tronix design

8/2/2019 Tronix Design

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ON-LINE

UPS

Design of power

electronic circuits

Siddharth Bhowmik -07000418

Kumar Utkarsh -07000419

Chandan Kumar -07000420

Smriti Agarwal -07000421

Sharath M -07000422

N Viswanath -07000424

BTech IIIElectrical Engineering


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IntroductionThis reference design describes the design of a single phase on-line uninterruptable power supply (UPS).

UPSs are used to protect sensitive electrical equipment such as computers, workstations, servers, and

Other power-sensitive systems.

The online ups or a true ups is totally opposite to the conventional standby UPS. Both of these are

similar in that they have the same two power source and a transfer switch that selects between them.

The online UPS is exactly opposite from the standby UPS because here the primary power source is the

UPSs battery and utility power source is the secondary source.

Under normal operation, the online UPS is always running off the battery using its inverter while the line

power runs battery charger. Thus, it is also called a double conversion online UPS. If the power goes out,

the load continues to get power through the inverter and only the battery charging fails. Thus, there is

no transfer time in the event of power failure, only the battery starts to rundown.

If the primary equipment fails, then the transfer switch is used to switch to the utility power source.

Here transfer time comes into play. Another key advantage to having the equipment running off the

battery most of the time is that the double conversion process completely isolates the load from the line

power.

On-line UPS works on double conversion topology. This name arises from the operating principle of an

on-line UPS. When the UPS works in normal operation mode, while the mains line (or the power cord for

the ac line) is available, the input voltage is rectified to the dc bus. The output inverter converts the dc

bus voltage back to a pure sinusoidal voltage. The dc/dc converter is connected to the dc bus and

converts the battery voltage to the dc bus level. The converter is activated during a power failure, and

delivers the energy stored in the batteries to the dc bus. The dc bus voltage is again converted to a pure

sine voltage. A battery charger is used to charge the batteries. The charger can be powered from the

mains line or from the dc bus.


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Primary Circuit


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Various parts of online UPS1. Rectifier

2. Battery charger

3. Battery

4. Buck converter

5. Boost converter

6. Inverter

7. Transfer switch

Battery charger consists of rectifier, buck converter and power BJT switch for pulsed charging.

Rectifier

We use a full bridge rectifier with an output filter in our circuit. This converts the output to a rectified

DC. The schematic and values of LC filter are as follows:

L = 0.03682H and C = 0.00039307F.


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Battery Charger

Types of battery charging methods:

Constant Voltage Constant Current Pulsed Charging Taper Current Burp Charging IVI Charging Trickle Charging Float Charging Random Charging

The battery charger is actually a buck converter circuit designed to produce the voltage levels necessary

to meet the battery specification. Pulse charging technique is implemented to charge the battery. Pulse

chargers feed the charge current to the battery in pulses. The charging rate can be precisely controlled

by varying the width of pulses, typically about 1s. During the charging process, short rest periods of 20

to 30ms between pulses allow the chemical actions in the battery to stabilize by equalizing the reactions

throughout the bulk of the electrode before recommencing the charge. This enables the chemical

reaction to keep pace with the rate of inputting electric energy. This method can reduce unwanted

chemical reactions at electrode surface.

Operation of battery charger:

The battery voltage is monitored in a loop, it is compared to V th,lower and Vth,upper using the

comparator. As the battery charges to a voltage level beyond upper threshold the buck converter is

turned off. Similarly a drop in battery charge to a voltage level below lower threshold the converter is

turned on. Thus the battery voltage is maintained regulated well within the lower and upper threshold

limits neglecting the small ripple which is inevitable.


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Buck converter

0

R1

0.025k

2

1

+

-

+

-

S1

S

VON = 1.0V

VOFF = 0.0V

V1

1Vdc

1.000V

10.00V

C1

470u

1

2

V2

207.07Vdc

207.5V

V3

TD = 0

TF = 1n

PW = 0.017341m

PER = 0.05m

V1 = 10

TR = 1n

V2 = -1

L1

1mH

1 2

0

D2

UT268


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Boost converter:

V4

72Vdc

L1

10mH

1 2D2

UT268

C1

470u

1

2

0

R1

0.25k

2

1

V2

TD = 0

TF = 10ns

PW = 41u

PER = 50u

V1 = -1

TR = 10ns

V2 = 8

+ -

+- S1

S

VON = 1V

VOFF = 0.0V

V3

1Vdc

0


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Inverter using switch mode PWM:


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PWM output pulses:

Discrepancy in PWM pulses:

Inverter output:


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Base drive circuit:

Output of the base drive circuit:

BATTERY SPECIFICATION

The battery used in our design has the following specifications:

1.) Battery voltage rating -:72 volts2.) Battery capacity -:7 ampere-hour


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Input Specifications

Input frequency:- 50Hz Input voltage:-230V rms Single phase

Functional Modes

On-line: If the input power is available, the UPS supplies a load and eliminates all possibledefects on the line (online double conversion)

Battery: If the input power is not available, the UPS supplies a load from batteries. The backuptime is given by battery capacity.

Bypass: The UPS directly connects its output and input, so the load is directly connected to theinput line. The transition to this mode is set manually or automatically during overload or fault.

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