ijrde-analysis and simulation of pwm controlled buck-boost ac voltage regulator

International Journal for Research and Development in Engineering (IJRDE)

www.ijrde.com Vol.1: Issue.2, October-November 2012 pp- 28-36

28

ANALYSIS AND SIMULATION OF PWM CONTROLLED

BUCK-BOOST AC VOLTAGE REGULATOR

R.Ithaya1,V.Ponselvan

2

1(Dept of Electrical and Electronics, Udaya school of engineering,India)

Email :[email protected] 2(Dept of Electrical and Electronics, Udaya school of engineering,India)

Email :[email protected]

ABSTRACT

Thyristor controlled method in AC voltage

regulator has very low dynamic response and

discharge large amount of harmonic

components. PWM Controlled Buck-Boost AC

Voltage Regulator can efficiently and

economically be used in low and medium power

applications in the advantage of design

simplicity with operation reliability in a clear

withstand of naturally commutated schemes. It

has very fast response speed, low harmonics

component distortion and high power factor.

This paper propose a voltage controller with

output peak voltage and reference as feedback

signal and adopts PID control strategy to

regulate the output voltage. In this paper,

simulation of PWM Controlled Buck-Boost AC

Voltage Regulator is presented using PSIM

software. The waveforms of input and output

voltage and current, the power factor

characteristics are discussed and verified.

Keywords - Boost Converter, AC voltage

regulator, PID controller, Pulse width

modulation, Potential transformer

I. INTRODUCTION

AC voltage regulation is the important part of

power

conversion methods. There are some types of

AC/AC converter which regulate the input

voltage and input current to a lower or higher

output voltage. An ideal transformer is widely

used in the voltage regulation control fields

such as power system, motor speed control

and so on. The winding ratio is changed by the

servo motor or by manual regulation, and it

has very low regulation speed. There are also

some other researches which use thyristor

phase controlled circuit for voltage regulation.

These converters have been used as a soft-

starter and a speed regulator of pumps and

fans. Even though it has a higher regulating

speed than winding transformer, the low input

power factor and the large amount of the low-

order harmonic current are the major

problems. The size of the passive filter

becomes larger.

Furthermore, these shortcomings affect the

power quality. The reactive and harmonic

currents generated by the thyristor



29

commutation also produce extra power loss on

the transmission lines. These problems can be

solved by using high switching frequency AC

chopper. A Chopper type voltage transformer

adopts PWM control techniques and the above

problems are improved when it is operated in

chopping mode.

The input voltage is chopped into segments

and the output voltage is regulated by changing

the duty ratio of the control signal. The

advantages are nearly sinusoidal input-output

currents/voltage waveforms, improved power

factor, reduced harmonic current, a fast

response speed and a smaller input filter size. It

can protect sensitive equipment such as a

computer or communication equipment; it can

also be used to solve power quality problems

caused by line voltage sags and swells.

In order to reduce the power loss, researches

have been conducted to reduce the number of

the switching devices. Three switches and four

switches AC chopper were discussed in

previously presented papers. Different working

principles have also been presented to ensure

the safety of the converter. The switching

patterns are critical and an alternate path has

to be established in dead time. DC regenerative

snubber capacitor is used to realize the safe

commutation and enhance efficiency. Although

there are various researches that focus on the

topology of the AC chopper converter, little

attention has been given to the theoretical

analysis of the input power factor. In addition,

because most of the previous proposed control

methods are open loop control, voltage

regulation performance is restrained. To solve

the problems caused by the input voltage

fluctuation, the output voltage closed loop

feedback control system is proposed for a

better dynamic performance.

The remainder of this paper is divided into

four sections. First, the circuit description and

working principles are discussed in section II.

Then, the theoretical analysis method of the

input power factor and output voltage are

presented is section III. Based on the theoretical

analysis, the output voltage controller design is

shown in section IV. Digital simulation is

conducted in section V to test the proposed

analysis method and the voltage controller

performance.

II. CIRCUIT CONFIGURATION

The proposed circuit has the following

characteristic: it can operate directly from the

single-phase line and regulate the output

voltage higher or lower steplessly. Furthermore,

the input voltage phase synchronous circuit is

unnecessary in this scheme. As a result, the

circuit is simplified and the cost is reduced. The

input filter, consisting of inductor Li and

capacitor Ci, absorbs the harmonic currents. The

switches S1 and S2 are bi-directional.

The used bi-directional switch module is

composed of two insulated gate bipolar

transistors IGBT. This bi-directional switch

structure make the two IGBT share the common

the driver circuit, thus the circuit hardware

design is simplified. The used IGBT has inner

anti-parallel diode which provide. Freewheeling

currents path when the reverse voltage is

encountered. The inductor L is used to store

and transfer the energy to the output side. The

switch S1 is used periodically to connect and


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disconnect the inductor L to the supply, i.e., it

regulates the power delivered to the inductor

The switch S2 provides a freewheeling path for

the inductor current to discharge the stored

energy of the inductance L when the switch

turned off. These switches are contro

PWM signals with constant duty ratio.

R1, R2 are the snubber capacitors and resistors

respectively. The snubber circuits are connected

in parallel with the bi-directional switches. The

output filter capacitor reduces the output

voltage ripple.

Fig. 1. Buck boost AC voltage regulator.

The switches S1 and S2 work in complementary

mode. Because the output voltage polarity is

reversed with the input voltage polarity, the

switches S1 and S2 cannot be turned on

simultaneously. For the sake of safe

commutation, the switching dead

necessary. Furthermore, in this circuit, the

switching patterns of the controlled switches

are not decided by the polarity of the voltage or

the currents. The voltage or current polarity

detection is unnecessary. The switching pattern


Vol.1: Issue.2, October-November

30

to the supply, i.e., it

regulates the power delivered to the inductor L.

provides a freewheeling path for

the inductor current to discharge the stored

energy of the inductance L when the switch S1 is

turned off. These switches are controlled by

PWM signals with constant duty ratio. C1, C2 and

are the snubber capacitors and resistors

respectively. The snubber circuits are connected

directional switches. The

output filter capacitor reduces the output

work in complementary

mode. Because the output voltage polarity is

reversed with the input voltage polarity, the

cannot be turned on

simultaneously. For the sake of safe

commutation, the switching dead-time is

necessary. Furthermore, in this circuit, the

switching patterns of the controlled switches

are not decided by the polarity of the voltage or

voltage or current polarity

detection is unnecessary. The switching pattern

of the control signals. The operation is divided

into three modes: active mode, freewheeling

mode and dead-time mode.

Fig. 2. Switching patterns of the PWM signals

The active mode is defined when the switch

is turned on. During the active mode, the

inductor current is forced to flow through the

voltage source via the modulated switch

during its on-state periods and the inductor

storages the energy. The freewheeling mode

defined when the modulated switch

off. The inductor current paths can be formed

by the direction of the load current. In

freewheeling mode, the load current

freewheels and the inductor

energy through the switch S2 with the

body diodes according to the direction of the

load current. Finally, the dead

defined when the switches S

turned off. The dead-time td is short, only

about several microseconds. The snubber

circuits can absorb the bidirectional turn

spike energy due to line stray inductance.


November 2012 pp- 28-36

of the control signals. The operation is divided

into three modes: active mode, freewheeling

Switching patterns of the PWM signals

mode is defined when the switch S1

is turned on. During the active mode, the

inductor current is forced to flow through the

voltage source via the modulated switch S1

state periods and the inductor

storages the energy. The freewheeling mode is

defined when the modulated switch S1 is turned

off. The inductor current paths can be formed

by the direction of the load current. In

freewheeling mode, the load current

freewheels and the inductor L discharges the

with the help of its

body diodes according to the direction of the

load current. Finally, the dead-time mode is

S1 and S2 are both

time td is short, only

about several microseconds. The snubber

bidirectional turn-off

spike energy due to line stray inductance.


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Fig. 3. PWM pattern signal.

III. ANALYSIS

To facilitate the analytical procedure, the

following assumptions are made:

First, all components are assumed ideal. In

addition, because the switching frequency f

much higher than the line frequency

frequency input harmonic currents can be

absorbed by small input filter. The input power

factor is assumed not to be affected by the

input filter.

In the switching period, the input voltage

and the output voltage uo are considered to be

constant. When ui>0, the waveforms of

inductor voltage uL and current iL. The inductor

voltage uL is ui during the active mode or

during the freewheeling mode. In dead

mode, the inductor voltage uL

according to the direction of iL.



31

To facilitate the analytical procedure, the

First, all components are assumed ideal. In

frequency fs are

much higher than the line frequency f, the high

frequency input harmonic currents can be

absorbed by small input filter. The input power

factor is assumed not to be affected by the

switching period, the input voltage ui

are considered to be

>0, the waveforms of

. The inductor

during the active mode or uo

during the freewheeling mode. In dead-time

L is ui or -uo

Fig. 4. Waveforms of the inductor voltage

In ideal condition, the inductor voltage of

can be expressed as follows:

uL(t)=Dui(t)−(1−D)uO(t)

Where ui(t) and uO(t) are the average AC

input voltage and output voltage during the

switching period, respectively, and

ratio. Because the switching frequency is much

higher than the line frequency

ii(t)=DiL

io(t)=(1-D)iL(t) (3)

Where iL(t) is the average inductor current

during the switching period. The inductor

current produces the output current during the

freewheeling mode, and the inductor current is

caused by the input current during the active

mode

The PID controller is used as which the

derivative part is also included alo

integral part since the gain values increases

when PID is considered rather than the PI

controller.



aveforms of the inductor voltage uL and current iL

In ideal condition, the inductor voltage of uL

) (1)

(t) are the average AC

input voltage and output voltage during the

switching period, respectively, and D is the duty

ratio. Because the switching frequency is much

higher than the line frequency

L (2)

(t) (3)

(t) is the average inductor current

the switching period. The inductor

current produces the output current during the

freewheeling mode, and the inductor current is

caused by the input current during the active

The PID controller is used as which the

derivative part is also included along with the

integral part since the gain values increases

when PID is considered rather than the PI


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Fig. 5. PWM controlled buck boost AC voltage regulator

IV. VOLTAGE CONTROLLER

Voltage sags or swells are caused by the

disturbances or faults in power systems. The

input voltage fluctuation also affects the

voltage. From the output voltage can be

regulated by the duty ratio of the PWM control

signals. The voltage controller, which uses the

output peak-voltage as the feedback signal, is

designed to keep the stability of the output

voltage in case of input voltage fluctuation.

Where uf is the detected output peak

and ur is the reference value of output peak

voltage. The output peak-voltage is detected by

the circuit with diodes rectifier, capacitor and

resistor. When the input voltage decreases, the

capacitor discharges through the resistor, and

when increased, the capacitor is charged

directly.

The controller input ∆u is expressed as:



32

. PWM controlled buck boost AC voltage regulator

Voltage sags or swells are caused by the

disturbances or faults in power systems. The

input voltage fluctuation also affects the output

the output voltage can be

regulated by the duty ratio of the PWM control

which uses the

voltage as the feedback signal, is

designed to keep the stability of the output

voltage in case of input voltage fluctuation.

is the detected output peak-voltage

is the reference value of output peak-

voltage is detected by

the circuit with diodes rectifier, capacitor and

resistor. When the input voltage decreases, the

capacitor discharges through the resistor, and

when increased, the capacitor is charged

expressed as:

∆u=ur-uf

The controller output is duty ratio

the input voltage fluctuation happens, the

detected output peak-voltage

regulated to a constant reference value

with fast response speed. The proportional

integral (PI) controller satisfying these

performance requirements is used as follows.

D=Kp∆u+Ki∫∆u dt

Where kp and ki are proportional and

integral gains respectively. The integral part of

the designed controller makes the steady

output voltage error zero.

V. SIMULATION RESULTS

To show the feasibility of the proposed

analysis method and control strategy, the

simulation model of the proposed voltage

regulator is setup using PSIM software. The

parameters are as follows:

R1=R2=10KΩ, Cs1=Cs2=0.1µF, L

Ci=10µF, CO=20µF, f=50Hz, R

When the load is pure resistive

duty ratio D=0.4, the waveforms of the input

voltage, input current, output voltage, output

current and inductor current

4.

According to the diagram, t

results are consistent with the theoretical

analysis. The chopper type AC

has a high input power factor and can reach the

unit power factor in working zone



(4)

The controller output is duty ratio D. When

the input voltage fluctuation happens, the

voltage uf needs to be

regulated to a constant reference value ur

with fast response speed. The proportional-

integral (PI) controller satisfying these

performance requirements is used as follows.

∆u dt (5)

are proportional and

integral gains respectively. The integral part of

the designed controller makes the steady-state

output voltage error zero.

To show the feasibility of the proposed

analysis method and control strategy, the

simulation model of the proposed voltage

regulator is setup using PSIM software. The

parameters are as follows: Ui=220V,

L=4mH, Li=200µH,

RL=100Ω, td=0.5µs.

When the load is pure resistive RL=100Ω and the

the waveforms of the input

voltage, input current, output voltage, output

are shown in Fig.

According to the diagram, the simulation

consistent with the theoretical

analysis. The chopper type AC voltage regulator

has a high input power factor and can reach the

unit power factor in working zone.


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Fig. 6. Waveforms of input voltage, input current, output

output

current and inductor current when D=0.4

The input current is almost in phase with the

input voltage. Unlike the thyristor phase

controlled converter, the output voltage wave is

sinusoidal and the harmonics are highly

reduced.

The Fig. 7 shows the peak voltage waveform

of the given circuit. The input of this peak

voltage detector is from the output of buck

boost chopper type AC voltage regulator. The

output filter capacitor Co reduces the output

ripple and is regulated through the i

transformer to the peak voltage detector.

The detected peak voltage is given to the

error detector. The error detector transistor

conducts when the sense transistor saturates

indicating that the input voltage and output

voltage have come within a predetermined

voltage of one another. The reference v



33

Waveforms of input voltage, input current, output voltage,


Unlike the thyristor phase

voltage wave is


shows the peak voltage waveform

of the given circuit. The input of this peak

voltage detector is from the output of buck-

boost chopper type AC voltage regulator. The

reduces the output

ripple and is regulated through the isolation

transformer to the peak voltage detector.

The detected peak voltage is given to the

The error detector transistor

conducts when the sense transistor saturates

indicating that the input voltage and output

n a predetermined

voltage of one another. The reference voltage is

given to the detector. The voltage is regulated

by neglecting the error and controlled using the

PID controller and this signal is given to the

comparator with the sawtooth waveform to

generate the PWM signal for the Buck

converter.

Fig. 7. Peak voltage waveform

The switches S1 and S2 in the buck boost AC

voltage regulator works by the input of PWM

signal produced by the control circuit. The

comparator that compares the sawtooth

waveform and the reference voltage is shown

first and followed by that the produced PWM

signal is shown in the Fig. 8.

Fig. 8. Switching patters of PWM signals



given to the detector. The voltage is regulated

by neglecting the error and controlled using the

PID controller and this signal is given to the

comparator with the sawtooth waveform to

the PWM signal for the Buck-Boost AC

in the buck boost AC

voltage regulator works by the input of PWM

signal produced by the control circuit. The

comparator that compares the sawtooth

waveform and the reference voltage is shown

first and followed by that the produced PWM

. Switching patters of PWM signals


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The peak voltage signal is given to the PID

controller and the signal is controlled and gi

to the comparator. The comparator compares

the regulated signal and sawtooth signal to

produce PWM signal. In this graph the PWM

signal is noted as Sg1 and the inverted signal to

the switch is noted as Sg2.The PWM signal

produced is directly given to the S

PWM signal is inverted using a not gate and

given to the switch S2.




sinusoidal and the harmonics are h

reduced. This input supply voltage is given to

the buck-boost chopper type AC voltage

regulator for operation. It is noticed that to

input power supply and the output power

supply will be in phase considered to the

current and voltage .

Fig. 9.The input voltage and current waveforms PWM controlled

Buck-Boost AC voltage regulator.



34

The peak voltage signal is given to the PID

controller and the signal is controlled and given

to the comparator. The comparator compares

the regulated signal and sawtooth signal to

produce PWM signal. In this graph the PWM

and the inverted signal to

.The PWM signal

he S1 and the

PWM signal is inverted using a not gate and





reduced. This input supply voltage is given to

boost chopper type AC voltage

It is noticed that to

input power supply and the output power

supply will be in phase considered to the

nput voltage and current waveforms PWM controlled

Figure 10 shows the simulation results of

the output voltage when voltage sags or swells

of 20% in the input voltage occur.

controller can regulate the o

suppress the voltage fluctuation with fast

speed. According to Fig. 11, when the output

peak voltage is 100V, the total

distortion (THD) of output voltage is only 1.62%.

The output voltage has little harmonic

components.

(a)

(b)

Fig. 10. (a)Waveforms of output voltage voltage sags of 20% in the

input voltage (b) voltage swells of 20% in the input voltage



shows the simulation results of

the output voltage when voltage sags or swells

of 20% in the input voltage occur. The voltage

controller can regulate the output voltage and

suppress the voltage fluctuation with fast

11, when the output

peak voltage is 100V, the total harmonic

distortion (THD) of output voltage is only 1.62%.

The output voltage has little harmonic

aveforms of output voltage voltage sags of 20% in the

voltage (b) voltage swells of 20% in the input voltage



35

With duty ratio ranging from 0.2 to 0.7, the

theoretical analysis according to (10) and the

simulation results of input power factor are

shown in Figure 11. The theoretical analysis

according to (9) and simulation results of output

voltage root-mean- square (rms) value are

shown in Fig. 12.

Fig. 11. Variation of input power factor under different duty ratio

Fig. 12. Variation of output voltage under different duty ratio

VI. CONCLUSION

The PWM Controlled Buck-Boost AC Voltage

Regulator has many advantages compared to

the thyristor phase controlled voltage regulator.

The analysis method of the input power factor

is presented. Compared with other voltage

regulator, the input current is in a sinusoidal

waveform with less harmonic components. The

output voltage control system is designed using

PID control method and the peak-voltage

detector. The simulation results show that the

voltage controller has a good dynamic

performance when input voltage swells or sags

occur. The PWM Controlled Buck-Boost AC

Voltage Regulator can improve the power factor

and reduce the power loss caused by the

reactive and harmonic currents. In addition, it

has significant meaning in protecting the

voltage sensitive load against the line voltage

swells and sags.

REFERENCES

[1] J.H. Kim, B.D. Min, and B.H. Kwon, “A PWM Buck–Boost AC

Chopper Solving the Commutation Problem,” IEEE Transactions

On Industrial

[2] Jin Nan, Tang Hou-jun, Lin Wei, “Analysis and Control of Buck-

Boost Chopper Type AC Voltage Regulator,” IEEE Transactions On

Industrial Electronics Vol.36, No.1, pp.33-38, 2009

[3] N.A. Ahmed, Kenji Amei and Masaaki Sakui, “Improved Circuit

of AC Choppers for Single-Phase System,” Proceedings of the IEEE

Conference PCCON, vol.2, pp. 907-912,2010.

[4] Nabil A. Ahmed, Kenji Amei, and Masaaki Sakui, “A New

Configuration of Single-Phase Symmetrical PWM AC Chopper

Voltage Controller,” IEEE Transactions On Industrial Electronics,

Vol. 46, No. 5, pp. 942-952, 2008.

[5] Shinichiro Fujikura, Akiteru Ueda, and Akihiro Torii, “Analysis

of a Three-Phase Buck-Boost AC Chopper Controlled in Two

Phases,” Power Conversion Conference, pp.824-830, 2007



36

[6] Shinyama T, Ueda A, and Torii A, “AC chopper using four

switches,” Proceedings of Power Conversion conference, pp.

1056-1060, 2002

[7] Veszpremi K, Hunyar M., “New application fields of the PWM

IGBT AC chopper,” Eighth International Conference of Power

Electronics and Variable Speed Drives, pp. 46-51, 2000

[8] Balci M.E., Hocaoglu M.H. “Effects of Source Voltage Harmonic

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[9] B.H. Kwon, Gang Youl Jeong, “Novel Line Conditioner with

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ijrde-analysis and simulation of pwm controlled buck-boost ac voltage regulator

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