Controlled Rectifiers

LEARNING OBJECTIVES

To understand the operation and characteristics of controlled rectifiers.
To learn the types of controlled rectifiers
To understand the performance parameters of controlled rectifiers.
To learn the techniques for analysis and design of controlled rectifier circuits.
To study effects of load inductance on the load current.
To study Single-phase semi converter
To study Single-phase dual converter
To study Three-phase half-wave controller converter
To study Three-phase full wave controller converter
To study Three-phase dual converter

INTRODUCTION

Uncontrolled Rectifier (Natural Commutating Rectifier): Output voltage is constant if the input AC voltage (rms) is constant.

Controlled Rectifier (Phase Controlled Rectifiers): Output voltage is can be varied by varying firing angle (α) even if input AC voltage (rms) is constant.

Principles of phase-controlled converter operation

Half Controlled Rectifier with R Load

Conduction angle=π-α

Performance of Single-phase, half-wave controlled rectifiers with pure resistive load

For the positive half cycle of input voltage, the thyristor T1 is forward biased and when the thyristor is fired at ωt = α, it conducts and the input voltage appears across the load. When the input voltage goes negative at ωt = π, the thyristor is reversed biased and it is turned off. The delay angle α, is defined as the time the input voltage starts to go positive to the time the thyristor is fired.

${V_{dc}} = \frac{1}{{2\pi }}\int_\alpha ^\pi {{V_m}} \sin \omega t{\rm{ }}d\left( {\omega t} \right) = \frac{{{V_m}}}{{2\pi }}\left[ { - \cos \omega t} \right]_\alpha ^\pi$