is presented. Taking the system efficiency and output ripple into consideration, traditional two-level boost LED driver always employs additional active switch in order to deal with the dimming issue. However, the proposed TL boost converter has overcome the dimming control problem with only one switch by utilizing the “synchronous” PWM dimming approah, hence lower the system cost. Moreover, compared with the standard TL boost converter, the proposed topology not only maintains the advantage of using a lower voltage rating power switch that is rated half the output voltage, but also eliminates one active switch and its associated driving circuit. The operating principle and dimming scheme of the proposed TL boost converter is described in detail. A prototype of 11-W dimmable LED driving converter has been implemented to verify the design and analysis. The experimental result shows that single-switch TL boost converter can regulate the LED current from zero to the rated 350mA with fast slew rate. A peak efficiency of 95% was achieved with 400kHz switching frequency.

A novel soft-switching converter combining resonant half-bridge and phase shifted full-bridge configuration is proposed to ensure the switches in the leading-leg operating at zero-voltage switching from true zero to full load, and the switches in the lagging-leg at zero-current switching with minimum duty cycle loss and circulating conduction loss by significantly reducing leakage or series inductance. A 3.4 kW hardware prototype has been designed, fabricated and tested to verify the validity and performance of the proposed circuit. Experimental results show that the proposed topology achieves 98% maximum efficiency, compact the output inductor size and soft-switching over a wide output voltage and current range and is attractive for electrical vehicle battery charger applications.

Photovoltaic (PV) micro-inverter operating under burst mode tends to improve efficiency figure under light load conditions but on the other hand, it also creates power quality impact to the utility grid. In this paper, the burst mode operation has been tested extensively, and the results are used as the basis of study for high penetration PV in a large-scale system. In order to study the impact of burst mode in different penetration levels, small number of PV micro-inverters were tested, and the simplified models were established by matching the experimental and simulating results. The models were then applied to a large-scale power system for high-penetration PV study. The results indicate potential voltage flicker under high penetration levels, especially when PV is the main energy source in a micro grid.

This paper presents a method of smoothly transitioning between low-speed and high-speed position sensorless control algorithms of permanent magnet synchronous machines (PMSMs). The transition method estimates the load torque, synchronizes the estimated outputs of both algorithms, and then smoothly transitions from one algorithm to the other. This is achieved by commanding a calculated open-loop torque reference while the estimator that is taking over reaches steady-state. The effectiveness of the proposed method has been experimentally verified by transitioning between various low-speed and high-speed control algorithms using an 11-kW interior permanent magnet (IPM) motor.

This paper proposes a digital single-loop control method which enables a seamless mode transition between voltage and current control mode and current slew-rate control for a battery connected multi-phase dc-dc converter. The proposed algorithm consists of a current reference generator and a digital average current controller. The current reference generator changes the time constant of the digital integrator to implement ramp-up and ramp-down of the current reference command. The digital average current controller is designed to track the current reference accurately. A small signal model of the current control loop is derived and the control parameters are determined by the small signal analysis. A startup method when the output of the dc-dc converter is connected to a battery is also proposed to prevent reverse current flowing back to the converter input which is connected to the fuel-cell stack in the design. A prototype 5 kW four-phase dc-dc converter serving as an auxiliary power supply in heavy duty trucks has been built and tested to verify the effectiveness of the proposed method.

Islanding detection is necessary to detect the loss of the electric power system (EPS). The standard requirement for island detection is described in "IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems" [1] where an island must be detected within 2 seconds to turn off the distributed resource. Anti-islanding schemes use the fact that each distributed resource (DR) must synchronize to the EPS and the DR cannot regulate voltage. Many methods are possible to detect an island. The methods can be separated in four separate groups: active, passive, hybrid, and supervisory control and data acquisition (SCADA). This paper will discuss a passive method and a few active methods under the non-detection zone and parallel case. Two SCADA methods will be discussed briefly. Based off those results, a few suggestions of improvements and future work will be made.

A novel single-switch three-level (TL) converter is proposed for dimmable LED lighting. Compared with standard TL converters, the proposed topology not only maintains the advantage of using a lower voltage rating power switch that is rated half the input voltage, but also eliminates one active switch and its associated driving circuit. Moreover, it can naturally solve the voltage stress imbalance issue because of the resonant flying capacitor. The operation principle and dimming scheme of the proposed TL converters have been described. A prototype of 46-W dimmable LED driving converter has been implemented to verify the designs and analyses. The experimental result shows that single-switch TL buck converter can regulate the LED current from zero to the desired 1 A with fast slew rate. A peak efficiency of 98% was achieved with 400 kHz switching frequency.

Harmonic distortion in power systems is growing due to the popularity of switch-mode power electronic equipment. This equipment has recognized advantages, such as reducing weight and improving control and efficiency in power converters and supplies. A disadvantage of switch-mode power converters is that their lowest-cost circuit may burden the power system with harmonic loading. Methods to reduce this distortion are recognized, but economic incentives are yet to be realized. Standardization is the most effective means to influence equipment design and to control distortion in power systems. The authors compare the major European and American standards, as well as some of the electronic equipment design changes that are supposed to limit harmonics. >

A high-efficient bidirectional ac-dc converter is proposed for energy storage system. The proposed converter can transfer both active and reactive power between ac grid and dc sources. The proposed converter exhibits two distinct merits: (1) no shoot-through issues because the phase leg does not contain series connected switches, (2) the reverse recovery dissipation of the power switch is greatly reduced because the freewheeling current does not flow through the body diode of power MOSFET. Along with the admittance compensation, a quasi proportional-resonant controller has been designed to significantly increase the loop gain at the fundamental frequency, while maintaining enough phase margins. The proposed controller has been simulated and implemented in a FPGA-based 1-kW bidirectional ac-dc converter prototype. Experimental results validate the design of the proposed high-efficiency high-performance converter.

This paper proposed an easy, simple, and flexible control scheme for a three-phase grid-tie inverter system. A half-bridge single-phase grid-tie inverter was designed with a proportional-resonant control, an admittance compensator, and scalar control scheme. This single-phase control method was expanded in a three-phase grid-tie inverter system with duplicating three individual phases with 120° apart. Here are several benefits of the proposed control scheme: 1) it is easy to design by applying single-phase grid-tie inverter control method, 2) it requires less computation burden than that of the conventional three phase control scheme, 3) it provides either a constant power or a constant current to the utility grid with regardless three-phase grid voltage conditions, 4) it provides easily an active and reactive power, 5) it can be designed with a modular manner. A 3-kW power conditioning system has been built and tested in order to verify simulation results and experimental results.

A novel twin-bus converter using n + 1 active switches is proposed for the n-string LEDs to be dimmable from true zero to the rated current level. With the proposed twin-bus structure, the n-switches that perform the current-loop regulation can operate at very high frequency because of significantly reduced voltage stresses, while achieving high efficiency over a wide load range. With operating frequency exceeding 1 MHz in the test case, the proposed LED driver demonstrates ultra compact size inductor and fast slew rates of the LED current. The dimming controlled switch, however, can operate at a low frequency to ensure high-efficiency operation without light flicker. The detailed power stage operating principle and control scheme of the individual string current for the presented converter are described. Experimental results of a 3-string 50-W LED driver hardware prototype show that the independent string current can be regulated from zero to the desired 350 mA for dimming control. A peak efficiency of 98.3% was achieved with 1.08 MHz switching frequency.

The CoolMOS™+ transistor is a power MOSFET type device that utilizes a “super-junction” embedded within its drift region in order to improve the trade-off between on-resistance and breakdown voltage. The super-junction results in unique inter-electrode capacitance characteristics that require an advanced modeling approach to accurately represent switching performance. This paper describes a new compact circuit simulator model for the CoolMOS™ transistor and demonstrates the model performance using the Saber† simulator for a 650 V, 60 A device. The model is suitable for implementation in the Saber simulator that accurately describes all three inter-electrode capacitances (i.e., gate-drain, gate-source, and drain-source capacitances) for the full operating range of the device. The model is derived using the actual charge distribution within the device rather than assuming a lumped charge or one-dimensional charge distribution. Simulation results show excellent agreement with measurement results in contrast to previous modeling approaches used for this device. The compact model developed in this work is going to be utilized in the design of a high efficiency soft-switching inverter for electric vehicle motor drives and a high efficiency bidirectional DC-DC converter at zero-voltage switching (ZVS) operation.

This paper proposes an active technique to reconstruct and balance the phase currents in multiphase dc-dc converters implementing both of voltage- and current-mode controls. Only one current sensor at the dc link is required to measure and reconstruct the phase currents. Multiple current samples in the pulsewidth modulation switching period are synchronized with the carrier waveforms to actively reconstruct the phase currents using a simple active balancing algorithm that is implemented in a digital controller. The proposed technique improves system performance, stability, and efficiency, and prevents inductor saturation. A 5-kW four-phase dc-dc converter prototype for battery charging application is built to experimentally verify the proposed algorithm.

A single-phase grid connected transformerless PV inverter for residential application is presented. The inverter is derived from a boost cascaded with buck converter along with a line frequency unfolding circuit. High efficiency can be achieved because the converter allows the use of power MOSFET and ultra fast reverse recovery diode, which also features a robust structure because the phase-leg does not have shoot-through issue. By interleaving multiple phases, the ripple can be reduced, and thus the inductor size can also be reduced. This paper begins with theoretical analysis and modeling of this boost-buck converter based inverter to define the operation limit and to design the closed-loop controller. A two-phase interleaved inverter is then designed accordingly. Finally, the simulation and experiment results are shown to verify the concept.

Two-stage, grid-tied Photovoltaic (PV) systems commonly use boost-type converters at the front end. The charge-pumped reboost converter is a high-step-up dc-dc converter with continuous input-current which is suitable for this purpose. Using a tapped-inductor boost topology for the small-signal model, a high-bandwidth input-voltage loop can be designed which rapidly tracks reference changes, source transients, and can reject disturbances from the load. The practicality of this model is verified experimentally with frequency response analysis, transient response, and system-level testing.

A four-phase interleaved bidirectional dc-dc converter with coupled inductor is adopted in both boost- and buck-mode operations. The circuit allows synchronous mode operation to achieve zero-voltage switching. Together with the use of low R ds-on power MOSFET as the switching device, ultra high efficiency can be obtained. This paper shows a high-voltage example system operating completely in synchronous mode with 99.2% efficiency at the full load, but only 93% at 10% load. A low-voltage system example is then proposed to operate in synchronous mode under light-load condition and in continuous conducting mode under heavy load condition to achieve high efficiency over a wide load range. The peak efficiency of the second example system reaches 99.5% in between 10 and 20% load and maintains above 98% throughout the rest of load range.

Battery energy storage system are widely used and become the most popular form of energy storage system. This paper proposes a grid-tie Lithium-ion battery based energy storage system, which consists of LiFePO4 battery based energy storage and a high-efficiency bidirectional ac-dc converter. The battery management system (BMS) estimates the state of charge (SOC) and state of health (SOH) of each battery cell in the pack 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 1-kW prototype has been designed and implemented to further validate the proposed architecture.

A novel, high-efficiency inverter using MOSFETs for all active switches is presented for photovoltaic, non-isolated, 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, PWM scheme, and novel bootstrap power supply 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 are achieved.

This paper evaluates three different 600V-level super junction (SJ) MOSFETs employed in zero-voltage soft-switching inverter applications. Inverter efficiency was measured and compared with the same inverter test setup by only changing different MOSFETs. Besides high efficiency requirement, better switching performance is also highly appreciated in various inverter applications. Comparison test was done on each super junction MOSFET to investigate its body diode reverse recovery and associated problems. Based on performance of both efficiency and reverse recovery related issues, a high voltage super junction MOSFET selection for softswitching inverter was suggested.

The state-space model and implementation results of a power conditioning system are presented in this paper. Eigenvalues with different controller gains and load conditions for grid-tie mode and standalone mode are utilized to analyze the system stability. For standalone mode, higher controller gain and higher load resistance tend to make system more unstable. In grid-tie mode, higher controller gain is also found to make the system more unstable but load variation will not change the system stability much. Experimental and simulation results also verify the model. The state-space model is extended to a parallel-inverter system for investigation of the load variation and current-sharing controller effects to the system stability. A timedomain current ripple criterion is also suggested for light-load operation of the parallel-inverter microgrid system.

This paper presents a 55kW three-phase softswitching inverter for hybrid electric vehicle drives at high temperature conditions. Highly integrated softswitching modules have been employed to achieve switching loss as well as conduction loss reduction. Detailed experimental evaluations of inverter efficiency 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.

This paper presents a hybrid switching scheme for LLC series-resonant half-bridge (SRHB) dc-dc converter. The concept of the proposed hybrid switching scheme is changing the switching mode to improve power efficiency in a wide load range. The SRHB converter operates in three different switching modes depending on the output load condition. Digital control of the system facilitates the implementation of the proposed hybrid switching scheme. High efficiency is achieved with a constant output voltage over wide load range. Experimental results on a 5 kW prototype are presented to evaluate the feasibility of the proposed switching scheme for the SRHB converter.

This paper proposes a new bridgeless single-stage half-bridge ac-dc converter. The proposed converter integrates the operation of the bridgeless power factor correction (PFC) boost rectifier and the asymmetrical pulse-width modulation (APWM) half-bridge dc-dc converter. The proposed converter provides high power factor and direct power conversion from the line voltage to an isolated dc output voltage without using the full-bridge diode rectifier. Conduction losses are lowered with a simple circuit structure. Switching losses are also reduced by achieving zero-voltage switching (ZVS) of the power switches. The effectiveness of the proposed converter is verified on a 250 W (48 V/5.2 A) experimental prototype.

The feasibility of applying the double-layer capacitor to uninterruptible power systems and electric vehicles is addressed. The double-layer capacitor improves energy storage density by two orders of magnitude over the traditional electrolytic capacitors. Compared to batteries, the energy density of the double-layer capacitor is lower, but its charge/discharge rate is significantly higher. The application of double-layer capacitors can be tailored to auxiliary energy and burst mode storages which require fast charge/discharging and high energy density. A description is given of the double-layer capacitor technologies including its materials, structure, and characteristics; potential application areas of double-layer capacitors; and analytical and experimental results of double-layer capacitor applications. >

Existing photovoltaic (PV) panels have widely varying input voltages based on the panel configuration and size. In this paper, a novel topology with a single active switch — combining boost, flyback, and charge-pump circuits — is proposed in order to achieve wide input range, high voltage gain, high efficiency, and low cost simultaneously. It meets the input-voltage and power-level needs of the majority of modern PV panels while still being suitable for connection with a highvoltage dc bus. The circuit has been designed, simulated, and implemented with the 20 to 70 V input, 200±20 V output, and 220 W output power as a part of a PV ac module. Experimental results verify the validity of the novel circuit and show 97.4% peak efficiency and greater than 96.3% for 50 to 220 W.

This paper presents a high efficiency three-phase soft-switching inverter for electric vehicle drives application. A 12kW three-phase soft-switching inverter using CoolMOS as the main device and IGBT as the auxiliary device has been designed and fabricated. The electric vehicle drive test system has been assembled with soft-switching inverter, induction motor and dynamometer. The soft-switching inverter has been tested with closed-loop torque direction control under speed reversal conditions. The measured efficiency of the inverter in a wide load range is above 98.5%. The calorimeter test at 12kW shows 98.8% efficiency.

This paper presents a systematic design technique for a photovoltaic simulator. The proposed technique helps improve control loop bandwidth and system response. The photovoltaic equivalent circuit is used to generate the current-voltage reference curves. A novel technique is proposed and implemented with analog controllers to simplify the reference signal generator and to avoid sampling time delays in digital controllers. A two-stage LC output filter is implemented to push the resonant frequency higher and thus allowing a higher bandwidth control loop design while keeping the same switching ripple attenuation as in the conventional one-stage LC output filter. Design procedures for both control and power stage circuits are explained. Experimental results verify the steady state and transient performance of the proposed photovoltaic simulator at 2.7 kW output.

A novel soft switching inverter using two small coupled magnetics in one resonant pole is proposed to guarantee the main switches operating at zero-voltage-switching (ZVS) from zero load to full load and the auxiliary switches at zero-current-switching (ZCS) with load adaptability and small current stress. Since independent magnetics structure avoids the unwanted magnetizing current freewheeling loop, the size of the coupled magnetics can be minimized with low magnetizing inductance and the saturable inductor is eliminated. Detailed circuit operation is described and voltage-second balance condition of the magnetics is expressed mathematically. A 4-kW hardware prototype has been designed, fabricated and tested to verify the validity of the novel circuit and the improved performs of the proposed soft switching inverter. Experimental results show excellent agreement with analytical results.

In this paper, a microgrid architecture comprised of parallel inverters, critical loads, and CAN communication is studied. The controller designs in both grid-tie and islanding modes for the designed MG system are described. How to distribute the currents among paralleled inverters with CAN bus as communication interface is addressed. The mode transfer tests are conducted with an inverter-simulated grid to define the proper transfer procedures. Experimental results show that the inverter can work properly in different basic microgrid operation modes. With current sharing scheme, the output current is equally shared among different inverters without noticeable circulating current. Both the simulation and experimental results of mode transfer show that the inverter can switch between grid-tie and islanding modes smoothly, which indicates that the proposed mode transfer procedure is capable of minimizing the transients during mode transfer.

This paper presents a variable timing controlled soft-switching inverter. The proposed timing control is based on a simple voltage sensing circuit that detects zero voltage crossing condition to determine the main switch turn-on time. The proposed technique can be applied to different types of zero-voltage switching type inverters. In this paper, the coupled-magnetic type soft-switching inverter is used as example to show the implementation method and its simulation and experimental results. A 5-kW hardware single-phase inverter prototype using CoolMOS as the main device and IGBT as the auxiliary device has been built and tested. Simulation results were well verified with experimental results. Efficiency was compared between the proposed variable timing and the conventional fixed-timing controlled inverters. Significant efficiency improvement was found at light-load conditions.

High temperature inverter involves thermal management, packaging, semiconductor device, switching circuit, and control circuitry. This paper is to focus on the drivetrain inverter design consideration for electric and hybrid electric vehicles. Basic structure and switching characteristics of different insulated-gate-bipolar-transistors (IGBTs) will be discussed. The use of silicon carbide Schottky diode in parallel with silicon IGBT will also be evaluated and compared with pure silicon IGBT modules running under both hard- and soft-switching conditions. Experimental results of conduction and switching loss at different temperature conditions are used to predict the device loss and associated junction temperature for switching cases.

An induction motor drive using an improved high-frequency resonant DC link inverter is presented. The resonant circuit was systematically analyzed first to establish the criteria for initial current selection, and a new circuit was then proposed to establish the bidirectional initial current. The proposed current initialization scheme solves voltage overshoot and zero-crossing failure problems in the ordinary resonant DC link inverters. A three-phase 3 kW IGBT (insulated-gate bipolar transistor) based 60 kHz resonant link inverter has been constructed and successfully tested with an induction motor drive. The speed control system is implemented using two microprocessors: TMS320C25 for computation and INTEL 80386 for monitoring and user interface. Experimental results showing the superior operation of the proposed resonant DC link inverter drive are presented. >

For a thermoelectric generator based small battery energy storage system, the adaptive maximum power point tracking (MPPT) algorithm based on incremental impedance is presented. The small signal model is mathematically derived and analyzed in frequency domain. Based on the frequency domain information, the design procedure is proposed with some practical considerations. The design methodology has been implemented and verified with hardware experiments. Dynamic response agrees with the targeted bandwidth very well.

This paper first introduces the design of an ultra high-efficiency 50 kW bidirectional DC-DC converter at ZVS operation and then a high-precision efficiency measurement method using regenerative approach. The ultra high-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 (DUT) and the other as the regenerative unit. With the use of plusmn0.5% current shunt and regenerative measurement, the relative efficiency error stays below plusmn0.025%. Measured efficiency from 20% to 100% load consistently show above 97.50% and peaks at 99.05%.

The inductor-capacitor-inductor (LCL) filter allows higher noise attenuation and universal output in which a power conditioning system or an inverter can operate in both grid-tie and standalone modes. In this paper, the LCL filter design considerations including sensor position selection and component selections are discussed for single-phase paralleled inverters operating in both grid-tie and standalone modes. For grid-tie mode operation, each inverter is operating under a single current loop with proportional-resonant controller and admittance path compensation to reduce the steady-state error by providing a high gain at the fundamental frequency. For standalone mode operation, one of the inverters is implemented with a dual-loop controller to regulate the output voltage while the rest inverters operate in single current-loop controller with communication channels in between to ensure the uniformity of current sharing. Both the simulation and experimental results verify that the designed controllers are capable of paralleling inverter operation in grid-tie and standalone modes by adapting to different controller settings while keeping the same hardware setup.