Active Power Current Hysteresis Control Method

Figure 1 (a) shows the control principle of the hysteritic current control Boost PFC circuit. The current detected in the figure is the inductor current. The current upper limit value imax and lower limit value imin are generated by the current reference signal Z, forming a current hysteretic band. When the inductor current reaches the reference lower limit value imin, the switch tube V is turned on and the inductor current increases; when the inductor current reaches the reference upper limit value imax, V is turned off and the inductor current decreases.

The waveform of the inductor current iL of the Boost PFC converter controlled by the current hysteresis loop is shown in Figure 1 (b). The current reference limit values ​​imax and imin are shown as the upper and lower dotted lines in the figure; the solid sawtooth wave in the figure is the inductor current iL, which varies between the two dotted lines imax and imin. The middle dotted line (half-sine wave) is the average current value of each switching cycle. The current hysteresis loop width determines the size of the current ripple, which can be a fixed value or proportional to the instantaneous average current.

Figure 2 shows a schematic diagram of the current hysteresis control logic circuit. There are three comparators in the control circuit. The upper two comparators are used to form a hysteresis band, followed by a logic circuit to ensure that the switch tube V has a correct drive signal. The bottom comparator is used to turn off the switch tube V at the beginning and end of the half-wave sine of the high-frequency rectified voltage.

Current hysteresis control is suitable for CCM mode, which can control the input current to track the input voltage waveform well and have a high power factor. The main disadvantage is that the switching frequency is sensitive to the load and input voltage. Due to the large switching frequency variation, the lowest switching frequency should be considered when designing the output filter. Therefore, the design with the smallest volume and weight cannot be obtained.

Figure 1 Current hysteresis control Boost PFC

Figure 2 Schematic diagram of current hysteresis control logic circuit