高压电容器充电电源谐振变换器的定频控制

Constant Switching Frequency Control of Resonant Converter of High Voltage Capacitor Charging Power Supply

为有效控制高压电容器高频恒流充电电源谐振变换电路的开关频率,研制了定频控制(占空比为50%,开关频率在整个充电过程中保持不变)的20 kW高压电容器充电装置逆变电路开关电路。通过提出的充电电源电路的并联负载谐振(PLR)DC-DC变换电路的等效电路模型,研究了充电电源装置的恒流充电原理,找出了电容充电初始阶段谐振电流和开关频率的数值关系。实验研究结果表明,当谐振变换电路开关频率接近于等效电路固有谐振频率的奇数分之一时,产生较大的谐振电流;为了实现谐振变换电路开关器件的零电流开通和关断,开关频率的大小始终可控制在小于等效电路固有谐振频率的1/2的范围之内。

Effectively controlling the switching frequency of the high frequency resonant converter of the high voltage capacitor charging power supply is one of the key technologies to realize the design and manufacture of the charging power supply. Constant switehing frequency control method （duty ratio is fifty percent, and the resonant eonverter＇s switching frequency keep constant during the whole charging phase） is studied in the manufactured 20kW high eapacitor charging power supply. Because of the equivalent eapacitor of the high frequency transformer can not be ignored in the charging circuit, thus PLR DC-DC inverter is brought forward as the equivalent circuit model of the charging power supply. The operating principles of the constant charging are studied, and the numerical relations between the switching frequency of the resonant inverter and resonant circuit of the equivalent cireuit of the charging power supply during the initial charging phase are found out. In order to reduce the switching loss, the inverter＇s switching frequency is controlled below the half of the resonant frequency of the inverter＇s output circuit during the whole charging period to realize zero current switching （ZCS）. The simulation curve of RMS value of resonant current VS switching frequency shows that at the point of one third, one fifth, one seventh, and so on of the resonant frequency, several current peaks appear, and also these current peaks gradually decrease at the reducing frequency point mentioned above. Simulation and experimental waveforms at a switching frequency below the half of the resonant frequency shows that the switching components are working in a soft switching state, and in each half of the switching period there.is a series of digressive current waveforms. These results show the rationality of the equivalent circuit model （PLR 1312-1312 inverter） and the deduced numerical relations between the resonant current and switching frequency of the resonant inverter.