Why choose DC inverter Air Conditioner over Traditional Conditioner?

Power efficiency in electronics and other appliances is always something hot to talk on. Air Conditioning is one of those appliances which are energy hungry and where efficiency of its components from which compressor is the most power consuming needs to be looked after.

Function of traditional Air Conditioner

We have been using traditional Air Conditioning systems for so long and we know how the compressor does its job in maintaining the right temperature. When AC is connected to the mains, the compressor starts to work and tries to get to the right specified temperature as set by the user. As soon as it reaches that temperature, it shuts down until thermostat realizes that room temperature has again gone up. This makes the compressor to start again, lowers the temperature of the room and shuts down until next signal from thermostat is received. This start and stop of the compressor is the problem as it consumes a lot of power during this process.

Why is that? The cycle begins when the compressor draws in cool, low-pressure refrigerant gas from the indoors. The motor-driven compressor’s sole function is to squeeze the refrigerant, raising its temperature and pressure so that it exits the compressor as a hot, high-pressure gas.
Second problem with the compressors of traditional air conditioners is that as the speed of the motor cannot be controlled, it takes a lot of time for a compressor to be able to reach to a specific low temperature. In short, it is either on or off. Usually, this on and off characteristic of such air conditioners are not noticeable but it is still a problem as it draws either maximum power or no power at all.

This process requires a whole lot of power making traditional air conditioners to be very inefficient on these two terms.

DC Inverter Air Conditioner

Basic Inverter Circuit

Prior to what normal air conditioning was like, with all the inefficiencies and power hungry compressor; the so called DC inverter is used to solve them all. Let’s find out!

DC inverter Air Conditioner consist of a step down transformer to step down the main voltage to a desired voltage level, a full bridge rectifier, a capacitor, and four switches (FET). After the AC voltage is stepped down it is then rectified into pulsating DC voltage which is filtered into a smooth DC level by a smoothing capacitor. Now the trick is, switch Q1 and Q4 are synchronized while Q2 and Q3 are synchronized. Now when Q1 and Q4 are turned ON, current starts flowing and flows through an AC motor/load from left to right. After a suitable time, switch Q1 and Q4 are turned OFF while Q2 and Q3 are turned ON, current starts flowing through load from right to left. This makes an alternating current flowing through the load. This creation of alternating current is called an inverter.

The main problem is: when to switch ON and OFF the switches. This is done by a microcontroller by generating a square wave of period 20 ms to turn on/off switches at 50 Hz. Just simply give this square wave to Q1 and Q4, while give a 180 degree phase shifted version to Q2 and Q3. This will make a perfect AC square wave across the load. In the circuit below, a pulse square wave source is used. A NOT gate is also used to make a 180 degree phase shift.

AC voltage across the load (bulb)

As AC uses a three phase motor in its compressor, you’ll need to tweak the circuit above by adding a switching system to generate three phase AC square wave which will take another two or three pages with illustration to explain, so later.

But why prefer DC inverter AC? If you have noticed, PWM (Pulse Width Modulation) signal from microcontroller was used to turn the switches. By simply adjusting the duty cycle, we can increase or decrease the power given to the compressor. The compressor of an inverter AC can work at variable speeds. When temperature of room rises more than the set temperature, compressor speeds up and brings the temperature down. After reaching the desired temperature, compressor slows down reducing the power loss. Compressor needs a lot of power to start from rest as in the traditional AC but compressor in inverter AC remains in on state but is completely variable.

The compressor of inverter type is of smaller size, quieter, has faster cooling, regulates temperature far better than normal AC, and saves power (money). Based on the data on power consumption by BEE, inverter AC of 3 star ratings is 7% more efficient than normal AC of 3 star ratings.

Conclusion

Illustration of DC inverter vs Traditional Air Conditioner

The compressor of non-inverter AC is either on or off which means temperature is either less cool or cooler (comfortable or uncomfortable – improper regulation), compressor can’t be controlled so it will either draws maximum power or no power at all, and is noisy.

Inverter AC, however, have compressor that have variable speed (regulates temperature comfortably), draws power only to keep temperature stable, power efficient, and quieter.

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