PSIM MANUAL for Students

Power Electronics Laboratory Manual for PSIM Experiments

1. Experiment 8:

Title: Simulation of single phase controlled converter with and without source inductance.

Objective: To study the supply voltage, output voltage and output current waveforms for a single phase controlled converter with and without source inductance.

Theory:

1) Single phase controlled converter without source inductance:

Figure below shows a fully controlled bridge rectifier, which uses four thyristors to control the average load voltage and the half-controlled bridge rectifier "semi converter rectifier"; which uses two thyristors and two diodes.

Thyristors T1 and T2 must be fired simultaneously during the positive half wave of the source voltage Vs to allow conduction of current. Alternatively, thyristors T3 and T4 must

be fired simultaneously during the negative half wave of the source voltage. To ensure simultaneous firing, thyristors T1 and T2 use the same firing signal.

2) Single phase controlled converter with source inductance:

Fig. 1 shows a single phase fully controlled converter with source inductance. For simplicity it has been assumed that the converter operates in the continuous conduction mode. Further, it has been assumed that the load current ripple is negligible and the load can be replaced by a dc current source the magnitude of which equals the average load current. Fig. 2 shows the corresponding waveforms. It is assumed that the thyristors T3 and T4 were

conducting at t = 0. T1 and T2 are fired at ωt = α. If there were no source inductance T3 and

T4 would have commutated as soon as T1 and T2 are turned ON. The input current polarity

would have changed instantaneously. However, if a source inductance is present the commutation and change of input current polarity cannot be instantaneous. Therefore, when T1 and T2 are turned ON T3 T4 does not commutate immediately. Instead, for some interval

all four thyristors continue to conduct as shown in Fig. 2. This interval is called “overlap” interval.

During this period the load current freewheels through the thyristors and the output voltage is clamped to zero. On the other hand, the input current starts changing polarity as the current through T1 and T2 increases and T3 T4 current decreases. At the end of the overlap

interval the current through T3 and T4 becomes zero and they commutate, T1 and T2 starts

conducting the full load current. The same process repeats during commutation from T1 T2 to T3T4 at ωt = π + α.

Fig 1: Single phase controlled converter with source inductance circuit diagram

From Fig. 2 it is clear that, commutation overlap not only reduces average output dc voltage but also reduces the extinction angle γ which may cause commutation failure in the inverting mode of operation if α is very close to 180º. In the following analysis an expression of the overlap angle “μ” will be determined.

The required formulas are:

Fig 2: Single phase controlled converter with source inductance waveforms

Circuit Design:

Single phase controlled converter with and without source inductance Circuit parameters.

Block Name Library Value

Sinusoidal Voltage Source Elements/Sources/Voltage/Sine Peak Amplitude=230VFrequency=50Hz

Thyristor Elements/Power/Switches/Thyristor

Source Inductance(Ls) Elements/Power/RLC Branches/Inductor

Ls = 0.01H

R,L Elements/Power/RLC Branches/RL R=23 Ω;L=0.1 H

Gating Block(G1,G2,G5,G7)

Elements/Power/Switches/Gating Block

Frequency=50HzNo. of Points=2

Switching Points=30 180

Gating Block(G3,G4,G6,G8)

Elements/Power/Switches/Gating Block



Voltage Probe Elements/Other/Probes/Voltage Probe

Current Probe Elements/Other/Probes/Current Probe

Voltage Probe (between two nodes)

Elements/Other/Probes/Voltage Probe(node-to-node)

Ground Elements/Sources/Ground

Simulation Control Simulate/Simulation Control Total Time=0.06

Figure 1: Single phase controlled converter without and with source inductance

Apparatus Required:

a. PCb. Windows 95/98/NT/XP/7c. PSIM

Conclusion/Comments: The single phase controlled converter with and without source inductance has been simulated and the waveforms has been studied.

2. Experiment 9:

Title: Simulation of step up and step down chopper using MOSFET, GTO & IGBT.

Objective: To study the Gating Pulse, Inductor Current, Output Voltage and Output Current for step up and step down chopper using MOSFET, GTO & IGBT.

Theory:

Dc chopper primarily finds its application in dc drives. The output voltage of dc choppers is controlled by adjusting the on time of a switch, which in turn adjusts the width of a voltage pulse at the output. This is the so-called pulse width modulation (PWM) control. The dc choppers with additional filtering components form PWM dc-dc converters. Four basic dc-dc converter topologies are known in general buck, boost, buck-boost, and Cuk converters.

a) Buck converter: The step-down dc-dc converter is commonly known as a buck converter. It consists of dc input voltage source VS, a controlled switch S, diode D, filter inductor L, filter capacitor C, and load resistance R.

1) Duty Cycle, k=V OV S

2) Critical Values of Inductance and capacitance,

LC=(1−k )∗R

2∗f

CC= 1−k

16∗L∗f 2

b) Boost converter: The step-up dc-dc converter is commonly known as a boost converter. It consists of dc input voltage source VS, a controlled switch S, diode D, filter inductor L, filter capacitor C, and load resistance R.

1) Duty Cycle, k=1−

V SVO

2) Critical Values of Inductance and capacitance,

LC=(1−k )∗k∗R

2∗f

CC= k

2∗f∗R

Through the simulation of the buck and boost converters with the calculated values from the above formula we have studied the operation of the step up and step down converters.

Circuit Design:

a) Step-down Converter Parameters


DC Voltage Source Elements/Sources/Voltage/DC 12V

MOSFET/GTO/IGBT Elements/Power/Switches/MOSFET or GTO or IGBT

Diode Elements/Power/Switches/Diode

R,L,C Elements/Power/RLC Branches/Resistor,Inductor,capacitor

R=500 Ω;L=0.00583 H ; C=0.0000004 F

Gating Block Elements/Power/Switches/Gating Block

Frequency=25000 HzNo. of Points=2






Figure 1: Step-down converter (buck converter) with MOSFET and GTO.

b) Step Up Converter Parameters


DC Voltage Source Elements/Sources/Voltage/DC 5V

MOSFET/GTO/IGBT Elements/Power/Switches/MOSFET or GTO or IGBT


R,L,C Elements/Power/RLC Branches/Resistor,Inductor,capacitor

R=30 Ω;L=0.000133 H ; C=0.00000044 F

Gating Block Elements/Power/Switches/Gating Block

Frequency=25000 Hz

No. of Points=2Switching Points=0 240





Figure 2: Step-up converter (boost converter) with MOSFET and GTO.

Apparatus Required:

d. PCe. Windows 95/98/NT/XP/7f. PSIM

Conclusion/Comments: The step up and step down chopper using MOSFET & GTO has been simulated and the Gating Pulse, Inductor Current, Output Voltage and Output Current have been studied.

3. Experiment 10:

Title: Simulation of single phase half controlled symmetrical and asymmetrical bridge converters.

Objective: To study the supply voltage, output voltage and output current waveforms for single phase half controlled symmetrical and asymmetrical bridge converters.

Theory:

During the positive half-cycle, from α to π, a triggering pulse is applied to the forward biased thyristor T1. It turns ON and thyristor T2 turns OFF by line commutation. Therefore load current flows from T1 and D1. During the negative half-cycle, at the instant (π+α) to 2π, a triggering pulse is applied to the forward biased thyristor T2. It turns ON and thyristor T1 turns OFF by line commutation. Therefore load current flows from T2 and D2. Here we see that the conduction period of the thyristors and the diodes are equal, therefore the circuit is called symmetrical configuration.

During the postive half cycle of the ac supply, T1 and D1 are forward biased. T1 is turned ON at a firing angle α. Current flows through the path L—T1—A—L—R—B—D1—N . Hence T1 and D1 conduct from α to π. Similarly, T2 and D2 conduct from (π+α) to 2π in negative half cycle of the ac supply. The freewheeling action of the diodes D1 and D2 from 0 to α and from π to (π+α) in each cycle. In this converter configuration the conduction period of thyristors and diodes are unequal. Hence, this circuit configuration is known as the asymmetrical configuration.

Fig i) Symmetrical Configuration waveforms waveformsswaveforms.

Fig ii) Asymmetrical Configurations waveforms

Circuit Design:

Simulation of single phase half controlled symmetrical and asymmetrical bridge converters.


Sinusoidal Voltage Source Elements/Sources/Voltage/Sine Peak Amplitude=230VFrequency=50Hz



R Elements/Power/RLC Branches/Resistor

R=10 Ω;

Gating Block(G1,G3) Elements/Power/Switches/Gating Block












Figure 1: Single phase half controlled symmetrical and asymmetrical bridge converters.

Apparatus Required:


Conclusion/Comments: The single phase half controlled symmetrical and asymmetrical bridge converters have been simulated and the supply voltage, output voltage and output current waveforms are plotted.

4. Experiment 11:

Title: Simulation of PWM bridge inverter using MOSFET with R-L load.

Objective: To study the PWM generation, supply voltage and output voltage waveform for a 3-phase PWM bridge inverter using MOSFET with R-L load.

Theory:Pulse width modulated (PWM) inverters are among the most used power-electronic

circuits in practical applications. These inverters are capable of producing ac voltages of variable magnitude as well as variable frequency. The quality of output voltage can also be greatly enhanced, when compared with those of square wave inverters discussed in. The PWM inverters are very commonly used in adjustable speed ac motor drive loads where one needs to feed the motor with variable voltage, variable frequency supply. For wide variation in drive speed, the frequency of the applied ac voltage needs to be varied over a wide range. The applied voltage also needs to vary almost linearly with the frequency. PWM inverters can be of single phase as well as three phase types. Their principle of operation remains similar and hence in this lesson the emphasis has been put on the more general, 3-phase type PWM inverter. There are several different PWM techniques, differing in their methods of implementation. However in all these techniques the aim is to generate an output voltage, which after some filtering, would result in a good quality sinusoidal voltage waveform of desired fundamental frequency and magnitude.

Unlike in square wave inverters the switches of PWM inverters are turned on and off at significantly higher frequencies than the fundamental frequency of the output voltage waveform. The typical pole voltage waveform of a PWM inverter is shown in figure below over one cycle of output voltage. In a three-phase inverter the other two pole voltages have identical shapes but they are displaced in time by one third of an output cycle. Compared to the square pole voltage waveform, the pole voltage waveform of the PWM inverter changes polarity several times during each half cycle. The time instances at which the voltage polarities reverse have been referred here as notch angles. It may be noted that the instantaneous magnitude of pole voltage waveform remains fixed at half the input dc voltage (Edc). When upper switch (SU), connected to the positive dc bus is on, the pole voltage is +

0.5 Edc and when the lower switch (SL), connected to the negative dc bus, is on the

instantaneous pole voltage is -0.5 Edc.

Fig 1: Typical Pole voltage waveform of a PWM inverter.

The switching transition time has been neglected in accordance with the assumption of ideal switches. It is to be remembered that in voltage source inverters, meant to feed an inductive type load, the upper and lower switches of the inverter pole conduct in a complementary manner. That is, when upper switch is on the lower is off and vice-versa. Both upper and lower switches should not remain on simultaneously as this will cause short circuit across the dc bus. On the other hand one of these two switches in each pole (leg) must always conduct to provide continuity of current through inductive loads. A sudden disruption in inductive load current will cause a large voltage spike that may damage the inverter circuit and the load.

Various PWM control methods are: 1. Single-pulse width modulation (SPWM)2. Multiple-pulse width modulation (MPWM)3. Sinusoidal-pulse width modulation (sin PWM)4. Space Vector-pulse width modulation (SVPWM)

Circuit Design:

Simulation of PWM bridge inverter using MOSFET with R-L load.


DC Voltage Source Elements/Sources/Voltage/DC Vdc,Amplitude=100V VDC1,Amplitude=0M,Amplitude=0.92

Three phase VSI Elements/Power/Switches/VSI3(MOSFET)

PWM Controller Elements/Others/Switch Controllers/PWM pattern Controller

Comparator Elements/Control/Comparator

Sinusoidal voltage source

Elements/Sources/Voltage/Sine Peak Amplitude=100VFrequency=50 Hz

Step Voltage Source (Enable)

Elements/Sources/Voltage/Step Vstep=1

Three phase RL load Elements/Power/RLC Branches/RL3 R=1 Ω;L=0.1H






Figure 1: Three phase of PWM bridge inverter using MOSFET with R-L load.

Apparatus Required:


Conclusion/Comments: A 3-phase PWM bridge inverter using MOSFET with R-L load has been simulated and the PWM generation, supply voltage and output voltage waveform has been plotted.

5. Experiment 12:

Title: Simulation of three phase AC regulator (α = 1200)

Objective: To study the supply voltage, output voltage waveforms for three phase AC regulator.

Theory:

The circuit of a three-phase, delta-connected ac regulator (termed as ac to ac voltage converter) with balanced resistive load is shown in Fig i. It may be noted that the resistance connected in all three phases are equal. Two thyristors connected back to back are used per phase, thus needing a total of six thyristors. As stated earlier, the numbering scheme may be

noted. Since the phase current in a balanced three-phase system is only

1√3 of the line

current, the current rating of the thyristors would be lower than that if the thyristors are placed in the line.

Fig i) Three Phase Delta connected AC Voltage regulator

Assuming the line voltage EAB as the reference, the instantaneous input line voltages are,

eAB = √2Es sin ωt ; eBC = √2Es sin (ωt-120ᵒ) ; eCA = √2Es sin (ωt-240ᵒ) .

It may be noted that is the rms value of the line voltage in this case. The waveforms of the input line voltages, phase and line currents, and the thyristor gating signals, for α = 120 ᵒ are shown below.

Fig ii) Waveforms for three Phase Delta connected AC Voltage regulator

Circuit Design:

Simulation of three phase AC regulator (α = 1200)


Sinusoidal Voltage Source

Elements/Sources/Voltage/Sine Peak Amplitude=110VFrequency=50Hz


R Elements/Power/RLC Branches/R R=11 Ω



Switching Points(G1)=120 210

Switching Points(G4)= 0 30 300 360







Switching Points(G2)=180 270Switching Points(G5)=0 90







Figure 1: Three phase AC Regulator

Apparatus Required:

g. PCh. Windows 95/98/NT/XP/7i. PSIM

Conclusion/Comments: The three phase AC regulator has been simulated and the supply voltage, output current and voltage waveforms has been studied.

PSIM MANUAL for Students

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