INVERTER

What is Inverter?

A power inverter, or inverter, is an electronic device/circuitry that converts direct current (DC) into alternating current (AC). The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry.

An inverter mainly consists of 1) batteries, 2) Oscillator & 3) transformer

Batteries –

Battery is used as a DC power source. Ac supply is used to charge the batteries through charger.

Oscillator –

The function of oscillator is to cut continuous DC signal (say 12V) into multiple positive & negative signals (magnitude 12V) which are in square form at a fixed frequency (say 50 Hz). Output waveform depends on the design of the oscillator. The low magnitude oscillated signal can be amplified (say 50V) by using an Amplifiers.

Transformer –

The function of transformer is to step up input signal (which is the output of oscillator) from 50V to 220V.Output voltage of transformer depends on winding ratio of transformer.

WORKING PRINCIPLE –

When normal AC supply is available, the load is fed directly from normal AC supply & this AC supply charges the batteries through battery charger.

When normal AC supply is not available, this is sensed by sensors &change over relays and oscillator starts producing 50Hz signal. This signal is further amplified by amplifier circuits. This amplified signal is fed to inverter transformer which produces output signal of 220V.

Changeover from AC mains to Inverter takes a few seconds. That is why inverters are suitable for domestic equipment like lamps, fans, fridge, radio etc but not suitable for electronic equipment like Computers etc where this delay in changeover may corrupt/lose the data. So UPS is the best option for Computer applications where changeover takes place immediately (without any interruption of power).

Output waveform from Inverter –

An inverter can produce a square wave, modified sine wave, pure sine wave, pulse width modulated wave (PWM) or sine wave depending on circuit design.

a) Square waveform

This is one of the simplest waveforms an inverter design can produce and is best suited to low-sensitivity applications such as lighting and heating. Square wave output can produce “humming” when connected to audio equipment and is generally unsuitable for sensitive electronics.

b) Modified sine wave

A modified sine wave inverter has a non-square waveform that is a useful approximation of a sine wave for power translation purposes.

Most inexpensive power inverters produce a modified sine wave rather than a pure sine wave. The operation of the modified sine wave inverters will be same as a square wave inverter. These modified sine waves can be used by most household electrical devices. It is extremely common to see this type of inversion in industrial quality inverters. It acts like a pure sine-wave, modified sine waves are mainly used for very high efficiency equipments such as microwaves, drills and clocks or motors.

c) Pure Sine wave

A power inverter device which produces a sinusoidal AC waveform is referred to as a sine wave inverter. Such inverters are very expensive & use rotating electrical machinery & mostly used in industries. A pure sign wave inverter improves the functions of equipment.

Harmonics –

Harmonics are the frequencies that are produced along with the main or fundamental frequency which is produced by inverter. These additional/extra frequencies/harmonics reduces the efficiency of the invertor by heating the equipment. When harmonics are present in the system then motors make noise while in operation. Harmonics are produced in multiple wave forms, normally 3 step, 5 step,..frequency so these harmonics are called 3^rd or 5^th or…harmonics.

DIFFERENCE BETWEEN UPS&INVERTER –

S.No.	PARAMETERS	UPS	INVERTER
1	Change-over time	There is no time gap when power goes off & power is supplied by UPS to the load	There is some delay of few seconds in changeover by inverter.
2	Design technology	Batteries, charger & inverter are used for UPS	Batteries, charger, Oscillator, Amplifier & transformer are used for inverter
3	Output voltage	Pure sign wave output voltage is produced by UPS	Various types of out voltages are produced by Inverter depending on the design like square wave, modified sign wave, pure sign wave
4	Harmonics/distortion	Harmonics produced which are subsided by suitable filters	Some harmonics are present in the inverter depending of the type of design. Motors makes noise during operation if harmonics are present in the output voltage
5	Maintenance	No maintenance is required as sealed batteries (maintenance free batteries) are used	Battery maintenance is required as Led Acid batteries are used
6	Application	It is suitable for computer back up, sophisticated electronic equipment etc	It is suitable for domestic lighting, fans, TV & other appliances
7	Prize	UPS is expensive as compared to inverter as there is no gap in power change-over	Its less expensive than UPS as some time delay is there in power change-over

Frequently Asked Questions (FAQs) on Inverter-

Q1) What is dual inverter?

Ans) Dual inverter term is used for air conditioners (AC), it is an advanced technology of inverter which has two (or dual) rotary compressors. This technology makes AC more energy efficient, produce less vibration & ensures faster cooling.

Q2) What is the difference between dual inverter AC & single inverter AC?

Ans) The difference between single inverter and dual inverter is given below –

Single compressor/inverter AC – It has a variable speed single cylinder compressor with a single compressor chamber. The function of this compressor is to regulate the cooling of AC. Single Inverter AC uses BLDC (Brushless Direct Current) motor that is able to regulate compressor’s speed as per demand.

Non-inverter AC– Before inverter technology in AC, reciprocating compressors were used that produces lot of noise, vibration & consume lot of energy. Therefore, we can say that single inverter AC is also energy efficient & produce lass vibration as compared to normal ACs (or non-inverter AC) which has reciprocating compressors.

Dual inverter AC – The dual inverter AC uses twin rotary compressor with two compressor chambers which produces a phase difference of 180 degree compressing timing. These inverters also use more advanced BLDC motor that boost rotational speed & reduces vibration. Therefore, in simple words we can say that dual inverter provides more flexibility to regulate the cooling of AC which makes AC more energy efficient, less vibration & faster cooling. The life span of dual inverter AC is more than the single inverter AC.

Q3) Is triple inverter AC level available & how it is different from dual inverter AC.

Ans) Triple inverter AC is also available but very limited produced by few brands. Triple inverters use 8-pople motor while dual inverter uses 4-pole motor. The advantage of 8-pole motor is to produce less torque fluctuation & reduce vibration further. This makes AC even more silent. But, the cost is much higher than dual inverter AC.

Q3) Which battery is best for inverter?

Ans) A battery is a very important part of inverter because it provides power to the load when power goes off. Therefore, we should select an inverter battery very carefully.

Technology wise if we talk about batteries then Tubular batteries are best batteries for home or office inverters. The reason is that these batteries are suitable in areas where more power cuts are there with longer duration because –

It has longer service life,
It requires less maintenance & need fewer water top-ups,
It is reliable & comes with longer warranty period,

Generally, two types of tubular batteries are available in market – short tubular batteries & tall tubular batteries.

Short tubular battery – It is smaller in height & wider that is why it is easy to carry & store.

Tall tubular battery – It is taller & has less width as compared to short tubular battery. But it provides a slightly more back up time & is suitable homes which have no space constrain.

Q4) How to calculate inverter back up time?

Ans) Inverter back up is also very important before buying an inverter for home or office because it ensures the continuity of power supply in case of power failure. Following procedure must be followed for calculation of inverter back up –

Duration of power back up – first we should check that on an average how long power is not available e.g. 2 Hrs, 5 Hrs etc.
Load that is to be fed with inverter during power failure – such as number of lights, fans etc.
The above two factors decide Ah (Ampere hour) rating of battery. Battery capacity will be more if load is more & more duration of power back is required. Now, let’s calculate Ah rating of battery –

Let’s consider – 4 ft tube lights, 2 ceiling fans & 1 LED which are to be connected with inverter. Calculate total load –

4 ft lights – 40W x 4 = 160W
2 ceiling fan – 75W x 2 = 150W
1 LED light – 9W x 1 = 9W

Total wattage = 319 W

Let’s say we select 150Ah battery & battery voltage is 12V. Power of single phase supply – P = V I Cosɸ or I = P/ V Cosɸ

Where, P = 319 W, V = 12V, Cosɸ = 1

Current, I = 319/(12 x 1)= 26.58 A

Therefore, Time formula in hour for battery, h = battery capacity / Current, I

Or Time, h = 150/26.58 = 5.6 Hr

Therefore, we can say that 150Ah battery will provide 5.6 hr power to the load mentioned above in case of power failure.

Q5) What is sign wave inverter?

Ans) A sign wave inverter which provides output voltage with sinusoidal sign waveform. Sign wave inverter are costly because it is better than other inverters & it improves the performance of the equipment.

Detail of working of sign wave inverter is given in above sections of this page.