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CONTROLABLE SWITCHING DEVIES DESIGNED BY DR. SAMEER KHADER PPU “E-learning Project” CHAPTER SEVEN (New textbook)

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Diac Circuits Triac Circuits Thryristor Circuits CONTENT Introduction, Classification &Applications, Practical Firing ( Triggering) Circuits Thyristor Commutation (turning-off)

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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 P N P N AK G A G K Principle of operation : The thyristor construction Presents three diodes In series ( two forward 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 : AK G D3 D2 D1 Th.

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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

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Thyristor Main Parameters: There’re several parameters related to static & dynamic performance of the thyristor, these parameters are as follow : 1-V AK - thyristor voltage at steady state 2 V; 2-V BO - -break over voltage, voltage after which thyristor will turning on at constant gate current ; 3-V BR - break down voltage in reverse biasing state; 4-I H - 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- I L - thyristor latching current :this a minimized load current keeping the thyristor in conducting state after removing the gate signal ; 6-V GT - minimum gate voltage required to firing the thyristor at given loadind condition, VGT 0.8…12V; 7-I GT - 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.

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Thyristor Dynamic Performances V-source V-gate V-thyris P-load

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V-source V-gate V-thyris P-load V-source V-gate V-thyris P-load AC - circuit DC - circuit 2-Phase Control Gate Firing Circuits: 1- RC relaxation oscillator Th2 Th1 Th2 C C R-load R1 R2 R-load

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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<

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I-V curve

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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 > V at least; VBR > Vm ; I L min > I L at firing( remains conduct); and I L min < I H ( swith off). By increasing di/dt at given Ig the thyristor capable to carry additional current I Load. By increasing Ig, V BO ( 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. Conclusion

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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:

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Triac Firing Circuits V Triac voltage Load current Gate voltage Load 35.00ms 50.00ms 65.00ms 80.00ms V V V V V A: r2_2 Triac voltage 35.00ms 50.00ms 65.00ms 80.00ms A A A A A A A: r2[i] Load current 35.00ms 50.00ms 65.00ms 80.00ms V V V V A: d1_k Gate voltage 0.000ms 15.00ms 30.00ms 45.00ms V V V V V V V 0.000ms 15.00ms 30.00ms 45.00ms A A A A A A A 0.000ms 15.00ms 30.00ms 45.00ms V V V V V V V 1- Phase angle control without diode 2- Phase angle control with diode

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0.000ms 10.00ms 20.00ms 30.00ms V V V V V V A: tr_ ms 10.00ms 20.00ms 30.00ms V V V V V V A: v3_ ms 10.00ms 20.00ms 30.00ms V V V V V V A: tr_ ms 10.00ms 20.00ms 30.00ms V V V V V V A: tr_ ms 10.00ms 20.00ms 30.00ms V V V V V V A: tr_ ms 15.00ms 25.00ms 35.00ms V V V V V V A: c1_2 UJT needles Load voltage Pulse generator Load voltage Capacitor voltage Source voltage 3-Triac firing circuits using UJT B1 B2

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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 0

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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:

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5- Time-varying performances: Phase control circuit with Diac & Triac:

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The main equations are as follow, and can derives when Vdiac =Vc at given angle. The firing angle

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Additional Firing circuits

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0.000ms 15.00ms 30.00ms 45.00ms V V V V V V A: d1_ ms 15.00ms 30.00ms 45.00ms V V V V V V A: r4_ ms 15.00ms 30.00ms 45.00ms V V V V V V A: r4_ ms 15.00ms 30.00ms 45.00ms V V V V V V A: scr2_ ms 15.00ms 30.00ms 45.00ms V V V V V V A: scr2_ ms 15.00ms 30.00ms 45.00ms W W W W W W A: r5[p] 0.000ms 15.00ms 30.00ms 45.00ms V V V V V V A: scr2_ ms 15.00ms 30.00ms 45.00ms V V V V V V A: scr2_ ms 15.00ms 30.00ms 45.00ms W W W W W W A: r5[p] Source voltage Zener voltage Capacitor voltage Gate needles Thyristor voltage Load power Gate needles Thyristor voltage Load power 1- Practical circuit using UJT: 1- Low = R4C1 2- High = R4C1

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0.000ms 15.00ms 30.00ms 45.00ms V V V A: c2_ ms 15.00ms 30.00ms 45.00ms V V V A: q2_ ms 15.00ms 30.00ms 45.00ms V V V A: scr1_ ms 15.00ms 30.00ms 45.00ms V V V A: scr1_ ms 20.00ms 35.00ms 50.00ms W W W A: r10[p] Gate needles Capacitor voltage Thyristor voltage Load power UJT Signal at B2 B1 B2 2- Practical circuits using UJT and Isolation Transformer: 5.000ms 20.00ms 35.00ms 50.00ms V V V A: c2_ ms 20.00ms 35.00ms 50.00ms V V V A: scr1_ ms 20.00ms 35.00ms 50.00ms V V V A: scr1_ ms 20.00ms 35.00ms 50.00ms W W W A: r10[p] Capacitor voltage Gate needles Thyristor voltage Load power

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0.000ms 30.00ms 60.00ms 90.00ms V V V V V V A: r6_ ms 30.00ms 60.00ms 90.00ms V V V V V V A: r8_ ms 30.00ms 60.00ms 90.00ms V V V V V V A: r5_ ms 15.00ms 30.00ms 45.00ms V V V V V V A: r6_ ms 15.00ms 30.00ms 45.00ms A A A A A A A: r6[i] 0.000ms 15.00ms 30.00ms 45.00ms W W W W W W A: r6[p] 0.000ms 15.00ms 30.00ms 45.00ms W W W W W W A: c1[p] 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. Source voltage Vg-th1 Vg-th2 V-triac I-load P-load Ic1 Load

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Zero-Voltage switching S=OffS=ON SS V- source Vg-th1 Vth1 Load power

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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.

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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: I Load *
*

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Self Commutation Complementary Commutation Resonant Commutation Impulse Commutation Load-side commutation Line-side commutation 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: I Load *
*

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*- 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:

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*- 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 Let Vs=200V; R=5Ω; =10µF Therefore: t o ff =34.4 µS

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Waveforms: Hereinafter the circuit waveforms for both T1, T2, Vg1, Vg2, I1,I2, and V R1.

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*- Impulse Commutation: In this case, second thyristor T 2 which called " Auxiliary" used to connect the capacitor across T1 with inverse voltage, therefore reducing the thyristor current below I H. The figure shown below illustrates the principle circuit, where the circuit waveforms illustrates these behaviors. Mathematical modeling: T1=ON, after then T2=ON Let Vs=200V; R=5Ω; =10µF Therefore: t o ff =34.6 µS

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Waveforms: Hereinafter the circuit waveforms for both T1, T2, Vg1, Vg2, I1, and V load.

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*- 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

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