AC Power Load Controlling by Using - 2010

8/2/2019 AC Power Load Controlling by Using - 2010

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AC Power Load Controlling by Using PWM Based

on Phase Locked LoopA. Kitipongwatana

1, P. Koseeyaporn

2, J. Koseeyaporn

3, and P.Wardkein

3

1Department of Telecommunication Engineering, Faculty of Engineering,

Mahanakorn University of Technology, Nongjok, Bangkok, THAILAND 105302Department of Teacher Training in Electrical Engineering, Faculty of Technical Education,

King Mongkuts Institute of University North Bangkok, Bangsue, THAILAND 108003Department of Telecommunication Engineering, Faculty of Engineering,

King Mongkuts Institute of Technology Ladkrabang, Bangkok, THAILAND 10520

ABSTRACT-This paper proposes power load controlling byusing PWM signal to on-off an electronic switch. With this

technique, load current can be easily adjusted. For PWM signal,

it is derived by using PLL. With the property of PLL, PWM

signal whose frequency is synchronized with that of load power is

generated. Consequently, phase of signal which is fed to load can

be controlled all range of 360 degrees or 180 degrees. In addition,

the experiment results show that linear relation between phase of

signal and DC voltage.Key Words: Phase Locked Loop, PWM

I. INTRODUCTION

In general, the principle that employs to control load

power (either AC or DC power) is classified into 2 main

approaches. The first technique is of controlling voltage across

a load. The second one is of controlling average current that

flow through a load. It is noted that Pulse Width Modulation

(PWM) is an important technique that is used in the power

controlling of both methods. For example, M.J. Nasila [1]

proposed phase locked loop pulse width modulation system

and was applied to be a basic buck converter. The circuit

which is used to control load power of these techniques then iscomprised of 1) a semiconductor device, for example, Triac,

SCR, MOSFET, BJT. It is relative to an electronic switch

which is used to on-off current delivered to a load. 2) a circuit

which is used to generate a timing signal for controlling a

semiconductor device. Various methods can be employed for

this purpose. For power load controlling that uses DC signal,

the current that flow through the load can be easily controlled

by using PWM signal to on-off Triac or SCR without

synchronization requirement. But in case of alternate current

power source, synchronization is required in order to control

timing for on-off appropriate current flowing. Otherwise, it is

not able to precisely controlled power delivering from source

to load.From literature review, there are various techniques for

electronic power controlling for alternate current power source.

For example, RC phase-shifter is used to shift phase of power

source (50Hz or 60Hz) to generate synchronized signal to on-

off electronic power switch [2, 3]. With this technique, power

delivered to load can be adjusted with a variable resistor but it

does not provide electronic control (with voltage or current).

To obtain electronic power control, a synchronization system

is needed to generate a controlling signal which synchronizes

with power source. In [4], AC power signal is rectified by full

wave rectifier and then fed to be an input of LED diode of

optocoupler to drive a BJT. The BJT output signal is

employed to enable IC555 timer (in monostable mode) to

generate a pulse to on-off Triac. Consequently, power

controlling can be achieved by RC adjustment. Another

popular method is of using a microcontroller [5] to construct a

synchronized signal to provide timing for on-off a powerswitch. Hence, electronic power controlling is simply obtained

by feeding control (voltage or current) signal to A/D of

microcontroller. However, these techniques [2-5] are very

sensitive to frequency changing of AC power source. It

implies that error of power controlling exists when frequency

of power source is changed. Later, power controlling based on

microcontroller is improved by software program [6] to

response to frequency changing of power source. It results to

complex program and support to 50Hz or 60Hz power source

only.

Recently, pulse width modulation based on phase locked

loop is proposed [7]. It is found that the characteristic of this

system can be applied for AC power controlling. Thus,frequency insensitive AC power controlling by using PWM

based on phase locked loop is proposed in this article. By

using an attenuated AC power line signal as a reference signal

of the PLL, the PWM signal is simply obtained. In case that an

RS Flip-Flop phase detector is employed, it is called single

phase AC power controlling. Alternately, if Ex-OR gate

phase detector is used, it is called biphase AC power

controlling whose frequency of the PWM signal is twice of

AC power line signal.

This paper is organized as follows: The principle of PWM

generated by PLL [7] is first reviewed in section II. Then, a

basic AC-to-AC converter is described. The proposed AC

power controlling by PLL is presented in section III where

experimental results for AC power controlling (220V/50Hz)

are demonstrated in section IV. Finally, section V is devoted

for the conclusion.

978-1-4244-3388-9/09/$25.00 2009 IEEE


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II. PRINCIPLES

A. Phase Locked Loop (PLL)

Phase locked loop is a negative feedback system whose

frequency of a generated output signal is equal to that of an

input signal. Whenever input frequency is changed the PLL

will generate an output signal to track input frequency. It thus

has a synchronization property. In practical, the PLL is

composed of important three parts. The first part is a phase

detector which determines phase difference between a

reference signal and an output signal. The second part is a

low-pass filter, and the third part is a voltage control oscillator

(VCO). PLL has been applied to many applications, such as

clock recovery, frequency synthesizer, phase modulation,

frequency modulation and pulse width modulation (PWM) [1,

7]. The block diagram of PLL proposed by [7] which is

adopted in this paper is shown in Fig. 1.

Let the input signal be ( )i i i

t t = + , wherei

andi

are input frequency and absolute phase respectively, the

output signal ( )o

t then is [7]

( ) r io i iB

t tK K

= + + (1)

whered o

K ABk k = , A and B are dc gain of loop filter and

integrator respectively. In addition,d

k and o

k are respectively

gain of phase detector and VCO. The phase difference

( )D

t between input and output signal can be shown as

( ) ( ) ( ) r iD i o

Bt t t

K K

= = . (2)

Figure 1. Block diagram of PLL.

B. Pulse Width Modulation based on PLL

The block diagram of Pulse Width Modulation based on

PLL which is proposed in [1] and [7] is depicted in Fig. 2. It is

seen that an input signalc

V is fed to sum with an output of a

loop filter. By using mathematical model of the PLL given in

[7], the output phase response ( )o

t is found to be

( ) ( )c o r i o i i

BV k B t t t

K K K

= + + . (3)

and phase difference can be written as

( ) ( ) ( )

.

D i o

i c o r

t t t

BV k B

K K K

=

= +

(4)

Figure 2. Block diagram of PWM based on PLL.

From (4), it is obvious that phase difference is directly

proportional to inputc

V term. It thus provides electronic

control ability and can also be applied to be a controlling

signal for AC power load control.

C. AC-to-AC Converter

Many techniques can be employed control ac electric

power from source to load such as phase controlling method,

and cycle controlling method and etc. These approaches can

also be applied to control motor speed, heater and lighting,independently on phase type (single phase or three phases) of

power line source. A simple AC-to-AC converter is illustrated

in Fig. 3. It is composed of a thyrister and a controlling circuit

which generates a controlling signal to on-off the thyrister.

Generally, the controlled circuit is often made of a

microcontroller [4-6]. This is because its circuit is simple and

the controlled signal, for trigger or phase control, can be

simply generated by software code. But the main drawback is

that it is sensitive to frequency changing of power line source.

Figure 3. Basic structure of single phase AC-to-AC converter circuit.

III. THE PROPOSED CIRCUIT

In order to control AC electric power that delivers to load

by using PWM based on PLL circuit to generate a controlling

signal, it is important that phase of the controlling signal must

be synchronized with every cycle of AC power source. In this

paper, a PWM based PLL system [7] is applied to generate a

controlling signal whose pulse width can be electronically

controlled. In addition, with synchronization property of the

PLL, the proposed circuit is therefore insensitive to frequency

changing of AC power source.

It should be mentioned that electrical power switch

controlling to deliver power from AC source to load is divided

into two categories. The first one is single phase which trigs a

power switch only one time to control current flowing in one

cycle. The other one is biphase which trigs a power switch


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twice to control current flowing in one cycle. The first trig is

between 0 and 180 (positive half cycle) and the second trig

is between 180 and 360 (negative half cycle).

Based on the described principle of power controlling,

block diagram of the proposed circuit can be depicted in Fig. 4.

It is noted that an IC3020 is employed as a power electronic

switch driver where a power switch is a Triac. For the PWM

based on PLL circuit, both types which are single phase andbiphase are experimented. For a biphase electrical power

controlling, it is composed of an RC loop filter, a VCO

(IC4046) and a phase detector (IC4046 Ex-OR gate). For

single phase electrical power controlling, it is similar to the

biphase case, except that monostable multivibrator (IC 4528)

and RS Flip-Flop (IC 4043) are employed for a phase detector.

The overall circuit is shown in Fig. 5 where the switch s1 is

used to select type of PWM based on PLL.

Figure 4. Power load controlling circuitby using Pulse Width Modulation based on PLL.

Figure 5. The Pulse Width Modulation based on PLL circuit.

IV. EXPERIMENTAL RESULTS

To verify the proposed principle, laboratory experiment of

the proposed circuit is accomplished which is divided into

three parts. The first part is to generate PWM signal which

synchronizes with the 220V/50Hz AC power source. The

obtain signals are shown in Fig. 6. The second part is to

control electrical power which delivers from source to load by

using a single phase controlling. The experimental results are

demonstrated in Fig. 7 and 8 for trigger angle at 90 and 225,

respectively.

Figure 6. (1) PWM trigger signal,(2) 220V/50Hz AC signal.

Figure 7. (1) Single phase PWM trigger signal (trig at 90),

(2) The resulted voltage across load.

Figure 8. (1) Single phase PWM trigger signal (trig at 225),


In addition, the relationship between DC voltage inputc

V

and trigger angle is tested. The obtained experimental result

shows that trigger angle is linearly varied with DC voltage

inputc

V as given in Fig. 9.

Finally, the control power delivering from AC power

source to load resistance by using biphase power controlling is

experimented. In this case, biphase controlling signal must trig


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the electronic switch twice in everyone cycle of AC signal.

Fig. 10 shows the resulted voltage across load when it is

trigged at 45 for positive half cycle and at 225 for negative

half cycle. Similarly, Fig. 11 illustrates the voltage across load

when it is trigged at 120 and 300 for positive and negative

half cycle, respectively.

DC voltage input (volt)

0 1 2 3 4

ConductionAngle(Degree)

0

50

100

150

200

250

300

Figure 9. Relationship between DC input signal ( )cV and phase angle of

single phase power controlling.

Figure 10. (1) Biphase PWM trigger signal (trig at 45

and 225),


Figure 11. (1) Biphase PWM trigger signal (trig at 120 and 300),


In addition, the relationship between DC voltage inputc

V

and trigger angle of biphase power controlling is determined

which is shown in Fig. 12. It is also found that trigger angle is

linearly varied with DC voltage input.

DC Voltage Input (Volt)

1.0 1.5 2.0 2.5 3.0 3.5

ConditionAngle(Degree)

60

80

100

120

140

160

Figure 12. Relationship between input signal ( )cV and phase angle of

biphase power controlling.

V. CONCLUSIONS

In this article, AC electrical power controlling by using

PWM based on PLL is proposed. The main advantages of the

proposed circuits are 1) the PWM trigger signal can be

electronically controlled by DC input signal and 2) it is

insensitive to frequency changing of AC power source due tosynchronization property of the PLL. The experimental results

illustrate that the proposed principle can be applied for power

load control for both single phase and biphase power

controlling. Furthermore, the relationship between trigger

angle and DC input signal is shown to be linear for both single

phase and biphase power controlling.

REFERENCES

[1] M. J. Nasila, Phase-Locked Loop Pulse-Width Modulation System,United States Patent, Patent No. US6208216B1, 27 Mar. 2001.

[2] Phase Control Using Thyristors,Application note, Teccor Electronics,2002.

[3] M.S. JAMIL ASGHAR, POWER ELECTRONICS, Prentice-Hall ofIndia Private Limited, 2004[4] Optically Isolated Phase Controlling Circuit Solution, Application

note, Fairchild semiconductor, 2002.[5] BURST MODE TRIAC CONTROL BY USING ST52x301,

Application note, STMicroelectronics , 1999.[6] Using an ST7ULTRALITE microcontroller to drive a TRIAC or an

AC switch for a Mains supply, Application note, STMicroelectronics ,2006.

[7] P. Wisartpong, J. Koseeyaporn, and P.Wardkein, Pulse WidthModulation Based On Phase Locked Loop, Proc. ECTI-CON,pp.697-700, 2008.

[8] J. Koseeyaporn,Electronic Engineering, Faculty of Engineering, King

Mongkuts Institute of Technology Ladkrabang, 2008.

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AC Power Load Controlling by Using - 2010