**3. Design and analysis of switching-mode AC voltage regulator**

### **3.1. Operation principle of switching-mode AC voltage regulator**

#### *3.1.1. Operation of power circuit*

Voltage sag is an important power quality problem, which may affect domestic, industrial and commercial customers. Voltage sags may either decrease or increase in the magnitude of system voltage due to faults or change in loads. Momentary and sustained over voltage and under voltage may cause the equipment to trip out, which is highly undesirable in certain application. In order to maintain the load voltage constant in case of any fluctuation of input voltage or variation of load some regulating device is necessary.

In this chapter the principle of operation of high frequency switching AC voltage regulator, design of its filter circuit and snubber circuit are described. Performance of the regulator is also analyzed using simulation software OrCAD version 9.1. Switch-mode power supplies (SMPS) incorporate power handling electronic components which are continuously switching on and off with high frequency in order to provide the transfer of electric energy from input to output. The design of AC voltage regulator depends on power requirement, degree of stability and efficiency. Solid state AC regulator using phase control technique are not new and are widely used in many application such as heating and lighting control etc. These regulators are not suited for critical loads because the output waveforms are truncated sine waves, which contain large percentage of distortion. The input power factor is low. These drawbacks are largely overcome and the voltage can be efficiently controlled by means of a solid-state AC regulator using PWM technique.

Power Quality Improvement Using Switch Mode Regulator 131

gate signal 1

gate signal 2

5

0

5

0

The gate signal generating circuit for a manually controlled AC voltage regulator is shown in Fig. 11. The control circuit incorporates an Operational Amplifier (OPAMP) whose positive input is a variable DC voltage V1, and negative input is a fixed saw-tooth signal V2. In this circuit the OPAMP acts as a comparator, output of the OPAMP depends on the difference of the two inputs. The negative input (saw-tooth wave) is kept constant and positive input (DC voltage) is varied. So output pulse width depends on DC input voltage of OPAMP i.e. when DC input is higher the output of comparator will be wider and when

The outputs of OPAMP are used to turn on/off the switches of the power circuit of the regulator to regulate the output voltage. The output of OPAMP is directly passed through limiter-1 which is the gate signal for switch-1 and after inverting the output of the comparator is passed through the limiter-2 which is the gate signal for switch-2. The function of the limiter is to limit the output of comparator from 0 to 5 V. When switch-1 of the power circuit is on then switch-2 should be off. So the gate signal generating circuit is arranged in such a way that when gate signal of switch-1 is on then gate signal for switch-2

**Figure 11.** Gate signal generation circuit of manually controlled AC voltage regulator.

0

AD648A

12Vdc

V4

V3 12Vdc

0

1


When the stability is not very stringent, manually controlled AC voltage regulator is

The basic circuit of a manually controlled AC voltage regulator is shown in Fig. 12. When any change in output voltage occurs due to change in input voltage or change in load, the voltage can be regulated to the desirable value by changing the DC voltage of the gate signal generating circuit manually. The power circuit of the proposed regulator shown in Fig. 12 is implemented using ideal switches; later part of this chapter the ideal switches is replaced by practical switches. The regulator proposed in this chapter is employed to regulate the output

**3.2. Manually controlled AC voltage regulator** 

generally preferred from economic considerations.

*3.1.2. Operation of control circuit* 

is off and vice versa.

5Vdc

V1

0

TD = 0 TF = .125ms PW = .005ms PER = .255ms

TR = .125ms V2 = 0

V1 = 10

DC input is lower the output of comparator will be narrower.

3

+


8

> V+

V-OUT

4

2

V2

0

The power circuit of the proposed AC voltage regulator is shown in Fig. 9. The circuit operation can be explained with the help of Fig. 10. During positive half cycle of the input voltage, at mode 1, when switch-1 is on and switch-2 is off, the current passes through diode D1, switch-1, diode D4 and through the inductor and the energy is stored in the inductor. At mode 2, when switch-1 is off and switch-2 is on, the energy stored in the inductor is transferred through diode D8, switch-2 and diode D5. At mode 1, power is transferred from source and at mode 2, power is not transferred from the source, so by controlling the on and off duration of switch-1 output power can be controlled.

During negative half cycle of the input voltage, at mode 1, when switch-1 is on and switch-2 is off the current passes through the inductor, diode D3, switch-1, and diode D2 and the energy is stored in the inductor. At mode 2, when switch-1 is off and switch-2 is on the energy stored in the inductor is transferred through diode D6, switch-2 and diode D7.

**Figure 9.** Power circuit of the proposed AC voltage regulator.

**Figure 10.** Operation of the power circuit of AC voltage regulator (a) Operation during positive half cycle (b) Operation during negative half cycle

#### *3.1.2. Operation of control circuit*

130 An Update on Power Quality

These regulators are not suited for critical loads because the output waveforms are truncated sine waves, which contain large percentage of distortion. The input power factor is low. These drawbacks are largely overcome and the voltage can be efficiently controlled

The power circuit of the proposed AC voltage regulator is shown in Fig. 9. The circuit operation can be explained with the help of Fig. 10. During positive half cycle of the input voltage, at mode 1, when switch-1 is on and switch-2 is off, the current passes through diode D1, switch-1, diode D4 and through the inductor and the energy is stored in the inductor. At mode 2, when switch-1 is off and switch-2 is on, the energy stored in the inductor is transferred through diode D8, switch-2 and diode D5. At mode 1, power is transferred from source and at mode 2, power is not transferred from the source, so by controlling the on and

During negative half cycle of the input voltage, at mode 1, when switch-1 is on and switch-2 is off the current passes through the inductor, diode D3, switch-1, and diode D2 and the energy is stored in the inductor. At mode 2, when switch-1 is off and switch-2 is on the energy stored in the inductor is transferred through diode D6, switch-2 and diode D7.

+

+



D5 Gate signal 2

Switch 2

D8

L L

Mode 1, current path

Mode 2, current path

Switch 2

Switch 1

D6

0

Lo ad

TX1

**Figure 10.** Operation of the power circuit of AC voltage regulator (a) Operation during positive half

(a) (b)

0

D7

D4 0

by means of a solid-state AC regulator using PWM technique.

off duration of switch-1 output power can be controlled.

**Figure 9.** Power circuit of the proposed AC voltage regulator.

cycle (b) Operation during negative half cycle

Switch 1

Mode 1, current path

Mode 2, current path

Switch 2

D2

D1

Gate signal 1

+ - +

0


D3

The gate signal generating circuit for a manually controlled AC voltage regulator is shown in Fig. 11. The control circuit incorporates an Operational Amplifier (OPAMP) whose positive input is a variable DC voltage V1, and negative input is a fixed saw-tooth signal V2. In this circuit the OPAMP acts as a comparator, output of the OPAMP depends on the difference of the two inputs. The negative input (saw-tooth wave) is kept constant and positive input (DC voltage) is varied. So output pulse width depends on DC input voltage of OPAMP i.e. when DC input is higher the output of comparator will be wider and when DC input is lower the output of comparator will be narrower.

The outputs of OPAMP are used to turn on/off the switches of the power circuit of the regulator to regulate the output voltage. The output of OPAMP is directly passed through limiter-1 which is the gate signal for switch-1 and after inverting the output of the comparator is passed through the limiter-2 which is the gate signal for switch-2. The function of the limiter is to limit the output of comparator from 0 to 5 V. When switch-1 of the power circuit is on then switch-2 should be off. So the gate signal generating circuit is arranged in such a way that when gate signal of switch-1 is on then gate signal for switch-2 is off and vice versa.

**Figure 11.** Gate signal generation circuit of manually controlled AC voltage regulator.

#### **3.2. Manually controlled AC voltage regulator**

When the stability is not very stringent, manually controlled AC voltage regulator is generally preferred from economic considerations.

The basic circuit of a manually controlled AC voltage regulator is shown in Fig. 12. When any change in output voltage occurs due to change in input voltage or change in load, the voltage can be regulated to the desirable value by changing the DC voltage of the gate signal generating circuit manually. The power circuit of the proposed regulator shown in Fig. 12 is implemented using ideal switches; later part of this chapter the ideal switches is replaced by practical switches. The regulator proposed in this chapter is employed to regulate the output voltage to 300V (peak) for variations of input voltage from 200V (peak) to 400V (peak), also for variation of load from 100 ohm to 200 ohm. However, the output voltage can be set to any desirable value according to requirement. The values of all voltages and currents indicated in this chapter are in peak values.

Power Quality Improvement Using Switch Mode Regulator 133

**Figure 13.** Input current and output voltage waveforms of the regulator shown in Fig. 12.

 Time 0s 4ms 8ms 12ms 16ms 20ms

**Figure 14.** Spectrum of input current and output voltage waveforms. -I(V5):Input current V(R3:2):

For getting smooth output voltage, a low pass LC filter of proper L and C value is needed at the output of this regulator. The output filter circuit and the corresponding AC sweep are

0

 Frequency 0Hz 10KHz 20KHz 30KHz 40KHz 50KHz

> V JC <sup>V</sup> J( L-1 C)

 or <sup>0</sup> in

V 1 V C( L-1 C)


V2(R3)



0V

500V


0A

10A

Output voltage.

0V

200V

SEL>>

400V

0A

5A

10A

**3.3. Filter design** 

*3.3.1. Output filter design* 

V2(R3)


shown in Fig. 15. From this circuit we can write, in

The input current and output voltage waveforms of the manually controlled AC voltage regulator as shown in Fig. 12, is shown in Fig. 13, when the input voltage is 300V and output voltage is also 300V. The spectrum of the input current and output voltage as shown in Fig. 13 is shown in Fig. From the waveforms it is seen that the waveforms are not smooth, sinusoidal and from the spectrum it is seen that due to high frequency switching the significant number and amount of harmonics occur. The switching frequency is selected to 4 KHz. Harmonics occurs at switching frequency and its odd multiple frequencies. So, filters are required at input and output side to filter out these harmonics to get desired sinusoidal waveforms.

**Figure 12.** Fundamental circuit of manually controlled AC voltage regulator (ideal switch implementation).

**Figure 13.** Input current and output voltage waveforms of the regulator shown in Fig. 12. -I(V5): Input current, V(R3:2): Output voltage.

**Figure 14.** Spectrum of input current and output voltage waveforms. -I(V5):Input current V(R3:2): Output voltage.

#### **3.3. Filter design**

SW2

R6 100

0

5

TX1

0

5

0

SW1

132 An Update on Power Quality

waveforms.

Input

SW1

+ - + -

0

S1

implementation).

V1

FREQ = 50 VAMPL = 300 VOFF = 0

> TD = 0 TF = .125ms PW = .005ms PER = .255ms

TR = .125ms V2 = 0

V1 = 10

5Vdc

indicated in this chapter are in peak values.

voltage to 300V (peak) for variations of input voltage from 200V (peak) to 400V (peak), also for variation of load from 100 ohm to 200 ohm. However, the output voltage can be set to any desirable value according to requirement. The values of all voltages and currents

The input current and output voltage waveforms of the manually controlled AC voltage regulator as shown in Fig. 12, is shown in Fig. 13, when the input voltage is 300V and output voltage is also 300V. The spectrum of the input current and output voltage as shown in Fig. 13 is shown in Fig. From the waveforms it is seen that the waveforms are not smooth, sinusoidal and from the spectrum it is seen that due to high frequency switching the significant number and amount of harmonics occur. The switching frequency is selected to 4 KHz. Harmonics occurs at switching frequency and its odd multiple frequencies. So, filters are required at input and output side to filter out these harmonics to get desired sinusoidal

**Figure 12.** Fundamental circuit of manually controlled AC voltage regulator (ideal switch

0

V2

3

+


2

0 0

V4 12Vdc

AD648A

V3

8

> V+

V-

4

0

0

0



+

+


SW2

S2

12Vdc

OUT

1

#### *3.3.1. Output filter design*

For getting smooth output voltage, a low pass LC filter of proper L and C value is needed at the output of this regulator. The output filter circuit and the corresponding AC sweep are shown in Fig. 15. From this circuit we can write, in 0 V JC <sup>V</sup> J( L-1 C) or <sup>0</sup> in V 1 V C( L-1 C)

The input to the filter is high frequency modulated 50 Hz AC input. The switching signal that modulates the 50 Hz signal is taken to be 4 KHz in this case. So, we will have to make a filter that would pass signal up to 1 KHz (say) and attenuate all other frequencies. This would result a nearly sinusoidal output voltage. In the LC filter section we choose a capacitor of 5µF and determine the value of inductor for a cutoff from AC sweep analysis through OrCAD simulation. We found the value of the inductor to be 30 mH.

Power Quality Improvement Using Switch Mode Regulator 135

C2 5u

L2 30mH

TX1

0

R3 100

**3.4. Free wheeling path and surge voltage across switching devices** 

freewheeling path in restricts such occurrence.

switch-1, V(S2:3)-V(S2:4): Voltage across switch-2.

V(S2:3)- V(S2:4)

V(S1:3)- V(S1:4)

*3.4.1. Surge voltage across switches* 

intervals as shown in Fig. 18.

L1 30mH

Input

0V

200KV

400KV

200KV

SEL>>

400KV

0V

FREQ = 50 VAMPL = 300

0

C1 5u

0

+ - + - S1

SW1

The power circuit of the proposed regulator with input and output filter is shown in Fig. 17. In an inductor, current does not change instantaneously. When the switches of power circuit switched on and off the current into the inductor of input and output filter are changed abruptly. Abrupt change of current causes a high di/dt resulting high voltage which is equal to Ldi/dt. These voltages appear across the switches as surge. Usually providing

In the proposed circuit, two switches serve as the freewheeling path for each other. However, for very short period when one switch is turned off and other is turned on, an interval elapses due to delay in the switching time. As a result, freewheeling during this interval is disrupted in the proposed circuit. If the current in any inductive circuit is abruptly disrupted, a high Ldi/dt across the switch appears due to the absence of freewheeling path. High spiky surge voltage appears across the switches during these short

**Figure 17.** The power circuit of the proposed AC voltage regulator with input and output filters.



0

+

+

S2

SW2

**Figure 18.** Voltage across switches with filters and without snubbers. V(S1:3)-V(S1:4): Voltage across

 Time 0s 4ms 8ms 12ms 16ms 20ms

**Figure 15.** Output voltage filter and AC sweep analysis (a) Output voltage filter (b) AC sweep analysis.

#### *3.3.2. Input filter design*

A low pass LC filter of proper L and C value is needed at the input of the regulator to filter out some of the harmonics from the supply system. The input filter circuit and the corresponding AC sweep are shown in Fig. 16. Input current contains harmonics at switching frequency 4 KHz and its odd multiple. In order to remove harmonics above 1 KHz, we choose a capacitor of 5µF and determine the value of inductor for a cutoff from AC sweep analysis through OrCAD simulation. We found the value of the inductor to be 30 mH.

**Figure 16.** Input current filter and corresponding AC sweep analysis (a) Input current filter (b) AC sweep analysis.

### **3.4. Free wheeling path and surge voltage across switching devices**

The power circuit of the proposed regulator with input and output filter is shown in Fig. 17. In an inductor, current does not change instantaneously. When the switches of power circuit switched on and off the current into the inductor of input and output filter are changed abruptly. Abrupt change of current causes a high di/dt resulting high voltage which is equal to Ldi/dt. These voltages appear across the switches as surge. Usually providing freewheeling path in restricts such occurrence.

#### *3.4.1. Surge voltage across switches*

134 An Update on Power Quality

300Vac Input

L1 30mH

> C1 5u

> > 0

0Vdc

*3.3.2. Input filter design* 

30mH

0Adc 20Aac

sweep analysis.

Input

The input to the filter is high frequency modulated 50 Hz AC input. The switching signal that modulates the 50 Hz signal is taken to be 4 KHz in this case. So, we will have to make a filter that would pass signal up to 1 KHz (say) and attenuate all other frequencies. This would result a nearly sinusoidal output voltage. In the LC filter section we choose a capacitor of 5µF and determine the value of inductor for a cutoff from AC sweep analysis

**Figure 15.** Output voltage filter and AC sweep analysis (a) Output voltage filter (b) AC sweep analysis.

0V

250V

500V

Frequency

Frequency

10Hz 100Hz 1.0KHz 10KHz


10Hz 100Hz 1.0KHz 10KHz

V(R1:2)

(a) (b)

A low pass LC filter of proper L and C value is needed at the input of the regulator to filter out some of the harmonics from the supply system. The input filter circuit and the corresponding AC sweep are shown in Fig. 16. Input current contains harmonics at switching frequency 4 KHz and its odd multiple. In order to remove harmonics above 1 KHz, we choose a capacitor of 5µF and determine the value of inductor for a cutoff from AC sweep analysis through

**Figure 16.** Input current filter and corresponding AC sweep analysis (a) Input current filter (b) AC

(a) (b)

0A

10A

OrCAD simulation. We found the value of the inductor to be 30 mH.

20A L1

R1

0

C1 5u

through OrCAD simulation. We found the value of the inductor to be 30 mH.

R1 100 In the proposed circuit, two switches serve as the freewheeling path for each other. However, for very short period when one switch is turned off and other is turned on, an interval elapses due to delay in the switching time. As a result, freewheeling during this interval is disrupted in the proposed circuit. If the current in any inductive circuit is abruptly disrupted, a high Ldi/dt across the switch appears due to the absence of freewheeling path. High spiky surge voltage appears across the switches during these short intervals as shown in Fig. 18.

**Figure 17.** The power circuit of the proposed AC voltage regulator with input and output filters.

**Figure 18.** Voltage across switches with filters and without snubbers. V(S1:3)-V(S1:4): Voltage across switch-1, V(S2:3)-V(S2:4): Voltage across switch-2.

These spiky voltages across the switches may be excessively high, about thousand of kilovolt and which may destroy the switches during the operation of the circuit. Remedial measures should be taken to prevent this phenomenon to make the circuit commercially viable. In the proposed circuit RC snubbers are used for suppressing surge voltage across the switches. The power circuit of the proposed regulator with input output filter and snubbers is shown in Fig. 19.

Power Quality Improvement Using Switch Mode Regulator 137

TX1 Z2 R14

U4

R6

0

R13 1

D8

D10

2 6 0

R16 0 R9

U2A

C5 0.1u D6

U3

0

R15

G2 C4

L2 30mH

R7

15V

R8

5u

V3

S2

G2

15V

100

G1

S1

V4

0

**3.5. Proposed AC voltage regulator with practical switches** 

**Figure 21.** Manually controlled AC voltage regulator circuit with practical switches.

D4

D3

0

R1

V2 10Vdc

SG1524B

0

A4N25A <sup>0</sup>

R11 0.001

D7

D5 S2

A4N25A V6

CD4009A

3 2

R5

2 6 0

0

0

1 R10

0

9

0

COMP

8

GND

10

R2 1k

0

C2 0.001u

SHUT

C\_A E\_A E\_B C\_B

OSC

C6 0.1u

D9

R12 0.001

D1

100uVdc

0

Z1

G1

D2

S1

The Block diagram of the internal circuitry of the chip SG1524B is shown in Fig. 22. By controlling the error signals of the error amplifier the duty cycle of the gate signal to the

*3.5.1. Chip SG1524B for generation of gate signal* 

C3 5u

L1 30mH

0

0

V1 20Vdc

R4 1

R3 50k

V5

FREQ = 50 VAMPL = 300

S-break switch is replaced by IGBT.

signaling voltage with ground isolation.

15

C1 4000pf

> 7 6

U1

VIN

CT RT

ERR-ERR+ CL+ CL-

16

3

VREF

In the previous section, we have studied the regulator using ideal S-break switches which have been operated by the pulses from the limiter. But for practical application, real switches are essential which are to be controlled by the pulses having ground isolation. The proposed AC voltage regulator circuit with practical switches is shown in Fig. 21. The ideal

In the proposed regulator chip SG1524B is used to control the gate signal. Signal from the chip is fed to the Limiter and finally to the optocoupler. The output of the optocoupler is used to control the on off time of the IGBTs. The function of the Limiter is to limit the output voltage of the gate signal generating IC from 0 to 6 volts. Optocoupler is used to generate

Snubber enhances the performance of the switching circuits and results in higher reliability, higher efficiency, higher switching frequency, smaller size and lower EMI. The basic intent of a snubber is to absorb energy from the reactive elements in the circuit. The benefits of this may include circuit damping, controlling the rate of change of voltage or current or clamping voltage overshoot. The waveforms of voltages across switches with input output filters and snubbers are shown in Fig. 20.

Use of snubbers reduces the spiky voltage across the switches to a tolerate limit for practical application of the AC voltage regulator.

**Figure 19.** The power circuit of the proposed AC voltage regulator with input output filters and snubbers.

**Figure 20.** Voltage across switches with filters and snubbers. V(S1:3)-V(S1:4): Voltage across switch-1, V(S2:3)-V(S2:4): Voltage across switch-2.

### **3.5. Proposed AC voltage regulator with practical switches**

136 An Update on Power Quality

snubbers.

snubbers is shown in Fig. 19.

filters and snubbers are shown in Fig. 20.

application of the AC voltage regulator.

C1 5u

0

Input

L1 30mH

FREQ = 50

V(S2:3)-V(S2:4): Voltage across switch-2.

0V

200V

SEL>>

400V

200V

400V

0V

V(S2:3)- V(S2:4)

V(S1:3)- V(S1:4)

These spiky voltages across the switches may be excessively high, about thousand of kilovolt and which may destroy the switches during the operation of the circuit. Remedial measures should be taken to prevent this phenomenon to make the circuit commercially viable. In the proposed circuit RC snubbers are used for suppressing surge voltage across the switches. The power circuit of the proposed regulator with input output filter and

Snubber enhances the performance of the switching circuits and results in higher reliability, higher efficiency, higher switching frequency, smaller size and lower EMI. The basic intent of a snubber is to absorb energy from the reactive elements in the circuit. The benefits of this may include circuit damping, controlling the rate of change of voltage or current or clamping voltage overshoot. The waveforms of voltages across switches with input output

Use of snubbers reduces the spiky voltage across the switches to a tolerate limit for practical

SW2

S2

L2 30mH

TX1

5u

0

R3 100

**Figure 19.** The power circuit of the proposed AC voltage regulator with input output filters and

VAMPL = 300 C2

C3 0.1u

0



+

+

R6 1

C5 0.1u

R5 1

+ - + - S1

0

SW1

**Figure 20.** Voltage across switches with filters and snubbers. V(S1:3)-V(S1:4): Voltage across switch-1,

 Time 0s 5ms 10ms 15ms 20ms In the previous section, we have studied the regulator using ideal S-break switches which have been operated by the pulses from the limiter. But for practical application, real switches are essential which are to be controlled by the pulses having ground isolation. The proposed AC voltage regulator circuit with practical switches is shown in Fig. 21. The ideal S-break switch is replaced by IGBT.

In the proposed regulator chip SG1524B is used to control the gate signal. Signal from the chip is fed to the Limiter and finally to the optocoupler. The output of the optocoupler is used to control the on off time of the IGBTs. The function of the Limiter is to limit the output voltage of the gate signal generating IC from 0 to 6 volts. Optocoupler is used to generate signaling voltage with ground isolation.

**Figure 21.** Manually controlled AC voltage regulator circuit with practical switches.

#### *3.5.1. Chip SG1524B for generation of gate signal*

The Block diagram of the internal circuitry of the chip SG1524B is shown in Fig. 22. By controlling the error signals of the error amplifier the duty cycle of the gate signal to the regulator can be controlled. Thus it is a very suitable device for using in the regulator circuits.

Power Quality Improvement Using Switch Mode Regulator 139

**Figure 24.** Input and output voltage waveforms, Input 400V output 300V. V1(V5): Input voltage –

Time

0s 50ms 100ms 150ms 200ms

**Figure 25.** Input and output current waveforms for input 200V output 300V. -I(V5): Input current -

Time

0s 50ms 100ms 150ms 200ms

**Figure 26.** Input and output current waveforms for input 400V output 300V. -I(V5): Input current –

Time

0s 50ms 100ms 150ms 200ms

dotted line, V(R14:2): Output voltage – solid line.




0A

4.0A

0A

5.0A

0V

400V

V1(V5) V(R14:2)

dotted line, -I(R14): Output current – solid line.


dotted line, -I(R14): Output current – solid line.


#### *3.5.2. Results of proposed AC voltage regulator (practical switch implementation)*

The waveforms of the input and output voltages of the proposed regulator are shown in Fig. 23 and Fig. 24. Fig. 23 shows the input and output voltages waveform when the input voltage is 200V and output voltage is 300V. Fig. 24 shows the input and output voltages waveform when the input voltage is 400V and output voltage is 300V. Fig. 25 and Fig. 26 show the input and output current waveforms corresponding to Fig. 23 and Fig. 24.

**Figure 22.** Block diagrm of IC chip SG1524B

**Figure 23.** Input and output voltage waveforms, Input 200V output 300V. V1(V5): Input voltage – dotted line, V(R14:2): Output voltage – solid line.

**Figure 22.** Block diagrm of IC chip SG1524B

10 1 kΩ

GND <sup>8</sup>

SHUTDOWN


0V

400V

CURR LIM - CURR LIM + 5

COMP <sup>9</sup>

IN - IN + 1 2

7 CT RT 6

VCC 15

dotted line, V(R14:2): Output voltage – solid line.

V1(V5) V(R14:2)

circuits.

regulator can be controlled. Thus it is a very suitable device for using in the regulator

The waveforms of the input and output voltages of the proposed regulator are shown in Fig. 23 and Fig. 24. Fig. 23 shows the input and output voltages waveform when the input voltage is 200V and output voltage is 300V. Fig. 24 shows the input and output voltages waveform when the input voltage is 400V and output voltage is 300V. Fig. 25 and Fig. 26

Vref

*3.5.2. Results of proposed AC voltage regulator (practical switch implementation)* 

show the input and output current waveforms corresponding to Fig. 23 and Fig. 24.

Oscillator

Vref

Error Amplifier

Vref

Comparator

Vref

16

REF OUT

COL 1

COL 2 EMIT 1

EMIT 2 OSC OUT

**T** 

+ –

Vref

Reference Regulator

+ –

<sup>4</sup>Vref

10 kΩ

**Figure 23.** Input and output voltage waveforms, Input 200V output 300V. V1(V5): Input voltage –

Time

0s 50ms 100ms 150ms 200ms

**Figure 24.** Input and output voltage waveforms, Input 400V output 300V. V1(V5): Input voltage – dotted line, V(R14:2): Output voltage – solid line.

**Figure 25.** Input and output current waveforms for input 200V output 300V. -I(V5): Input current dotted line, -I(R14): Output current – solid line.

**Figure 26.** Input and output current waveforms for input 400V output 300V. -I(V5): Input current – dotted line, -I(R14): Output current – solid line.

From the waveforms shown in Fig. 23 to Fig. 26, it is seen that the waveforms of output voltage and input current is perfectly sinusoidal. The variation of output voltage of the proposed regulator with the duty cycle is shown in Fig. 27. The value of input voltage is kept constant to 300V. From Fig. 23 it is seen that the variation of output voltage with duty cycle is almost linear. The variation of duty cycle with the variation of input voltage from 200V to 400V to maintain the output voltage constant to 300V is shown in Fig. 28.

Power Quality Improvement Using Switch Mode Regulator 141

There are two types of automatic control voltage regulator, discontinuous control and continuous control. The automatic control system consists of a sensing or measuring unit and a power control or regulating unit. The sensing unit compares the output voltage or the controlled variable with a steady reference and gives an output proportional to their difference called the error signal. The error voltage is amplified, integrated or differentiated or modified whenever necessary. The processed error voltage is fed to the main control unit

In the discontinuous type of control, the measuring unit is such as to produce no signal as long as the voltage is within certain limits. When the voltage goes outside this limit, a signal is produced by the measuring unit until the voltage is again brought within this limit. In this type of measuring or sensing unit, the correcting voltage is independent of percentage of error. When the voltage is brought back to this limit, the signal from the measuring unit is zero and the regulating unit remains at its new position until another signal is received from

In continuous control, the measuring unit produces a signal with amplitude proportional to the difference between the fixed reference and the controlled voltage. The output of the measuring unit is zero when the controlled voltage or a fraction of it is equal to the reference voltage. The regulating or the controlling unit, which is associated with the continuous measuring unit, gives a correcting voltage proportional to the output of the measuring unit. The principle of operation of a continuous control AC voltage regulator is described in this

Figure 29 shows the circuit of the proposed automatic controlled AC voltage regulator including the control and gate signal generating circuit. A fraction of the output voltage after capacitor voltage dividing and rectifying is passed through an OPAMP buffer. Buffer is used to remove the loading effect. Output voltage of the buffer is same as its input voltage. The output voltage of the buffer is further reduces using resistive voltage divider and taken as the negative input of the error amplifier of the PWM voltage regulating IC SG1524B.

The positive input of the error amplifier is taken from the reference voltage of the chip, after voltage dividing using 50K and 1 ohm resistance. The positive input of the error amplifier is fixed and the negative input is error signal which will vary according to the output voltage. Since the error signal is applied to the negative input of the error amplifier, the duty cycle

When the output voltage increases above the set value which is 300V either due to change in input voltage or load, the error signal will be increased, therefore the duty cycle will decrease. As a result less power will be transferred from the input to output, and output

When the output voltage decreases below the set value either due to change in input voltage or load then error signal will be decreased which will increase the duty cycle. As a result,

will be increased if the error signal is decreased and vice versa.

voltage start to decrease until it reaches to the set value.

**4.1. Control and gate signal generating circuit for controlled AC voltage** 

to have required corrective action.

the measuring unit.

section.

**regulator** 

**Figure 27.** Variation of output voltage with duty cycle. Input voltage is 300V.

**Figure 28.** Variation of duty cycle with input voltage to maintain output voltage constant to 300V.

### **4. Automatic controlled AC voltage regulator**

In manually controlled AC voltage regulator control, the output voltage is sensed with a voltmeter connected at the output; the decision and correcting operation is made by a human judgment. The manual control may not be feasible always due to various factors. In automatic voltage regulators, all functions are performed by instruction, and give much better performance, so far as stability, speed of correction, consistency, fatigue, etc. are concerned.

There are two types of automatic control voltage regulator, discontinuous control and continuous control. The automatic control system consists of a sensing or measuring unit and a power control or regulating unit. The sensing unit compares the output voltage or the controlled variable with a steady reference and gives an output proportional to their difference called the error signal. The error voltage is amplified, integrated or differentiated or modified whenever necessary. The processed error voltage is fed to the main control unit to have required corrective action.

140 An Update on Power Quality

From the waveforms shown in Fig. 23 to Fig. 26, it is seen that the waveforms of output voltage and input current is perfectly sinusoidal. The variation of output voltage of the proposed regulator with the duty cycle is shown in Fig. 27. The value of input voltage is kept constant to 300V. From Fig. 23 it is seen that the variation of output voltage with duty cycle is almost linear. The variation of duty cycle with the variation of input voltage from

> 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Duty cycle

200V to 400V to maintain the output voltage constant to 300V is shown in Fig. 28.

**Figure 27.** Variation of output voltage with duty cycle. Input voltage is 300V.

0.2 0.3 0.4 0.5 0.6 0.7 0.8

Duty cycle

Output voltage (V)

**4. Automatic controlled AC voltage regulator** 

concerned.

**Figure 28.** Variation of duty cycle with input voltage to maintain output voltage constant to 300V.

In manually controlled AC voltage regulator control, the output voltage is sensed with a voltmeter connected at the output; the decision and correcting operation is made by a human judgment. The manual control may not be feasible always due to various factors. In automatic voltage regulators, all functions are performed by instruction, and give much better performance, so far as stability, speed of correction, consistency, fatigue, etc. are

175 225 275 325 375 425 Input voltage (V)

In the discontinuous type of control, the measuring unit is such as to produce no signal as long as the voltage is within certain limits. When the voltage goes outside this limit, a signal is produced by the measuring unit until the voltage is again brought within this limit. In this type of measuring or sensing unit, the correcting voltage is independent of percentage of error. When the voltage is brought back to this limit, the signal from the measuring unit is zero and the regulating unit remains at its new position until another signal is received from the measuring unit.

In continuous control, the measuring unit produces a signal with amplitude proportional to the difference between the fixed reference and the controlled voltage. The output of the measuring unit is zero when the controlled voltage or a fraction of it is equal to the reference voltage. The regulating or the controlling unit, which is associated with the continuous measuring unit, gives a correcting voltage proportional to the output of the measuring unit. The principle of operation of a continuous control AC voltage regulator is described in this section.
