Conventional Forward Converter Research Articles

A High Efficiency Modified Forward Converter for Solar Photovoltaic Applications

In this paper, a modification of a conventional forward converter and a new mixed-stranded transformer winding technique are proposed for the development of a simple and high efficiency isolated dc-dc boost converter for solar photovoltaic applications. The conventional single switch forward converter topology is modified for simplification and elimination of losses due to the output filter components. A new mixed-stranded transformer winding technique is proposed to minimize the leakage inductance between the primary and tertiary windings for reducing losses. A pulse frequency modulation technique (PFM) is employed for reducing switching losses at low power operation. An experimental prototype of 300 W with a voltage step-up ratio of 1:12 has been built to obtain dc output voltage between 360-480 V for the dc input voltage of 30-40 V. Through the experimental results, it is shown that the converter can boost the input voltage according to the step-up ratio and exhibits a remarkably high dc-dc power conversion efficiency with a flat response curve. The average efficiency of around 95.5 % and peak efficiency of 97.6% are obtained.

Three-Port Forward Converters With Compact Structure and Extended Duty Cycle Range

A series of three-port forward converters with a compact structure and extended duty cycle range is presented for the standalone renewable energy system. Bidirectional power-flow port embedding and switch device sharing can be used to derive these converters from conventional two-switches forward converters. In comparison to the conventional two-switch forward converter, only one switch and one diode are added to build an energy storage port with bidirectional power flow characteristics, which has the benefits of compact structure and low cost. Meanwhile, the embedding of the energy storage port provides an additional demagnetization loop for the magnetic inductor, which extends the duty cycle range of the forward converter so that the proposed converter no longer requires a duty cycle of less than 0.5 as in the case of conventional forward converters. The proposed converters also offer the advantages of fewer components, easy control, and independent control of power flow between multiple ports when compared to similar solutions. Finally, an experimental setup with a photovoltaic battery as an application is developed, and the experimental results verify the effectiveness and flexibility of the proposed topology and control method.

Dual Voltage Forward Topology for High Efficiency at Universal Mains

This paper introduces a forward converter aimed at the universal mains voltages, i.e., 220–230 Vac and 115 Vac, named the ‘dual voltage forward converter’. The suggested converter has a narrow dynamic range at the universal mains voltages, which results in lower stress on devices, optimal duty cycles, and better overall efficiency. The topology comprises two primary power loops reconfigurable by additional two-state switches and a passive diode, which allows the converter to run in parallel or in series modes and increase the performance over the full universal mains range of 90–265 Vac. The utilization of the devices is better, as they experience lower voltage and current stress by supporting two optimized working points. A converter operating at 100 kHz with an output power of 75 W and output voltage of 12 Vdc was designed and tested. The results were compared with a conventional forward converter with the identical specification. The results at the low mains were similar between the converters; however, at the high mains, the efficiency improvement was between 5% and 23%.

A new magnetron driving method using a phase‐shifted active clamp forward converter for sulfur plasma tube applications

This paper presents a new method for driving the magnetron for a sulfur plasma tube using the two-switch forward converter structure with a phase-shifting active clamp (1000±40 W, 285 mA, 4 kV). Depending on the output voltage level required, the magnetron driver circuit is boosted and insulated and also has high gain. The use of the two-switch forward converter reduces the transistor voltage stress. In addition, applying the clamp structure balances the magnetization current. Besides, by controlling the phase shift of the clamp transistor, while maintaining the magnetic current balance of the power transformer, the duty cycle of the main transistors can be increased. This allows more voltage level transfer to the secondary winding of the transformer. Therefore, with a fixed transformer core, more voltage transmission is possible in comparison with a conventional forward converter. Moreover, using the PFC converter improves the power factor and stabilizes the DC-link voltage. The magnetron driver circuit provides a maximum power of 1 kW with an average power of 125–250 W by adjusting the converter's active time under minimum loss conditions. The magnetron driver circuit provided is validated by the simulation and experimental results.

A Comparative Study of GaN HEMT and Si MOSFET-Based Active Clamp Forward Converters

Compared with conventional forward converters, active clamp forward (ACF) converters have many advantages, including lower voltage stress on the primary power devices, the ability to switch at zero voltage, reduced EMI and duty cycle operation above 50%. Thus, it has been the most popular solution for the low bus voltage applications, such as 48 V and 28 V. However, because of the poor performance of Si MOSFETs, the efficiency of active clamp forward converters is difficult to further improved. Focusing on the bus voltage of 28 V with 18~36 V voltage range application, the Gallium Nitride high electron-mobility transistors (GaN HEMT) with ultralow on-resistance, low parasitic capacitances, and no reverse recovery, is incorporated into active clamp forward converters for achieving higher efficiency and power density, in this paper. Meanwhile, the comparative analysis is performed for Si MOSFET and GaN HEMT. In order to demonstrate the feasibility and validity of the proposed solution and comparative analysis, two 18~36 V input, 120 W/12 V output, synchronous rectification prototype with different power devices are built and compared in the lab. The experimental results show the GaN version can achieve the efficiency of 95.45%, which is around 1% higher than its counterpart under the whole load condition and the same power density of 2.2 W/cm3.

Center Clamped Forward Converter for High Current Applications

High current applications like Microprocessors, Fuel cells, Electric Hybrid Vehicles, Solar Cells etc., use interleaved isolated buck derived converter. Interleaving of converters for such high current applications converters is done to achieve reduced input capacitor ripple voltages, output capacitor ripple current cancellation and reduced peak currents of output inductors. Generally, interleaving requires a higher number of transformers through which distributed magnetics can be achieved. i.e., one bulky transformer can be replaced with low power profile transformers. The performance of forward converter depends on core resetting of the main transformer. The core’s magnetizing energy is recycled by resetting it. In the absence of core reset, the current builds up at each switching cycle, saturates the core, causes reverse recovery problem in the diode and the active clamp will no longer in zero voltage state during turn on of the main switch. The transformer secondary output is used as a gating pulse for Synchronous Rectifiers. These have very low forward drop which are most suitable for high current applications. Among various used clamping methods, the transformer core is optimized effectively by Active center clamp reset approach. The proposed method results in less number of switches and clamping capacitor, and lower cost compared to conventional forward converter. Reduction in voltage stress without losing duty-cycle ratio is also achieved by means of a series-parallel connected switch structure with Self Driven Synchronous Rectifiers. The proposed center clamp converter overcomes the Maximum Duty cycle limitation of 50%. This paper mainly focuses on active center clamp forward converter and is also compared with Active Positive Negative clamping techniques.

Analysis Design and Experimental Verification of a Two-Switch Forward Converter

A forward converter is an isolated DC-DC converter widely used in switching power supplies with output power ratings ranging from 50W to 400W. The conventional forward converter requires a transformer with a tertiary winding to assist in magnetic core reset and subjects its power switch to a high voltage at turn-off. These shortcomings are eliminated in the two-switch forward converter. This paper presents analysis, design and experimental verification of a two-switch forward converter. First, the converter operation is analyzed, enabling its key equations and important waveforms to be established. Then, the converter design, including both the power circuit and feedback controller, is illustrated in detail. Finally, experimental results from the prototype circuit are presented to confirm the validity of the analysis and design.

Modelling, control and realisation of the single‐ended forward converter with resonant reset at the secondary side

This study presents modelling, control and realisation of a forward converter with resonant reset at the secondary side. The transformer reset occurs through the resonance between its magnetising inductance and the resonant capacitor during the switch off time. The mechanism is similar to a forward converter with resonant reset at the primary side. The only difference is that the transformer-stored energy can now be partially delivered to the load instead of being dissipated in the switch at turn-on. Another advantage compared with conventional forward converters is the lower switch voltage stress and transformer size, which are theoretically proved to be lower. Furthermore, this converter can be used as a step-up and step-down converter. To verify all the mentioned features, simulations were carried out and a 600 W prototype was implemented experimentally, reaching a maximum efficiency of 94.3%.

Conducted electromagnetic interference evaluation of forward converter with symmetric topology and passive filter

Forward converter is popular for isolated switching power supply. Generally, power switching converters are the sources of electromagnetic interference (EMI) because of their high transient voltage and current. In this study, reduction of conducted EMI in the single-switch forward converter is examined using a symmetric topology. At this end, the forward converter topology is modified to achieve a symmetric topology. EMI model of the conventional forward converter and symmetric forward converter are derived taking into account the main parasitic of components and printed circuit tracks. Accuracy of the predicted EMI is verified by the measured EMI for two converters. In addition to the symmetric approach evaluation from the EMI viewpoint, the effect of this approach on the output voltage noise is examined. Finally, the combination of a passive EMI filtering with the symmetric method is utilised for EMC compliance.

고효율 및 고역률 LED 구동회로 위한 Balanced Forward-Flyback 컨버터

A balanced forward-flyback converter for high efficiency and high power factor using a foward and flyback converter topologies is proposed in this paper. The conventional AC/DC flyback converter can achieve a good power factor but it has the high offset current through the transformer magnetizing inductor, which results in a large core loss and low power conversion efficiency. And, the conventional forward converter can achieve the good power conversion efficiency with the aid of the low core loss but the input current dead zone near zero cross AC input voltage deteriorates the power factor. On the other hand, since the proposed converter can operate as the forward and flyback converters during switch turn-on and turn-off periods, respectively, it cannot only perform the power transfer during an entire switching period but also achieve the high power factor due to the flyback operation. Moreover, since the current balanced capacitor can minimize the offset current through the transformer magnetizing inductor regardless of the AC input voltage, the core loss and volume of the transformer can be minimized. Therefore, the proposed converter features a high efficiency and high power factor. To confirm the validity of the proposed converter, theoretical analysis and experimental results from a prototype of 24W LED driver are presented.

Analysis of Active Clamp Forward Converter of UAV <sup></sup>

The Forward Switch mode power supply is good selection for power supplies of Unmanned Aerial Vehicle (UAV). Compared with the conventional forward converter, there is one auxiliary switch in the active clamp forward converter to recycle the energy stored in the transformer leakage in order to minimize the voltage stress of the main switch. The power system is designed and the operation characteristics of the active switching power supply are revealed by analysis a typical second-order system in this paper. Active Clamp Forward Converter reduce the generation of EMI, the EMC of UAV equipment is greatly improved. The results of the analysis are verified by SPICE simulation.

Partial Power Conversion Device Without Large Electrolytic Capacitors for Power Flow Control and Voltage Compensation

A novel partial power conversion device (PPCD) is proposed to realize power flow control and voltage compensation in a three-phase power distribution system in this paper. The PPCD circuit, which is derived from the conventional push-pull forward converter, can achieve arbitrary voltage output without any large electrolytic capacitors. Thus, the system reliability can be enhanced. Furthermore, the converter has no full-rated components, which reduces the cost. In this paper, an injection model for power flow control is derived. A minimum power transfer control strategy is proposed to minimize the power losses during the operation. A closed-loop control method employing the synchronous reference frame theory for voltage compensation is also developed to enable the precise control. The systems with PPCD are simulated by MATLAB/Simulink to verify the functions. The experiments for voltage compensation are carried out based on a 30-kW prototype, which shows the effectiveness.

Implementation of a parallel zero-voltage switching DC–DC converter with fewer active switches

A parallel soft-switching DC–DC converter with fewer switch count is presented to achieve zero-voltage switching (ZVS), load current sharing and partially output ripple current cancellation. Two buck-type converters are connected in parallel to achieve load current sharing. Only two MOSFETs are used in the proposed converter instead of four switches in a conventional parallel ZVS forward converter. Therefore the proposed converter has fewer active switches. Current-doubler rectifiers are used in the output side in order to achieve partially ripple current cancellation. Therefore the current ripple on output capacitor is decreased and the size of the output choke and output capacitor are reduced. An active snubber is connected between two power transformers to absorb the energy stored in the leakage and magnetising inductances of transformers, to limit voltage stresses across switches, and to achieve ZVS turn-on for all switches. The ZVS turn-on is implemented in the transition interval of two complementary switches such that the switching losses and thermal stresses on semiconductors are reduced. Operation principle, circuit analysis and design example are discussed in detail. Finally, experimental results for a 360 W (12 V/30 A) prototype were presented to verify the effectiveness of the proposed converter.

Interleaved DC–DC zero-voltage switching converter with series-connected in the primary side and parallel-connected in the secondary side

An interleaved zero-voltage switching (ZVS) forward converter is presented in this study. Two forward converter circuits with active snubber are used in the proposed circuit to share the load current. The interleaved pulse-width modulation (PWM) scheme is adopted to achieve current ripple reduction in the output capacitor. Thus, the size, weight and conduction losses of the output chokes are reduced. Only two switches instead of four switches in the conventional parallel ZVS forward converter are used in the proposed converter. Thus, the switch counts are reduced in the proposed circuit. The PWM signals of two switches are complementary each other with a small delay time in order to realise the ZVS turn-on at the transition interval. Thus, the switching losses and thermal stresses of the power switches are reduced. Experiments based on a 650 W prototype were provided to verify the theoretical analysis and the effectiveness of the proposed converter.

Implementation of a ZVS interleaved converter with two transformers

This paper presents an interleaved converter with the feature of zero voltage switching (ZVS). Two buck-type converters connected in parallel have the same switching devices and operate under the interleaved pulse-width modulation (PWM). Thus the output ripple current in the proposed circuit is less than that in the conventional forward converter. Thus the size of the output choke and capacitor is reduced. Only two switches are used in the proposed circuit instead of four switches in the conventional parallel ZVS converter. Therefore the circuit components in the proposed converter are reduced. ZVS turn-on is achieved during the commutation stage of two complementary switches such that the switching losses thermal stresses on the semiconductors are reduced. Experiments based on a 330 W prototype are provided to verify the theoretical analysis and the effectiveness of the proposed converter.

Analysis of ZVS PWM active clamp isolated converter with secondary voltage step up

This article presents an isolated converter with the function of voltage step-up. An active clamp circuit is used to achieve zero voltage switching (ZVS), absorb the stored energy in the transformer leakage inductance and limit the voltage stresses on power switches. During the commutation stage of two complementary switches, the output capacitance of the switches and the leakage inductance of the transformer are resonant. Thus, power switches are turned on at ZVS. Compared to the conventional active clamp forward converter, the proposed circuit has no large output filter inductor. Thus, it has the features of simpler structure, lower cost and no effective duty loss. The voltage stresses on the output diodes are clamped on the output voltage. The circuit configuration, operation principles and design considerations are presented. Finally experimental results are presented for a converter with an input voltage of 24 V, an output voltage of 200 V and operating at switching frequency of 73 kHz, to verify the effectiveness of the proposed converter.

Active clamp ZVS converter with output voltage doubler

An isolated converter with boost voltage conversion ratio is presented. The active clamp circuit is used to achieve zero voltage switching, release the energy stored in the transformer leakage inductance and limit the voltage stresses on power switches. Compared with the conventional active clamp forward converter, the adopted circuit has no large output filter inductor. Thus, it has features of simpler structure, lower cost and no effective duty loss. Experimental results for a converter with an input voltage of 24 V, an output voltage of 200 V and operating at switching frequency of 73 kHz are provided to verify the effectiveness of the proposed converter.

Analysis and Implementation of a ZVS-PWM Converter With Series-Connected Transformers

This brief presents the analysis, design, and implementation of zero-voltage switching (ZVS) active clamp converter with series-connected transformer. A family of isolated ZVS active clamp converters is introduced. The technique of the adopted ZVS commutation will not increase additional voltage stress of switching devices. In the adopted converter with series-connected transformer, each transformer can be operated as an inductor or a transformer. Therefore, no output inductor is needed. To reduce the voltage stress of the switching device in the conventional forward converter, the active clamp technique is used to recycle the energy stored in the transformer leakage back into the input dc source. Finally, experimental results are presented taken from a laboratory prototype with 100-W rated power, input voltage of 155 V, output voltage of 5 V, and operating at 150 kHz.

Analysis and implementation of soft switching converter with series-connected transformers

The system analysis and design consideration of a zero voltage switching (ZVS) converter with series-connected transformers are presested. Based on the operational behaviour, each transformer in the adopted converter can be operated as an inductor or a transformer. Therefore no output filter inductor is needed in the adopted converter. To reduce the voltage stress of the switching device in the conventional forward converter, an active snubber based on a clamp switch and a clamp capacitor is used to recycle the energy stored in the transformer leakage. During the transition interval, the resonance based on the junction capacitance of switches and transformer leakage inductance can achieve ZVS operation of switches. The centre-tapped rectifier is used at the secondary side to achieve full-wave rectification. The operating principles, steady-state analysis and design equations of the proposed converter are provided. Finally, experimental results for a 100 W (5 V/20 A) prototype circuit are provided to verify the converter performance.

Analysis and implementation of a zero-voltage switching forward converter with a synchronous rectifier

The system analysis, circuit design and implementation of an active-clamp forward converter with a synchronous rectifier is presented. Different to a conventional forward converter, there is an auxiliary switch in the active-clamp forward converter. The clamp circuit is used to reset the energy stored in the leakage inductor in order to minimise the spike voltage at the transformer's primary side. Thus, the voltage stress on the main switch can be reduced. A resonant circuit based on the output capacitor and leakage inductor of the transformer is able to achieve a zero-voltage switching turn-on for both the main and auxiliary switches which will increase the circuit efficiency. A synchronous rectifier is used at the transformer's secondary side to further reduce the conduction losses. The operational principles of the active-clamp forward converter are analysed in detail and the circuit performance is compared with that of a conventional forward converter. The design procedure and an example of an active-clamp forward converter are presented. Finally experimental results are presented for a converter with an AC input voltage of 90∼130 Vrms, an output voltage of 5 V/20 A operating at a switching frequency of 150 kHz which verify the zero-voltage switching at turn-on.