Thyristor Converters EE 442-642 6-1 Thyristor Converters • Two-quadrant conversion 6-2 Simple half-wave circuits with thyristors 6-3 Thyristor Triggering v o 180o control ˆ Vst • ICs available 6-4 Case of Pure Resistive Load 6-5 Full-Bridge Thyristor Converters – Constant DC Current 6-6 DC-Side Voltage Average DC voltage: Vd Vdo cos where Vdo 0.9Vs 6-7 AC-Side Current P Vd Id 0.9Vs Id cos RSM value of source current I s Id RMS value of fundamental current I s1 (2 2 / )Id 0.9Id RMS value of harmonic current I sh I s1 / h, h 3,5,7,... Current THD THD 100 ( 2 /8) 1 48.43% Displacement Power Factor DPF cos Power Factor PF 0.9cos 6-8 Effect of Source Inductance 2L I Commutation angle: cos( ) cos s d 2Vs 2Ls Id Average of DC-side voltage: Vd 0.9Vs cos Displacement Power Factor DPF cos( 0.5) 2 Vd Id 0.9Vs Id cos (2 / )Ls Id RMS fundamental current I s1 Vs DPF Vs cos( 0.5) 6-9 Thyristor Converter with DC Source Continuous current conduction mode Discontinuous current conduction mode 6-10 AC-Side Current Waveform (continuous conduction mode) PSpice-based simulation example: Vs = 240 V, f = 60 Hz, Ls = 1.4 mH, α = 45 deg., Ld = 9 mH, Ed = 145 V. Solution: Is = 60.1 A, Is1 = 59.7 A, DPF = 0.576, PF = 0.572, THD = 12.3% 6-11 DC Voltage versus Load Current 6-12 Inverter Mode (α > 90o) 6-13 Inverter Mode with DC Voltage Source • For a large value of Ld, id can be assumed constant (= Id), then 2 Ed Vd 0.9Vs cos LS Id 6-14 Inverter Mode: Extinction Angle 180o ( ) Importance of extinction angle in inverter mode: The extinction time interval should be greater than the thyristor turn-off time: t t q 6-15 3-Phase Thyristor Converters: Simplified Case 6-16 DC-side voltage waveforms assuming zero ac-side inductance Vd Vdo cos 3 2V cos LL 1.35VLL cos 6-17 Input Line-Current Waveform 6-18 Input line-current waveforms assuming zero ac-side inductance I s 2 / 3Id 0.816Id I s1 ( 6 / )Id 0.78Id I sh I s1 / h, h 3,5,7,... THD 100[ ( 2 / 9) 1] 31% DPF cos 3 PF cos 0.955cos 6-19 3-Phase Thyristor Converter with AC-side Inductance 2L I cos( ) cos s d 2VLL 3L I V 1.35V cos s d d LL DPF cos( 0.5) 6-20 Input Line-Current Harmonics 6-21 Input Line-Current Harmonics Typical Passive Filter Block (for each phase) 6-22 12-Pluse Phase Controlled Rectifier Harmonic Order: 1, 11, 13, 23, 25, … 6-23 3-Phase Thyristor Converter with Realistic Load Continuous conduction Mode Discontinuous conduction mode 6-24 3-Phase Thyristor Inverter – Constant Current 6-25 Thyristor Inverter – Constant Voltage & Current 6-26 Thyristor Inverter Operation: Extinction Angle 6-27 Thyristor Converters: Voltage Notching Depth: Vn 2VLL sin Ls1 Ls Ls2 0 Area: An 2Ls Id 2Ls Id Width: 2VLL sin 6-28 Limits on Notching and Distortion In practice, the notch depth at PCC depends on Ls1 relative to Ls2. Let depth factor be defined by L s1 Ls1 Ls2 Given Ls1 , a higher value of Ls2 results in a smaller notch. 6-29 .