基于有源箝位的功率器件串联均压技术

功率器件串联的关键技术挑战是如何实现串联器件的动、静态均压。提出一种基于有源箝位的器件串联均压电路及其控制方法。所述均压电路仅由1个辅助开关管和1个箝位电容串联而成，该电路与各主功率管并联。主功率管的关断电压可自动被箝位电容电压箝位，从而将器件串联均压问题转化为各箝位电容电压均衡问题。提出了一种箝位电容均压方法，利用负向电流回收箝位电容电能，并能保证辅助开关管实现零电压开通。所提均压技术具有结构简单、损耗低、模块化等优点。此外，通过调整箝位电容放电时间差异，形成阶梯型桥臂电压，以减小桥臂电压的瞬时变化率dv/dt。搭建一台 3 kV/750 V 30 kW 谐振型直流变压器样机，每个桥臂采用6个SiC MOSFET串联。实验结果表明所提均压方法在各个工况下均能实现串联器件的动、静态均压，不均压度小于3 %，且在3 kV输入电压下峰值效率达98.4 %。

Voltage balancing method for series-connected power devices based on active clamping

The key technical challenge of series connection of power devices is the dynamic and static vol-tage balancing of series-connected devices. A voltage balancing circuit of series-connected power devices based on active clamping and its control method are proposed. This circuit consists of only one auxiliary switch and one clamping capacitor, which is connected in parallel with each main power switch. The turn off voltage of the main power switches can be clamped to the clamping capacitor voltage automatically, and the balancing of the series-connected power device voltages can be transferred into the balancing of the clamping capacitor voltages. A voltage balancing method for the clamping capacitors is proposed, which uses the negative current to recycle the electric energy from the clamping capacitor, and achieves the ZVS-on(zero voltage switching-on) of the auxiliary switch. The proposed voltage balancing method has the advantages of simple structure, low loss and modular structure. Besides, by adjusting the discharging period difference of the clamping capacitors, the staircase arm voltages can be generated to reduce the instantaneous change rate of the arm voltage dv/dt. A 3 kV/750 V 30 kW resonant DC transformer prototype is constructed, and 6 SiC MOSFETs are connected in series in each arm. Experimental results show that the proposed voltage balancing method can realize the dynamic and static voltage balancing of series-connected devices, the voltage unbalance degree is less than 3 %,and the peak efficiency is up to 98.4 % at 3 kV input voltage.