Showing papers by "Yan-Fei Liu published in 2005"

A New Digital Control Algorithm to Achieve Optimal Dynamic Performance in DC-to-DC Converters

Abstract: In this paper, a new optimal control algorithm is proposed to achieve the best possible dynamic performance for DC-to-DC converters under load changes and input voltage changes. Using the concept of capacitor charge balance, the proposed algorithm predicts the optimal transient response for a DC-to-DC converter during the large signal load current change, or input voltage change. The equations used to calculate the optimized transient time and the optimized duty cycle series are presented. By using the proposed algorithm, the best possible transient performance, including the smallest output voltage overshoot/undershoot and the shortest recovery time, is achieved. In addition, since the large signal dynamic response of power converters is successfully predicted, the large signal stability is guaranteed. Experimental results show that the proposed method produces much better dynamic performance than a conventional current mode PID controller

Digital control of switching power converters

Abstract: The paper reviews the latest advance of the digital control technologies in DC-DC converters. The research on digital control is mainly focused on two areas. One is the methods to generate digital PWM (DPWM) signals to meet the output voltage accuracy requirement. Various dithering techniques have been developed to improve the output voltage resolution and at the same time to reduce the clock frequency requirement. The other is to develop new control methods that can utilize these advantages of the digital controller so as to improve the dynamic performance of the switching power converters. Several new digital control methods have been proposed and significant dynamic performance improvement has been achieved

Resonant gate drive circuits

Abstract: A resonate gate drive circuit for driving at least one power switching device recovers energy loss for charging and discharging the gate capacitance of the power switching devices. The gate drive circuit uses a current source to charge and discharge the gate capacitance with a high current, reducing the switching loss of the power switching device. The gate drive circuit comprises four semiconductor bidirectional conducting switching devices connected in a full-bridge configuration. An inductor connected across the bridge configuration provides the current source. The gate drive circuit may be used in single and dual high-side and low-side, symmetrical or complementary, power converter gate drive applications.

A new resonant gate drive circuit with centre-tapped transformer

Abstract: This paper presents a new resonant gate drive circuit for a pair of low side switches with 50% duty cycle or less, which is suitable for variable frequency resonant converter, push-pull converter and so on. A centre-tapped transformer is utilized to boost switches' gate voltage twice high as Vcc voltage. Charging and discharging the gate input capacitance by a constant current source increases MOSFETs switching transition speed. The theoretical analysis and simulation waveforms are provided. A prototype board working at 1 MHz is built and experimental results are also given

A new resonant gate drive circuit with efficient energy recovery and low conduction loss

Abstract: In this paper, a new resonant gate drive circuit is proposed. The proposed circuit consists of four control switches and a small resonant inductance. The current through the resonant inductance is discontinuous in order to minimize circulating current conduction loss present in other methods. The proposed circuit also achieves quick turn-on and turn-off transition times to reduce switching loss and conduction loss in power MOSFETS. An analysis, design procedure and simulation results are presented for the proposed circuit

A novel nonisolated half bridge DC-DC converter

Abstract: The duty cycle of conventional multi-phase buck converters become extremely small as the output voltage becomes lower and lower. This is a severe challenge with the switching frequency goes up. This paper introduces a non-isolated half bridge converter , which extends duty cycle to a favorable range. Thus, the converter will have symmetrical dynamic response ability. The switching loss will reduce dramatically. The primary current is directly transferred to the output. The energy transferring is more effectively then that of conventional isolated half bridge converter. In addition, the voltage stress of the primary MOSFETs equals to the input voltage, which is much lower than that of non-isolated forward or push-pull topologies. A 12 V input, 1 V/30 A output, 350 kHz prototype was built to demonstrate the advantages

A New Transformer-Based Non-Isolated Topology Optimized for VRM Application

Abstract: The duty cycle of conventional multi-phase buck converters becomes extremely small as the output voltage becomes lower and lower. This is a severe challenge with the switching frequency goes up. This paper introduces a non-isolated half bridge converter which can extend the duty cycle to a favorable range. Thus, the converter will have symmetrical dynamic response ability. The switching loss will reduce dramatically. The primary current is directly transferred to the output. The energy transferring is more effectively then that of conventional isolated half bridge converter. In addition, the voltage stress of the primary MOSFETs equals to the input voltage, which is much lower than that of non-isolated forward or push-pull topologies. A 12 V input, 0.8 V/30 A output, 500 kHz prototype was built to demonstrate the advantages

A new duty cycle parallel control method and FPGA implementation for AC-DC converters with power factor correction (PFC)

Abstract: A new duty cycle parallel control method for AC-DC converter with power factor correction is proposed. The duty cycle required to achieve unity power factor consists of two terms: current term and voltage term. They are calculated directly based on the reference current and sensed inductor current, input voltage and output voltage. It requires only one multiplication and three addition operations for digital implementation so that the proposed PFC control method can be implemented by a low cost DSP, microprocessor, FPGA or an ASIC to achieve high switching frequency. This duty cycle parallel control essentially distinguishes from the conventional current mode control in which there are two regulators, one for voltage regulation and one for current regulation. Test results for a digital PFC implementation show that the proposed method can achieve unity power factor under both steady and transient state. Sinusoidal input current can be achieved under nonsinusoidal input voltage condition. The switching frequency of FPGA control boost PFC is 400 kHz. The proposed duty cycle parallel control strategy has high potential for the next generation of high switching frequency PFC implementation, due to its lower calculation requirement, lower cost and better performance than average current mode control

A new analysis and design method for fuzzy logic controllers used in power converter

Abstract: This paper proposes a novel design procedure of fuzzy logic controller (FLC) for DC-to-DC converters that integrates linear control techniques with fuzzy logic. The design procedure allows the small signal model of power converters and linear control design techniques to be used in the initial stages of FLC design. This simplifies the small signal design and the stability assessment of the FLC. By exploiting the fuzzy logic structure of the controller, heuristic knowledge is incorporated into the design, resulting in a non-linear controller with improved large signal performance over linear PI controllers

A New Non-Isolated Full Bridge Topology for Low Voltage High Current VRM Applications

Abstract: In this paper a new non-isolated full bridge topology is introduced. The primary side of this topology is a full bridge; however, the input voltage ground of the conventional full bridge is connected directly to the positive point of the output and not connected to the input ground. In this arrangement, the input current flows directly to the load without going through the transformer. The secondary side rectifier stage is a current doubler. The primary side can operate in either phase shift soft switching mode or hard switching mode. The advantages of this topology, include soft switching and reduced conduction loss. A 1.41 by 1.41 inch power module has been built and tested to verify the analysis