Ruxi Wang

Phase-shift soft-switching power amplifier with lower EMI noise

This work presents detailed analysis for a phase-shift soft switching inverter. The optimum soft switching operation algorithm is proposed based on the maximum soft switching operation range and also the smallest device current stress. Meanwhile, the soft switching control algorithm is proposed to guarantee the zero-voltage-switching (ZVS) within each switching period. A compact coupled circulating inductor based on the spiral structure is utilized to provide circulating current for the soft switching. Other design considerations such as the minimum circulating current for ZVS operation, dead time selection are also included. Finally, a 600V, 300A prototype is demonstrated to show the feasibility of reducing the EMI noise through soft-switching technique.

High performance two H-bridge in cascaded gradient driver design with SiC power MOSFET

In this paper, a detailed high efficiency two H-bridge in cascaded gradient driver design with 1700V SiC MOSFET is presented. Both module and system level stray inductance are minimized to better utilize the SiC high switching speed capability. The amplifier loss is calculated in simulation with device loss model and also verified in hardware experiment. The efficiency of the amplifier is higher than 99%. Higher output ripple frequency (up to 125 kHz) provides the opportunity to design a high density output filter without magnetic components. A novel ripple current cancellation circuit (RCCC) with embedded coolant pipe is also presented and demonstrated.

Rogowski current sensor design and analysis based on printed circuit boards (PCB)

This work presents a new Rogowski current sensor design implemented in printed circuit boards. The proposed structure utilizes a modular design for a variety of applications. Feasibility was first demonstrated using standard printed circuit boards. Test results detail performance with high repeatability with less than 0.8% difference in sensed voltages and less than 0.3% difference in sensed voltages with respect to position of installation. In order to have a less complex, more manufacturable and modular Rogowski current sensor, a flexible printed circuit (FPC) solution was also designed and demonstrated. By using the FPC solution, high sensitivity and much higher power density was achieved. Coupling analysis of a 3-phase system was also conducted both from simulation and experiments.

Reduced common-mode noise modulation strategies for gradient driver with cascaded H-bridge multilevel structure

This work presents detailed analysis for the Common Mode Voltage (CMV) in a two stages cascaded gradient driver system. The vector modulation method is proposed to eliminate or reduce the CM voltage in a cascaded system without a neutral or ground point. The method is demonstrated through two stages example but can be extended to topology with more stages in cascaded. Meanwhile, the power stage output ringing caused by the stray parameters is analyzed in detail and proper damping method is proposed. A hardware prototype is fabricated and tested to validate the analysis.

Reliability odometer of power semiconductor device used for high performance high power amplifiers

This paper presents a real-time evaluation of power semiconductor devices in a high performance high power amplifier. The proposed method can represent the life status of the semiconductor modules in ‘odometer’ format. A special challenging case are pulsating load applications like an MRI gradient driver system. The general concepts presented have been evaluated in detail for the MRI case. A detailed Cauer thermal network is proposed to estimate the temperature from junction to ambient with the combination of non-ideal heatsink. Rainflow counting method and Palmgren-Miner linear damage accumulation rule are introduced and designed for the on-line cycle counting and real-time lifetime consumption estimation. The paper explains the design of the method considerations to minimize the computing time and memory requirements different from standard off line or post analysis approaches. Simulation models and hardware prototype are built to validate the design and analysis.

H-bridge building block with SiC power MOSFETs for pulsed power applications

This paper presents a H-bridge building block with 1700V SiC MOSFET for a pulsed power application to achieve both high voltage, high current and high switching frequency capability. Both power module level and system level stray inductance is minimized to better utilize the SiC high switching speed capability. Meanwhile, since the large pulsed energy is required to drive the pulsed load, voltage sensing for active DC link voltage compensation is proposed and designed.