Ac to Dc Converter
Module 2
AC to DC Converters
Version 2 EE IIT, Kharagpur 1
Lesson 14
Operation and Analysis of Three Phase Half Controlled Converter
Version 2 EE IIT, Kharagpur 2
Instructional Objectives
On completion the student will be able to • • • • • • Draw the circuit diagram and waveforms of different variables associated with a three phase half controlled converter. Identify the constructional and operational difference between a three phase fully controlled and half controlled converter. Calculate the average and RMS value of the output dc voltage. Calculate the displacement factor, distortion factor and power factor of the input ac line current. Calculate the Fourier series components of the output voltage and input current waveforms. Derive the closed form expression for output dc current and hence identify continuous or discontinuous conduction mode of the converter.
Version 2 EE IIT, Kharagpur 3
14.1 Introduction
Three phase fully controlled converters are very popular in many industrial applications particularly in situations where power regeneration from the dc side is essential. It can handle reasonably high power and has acceptable input and output harmonic distortion. The configuration also lends itself to easy series and parallel connection for increasing voltage and current rating or improvement in harmonic behavior. However, this versatility of a three phase fully controlled converters are obtained at the cost of increased circuit complexity due to the use of six thyristors and their associated control circuit. This complexity can be considerably reduced in applications where power regeneration is not necessary. In that case three thyristors of the top group or the bottom group of a three phase fully controlled converter can be replaced by three diodes. The resulting converter is called a three phase half controlled converter. Replacing three thyristors by three diodes reduces circuit complexity but at the same time prevents negative
AC to DC Converters
Version 2 EE IIT, Kharagpur 1
Lesson 14
Operation and Analysis of Three Phase Half Controlled Converter
Version 2 EE IIT, Kharagpur 2
Instructional Objectives
On completion the student will be able to • • • • • • Draw the circuit diagram and waveforms of different variables associated with a three phase half controlled converter. Identify the constructional and operational difference between a three phase fully controlled and half controlled converter. Calculate the average and RMS value of the output dc voltage. Calculate the displacement factor, distortion factor and power factor of the input ac line current. Calculate the Fourier series components of the output voltage and input current waveforms. Derive the closed form expression for output dc current and hence identify continuous or discontinuous conduction mode of the converter.
Version 2 EE IIT, Kharagpur 3
14.1 Introduction
Three phase fully controlled converters are very popular in many industrial applications particularly in situations where power regeneration from the dc side is essential. It can handle reasonably high power and has acceptable input and output harmonic distortion. The configuration also lends itself to easy series and parallel connection for increasing voltage and current rating or improvement in harmonic behavior. However, this versatility of a three phase fully controlled converters are obtained at the cost of increased circuit complexity due to the use of six thyristors and their associated control circuit. This complexity can be considerably reduced in applications where power regeneration is not necessary. In that case three thyristors of the top group or the bottom group of a three phase fully controlled converter can be replaced by three diodes. The resulting converter is called a three phase half controlled converter. Replacing three thyristors by three diodes reduces circuit complexity but at the same time prevents negative
References: 1. “Power Electronics”’ P.C. Sen, Tata McGrawhill publishing company limited, 1995. 2. “Power Electronics, Converters, Applications and Design”; Mohan, Undeland, Robins; John Willey and Sons Inc, Third Edition, 2003.