What is Power Inverter?

What Is Power Inerter?

Almost everybody today hears of an inverter every day.
As Wikipedia explains it, "
An inverter, is an electronic device or circuitry that changes direct current (DC) to alternating current (AC)^.
The input voltage, output voltage and frequency, and overall power handling, are dependent on the design of the specific device or circuitry."

Well, the above lines explain an inverter in generality that is all inverters whether it is Power Inverter or Welding Inverter or any type of inverter.

Typical applications for power inverters include:

• Portable consumer devices that allow the user to connect a battery, or set of batteries, to the device to produce AC power to run various electrical items such as lights, televisions, kitchen appliances, and power tools.

• Use in power generation systems such as electric utility companies or solar generating systems to convert DC power to AC power.

• Use within any larger electronic system where engineering need exists for deriving an AC source from a DC source.

Input voltage

A typical power inverter device or circuit will require a relatively stable DC power source capable of supplying enough current for the intended overall power handling of the inverter. Possible DC power sources include: rechargeable batteries, DC power supplies operating off of the power company line, and solar cells. The inverter does not produce any power, the power is provided by the DC source. The inverter translates the form of the power from direct current to an alternating current waveform.
The level of the needed input voltage depends entirely on the design and purpose of the inverter. In many smaller consumer and commercial inverters a 12V DC input is popular because of the wide availability of powerful rechargeable 12V lead acid batteries which can be used as the DC power source.

The Main Inverter Types

1. Square wave or modified sine wave.
2. Sine wave (sometimes described as "Pure Sine wave")
3. Grid-Tied

Square Wave or Modified Sine wave

The square wave form will be as shown above right and the modified sine wave form will have had some attempt to round the corners off though will still have some sharp corners or spikes.

Compare this to the Sine wave form below right. 

Many AC appliances will work perfectly well a modified sine wave form wave.
Some appliances such as computers, televisions, radios or music centers have in built power supplies that reduce the voltage, rectify it to produce a DC current, and smooth it to give a steady DC voltage.
This process will often smooth out any spikiness that was in the original AC supply.
However, any inductive load (one where the power passes through a coil, as in a power supply transformer or a motor) causes the voltage and current to be out of phase (their appropriate graphs do not line up). Modified sign wave inverters do not cope with this so well, causing the appliance to use more power than it would otherwise. This extra power consumption will cause the motor or transformer to run hotter than it would otherwise and may reduce its life.
It will also mean that the inverter will need a slightly higher power rating to power the same appliance.

There is also the possibility that your television picture may not be as good as it should and anything with a timer (eg bread maker) may not run at the correct speed.

There may also be a noise problem. Any equipment that may give a quiet hum when connected to the mains supply is likely to give a more annoying buzz. My own experience has shown this to be true with a ceiling fan, particularly when running on the lower speeds.
These potential problems will need to be balanced against the price difference (modified sine wave converters will be significantly cheaper than pure sine wave) taking into account the appliances you expect to be using.

Grid-Tied

A Grid-Tied inverter is capable of synchronizing with an existing mains electricity supply (synchronizing its sine wave output so that it is at the peak voltage point at the same time as the mains supply). This type of inverter can be used (where your electricity utility company allows it and with a modified meter if required) to enable you to push your spare electricity into the grid system. In some cases your normal electricity meter will simply run backwards when you are supplying power.
A grid tied inverter designed to be used without a battery (and therefore no charge controller), may have MPPT technology built into its input circuitry.

String Inverters

Inverter designed to accept high input voltages (up to 600 volts in commercial systems) may be called String Inverters, referring to the series connected panels, used to produce the higher voltages, being connect as a string.

DC Input Voltage

You may already have the rest of your system setup and you are already committed to using a particular voltage. You may however still be able to choose.
The lower the input voltage you are using, the higher the current you will need to use. If you compare a 12 volt and a 24 volt inverter of the same power rating, the 12 volt item will need to draw twice the current. To carry that current, the cables from your battery to the inverter will need to be 4 times the size.
A higher voltage system is likely to be more efficient although you will find that most inverters on the market are either 12 or 24 volts. A 48 volt inverter will be more difficult to find and may therefore be more expensive.

AC Output Power

Any inverter will have a quoted output power which will be the maximum power level they can provide continuously, measured in watts or kilowatts. Inverters will normally however cope with higher levels of power for a short period, enabling them to deal with a short power surge that many appliances will draw at turn on. Practically all electrical appliances will draw extra current for a split second at switch on, including low energy light bulbs.
The power output characteristics will vary between different inverters but they may be able to produce 10% over the rated figure for 5 minutes, 50% over for 5 seconds, more for 1 second.
Continuous output power capabilities of any inverter may be affected by the battery supplying the DC input voltage. The battery will need to be large enough to be able to supply the high current needed for a large inverter without the battery voltage dropping too low (causing the inverter to shut down).
Continuous output power capabilities may also be affected by the ambient temperature. An inverter that is producing high power will produce heat that is normally dissipated with the help of a fan. If you are experiencing high air temperatures, your inverter may not be able to cope with continuous high outputs without overheating and shutting down.

Below are the pictures of my early Inverter devices.

Coming from left to right is:

1. The Inverter control board consisting: Driver & Oscillator, Low battery beeper, Low battery shutdown and Two temprarture dependent fan controllers.
2. Charger
3. IGBT Switching block
4. Transformer.

The charger is now very obsolete to my designs.