A single-phase boost-type Power Factor Correction (PFC) converter is a power electronics device used to improve the power factor of electrical loads, especially in applications where non-linear loads are present. The primary goal of a PFC converter is to draw current from the mains in a way that closely follows the voltage waveform, thus achieving a near-unity power factor.
The operation of a single-phase boost-type PFC converter involves the following steps:
Rectification: The incoming AC voltage from the mains is first rectified using a diode bridge, converting it into a pulsating DC voltage. This pulsating DC voltage typically oscillates between zero and the peak value of the AC voltage.
Input Filter: To smooth out the pulsating DC voltage and reduce ripple, an input filter, usually consisting of an inductor and a capacitor, is used. The inductor helps to store energy during the periods of high voltage and releases it during low-voltage periods, reducing the ripple and maintaining a more constant DC voltage.
Boost Converter: The main component of the PFC circuit is the boost converter. It consists of a high-frequency switch (usually a MOSFET or IGBT), a diode, and an output capacitor. The switch is controlled using a Pulse Width Modulation (PWM) technique.
Control Circuit: A control circuit is employed to regulate the duty cycle of the PWM signal based on the instantaneous DC voltage and the load current. The control circuit adjusts the duty cycle to maintain a constant output voltage and to ensure that the inductor current follows the input voltage waveform.
Inductor Operation: During the on-time of the switch (PWM high state), the inductor current increases, storing energy in the inductor. During the off-time of the switch (PWM low state), the diode conducts, and the inductor releases its stored energy into the output capacitor and the load.
Output Voltage Regulation: The output capacitor smooths the output voltage, ensuring that the load receives a steady DC voltage.
By regulating the duty cycle of the boost converter, the PFC converter adjusts its output current to track the input voltage waveform. This leads to a sinusoidal shape of the input current, closely in phase with the input voltage, resulting in a high power factor.
The PFC converter ensures that power drawn from the mains is better utilized, reducing harmonic distortion and minimizing the reactive power that would otherwise burden the power grid. This improves overall efficiency, reduces power losses, and helps comply with power quality standards.