Power Electroni cs Supplement: Practical Application Issues of Power Semiconductor Devices and Gate Triggering Control Circuit for Thyristor Rectifiers Power E l e ct r o n i cs 2 Outline Practical application issues of power semiconductor devices Gate drive circuit (Section 1.6 in the Chinese textbook) Protection of power semiconductor devices (Section 1.7 in the Chinese textbook) Series and parallel connections of power semiconductor devices (Section 1.8 in the Chinese textbook) Gate triggering control circuit for thyristor rectifiers (Section 2.9 in the Chinese textbook) Power E l e ct r o n i cs 3 1.6 Gate drive circuit Basic function of gate drive circuit: is to generate gate signals to turn-on or turn-off power semiconductor device according to the commanding signals from the control circuit. Other functions of gate drive circuit: Reduce switching time (including turn-on time and turn- off time) Reduce switching loss (including turn-on loss and turn- off loss) and improve efficiency Improve protection and safety of the converter Gate drive circuits provided by power semiconductor manufacturers and Integrated gate drive chips are more and more widely used. Power E l e ct r o n i cs 4 Electrical isolation in the gate drive circuit Gate drive circuit usually provides the electrical isolation between control circuit and power stage. Two ways to provide electrical isolation – Optical ? Optocoupler, fiber optics ? Transformer – Magnetic E R U in U out R 1 I C I D LED Photo transistor Schematic of an optocoupler Power E l e ct r o n i cs 5 Thyristor gate current pulse requirments Shape of gate current pulse waveform: – Enhanced leading part Magnitude requirement (for the enhanced leading part and the other part) Width requirement (for the enhanced leading part and the whole pulse) Power of the triggering signal must be within the SOA of the gate I-V characteristics I t I M t 1 t 2 t 3 t 4 Ideal gate current pulse waveform for thyristors Power E l e ct r o n i cs 6 Typical thyristor gate triggering circuit TM R 1 R 2 R 3 V 1 V 2 VD 1 VD 3 VD 2 R 4 +E 1 +E 2 Input from control circuit Power E l e ct r o n i cs 7 Typical gate signal and gate drive circuit for GTO O t t O u G i G 50kHz 50V GTO N 1 N 2 N 3 C 1 C 3 C 4 C 2 R 1 R 2 R 3 R 4 V 1 V 3 V 2 L VD 1 VD 2 VD 3 VD 4 Power E l e ct r o n i cs 8 A typical gate drive circuit for IGBT based on an integrated driver chip 13 Error indicating Sensing V CC Interface circuit Turn-off circuit Timer and reset circuit Detection circuit        u o V EE 8 1 5 4 6 10V +15V 30V +5V M57962L 14 u i 1 Fast recovery diode t rr ≤ 0.2μs 4.7k? 3.1? 100μF 100μF M57962L integrated driver chip Power E l e ct r o n i cs 9 1.7 Protection of power semiconductor ` ` devices Protection circuits Overvoltage protection Overcurrent protection Snubber circuits—specific protection circuits that can limit du/dt or di/dt Turn-on snubber Turn-off snubber Power E l e ct r o n i cs 10 Causes of overvoltage on power semiconductor devices External reasons Overvoltage caused by operation of mechanic swithes Overvoltage caused by thunder lightening Internal reasons Overvoltage caused by the reverse recovery of diode or thyristor Overvoltage caused by the turning-off of fully- controlled devices Power E l e ct r o n i cs 11 Measures to protect power semiconductor devices from overvoltage S F RV RCD T D C U M RC 1 RC 2 RC 3 RC 4 L B S DC Lightening arrestor RC or RCD snubbers (will be discussed later) Zener diode, Metal Oxide Varistor (MOV), Break Over Diode (BOD) Power E l e ct r o n i cs 12 Measures to protect power semiconductor devices from overcurrent Fuse Circuit breaker Protection with current feedback control in the control circuit Protection with overcurrent detection in the gate drive circuit—the fastest measure Power E l e ct r o n i cs 13 Functions and classifications of snubbers Functions Limiting voltages applied to devices during turn-off transients Limiting device currents during turn-on transients Limiting device current rising rate (di/dt) at device turn-on Limiting the rate of rise (du/dt) of voltages across devices during device turn-off Shaping the switching trajectory of the device Classifications According to different switching transients – Turn-off snubber (sometimes just called snubber) – Turn-on snubber According to the treatment of energy – Power dissipating snubber – Lossless snubber Power E l e ct r o n i cs 14 Operation principle of typical snubbers Circuit configuration R i VD L V Turn-on snubber Turn-off snubber L i VD i R s C s VD s t u CE i C O without turn-on snubber with turn-on snubber with turn-off snubber without turn-off snubber u CE i C A D C B without turn-off snubber Xith turn-off snubber u CE i C O Switching trajectory Power E l e ct r o n i cs 15 Other turn-off snubbers L Turn-off snubber L Turn-off snubber Load Load E d R s C s E d R s C s VD s Power E l e ct r o n i cs 16 1.8 Series and parallel connections of power semiconductor devices Object To increase the capability to deal with voltage or current Issues and solutions Series connection – Issue: even voltage sharing – Solutions: ? Selection of devices that are closer to each other in the characteristics ? Voltage sharing circuit Parallel connection – Issue: even current sharing – Solutions: ? Selection of devices that are closer to each other in the characteristics ? Current sharing circuit and symmetrical circuit layout Power E l e ct r o n i cs 17 Series Connection of thyristors b)a) R C R C VT 1 VT 2 R P R P I O U U T1 I R U T2 VT 1 VT 2 Voltage sharing circuit – Steady-state voltage sharing circuit – Dynamic voltage sharing circuit Power E l e ct r o n i cs 18 Parallel Connection of Power MOSFETs Easy to realize because of the positive temperature of their on- state resistance Need a small damping resistor in series with the individual gate connections Still need to select devices that are closer to each other in the characteristics Circuit layout should be symmetrical Power E l e ct r o n i cs 19 2.9 Gate triggering control circuit for ` ` thyristor rectifiers Object How to timely generate triggering pulses with adjustable phase delay angle Constitution Synchronous circuit Saw-tooth ramp generating and phase shifting Pulse generating Integrated gate triggering control circuits are very widely used in practice. Power E l e ct r o n i cs 20 A typical gate triggering control circuit 220V 36V + B TP +15V A VS +15V 15V 15V XY Disable R Q u ts VD 1 VD 2 C 1 R 2 R 4 T S V 2 R 5 R 8 R 6 R 7 R 3 R 9 R 10 R 11 R 12 R 13 R 14 R 16 R 15 R 18 R 17 RP 1 u co u p C 2 C 3 C 3 C 5 C 6 C 7 R 1 RP 2 V 1 I 1c V 3 V 4 V 6 V 5 V 7 V 8 VD 4 VD 10 VD 5 VD 6 VD 7 VD 9 VD 8 VD 15 VD 11 ~VD 14 Power E l e ct r o n i cs Waveforms of the typical gate triggering control circuit 21 Power E l e ct r o n i cs 22 How to get synchronous voltage for the gate triggering control circuit of each thyristor D y  D y  TR TS u A u B u C u a u b u c  u sa  u sb  u sc  u sa  u sb  u sc U c U sc U sa U b U sb U sc U sb U a U sa U AB For the typical circuit on page 20, the synchronous voltage of the gate triggering control circuit for each thyristor should be lagging 180o to the corresponding phase voltage of that thyristor.