Asymmetrical Half-bridge Converter Research Articles

A High-Efficiency Asymmetrical Half-Bridge Converter With Integrated Boost Converter in Secondary Rectifier

A conventional asymmetrical half-bridge (AHB) converter is one of the most promising topologies in low-to-medium power applications because of zero-voltage switching of all switches and small number of components. However, when the converter is designed taking a hold-up time into consideration, it has a large DC offset current in a transformer and a small transformer turns-ratio. To solve these problems, a new AHB converter with an integrated boost converter is proposed in this letter. Because the proposed converter compensates for the hold-up time using the integrated boost converter without additional loss in the nominal state, it can achieve the optimized efficiency regardless of the hold-up time. The effectiveness and feasibility are verified with a 250–400-V input and 45 V/3.3 A output prototype.

An Asymmetric Three-Level Neutral Point Diode Clamped Converter for Switched Reluctance Motor Drives

An asymmetric three-level neutral point diode clamped converter for switched reluctance motor drives is proposed in this paper. The modulation method, the dc-link voltage balancing algorithm, and the current control scheme of this converter are presented. The proposed three-level converter is compared with the conventional two-level asymmetric half-bridge converter in terms of cost, current ripple, noise, and power losses. Compared to the conventional two-level converter, the proposed three-level converter has much lower current ripple, lower noise, and higher efficiency. The effectiveness of the proposed converter is verified by both simulation and experimental results.

Adaptive Neural Fuzzy Inference System Optimization in Converter

A new technique of AFIS speed control of DC drives with Asymmetrical Half-Bridge converter is proposed. The PI controller is the most common feedback controller used in the process industries. PI is easily understood algorithm, which give good control action of varied dynamic characteristics. However, PI controller have drawback of not giving the optimum response for non-linear systems. By the introduction of novel intelligent techniques, the PI controller and FLC are optimized by Adaptive Neural Fuzzy Inference Systems. In this paper the ANFIS optimization method is applied for speed control of DC to DC converter fed drive. The main motive of this work is to attain minimum transient and switching losses to decrease the energy loss by which the efficiency gets increased.

High-Efficiency Asymmetric Forward-Flyback Converter for Wide Output Power Range

This paper proposes an asymmetric forward-flyback dc–dc converter that has high power-conversion efficiency $\eta _{e}$ over a wide output power range. To solve the problem of ringing in the voltage of the rectifier diodes and the problem of duty loss in the conventional asymmetric half-bridge (AHB) converter, the proposed converter uses a voltage doubler structure with a forward inductor $L_{f}$ in the second stage, instead of using the transformer leakage inductance, to control output current. $L_{f}$ resonates with the capacitors in the voltage doubler to achieve a zero-voltage turn-on of switches and a zero-current turn-off of diodes for a wide output power range. The proposed converter could operate at a wider input voltage range than the other AHB converters. $\eta _{e}$ was measured as 95.9% at output power $P_{O} = 100$ W and as 90% at $P_{O} = 10$ W, when the converter was operated at input voltage 390 V, output voltage 142 V, and switching frequency 100 kHz.

Control method of high-speed switched reluctance motor with an asymmetric rotor magnetic circuit

Abstract In the paper, the modified (compared to the classical asymmetric half-bridge) converter for a switched reluctance machine with an asymmetric rotor magnetic circuit was analysed. An analysis for two various structures of switched reluctance motors was conducted. The rotor shaping was used to obtain required start-up torque or/and to obtain less electromagnetic torque ripple. The discussed converter gives a possibility to turn a phase off much later while reduced time of a current flows in a negative slope of inductance. The results of the research in the form of waveforms of currents, voltages and electromagnetic torque were presented. Conclusions were formulated concerning the comparison of the characteristics of SRM supplied by the classic converter and by the one supplied by the analysed converter.

Control Performance Analysis and Improvement of a Modular Power Converter for Three-Phase SRM With Y-Connected Windings and Neutral Line

In this paper, the control performances of a modular power converter for a three-phase switched reluctance machine (SRM) are analyzed and improved. The converter is implemented by a dual and a six-pack IGBT module, and the phase windings of the SRM are Y-connected and bipolar excited. The performances of the existing control method for this converter are evaluated by simulation and compared with those for the traditional asymmetric half-bridge converter, and the drawbacks, such as big torque ripple and small average torque, are presented. With the new operating modes of phase branch, namely magnetization, freewheeling, and demagnetization, improved basic control methods are proposed, which can effectively enhance the performances, flexibility, and applicability of the converter. Furthermore, the direct instantaneous torque control, which can reduce the torque ripple, is realized with the converter as well. Several simulations and experiments under different working conditions are carried out to verify the performances of the improved control methods.

Wide ZVS Range Asymmetric Half-Bridge Converter With Clamp Switch and Diode for High Conversion Efficiency

A conventional asymmetrical half-bridge (AHB) converter is widely used for dc–dc stage in low-to-medium power system. However, since the asymmetric operation of AHB converter causes the low efficiency over entire load condition, the conventional AHB converter is not usually considered for the candidate of server power system. In order to overcome the problems of the conventional AHB converter, a wide zero-voltage-switching (ZVS) range AHB converter with a clamp switch and a clamp diode is proposed in this paper. The proposed AHB converter (PAHBC) replaces a low-side clamp diode with a MOSFET switch and adds an auxiliary winding, which changes the transformer turns-ratio. From these modifications and the pulsewidth-modulation (PWM) control of clamp switch, the PAHBC can be designed optimally at nominal input condition and obtains additional dc gain at hold-up time condition. These advantages achieve the high conversion efficiency over the entire load condition. The operational principle and analysis of the PAHBC are presented in this paper and verified by a 340–400 V input and 50 V/500 W output laboratory prototype.

Wavelet Packet Decomposition-Based Fault Diagnosis Scheme for SRM Drives With a Single Current Sensor

Power converters are a key, but vulnerable component in switched reluctance motor (SRM) drives. In this paper, a new fault diagnosis scheme for SRM converters is proposed based on the wavelet packet decomposition (WPD) with a dc-link current sensor. Open- and short-circuit faults of the power switches in an asymmetrical half-bridge converter are analyzed in details. In order to obtain the fault signature from the phase currents, two pulse-width modulation signals with phase shift are injected into the lower-switches of the converter to extract the excitation current, and the WPD algorithm is then applied to the detected currents for fault diagnosis. Moreover, a discrete degree of the wavelet packet node energy is chosen as the fault coefficient. The converter faults can be diagnosed and located directly by determining the changes in the discrete degree from the detected currents. The proposed scheme requires only one current sensor in the dc link, while conventional methods need one sensor for each phase or additional detection circuits. The experimental results on a 750-W three-phase SRM are presented to confirm the effectiveness of the proposed fault diagnosis scheme.

An Improved Asymmetrical Half-Bridge Converter With Self-Driven Synchronous Rectifier for Dimmable LED Lighting

This paper proposes an adaptive feedback gain compensation technique and adaptive feedforward loop control based on analog design for an asymmetrical half-bridge converter without electrolytic capacitor to improve the system dynamic response and the system performance (i.e., low flickering and low ripple) for dimmable high-brightness light-emitting diode (LED) applications. In addition, an improved driving circuit of self-driven synchronous rectification (SR) is proposed for switching loss reduction at the secondary of the transformer. The control circuit is designed such that the SR metal–oxide–semiconductor field-effect transistor switch operates under zero-voltage switching (ZVS) mode while the driving signals are maintained within the acceptable voltage limits under duty cycle variations of the LED dimming applications. Simulation and experimental results obtained from a 60-W hardware prototype have confirmed the validity of the proposed method, where the settling time of the output current has been improved by 90% and the ripple of the output current has been reduced to less than 4% under rated current. The SR switches operate under ZVS condition throughout all operating regions where the maximum efficiency at 96.4% has been achieved.

Fault diagnosis scheme for open‐circuit faults in switched reluctance motor drives using fast Fourier transform algorithm with bus current detection

Reliability of power converters is of crucial importance in switched reluctance motor drives used for safety-critical applications. Open-circuit faults in power converters will cause the motor to run in unbalanced states, and if left untreated, they will lead to damage to the motor and power modules, and even cause a catastrophic failure of the whole drive system. This study is focused on using a single current sensor to detect open-circuit faults accurately. An asymmetrical half-bridge converter is considered in this study and the faults of single-phase open and two-phase open are analysed. Three different bus positions are defined. On the basis of a fast Fourier transform algorithm with Blackman window interpolation, the bus current spectrums before and after open-circuit faults are analysed in details. Their fault characteristics are extracted accurately by the normalisations of the phase fundamental frequency component and double phase fundamental frequency component, and the fault characteristics of the three bus detection schemes are also compared. The open-circuit faults can be located by finding the relationship between the bus current and rotor position. The effectiveness of the proposed diagnosis method is validated by the simulation results and experimental tests.

A New Center-Tapped Half-Bridge Zeta Converter With Small Transformer DC-Offset Current and Low Voltage Stress

In this paper, an asymmetrical half-bridge (AHB) converter employing a new center-tapped zeta rectifier (CTZR) is proposed to achieve a high efficiency in wide-input-voltage and low-output-current applications. Due to the proposed CTZR with high dc conversion ratio and extended maximum duty cycle above 0.5, the transformer turns ratio of the proposed converter can be increased, which decreases the transformer dc-offset current compared with that of the AHB converter. Therefore, its transformer core size is decreased. Moreover, it has a wide zero-voltage-switching range with small transformer leakage inductor, which improves light and medium load efficiency. Furthermore, since it has low voltage stress on the secondary diode, its conduction loss can be reduced. In addition, due to the elimination of a diode, the snubber loss in the secondary side is reduced compared with the AHB converter. Therefore, the proposed converter can achieve a higher efficiency compared with the AHB converter without additional devices. To confirm the operation, features, and validity of the proposed converter, a 250–400 V input and 50 V/250 W output laboratory prototype is built and tested.

Integrated Asymmetrical Half-Bridge Zeta (AHBZ) Converter for DC/DC Stage of LED Driver With Wide Output Voltage Range and Low Output Current

The conventional half-bridge converter for a dc/dc stage in wide-output-voltage and constant-output-current applications such as LED drivers is limited in achieving high efficiency because it is difficult to be designed optimally. To overcome this limitation, an integrated asymmetrical half-bridge zeta converter is proposed for high efficiency in the overall output voltage range. The proposed converter can be simply implemented by replacing a snubber diode with a switch. The proposed converter operates similar to the asymmetrical half-bridge converter by turning off the switch in the low-output-voltage region, which enables it to have a small dc-offset current in the transformer. In the high-output-voltage region, the proposed converter operates similar to the half-bridge zeta converter by turning on the switch, which has small transformer core loss. Therefore, the proposed converter can achieve high efficiency over the entire output voltage range compared with the conventional converters. The validity of the proposed converter is confirmed by experimental results from a prototype with 400-V input and 90–180-W/3-A output.

An Improved Asymmetric Half-Bridge Converter for Switched Reluctance Motor in Low-Speed Operation with Current Regulated Mode

This study presents a novel method for reducing the switching losses of an asymmetric half-bridge converter for a three-phase, 12/8 switched reluctance motor operated in low speed. In particular, this study aims to reduce the switching-off losses of chopping switches in the converter when operated in the current regulated mode (chopping mode). The proposed method uses the mixed parallel operation of IGBT (chopping switch) and MOSFET (auxiliary switch). MOSFET is precisely controlled to momentarily conduct prior to the turn-off interval of the IGBT. Consequently, the voltage across the switches is clamped to approximately zero, substantially decreasing the turn-off switching losses. The analytical expressions of power losses are extensively elaborated. Compared with the conventional asymmetric half-bridge converter, the modified converter can effectively minimize the switching losses. Therefore, the efficiency of the converter is eventually improved. Computer simulation and experimental results confirm the effectiveness of the proposed technique.

Winding‐centre‐tapped switched reluctance motor drive for multi‐source charging in electric vehicle applications

Switched reluctance motors (SRMs) can provide an attractive traction drive for electric vehicle applications. To lower the investment in the off-board charging station facilities, a multi-functional switched reluctance motor topology is proposed on the basis of the traditional asymmetrical half-bridge converter. The SRM phase windings are employed as input filter inductors and centre-tapped windings are also developed to form symmetrical inductors for three-phase grid supply. Owing to the varying rotor position, phase inductors are unequal between one another. A hysteresis control scheme is therefore developed for grid-connection operation. In addition to AC supplies, the proposed topology can also supports the DC-source charging. A new current sharing strategy is employed to diminish the influence of the unequal winding inductances. The simulation and experimental tests are carried out to verify the proposed topology and control methods. Since this work eliminates the need for building charging station infrastructure, its potential economic impact on the automotive market can be significant.

Low‐current ripple LED driver by two‐phase driving approach

A two-phase driving approach for light-emitting diode (LED) power supply is proposed. The approach uses two rectangular current sources working complementarily to supply a constant current to the LED string so that the output current can contain very low ripple even without the use of any electrolytic capacitor in the driver circuit. A dual asymmetrical half-bridge converter with power factor correction is used to realise the approach. A 60 W prototype is built and tested to validate the idea.

Digital Implementation of the Feedforward Loop of the Asymmetrical Half-Bridge Converter for LED Lighting Applications

An asymmetrical half-bridge converter (AHBC) has proved to be a promising candidate for LED lighting applications. It provides high efficiency and galvanic isolation, and it can be easily built without electrolytic capacitor. On the other hand, its main drawback is its poor attainable bandwidth. In any two-stage ac–dc LED driver based on the AHBC, the first stage is a power factor corrector converter, which has to be also implemented without electrolytic capacitor. As a consequence, its output voltage (input voltage of the AHBC) presents a low-frequency ripple. Due to the poor bandwidth of the AHBC, this voltage ripple will be transferred to the converter output voltage, leading to flickering. Due to the complex and nonlinear transfer function of the AHBC, any analog feedforward loop has to be tuned for a given operating point, leading to a poor performance when the AHBC moves away from that point. In this paper, a digital feedforward loop is proposed in order to solve this problem. The digital implementation allows the feedforward loop to perfectly cancel the ripple under any condition (e.g., output voltage variation due to dimming). Besides, this digital feedforward loop has been designed and simplified considering the specific purpose of canceling flickering in the emitted light. In this way, it can be easily implemented in small-size microcontrollers. Experimental results with a 40-W prototype prove the usefulness of the proposed feedforward loop.

Grid-connected Switched Reluctance Generator based Wind Farm Control using Modified Hybrid Multicell Converter

This study deals with analysis of grid integrated Switched Reluctance Generator (SRG) based wind farm control using Modified Hybrid Multicell Converter (MHMC). A Finite Element Analysis (FEA) model is developed for the existing machine geometry using MagNet 7.1.1 and solved to obtain the parameters like flux linkage, inductance and torque. The data obtained from FEA Model is utilized to develop model of SRG in the MATLAB/SIMULINK environment. Asymmetric Half Bridge Converter (AHBC) with dedicative buses for source and load is used for excitation. Developed wind turbine with Maximum Power Point Tracking (MPPT) algorithm to extract maximum power from the wind turbine. Output of the SRG is integrated with grid through Modified Hybrid Multicell Converter. The MHMC uses a flying capacitor module on each cell to generate a positive variable dc-link voltage. The variable dc link is inverted at fundamental switching frequency by an H-bridge to generate the cell output voltage. Phase-Disposition level-shifted Pulse Width Modulation (PD-PWM) Technique is used to obtain the high performance waveforms. In this study wind farm having four SRG’S controlled through MHMC is proposed.

Switch Short-Circuit Fault Diagnosis and Remedial Strategy for Full-Bridge DC–DC Converters

Switch fault diagnosis and remedial actions are an important design aspect for isolated full-bridge dc-dc converters, and they can highly improve reliability of the whole system. In this paper, a fast switch short-circuit fault (SCF) diagnostic method is proposed for the phase-shifted full-bridge (PSFB) converter. The dc-link current and transformer primary voltage are treated as diagnosis criteria. Based on the combination of real-time criteria and switch gate-driver signals, the switch SCF can be identified rapidly, and thus further damage can be avoided. Besides, a remedial action for the faulty PSFB converter is introduced to keep the continuity of the system. The converter under fault can be reconfigured into an asymmetrical half-bridge converter. Moreover, a boost unit, including a switch and a diode, is inserted into between the output rectifier and filter capacitor to compensate the output voltage. The operational principle, design considerations, and implementation are discussed in this paper. Experimental results are shown to verify the validity of theoretical analysis.

Closed Loop Control of Zero Voltage Switching DC-DC Converter to Generate Three Outputs

Hard switching specifies the stressful switching behavior of the controlled switches. During the turn-off and turn-on processes, the power electronic device has to withstand high current and voltage simultaneously, resulting in high stress and switching losses. The switching loss is directly proportional to the switch frequency, thus reducing the maximum switch frequency of the power electronic converter. The concept was to incorporate resonant tanks in the converters to create oscillatory (usually sinusoidal) voltage and/or current waveforms, so the zero current switching (ZCS) or zero voltage switching (ZVS) conditions can be achieved for the power control switches. The Soft-switched power converters are generally utilizing the resonance condition. Resonance condition is generally occurred just during the turn-off and turn-on processes, so as to create ZCS and ZVS across each switch. The Regulated three and five multiple-output dc-dc converter under zero-voltage switching (ZVS) condition is proposed. The converter is consists of three outputs altogether. With the help of two asymmetric half bridge converters, the first and second outputs are controlled. Based on the phase shift between two asymmetric half bridge converters, the third output is controlled. At high switching frequency, these multiple-output dc–dc converters can give higher efficiency. The various stages of operation, soft switching condition and controlling schemes are also explained. A closed loop and open loop control techniques of the three multiple output converter is explained.

Online Sensorless Position Estimation for Switched Reluctance Motors Using One Current Sensor

This paper proposes an online sensorless rotor position estimation technique for switched reluctance motors (SRMs) using just one current sensor. It is achieved by first decoupling the excitation current from the bus current. Two phase-shifted pulse width modulation signals are injected into the relevant lower transistors in the asymmetrical half-bridge converter for short intervals during each current fundamental cycle. Analog-to-digital converters are triggered in the pause middles of the dual pulse to separate the bus current for excitation current recognition. Next, the rotor position is estimated from the excitation current, by a current-rise-time method in the current-chopping-control mode in a low-speed operation and a current-gradient method in the voltage-pulse-control mode in a high-speed operation. The proposed scheme requires only a bus current sensor and a minor change to the converter circuit, without a need for individual phase current sensors or additional detection devices, achieving a more compact and cost-effective drive. The performance of the sensorless SRM drive is fully investigated. The simulation and experiments on a 750-W three-phase 12/8-pole SRM are carried out to verify the effectiveness of the proposed scheme.