CHAPTER 3 DYNAMIC VOLTAGE RESTORER - …shodhganga.inflibnet.ac.in/bitstream/10603/9826/8/08_chapter 3.pdf · shows the FFT analysis of the closed loop DVR system for sag ... power

55

CHAPTER 3

DYNAMIC VOLTAGE RESTORER

3.1 GENERAL

The DVR injects voltage in series with the line to compensate the

voltage sag. In this chapter, a single phase DVR with an H bridge inverter, a

single phase DVR with ZSI and three phase DVR systems are modeled using

MATLAB simulink.

3.2 MODEL OF SINGLE PHASE DVR SYSTEM

The simulink models of closed loop controlled DVR systems with

an H bridge inverter and Z source inverter are developed and the simulation

results are presented.

3.2.1 Model of the Closed Loop Controlled DVR System with an H

Bridge Inverter

The simulink model of the closed loop controlled DVR with an H

bridge inverter using a PI controller in a simple power system to protect a

sensitive load in a large distribution system, is shown in Figure 3.1. The block

diagram of the control system is shown in Figure 3.2. A Proportional Integral

(PI) controller is a feedback controller, which drives the plant to be controlled

with a weighted sum of the error (difference between the output and desired

set point), and the integral of that value. The integral term in a PI controller

causes the steady-state error to be zero for a triangular input.

56

v+-

v+-

v+-

Out1

in1

in2

Subsystem2

In1

Conn1

Conn2

Subsystem1

7 ohm

70mH

5ohm

18mH

12

200V 10 ohm

100mH

0.3 to 0.7

0.3 to 0.7

Figure 3.1 Closed loop controlled DVR with an H bridge inverter

The inverter is a four-pulse switch controlled bridge. The currents

follow different directions at outputs depending on the control scheme,

eventually supplying AC output power to the critical load during power

disturbances. The control of this bridge lies in the control of the switch firing

angles. The time to open and close the gates will be determined by the control

system. To model a DVR protecting a sensitive load against voltage sag /

swell, a simple method of using the measurement of a single phase RMS

output voltage for controlling signals can be applied. The amplitude

modulation is then used. In addition to providing appropriate firing angles to

switches, a switching control using SPWM technique is employed.

57

Figure 3.2 Block diagram of the control system

The subsystem2 of the closed loop DVR is shown in Figure 3.4. It

consists of a full bridge inverter with a filter. Subsystem1 consists of a

rectifier with a capacitor filter, as shown in Figure 3.3. The output of the load

voltage is rectified using a rectifier circuit. The rectifier output voltage is

compared with the reference voltage. To correct the error between a measured

process variable and a desired set point, the PI controller is used. To decrease

the error signal, it is compared with a triangular signal to produce sine PWM

pulses. The Pulse Width Modulation technique is used to control the H bridge

inverter. Varying the width of the pulses controls the output voltage. The

SPWM control technique is used to reduce the harmonic content at the output

voltage.

Control

signals toIGBT

58

2

Conn2

1

Conn1

g 12

S5

g 12

S4

g 12

S2

g 12

S1

>=

AND

AND

DC Voltage Source

1000

1

In1

Figure 3.3 Subsystem 1 of the closed loop DVR with an H bridge inverter

1

Out1

2

in2

1

in1v

+-

Sine Wave

1

s9.6

0.96

0.5|u|

Abs

1kohm

Figure 3.4 Subsystem 2 of the closed loop DVR with an H bridge inverter

Figure 3.5 shows the simulation result for the closed loop DVR

system response to the voltage sag. Initially, the system was subjected to a sag

of 22.7 % magnitude and 0.4s duration. The first graph shows the input

supply voltage. The second graph indicates the injected voltage and the third

graph shows the compensated load voltage after voltage injection. The driving

59

pulses of the inverter switches are shown in Figure 3.6(a). Figure 3.6(b)

shows the FFT analysis of the closed loop DVR system for sag condition. The

THD value is found to be 0.08 %.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-200

0

200

volt

a.Uncompensated voltage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-200

0

200

volt

b. Injected voltage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-200

0

200

Time(sec)

volt

c. Compensated voltage

0.4 0.405 0.41 0.415 0.42 0.425 0.43 0.435 0.440

0.5

1

1.5

2

volt

a. Gate pulse 1,2

0.4 0.405 0.41 0.415 0.42 0.425 0.43 0.435 0.440

0.5

1

1.5

2

Time(sec)

volt

b. Gate pulse 3,4

Figure 3.5 Response of the DVR to a voltage sag

a. Uncompensated voltage (v)

b. Injected voltage (v)

c. Compensated volt (v)

Figure 3.6(a) Driving pulses of inverter switches

a. Driving pulse for switch1,2

b. Driving pulse for switch3,4

60

Figure 3.6(b) FFT analysis of the H inverter based DVR for sag

Figure 3.7 shows the response of the closed loop DVR system to

the voltage swell. The system was subjected to a swell of 29.2 % magnitude

and 0.4s duration. Simulation is done and the transient performance at the

swell front and recovery was observed. The first graph shows the swell in

voltage. The second graph indicates the injected voltage and the third graph

shows the compensated load voltage after voltage injection. From Figure 3.7,

it is seen that the DVR has successfully compensated the swell. Figure 3.8

shows the FFT analysis of the closed loop DVR system for swell condition.

The THD value is found to be 0.12 %. From reference Paisan Boonchiam and

Nadarajah Mithulanathan (2006), voltage sag is defined as a sudden increase

of supply voltage down 90 % to 10 % in RMS voltage at the fundamental

frequency with duration from 10 ms to 1 min and voltage swell is defined as a

sudden increase of supply voltage up 110 % to 180 % in RMS voltage at the

fundamental frequency with duration from 10 ms to 1 min. This simulation

results for sag and swell are in close agreement with the results of Chellai et

al (2008) and Paisan Boonchiam (2006).

61

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-200

0

200

vo

lta.uncompensated voltage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-200

0

200

vo

lt

b. Injected voltage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

-200

0

200

Time(sec)

vo

lt

c. Compensated voltage

Figure 3.8 FFT analysis of the H inverter based DVR for swell

Figure 3.7 Response of the DVR to a voltage swell




62

The circuits of model of the power system network and model of

power system network during sag are shown in Figures 3.9(a) and 3.9(b)

respectively. The appropriate values of impedance, current and line drop are

calculated. Using these values voltage sag and swell are calculated.

5ohm

23mH

200V 10 ohm

100mH

Figure 3.9(a) Model of the power system network

Z = (5+j7.22)+(10+j31.4) = 41.33 68.7

I = V/Z = 200 /41.33 68.7 = 4.82 -68.7A

Voltage drop IZ = 159 72V

7 ohm

70mH

5ohm

23mH

200V 10 ohm

100mH

Figure 3.9(b) Model of the power system network during sag

ZT = (5+j7.22) x [(10+j31.4) (7+j21.98) /(17+j43.38)] = 22.1 65.1

IT = V/ZT = 9.09 -65.1A

Voltage drop IL1 x ZL1=123 72 V

Voltage sag = 159 – 123 / 159 = 22.6%

Voltage swell = 123 – 159 / 123 = 29.2%

63

3.2.2 Model of the Closed Loop Controlled DVR System with the Z

Source Inverter

A typical Closed Loop Controlled DVR with the voltage type Z

Source Inverter (ZSI) in a simple power system to protect a sensitive load in a

large distribution system is presented in Figure 3.10.

v+-

v+-

v+-

In1

Out1 Conn1

Conn2

Subsystem1

In1

Ou

t1

Ou

t2

Ou

t3

Ou

t4

Co

nn

1

Co

nn

2

Subsystem 2

7 ohm

70mH

5ohm

23mH

12

30/100

70/100

240V

10 ohm

100mH

0.1ohm

0.001mH

Figure 3.10 Closed loop controlled DVR with an Z source inverter

Subsystem1 contains the rectifier and the inverter as shown in

Figure 3.11. The multiple Pulse Width Modulation technique was used to

control the Z source inverter. Subsystem2 consists of PWM pulse generation

blocks as shown in Figure 3.12.

64

1

Out1

2 Conn2

1

Conn1v

+-

1

s9.6

0.96

k0.9

1

In1

Figure 3.11 Subsystem 1 of DVR with an Z source inverter

4 Out43 Out3

2 Out21 Out1

2

Conn2

1

Conn1

gm

ds

gm

ds

gm

ds

gm

ds

OR

AND

ANDOR

AND

AND

i+

-

Current Measurement

500 ohms1

405mH

1uf 1k

1e-4

1e-3

100v/50hz

1

In1

Figure 3.12 Subsystem 2 of DVR with an Z source inverter

The simulation is done using MATLAB and the results are

presented here. Initially, the system was subjected to a sag of 25 % magnitude

and 0.4s duration. Simulation is done and the transient performance at the sag

front and recovery was observed. Figure 3.13 shows the response of the

closed loop DVR system to voltage sag. The first graph shows the input

supply voltage. The second graph indicates the injected voltage and the third

65

graph shows the compensated load voltage after voltage injection. Figure 3.14

shows the FFT analysis of the closed loop DVR system for swell condition.

The THD value is found to be 11.2 %. The driving pulses of the inverter

switches are shown in Figure 3.15.

Figure 3.14 FFT analysis of the ZSI based DVR for sag

Figure 3.13 Response of ZSI based DVR to voltage sag




66

0.32 0.325 0.33 0.335 0.34 0.345 0.35 0.355 0.360

1

2volt

a.gate pulse s1

0.32 0.325 0.33 0.335 0.34 0.345 0.35 0.355 0.360

1

2

volt

b.gate pulse s3

0.32 0.325 0.33 0.335 0.34 0.345 0.35 0.355 0.360

1

2

volt

c.gate pulse s2

0.32 0.325 0.33 0.335 0.34 0.345 0.35 0.355 0.360

1

2

Time(sec)

vo

lt

d.gate pulse s4

The system was subjected to a swell of 30 % magnitude and 0.4s

duration. Simulation is done and the transient performance at the swell front

and recovery was observed. Figure 3.16 shows the response of the closed loop

DVR system to the voltage swell. The first graph shows the sag in voltage.

The second graph indicates the injected voltage and the third graph shows the

compensated load voltage after voltage injection. This simulation results for

voltage sag and swell are in close agreement with the results of Mahinda

Vilathgamuwa et al (2006).

Figure 3.15 Driving pulses of inverter switches

a. Driving pulse for switch 1,2

b. Driving pulse for switch 3,4

67

Figure 3.17 shows the FFT analysis of the closed loop DVR system

with an Z source inverter. The Total Harmonic Distortion (THD) value is

9.57%.

Figure 3.17 FFT analysis of the ZSI based DVR

Figure 3.16 Response of the ZSI based DVR to voltage swell



c. Compensated voltage (v)

68

3.3 MODEL OF THE THREE PHASE DVR SYSTEM WITH THE

H BRIDGE INVERTER

The dqo transformation or Park’s transformation is used to control

the DVR. The detection is carried out in each of the three phases. The control

scheme for the proposed system is based on the comparison of a voltage

reference and the measured terminal voltage (Va, Vb, Vc). Simulation results

are obtained with a 10kVA, 240V system to allow the evaluation of the

proposed methodologies. Table 3.1 shows the parameters used for simulation

studies. The parameters are selected from the reference Rosli Omar and

Nasrudin Abd Rahim (2008).

Table 3.1 Parameters of the three phase DVR

Supply voltage 240V

Source Impedance (0.1+j3.142*e-4)

Line impedance (for 100km) (1.6+j0.34)

Series transformer turns ratio 1:1

Injection transformer ratio 1:1

DC voltage 240V

Fixed Load resistance 40

Fixed Load inductance 60mH

Filter inductance 10mH

Filter capacitance 0.0177µF

Line frequency 50Hz

Carrier frequency 12003Hz

3.3.1 Model of the Three Phase DVR System with the Sinusoidal

PWM Technique

Figure 3.18 shows the closed loop controlled three phase DVR with

the Sinusoidal PWM (SPWM) technique using the dqo algorithm. Once a

voltage sag is detected, the error between the measured and reference values

is converted from the dq-frame to the abc-frame. This is used to trigger the

inverter switches and the required voltage is fed to the injection transformer

from the inverter. The transformer is connected in series with the main line.

69Figure 3.18 Closed loop controlled three phase DVR with the SPWM technique using the dqo algorithm

70

The SPWM Inverter model and filter circuit are shown in

Figures 3.19 and 3.20 respectively.

Figure 3.19 Model of the SPWM inverter

Figure 3.20 Filter circuit of the SPWM inverter

71

Figure 3.21 shows the modulation sine wave for the three phases of

the sine PWM inverter. The dqo to abc frame transformation results in the

waveform as shown below.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-200

0

200

400

vo

lt

Va

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-200

0

200

400

vo

lt

Vb

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-200

0

200

400

Time(sec)

volt

Vc

Figure 3.22 shows the filter output of the inverter using the sinusoidal

PWM. The quasi square wave output of the inverter given to the LC filter

results in a sine wave. The DVR injects the required voltage during the sag

period.

Figure 3.21 Modulation wave for the SPWM inverter

a. Phase a voltage

b. Phase b voltage

c. Phase c voltage

72

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-100

0

100

volt

Va

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-100

0

100

volt

Vb

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-100

0

100

Time(sec)

volt

Vc

Figure 3.23 shows 28.12 % voltage sag on the load side using

SPWM technique. Figure 3.24 shows the simulation results of the DVR

response to the voltage sag. Graph 1 indicates the voltage to be injected and

graph 2 indicates the compensated voltage on the load side using the SPWM

inverter. The DVR injects the required voltage during the sag period.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-300

-200

-100

0

100

200

300

400

Time(sec)

volt

Figure 3.23 Voltage sag using SPWM

Figure 3.22 Filtered output of the inverter using the sinusoidal PWM

a. Phase a voltage

b. Phase b voltage

c. Phase c voltage

73

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-200

0

200

400

volt

a. Injected voltage

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-200

0

200

400

Time(sec)

volt

b. Compensated voltage

3.3.2 Model of the Three Phase DVR System with the Space Vector

Modulation Technique

The proposed DVR circuit with the Space Vector PWM is shown in

Figure 3.25. Here, the error voltage in the dq-frame is used to calculate the

resultant reference voltage and angle of the space vector eight sector

framework. Angle is used to obtain the useful sectors, which are utilized to

calculate the switching pulses. At any instant, the combination of the

upper/lower switch signals will give an ‘M’ wave, which is compared with a

ramp signal to give gate pulses to the switches in the converter.

Figure 3.24 Response of the DVR to the voltage sag using the SPWM

technique

a. Injected voltage (v)

b. Compensated voltage (v)

74Figure 3.25 Closed loop controlled three phase DVR using the SVPWM technique

75

The switching pulse calculator for the Space Vector PWM is shown

in Figure 3.26. T1, T2 and T0 are the switching times for the voltage vectors at

any given time.

The switching pulse generator for the Space Vector PWM is shown

in Figure 3.27. The switching times thus obtained from the switching pulse

calculator are used to generate the switching pulses for the upper/lower three

switches. The pulse time for the switches in each sector is calculated from

Table 2.2. Figure 3.28 shows the inverter and filter circuit of the SVPWM

technique.

Figure 3.26 Switching pulse calculator for the SVPWM technique

Figure 3.27 Switching pulse generator for the SVPWM technique

76

Time (sec)

Figure 3.28 SVPWM inverter and filter circuit

Figure 3.29 shows the error voltage in the dq frame. This error

voltage is used for calculating the switching times.

Figure 3.29 Error voltage Vd, Vq, Vo

a. Voltage Vd

b. Voltage Vq

c. Voltage Vo

Volt

age

(v)

a

b

c

77

bAlp

ha

(deg

ree)

a

Time (sec)

Volt

age

(v)

Time (sec)

Figure 3.30 shows the waveform of alpha. Alpha is the deviation

between the resultant and the reference axis Vd. It has a maximum span of 60º

in each sector. The output of alpha ranges from -180º to +180º. In order to

obtain the six sectors using alpha for every 60º, alpha is shifted to the range 0

to 360º.

Figure 3.31 shows the division of the six useful sectors in the

SVPWM. Alpha is used for obtaining the six sectors through a MATLAB

function.

Figure 3.31 Sector division

Figure 3.30 Waveform of alpha

a. Alpha from -180 to 180 degrees

b. Alpha from 0 to 360 degrees

78

The output of the switching pulse generator is an ‘M’ shaped wave,

also called the modulation signal, which is compared with a triangular wave

to generate triggering pulses for the switches. Figure 3.32 shows the

modulation wave or ‘M’ shaped wave. Figure 3.33 shows the SVPWM

inverter output with filter. The quasi square waveform is filtered and the

sinusoidal output is fed through the injection transformer.

Figure 3.32 Modulation wave

a. Phase a

b. Phase b

c. Phase c

Figure 3.33 Filtered output of the SVPWM inverter

a. Phase a

b. Phase b

c. Phase c

Volt

age

a

b

c

Vo

ltag

e

a

b

c

Time (Sec)

Time (Sec)

79

Figure 3.34 shows 28.12% voltage sag initiated at 300ms, and it is

kept until 800ms, with a total voltage sag duration of 500ms. Figure 3.35 (a)

and (b) shows the voltage injected by the DVR and the compensated load

voltage respectively. As a result of the DVR, the load voltage is kept at the

same value throughout the simulation, including the voltage sag period. The

THD of the SVPWM system is found to be 6.54%.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-300

-200

-100

0

100

200

300

400uncompensated voltage(v)

Time (sec)

volt

Figure 3.34 Voltage sag of the DVR with the SVPWM technique

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-200

0

200

400

volt

a. Injected voltage(v)

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-400

-200

0

200

400

Time (sec)

volt

b. Compensated voltage(v)

Figure 3.35 Response of the DVR to a voltage sag using the

SVPWM technique

a. Injected voltage

b. Compensated voltage

80

The total harmonic distortion (THD) of a signal is a measurement

of the harmonic distortion present, and is defined as the ratio of the sum of the

powers of all harmonic components to the power of the fundamental

frequency. A common use of the Fourier transform is to find the frequency

components of a signal buried in a noisy time domain signal. It is difficult to

identify the frequency components by looking at the original signal.

Converting to the frequency domain, the discrete Fourier transform of the

noisy signal is found by taking the fast Fourier transform (FFT). Figure 3.36

shows the FFT analysis of the SPWM model. The total harmonic distortion of

the SPWM model is 7.07%. Figure.3.37 shows the FFT analysis of the

SVPWM model. The THD of the SVPWM systsem is found to be 6.54%.

Figure 3.36 FFT analysis of the DVR with the SPWM model

81

Figure 3.37 FFT analysis of the DVR with the SVPWM model

3.4 HARDWARE IMPLEMENTATION OF THE DVR

Experimental set up was realized using digital signal processor by

bingsen Wang etal (2006). In the present work, a laboratory model of

embedded controlled ZSI based DVR is implemented. An inverter using

MOSFET as the switching device with X shaped impedance is used as a Z

source, which forms the heart of the DVR. The DC input to the inverter is

provided using a rectifier. The rectifier is provided with a 12V DC supply. A

capacitor is connected at the output to reduce the ripple. The MOSFET

switches of the inverter are driven by a driver circuit which consists of a

programmed microcontroller, a buffer, an optocoupler and a 12 V supply. The

microcontroller is programmed to drive the MOSFETs at pre-determined

intervals. The outputs of the microcontroller are applied to the gate terminals

of the MOSFETs through a buffer.

82

3.4.1 Control circuit

The control circuit comprises of:

Microcontroller circuit

Driver circuit

Inverter circuit

3.4.1.1 Microcontroller Circuit

The gating pulses for the Metal Oxide Semiconductor Field Effect

Transistors (MOSFET) are generated by the AT89C2051 microcontroller. It

has a central processing unit in addition to a fixed amount of on-chip read

access memory, read only memory and a number of input/ output ports that

makes it ideal for many applications in which cost and space are critical. It is

a microcontroller with 128 bytes of read access memory, 2K bytes of on-chip

read only memory, 15 input / output lines, two 16- bit timers/counters, a full

duplex serial port, an on-chip oscillator and a clock circuitry. It is a powerful

controller which provides a highly flexible and cost-effective solution to

many embedded control applications.

3.4.1.2 Driver circuit

Figure 3.38(a) shows the driver circuit diagram. The 6N136 IC is

used as the driver for the MOSFET switches. The opto-coupler 6N136 IC

consists of a photo diode connected between the pins 2 and 3 internally. The

output from the pulse generator circuit is given to the pin 3 through a BJT.

The pin 2 is connected to the DC supply of 5V through the pull-up resistance

of 100 . The photo diode emits light according to the input given in the pin 3.

The light is detected by the photo transistor which acts as a photo detector.

The resistors connected to the output side of the IC are used to bias the

transistor. At pin 6 the output wave from is obtained with the optical isolation.

83

The output of the buffer is then given to amplifier circuits which controls the

turn ON and turn OFF time of the MOSFET. Thus the output of the MOSFET

driver circuit is exactly same as its input with optical isolation. The pulse

generated by the microcontroller is given to the driver circuit. The amplified

pulses from the driver circuit are given to the MOSFET switches. Z-source

inverter gives the boosted output voltage.

Figure 3.38(a) Driver circuit

The design parameters for the power supply circuit and crystal

oscillator circuit as shown in Figure 3.38(b) and 3.38(c) are given below:

Figure 3.38(b) Power supply ciruit

R= (V-VD) / I = (5 - 0.7) / 0.004 = 1 k

84

Figure 3.38(c) Crystal oscillator circuit

1f

2 LC

Assume C = 16.5pF

L = 15 mH

C = C’/2

C’=2 * C = 33pF

3.4.2 Experimental Verification

A VSI system using MOSFET as the switching device is used as a

voltage source, which forms the heart of the DVR. The hardware

implemented circuit for ZSI based DVR is shown in Figure 3.39. The

MOSFET switches of the inverter are driven by a driver circuit which consists

of a programmed microcontroller, a buffer, an optocoupler and a 12 V supply.

The gating pulses for the MOSFETs are generated by the AT89C2051

microcontroller. The pulse generated by the microcontroller is amplified using

the pulse amplifier 6N136 IC. The microcontroller is programmed to drive the

MOSFETs at pre-determined intervals. The output pulses of the

microcontroller are applied to the gate terminals of the MOSFETs through a

buffer. The top view of the hardware circuit is shown in Figure 3.40.

85

Figure 3.39 Control and power circuits for DVR

86

Figure 3.40 Top view of the hardware

3.4.2.1 Multiple PWM Technique

The flow chart for multiple or equal pulse generation is shown in

Figure 3.41. Flow chart for delay routine of multiple PWM technique is

shown in Figure 3.42.

87

Figure 3.41 Flow chart for main routine of multiple PWM technique

START

SET PULSE FOR S1 & S2

SET COUNTER = 20

CALL DELAY

COMPLEMENT PULSES FOR S1 & S2

DECREMENT COUNTER

IF COUNTER 0

SET COUNTER = 20

CALL DELAY

COMPLEMENT PULSES FOR S4 & S2

DECREMENT COUNTER

SET PULSE FOR S3 & S4

IF COUNTER 0

No

No Yes

Yes

88

Figure 3.42 Flow chart for delay routine of multiple PWM technique

Oscillograms of the experimental results using multiple PWM

technique are obtained. Multiple pulses with 5 volt magnitude is obtained

at the output port P2.1 to 2.4 of the microcontroller and they are shown in

Figure 3.43. The output of the inverter is shown in Figure 3.44. Figure 3.45

shows the uncompensated voltage. The compensated voltage is shown in

Figure 3.46. From Figures 3.13, 3.45 and 3.46, it can be seen that the

experimental results are similar with the simulation results.

X axis 50 s/iv ; Y axis 5v/div

Figure 3.43 Oscillogram of driving pulses for equal PWM

Yes

No

SET COUNTER = 20

DECREMENT COUNTER

IF COUNTER

0

RETURN

Time

Vo

lt

89

X axis 5ms/div ; Y axis 20v/div

Figure 3.44 Oscillogram of the inverter for equal PWM

X axis 5ms/div; Y axis 20v/div

Figure 3.45 Oscillogram of the uncompensated voltage for equal PWM


Figure 3.46 Oscillogram of the compensated voltage for equal PWM

Time

Vo

lt

Time

Vo

lt

Time

Vo

lt

90

3.4.2.2 SPWM Technique

Oscillogram of the experimental results using SPWM technique is

obtained. Pulses with 5 volt magnitude is obtained at the output port P2.1 to

2.4 of the microcontroller and they are shown in Figure 3.47. The output of

the inverter is shown in Figure 3.48. Figure 3.49 shows the uncompensated

voltage. The compensated voltage is shown in Figure 3.50. The flow chart for

SPWM technique is shown in Figure 3.51.

X axis 50 s/div ; Y axis 5v/div

Figure 3.47 Oscillogram of driving pulses for SPWM


Figure 3.48 Oscillogram of the inverter for SPWM

Time

Vo

lt

Time

Vo

lt

91


Figure 3.49 Oscillogram of the uncompensated voltage for SPWM


Figure 3.50 Oscillogram of the compensated voltage for SPWM

Time

Vo

lt

Time

Vo

lt

92

Figure 3.51 (Continued)

NO

Start

Check P1.0

If

P1.0=0

Set pulses for S1 and S2

Set pulses for

S3 and S4

YES

Run timer to delay for 0.216ms

Complement pulses for S3 and S4

Run timer for delay of (1- 0.216) ms




C

A

93

Figure 3.51 (Continued)




C










C

94

Figure 3.51 Flow chart for SPWM technique

C













A

95

3.5 CONCLUSION

In this chapter, the performance of a DVR in mitigating voltage

sag/ swell is demonstrated with the help of MATLAB. The modelling and

simulation results of a single phase DVR with an H bridge inverter and Z

source inverter are presented. The Z source inverter is a viable alternative to

the conventional inverters, since it can boost the input voltage and control the

short circuit current.

The modelling and simulation results of the three phase DVR using

sine PWM and space vector PWM techniques are presented. The simulation

results validate that the implemented control strategy compensates the voltage

sags with high accuracy. Heating is reduced due to the reduction of harmonics

in the output. The cost of the system is reduced since the ATMEL controller

89C2051 is cheaper. The volume of the converter is reduced since the ports

and timer are embedded in the micro controller chip. A laboratory model of

the ZSI based DVR system using multiple PWM and SPWM technique is

implemented and the experimental results are presented. The experimental

results are similar with the simulation results. The simulation and

implementation are done by considering single phase circuit modelling. This

work has assumed a balanced load at the receiving end.

Documents

CHAPTER 3 DYNAMIC VOLTAGE RESTORER - …shodhganga.inflibnet.ac.in/bitstream/10603/9826/8/08_chapter 3.pdf · shows the FFT analysis of the closed loop DVR system for sag ... power