基于定频控制的对称式倍压整流输出两级式变换器

针对高压输出、宽负载变化的行波管(TWT)电源,提出一种基于定频控制的Buck+半桥LLC倍压谐振两级式DC/DC变换器。该变换器通过定频控制解决了变频控制时磁性元件的优化设计问题,并通过合理地选择LLC的工作频率,使LLC的开关管和整流二极管在全负载范围内分别实现了ZVS和ZCS。通过对传统的Cockcroft-Walton倍压整流电路进行改进,得到对称式倍压整流电路,有效地降低了输出电压纹波和电压跌落,却不用增加器件的数量,更适用于高压、小电流输出场合。首先利用电容充放电原理对任意方波输入的倍压整流电路进行定量分析,得到输出电压纹波和电压跌落的公式。其次,从时域对LLC进行详细的稳态分析。然后,对两级式变换器进行优化设计,并给出定频LLC的优化设计方法。最后,通过实验验证了以上分析的正确性。

A Two-stage Converter with Symmetrical Voltage-multiplying Rectifier Output Based on Frequency-fixed Control

For the high-voltage output and wide range load of Travelling Wave Tube(TWT)power conditioner,a frequency-fixed two-stage DC/DC converter combined of Buck and half-bridge LLC voltage-multiplying resonance is presented.Based on the frequency-fixed control,the optimal design of magnetic elements was realized.Through the reasonable selection of switching frequency of LLC,the switches and the rectifier diodes of LLC can respectively operate under ZVS and ZCS.A symmetrical voltage-multiplying rectifier was proposed,based on the improvement of the traditional Cockcroft-Walton structure,then the ripple and drop of output voltage were both effectively reduced without the added components,which was better for the high-voltage and low-current output.Firstly,voltage-multiplying rectifier circuit with any square wave input was analyzed quantitatively using the principle of capacitor charging and discharging to get the formula of output ripple voltage and voltage drop.Secondly,the steady state analysis of LLC was analyzed in detail from the time domain.Then,the optimal design method of two-stage converter was given.Finally,the analysis above was verified by experiments.