Power Electronics, A First Course, 2nd Edition

6 POWER-FACTOR-CORRECTION (PFC) CIRCUITS AND DESIGNING THE FEEDBACK CONTROLLER

In diode rectifiers discussed in Chapter 5, power is drawn by means of highly distorted currents, which have a deleterious effect on the power quality of the utility source. In single-phase diode-rectifier systems, a corrective action such as that described in this chapter is often taken. This discussion is also useful in the learning process since it shows a real-world application of DC-DC converters discussed in Chapter 3 and their control in Chapter 4.

6.1 INTRODUCTION

Technical solutions to the problem of distortion in the input current have been known for a long time. However, only recently has the concern about the deleterious effects of harmonics led to the formulation of guidelines and standards, which in turn have focused attention on ways of limiting current distortion.

In the following sections, power-factor-corrected (PFC) interface, as they are often called, are briefly examined for single-phase rectification, where it is assumed that the power needs to flow only in one direction, such as in DC power supplies. The three-phase front-ends in motor-drives applications may require bi-directional power flow capability. Such front-ends, which also allow unity power factor of operation, are discussed in Chapter 12.

6.2 OPERATING PRINCIPLE OF SINGLE-PHASE PFCS

The operating principle of a commonly used single-phase PFC is shown in Figure 6.1a, where, between the utility supply and the DC-bus ...