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CHAPTER SEVEN (New textbook) CONTROLABLE SWITCHING DEVIES DESIGNED BY DR. SAMEER KHADER PPU “E-learning Project” CONTENT Introduction, Classification &Applications, Thryristor Circuits Triac Circuits Diac Circuits Practical Firing ( Triggering) Circuits Thyristor Commutation (turning-off) Chapter 7-A Thyristor Circuits 1- Construction : Four PNPN layers with special doping in each layer, with purpose to obtain different electron and holes in these layers. Each one has different potential voltage A P N P G N Th. K A K Principle of operation : G K The thyristor construction A Presents three diodes D1 D3 D2 In series ( two forward G biased and the third reverse biased). The thyristor will conduct only if D2 forward biased, therefore current will flow from A to K. This case could be achieved by different ways as follow : Methods for Switching- on the thyristor The switching process of the thyristor is called “ Firing”, because after Switching process is ceased, WHERE the firing signal may can removed with purpose to reduce the gate loss .There're several methodS Applied to realize this purpose : 1-Gate-firing method :by supplying the gate terminal with positive voltage ( this is the most applied method - major method). 2-by suddenly increasing the Anode voltage 3-by increasing the thyristor temperature over predetermined limit. 4- Photo effect method, which used in photo devices ( Photo thyristor) Gate-firing method: the firing circuit is shown below: Thyristor I-V curve Thyristor Main Parameters: There’re several parameters related to static & dynamic performance of the thyristor, these parameters are as follow : 1-VAK- thyristor voltage at steady state 2 V; 2-VBO- -break over voltage , voltage after which thyristor will turning on at constant gate current ; 3-VBR- break down voltage in reverse biasing state; 4-IH- thyristor holding current :this a minimized load current keeping the thyristor in conducting state ( if the current goes down the thyristor will switch-off); 5- IL- thyristor latching current :this a minimized load current keeping the thyristor in conducting state after removing the gate signal ; 6-VGT- minimum gate voltage required to firing the thyristor at given loadind condition , VGT 0.8…12V; 7-IGT- minimum gate current., IGmax- maximum gate current ; 8-di/dt- speed of (increasing/decreasing) of thyristor current ; 9-dv/dt - speed of (increasing/decreasing) of thyristor voltage . Thyristor Dynamic Performances R4 100 C V2 220/-220V R8 5k 90% D R3 10k D4 30% BAR74 50 Hz V5 85/-85V SCR2 2N5064 V-source A: s4_1 50.00 V R10 2.5k -250.0 V 35.00ms 100.0 V 50.00 V 0.000 V -150.0 V -50.00 V 50.00ms 65.00ms -100.0 V 0.000ms 80.00ms 15.00ms 30.00ms 45.00ms 1.250 V V-gate 0.750 V V-gate A: scr5_1 50.00 V -0.250 V -0.750 V 35.00ms 30.00 V 10.00 V 50.00ms 65.00ms 80.00ms 2.250 A -10.00 V 0.000ms P-load 1.750 A 0.750 A 15.00ms 30.00ms 45.00ms 15.00ms 30.00ms 45.00ms 150.0 W 100.0 W 0.250 A 50.00ms 65.00ms 50.00 W 80.00ms 250.0 V V-thyris 150.0 V 50.00 V -50.00 V -150.0 V -250.0 V 35.00ms P-load A: r10[p] 1.250 A -0.250 A 35.00ms 90.00 V 70.00 V 0.250 V A: scr2_1 + V-source -50.00 V A: r4[i] C3 1.0uF 250.0 V 150.0 V A: d4_k R9 50 SCR6 BRX44 50 Hz A: v2_1 SCR5 MCR22-4 S3 50.00ms 65.00ms 80.00ms 0.000 W 0.000ms Gate Firing Circuits: 2-Phase Control 1- S1RC relaxation oscillator S1 S2 R1 R5 5k 60% V3 120/-120V 50 Hz C A: r5_3 Th1 Th2 SCR3 BRX45 + + V4 80V R-load C2 1.0uF R2 R7 50 S2 A AC circuit DC circuit SCR4 MCR22-3 V3 120/-120V + V4 80V R6 0.5k C V-source 125.0 V V-source A: s1_1 R-load Th1 Th2 SCR3 BRX45 50 Hz R7 50 R5 5k 60% R1 SCR4 MCR22-3 + A C2 1.0uF R2 R6 0.5k 87.00 V 75.00 V 25.00 V 85.00 V -25.00 V -75.00 V -125.0 V 0.000ms A: scr3_1 15.00ms 30.00ms 83.00 V 0.000ms 45.00ms V-gate 2.000 V V-gate A: scr3_1 0.000 V 0.300ms 0.600ms 0.900ms 1.3940 V -2.000 V 1.3938 V -4.000 V -6.000 V 0.000ms A: scr4_1 15.00ms 30.00ms 1.3936 V 0.000ms 45.00ms V-thyris 25.00 V V-thyris A: scr4_1 0.300ms 0.600ms 0.900ms 1.65525 V 1.65475 V -25.00 V 1.65425 V -75.00 V 1.65375 V 1.65325 V -125.0 V 0.000ms A: r7[p] 15.00ms 30.00ms 1.65275 V 0.000ms 45.00ms P-load 300.0 W P-load A: r7[p] 0.300ms 0.600ms 0.900ms 138.936 W 138.934 W 200.0 W 138.932 W 100.0 W 0.000 W 0.000ms 138.930 W 15.00ms 30.00ms 45.00ms 138.928 W 0.000ms 0.300ms 0.600ms 0.900ms Mathematical . Modeling 1- Gate firing circuit using RC relaxation oscillator; 2- Gate firing circuits using RC circuit and called Phase control ; These circuits may can use to fire thyristor in AC or DC circuit: in both sources the connected elements must be with the following relations with purpose to realized successful operation: R2<<R1; and R-load << R1; * DC source VBOTh2 < Vs ; and IH2 < Vs/R1; thyristor ** AC source VBOTh2 < Vm; and IH2 < Vm/R1; Vs(t)=Vm.sin (t); The Th2 will t Vc( t ) Vs 1 e Vc( tp ) tp conduct when Vc=VBOTh2; This could be occurred at t=tp ; this time called (firing instant) VBOTh2 Vs R1 C ln Vs R1 C VBOTh2 The firing angle of previous firning circuits in AC circuit can Determine as follow : min sin VTG 1 R1min RGK max sin Vm Vm RGK R1max VGT IGT 9<<90 ( without C) Vm RGK IGmax IGT Vm 1 Vm tp 360 T I-V curve Conclusion •In DC source, tp- presents delay time , so by increasing Ig the thyristor allow more current to follow ; therefore increasing the load power ; • In AC source, tp- presents delay angle which corresponds to =tp.360/T, so by increasing Ig, decreases, thus load power increases P()=Pmax . Cos(), where Pmax-maximum allowable power. • may can change from 0 to 90 ( without C) or to 145 (with C) ; • The thyristor gate voltage must be > + 0.85 V at least; VBR > Vm ; ILmin > IL at firing( remains conduct); and ILmin < IH ( swith off) . • By increasing di/dt at given Ig the thyristor capable to carry additional current ILoad . • By increasing Ig, VBO ( ac circuits), which means that the thyristor is fired at earliest time , therefore increasing the load voltage and power . •The gate pulse must removed after successfully firing the thyristor , with aim to reduce the gate losses . Chapter 7-B Triac Circuits 1- Triac ( Triode Alternating Current Switch ) – presents two parallel connected thyristors with common gate, which energized with positive and negative voltage. The main purpose of the Triac is to control the RMS load voltage, therefore there're several applications such as : * Lighting control ( dimmer circuits); **- Temperature control ; *** Torque –speed control of induction machines. 2- Symbol: 3- Circuit application: 3- I-V Curve: Triac Firing Circuits 1- Phase angle control without diode R2 100 B V1 220/-220V A 50 Hz MAC210-6 C1 0.3uF A: r2_2 Load R1 10k 20% 100HF120PV D1 + 50 Hz R2 100 Triac voltage Triac voltage 200.0 V 100.0 V 0.000 V -100.0 V -200.0 V 35.00ms A: r2[i] 50.00ms 65.00ms 80.00ms Load current Load current 2.500 A 1.500 A 0.500 A -0.500 A -1.500 A -2.500 A 35.00ms A: d1_k 50.00ms 65.00ms 80.00ms 1.500 V 0.500 V -0.500 V -1.500 V 35.00ms 50.00ms 65.00ms 80.00ms R1 10k 5% 100HF120PV D1 + B V1 220/-220V 2- Phase angle control with diode Gate voltage Gate voltage C1 1uF 300.0 V 200.0 V 100.0 V 0.000 V -100.0 V -200.0 V -300.0 V 0.000ms 15.00ms 3.000 A 2.000 A 1.000 A 0.000 A -1.000 A -2.000 A -3.000 A 0.000ms 15.00ms 1.500 V 1.000 V 2.500 0.500 V V 0.000 V -0.500 V -1.000 V -1.500 V 0.000ms 15.00ms 30.00ms 30.00ms 30.00ms A MAC210-6 45.00ms 45.00ms 45.00ms 3-Triac firing circuits using UJT A: v3_1 Source voltage AC source 120/-120V C 125.0 V 75.00 V 25.00 V -25.00 V 50 Hz -75.00 V -125.0 V 0.000ms Rload 100 0/15V A Q2004L4 100 Hz Pulse generator Tr B 20V LoadA: tr_2 voltage 2N2646 0.5uF B2 D 30.00ms 10.00ms 20.00ms 30.00ms 10.00ms 20.00ms 30.00ms 10.00ms 20.00ms 30.00ms 125.0 V 75.00 V 25.00 V -125.0 V 0.000ms UJT A: tr_3 needles 5.000 V 3.000 V 15.00 V 1.000 V 5.000 V -1.000 V -5.000 V -3.000 V -15.00 V -5.000 V 0.000ms 15.00ms 20.00ms -75.00 V 25.00 V -25.00 V 5.000ms 10.00ms 15.00 V 5.000 V -25.00 V R3 47 Capacitor voltage A: c1_2 30.00ms 25.00 V -15.00 V -25.00 V 0.000ms S1 B1 UJT 20.00ms -5.000 V R1 20 R4 150 R5 9k PulseA: tr_3 generator 10.00ms 25.00ms 35.00ms Load A: tr_2 voltage 250.0 V 150.0 V 50.00 V -50.00 V -150.0 V -250.0 V 0.000ms Mathematical Modeling of Triac Circuits Three main circuits are introduced with purpose to fire the Triac device( Phase control with or without diode, with UJT and with Diac device). The presence of diode in the gate circuit remove one half cycle , therefore convert the Triac into Thyristor . In both circuits there are several relations characterized the application of such a device . These relations are as follow : 1- when 0<</2 Prms ( ) T Vdc 2 2 Vm sin ( t ) d t T Vrms T Pdc( ) 2 2 ( Vmsin t ) d t R1 C ln Pdcmax Pdcmax cos Vdc( 0 ) RLoad 0 UJT – circuit: tp 2 RLoad T 2 Vrms ( 0 ) Pmax 0 Pmax cos Vp ( t tp ) Vc( tp ) VBB tp VBB Vp( tp ) Vp( tp ) ujt Xr VBB * 0.6 Vc( tp ) Xr VBB 1 RBB RBB R4 e 2 0<Vrms<Vs; 2- Vdc=0 for symmetrical firing 3- Vdc0 for asymmetrical firing 4- the existing of inductance , reduced The control rang of Prms=F(). ,VBB-base to base UJT’s voltage: , ujt- UJT’s intrinsic factor <=1 ,Vp- UJT’s peak voltage; , tp-delay time ( firing instant) . Chapter 7C Diac Circuits 1- Diac ( Diode Alternating Current Switch ) – presents two anti-parallel connected diodes with special construction , aiming to maintain relatively high threshold voltage across its terminals . The main purpose of the Diac is to divide the source voltage between its terminals and the load terminals , therefore there're several applications such as : * Firing device in Triac –gate circuit ; **- Over voltage protective device ; 2- Symbol: 3- Circuit modification: 4- I-V Curve: 5- Time-varying performances: Phase control circuit with Diac & Triac: Vd Vc( x) Vc( C ) Vcm s in x Vcm Vs 2 1 The main equations are as follow , and can derives when Vdiac =Vc at given angle. c tan c 2 RC 1 x The firing angle ( RC ) Additional Firing circuits 1- Practical circuit using UJT: A: d1_3 Source voltage S1 65.00 V 45.00 V 25.00 V 5.000 V -15.00 V -35.00 V 0.000ms D1 18DB2 R6 50 R4 6k 10% V2 60/-60V 50 Hz D2 BZG03C30 C1 0.5uF R7 250 R5 50 Zener A: r4_3 voltage SCR2 10RIA20 Q1 2N2646 Capacitor A: r4_1 voltage R8 50 15.00ms 30.00ms 45.00ms 15.00ms 30.00ms 45.00ms 15.00ms 30.00ms 45.00ms 65.00 V 45.00 V 25.00 V 5.000 V -15.00 V -35.00 V 0.000ms 40.00 V 30.00 V 20.00 V 10.00 V Gate A: needles scr2_2 0.000 V -10.00 V 0.000ms 1.250 V 0.750 V Gate A: scr2_2 needles 0.250 V -0.250 V -0.750 V -1.250 V 0.000ms 30.00ms 45.00ms -1.500 V 0.000ms Thyristor A: scr2_1 voltage 0.000 V 15.00ms 30.00ms 45.00ms 15.00ms 30.00ms 45.00ms 61.00 V 41.00 V 21.00 V -20.00 V 1.000 V -19.00 V 15.00ms 30.00ms 45.00ms -39.00 V 0.000ms Load A: r5[p] power 60.00 W 40.00 W 20.00 W 0.000 W 71.00 W 51.00 W 31.00 W 11.00 W -20.00 W -40.00 W 0.000ms 1.500 V -0.500 V 20.00 V Load A: r5[p] power 2.500 V 0.500 V 15.00ms Thyristor 60.00 V A: scr2_1 voltage 40.00 V -40.00 V 0.000ms 3.500 V 15.00ms 2- High =R4C1 30.00ms 45.00ms 1- Low =R4C1 -9.000 W -29.00 W 0.000ms 15.00ms 30.00ms 45.00ms 2- Practical circuits using UJT and Isolation Transformer: S2 R9 50 R1 6k 30% V1 60/-60V R3 250 B1 D3 BZG03C30 C2 1.5uF R10 50 SCR1 10RIA20 UJT SignalA:atq2_2 B2 Q2 T1 2N26461TO1 B2 R2 7.500 V -2.500 V 5.000ms A: scr1_2 20.00ms 35.00ms A: scr1_2 Gate 30.00ms 45.00ms 30.00ms 45.00ms Gate needles 0.500 V 15.00ms 2.000 V needles 1.000 V 0.000 V 0.000ms 50.00ms 1.000 V 15.00ms 26.50 V -13.50 V 0.000ms Capacitor voltage 2.500 V -33.50 V 0.000ms 6.500 V 150 A: c2_2 66.50 V 16.50 V D4 18DB2 50 Hz A: c2_2 Capacitor voltage Thyristor A: scr1_1 voltage 15.00ms 30.00ms 45.00ms 15.00ms 30.00ms 45.00ms 20.00ms 35.00ms 50.00ms 50.00 V 0.000 V 0.000 V 5.000ms A: scr1_1 20.00ms 35.00ms 50.00ms 50.50 V Thyristor voltage 0.500 V -49.50 V 5.000ms A: r10[p] 20.00ms 35.00ms 50.00ms 100.5 W 0.500 W -99.50 W 5.000ms Load power -50.00 V 0.000ms Load A: r10[p] power 100.0 W 0.000 W -100.0 W 5.000ms 20.00ms 35.00ms 50.00ms 3: ON-OFF firing circuit :This circuit illustrates firing techniques used in AC Voltage controller based on so called ON-OFF method, where it’s necessary to fire the thyristor at the beginning of both half-cycles . S1 Load A: r6_2 Source voltage 250.1 V 150.1 V 50.10 V -49.90 V -149.9 V -249.9 V 0.000ms A: r8_2 Vg-th1 30.00ms 60.00ms 90.00ms 30.00ms 60.00ms 90.00ms 30.00ms 60.00ms 90.00ms 15.00ms 30.00ms 45.00ms 15.00ms 30.00ms 45.00ms 250.1 V 150.1 V 50.10 V SCR1 50 Hz SCR2 S2003LS1 S2003LS1 V3 120/-120V R8 0.9k R1 0.1k R6 0.1k R5 0.9k C4 2uF D1 1N5402 R4 0.1k A: r5_1 Vg-th2 -149.9 V -249.9 V 0.000ms A: r6_1 V-triac 15.00 V 5.000 V -5.000 V 100.0 W -15.00 V 50.00 W -25.00 V 0.000 W -35.00 V 0.000ms -50.00 W A: c1[p] 150.1 V -49.90 V 150.0 W -100.0 W 0.000ms 250.1 V 50.10 V R7 47 P-load A: r6[p] -149.9 V -249.9 V 0.000ms Q2 MAC15A6 C1 2uF D3 1N5402 -49.90 V 15.00ms 30.00ms 45.00ms Ic1 12.49 W A: r6[i] I-load 1.250 A 0.750 A 7.490 W 0.250 A 2.490 W -0.250 A -2.510 W -0.750 A -7.510 W -1.250 A 0.000ms -12.51 W 0.000ms 15.00ms 30.00ms 45.00ms D1 1N5402 C1 2uF V1 120/-120V R1 5.1k R4 0.1k S S1 SCR2 S2003LS1 SCR1 S2003LS1 S=Off 0.000 V A: scr1_3 S1 SCR2 S2003LS1 SCR1 S2003LS1 250.0 V 50.00 V -50.00 V -150.0 V -250.0 V 20.00ms 10.00 V A: v1_2 50.00ms 80.00ms 110.0ms 50.00ms 80.00ms 110.0ms 300.0 V 100.0 V Vg-th1 0.000 V S 150.0 V 110.0ms -100.0 V -10.00 V 20.00ms A: scr1_2 50.00ms 80.00ms -300.0 V 20.00ms 110.0ms 5.000 V A: scr1_2 250.0 V 150.0 V 50.00 V Vth1 0.000 V -50.00 V -150.0 V -5.000 V 20.00ms A: r4[p] 50.00ms 80.00ms -250.0 V 20.00ms 110.0ms 200.0 W A: r4[p] Load power 0.000 W -200.0 W 20.00ms 50.00ms 80.00ms 110.0ms R3 0.9k C2 2uF S=ON Vsource 80.00ms R5 5.1k R4 0.1k 50 Hz A: v1_1 50.00ms R1 5.1k R3 0.9k 200.0 V -200.0 V 20.00ms D1 1N5402 C1 2uF V1 120/-120V C2 2uF 50 Hz A: v1_1 R5 4.1k Zero-Voltage switching 50.00ms 80.00ms 110.0ms 250.0 W 150.0 W 50.00 W -50.00 W -150.0 W -250.0 W 20.00ms 50.00ms 80.00ms 110.0ms Chapter 7D Thyristor Commutation 1. Objectives: 1. to study the concept of thyristor commutation 2. to illustrate some of commutation techniques 3. to study how to express the required mathematical model 4. To determine the turning-off time, and how could be affected 5. Describing some examples 2. The Concept of Commutation Process: - This is a process of removing the circuit current by forcing it to flow in another loop with purpose to be ceased “eliminated”. - Depending on the source voltage, there are two types of commutation strategies: - Natural commutation : applied in AC circuits - Forced commutation : Applied in DC circuits. 2.1 Natural Commutation: Because of the load current varies sinusoidally, the thyristor should be turned –off when the load current falls below the holding value: ILoad<IH . Furthermore, in the negative half cycle, the applied source voltage being negative with respect to anode-cathode terminals, causing reverse biasing of the device. Principle electrical circuit is shown below: 2.1 Forced Commutation: In this case, because of no alternating character of the current “ DC “, therefore it must force decreases by applying the following approaches: - the load current must reduced below the holding value: ILoad<IH - by applying negative voltage across the thyristor, causing forced removing of internal charge, therefore the load current falls below the holding value IH . Several techniques realized these approaches: • • • • • • Self Commutation Complementary Commutation Resonant Commutation Impulse Commutation Load-side commutation Line-side commutation *- Self Commutation: The thyristor is self turning-off due to resonant behavior of the current flows in RLC circuit as well shown on the figure below, where it is clearly shown that when the current becomes negative the thyristor turned-off. Mathematical modeling: i( t ) Im . sin t C 1 ; L L.C Vc ( t ) Vs (1 cos t ); Im Vs. to L.C *- Complementary Commutation: In this case, second thyristor which called " Auxiliary" operates in complementary sequence ( turning-on first thyristor caused turning-off second device) . The figure shown below illustrates the principle circuit, where it is clearly shown that each thyritor operates for predetermine time with complementary sequence. The connected capacitor play the role of applying negative voltage across T1 and T2. Mathematical modeling: T1=ON Vs R.i( t ) Vc ( t ) i1( t ) 2. Vs R . t / ; R.C The turning off time : toff R.C. ln 2 R R1 R 2; Vc (0) Vs; Let Vs=200V; R=5Ω; =10µF Therefore: toff=34.4µS Waveforms: Hereinafter the circuit waveforms for both T1, T2, Vg1, Vg2, I1,I2, and VR1. *- Impulse Commutation: In this case, second thyristor T2 which called " Auxiliary" used to connect the capacitor across T1 with inverse voltage, therefore reducing the thyristor current below IH. The figure shown below illustrates the principle circuit, where the circuit waveforms illustrates these behaviors. Mathematical modeling: T1=ON, after then T2=ON Vs R.i( t ) Vc ( t ) t 1 R.i( t ) i( t ) Vc (0) C0 i( t ) Let Vs=200V; R=5Ω; =10µF Therefore: toff=34.6µS 2.Vs R . t / ; R.C Vc ( t ) Vs.(1 2 t / ) The turning off time : toff R.C. ln 2 Vc (0) Vs; Waveforms: Hereinafter the circuit waveforms for both T1, T2, Vg1, Vg2, I1, and Vload. *- Resonant Commutation: In this case, second thyristor T2 used to connect the capacitor across T1 with inverse voltage, therefore reducing the thyristor current below IH, while third thyristor T3 is used to recharging the capacitor with polarity appropriate to turning-off T1. The figure shown below illustrates the principle circuit, where the circuit waveforms illustrates these behaviors. Waveforms: Hereinafter the circuit waveforms for two cases: 1- C is recharged through resistance R2; 2- C is recharged throug inductance L2 THANK YOU FOR YOUR LISTENING IF YOU HAVE QUESTIONS, PLEASE DON’T HESTATE TO CONTACT ME BY EMAIL ON [email protected]