PDF《balancing for an》

1 Time (2 ms/div)

2 L1 and L2 Inductor Current (2 A/div) Figure 4. Inductor currents

1 Time (2 ms/div)

2 L1 and L2 Inductor Current (2 A/div) (a) Before cycle-by-cycle current balancing (b) After cycle-by-cycle current balancing Time (2 ms/div)

2 AC Input Current (2 A/div) Figure 5. AC input current Time (2 ms/div)

2 AC Input Current (2 A/div) (a) Before cycle-by-cycle current balancing (b) After cycle-by-cycle current balancing 由于在每个开关周期都对第二个相位占空比进行调 节,并且由于各个周期之间的电流差异不同,每个周 期的调节可能也不同,因此这种方法必然会给AC输入 电流带来高频噪声.图5a显示了电流平衡变得平滑且 干净以前的AC输入电流波形.一旦使用了电流平衡, 高频噪声便会出现(图5b). 方法2:半AC周期占空比调节 由于在每个开关周期都对占空比进行调节会给总输入电 流带来高频噪声,因此尝试仅在每个半AC周期对占空比 进行调节看似为一种合理的办法.每个半AC周期的平均 图4 电感电流 图5 AC输入电流 或者峰值电感电流均可用于电流平衡.例如,利用与图 2所示类似的配置,强制每个半AC周期的峰值电感电流 均相等.仍然在每个开关周期对I_CT1和I_CT2采样,并 且固件在每个半AC周期发现I_CT1和I_CT2的峰值.然后,比较这些峰值,并且使用误差来调节占空比.在每 个半AC周期计算电流差异一次,因此相同的占空比调节 运用于下一个半AC周期.这样,便从根本上解决了高频 噪声问题.测试结果表明,AC电流波形几乎与使用电流 平衡以前一样;

高频噪声消失了. Texas Instruments Incorporated

22 Analog Applications Journal High-Performance Analog Products www.ti.com/aaj 2Q

2013 Power Management the same duty-ratio adjustment is applied to the next half AC cycle. This essentially solves the issue of high-frequency noise. Test results showed that the AC current'

s waveform was almost the same as before current balancing was enabled;

the high-frequency noise went away. This approach also has a drawback. Because the relation- ship of the duty ratio to the input-current transfer function is different for continuous-conduction mode (CCM) and discontinuous-conduction mode (DCM),5 the converter dyn........