Browsing by Author "Fu, Dianbo"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
- Improved Resonant Converters with a Novel Control Strategy for High-Voltage Pulsed Power SuppliesFu, Dianbo (Virginia Tech, 2004-07-26)The growing demand for high voltage, compact pulsed power supplies has gained great attention. It requires power supplies with high power density, low profile and high efficiency. In this thesis, topologies and techniques are investigated to meet and exceed these challenges. Non-isolation type topologies have been used for this application. Due to the high voltage stress of the output, non-isolation topologies will suffer severe loss problems. Extremely low switching frequency will lead to massive magnetic volume. For non-isolation topologies, PWM converters can achieve soft switching to increase switching frequency. However, for this application, due to the large voltage regulation range and high voltage transformer nonidealities, it is difficult to optimize PWM converters. Secondary diode reverse recovery is another significant issue for PWM techniques. Resonant converters can achieve ZCS or ZVS and result in very low switching loss, thus enabling power supplies to operate at high switching frequency. Furthermore, the PRC and LCC resonant converter can fully absorb the leakage inductance and parasitic capacitance. With a capacitive output filter, the secondary diode will achieve natural turn-off and overcome reverse recovery problems. With a three-level structure, low voltage MOSFETs can be applied for this application. Switching frequency is increased to 200 kHz. In this paper, the power factor concept for resonant converters is proposed and analyzed. Based on this concept, a new methodology to measure the performance of resonant converters is presented. The optimal design guideline is provided. A novel constant power factor control is proposed and studied. Based on this control scheme, the performance of the resonant converter will be improved significantly. Design trade-offs are analyzed and studied. The optimal design aiming to increase the power density is investigated. The parallel resonant converter is proven to be the optimum topology for this application. The power density of 31 W/inch3 can be achieved by using the PRC topology with the constant power factor control.
- Multi-element resonant converters(United States Patent and Trademark Office, 2010-06-22)A resonant switched power converter having switching frequency controlled in response to an output voltage thereof achieves over-current protection such as at start-up or under short circuit conditions using a resonant tank circuit which provides a notch filter in addition to a band pass filter. A additional band pass filter provided in the resonant tank circuit achieves increased power transfer to a load and reduced circulating resonant currents and conduction losses. The inductances of the preferred LCLCL tank circuit or other tank circuit with two pass band filters and a notch filter may be integrated into a single electrical component.
- Phase compensation driving scheme for synchronous rectifiers(United States Patent and Trademark Office, 2009-10-13)Phase compensation of a voltage appearing on physical terminals of a synchronous rectifier switching element such as a MOSFET is used to substantially eliminate effects of package inductance of the synchronous rectifier and thus approximate the actual voltage across the circuit element providing synchronous rectification in, for example, a switching power converter. By doing so and using the phase compensated signal to control the synchronous rectifier, switching time may be more suitably controlled to improve efficiency of the synchronous rectifier by substantially eliminating body diode conduction and body diode reverse recovery effects.
- Topology Investigation and System Optimization of Resonant ConvertersFu, Dianbo (Virginia Tech, 2010-02-04)Over the past several years, energy efficiency and power density have become the top concerns for power conversion. Rising energy intensity leads to a higher cost of delivering power. Meanwhile, the demand for compact power supplies grows significantly. It requires power supplies with high efficiency, low profile and high power density. Dc-dc power conversion has been widely applied for industry, medial, military and airspace applications. Conventional PWM dc-dc converters have relatively low power transfer efficiency and low power density. In contrast, resonant dc-dc converters have numerous advantages for dc-dc power conversions. In this work, topologies and system optimization of resonant converters are investigated to meet challenges of high efficiency, high power density, low EMI, easy startup and over current protection. LLC resonant converters can achieve zero-voltage-switching (ZVS) for primary side devices and zero-current-switching (ZCS) for the secondary side rectifiers. The switching loss is minimized. LLC is very attractive to overcome the issues of conventional circuits. However, challenges still remain. First of all, for low-voltage high-current applications, the synchronous rectifier (SR) with lower conduction loss is a must for high efficiency. To solve the driving issues of SRs, a novel synchronous driving scheme is proposed. Experimental results demonstrate the considerable loss reduction with utilization of the proposed driving scheme. Secondly, dc-dc converters are required to meet EMI standard. This work proposes an EMI mode. Based on the proposed model, EMI analysis and noise attenuation techniques are proposed and verified by experiments. Thirdly, startup and over-load protection are another issues of LLC resonant converters. With proposed multi-element resonant converters, the current limit issues can be resolved. In addition, the proposed multi-element resonant converters can utilize higher-order harmonics to enhance power transfer. Fourthly, for high-current applications, the secondary side structure becomes very critical. An improved secondary side construction is proposed to alleviate ac termination losses and SR paralleling issues. Novel winding structures are proposed to reduce the winding loss. The magnetic integration technique is proposed and analyzed, and an optimal integrated transformer design is proposed, which has low loss and compact size.