Bor-Ren Lin

Single-phase three-level PWM rectifier

This paper presents a new PWM control scheme for a single-phase three-level PWM rectifier to improve the power quality. A diode bridge with two power switches is adopted as a PFC circuit to achieve a high power factor and low harmonic distortion. The control scheme is based on a look-up table with hysteresis current controller (HCC). Based on the proposed control scheme, the line current is driven to follow the sinusoidal current command which is in phase with the supply voltage. The software simulation and experimental results are shown to verify the proposed control scheme. It is shown that the measured line current harmonics and power factor satisfy the IEC 1000-3-2 requirements.

Analysis and operation of hybrid active filter for harmonic elimination

This paper presents a hybrid active filter topology and its control to suppress the harmonic currents from entering the power source. The adopted hybrid active filter consists of one active filter and one passive filter connected in series. By controlling the equivalent output voltage of an active filter, the harmonic currents generated by the nonlinear load are blocked and flow into the passive filter. The power rating of the converter is reduced compared with the pure active filters to filter the harmonic currents. The harmonic current detection approach and DC link voltage regulation are proposed to obtain equivalent voltage of the active filter. The effectiveness of the adopted topology and control scheme has been verified by the computer simulation and experimental results in a scaled-down laboratory prototype.

Analysis and implementation of shunt active power filter with three-level PWM scheme

A three-phase four-wire voltage source inverter for power quality compensator under the balanced and unbalanced conditions is proposed to provide balanced three-phase source currents and improve input power factor. The proposed inverter is based on the conventional three-phase voltage source inverter with three additional AC power switches to perform three-level pulse width modulation. The voltage stress of three AC power switches is clamped to half DC-link voltage. The balanced reference line currents are estimated using the DC bus voltage and load currents. A voltage controller is used in the outer loop control to compensate the switching losses of the voltage source inverter. To perform the integrated power quality compensation, hysteresis current control scheme is adopted to track the balanced line current commands in phase with mains voltages. Three voltage levels are generated on the AC terminal of the proposed inverter. Simulation results were provided to verify the effectiveness of the proposed control scheme.

Analysis of an Active Clamp Forward Converter

This paper studies the detailed circuit operation, mathematical analysis and design example of the active clamp forward converter with synchronous rectifier. There is one auxiliary switch and one clamp capacitor used in the forward converter to recycle the energy stored in the transformer leakage in order to minimize the spike voltage at the transformer primary side. Therefore the voltage stress of main switch can be reduced. The active clamped circuit can also help the main switch to turn on at zero voltage switching using the switch output capacitor and transformer leakage inductance. The synchronous rectifier is used at the secondary side to reduce the conduction losses at the rectifier switches. Therefore the system efficiency can be increased. First the circuit operation and mathematical analysis are discussed. The design example of active clamp forward converter is presented. Finally the experimental results based on the AC input voltage of 110 Vrms and DC output voltage of 5 V prototype operating at rated output load of 20 A and a switching frequency of 100 kHz are provided to verify the zero voltage switching at turn-on

Analysis and implementation of dual-output LLC resonant converter

A dual-output LLC resonant converter for LCD-TV applications is presented in this paper. Based on the LLC resonant behavior, the power MOSFETs are turned on at zero voltage switching (ZVS) and secondary rectifier diodes are turned off at zero current switching (ZCS). In the proposed converter, the primary windings of two transformers are connected in series so that the primary currents of two transformers are equal. In the secondary side of transformers, two full-wave rectifiers with dual-output configuration are connected in parallel to share the load current and to reduce the current stresses of the secondary windings of transformers. The principle of operation, steady state analysis and design consideration of the proposed converter are provided in detail. Experimental results based on a laboratory prototype with 12 V/14 A and -12 V/14 A outputs with 92.7% efficiency for LCD-TV applications were provided to verify the effectiveness of the proposed converter.

Single-phase high-power-factor rectifier with capacitor-clamped topology

A single-phase high power factor rectifier based on capacitor-clamped scheme is proposed to achieve high power factor, low current distortion and low voltage stress of power semiconductors. The carrier-based current controller is used in the inner control loop to track the line current command. A voltage compensator is used to balance capacitor voltages to obtain high quality PWM voltage waveform. A PI-based voltage controller is used in the outer control loop to keep DC-link voltage constant. The proposed control scheme illustrates its validity and effectiveness through the respective simulation and experimental results.

Multilevel inverter with series connection of H-bridge cells

A novel AC/DC/AC converter topology, a three-phase switching mode rectifier (SMR) and a three-phase multilevel inverter with separate DC power supplies, is proposed in this paper. To improve the power quality, three-phase SMR is adopted to supply sinusoidal wave with high power factor and current distortion. The separate DC bus voltages are provided by switching mode DC-DC converters. The full-bridge cells are adopted to provide multilevel line voltage. The control schemes of three-phase multilevel inverter are based on look-up table with sine-triangular PWM method. The voltage unbalance problem between the separate DC bus voltages is improved by using the proposed control scheme. The proposed AC/DC/AC converter is verified by computer simulations.

Multilevel AC/DC/AC converter by using three-level boost rectifier and five-level diode clamped inverter

This paper presents a control scheme for single-phase rectifier with three-level boost converter to improve power quality. The hysteresis current controller is adopted to control power switches for achieving a high power factor and low current distortion. The voltage balance problem in the DC bus capacitors is achievable based on the proposed control scheme for a single-phase rectifier. A five-level voltage source inverter is used to reduce the harmonic distortion, increase inverter voltage rating and decrease the filter requirement. Computer simulations are given to confirm the high power factor and low current distortion at the rectifier, and low harmonic distortion at the multilevel inverter.

Single-phase ac/ac converter based on half-bridge NPC topology

A novel single-phase ac/ac converter is proposed to draw a sinusoidal line current with nearly unity power factor and to provide a stable ac voltage to the critical loads. The proposed ac/ac converter is based on the half-bridge neutral-point diode-clamped topology. The rectifier part is controlled to generate a unipolar PWM waveform on the ac terminal using the power switches with voltage stress of half the DC link. The current control scheme with fixed switching frequency is employed in the inner control loop to track the line current command. To regulate the dc bus voltage, a proportional-integral (PI) control is adopted in the outer control loop. The inverter part with half-bridge neutral point clamped scheme is employed to generate a stable and clean sinusoidal output voltage to the critical load. The experimental results based on a laboratory prototype were implemented to verify the effectiveness of the proposed control scheme.

Analysis of ZVS/ZCS soft-switching dual-resonant converter

A soft-switching converter with dual resonant structures is presented in this paper. The dual resonant tanks are composed by the leakage inductors and resonant capacitors to achieve zero-current-switching (ZCS) turn-off mechanism for diodes at the secondary side of transformer. Moreover, the voltage stresses of power switches are clamped by the active clamp circuit at the primary side of transformer. The active clamp circuit is not only absorbed the energy stored in the leakage inductor but also create zero-voltage-switching (ZVS) turn-on feature for power switches. Hence, the reverse-recovery problem can be eliminated. The operational principles, design consideration and realization are discussed. Finally, experimental results from a 400W prototype are presented to confirm the effectiveness of the proposed converter.