12.3: POWER FACTOR CORRECTION

12.3 POWER FACTOR CORRECTION

PFC is the capacity of generating or absorbing the reactive power to a load without the use of the supply. The major industrial loads have an inductive power factor (they absorb reactive power); hence the current tends to go beyond the power is usually used for the power conversion, and an excessive load current represents a loss for the consumer, who not only pays for the over-dimensioning of the cable, but also for the excess power loss in the cables. The electric companies do not want to transport the useless reactive power of the alternators toward the loads; these and the distribution network cannot be used at high efficiency, and the voltage regulation in the various points becomes complicated. The principle used by these electric companies almost always penalizes the low-power factor of the clients; hence the great development of systems for power-factor improvement for industrial processes.

PFC technique has the following methods:

• Single-phase active power factor correctors

• Three-phase active power factor correctors

• Soft-switching active power factor correctors

• Pulse-width-modulation (PWM) active power factor correctors

• Passive power factor correctors

• Single-stage AC/DC converters.

We take a single-stage high-PFC AC/DC converter as an example for digital control application in this section. The system consists of an AC/DC diode rectifier and a double-current synchronous rectifier (DC-SR) Luo-converter as shown in Figure 7.30 [1]. Although SR DC/DC converters are generally used for low-voltage high-current (LVHC) applications, they are available to perform in normal output voltage...