LABORATORY MANUAL - …powerelectronicsrvce.wikispaces.com/file/view/PELabManual2018.pdf/... · 2. Static characteristics of MOSFET and IGBT. 3. SCR turn-on circuit using synchronized

LABORATORY MANUAL

POWER ELECTRONICS LAB ( 12EE63 )

SEMESTER: VI EEE

Compiled & Prepared by 1. Mrs. Hemalatha J N 2. Mrs. Prema V

DEPATRMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

R V COLLEGE OF ENGINEERING (AUTONOMOUS UNDER VTU)

BANGALORE-560059.

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

R V COLLEGE OF ENGINEERING ( AUTONOMOUS UNDER VTU )

POWER ELECTRONICS LAB ( 12EE63 )

LIST OF EXPERIMENTS

1. Static characteristics of SCR 2. Static characteristics of MOSFET and IGBT. 3. SCR turn-on circuit using synchronized UJT relaxation oscillator. 4. SCR digital firing circuit for a single phase controlled rectifier 5. Single phase semi-converter and full-converter using R and R-L loads (conventional &

simulation) 6. An improved Series Inverter ( conventional & simulation) 7. Auxiliary Commutation ( conventional & simulation) 8. Single phase parallel inverter connected to R load (conventional & simulation )

9. Complementary Commutation ( conventional & simulation)

10. 3-phase semi-converter ad full-converter with R and R-L loads 11. Speed control of a separately excited DC motor using a MOSFET chopper 12. Speed control of single phase induction motor using AC voltage controller 13. Single phase full bridge inverter with various voltage control schemes

Prof. & HOD, EEE Department.

LIST OF EXPERIMENTS I CYCLE Expt. No Page No

1. Static characteristics of SCR 1 2. Static characteristics of MOSFET and IGBT. 3

3. SCR turn-on circuit using synchronized UJT relaxation oscillator. 8

4. SCR digital firing circuit for a single phase controlled rectifier 11

II CYCLE

5. Single phase semi-converter and full-converter using R and R-L loads (conventional &

simulation) 16 6. a. An improved Series Inverter (conventional & simulation) b. Auxiliary Commutation (conventional & simulation) 20

7. a. Single phase parallel inverter connected to R load

b. Simulation of bridge inverter 23

8. Complementary Commutation ( conventional & simulation ) 26

III CYCLE

9. 3-phase semi-converter and full-converter with R and R-L loads 29

10. Speed control of a separately excited DC motor using a MOSFET chopper 32 11. Speed control of single phase induction motor using AC voltage controller. 34 12. Single phase full bridge inverter with various voltage control schemes

ALSO Question Bank 38

Viva Questions 40

POWER ELECTRONICS LAB(12EE63)

I CYCLE EXPT. NO 1

STATIC CHARACTERISTICS OF SCR AIM: To obtain the static V-I characteristics of the given SCR APPARATUS REQUIRED: Triac(BT-136), milli ammeter, rheostats, general purpose connecting board. CIRCUIT DIAGRAM:

PROCEDURE: The SCR is a unilateral device. It is a current controlled device. Separate DC supplies are given to the gate and anode of the device as shown. The supply to the gate is lower than the anode supply.

1. The circuit is connected as shown. The terminals of the device are identified according to the pin diagram shown below:

C A G

2. Measuring the resistances between the gate and cathode and anode and cathode checks the healthiness of the device. The resistances have to be high. The resistance between anode and cathode is higher than the one between gate and cathode.

BT136

Department of EEE RVCE 1


3. Initially, a gate current of 1.5mA is supplied to the gate by adjusting the gate supply as well as the 145Ω resistor in the gate circuit.

4. The anode supply is now gradually increased. The voltage will be blocked by the device, which

will be recorded by the voltmeter which is connected across the anode and cathode of the device.

5. As the voltage is further increased, for some value of the forward voltage, the device will breakdown. This condition is called turn-on of the device. This condition is indicated by the voltmeter across the device collapsing to about 1V. The voltage at which the device breaks down is called the forward break over voltage, VBO. This voltage is noted down.

6. After the device starts conducting, which is also indicated by the ammeter in the anode circuit

indicating a current, the anode supply is increased and the corresponding increase in the anode current is noted and the readings are tabulated as shown. The procedure outlined in the above steps is repeated for another gate current, and tabulated.

Ig1= -- mA: VBO1= -- V Ig2= -- mA: VBO2= -- V

7. Using the readings tabulated for two values of gate currents. The V-I characteristics of the

SCR are plotted as shown below:

Ia (mA) Ig2 Ig1

IL

Vak (V) VBO2 VBO1

Ig1 > Ig2

-Ia (mA)

Sl. No.

Anode current Ia, in mA

Vak, Across device in V

Sl. No.

Anode current Ia, in mA

Vak, Across device in V



TO FIND THE VALUE OF HOLDING CURRENT: To find the value of holding current, after turning the SCR, the forward voltage is slowly reduced just until the forward blocking voltage reappears across the device. The anode current at this point is noted down. Typically its value will be around 5mA to 10mA. EXPT. NO 2:

STATIC CHARACTERISTICS OF MOSFET AND IGBT AIM: To obtain the static V-I characteristics of MOSFET and IGBT . APPARATUS REQUIRED: MOSFET (IRF 730), two 0-30V power supplies, rheostat, 0-100 milliammeter, multimeter, connecting board and connecting wires/patch cords. A. CHARACTERISTICS OF MOSFET

CIRCUIT DIAGRAM:

PROCEDURE: The MOSFET is a voltage controlled static switch. It can be considered as the static equivalent of the vacuum tube triode.

1. The circuit can be connected as shown above after verifying that the device is healthy and identifying the terminals of the device by means of the pin diagram below:



G D S

2. Apply a suitable voltage (15V) across the drain and source terminals of the device. Now slowly increase the gate to source voltage by adjusting the supply till the device turns on which is indicated by the ammeter showing a reading. The corresponding voltage across the gate and source is called the threshold voltage whose value is noted down.

3. The readings for the drain characteristics are noted by increasing the Vds supply by keeping

Vgs constant. The procedure is repeated for another higher value of Vgs and Vds is increased in steps and the corresponding increases in drain current Id are noted and tabulated as below:

Vgs1= ---V Vgs2= ---V

Drain Characteristics Id(mA)

Vgs1

Vgs2

Vgs1 > Vgs2 Vds(volts)

3. For obtaining the transfer characteristics, the drain voltage Vds is fixed at some value (15v) and the gate to source voltage is increased in steps and the increase in the drain current is noted and tabulated. The procedure is repeated for a larger value of drain voltage (30V) and the

Sl. No. Vds (v) Id (mA)

Sl. No. Vds (v) Id (mA)

IRF 730



corresponding values of Vgs and Id are noted and tabulated as shown. The drain and transfer characteristics are also shown below: Vds1= ---V Vds2 = ---V

Transfer Charecteristics Id (mA) Vds1 Vds2 Vds1 > Vds2

Vgs(volts)

Vth CALCULATION: From the drain characteristics’ and transfer characteristics the device parameters like drain resistance rd, trans conductance gm and amplification factor can be found using following equations. gm = ΔId / ΔVg = ________ ohm-1 rd = ΔVds / ΔIds= ________ ohm μ = rd x gm B. CHARACTERISTICS OF IGBT

Sl. No. Vgs (V) Id(mA)

Sl. No. Vgs (V) Id(mA)



APPARATUS REQUIRED: IGBT, two 0-30V power supplies, 0-2A ammeter, multi-meter connecting board, connecting wires etc. CIRCUIT DIAGRAM:

PROCEDURE:

1. After checking that the device is healthy, in the usual way, the circuit given above is connected. The supplies are kept at the minimum (zero volts).

2. The IGBT is a switching device which is a voltage controlled device. From the output end it

works a NPN transistor. A minimum voltage at the gate is required to turn on the device, the value of which is called the threshold voltage.

4. To start with, a voltage of 15V is applied to the collector circuit. 5. The gate to emitter voltage Vge is very slowly increased till the device switches on which is

indicated by the ammeter in the collector circuit showing a reading. The value of Vge is noted down.

6. The collector to emitter voltage (Vce) is further increased to record the corresponding increases

in the collector current till it reaches saturation.

7. This procedure is repeated for another value of Vge and the readings are tabulated & a graph of Vce against Ic is drawn for the two different values if Vge as shown below:

Vge1 = ----V Vge2 = ----V

Sl.No. Vce in V Ic in A Sl.No. Vce in V Ic in A



Ic(mA) Vge1

Vge2 Vge1 > Vge2

Vce (volts)

EXPT.NO 3

LINE SYNCHRONISED UJT TRIGGERING CIRCUIT AIM: To study the UJT as a triggering device and obtain the waveforms of the triggering circuit. To also study how the UJT can be used as a line synchronized device and record the waveforms of the load voltage and the SCR voltage. APPARATUS REQUIRED: One UJT (2N2646), one 230V/18V, 150VA transformer, load resistor, one SCR, resistors, one 15V, 400mW zener diode, one pulse transformer, diodes (BY127/1N4001), connecting board, patch cords, CRO. CIRCUIT DIAGRAM: A line synchronized UJT triggering circuit for triggering an SCR connected in a half wave rectifier circuit is shown below:



PROCEDURE:

1. After checking all the components, wire up the circuit as shown. 2. After connecting the circuit, switch on the AC supply to the transformer. Connect the

oscilloscope across the points shown and record the waveforms. One precaution to be taken is that only one channel of the CRO is to be connected across the pulse transformer output and the other cannel should not be connected to any other part of the circuit.

3. The waveforms are shown below:



V ωt

VZ ZENER VOLTAGE WITH SUPER IMPOSED PULSES ωt

VC

VPEAK

ωt VPUL

ωt 4. After verifying that the triggering circuit is working satisfactorily and the Pulses are

transferred to the secondary of the pulse transformer; the triggering circuit is connected to the half wave controlled rectifier circuit shown:

5. The terminals marked G and K in the triggering circuit are connected to the gate and cathode terminals of the SCR in the half wave rectifier circuit shown. The variable resistor R in the triggering circuit is varied and the variation of the delay/triggering angle α is



observed on the CRO. The voltage across the load and SCR are recorded and drawn to scale as shown below:

V V = Vmsinωt ωt

VL

ωt α VSCR

α ωt

Sl No:

Firing Angle (α) Vo (Practical) Vo (Theretical) = 𝑬𝑬𝑬𝑬π𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪



EXPT. NO 4

SCR DIGITAL TRIGGERING CIRCUIT FOR A SINGLE PHASE

CONTROLLED RECTIFIER

AIM: To assemble a digital firing scheme to trigger an SCR in a half wave rectified circuit using CD4047. To also study the method of trigger angle control or phase control of SCR. APPARATUS REQUIRED: IC 741, IC CD 4047( 2 Nos), CL 100 ( 3 NOs) resistors and capacitors. CIRCUIT DIAGRA: STAGE 1;

The above circuit is called a Zero Crossing Detector or ZCD which is a synchronizing circuit to be synchronized to the ac supply. The op-amp 741 works as a comparator. The waveforms at point “A” are shown below. Input signal to ZCD from Vi transformer

wt out put of ZCD

12v

wt -12v

o/p at A wt



STAGE 2: CIRCUIT DIAGRAM In stage 2 the square wave signal obtained is given as an input signal to a negative edge triggered monostable multivibrator using a CD 4047 I.C. The circuit of stage 2 is given below

Description of CD 4047 CD 4047 is a very versatile timer digital IC which has three important modes of operation, namely free running astable, positive edge triggered and negative edge triggered monostable and gated astable modes. The connections given above are for negative edge triggered monostable. The 4047 IC also has two outputs obtainable at pins 10 and 11. one output at pin 10 is the normal output. Its complimentary output is available at pin 11. the pulse width of the output can be designed using the relationship tm=2.48RC, where tm is the width of the pulse to be designed, R and C are the externally connected components as shown. A fixed resistor potentiometer combination has been used to vary the triggering angle of the line commutated SCR. The associated waveforms are shown below. A wt

o/p at pin 10

wt o/p at

pin 11



STAGE 3: CIRCUIT DIAGRAM The output signal from pin 11 of the negative edge monostable vibrator is given as a trigger input to another CD 4047 operated in the true gated astable mode as shown in the diagram below.

The CD 4047 in the true gated astable mode, will convert an input pulse at pin 5, into very high frequency pulses suitable for triggering an SCR. The input to pin5, called trigger input is given from the emitter follower as shown which acts as a buffer. CL100 is the transistor used for the buffer. The output from pin 10 ( normal output ) is obtained as a high frequency train of pulses. The associated input and output waveforms of stage 3 are as shown below: o/p at 11 wt high frequency o/p at 10 of gated Astable wt



STAGE 4: CIRCUIT DIAGRAM The output obtained from gated astable at pin 11 shown above which will be in the form of high frequency pulses have to be amplified suitably in order to trigger an SCR. Therefore , from pin 10 of the gated astable, the pulses are amplified using the following amplifier circuit .

The output of the gated astable is given to a CL 100 based pulse amplifier. P and S are the windings of a pulse transformer which will transmit the pulse from the input to the input.

These pulses are given to the gate of an SCR connected as a half wave rectifier circuit shown below



The output pulses obtained from secondary winding of pulse transformer are given to the gate of the SCR. The output waveform is shown below. V = Vmsinωt

V ωt

VL ωt α Vscr α ωt Triggering angle can be varied by varying 100K pot in the monostable.

Sl No:

Firing Angle (α) Vo (Practical) Vo (Theretical) = 𝑬𝑬𝑬𝑬π𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪



II CYCLE EXPT NO 5

SINGLE PHASE FULL WAVE RECTIER USING R AND R-L LOADS

( CONVENTIONAL AND SIMULATION )

a. AIM: To rig up a single phase semi-converter and to study the waveforms of the load voltage. To calculate the average value of the output voltage for triggering angles above and below 90°.

APPARATUS REQUIRED: One single phase full wave rectifier module, load inductance of 15mH, 330Ω, connecting wires, one CRO. CIRCUIT DIAGRAM: The circuit diagram for semi-converter is shown below:

The circuit diagram for full-converter is shown below:

PROCEDURE:

1. The circuit shown above is connected after ensuring that the SCRs are healthy by checking their gate to cathode and anode to cathode resistances.



2. To start with, the inductance of the load, i.e. the 15mH inductor is removed and the waveforms

across the load and the devices are observed as shown below, the CRO being connected across the load resistor RL.

3. The triggering angle is varied by varying the pot in the triggering circuits of the SCRs and the corresponding waveforms are observed and recorded for value of ‘α’ above and below 90°.

4. Typical waveforms across the load and one of the SCRs are shown below:

5. Repeat the procedure for full-converter also. vL vSCR1 vLOAD α β ωt α = Triggering angle β = Conduction angle [It should be observed that across the nonconducting SCR, the voltage will be twice the peak voltage of the input which is the drawback of this circuit.]

The above procedure is repeated by including the load inductance of 15mH as shown in the circuit diagram above. From the waveforms it should be observed that the SCRs will be conducting beyond 180°. A typical set of waveforms are shown below: vL vSCR1 vLOAD

ωt

For resistive load: Vdc = (Vm/π)* (1 + cosα), where α is the triggering angle and Vm is the maximum value of the input voltage to the rectifier that is √2 * 12V. For inductive load: Vdc = (2Vm/π)* (cosα).

α β



Sl No:

Firing Angle (α) Vo (Practical) Vo (Theretical)

SIMULATION OF FULL WAVE CONTROLLED SEMICONVERTER

CIRCUIT DIAGRAM :

PROCEDURE:

1. Circuit is drawn as shown in pspice schematics

2. The values and attributes of components to be se as indicated in diagram

3. select transient analysis and set step time as 10ns and final time as 35ms.

4. save the file and simulate circuit and observe the waveform across load as shown.

5. the same be repeated for RL- load and observe the output wave form



. OUTPUT WAVE FORM: R-L load

R-LOAD



EXPT NO 6 a: IMPROVED SERIES INVERTER

AIM: To rig up a class-A based SCR series inverter and study its operation and observe the waveforms of the load and capacitor voltage and to verify that the circuit behaves as an under damped oscillatory circuit. APPARATUS REQUIRED: Two SCRs, one 0-30V DC supply, commutating capacitor (4uF), center-tapped inductance, CRO, load resistance, triggering card and patch cords. CIRCUIT DIAGRAM:

TRIGGERING CARD :

ASTABLE

MONO - STABLE

BLOCKING OSCILLATOR

PULSE AMPLIFIER

INVERTER

MONO – STABLE

BLOCKING OSCILLATOR

PULSE AMPLIFIER

G1K1

G2 K2



TRIGGERING REQUIREMENT: In the power circuit, there are two SCRs, which have to be alternately turned on, and therefore, two sets of high frequency pulses have to be generated which are out of phase and there is no overlap between the pulses. PROCEDURE: 1. The circuit is connected after checking all the components. The power supply voltage knobs are kept in minimum position and the current knobs are kept in maximum position. 2. The triggering card is also checked as indicated above and the pulses in both the channels of the card are checked on the oscilloscope. 3. The supply to the power (SCR) circuit is energized by applying about 15V. 4. The supply to the triggering card is also varied very slowly, taking the precaution mentioned above. 5. Once the required waveform is obtained, the voltage to the triggering card is not increased further. 6. The CRO channels are connected once across the load and once again across the capacitor and the waveforms are noted down. Typical waveforms are shown below. The values of the inductance (one half), capacitance and the load resistance are measured using a digital L C R meter. These values are used to check whether the circuit is behaving as an under damped oscillatory circuit by using the equation: R<=2√L/C. vL Vl Vc iC Tr / 2 βt f =1/2π(1/ LC) – (R2 /4 L2)1 / 2 SIMULATION OF BASIC SERIES INVERTER



CIRCUIT DIAGRAM:

PROCEDURE:

1. Circuit is drawn as shown using pspice schematic editor, the values & attributes of the components are set. The different attributes are DC=0, AC=1, V1=0, V2=10, TD=0, TR=1ns, TF=1ns, PW=100us, PER=1ms for vpulse part for the thyristors 1 and DC=0, AC=1, V1=0, V2=10, TD=.05m, TR=1ns, TF=1ns, PW=100us, PER=1ms for vpulse part for the thyristors

2. In the set up analysis select transient analysis, and set print time as 10ns and final time as 3ms.

3. save the file and simulate to observe the output waveform. OUTPUT:



EXPT NO 6 b: AUXILIARY COMMUTATION

AIM: To study the principle of auxiliary commutation or impulse commutation. APPARATUS REQUIRED: Two 0-30V DC supplies, two SCRs, one triggering card (both channels), L, C, CRO and patch cords. CIRCUIT DIAGRAM:

PROCEDURE: As two SCRs are used, the triggering requirements are the same as the series inverter. Two sets of pulses out of phase with each other are to be generated.

1. The circuit is connected as shown in the figure.

2. Power supply is first given to the SCR circuit (about 15V).

3. To start with; the auxiliary SCR is triggered, with the gate of the main SCR kept open.

4. The capacitor will charge with its upper plate positive to VDC.

5. The main SCR is now turned on by connecting the gate of this SCR to the gate terminal on the triggering card. (The triggering card would already be checked as given earlier).



6. The relevant waveforms across the load and across the capacitor are obtained, noted down and plotted to scale. Typical waveforms are shown below.

GATE PULSES iGA iGM iGA t iC vC

2VDC / RL

VDC VDC / RL t VDC / RL vL

VDC / RL t



SIMULATION OF AUXILIARY COMMUTATION

PROCEDURE: 1. The circuit diagram is drawn as shown using pspice schematic editor 2. The values of components are set and the attributes for VPULSE part to be set are for thyristor

1 DC=0, AC=1, V1=0, V2=10, TD=0, TR=1ns, TF=1ns, PW=0.5ms, PER=1ms for thyristor 2 DC=0, AC=1, V1=0, V2=10, TD=0.5m, TR=1ns, TF=1ns, PW=0.5ms, PER=1ms

3. select transient analysis set print time as 10us and final time as 4ms 4. save the file and simulate to see the output. OUTPUT:



EXPT NO 7:

MOSFET BASED SINGLE PHASE FULL BRIDGE INVERTER CONNECTED TO R LOAD

a. AIM: To study the load voltage waveforms for different load resistances and observe and

record the load voltage waveforms with the switching transients. APPARATUS REQUIRED: One parallel inverter module, a 40Ω tubular resistor, CRO, connecting wires. CIRCUIT DIAGRAM:

PROCEDURE:

1. The circuit is connected as shown in the circuit diagram shown above. All the connections are externally made on the module where the terminals are provided.

2. The load resistor is kept in the maximum position and the supply voltage is kept in minimum position.

3. The supply switch is closed and the external switch shown which is provided on the module is also switched on.

4. With the load in maximum position, the supply voltage is increased to about 15- 20V. The load resistor is reduced a little and for this value of load, the waveforms across the load and one of the SCRs are noted down, by connecting the CRO first across the load and then across one of the SCRs.

5. The load resistor is reduced further and for this value of load resistance, the waveforms are noted down.



The load voltage waveform is as shown below:

b. SIMULATION OF 1 PHASE BRIDGE INVERTER:

t

VL



PROCEDURE:

1. Circuit is drawn as shown using the pspice schematics

2. The values of the components and attributes of VPULSE are set for Q! and Q3 the attributes for VPULSE are DC=0, AC=1, V1=0, V2=10, TD=0, TR=1ns, TF=1ns, PW=0.5ms, PER=1ms and for Q2 and Q4 the attributes are DC=0, AC=1, V1=0, V2=10, TD=0.5ms, TR=1ns, TF=1ns, PER=1ms,PW=0.5ms

3. Select transient analysis set print step as 10ns and final time as 4 ms

4. save the file and simulate to observe the output. OUTPUT:



EXPT NO 8: COMPLEMENTARY COMMUTATION

AIM: To connect a complementary commutation circuit and study and record the relevant wave forms and to calculate and verify the critical turn-off time or available circuit turn-off time from the waveforms. To also observe the condition for commutation failure and identify the condition from the waveforms. APPARATUS REQUIRED: A 0-30V regulated supply, two SCRs, one 4uF capacitor, two tubular 145Ω resistors, one CRO, one triggering module, one digital LCR meter, connecting wires one multimeter. CIRCUIT DIAGRAM:

PROCEDURE:

1. The power circuit shown above is connected after ensuring all the components are in working order.

2. The triggering module is tested by energizing it by 10V DC supply and ensuring that the current

is well within the normal limits (0.25A).

3. The duty cycle of the astable in the triggering card is adjusted to 50%. 4. The outputs of the triggering card namely G1K1 and G2K2 are checked.

5. The gates of both the SCRs are connected to the triggering card outputs.

6. To start with the power circuit is energized with 15V.

7. The supply to the triggering card is slowly increased till the proper output is observed in the

CRO, which is connected across one of the 145Ω load resistors.



8. The CRO is next connected across the capacitor and the voltage across the capacitor is observed and recorded.

9. The CRO is connected across one of the SCRs and the voltage across it is recorded. From this waveform, the critical or circuit turn-off time is ‘toff’ is noted down.

10. The load resistance is varied and the influence of load current on ‘toff’ is noted down.

11. The digital LCR meter is used to measure the values of C and R and ‘toff’ is calculated as:

toff = 0.6931RC.

A set of typical waveforms are shown below: iC vC vC iC t - V iC = Capacitor current

vC = Capacitor voltage

vL t



SIMULATION OF COMPLEMENTARY COMMUTATION

PROCEDURE: 1. The circuit diagram is drawn as shown using pspice schematic editor 2. The values of components are set and the attributes for VPULSE part to be set are for

thyristor 1 DC=0, AC=1, V1=0, V2=10, TD=0, TR=1ns, TF=1ns, PW=0.5ms, PER=1ms for thyristor 2 DC=0, AC=1, V1=0, V2=10, TD=0.5m, TR=1ns, TF=1ns, PW=0.5ms, PER=1ms

3. select transient analysis set print time as 10us and final time as 4ms

4. save the file and simulate to see the output.



III CYCLE EXPT NO 9:

3-PHASE SEMI CONVERTER AND FULL-CONVERTER

b. AIM: To rig up a three phase semi-converter and to study the waveforms of the load voltage. To calculate the average value of the output voltage for triggering angles above and below 90°.

APPARATUS REQUIRED: One three phase full wave rectifier module, load inductance of 15mH, 330Ω, connecting wires, one CRO. CIRCUIT DIAGRAM: The circuit diagram for semi-converter is shown below:

The circuit diagram for full-converter is shown below:

PROCEDURE:

6. The circuit shown above is connected after ensuring that the SCRs are healthy by checking their gate to cathode and anode to cathode resistances.

7. To start with, the inductance of the load, i.e. the 15mH inductor is removed and the waveforms across the load and the devices are observed as shown below, the CRO being connected across the load resistor RL.



8. The triggering angle is varied by varying the pot in the triggering circuits of the SCRs and the

corresponding waveforms are observed and recorded for value of ‘α’ above and below 90°.

9. Typical waveforms across the load and one of the SCRs are shown below:

10. Repeat the procedure for full-converter also.

The above procedure is repeated by including the load inductance of 15mH as shown in the circuit diagram above. From the waveforms it should be observed that the SCRs will be conducting beyond 180°. A typical set of waveforms are shown below: Voltage waveform for 3-phase semi-converter

Voltage waveform for 3-phase semi-converter



For resistive load: 3 3 3cos cosm mLdc

V VV α απ π

= =

Where mLV 3 Max. line-to-line supply voltagemV= = Sl No:

Firing Angle (α) Vo (Practical) Vo (Theretical)



EXPT NO 10:

SPEED CONTROL OF A SEPARATELY EXCITED DC MOTOR USING A MOSFET CHOPPER

AIM: To build a single quadrant MOSFET based chopper using a suitable control circuit. To vary the duty cycle of the chopper and hence vary the average voltage of the chopper. To also study the variation in speed of the motor with respect to the duty cycle of the chopper. APPARATUS REQUIRED: 4047 CMOS timer IC’s (2 Nos),resistors and capacitors, CL100 (2 Nos), one PMDC 12V motor. CIRCUIT DIAGRAM: FIRST STAGE: The CMOS timer IC(4047) is connected as an astable in the free running mode as shown.

Pins 4,5,6 and 14 connected to vcc . Pins 7,8,9,12 connected to ground. The output from pin 10 is taken through an emitter follower which is a buffer. The output of the emitter follower is given as a trigger input to another CD 4047 timer IC connected to work as a monostable which is negative edge triggered. The circuit of the second stage is as shown below.



CIRCUIT DIAGRAM:

Pins 4,8,14 are shorted and connected to VCC . Pins 5,9,7 and 12 are shorted and connected to ground. In the monostable, the duty cycle can be varied by including a variable resistance between pins 2 & 3.The waveforms of the two stages are shown below.



Pulse of various widths can be obtained, by simply varying the variable resistance in the monostable circuit. The power circuit using the MOSFET is rigged up as shown in the figure. POWER CIRCUIT:

The PMDC motor is connected as shown. The output of the monostable is buffered and connected to the MOSFET between the gate and source as shown. PROCEDURE:

1. Rig up the control circuit stage by stage and check the outputs.

2. Connect the control circuit to the gate of the MOSFET after connecting the power circuit .

3. Vary the duty cycle and record the voltage across the motor in the DMM connected across the

motor as shown.

4. Plot a graph of duty cycle versus the voltage across the motor.



EXPT NO 11: SPEED CONTROL OF 1-PHASE INDUCTION MOTOR

USING AC VOLTAGE CONTROLLER.

AIM: To control the speed of a universal motor and a single-phase induction motor and to study the variation of the output voltage with the control voltage and to draw the graph of the same. APPARATUS REQUIRED: Two SCRs, one triggering card (both channels)I phase induction motor and patch cords. CIRCUIT DIAGRAM:

PROCEDURE:

1) The circuit is connected as shown in the figure, after ensuring that the devices are in good working condition. The triggering module for the above circuit is energized with a 10V dual supply and the triggering signals are observed on the CRO.

2) The triggering circuit is connected to the gates of the respective SCRs and the supply to the power circuit is given.

3) A moving 0-250V voltmeter is connected across the motor terminals and a DMM is connected across the pedestal voltage pot. The pedestal pot is slowly varied and the corresponding pedestal voltage and the voltage across the motor are noted down and tabulated as shown below: Sl No: Pedestal Voltage Motor Voltage



EXPT NO 11: SINGLE PHASE FULL BRIDGE INVERTER

AIM: To study single-phase IGBT base PWM inverter APPARATUS REQUIRED: single-phase Inverter module, 100ohm/5A resistive load, CRO and patch cords. CIRCUIT DIAGRAM:

PROCEDURE

1. Make the connections as given in the circuit diagram.

2. Connect DC supply from (0-30) V regulated power supply unit.

3. Connect resistive load 0–100 ohms 5 Amps Rheostat at load terminals (keep the sliding

switch in middle position).

4. Connect driver output signals to the Gate and Emitter of corresponding IGBTs.

5. Switch ON the DC supply and apply 20 Volts.

6. Switch ON the mains supply. The LCD display shows 1-ph PWM inverter with modulation

type and M- (modulation index) 00 and F-100 Hz and in OFF position.

7. Now M-00 Blinks. Press INC key to set the M.I. from 00- 100%.

6. Set the Modulation Index value in steps (keep the frequency as constant) and press the

Run/STOP button then measure the output voltage and tabulate it.

7. Set the frequency value in steps (keep the M.I value as constant) and press the Run/STOP

button then measure the output voltage and tabulate it.

NOTE: The SET key works only when it is in OFF position. This is to avoid change of Modulation

type when the power circuit is ON.

~~**~~**~~**~~





QUESTION BANK.

1. Obtain the static characteristics of the given SCR, clearly indicating the switching region.

Demonstrate that the gate current has no effect on the device after it is turned on. 2. Experimentally obtain the latching current of the given SCR. Also demonstrate that there will

be a drastic fall in the break-over voltage with a marginal increase in the gate current 3. Experimentally obtain the constants of the given MOSFET?

4. Obtain experimentally, the static characteristics of the given MOSFET and hence find its

constants. 5. Experimentally obtain the static characteristics of the given IGBT. 6. Obtain the characteristics of the given IGBT, clearly indicating the various regions of operation 7. Generate high frequency pulse using a UJT, relaxation oscillator. Using these pulses, trigger an

SCR operating off a sinusoidal supply. Show that the triggering circuit is synchronized with the power circuit from waveforms.

9. Rig-up a line synchronized UJT relaxation oscillator circuit to trigger an SCR in a HW rectifier

circuit. Measure the range of trigger/delay angles that can be obtained. 10. Rig up circuit for improved series inverter.. Form the load waveform, calculate the frequency

of oscillation. Also obtain the capacitor voltage waveform.. 11. Simulate a basic series inverter. From the load waveform calculate the frequency of oscillation.

Also obtain the capacitor voltage waveform . 12. Assemble a suitable circuit to control a stepper motor in both the directions. 13. Wire up circuit to demonstrate how it is possible to commutate a load carrying SCR by another

SCR. Obtain all the relevant waveforms and draw to scales and hence calculate the frequency of oscillation.

14. Simulate complementary commutated circuit to obtain relevant waveforms and calculate

frequency of oscillations. 15. Experimentally demonstrate the principal of auxiliary commutation. Draw all the relevant

waveforms to scale. Verify the frequency of oscillation obtained by measuring the commutating elements.



16. Simulate a circuit for an auxiliary commutation. Draw all the relevant waveforms to scale. Verify the frequency of oscillation obtained by measuring the commutating elements.

17. Show experimentally how turning on and SCR will automatically turn-off another conducting SCR. Record all the waveforms and hence obtain critical turn off time verify the value obtained by measuring the commutating capacitor.

18. Demonstrate the principal of complementary commutation. Draw all the relevant wave forms

to scale. Find the value of the commutating capacitor from the critical turn-off time. 16. Rig-up a simple triggering circuit to generate high frequency pulse, using digital IC’s. Show

the waveforms at various stages of the circuit. 17. Wire-up digital firing circuit and hence generate high frequency firing pulse. Using these pulses,

trigger an SCR. Draw the waveforms at all the stages to scale. 18. Control the speed of a PMDC motor using a suitable DC chopper circuit. Experimentally

demonstrate that the speed of the motor controlled is directly proportional to the duty cycle of the chopper.

19. Design and assemble a FWR circuit (using 2 SCRs) using the RC triggering principle. Obtain

and draw to scale the following waveforms. (i) Voltage across load and SCR for a resistive (R) load. (ii) Voltage across the load and SCR for an inductive load (R-L) load. Also for an R-L load determine from the waveforms, the triggering angle for conduction and discontinuous conduction.

20. Design a UJT firing circuit to generate triggering pulses of a frequency of 500 Hz to fire an

SCR in a HWR circuit. Obtain the range of triggering angles. Show all the relevant waveforms in the UJT firing circuit.

21. Rig up a circuit for capacitor commutated single phase parallel inverter feeding a resistive load

and obtain load waveform. 22. Control the speed of the given 1φ Induction motor using a suitable power circuit. Draw a graph

of the stator voltage against the control voltage. 23. Rig-up a single phase voltage controller circuit with its associated triggering circuit. Control

the speed of the given 1φ Induction motor from the converter in the open loop. Draw a graph of converter output versus the control voltage.

24. Simulate single phase bridge inverter circuit and obtain the relevant waveforms. *****



VIVA VOCE QUESTIONS.

1. What are the various types of thyristors?

2. What is a commutation circuit?

3. What is the difference between a thyristor and TRIAC?

4. What is the gating characteristics of a GTO?

5. What is a converter?

6. What is the principle of ac – dc conversion?

7. What is the principle of ac – ac conversion?

8. What is the principle of dc – dc conversion?

9. What is the principle of dc – ac conversion?

10. What are the steps involved in designing power electronic equipments?

11. What are the peripheral effects of power electronic equipments?

12. What are the differences in the gating characteristics of thyristors and transistors?

13. What are the differences in the gating characteristics of BJTs and MOSFETs?

14. What is the gating characteristics of an IGBT?

15. What are the differences between BJTs and MOSFETs?

16. Explain the V I characteristics of a thyristor and point out the various regions.

17. What is the OFF state of a thyristor?

18. What is the ON state of a thyristor?

19. What is the relevance of latching current of a thyristor?

20. What is the relevance of holding current of a thyristor?

21. Analyze the behavior of thyristor by using two transistor models.

22. What is the process of regeneration during the turn ON process of thyristor?



23. What is the process of turn OFF of a thyristor? Explain the dynamic turn OFF characteristics

of thyristors.

24. What are the necessary conditions to be satisfied for effective turn OFF of thyristor?

25. What are the components of turn ON time of thyristors?

26. With the help of a circuit diagram explain how a thyristor can be protected against di/dt.

27. Explain the design of a circuit which can be used to protect the thyristor against dv/dt.

28. What is a snubber circuit? Explain the design of a typical snubber circuit to protect against dv/dt.

29. What are the conditions to be satisfied to connect a set of thyristors in series?

30. What conditions must be satisfied to operate a set of thyristors in parallel?

31. What is the derating factor of series connected thyristors?

32. What is an UJT? Explain its static V I characteristics.

33. How can a UJT be designed to work as an oscillator?

34. What conditions must be satisfied to operate an UJT as an oscillator?

35. Why is an UJT considered to be an ideal triggering device?

36. What are the requirements of triggering a thyristor?

37. What is meant by hard driving the gate?

38. What is the intrinsic stand off ratio of an UJT?

39. What are the peak and valley point voltages of an UJT?

40. What are the two general types of commutation?

41. What is forced commutation? When is it required?

42. What are the types of forced commutation?

43. What is the difference between self commutation and natural commutation?

44. Explain with the help of a circuit the principle of self commutation?



45. What is meant by reversal time in a self commutated circuit?

46. Explain the principle of impulse commutation. Why is it called so?

47. Explain the principle of resonant pulse commutation. Why is it called so?

48. Explain the complementary commutation principle.

49. Why is commutation time a critical factor in choppers and inverters?

50. Why should the available reverse bias time be greater than the turn OFF time of a thyristor?

51. What is the purpose of connecting an anti-parallel diode across the main thyristor with or

without a series inductor?

52. What are the requirements of a commutating capacitor?

53. What is the ratio of peak resonant to load current for resonant pulse commutation that would minimize commutation losses?

54. How is the voltage of the commutating capacitor reversed in a commutation circuit?

55. What is line commutation?

56. What is a controlled rectifier?

57. What is delay angle control of converters?

58. What is a semi converter? Draw two semi converter circuits.

59. What is the function of a free wheeling diode? Does a semi converter require a free wheeling

diode?

60. What is a full converter circuit? Does this circuit require a free wheeling diode?

61. What is the principle of phase control?

62. What is the inversion mode of converter?

63. Why are harmonics present in converter circuits?

64. What is extinction angle of converters?

65. What are continuous and discontinuous current modes in converters? Why is discontinuous current mode not preferable?



66. How is the output voltage of a phase controlled converter varied?

67. Why is it preferable to have an inductor in a converter circuit?

68. What is the effect of line inductance in converter circuit?

69. What is overlap angle in line commutated circuits?

70. What is a commutation “notch” in a line commutated circuit?

71. Why is a fully controlled converter preferable over a half controlled (semi converter) from the

point of view of harmonics?

72. Does the input power factor of a converter depend on the load power factor?

73. In a fully controlled single phase converter, if one of the thyristor fails, what is the effect on the converter?

74. What are the advantages and disadvantages of on - off control?

75. What are the advantages and disadvantages of phase angle control?

76. What are the effects of load inductance on the performance of ac voltage controllers?

77. What is a unidirectional controller? What are its disadvantages?

78. What is a universal motor? Explain its principle of operation.

79. What is the principle of operation of a step down chopper?

80. What is pulse width modulation control of a chopper?

81. What is time ratio controller (TRC)?

82. What is the effect of load inductance on ripple current?

83. What are the performance parameters of a chopper?

84. What are the advantages and disadvantages of auxiliary commutation?

85. What is duty cycle of a chopper circuit?

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Documents

LABORATORY MANUAL - …powerelectronicsrvce.wikispaces.com/file/view/PELabManual2018.pdf/... · 2. Static characteristics of MOSFET and IGBT. 3. SCR turn-on circuit using synchronized