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Paralleled power systems require a hot swap which indicates the replacement of a converter module without shutting down the whole system for easy maintenance, repair, and upgrade. A practical issue for the hot swap is an overcurrent toward a newly activating module due to inevitable nonuniformity among the paralleled modules, which causes the excessive current and thermal stresses and even leads to a device failure. In this paper, by analyzing the start-up operation of a converter module during the hot swap, the reason for the overcurrent is demonstrated. Then, based on this analysis, a method increasing the voltage reference exponentially is presented, which can contribute to reduce the overcurrent. However, the overcurrent still remains and causes a problem as the number of paralleled modules or difference in output voltage set points increases. Therefore, a control scheme adjusting the output voltage reference during the start-up is proposed to eliminate the overcurrent effectively. Experimental results from 1-kW paralleled phase-shifted full-bridge converters are shown to verify the proposed works.

In this paper, a simple and low-cost open-circuit fault detection and identification method for a pulse-width modulated (PWM) voltage-source inverter (VSI) employing a permanent magnet synchronous motor is proposed. An open-circuit fault of a power switch in the PWM VSI changes the corresponding terminal voltage and introduces the voltage distortions to each phase voltage. The proposed open-circuit fault diagnosis method employs the model reference adaptive system techniques and requires no additional sensors or electrical devices to detect the fault condition and identify the faulty switch. The proposed method has the features of fast diagnosis time, simple structure, and being easily inserted to the existing control algorithms as a subroutine without major modifications. The simulations and experiments are carried out and the results show the effectiveness of the proposed method.

The LLC resonant converter employing a center-tap rectifier can suffer from a high voltage oscillation across rectifier diodes owing to a leakage inductance of a transformer secondary. The amplitude of this voltage oscillation is varied according to design parameters, parasitic components, and operation regions, i.e., below-resonant region and above-resonant region. To reduce the diode voltage stress, this paper analyzes the voltage oscillation mechanism and presents the design consideration.

In this paper, a new cell-to-cell charge equalization converter using a multiwinding transformer is proposed. The proposed scheme achieves the direct cell-to-cell charge transportation by buck-boost and flyback operation. In this operation, the adjacent two cells share either a current path or a tap of multiwinding transformer. Therefore, the number of windings ia cut in half in comparison to the number of batteries, resulting in a small circuit size. To verify the operation of the proposed charge equalization converter, an experiment with a lithium-ion battery stack is performed.

This paper proposes a simple position observer based on the instantaneous power and a tuning procedure for the proposed observer in driving the surface-mounted permanent magnet synchronous motor. In the instantaneous power of a three-phase system, the imaginary and real powers have the information related to the position and velocity. Using the instantaneous power, the difference between real rotor position and estimated rotor position is calculated. For easy design, gain parameters are described as a bandwidth of position observer. The proper bandwidth is expressed in terms of the desired load transient response, system inertia, and permitted acceleration range. Also, the sensitivity of phase resistance and inductance is analyzed. The described mathematical results show the necessity of accurate parameter information. Simulation and experimental results show the validity of the proposed design method and analysis.

Stacking an auxiliary step-up circuit on top of a boost converter is one of the most attractive structures for nonisolated high step-up applications. In this paper, in order to avoid the large input current ripple of coupled-inductor-based circuits, an auxiliary step-up circuit is integrated via an additional transformer and its balancing capacitor. A voltage-doubler is adopted as an auxiliary step-up circuit, which is inherently suitable for high-voltage applications due to its simple structure and low-voltage stress. Moreover, the transformer leakage inductor and the balancing capacitor constitute a resonant tank so that the quasi-resonant operation makes the current sinusoidal. As a result, a reduced switch turn-off loss and reverse recovery of the diode can be expected. The proposed converter is verified with a 24 V input, 160 W - 200 V output prototype.

This paper describes nonisolated high step-up DC-DC converters using zero voltage switching (ZVS) boost integration technique (BIT) and their light-load frequency modulation (LLFM) control. The proposed ZVS BIT integrates a bidirectional boost converter with a series output module as a parallel-input and series-output (PISO) configuration. It provides many advantages such as high device utilization, high step-up capability, power and thermal stress distribution, switch voltage stress clamping, and soft switching capability. As an example of ZVS BIT, a flyback converter with a voltage-doubler rectifier (VDR) as a series output module is presented and analyzed in detail. In addition, to overcome the efficiency degradation at a light load due to the load-dependent soft switching capability of the proposed ZVS BIT, a control method using a frequency modulation (FM) proportional to the load current is proposed. By means of ZVS BIT and LLFM control, the overall conversion efficiency is significantly improved. The experimental results are presented to clarify the proposed schemes.

A transformer magnetizing current offset for a phase-shift full-bridge (PSFB) converter is dealt with in this paper. A model of this current offset is derived and it is presented as a first-order system having a pole at a low frequency when the effects from the parasitic components and the switching transition are considered. A digital offset compensator eliminating this current offset is proposed and designed considering the interference in an output voltage regulation. The performances of the proposed compensator are verified by experiments with a 1.2-kW PSFB converter. The saturation of the transformer is prevented and the efficiency is improved by this compensator.

A new interleaved forward (IF) converter, adopting the series-input series-rectifier (SISR) structure with a common transformer reset circuit (CTRC), is proposed in this paper. The series-input structure distributes the switch voltage stress so that it is suitable for high-input-voltage applications. Moreover, in order to simplify the total circuit, one active-clamp circuit is shared with two forward converters as a CTRC for transformer reset. In addition, the series-rectifier structure with a common output inductor guarantees a fair current balance between the primary modules, while the interleaving technique reduces the output-filter size. All these features make the proposed SISR IF converter promising for high-input-voltage applications with a high efficiency and a simple structure.

An active-clamp forward (ACF) converter, which is popular in low-to-medium power applications, suffers from the high-voltage stress on switches, i.e., the sum of input voltage and reset capacitor voltage. To relieve this problem, a two-switch (2-SW) ACF converter, where the voltage stresses on the main switches are clamped to either the input voltage or the reset capacitor voltage by simply employing one clamping diode and a delayed turnoff gate signal, is proposed in this paper. Therefore, in view of utilizing high-performance low-voltage switches, the proposed 2-SW ACF converter can be promising for high-input-voltage applications.

Till now, various types of current-fed converters have been developed, and they exhibit good performance in isolated step-up applications. However, they have a common limitation in that the duty cycle must be larger than 0.5 for a proper operation, which guarantees a conducting path for the boost-inductor current. The limited duty cycle causes an inrush current at start-up and it makes it difficult to regulate the output voltage in a light-load condition. Although various auxiliary circuits have been developed that can be solutions for a duty cycle below 0.5, they increase the size and complexity of the total circuit. To relieve these problems, a new two-transformer current-fed (TTCF) converter, which can be operated along a wide duty cycle range with a simple structure, is proposed in this paper. In the TTCF converter, a magnetizing inductor of the transformer acts as a boost inductor, thus no additional boost inductor is needed. Moreover, only one auxiliary diode is employed for operation with a duty cycle below 0.5. Therefore, the proposed converter can be promising for isolated step-up applications with a simple structure.

To obtain a high step-up gain with high efficiency in nonisolated applications, a high step-up technique based on isolated-type converters is introduced in this paper. By stacking the secondary side of an isolated converter in addition to its primary side, a high step-up conversion ratio and a distributed voltage stress can be achieved. Moreover, a careful choice of an isolated converter can provide zero-voltage switching, continuous input current, and reduced reverse recovery on diodes. Based on a conventional voltage-doubler-rectifier boost-integrated half-bridge converter, the derived converter satisfies all these features, which make it suitable for high step-up applications. The operational principle and characteristics of the proposed converter are presented, and verified experimentally with a 135-W, 24-V input, 250-V output prototype converter for a LED driver.

For a nonisolated high step-up converter, the combination of a boost converter with a series output module is investigated in this paper. As a solution to supplement the insufficient step-up ratio and distribute a voltage stress of a classical boost converter, a sepic-integrated boost (SIB) converter, which provides an additional step-up gain with the help of an isolated sepic converter, is proposed. Since the boost converter and the sepic converter share a boost inductor and a switch, its structure is simple. Moreover, the SIB converter needs no current snubber for the diodes, since the transformer leakage inductor alleviates the reverse recovery. The operational principle and characteristics of SIB converter are presented, and verified experimentally with a 200 W, 42 V input, 400 V output prototype converter.

A novel method of the gate signal generation for the interleaved LLC converter is proposed, which is based on the relationship between the output signal of a toggle flip-flop having the double period of the input clock signal and the output gate signal of the LLC controller having almost half-duty cycle. The gate signals for the master and slave converters are generated using the rising and falling edge instants from the original control gate signal of the controller, respectively. Therefore, the required 90° phase difference between two signals can be always kept at any instant and at any output load condition. Copyright © 2010 John Wiley & Sons, Ltd.

A new single-stage isolated ac-dc converter, which can achieve a better efficiency and a better power factor, is proposed. It is based on a general forward topology so that it can utilise the transformer more than converters based on flyback topology. In addition, since the capacitive output filter is adopted instead of an inductive type filter, the voltages on the secondary rectifiers can be clamped to the output voltage; meanwhile, the capacitor used in the output filter can be utilised for the resonance with the leakage inductance, and the turn-off loss in the primary main switch and the dissipative loss in the snubber can be reduced. Moreover, since this converter can be operated at the boundary conduction mode, the line input current can be automatically shaped as the waveform of a line voltage and quasi-resonant zero voltage switching can be also obtained. Therefore, it features higher efficiency, lower voltage stress and a smaller-sized transformer than other topologies. A 100 W prototype has been ...

A new single-stage-isolated ac–dc converter that can guarantee both high efficiency and high power factor is proposed. It is based on a new dc–dc topology that has prominent conversion ratio similar to that of boost topology so that it is adequate to deal with the universal ac input. In addition, since it utilizes the transformer more than others based on the general flyback topology, the size of whole power system can be reduced due to the reduced transformer. Moreover, the voltage stresses on the secondary rectifiers can be clamped to the output voltage by adopting the capacitive output filter and clamp diode, and the turn-off loss in the main switch can be reduced by utilizing the resonance. Furthermore, since this converter operates at the boundary conduction mode, the line input current can be shaped as the waveform of a line voltage automatically and the quasi-resonant zero-voltage switching can be obtained. Consequently, it features higher efficiency, lower voltage stress, and smaller sized transformer than other topologies. A 100 W prototype has been built and tested as the validation of the proposed topology. Copyright © 2010 John Wiley & Sons, Ltd.

In low-to-medium power applications, an active-clamp forward (ACF) converter is popular for its simple structure and zero-voltage switching (ZVS) capability. However, the high voltage stress on switches can be a burden in high-input-voltage applications. To relieve this, a three-switch ACF (TS-ACF) converter, which employs two main switches for a forward converter and one auxiliary switch for an active-clamp circuit (ACC), is proposed in this paper. With a repositioned ACC, all the switches of TS-ACF converter have relatively low voltage stress compared to the conventional one. In addition, one of the main switches always ensures ZVS during the transformer reset. Consequently, the TS-ACF converter can be promising for high-input-voltage applications with high efficiency.