Selection of Various Types of Inverter-(Part-1)



  • In this modern society, electricity has vital role on the most daily activities for domestic and industrial utilization of electric power for operations.
  • An inverter is used to provide uninterrupted 220V AC supply to the load connected to its output socket. It provides constant AC supply at its output socket, even when the AC mains supply is not available.
  • There are many factors, which are affecting on selecting of the best inverter for our application

Block Diagram of Inverter:

  • Power inverter is a device that converts electrical power from DC form to AC form using electronic circuits. It is typical application is to convert battery voltage into conventional household AC voltage to use Equipments, when an AC power is not available.
  • There are two methods, in which the low voltage DC power is inserted into AC Power.
  • In First Method first is the conversion of the low voltage DC power to a high voltage DC source, an then It is the conversion of the high DC source to an AC waveform using pulse width modulation.
  • In Second method the outcome would be to first convert the low voltage DC power to AC, and then use a transformer to boost the voltage to 220 volts.
  • The widely used method in the current residential inverter is the second.
  • An Inverter not only converts the DC Voltage of battery to 220V V AC Signals but also charge the Battery when the AC mains are present.
  • The block diagram shown above is a simple depiction of the way an Inverter Works.

When the AC mains power supply is available.

  • When the Utility Company AC mains supply is available.
  • C Main Sensor: the AC sensor senses it and the 230V A.C supply feeds to the Relay and battery charger.
  • Relay or Change over Switch: AC main sensor activates a relay and this relay will directly pass the 230V AC mains supply to the Load.
  • Battery Charger: Battery Charger converts line A.C Voltage to DC Voltage and Charges the Battery even when A.C Power is available.
  • Battery: Battery is charged and it is stopped when it is full charged.

 When the AC mains power supply is not available.

  • When the AC mains power supply is not available.
  • Relay or Change over Switch: AC main sensor activates a relay and this relay will connected to battery in absent of the AC mains supply.
  • Battery: Battery is providing DC Power to Oscillator circuit through Relay.
  • Oscillator Circuit: An oscillator circuit inside the inverter use pulse width modulator to generate the 50Hz frequency required to generate AC supply by the inverter.
  • The battery DC supply is connected to the Oscillator. The flip-flop converts the incoming signal into signals with changing polarity such that in a two-signal with changing polarity.
  • The first is positive while the second is negative and vice versa. This process is repeated 50times per second to give an alternating signal with 50Hz frequency. This alternating signal is known as “MOS Drive Signal “.
  • Driver Circuit: The MOS drive signals are given to the base of driver transistor which separated into two different channels.
  • Amplifier Circuit: The transistors amplify the 50Hz MOS drive signal at their base to a sufficient level and output them from the emitter.
  • Inverter Transformer: The transformer used for this is a center-tapping which divides the primary into two equal sections.
  • This center-tapping is connected to the positive terminal of the battery. Two ends of the primary are connected to the negative terminal of the battery through switches S1 and S2.
  • MOSFETs or Transistors are used for the switching operation. These MOSFETs or Transistors are connected to the primary winding of the inverter transformer.
  • When these switching devices receive the MOS drive signal from the driver circuit, they start switching between ON & OFF states at a rate of 50 Hz. This switching action of the MOSFETs or Transistors creates a 50Hz current to the primary of the inverter transformer. This results in a 220V AC or 2300V AC (depending on the winding ratio of the inverter transformer) at the secondary or the inverter transformer. This secondary voltage is made available at the output socket of the inverter by a changeover relay.

 Type of Inverter

  • The inverters are classified by depending on their output
  • Sine wave
  • Modified sine wave
  • Square wave.

(1) Sine Wave Inverter:

  • In utility Company Sine wave generated by rotating AC machinery and sine waves is a natural product of rotating AC machinery.
  • Pure sine wave inverters provide an output same as a sine wave which is similar to the utility supplied grid power, hence Pure Sine Wave inverter produces a better and cleaner current

  • All commercial instruments are designed to run on pure sine wave. Characteristics of such devices are greatly depending upon the input wave shape. A change in wave shape will affect the performance and efficiency of the appliances.
  • Sine Wave guarantees by Sine way Inverter is pure so the equipment will work to its full specifications as per its design. Appliances like Motors, refrigerators, Ovens etc will generate full power on pure sine wave input only.
  • A few appliances, such as Toaster, light dimmers, and some battery chargers require a sine wave to work propellerly. Operation of these appliances in Square or stepped waves will considerably affect the life of such equipment due to the generation of heat.
  • Distortion in the sine wave creates humming noise in transformers, and audio devices
  • Some time we noticed that audio amplifiers, Televisions, Fluorescent lamps etc make noise on inverter power. This indicates that inverter output is not pure sine wave.
  • It is always advisable and recommended to go for a pure sine wave inverter for the safety and effective performance of your appliances.


  • Output voltage wave form is pure sine wave with very low harmonic distortion and clean power like utility-supplied electricity.
  • Inductive loads like microwave ovens and motors run faster, quieter and cooler.
  • Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game consoles, Fax, and answering machines.
  • This type of inverters will save your current bill compared to square wave inverters.
  • Prevents crashes in computers, weird print out, and glitches and noise in monitors.
  • Back up time will be better than square wave inverters.


  • Sine wave inverters are 2 to 3 times expensive compared to square wave and modified sine wave inverters.


  • More sensitive electrical or electronic items
  • Desktop computers, laptops, Laser printers, photocopiers,
  • Camera battery chargers, cell phone chargers,
  • Mixer,
  • Fluorescent lights with electronic ballasts ,
  • Digital clocks ,
  • Sewing machines with speed/microprocessor control ,
  • Medical equipment,
  • Small house hold water pumping motors, Drives etc.

(2) Modified Sine Wave:

  • A modified sine wave inverter has a waveform like a square wave, but with an extra step.
  • Modified sine wave is a simulation of the pure sine wave output when the inverter sharply drops or increases voltage to switch polarity. As a result, the output form closely matches pure sine wave but still has much greater distortions.
  • A modified sine wave inverter will work fine with most equipment, although the efficiency or power will be reduced with some.

  • The devices are usually about 70% efficient, so we can expect some significant power losses if we are using a modified sine wave inverter in your system.
  • Motors, such as refrigerator motor, pumps, fans etc will use more power from the inverter due to lower efficiency. Most motors will use about 20% more power.
  • Some fluorescent lights will not operate quite as bright, and some may buzz or make annoying humming noises.
  • Because the modified sine wave is noisier and rougher than a pure sine wave, clocks and timers may run faster or not work at all. They also have some parts of the wave that are not 50 Hz, which can make clocks run fast. Items such as bread makers and light dimmers may not work at all in many cases appliances that use electronic temperature controls will not control. The most common is on such things as variable speed drills will only have two speeds on and off.
  • The difference between Sine wave and modified Sine wave inverter is the cost. Sine wave is considerably more expensive. We can find it practical way from it .We can install a small Pure Sine Wave inverter for any “special need” and also a larger Modified Sine Wave inverter for the rest of our applications.


  • Cheaper than pure sine wave inverters
  • Output correction waveform; relatively stable; suitable for ordinary personal users with TV, fan, lamp, computer, hot pot etc.
  • Output wave form have a very low harmonic distortion compare to Square wave inverter


  • Lower efficiency than pure sine wave inverters.
  • Power Loss is more compared to sine wave inverter.
  • Modified Sine Wave output is not suitable for continuous long time operation of certain appliances with capacitive and electromagnetic devices such as a fridge, microwave oven and most kinds of motors, printers as well as capacitive fluorescent lights etc
  • Some fans with synchronous motors may slightly increase in speed (RPM) when powered by a modified sine wave inverter. This is not harmful to the fan or to the inverter.
  • Certain rechargers for small nickel-cadmium batteries can be damaged if plugged into a modified sine wave inverter


  • Some household appliances and power tools.
  • Inductive loads like micro ovens and motors.
  • Fans and fluorescent lights,
  • Audio amplifiers, TVs, game consoles, fax and answering machines.

 (3) Square Wave Inverter:

  • The Output wave form of the Inverter is like square.
  • This is old-fashioned and the cheapest inverters, but the hardest to use.
  • A square wave inverter will run simple things like tools with universal motors without a problem, but not much else.

  • The current we get from grid is neither square wave nor pure sine wave, it’s nearly sine wave. So, our electronic devices like fan and tube light will emit some buzz noise while operating in square wave current. In some rare cases, these square wave inverters have spoiled the speed control dimmers of ceiling fans.
  • In the form of square wave, The load voltage must be switched majorly from high voltage  to low Voltage, without  using  for an intermediate step of 0Volt.
  • The main reason for this fault is high voltage output. Normally, voltage output from square wave inverters is 230 volt to 290 volt, hence it is not recommended to sensitive electronic devices like computers.
  • They just flip the voltage from plus to minus creating a square waveform. They are not very efficient because the square wave has a lot of power in higher harmonics that cannot be used by many appliances. Synchronous motors, for example, use the 50Hz component and turn the rest of the frequencies into heat
  • Square wave inverters are seldom seen any more.


  • It is very cheap


  • Life of Application is less.
  • Speed control of some equipment is not possible
  • Voltage Variation is high.
  • Large 3rd and 5th harmonic components which burn power and severely cut down on the efficiency of devices


  • Low cost AC motor drives
  • Some electronic ballast for fluorescent lamps