Guoen Cao

A Novel Circuit for Characteristics Measurement of SiC Transistors

This paper proposes a novel test circuit for SiC transistors. On-state resistance under practical application conditions is an important characteristic for the device reliability and conduction efficiency of SiC transistors. In order to measure the on-state resistance in practical applications, high voltage is needed, and high current is also necessary to ignite performance for the devices. A soft- switching circuit based on synchronous buck topology is developed in this paper. To provide high- voltage and high-current stresses for the devices without additional spikes and oscillations, a resonant circuit has been introduced. Using the novel circuit technology, soft-switching can be successfully realized for all the switches. Furthermore, in order to achieve accurate measurement of on-state resistance under switching operations, an active clamp circuit is employed. Operation principle and design analysis of the circuit are discussed. The dynamic measurement method is illustrated in detail. Simulation and experiments were carried out to verify the feasibility of the circuit. A special test circuit has been developed and built. Experimental results confirm that the proposed circuit gives a good insight of the devices performance in real applications.

An interleaved buck converter with reduced reverse-recovery problems

An interleaved buck converter with low conduction losses and reduced diode reverse-recovery problems is proposed in this paper. The circuit consists of two interleaved buck converters with one coupled inductor for each phase, operating in continuous conduction mode (CCM). Zero-current switching (ZCS) condition duting turn-on transitions and significant reduction of the losses associated with diode reverse recovery are accomplished through the coupled inductors. The two phases operate in out of phase mode. Thus, the input and output currents can be continuous with low ripple. Constant frequency operation with low switching losses and low output current ripple is very suitable for the realization of battery chargers in standalone PV applications. The operating principle of the proposed converter are presented in detail. Finally, an 400 W, 100 kHz experimental prototype was built to verify the theoretical analysis and feasibility of the proposed converter, with the efficiency up to 94.5 %.

A New Measurement Circuit to Evaluate Current Collapse Effect of GaN HEMTs Under Practical Conditions

The gallium nitride transistors suffer from current collapse effect in operation regions, which leads the dynamic ON-resistance to increase when high voltage is applied to the transistor. Dynamic ON-resistance under practical application conditions is also an important factor for the reliability and conduction efficiency of transistors. To measure the dynamic ON-resistance and evaluate the current collapse effect, a softswitching circuit based on synchronous buck topology is proposed in this paper. To apply high-voltage and high-current stresses to the device without additional spikes and oscillation, resonance technique has been employed. As a result, the proposed circuit could produce sufficient power stresses to the devices with general equipment. To achieve accurate measurement of ON-resistance under switching operations and eliminate the saturation of oscilloscope probes, an active voltage clamp circuit is developed. Operation principles and design analysis of the circuit are described in this paper. The dynamic ON-resistance measurement method is illustrated in detail. Furthermore, a prototype circuit has been built. A simulation and experiments were carried out to verify the performance of the system. A comparison of the active clamp circuit with common voltage probes is presented through the measurement results. The experimental results confirm that dynamic ON-resistance can be accurately measured using the proposed circuit and the current collapse effect can be evaluated under practical operation conditions with high precision.

A High Performance Interleaved Bridgeless PFC for Nano-grid Systems

A high performance interleaved bridgeless boost power factor correction (PFC) rectifier operating under the critical current conduction mode (CrM) is proposed in this paper to improve the efficiency and system performance of various applications, such as nano-grid systems. By combining the interleaved technique with the bridgeless topology, the circuit contains two independent branches without rectifier diodes. The branches operate in interleaved mode for each respective half-line period. Moreover, when operating in CrM, all the power switches take on soft-switching, thereby reducing switching losses and raising system efficiency. In addition, the input current flows through a minimum amount of power devices. By employing a commercial PFC controller, an effective control scheme is used for the proposed circuit. The operating principle of the proposed circuit is presented, and the design considerations are also demonstrated. Simulations and experiments have been carried out to evaluate theoretical analysis and feasibility of the proposed circuit.

Design of a wireless power transmission system for portable electronic equipment

This paper presents a wireless power transmission system based on inductive coupling for portable electronic equipment. The system consists of a transmitter inverter, an inductively coupling link, and a receiver rectifier. The power transmitter is based on a full-bridge phase-shift inverter, and the inductive link is composed of two loosely coupled inductors. A high frequency bridge rectifier and a DC/DC converter consist the receiver part. To improved the performance of the system, modeling method of the magnetically coupled link is addressed and analyzed. A 20W prototype circuit is built and tested. As performance of soft magnetic composite sheet is essential for the system efficiency and reliability, evaluation experiments of different Fe-based soft magnetic composites were carried out and analyzed. The results show that the system efficiency is up to 65% at full load.

Design and control of a novel electromagnetic driver for wireless micro-robots

Electromagnetic actuator (EMA) is considered as a promising mechanism for the wireless micro-robotic locomotion control. Generally, EMA systems employ function generators and power amplifiers to drive coil pairs, and operated in open loop mode, by which system dynamic response and steady state accuracy are no good enough. This paper presents a novel prototype of a real time, two-stage, and close-loop EMA system. The proposed circuit consists of a phase-shift full-bridge (PSFB) converter, a two-phase inverter, and a digital controller based on DSP. The function of the PSFB converter is to supply stable dc voltage, while the current-source two-phase inverter is used to generate independent sine and cosine power signals. The relationship between DC link voltage and output regulation of the inverter is studied and a novel control strategy based on feedforward complex PI controller for the two-stage driver is proposed to achieve high accuracy and fast dynamic response. The experimental results based on a 360W prototype are discussed to evaluate the proposed driver circuit and control method.