Rectifiers, their advantages, and disadvantages

2.1 Introduction

Power electronics in broader aspect actually controls the flow of power to make it suitable to be used by diverse type of instruments and appliances. The ability to control the flow of power is derived from using solid state switches along with their controllers. In most of the cases the power input are in the form of a 50-Hz sine-wave ac voltage provided by the electric utility, which is first converted to a dc voltage. This conversion can be done by using uncontrolled (diode rectifiers) rectifiers or controlled (Thyristor, MOSFET, IGBT rectifiers) rectifiers. Different types of rectifiers have different advantage and disadvantages. Main disadvantage is distorted input line current due to harmonic contents in line current. It creates different serious problems and pollute the utility supply. So it’s necessary to minimize the harmonic contain in line current.

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PWM Rectifier

The most interesting reduction technique of current harmonic is a PWM (active) rectifier (Fig. 1.3). Two types of PWM converters, with a voltage source output (Fig. 1.4) and a current source output (Fig. 1.5) can be used.

Active PWM filter

An alternative to the passive filter is use of the active PWM filter (AF), which displays better dynamics and controls the harmonic and fundamental currents. Active filters are mainly divided into two different types..

Multi-pulse rectifier

1.4.3 Multi-pulse rectifier.

Mixing single and three phase diode rectifier

1.4.2 Mixing single and three phase diode rectifier

Traditional harmonic reduction technique

The traditional method of current harmonic reduction involves passive filters LC, parallel-connected to the grid. Filters are usually constructed as series-connected legs of capacitors and chokes [the number of legs depends on number of filtered harmonics (5th, 7th, 11th, 13th) ].