Power Inverter Definition, History, Working Principle, and Types
A power inverter is an electronic device that is used to convert direct current (DC) to alternating current (AC) [6]. This article discusses power inverter definition, history, working principle and types, according to the outline below;
-What is a Power Inverter? Power Inverter Definition
-History of The Power Inverter
-How Does a Power Inverter Work?
What is a Power Inverter? Power Inverter Definition
A power inverter is a circuitry that is used to convert current electricity from one form to another.
This conversion may be from direct current to alternating current (DC-AC) or vice-versa (AC-DC). However, it is conventional for a power inverter to convert DC to AC, because AC is the more usable form of current electricity.
The following definition embodies this understanding.
A power inverter is an electronic device that changes direct current (DC) from batteries, to the more conventional alternating current (AC) which can be used in a wide range of appliances [10].
Another factor which can be included in the description of a power inverter, is voltage;
A power inverter is a device which is used to produce a converted output voltage from an input voltage.
It is important to note that the sole function of a power inverter is to convert power to a more usable form. Therefore, inverters do not produce any power.
The input voltage for a power inverter depends on its design and capacity [12]. Based on these characteristics, a power inverter may be high-voltage or low-voltage type.
With regards to design, power inverters can be defined based on their design and compositional characteristics, as follows;
A power inverter is an electronic device that may be static or dynamic, which changes direct current (DC) to alternating current (AC).
There are numerous possible uses of power inverters. These uses can be used as a factor of characterization;
A power inverter is an electronic device that can be used in a house or vehicle, to convert current from DC form to AC.
With regards to house-usage, power inverters have increasingly become a component of the building sector, thereby bearing technical relationships to other concepts like smart house technology, artificial intelligence and internet of things (IoT).
A power inverter is a device used in smart buildings [1], to convert direct current to alternating current, for use within the building.
With the development and adoption of renewable energy, power inverters have become even more significant to convert the energy produced by such technologies, in a manner that ensures that energy conservation and energy efficiency are not compromised.
A power inverter is a device which may be part of a solar panel assembly, and may be used to convert the direct current (DC) produced by the panels and stored in the solar battery, to alternating current (AC) that can be used to power electronic appliances.
History of The Power Inverter
The development of the power inverter can be traced back to the late nineteenth century, during which it was invented as a consequence of extensive studies in the field of current electricity.
Early inverters were electromechanical devices that resembled generators, and worked based on a rotating-coil mechanism [2].
In the twentieth century, the power inverter was modified to improve its aesthetic and performance characteristics. This improvement included the use of vacuum tubes.
In 1925, David Prince; a researcher and inventor, made the earliest-known use of the term “inverter”, in a publication discussing current electricity and conversion [8].
Transistors and silicon-controlled rectifiers (SCRs) were introduced into the design of inverters between the 1940s and 1950s. These components helped to drive the upgrade from square-wave to sine wave power inverter.
The 1970s saw some innovation in the form of Insulated Gate Bipolar Transistor (IGBT) and Gate Turn-Off (GTO) thyristor [3], both of which improved the energy efficiency of the power inverter.
Improvements since the 1980s till present include other types of thyristors like MOS and IGFET, microelectronics and energy efficient configurations.
How Does a Power Inverter Work?
A power inverter works by changing the transmission pattern of direct current (DC) from a source, to that of alternating current (AC), which becomes the output.
As implied above, an inverter changes a direct current (DC) to an alternating current (AC).
A power inverter works to change DC to AC, by a two-stage process; which comprises of conversion and rectification.
For clarity, these two stages are discussed individually below;
Stage 1: Conversion
During conversion, a power inverter changes direct current to square wave-alternating current.
This stage of conversion involves a change in the current flow trend, from a unidirectional pattern to an oscillating pattern. To achieve this, the polarity of the current is switched rapidly from positive to negative, in an alternating manner.
The conversion at this stage usually produces an output that has a higher voltage and lower current than the input.
However, there are some disadvantages of the square wave alternating current. This type of current has a non-uniform flow pattern, and can damage appliances when used.
Stage 2: Rectification
The goal of rectification is to modify the square wave AC that was produced during initial conversion, and make it more uniform and suitable for use.
In order to achieve this purpose, a power inverter is equipped with components that are generally referred to as rectifiers. These components modify the square wave AC to pure (or modified) sine wave AC.
Types of Power Inverter
Types of power inverter are; sine wave, modified sine wave, square wave, single phase, three phase, series, parallel, central, string, micro, full bridge and half bridge inverters.
These different types of inverters are classified based on a variety of factors, including wave model, input source, mode of connection, commutation, and bridge type. They are discussed below;
-Types of Power Inverters Based on Wave Model
The ‘wave model’ here refers to the pattern of transmission of current after it has been passed through the power inverter. Based on this criterion, the three types of inverters are square wave, sine wave, and modified sine wave inverters.
1). Square Wave Power Inverter
Square wave power inverter is the most basic, and the cheapest type of inverter.
This type of power inverter does not perform a complete conversion of direct current to usable sinusoidal alternating current. Rather is only performs the first, rudimentary stage of DC conversion, thereby producing AC that flows in a square wave pattern.
The final output from this type of power inverter is square wave AC, and the working principle is relatively simple; involving an alternating switch that turns on and off to change the flow pattern of the output current.
2). Sine Wave Power Inverter
Also known as “pure” sine wave power inverter, this type of inverter can convert a unidirectional direct current (DC) to a (nearly) pure sinusoidal alternating current (AC) [11].
Compared to square wave power inverter, this type of inverter is complex in both design and operation. It is also more expensive.
However, the sine wave power inverter the advantage of producing a more usable output than all other types of inverters.
In most sine wave inverters, a filter is incorporated into the system, to further rectify the output current. In terms of practical usage, the sine wave power inverter is the most relevant type.
3). Modified Sine Wave Power Inverter
The modified sine wave power inverter (also called the “Quasi sine wave inverter”) is in-between the square wave and pure sine wave inverters, in terms of complexity, cost, and applicability.
This type of power inverter, produces a sinusoidal AC output from DC input, however, the harmonic distortion (or irregularity) of the output is usually more than that of pure sinusoidal AC.
Alternating current produced by this type of inverter, has a high frequency and abrupt flow pattern, and is not suitable for many appliances and operations involving electricity.
Modified sine wave power inverter also operates based on a similar principle to the square wave type, which involves an alternating switch mechanism that serves to alter the output flow pattern of a unidirectional input current.
-Types of Power Inverters Based on Source of Input
There are two types of power inverter, based on source of input. These are the current source inverter and voltage source inverter. They are each discussed as follows;
1). Current Source Power Inverter
The current source inverter (CSI) is a type of power inverter that capitalizes on DC current input to produce usable alternating current.
For this type of power inverter, the source of input is usually a DC source which supplies a constant unidirectional stream of direct current to the system [5]. This source is often a high-capacity inductor.
As a result of the constant pattern of DC supply, the current source inverter is able to produce a nearly-equivalent magnitude of AC after conversion.
2). Voltage Source Power Inverter
The voltage source inverter (VSI) operates based on a constant supply of DC voltage.
Like the current source inverter, this type of power inverter, is capable of producing a nearly-equivalent magnitude of AC output voltage from input voltage.
The input voltage usually has a very low impedance, and the entire conversion process usually occurs at constant voltage.
-Types of Power Inverters Based on Circuit Connection
The two types of power inverter are parallel and series inverters.
1). Parallel Power Inverter
Parallel inverters have the advantages of being cheap and producing stable AC output.
This type of power inverter is usually connected in parallel with the load.
Components of parallel inverters include a transformer, two thyristors, an inductor, and a commutator.
The transformer is usually connected between the load and the rest of the components in what is called a ‘center-tapped’ arrangement.
2). Series Power Inverter
Also known as the “load commutated inverter”, this type of power inverter is usually connected in series with the load.
Components which make up a series inverter are two thyristors, a resistor, inductor and capacitor (RLC).
Advantages of this type of inverter include high-frequency tolerance and induction heating.
-Types of Power Inverters Based on Operation
Based on mode of operation, the two types of power inverters are grid-connected and standalone inverters.
1). Grid-Connected Inverters
As the name implies, this type of power inverter operates with direct connection to the utility grid.
The main purpose of the grid-connected (or grid-tie) power inverter is to supply AC power directly to the grid, from a storage device like a solar battery.
This AC power may either be needed to support a load, or may be excess power from the storage device, that is being sent to the grid.
There are four (4) types of grid-connected inverters. These are string, central, micro and bimodal inverters.
Advantages offered by this type of power inverter include flexibility, and relative ease of monitoring.
2). Stand-Alone Power Inverter
Also known as “off-grid” inverters, the stand-alone power inverter is a type of inverter which is designed to function without being connected to the utility grid.
This type of power inverter, is usually required in remote areas, where there is no access to the grid.
In such areas, the source of power is often renewable energy, like solar.
Advantages of this type of inverter include reliability, stability and low cost.
-Types of Power Inverters Based on Bridge Model
Based on bridge model, the two types of power inverter are the full bridge and half bridge (H-bridge) inverters.
1). Full Bridge Inverter
The full bridge power inverter, produces alternating current from direct current, by repeatedly switching between negative and positive polarities [13].
Full bridge inverters comprise of four (4) thyristors and four (4) feedback diodes [4].
The thyristors help to switch between polarities in order to produce AC, while the diodes help to conduct the alternating current.
A type of full bridge inverter; the three-phase bridge inverter, changes a DC current into a three-phase alternating current. This type of AC has waveforms whose crests and troughs 120° apart from each other.
To achieve this, the inverter is equipped with at least 6 thyristors that switch direct current between negative and positive polarities to produce an alternating current.
-Types of Power Inverters Based on Commutation
Based on commutation, the types of power inverters are force-commutation, line-commutation, and simple-commutation inverters.
Commutation itself is the flow or transfer of electric current across a circuit, or from one circuit to another [7]. It usually involves the use of inductors and rectifiers to control and convert the flowing current.
Commutation means transfer of current from one circuit to another.
1). Force-Commutation Power Inverter
The force commutation (or force-commutated) inverter operates by using a reverse voltage to force the forward current to zero.
In forced commutation, the rectifier (or silicon-controlled rectifier; SCR) resolves the output current to a point of minimum harmonics, by performing repeated voltage reversals on the DC current supply.
2). Line-Commutation Power Inverter
The line-commutated inverters, the change of DC to AC current, is controlled by the utility grid or power line.
Unlike the force-commutated power inverter which uses a reverse voltage to ‘force’ the current into a zero state, the line-commutated inverter allows current to flow through an inductor in a near-constant pattern. This can be referred to as “natural commutation” [9].
Compared to the force-commutated type, this type of inverter has advantages such as low cost and effective energy conservation.
However, it has the disadvantage of being too dependent on the utility grid.
Conclusion
A power inverter is an electric device that is designed to change direct current to alternating current, which can be used to power electrical appliances.
Power inverters work based on a two-stage process that leads to the production of AC from DC. The two stages are conversion and rectification.
There are various criteria that are used to classify inverters. The types of power inverters include;
- Square Wave Power Inverter
- Sine Wave Power Inverter
- Modified Sine Wave Power Inverter
- Current Source Power Inverter
- Voltage Source Power Inverter.
- Parallel Power Inverter.
- Series Power Inverter
- Grid-Connected Inverters
- Stand-Alone Power Inverter
- Full Bridge Inverter
- Force-Commutation Power Inverter
- Line-Commutation Power Inverter
References
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