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Ahmed M. Ammar, Frederik M. Spliid, Yasser Nour, Arnold Knott, IEEE Journal of Emerging and Selected Topics in Power Electronics, January 2020
Abstract:This paper presents the analysis and design of a resonant power factor correction (PFC) rectifier for the first stage in single-phase front-end offline converters targeting low-power applications (up to 100 W). With the addition of a charge pump circuit comprised of a capacitor and a diode to a class-DE resonant converter, PFC functionality is achieved inherently. The operation is based on soft switching, allowing for increased switching frequencies with reduced switching losses. A 1 MHz prototype employing wide-bandgap (WBG) switching devices is built and tested to validate the analysis and proposed design method. The prototype achieves up to 50 W of output power with a power factor of 0.99, a total harmonic distortion (THD) of 8.6 %, and an efficiency of up to 88 %; with harmonic magnitudes well-within the IEC 61000-3-2 standard class-C device limits, making it suitable for use as the rectifier stage in LED drivers. Despite the additional circuit stresses from the charge pump operation, the proposed converter offers simplicity and low component overhead, with the potential for higher frequency operation towards higher power densities. Index Terms—AC-DC power conversion, power factor correction, resonant power conversion, charge pump, wide-bandgap semiconductors.
Ahmed M. Ammar, Frederik M. Spliid, Yasser Nour, Arnold Knott, IEEE COMPEL 2019, Toronto, Canada. June 2019
Abstract: This paper presents a power factor correction (PFC) rectifier for single-phase offline converters. With the addition of a charge pump circuit comprised of a capacitor and a diode to a class-DE series-resonant converter, PFC is achieved inherently.The converter operation is based on soft-switching, and a 1 MHz50 W prototype employing wide bandgap devices is implemented, achieving a power factor of 0.99 and a total harmonic distortion (THD) of 8.6 %, at an efficiency of 84 %, with substantially low input current harmonic magnitudes compared to the limits set bythe IEC 61000-3-2 standard
Ahmed M. Ammar, Yasser Nour and Arnold Knott, IEEE CPERE 2019, Aswan City, Egypt. October 2019
Abstract: This paper presents an LLC resonant DC-DC converter for single-phase offline converters. A 1 MHz 400 V to 48 V prototype employing gallium nitride (GaN) switching devices is designed and implemented. A high-frequency magnetic material isused for the magnetic devices, with the resonant inductor integrated in the transformer. The converter operation is based on soft switching and achieves up to 65 W of output power with a peak efficiency of 96 % at full-load. Inherent load regulation capability is demonstrated from 5 to 65 W of power with fixed switching frequency, while line regulation for 360 to 440 V input is verified with a frequency modulation range of 816 to 1256 kHz respectively.Keywords—resonant power conversion, dc-dc converters, offline converters, wide bandgap semiconductors, zero voltage switching (ZVS)
Nicolai J. Dahl, Ahmed M. Ammar, Arnold Knott, Michael A. E. Andersen, IEEE Journal of Emerging and Selected Topics in Power Electronics, October 2019
Abstract:As the operating frequency of power convertersincreases, the passive component values likewise decrease. Thisresults in the effect of the parasitic components becomingmore prominent, leading to significant modeling errors if notconsidered. For resonant converters this especially becomes aproblem at high frequencies. This paper presents a reduced modelfor a class-DE series resonant converter based on generalizedaveraging that incorporates the relevant parasitics and uses mul-tiple harmonics to obtain an accurate linear model. Comparisonbetween the proposed model, prior art, and a prototype converterrunning at 1 MHz is conducted, and a PI-controller is designedbased on each model and tested. The results show that theparasitics have a significant impact on the DC-gain and dynamicsof the converter, and that the proposed model improves on theprior art by reducing the DC-gain error by more than 7 dB,and the error in the low frequency pole from 168 % to 16.9%. Furthermore, the PI-controller designed on the prior artwas found to have more than 40 times larger overshoot in thecontrol signal when measured compared to the model prediction,while the controller based on the proposed model showed correctperformance when simulated and measured.Index Terms—Resonant converters, Modeling, PI control,State-space methods, DC-DC power converters.
Christopher H. K. Jensen, Rasmus B. Lind, Jens C. Hertel, Ahmed M. Ammar, Arnold Knott, Michael A. E. Andersen, IEEE NORCAS 2019. October 2019
Abstract: A time-based control scheme for the power factorcorrection (PFC) boost rectifier is presented. Average-current-mode control in time is achieved using time-based compen-sators performing a proportional-integral control action. Thecontroller is fully CMOS compatible, which allows for monolithicintegration with the power switching elements. The time-basedcontroller also eliminates the need for the pulse-width-modulation(PWM) generator required in the conventional analog and digitalcontrollers. The proposed controller draws a sinusoidal inputcurrent in phase with the input mains voltage and delivers a dcoutput voltage. The control scheme model is verified on a600WPFC boost converter, achieiving a power factor of0:99and a400Vdc output from a230Vrms50Hzinput voltage.Index Terms—AC-DC converter, time-based control, powerfactor correction, voltage-controlled oscillator, boost converte
Frederik M. Spliid, Ahmed M. Ammar, Arnold Knott, IEEE Journal of Emerging and Selected Topics in Power Electronics, December 2019.
Abstract: Resonant converter topologies have the ability toeliminate switching losses through zero-voltage switching, makingthem well-suited for switching operation in the MHz frequencyrange. However, these types of converters are traditionally verysensitive to changes in input voltage and power level, makingthem unsuitable as power factor correcting AC-DC converters.This paper present a throughout analysis of the operation ofa class DE converter in order to derive a set of conditions,under which it can achieve constant input impedance over awide input voltage range (60-325 V DC) with constant outputvoltage (450 V DC) and thus be operated as a PFC converter,while maintaining zero voltage switching across the full range.The operation is experimentally verified under DC-DC operationfor different power levels at a series of input voltages within thespecified range. The implemented prototype achieves conversionefficiencies of up to 94 % and handles up to 105 W of powerat switching frequencies of 2 MHz and above, while achievingconstant input impedance over the full input voltage range,enabling its use as a power factor correcting converter.Index Terms—AC-DC power conversion, power factor correc-tion, resonant converters, zero voltage switching, wide-bandgapsemiconductors
Christopher Have Kiaerskou Jensen, Frederik Monrad Spliid, Jens Christian Hertel, Yasser Nour, Tiberiu-Gabriel Zsurzsan, Arnold Knott, IEEE APEC 2018, San Antonio, Texas, USA. March 2018.
Abstract: Connectivity in smart devices is increasingly realized by wireless connections. The remaining reason for using connectors at all is for charging the internal battery, for which wireless power transfer is an alternative. Two industry standards, AirFuel and Qi, exist to support compatibility between devices. This work is focusing on the AirFuel standard, as it is operating at a higher frequency (6.78 MHz), than the Qi standard, and therefore allows smaller passive components, including the coupling coils. Whereas gallium-nitride (GaN) devices are being widely used on the transmitter (Tx) side, this work uses low voltage GaN transistors on the receiver (Rx) side to allow synchronous rectification and soft switching, thereby achieving high efficiency. After analyzing adequate Class-DE rectifier topologies, a Class-DE full-bridge 5 W rectifier using 15 V GaN transistors are designed and implemented. The experimental results show an efficiency above 80 % over a wide operating range and a peak efficiency of 89 %, at an arbitrary alignment of Tx and Rx coils with 3 cm distance between them.