Page 194 - Rashid, Power Electronics Handbook

12

Three-Phase Controlled Recti®ers

Juan W. Dixon, Ph.D. 12.1 Introduction........................................................................................ 183
Department of Electrical 12.2 Line-Commutated Controlled Recti®ers................................................... 183
Engineering, 12.2.1 Three-Phase Half-Wave Recti®er 12.2.2 Six-Pulse or Double Star
Catholic University of Chile,
Vicuna Mackenna 4860 Recti®er 12.2.3 Double Star Recti®er with Interphase Connection 12.2.4 Three-Phase
˜
Santiago, Chile 6904411 Full-Wave Recti®er or Graetz Bridge 12.2.5 Half-Controlled Bridge
Converter 12.2.6 Commutation 12.2.7 Power Factor 12.2.8 Harmonic
Distortion 12.2.9 Special Con®gurations for Harmonic Reduction 12.2.10 Applications of
Line-Commutated Recti®ers in Machine Drives 12.2.11 Applications in HVDC Power
Transmission 12.2.12 Dual Converters 12.2.13 Cycloconverters 12.2.14 Harmonic
Standards and Recommended Practices
12.3 Force-Commutated Three-Phase Controlled Recti®ers ............................... 196
12.3.1 Basic Topologies and Characteristics 12.3.2 Operation of the Voltage Source
Recti®er 12.3.3 PWM Phase-to-Phase and Phase-to-Neutral Voltages 12.3.4 Control of the
DC Link Voltage 12.3.5 New Technologies and Applications of Force-Commutated Recti®ers
References........................................................................................... 210

12.1 Introduction voltage n AK begins to be positive. Figure 12.3 shows that the
possible range for gating delay is between a ¼ 0 and

Three-phase controlled recti®ers have a wide range of applica- a ¼ 180 , but because of commutation problems in actual

tions, from small recti®ers to large high voltage direct current situations, the maximum ®ring angle is limited to 160 .As
(HVDC) transmission systems. They are used for electro- shown in Fig. 12.4, when the load is resistive, current i has the
d
chemical processes, many kinds of motor drives, traction same waveform as the load voltage. As the load becomes more
equipment, controlled power supplies, and many other appli- and more inductive, the current ¯attens and ®nally becomes
cations. From the point of view of the commutation process, constant. The thyristor goes to the nonconducting condition
they can be classi®ed into two important categories: line- (OFF state) when the following thyristor is switched ON, or
commutated controlled recti®ers (thyristor recti®ers); and the current tries to reach a negative value.
force-commutated PWM recti®ers. With the help of Fig. 12.2, the load average voltage can be
evaluated and is given by
12.2 Line-Commutated Controlled V max ð p=3þa
Rectifiers V ¼ 2=3p ÿp=3þa cos ot dðotÞ
D
sin p=3
12.2.1 Three-Phase Half-Wave Rectifier ¼ V cos a 1:17 V rms cos a ð12:1Þ
max f ÿN
p=3
Figure 12.1 shows the three-phase half-wave recti®er topology.
To control the load voltage, the half-wave recti®er uses three where V max is the secondary phase-to-neutral peak voltage,
common-cathode thyristor arrangement. In this ®gure, the V rms its root mean square (rms) value, and o is the angular
f ÿN
power supply and the transformer are assumed ideal. The frequency of the main power supply. It can be seen from
thyristor will conduct (ON state), when the anode-to-cathode Eq. (12.1) that the load average voltage V D is modi®ed by

voltage n AK is positive, and a ®ring current pulse i is applied changing ®ring angle a. When a is <90 , V is positive and
G
D
to the gate terminal. Delaying the ®ring pulse by an angle a when a is >90 , the average dc voltage becomes negative. In

controls the load voltage. As shown in Fig. 12.2, the ®ring such a case, the recti®er begins to work as an inverter, and the
angle a is measured from the crossing point between the phase load needs to be able to generate power reversal by reversing
supply voltages. At that point, the anode-to-cathode thyristor its dc voltage.
183
Copyright # 2001 by Academic Press.
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