Conventional Asymmetrical Half-bridge Converter Research Articles

A quick demagnetization approach for low torque ripple in three‐phase switched reluctance motor drive system for electric vehicle applications

SummaryElectric vehicles (EVs) have gained a forward approach for achieving the low carbon economy and green transportation. Switched reluctance (SR) motor‐based propulsion mechanisms have been popularly used for EVs due to the wide speed range capability. The conventional phase current regulation technique does not give the satisfactory reduction of torque ripple in SR motor drive, particularly for automotive applications. To overcome the issue, a frontend boost converter (FEBC) is proposed to realize the quick excitation and demagnetization. Initially, the problems associated with the conventional asymmetric half bridge converter are investigated at various levels of phase current. The various operating modes of proposed drive system with FEBC are explained in detail. The proposed FEBC has the significant benefit of being able to provide variable boosting voltages based on the dynamic behavior of the SR motor. The phase voltages are increased during the fast magnetization and demagnetization modes due to the inclusion of FEBC, and hence, quick magnetization and demagnetization have been achieved. The proposed FEBC drive system has been simulated through the Matlab Simulink toolbox. The experimental results are also carried out in order to validate the simulation results.

A Comprehensive Performance Comparison between Segmental and Conventional Switched Reluctance Machines with Boost and Standard Converters

This paper presents the comparisons between two types of switched reluctance machines (SRMs) and SRM converters. An SRM with a segmental rotor is compared with a conventional SRM (CSRM), and an SRM converter containing a passive boost circuit is compared with a conventional asymmetric half-bridge (AHB) converter. The segmental SRM has an asymmetric rotor with a segmented structure. The four rotor segments are made of steel laminations. Two segments are misaligned with the other two by 15 degrees. The torque ripple of the SRM with this structure is decreased, and the static torque is increased compared to a conventional SRM. The boost converter comprises a front-end circuit and a conventional AHB converter. The front-end circuit boosts the voltage level. The boosted voltage accelerates the rising and falling progress of the phase current. In this way, the SRM can obtain a greater speed and a smaller torque ripple. The comparison is conducted in simulation and validated through the experimental results. The experiment results have demonstrated that the segmental SRM obtains a maximum 7% torque ripple reduction at a low-speed range, compared to the CSRM. With the boost converter, both the CSRM and the segmental SRM can achieve a lower torque ripple and a higher maximum speed.

A High-Power-Factor Dimmable LED Driver with Integrated Boost Converter and Half-Bridge-Topology Converter

This paper proposes a dimmable light-emitting diode (LED) driver featuring a high power factor and zero-voltage switching on (ZVS). The circuit is obtained by integrating a boost converter and a dc-dc converter with half-bridge topology. The high power factor is achieved by operating the boost converter in discontinuous current mode (DCM). The LEDs are dimmed by the control scheme of asymmetrical pulse-width modulation (ASPWM). The developed circuit eliminates the inherited dc-offset current of the transformer in a conventional asymmetrical half-bridge converter by introducing a balance capacitor. Both active switches can operate at ZVS by freewheeling the boost inductor current and the transformer magnetizing current to discharge the energy stored in their parasitic capacitance. The circuit operation is analyzed in detailed, and mathematical equations are derived. Finally, a 115-W prototype circuit for driving high brightness LEDs was built and tested. The experimental results verify the feasibility of the proposed LED driver with satisfactory performance. It can achieve a high power factor and ZVS operation.

Cost-Effective and High-Efficiency Variable-Speed Switched Reluctance Drives With Ring-Connected Winding Configuration

This paper presents a novel converter topology for six-phase switched reluctance motor (SRM) drives, which reduces the number of switches and diodes by half, compared with the conventional asymmetric half-bridge converter, but needs no additional energy storage component. A dynamic model of a six-phase SRM is developed in the MATLAB/SIMULINK environment and conventional current chopping and angle position control techniques are applied to the proposed converter, demonstrating successful operation across the full speed range with modified conventional control techniques, lower converter losses, and higher system efficiency compared with the asymmetric half-bridge converter. Experimental tests comparing two versions of the proposed converter with an asymmetric half-bridge are described and verify the predictions of the simulations.

Performance Improvement for Segmented-Stator Hybrid-Excitation SRM Drives Using an Improved Asymmetric Half-Bridge Converter

This paper presents an improved asymmetric half-bridge converter (AHBC) to enhance the output performance of a segmented-stator hybrid-excitation switched reluctance motor (SSHE-SRM) drive. Differences from conventional AHBC include an additional boost capacitor, a power switch, and two diodes added between the dc-bus and the AHBC. The static torque characteristic of a 12/8 SSHE-SRM is briefly analyzed and compared with a conventional SRM (CSRM). Based on the magnetic characteristic, the SSHE-SRM appears to have higher torque production capability. The improved AHBC is employed in order to increase the dc-bus voltage under dynamic operation. Higher voltage can be applied to phase windings and faster excitation and demagnetization currents can be obtained owing to the addition of capacitor voltage. Detailed simulations of the SSHE-SRM drive with the improved AHBC are carried out as well as compared with conventional AHBC. Finally, a 12/8 SSHE-SRM is prototyped. The SSHE-SRM drive based on the improved AHBC and conventional AHBC are experimentally tested. The measured results of static magnetic characteristic and dynamic performances are presented to validate the analysis and effectiveness of the novel converter.

A New Phase Current Reconstruction Scheme for Four-Phase SRM Drives Using Improved Converter Topology Without Voltage Penalty

Accurate current detection is of crucial importance for the operation and fault diagnosis of motor drives. In this paper, a new phase current reconstruction scheme is proposed for four-phase switched reluctance motors (SRMs) by using one dc-link current sensor without voltage penalty. First, an improved converter topology is proposed, which has fewer electronic components and a more compact structure compared with the conventional asymmetrical half-bridge converter. Then, an advanced pulse injection technology is developed to obtain the phase currents. By using the proposed approach, the cost and volume of the motor drive are reduced and the reliability of the system is improved. Most importantly, the scheme proposes a promising solution to the voltage penalty problem caused by the other existing strategies, which significantly increases the sampling accuracy without the restriction of the duty cycle of injected pulse. In order to verify the effectiveness of the proposed method, three classical control schemes including angular position control, current chopping control, and voltage pulse-width modulation control are all performed in the closed-loop system. The simulation and experiments based on a 150-W four-phase 8/6 SRM are carried out to validate the feasibility of this proposed scheme.

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.

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.

A New Asymmetrical Half-Bridge Converter With Zero DC-Offset Current in Transformer

This paper proposes an asymmetrical half-bridge (AHB) converter with a new secondary rectifier. Due to the new rectifier stage, the proposed AHB converter has a zero dc-offset current in the transformer at any operating conditions so that the transformer core loss becomes very small compared to the conventional AHB converter. This results in higher efficiency. Besides, magnetic components can be optimally utilized because maximum flux density can be applied when designing the magnetic components. It also allows a flexible design to improve the efficiency or reduce the cost. This paper presents the operation principle and relevant analysis results of the proposed converter. A 300 W, 200-400-V input, and 50-V output laboratory prototype operating at 100 kHz is built and tested to verify the effectiveness of the proposed converter.

Reduced Switch Count Converter For Switched Reluctance Generators

This paper deals with electronic converters to drive the switched reluctance generator – SRG. An alternative reduced switch count converter is compared with the conventional asymmetric half bridge converter. The SRG is driven with constant speed and excited with DC power from a three-phase rectifier bridge and supplies pulsed DC power to the load at the output. Mathematical and computing models for the SRG are presented, as well as simulation and experimental results. The aim is to show that the alternative converter, which is cheaper, works better than the half bridge converter commonly used to drive these machines.

High efficiency asymmetrical half-bridge converter using a self-driven synchronous rectifier

A novel high efficiency asymmetrical half-bridge converter using a self-driven synchronous rectifier is presented. The proposed converter improves the system efficiency using the characteristics of the asymmetrical half-bridge converter and the self-driven synchronous rectifier. The synchronous rectifier applied to the proposed converter is the new topological synchronous rectifier, which is a slightly modified type of the conventional synchronous rectifier used in the conventional asymmetrical half-bridge converter. The type of the new topological synchronous rectifier slightly changes the transformer structure and the synchronous switch connection in the asymmetrical half-bridge converter with a conventional self-driven synchronous rectifier. The operational principle of the proposed converter is explained in detail. Since the proposed converter utilises the transformer leakage inductor as its resonant inductor, its structure is simplified. A design example for a 90 W (12 V/7.5 A) prototype is discussed in detail. Experimental results are shown for the designed prototype converter under universal AC input voltage (180–265 V). It is shown that the efficiency of the proposed converter can be significantly improved.