In this applet, two different control methods are used to realise the boost PFC operating in continuous conduction mode. The first is the ramp comparison method, where the switching frequency is constant, and the second is the hysteresis control method, where the switching frequency is not constant.

For both methods a rectified sinusoidal reference inductor current has to be generated. This is achieved by measuring the voltage at the output of the bridge rectifier. This voltage signal is then multiplied by an adjustable signal called ‘G,ref’. This signal effectively adjusts the amplitude of the reference current signal. The measured inductor current is then subtracted from the reference signal to produce a current error signal. This error signal is used by both controllers to generate the switching signal.

For the ramp comparison method the error signal goes into a proportional-integral (PI) controller. The output of the PI controller is then compared to a fixed frequency carrier signal to produce the switch signal. The duty cycle of the switch changes over the half mains period to maintain the rectified sinusoidal current shape.

For the hysteresis control method the current error signal is passed into a comparator with hysteresis. When the current error is more positive than the positive hysteresis value (+h) then the switch is turned on, and when the current error is less than the negative hysteresis value (-h) then the switch is turned off. Therefore the current error waveform is always switching between the upper and lower hysteresis values and results in a variable switching frequency.

• Use the red timeline to observe the current paths in the boost rectifier circuit.
• Adjust the level of the ‘G,ref’ signal and observe the changes in the output voltage level and inductor current waveforms.
• With the ‘Ramp Comparison’ check box selected, observe the duty cycle pattern over the half mains period.
• Adjust the carrier frequency and observe the change in the inductor current waveform.
• With the ‘Hysteresis Control’ check box selected, observe the duty cycle pattern and switching frequency over the half mains period.
• Adjust the hysteresis level ‘h’ and observe the inductor current and error current waveforms.
• Change the input voltage magnitude, inductor and load resistor values and view the changes in the output voltage and inductor current waveforms.
• Observe that the maximum inductor current ripple occurs at the intersection of u2/2 and u1 waveforms for the ramp comparison control method.