Inverter Buying Guide

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What are the different type of Inverter?

Description: A square wave inverter is simply among the simplest types of inverters that are available in the market. It converts a straight DC electric signal to a phase-shifting AC electric signal. However, the output comes in the form of a square wave instead of a pure sine wave; i.e. it is not a pure AC current. These inverters are also much cheaper than many of the other models. A square wave inverter can be simply constructed by making use of an on-off switch with the standard voltage amplifying circuitry of a transformer.

Benefits: The output voltage produced by a sine-wave inverter has got a sine wave-form, much like that produced by mains / utility voltage. In case of a sine wave, there is a smooth rise and fall of voltage along with a smooth changing phase angle. There is also an instant change of polarity when the volts are crossed. With a modified sine wave, there is abrupt rise and fall of the voltage. The phase angle is also changed abruptly and rests at 0 Volts for a short while before finally changing its polarity. Therefore, any device which makes use of a control circuitry capable of sensing the phase (i.e. for voltage / speed control) or even instantaneous 0 voltage crossing (timing control) is not going to function properly from a modified sine wave voltage. Also, since a modified sine wave is a type of square wave, it’s made of multiple sine waves made of odd harmonics or multiples of the fundamental frequency of modified sine wave. For instance, a modified sine wave of 60 Hz. will consist of sine waves that have odd harmonic frequencies like 3rd (180 Hz.), 5th (300 Hz.), 7th (420 Hz.), 9th (540 Hz.) and so on. High-frequency harmonic content within a modified sine wave creates enhanced radio interference and higher heating effects in motors and microwaves as well as produces overloading because of lowering of an impedance of the low-frequency filter capacitors or power factor improvement capacitors.

Description: The construction of a sine wave inverter or a quasi sine wave inverter is somewhat more complex than standard square wave inverter. However, it is still much simpler than a typical pure sine wave inverter. Some pauses can be observed with a modified sine wave inverter before phase shifting of the wave. Unlike a square wave, it doesn’t shift its phase suddenly from a positive to a negative or even makes a smooth transition either like a sine wave but shifts its phase with brief pauses in between.

Benefits: The output wave form produced by this inverter is a sine wave form that has very low harmonic distortion and produces clean power like that used for utility-supplied electricity. Various inductive loads such as motors and microwaves run faster, cooler and quieter. It also reduces electrical and audible noise in fans, TV, audio amplifiers, fluorescent lights, fax machines and answering machines. The inverter also helps in preventing computer crashes, glitches in monitors and weird print outs.


Description: A pure sine wave inverter is characterized by the presence of an electrical circuit that is comparatively far more complex in nature than that of a square wave inverter or a modified sine wave inverter. To get a sine output, a good way would be to obtain one square wave output from square wave inverter. This can then be modified for achieving a pure sine wave. Typically, a pure sine wave inverter has got numerous advantages over the other two forms. It presents with more efficiency and thereby consumes less power. These inverters can also be adjusted according to the personal power requirements of the user, as they come in different types with varying power outputs. While the output of pure sine wave inverter is quite reliable, there is always a tradeoff between their price and reliability. This makes them the perfect choice when it comes to sensitive equipment.

Benefits: The output voltage produced by a sine wave inverter has got a sine wave form, like that which is produced by the mains / utility voltage. Have a look at sine wave that is represented for comparison in shows with modified sine wave and square wave. In a sine wave, the voltage always rises and falls in a smooth way with an easily changing phase angle. It also instantly changes its polarity when it crosses the 0 Volts mark. In modified sine wave, on the other hand, the rise and fall of the voltage are abrupt and the same applies with the change of the phase angle. It also sits for some time at 0 Volts before finally changing its polarity. Therefore, any device that makes use of a control circuitry which senses the phase for the purpose of voltage / speed control or an instantaneous zero voltage crossing meant for timing control is not going to work properly from the voltage that is characterized by a modified sine wave-form. Moreover, since the modified sine wave can be stated as a type of square wave, it’s made up of multiples or multiple sine waves made of odd harmonics of the fundamental frequency of modified sine wave. For instance, a 60 Hz. modified sine wave is going to include sine waves having odd harmonic frequencies such as 3rd (180 Hz), 5th (300 Hz.) and 7th (420 Hz.). The high-frequency harmonic content present within a modified sine wave creates enhanced radio interference, a greater heating effect in microwaves / motors as well as produces overloading because of lowering of the impedance of the low-frequency filter capacitors or the power factor improvement capacitors.

Meaning of some frequently used terms

Meaning: The power distribution lines that are energized by the utility companies for delivering electric power to the various customers of the utility company. The power sources that are commonly used include coal, hydroelectric, nuclear, natural gas and various others.

Benefits: Solar power presents numerous benefits to the owners of home and property, most particularly reduction in the costs and usage of electricity. However, there are also other benefits that depend on the system that you choose. It is also important to consider the various pros and cons of using the grid-tied solar power systems as well as the off-grid systems so that you can select a solar power system that is ideal for you.

Example Usage of Terminology: The grid-tied solar power systems are by far the most widely used variant of solar electric systems in the United States. It is tied or attached to existing electrical grid. The electricity that is produced by this solar array easily flows back to the grid and to the utility company. The commercial or household property benefitting from the system gets credited for this electricity that is generated by solar panels. Until the solar array keeps on generating more electricity than what is required by the household, this electricity will be provided free. On the other hand, if the business or household consumes more electricity than what is actually generated, then the house or company will be required to pay for the excess consumption.

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Meaning: This is an inverter that is designed to be connected to the commercial power grid and then feeds the power back to the grid. Grid-tie inverters must be connected into the grid for them to function properly. Safety regulations for these type of inverters require them to automatically cease operating in case there is a power failure within a commercial power grid. For the residential grid-tie inverter, the most common source of energy is the “solar modules” that are capable of making electricity from sunlight.

Benefits: The features included in a solar power system that comes with grid tied installations provide users with the opportunity to sell, earn and generate revenue from SRECs or Solar Renewable Energy Credits. In such cases, a utility company is going to pay you charges for the electricity that your home generates. In cases where a solar array is unable to generate sufficient electricity to power a home, electricity will be supplied by the electrical grid whenever needed.

Example Usage of Terminology: This is really great news for the home owners who may not have the advantage of getting enough sun exposure or their property may not have enough space for all the panels to generate enough electricity to power their own home. They can still discount on their current electricity rates as well as reduce their impact on the environment.

Meaning: A hybrid inverter aptly combines the features of a stand-alone inverter with that of the grid-tie inverter. The hybrid systems make use of batteries for storage. They can provide power for major or critical loads in case grid power failure takes place. The Hybrid systems achieve such an intentional islanding by initially disconnecting itself from the commercial power grid with the help of a heavy duty mechanical relay, then operating as a standalone inverter until utility power gets restored. Once it is restored, the hybrid inverter gets back to its grid-tie mode.

Benefits: A smart grid inverter or an intelligent hybrid inverter can be described as a new generation of high-end dedicated UPS or uninterruptible power supply applications that make use of renewable energy for the purpose of home consumption, particularly for the solar photovoltaic installations. The solar panel electricity is produced only during day time, with peak production around the midday. This electricity is by nature fluctuating, thereby not synchronized with electric consumption needs of the household. In order to overcome such a gap between production and requirement during evenings when no solar electricity is produced, it is important to store the energy for later use along with managing energy storage and its consumption in a smart grid. As more systems that make use of renewable energy develop and the prices of electricity keep on rising, research laboratories and private companies have developed top quality smart inverters that enable efficient correlation between production and consumption of energy.

Example Usage of Terminology: Use in an off-grid mode (i.e. without network) with the possibility of linking into a generator. The Inverter must be well connected to the battery bank.

Use in an on-grid or grid-tie mode (connected to a network) with the possibility of selling excess energy. According to the DIN VDE 0126.1, there is a strong need to comply with the protection and decoupling rules. When used in hybrid-mode, this inverter functions with the battery bank, while at the same time stays connected to the grid. The dual functionality is a major characteristic of the hybrid inverters that enable efficient energy management (i.e. smart grid). Using it in the backup mode or the storage mode allows preventing blackouts by switching to the off-grid mode from the on-grid mode just at the instant of an electric outage, thus eliminating network cuts.

Meaning: An “island” condition is said to exist when the inverter keeps on providing electricity to one or additional residences or any other structures. The inverter is said to be malfunctioning if it occurs within a grid-tie inverter. Sometimes, certain systems are made to island intentionally (refer to “Hybrid system”).

Benefits: Islanding refers to a situation in which a DG or distributed generator keeps on powering a location even though the electrical grid power from the electric utility is not present anymore. Islanding can be a dangerous thing for utility workers as they might not realize that power is still flowing through a circuit and it may hinder automatic reconnection of the devices. Due to this reason, the distributed generators need to detect islanding and stop producing power immediately, a process which is known as anti-islanding. A common example for islanding is a standard grid supply line with solar panels connected to it. If there is a blackout, these solar panels will keep on delivering electricity as long as the irradiance is sufficient. The supply line turns into an “island” of power in these cases even with unpowered lines surrounding it. For this reason, the solar inverters designed for supplying power to the grid are usually needed to have some kind of automatic anti-islanding circuitry within them. With intentional islanding, a generator gets disconnected from the grid, thus forcing a distributed generator to supply power to the local circuit. It is frequently used as power backup system for the buildings that generally sell excess power produced by them to the grid.

Example Usage of Terminology: Electrical inverters are special devices that convert the DC (direct current) to AC (alternating current). The grid-interactive inverters also have an additional requirement of producing AC power which matches the currently existing power that is presented on the grid. A grid-interactive inverter specifically needs to match the voltage, phase and frequency of the particular power line that it connects to. Numerous technical requirements are associated with the accuracy of such a tracking. For instance, let’s consider a house with numerous solar panels on the roof. The inverter(s) that are attached to the panels help to convert the DC current that is provided by these panels into the AC power that aptly matches grid supply. In case the grid gets disconnected, the gird line voltage can be expected to get down to zero which is an obvious indication of service interruption. On the other hand, if the load of the house matches exactly the output produced by the panels just at the very instant of grid interruption, the panels can keep on supplying the power that is used by the load of the house. In a case like this, there is no definite indication that any interruption has taken place. In normal conditions even when production and load are matched exactly, i.e. the “balanced condition”, failure of a grid is going to result in the production of numerous additional transient signals. For example, in most cases there might be a brief reduction in line voltage that is going to indicate a potential fault. However, events like these can also be technically caused by normal operations such as starting of large electric motors. The methods that help to detect islanding without significant numbers of false positives are now being researched by experts. Each method comes with a threshold point that has to be crossed before it presents with a condition that can be seen as a sign of grid interruption and leads to NDZ or “non-detection zone” the conditions wherein the real grid failure can be filtered out.

Meaning: This is an inverter that is designed to operate independently from the commercial power grid. The stand-alone inverter can create its very own 60Hz (50Hz for the international models). It is not meant to connect to a commercial power grid or feed power back to it. Mechanical relays can be used in with the stand-alone inverters for allowing a load to be electrically powered from either the inverter or the grid, then have this relay change its position to use another source of power as it is needed. However, the stand-alone inverter is never connected to the power grid at any time under any circumstances.

Benefits: A SAPS or SPS (stand-alone power system), also referred to as a remote area power supply or RAPS, can be described as an off-the-grid electricity system that can be used for locations not fitting within an electricity distribution system. Generally, typical SAPS may include one or additional methods of power generation, regulation and energy storage.

Example Usage of Terminology:

  • Energy Storage Capacity and Greater Autonomy- For storing the energy if there is excess so that it can be used later when needed.
  • Voltage and Current Stabilization– For providing stable voltage and current by eradicating the transients.
  • Supply Surge Currents– For providing surge currents to the loads like motors whenever needed.

Meaning: The Line-Latch protection feature helps to prevent the battery from resuming its operations prematurely after a Low Battery Voltage Disconnect. For preventing deep discharge, a battery is not going to resume emergency operation until the AC power is restored and the battery is charged to sufficient levels.

Benefits: A latch-up can be defined as a short circuit that can take place within an integrated circuit or IC. In other words, it is an inadvertent creation of a low-impedance path between power supply rails of MOSFET circuit that triggers a parasitic structure disrupting the proper functioning of a part. It can even lead to over-current which can ultimately destroy it. This situation can only be corrected by a power cycle.

Example Usage of Terminology: The parasitic structure is commonly equivalent to an SCR or thyristor, a PNPN structure that acts as PNP and an NPN transistor is placed next to one another. When one of these transistors is conducting during a latch-up, the other system starts conducting as well. They both constantly keep on saturating each other as long as this structure is forward biased and some amount of current smoothly flows through it until it is a power down. This SCR parasitic structure gets developed as a part of PMOS-NMOS transistor pair on output drivers of gates. The latch-up doesn’t need to happen between power rails; it can develop at any spot where the needed parasitic structure exists. One of the common causes of latch-up is negative or positive voltage spike on output or input pin of a digital chip that easily exceeds rail voltage by more than one diode drop. The other cause is that the supply voltage that exceeds absolute maximum rating, frequently from some transient spike within the power supply. This causes a breakdown of an internal junction. It often happens in the circuits that make use of multiple supply voltages which do not come up in required sequence on the power-up, thus leading to the voltages on the data lines that exceed the input ratings of the parts that have not reached a minimum supply voltage. The latch-ups can be caused by electrostatic discharge events as well.

Intrinsic BJTs in CMOS technology– Ionizing radiation is another common factor that causes latch-ups. This makes it a major problem with electronic products that are designed for space or with applications that are meant for very high-altitude. The high-power microwave interference can lead to latch-ups. Both the TTL integrated circuits and CMOS integrated circuits are more prone to suffer from latch-ups at higher temperatures.

Meaning: A modified sine wave, also sometimes known as ‘simulated’ sine wave is a type of AC current that’s not really a pure sine wave. The modified sine waves come with some load limitations when it comes to electronic equipment. Lighting loads generally remain unaffected by the modified sine wave current.

Benefits: All kinds of equipment that are currently available in the market are meant for being used with sine waves. Certain appliances, such as variable speed motors and microwaves are not going to produce their full output unless they can work with sine wave power. On the other hand, devices such as medical equipment are not going to function at all if they are not driven by a pure sine wave inverter. True sine wave gives rise to much higher levels of wattage than a modified sine wave power inverter. Hence, it is believed that the more a sine wave inverter is used, the greater will be the number and variety of the electrical devices that can be powered.

Example Usage of Terminology: The output voltage wave form comes in pure sine wave form with very low levels of harmonic distortion and absolutely clean power-like utility supplied electricity. The inductive loads such as motors and microwave ovens run faster, cooler and quieter. It reduces the electrical and audible noise in fluorescent lights, fans, TV, audio amplifiers, fax, game consoles and answering machines. This inverter also prevents weird print outs, crashes in computers, as well as glitches and noises in monitors. It reliably powers all of these devices that are not going to work with a modified sine wave.

Meaning: An uninterruptible inverter helps to switch the power from normal AC supply to emergency supply without causing interruption to the connected load. The HID fixtures need uninterrupted power supplies for maintaining the electrical arc which lights the lamp. If power is interrupted within an HID fixture, it will cause the lamp to be extinguished and require a long pause before it can return to the appropriate illumination levels.

Benefits: UPS denotes uninterruptible power supply and when there is a complete system; one can safely forget all worries associated with a power outage. This technology is going through continuous improvement as an importance of maintaining the power for essential operations and systems becomes more important day by day. Many people do not realize the power needs of the modern data-driven world and the usage of internet and data banks in general increase the demand for reliable and cleaner power. Energy dips, spikes or surges cause irregularities and fluctuations that can negatively affect equipment and data. Hence, these inverters provide with consistent, clean and uninterrupted flow of power that offers protection against those effects.

Example Usage of Terminology: Many people refer to the idea of backup power as an important backup plan; the UPS plays a major role in it. UPS systems may come in the form of single phase or triple phase units and can be powered with different batteries or flywheel component. An uninterruptible power supply system can range from being those systems that run personal computers to the large megawatt, mega-ton models that can provide power to big business houses.

Meaning: A VRLA battery can be defined as a sealed maintenance free lead acid battery. Its valve design keeps battery sealed while letting the gasses that are produced due to over-charging to pass out.

Benefits: India’s battery industry is growing very fast and it is estimated that around 25% annual growth rate has been observed for the last four years. This positive trend is expected by all to continue in future as well as the government makes substantial efforts for infrastructure development, improvements within the telecom sector as well as focus on enhancing renewable energy in the current budget. Currently, India’s battery market is worth almost Rs 100 billion with organized sector contributing about 65% of total market. Share for the SMF VRLA (sealed maintenance-free valve-regulated lead-acid) batteries is around 20% to 22%. The SMF/VRLA batteries are at present manufactured by organized sector. They find applications in the automotive and non-automotive sectors across industrial, office and business and home applications. Customers’ expectations from these batteries are rising with every passing day. They are searching for the off-track unexplored technologies in this country that are very popular overseas. The practice is to install the batteries that require minimal maintenance with the improved reliability of electronics. Switchover to the SMF VRLA batteries is currently on the rise as price difference for required maintenance narrows down.

Example Usage of Terminology: Solar and telecom equipment need standby battery systems which increase the demand for the SMF VRLA batteries. Managing director of Su-Kam Power Systems Mr. Kunwer Sachdev says that currently the inverter market is shifting towards the SMF batteries as well because of their environment-friendly properties. Although inverters are kept inside the living rooms, this is quite dangerous. While charging batteries in the homes, the lead fumes can cause significant damage to body parts like kidney and brain. Director of Best Power Equipment Amitansu Satpathi comments that there is now a shortage of supply since the base of production in India is rather small. However, increasing demand in India is leading the existing facilities to be scaled up. New facilities are also being constructed to reduce the existing gap between demand for these systems and their supply.

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