A power inverter, inverter, or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC).[1] The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of rectifiers which were originally large electromechanical devices converting AC to DC.[2]
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The input voltage, output voltage and frequency, and overall power handling depend on the design of the specific device or circuitry. The inverter does not produce any power; the power is provided by the DC source.
A power inverter can be entirely electronic or maybe a combination of mechanical effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use moving parts in the conversion process.
Power inverters are primarily used in electrical power applications where high currents and voltages are present; circuits that perform the same function for electronic signals, which usually have very low currents and voltages, are called oscillators.
A typical power inverter device or circuit requires a stable DC power source capable of supplying enough current for the intended power demands of the system. The input voltage depends on the design and purpose of the inverter. Examples include:
An inverter may produce a square wave, sine wave, modified sine wave, pulsed sine wave, or near-sine pulse-width modulated wave (PWM) depending on circuit design. Common types of inverters produce square waves or quasi-square waves. One measure of the purity of a sine wave is the total harmonic distortion (THD).[4] Technical standards for commercial power distribution grids require less than 3% THD in the wave shape at the customer's point of connection. IEEE Standard 519 recommends less than 5% THD for systems connecting to a power grid.
There are two basic designs for producing household plug-in voltage from a lower-voltage DC source, the first of which uses a switching boost converter to produce a higher-voltage DC and then converts to AC. The second method converts DC to AC at battery level and uses a line-frequency transformer to create the output voltage.[5]
A 50% duty cycle square wave is one of the simplest waveforms an inverter design can produce, but adds ~48.3% THD to its fundamental sine wave.[4] Thus, a square wave output can produce undesired "humming" noises when connected to audio equipment and is better suited to low-sensitivity applications such as lighting and heating.
A power inverter device that produces a multiple step sinusoidal AC waveform is referred to as a sine wave inverter. To more clearly distinguish the inverters with outputs of much less distortion than the modified sine wave (three-step) inverter designs, the manufacturers often use the phrase pure sine wave inverter. Almost all consumer grade inverters that are sold as a "pure sine wave inverter" do not produce a smooth sine wave output at all,[citation needed] just a less choppy output than the square wave (two-step) and modified sine wave (three-step) inverters. However, this is not critical for most electronics as they deal with the output quite well.
Where power inverter devices substitute for standard line power, a sine wave output is desirable because many electrical products are engineered to work best with a sine wave AC power source. The standard electric utility provides a sine wave, typically with minor imperfections but sometimes with significant distortion.
Sine wave inverters with more than three steps in the wave output are more complex and have significantly higher cost than a modified sine wave, with only three steps, or square wave (one step) types of the same power handling. Switched-mode power supply (SMPS) devices, such as personal computers or DVD players, function on modified sine wave power. AC motors directly operated on non-sinusoidal power may produce extra heat, may have different speed-torque characteristics, or may produce more audible noise than when running on sinusoidal power.
The modified sine wave is the sum of two square waves, one of which is delayed one-quarter of the period with respect to the other. The result is a repeated voltage step sequence of zero, peak positive, zero, peak negative, and again zero. The resultant voltage waveform better approximates the shape of a sinusoidal voltage waveform than a single square wave. Most inexpensive consumer power inverters produce a modified sine wave rather than a pure sine wave.
If the waveform is chosen to have its peak voltage values for half of the cycle time, the peak voltage to RMS voltage ratio is the same as for a sine wave. The DC bus voltage may be actively regulated, or the "on" and "off" times can be modified to maintain the same RMS value output up to the DC bus voltage to compensate for DC bus voltage variations. By changing the pulse width, the harmonic spectrum can be changed. The lowest THD for a three-step modified sine wave is 30% when the pulses are at 130 degrees width of each electrical cycle. This is slightly lower than for a square wave.[6]
The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a constant frequency with a technique called pulse-width modulation (PWM). The generated gate pulses are given to each switch in accordance with the developed pattern to obtain the desired output. The harmonic spectrum in the output depends on the width of the pulses and the modulation frequency. It can be shown that the minimum distortion of a three-level waveform is reached when the pulses extend over 130 degrees of the waveform, but the resulting voltage will still have about 30% THD, higher than commercial standards for grid-connected power sources.[7] When operating induction motors, voltage harmonics are usually not of concern; however, harmonic distortion in the current waveform introduces additional heating and can produce pulsating torques.[8]
Numerous items of electric equipment will operate quite well on modified sine wave power inverter devices, especially loads that are resistive in nature such as traditional incandescent light bulbs. Items with a switched-mode power supply operate almost entirely without problems, but if the item has a mains transformer, this can overheat depending on how marginally it is rated.
However, the load may operate less efficiently owing to the harmonics associated with a modified sine wave and produce a humming noise during operation. This also affects the efficiency of the system as a whole, since the manufacturer's nominal conversion efficiency does not account for harmonics. Therefore, pure sine wave inverters may provide significantly higher efficiency than modified sine wave inverters.
Most AC motors will run on MSW inverters with an efficiency reduction of about 20% owing to the harmonic content. However, they may be quite noisy. A series LC filter tuned to the fundamental frequency may help.[9]
A common modified sine wave inverter topology found in consumer power inverters is as follows: An onboard microcontroller rapidly switches on and off power MOSFETs at high frequency like ~50 kHz. The MOSFETs directly pull from a low voltage DC source (such as a battery). This signal then goes through step-up transformers (generally many smaller transformers are placed in parallel to reduce the overall size of the inverter) to produce a higher voltage signal. The output of the step-up transformers then gets filtered by capacitors to produce a high voltage DC supply. Finally, this DC supply is pulsed with additional power MOSFETs by the microcontroller to produce the final modified sine wave signal.
More complex inverters use more than two voltages to form a multiple-stepped approximation to a sine wave. These can further reduce voltage and current harmonics and THD compared to an inverter using only alternating positive and negative pulses; but such inverters require additional switching components, increasing cost.
Some inverters use PWM to create a waveform that can be low pass filtered to re-create the sine wave. These only require one DC supply, in the manner of the MSN designs, but the switching takes place at a far faster rate, typically many kHz, so that the varying width of the pulses can be smoothed to create the sine wave. If a microprocessor is used to generate the switching timing, the harmonic content and efficiency can be closely controlled.
The AC output frequency of a power inverter device is usually the same as standard power line frequency, 50 or 60 hertz. The exception is in designs for motor driving, where a variable frequency results in a variable speed control.
Also, if the output of the device or circuit is to be further conditioned (for example stepped up) then the frequency may be much higher for good transformer efficiency.
The AC output voltage of a power inverter is often regulated to be the same as the grid line voltage, typically 120 or 240 VAC at the distribution level, even when there are changes in the load that the inverter is driving. This allows the inverter to power numerous devices designed for standard line power.
Some inverters also allow selectable or continuously variable output voltages.
A power inverter will often have an overall power rating expressed in watts or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. Smaller popular consumer and commercial devices designed to mimic line power typically range from 150 to watts.
Not all inverter applications are solely or primarily concerned with power delivery; in some cases the frequency and or waveform properties are used by the follow-on circuit or device.
The runtime of an inverter powered by batteries is dependent on the battery power and the amount of power being drawn from the inverter at a given time. As the amount of equipment using the inverter increases, the runtime will decrease. In order to prolong the runtime of an inverter, additional batteries can be added to the inverter.[10]
Formula to calculate inverter battery capacity:[11]
Battery Capacity (Ah) = Total Load (In Watts) × Usage Time (in hours) / Input Voltage (V)
When attempting to add more batteries to an inverter, there are two basic options for installation:
An inverter converts the DC electricity from sources such as batteries or fuel cells to AC electricity. The electricity can be at any required voltage; in particular it can operate AC equipment designed for mains operation, or rectified to produce DC at any desired voltage.
An uninterruptible power supply (UPS) uses batteries and an inverter to supply AC power when mains power is not available. When mains power is restored, a rectifier supplies DC power to recharge the batteries.
Inverter circuits designed to produce a variable output voltage range are often used within motor speed controllers. The DC power for the inverter section can be derived from a normal AC wall outlet or some other source. Control and feedback circuitry is used to adjust the final output of the inverter section which will ultimately determine the speed of the motor operating under its mechanical load. Motor speed control needs are numerous and include things like: industrial motor driven equipment, electric vehicles, rail transport systems, and power tools. (See related: variable-frequency drive) Switching states are developed for positive, negative, and zero voltages as per the patterns given in the switching Table 1. The generated gate pulses are given to each switch in accordance with the developed pattern and thus the output is obtained.
An inverter can be used to control the speed of the compressor motor to drive variable refrigerant flow in a refrigeration or air conditioning system to regulate system performance. Such installations are known as inverter compressors. Traditional methods of refrigeration regulation use single-speed compressors switched on and off periodically; inverter-equipped systems have a variable-frequency drive that controls the speed of the motor and thus the compressor and cooling output. The variable-frequency AC from the inverter drives a brushless or induction motor, the speed of which is proportional to the frequency of the AC it is fed, so the compressor can be run at variable speeds—eliminating compressor stop-start cycles increases efficiency. A microcontroller typically monitors the temperature in the space to be cooled, and adjusts the speed of the compressor to maintain the desired temperature. The additional electronics and system hardware add cost to the equipment, but can result in substantial savings in operating costs.[12] The first inverter air conditioners were released by Toshiba in , in Japan.[13]
Grid-tied inverters are designed to feed into the electric power distribution system.[14] They transfer synchronously with the line and have as little harmonic content as possible. They also need a means of detecting the presence of utility power for safety reasons, so as not to continue to dangerously feed power to the grid during a power outage.
Synchronverters are inverters that are designed to simulate a rotating generator, and can be used to help stabilize grids. They can be designed to react faster than normal generators to changes in grid frequency, and can give conventional generators a chance to respond to very sudden changes in demand or production.
Large inverters, rated at several hundred megawatts, are used to deliver power from high-voltage direct current transmission systems to alternating current distribution systems.
A solar inverter is a balance of system (BOS) component of a photovoltaic system and can be used for both grid-connected and off-grid (standalone) systems. Solar inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection.
Solar micro-inverters differ from conventional inverters, as an individual micro-inverter is attached to each solar panel. This can improve the overall efficiency of the system. The output from several micro-inverters is then combined and often fed to the electrical grid.
In other applications, a conventional inverter can be combined with a battery bank maintained by a solar charge controller. This combination of components is often referred to as a solar generator.[15]
Solar inverters are also used in spacecraft photovoltaic systems.
Inverters convert low frequency main AC power to higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power. Due to the reduction in the number of DC sources employed, the structure becomes more reliable and the output voltage has higher resolution due to an increase in the number of steps so that the reference sinusoidal voltage can be better achieved. This configuration has recently become very popular in AC power supply and adjustable speed drive applications. This new inverter can avoid extra clamping diodes or voltage balancing capacitors.
There are three kinds of level shifted modulation techniques, namely:
With HVDC power transmission, AC power is rectified and high voltage DC power is transmitted to another location. At the receiving location, an inverter in a HVDC converter station converts the power back into AC. The inverter must be synchronized with grid frequency and phase and minimize harmonic generation.
Electroshock weapons and tasers have a DC/AC inverter to generate several tens of thousands of V AC out of a small 9 V DC battery. First the 9 V DC is converted to 400– V AC with a compact high frequency transformer, which is then rectified and temporarily stored in a high voltage capacitor until a pre-set threshold voltage is reached. When the threshold (set by way of an airgap or TRIAC) is reached, the capacitor dumps its entire load into a pulse transformer which then steps it up to its final output voltage of 20–60 kV. A variant of the principle is also used in electronic flash and bug zappers, though they rely on a capacitor-based voltage multiplier to achieve their high voltage.
Typical applications for power inverters include:
In one simple inverter circuit, DC power is connected to a transformer through the center tap of the primary winding. A relay switch is rapidly switched back and forth to allow current to flow back to the DC source following two alternate paths through one end of the primary winding and then the other. The alternation of the direction of current in the primary winding of the transformer produces alternating current (AC) in the secondary circuit.
The electromechanical version of the switching device includes two stationary contacts and a spring supported moving contact. The spring holds the movable contact against one of the stationary contacts and an electromagnet pulls the movable contact to the opposite stationary contact. The current in the electromagnet is interrupted by the action of the switch so that the switch continually switches rapidly back and forth. This type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios. A similar mechanism has been used in door bells, buzzers, and tattoo machines.
As they became available with adequate power ratings, transistors, and various other types of semiconductor switches have been incorporated into inverter circuit designs. Certain ratings, especially for large systems (many kilowatts) use thyristors (SCR). SCRs provide large power handling capability in a semiconductor device, and can readily be controlled over a variable firing range.
The switch in the simple inverter described above, when not coupled to an output transformer, produces a square voltage waveform due to its simple off and on nature as opposed to the sinusoidal waveform that is the usual waveform of an AC power supply. Using Fourier analysis, periodic waveforms are represented as the sum of an infinite series of sine waves. The sine wave that has the same frequency as the original waveform is called the fundamental component. The other sine waves, called harmonics, that are included in the series have frequencies that are integral multiples of the fundamental frequency.
Fourier analysis can be used to calculate the total harmonic distortion (THD). The total harmonic distortion (THD) is the square root of the sum of the squares of the harmonic voltages divided by the fundamental voltage:
There are many different power circuit topologies and control strategies used in inverter designs.[16] Different design approaches address various issues that may be more or less important depending on the way that the inverter is intended to be used. For example, an electric motor in a car that is moving can turn into a source of energy and can, with the right inverter topology (full H-bridge) charge the car battery when decelerating or braking. In a similar manner, the right topology (full H-bridge) can invert the roles of "source" and "load", that is, if for example the voltage is higher on the AC "load" side (by adding a solar inverter, similar to a gen-set, but solid state), energy can flow back into the DC "source" or battery.
Based on the basic H-bridge topology, there are two different fundamental control strategies called basic frequency-variable bridge converter and PWM control.[17] Here, in the left image of H-bridge circuit, the top left switch is named as "S1", and others are named as "S2, S3, S4" in counterclockwise order.
For the basic frequency-variable bridge converter, the switches can be operated at the same frequency as the AC in the electric grid. However, it is the rate at which the switches open and close that determines the AC frequency. When S1 and S4 are on and the other two are off, the load is provided with positive voltage and vice versa. We could control the on-off states of the switches to adjust the AC magnitude and phase. We could also control the switches to eliminate certain harmonics. This includes controlling the switches to create notches, or 0-state regions, in the output waveform or adding the outputs of two or more converters in parallel that are phase shifted in respect to one another.
Another method that can be used is PWM. Unlike the basic frequency-variable bridge converter, in the PWM controlling strategy, only two switches S3, S4 can operate at the frequency of the AC side or at any low frequency. The other two would switch much faster (typically 100 kHz) to create square voltages of the same magnitude but for different time duration, which behaves like a voltage with changing magnitude in a larger time-scale.
These two strategies create different harmonics. For the first one, through Fourier Analysis, the magnitude of harmonics would be 4/(pi*k) (k is the order of harmonics). So the majority of the harmonics energy is concentrated in the lower order harmonics. Meanwhile, for the PWM strategy, the energy of the harmonics lie in higher-frequencies because of the fast switching. Their different characteristics of harmonics leads to different THD and harmonics elimination requirements. Similar to "THD", the conception "waveform quality" represents the level of distortion caused by harmonics. The waveform quality of AC produced directly by H-bridge mentioned above would be not as good as we want.
The issue of waveform quality can be addressed in many ways. Capacitors and inductors can be used to filter the waveform. If the design includes a transformer, filtering can be applied to the primary or the secondary side of the transformer or to both sides. Low-pass filters are applied to allow the fundamental component of the waveform to pass to the output while limiting the passage of the harmonic components. If the inverter is designed to provide power at a fixed frequency, a resonant filter can be used. For an adjustable frequency inverter, the filter must be tuned to a frequency that is above the maximum fundamental frequency.
Since most loads contain inductance, feedback rectifiers or antiparallel diodes are often connected across each semiconductor switch to provide a path for the peak inductive load current when the switch is turned off. The antiparallel diodes are somewhat similar to the freewheeling diodes used in AC/DC converter circuits.
Waveform SignalFourier analysis reveals that a waveform, like a square wave, that is anti-symmetrical about the 180 degree point contains only odd harmonics, the 3rd, 5th, 7th, etc. Waveforms that have steps of certain widths and heights can attenuate certain lower harmonics at the expense of amplifying higher harmonics. For example, by inserting a zero-voltage step between the positive and negative sections of the square-wave, all of the harmonics that are divisible by three (3rd, 9th, etc.) can be eliminated. That leaves only the 5th, 7th, 11th, 13th, etc. The required width of the steps is one third of the period for each of the positive and negative steps and one sixth of the period for each of the zero-voltage steps.[19]
Changing the square wave as described above is an example of pulse-width modulation. Modulating, or regulating the width of a square-wave pulse is often used as a method of regulating or adjusting an inverter's output voltage. When voltage control is not required, a fixed pulse width can be selected to reduce or eliminate selected harmonics. Harmonic elimination techniques are generally applied to the lowest harmonics because filtering is much more practical at high frequencies, where the filter components can be much smaller and less expensive. Multiple pulse-width or carrier based PWM control schemes produce waveforms that are composed of many narrow pulses. The frequency represented by the number of narrow pulses per second is called the switching frequency or carrier frequency. These control schemes are often used in variable-frequency motor control inverters because they allow a wide range of output voltage and frequency adjustment while also improving the quality of the waveform.
Multilevel inverters provide another approach to harmonic cancellation. Multilevel inverters provide an output waveform that exhibits multiple steps at several voltage levels. For example, it is possible to produce a more sinusoidal wave by having split-rail direct current inputs at two voltages, or positive and negative inputs with a central ground. By connecting the inverter output terminals in sequence between the positive rail and ground, the positive rail and the negative rail, the ground rail and the negative rail, then both to the ground rail, a stepped waveform is generated at the inverter output. This is an example of a three-level inverter: the two voltages and ground.[20]
Resonant inverters produce sine waves with LC circuits to remove the harmonics from a simple square wave. Typically there are several series- and parallel-resonant LC circuits, each tuned to a different harmonic of the power line frequency. This simplifies the electronics, but the inductors and capacitors tend to be large and heavy. Its high efficiency makes this approach popular in large uninterruptible power supplies in data centers that run the inverter continuously in an "online" mode to avoid any switchover transient when power is lost. (See related: Resonant inverter)
A closely related approach uses a ferroresonant transformer, also known as a constant-voltage transformer, to remove harmonics and to store enough energy to sustain the load for a few AC cycles. This property makes them useful in standby power supplies to eliminate the switchover transient that otherwise occurs during a power failure while the normally idle inverter starts and the mechanical relays are switching to its output.
A proposal suggested in Power Electronics magazine utilizes two voltages as an improvement over the common commercialized technology, which can only apply DC bus voltage in either direction or turn it off. The proposal adds intermediate voltages to the common design. Each cycle sees the following sequence of delivered voltages: v1, v2, v1, 0, −v1, −v2, −v1, 0.[18]
Three-phase inverters are used for variable-frequency drive applications and for high power applications such as HVDC power transmission. A basic three-phase inverter consists of three single-phase inverter switches each connected to one of the three load terminals. For the most basic control scheme, the operation of the three switches is coordinated so that one switch operates at each 60 degree point of the fundamental output waveform. This creates a line-to-line output waveform that has six steps. The six-step waveform has a zero-voltage step between the positive and negative sections of the square-wave such that the harmonics that are multiples of three are eliminated as described above. When carrier-based PWM techniques are applied to six-step waveforms, the basic overall shape, or envelope, of the waveform is retained so that the 3rd harmonic and its multiples are cancelled.
To construct inverters with higher power ratings, two six-step three-phase inverters can be connected in parallel for a higher current rating or in series for a higher voltage rating. In either case, the output waveforms are phase shifted to obtain a 12-step waveform. If additional inverters are combined, an 18-step inverter is obtained with three inverters etc. Although inverters are usually combined for the purpose of achieving increased voltage or current ratings, the quality of the waveform is improved as well.
Compared to other household electric devices, inverters are large in size and volume. In , Google together with IEEE started an open competition named Little Box Challenge, with a prize money of $1,000,000, to build a (much) smaller power inverter.[21]
From the late nineteenth century through the middle of the twentieth century, DC-to-AC power conversion was accomplished using rotary converters or motor-generator sets (M-G sets). In the early twentieth century, vacuum tubes and gas-filled tubes began to be used as switches in inverter circuits. The most widely used type of tube was the thyratron.
The origins of electromechanical inverters explain the source of the term inverter. Early AC-to-DC converters used an induction or synchronous AC motor direct-connected to a generator (dynamo) so that the generator's commutator reversed its connections at exactly the right moments to produce DC. A later development is the synchronous converter, in which the motor and generator windings are combined into one armature, with slip rings at one end and a commutator at the other and only one field frame. The result with either is AC-in, DC-out. With an M-G set, the DC can be considered to be separately generated from the AC; with a synchronous converter, in a certain sense it can be considered to be "mechanically rectified AC". Given the right auxiliary and control equipment, an M-G set or rotary converter can be "run backwards", converting DC to AC. Hence an inverter is an inverted converter.[22]
Since early transistors were not available with sufficient voltage and current ratings for most inverter applications, it was the introduction of the thyristor or silicon-controlled rectifier (SCR) that initiated the transition to solid-state inverter circuits.
The commutation requirements of SCRs are a key consideration in SCR circuit designs. SCRs do not turn off or commutate automatically when the gate control signal is shut off. They only turn off when the forward current is reduced to below the minimum holding current, which varies with each kind of SCR, through some external process. For SCRs connected to an AC power source, commutation occurs naturally every time the polarity of the source voltage reverses. SCRs connected to a DC power source usually require a means of forced commutation that forces the current to zero when commutation is required. The least complicated SCR circuits employ natural commutation rather than forced commutation. With the addition of forced commutation circuits, SCRs have been used in the types of inverter circuits described above.
In applications where inverters transfer power from a DC power source to an AC power source, it is possible to use AC-to-DC controlled rectifier circuits operating in the inversion mode. In the inversion mode, a controlled rectifier circuit operates as a line commutated inverter. This type of operation can be used in HVDC power transmission systems and in regenerative braking operation of motor control systems.
Another type of SCR inverter circuit is the current source input (CSI) inverter. A CSI inverter is the dual of a six-step voltage source inverter. With a current-source inverter, the DC power supply is configured as a current source rather than a voltage source. The inverter SCRs are switched in a six-step sequence to direct the current to a three-phase AC load as a stepped current waveform. CSI inverter commutation methods include load commutation and parallel capacitor commutation. With both methods, the input current regulation assists the commutation. With load commutation, the load is a synchronous motor operated at a leading power factor.
As they have become available in higher voltage and current ratings, semiconductors such as transistors or IGBTs that can be turned off by means of control signals have become the preferred switching components for use in inverter circuits.
Rectifier circuits are often classified by the number of current pulses that flow to the DC side of the rectifier per cycle of AC input voltage. A single-phase half-wave rectifier is a one-pulse circuit and a single-phase full-wave rectifier is a two-pulse circuit. A three-phase half-wave rectifier is a three-pulse circuit and a three-phase full-wave rectifier is a six-pulse circuit.[23]
With three-phase rectifiers, two or more rectifiers are sometimes connected in series or parallel to obtain higher voltage or current ratings. The rectifier inputs are supplied from special transformers that provide phase shifted outputs. This has the effect of phase multiplication. Six phases are obtained from two transformers, twelve phases from three transformers, and so on. The associated rectifier circuits are 12-pulse rectifiers, 18-pulse rectifiers, and so on...
When controlled rectifier circuits are operated in the inversion mode, they would be classified by pulse number also. Rectifier circuits that have a higher pulse number have reduced harmonic content in the AC input current and reduced ripple in the DC output voltage. In the inversion mode, circuits that have a higher pulse number have lower harmonic content in the AC output voltage waveform.
The large switching devices for power transmission applications installed until predominantly used mercury-arc valves. Modern inverters are usually solid state (static inverters). A modern design method features components arranged in an Hbridge configuration. This design is also quite popular with smaller-scale consumer devices.[24][25]
It doesn’t matter whether you install an on-grid, off-grid, or hybrid residential solar power system.
You need at least one solar inverter.
Depending on the size and type of solar panel array you choose, you may need more than one.
Inverters convert the solar power harvested by photovoltaic modules like solar panels into usable household electricity.
Some system configurations require storage inverters in addition to solar inverters.
But what exactly does a solar inverter do — and how does it work?
Read on to find out.
Solar inverters are an essential component in every residential photovoltaic system.
PV modules — like solar panels— produce direct current DC electricity using the photovoltaic effect.
However, virtually all home appliances and consumer electronic devices require alternating current (AC) electricity to start and run.
Similarly, utility grids worldwide primarily transmit and deliver AC electricity to homes and businesses. That’s why alternating current is commonly known as household electricity.
A solar inverter is built-in with compact off-grid electricity solutions like EcoFlow’s portable power stations.
In larger residential and commercial solar balance of systems, the inverter may be a standalone component.
For example, EcoFlow DELTA Pro Ultra can chain together up to 3 x solar inverters to deliver 21.6 kilowatts (kW) of AC output and 16.8kW of solar charge capacity with 42 x 400W rigid solar panels.
In off-grid or hybrid solar power systems, an additional component — the solar charge controller — directs DC current to a solar battery for storage or to the solar inverter for immediate use.
Solar systems that produce electricity use PV modules — usually solar panels with multiple photovoltaic cells — to harvest photons from sunlight and convert them into direct current.
A solar inverter uses solid-state components to convert DC to AC electricity.
Unlike older technologies like mechanical inverters, solar inverters have no moving parts. Instead, they utilize power semiconductors, like transistors and diodes, to switch direct current on and off at a very high frequency.
(Source: Electronics Tutorials)
Rapid binary switching produces alternating current — ideally with a pure sine waveform. Pure sine wave electricity is considered the gold standard of AC waveforms because it is “clean” and free of the distortion and noise that can harm sensitive electronics when inferior inverters are used.
There are numerous types of solar inverters available today.
Which option is best depends on your installation type and electricity production needs.
Here’s a brief overview of the different types of solar inverters.
(Source: Penn State)
String inverters are the oldest and most common type of solar inverters for small systems in the 500-watt to 3kW range. They are often used in portable and residential applications.
The principle behind string inverters for photovoltaic arrays is the same regardless of the installation’s scale.
In grid-tied systems, solar panels connect directly to each other and transmit their combined DC electricity to the string inverter.
The string inverter converts DC to AC electricity.
It transmits it to your home for immediate consumption or sends excess power back to the grid through a bidirectional or smart meter.
If you reside in a location that offers net metering, you’ll receive credits for solar electricity you sell back to the utility grid.
In off-grid or hybrid solar systems, PV modules may first send DC electricity to a solar charge controller. However, the solar inverter is still an integral part of the balance of the system.
(Source: Penn State)
Microinverters — also known as module inverters — are generally built into photovoltaic modules.
In a solar panel array that utilizes microinverters, each individual panel has a small dedicated inverter located on an underside made of non-photovoltaic material.
(Source: Penn State)
A central inverter utilizes multiple strings of solar panels that connect to a power conditioning combiner box before delivering DC electricity to the inverter.
Rather than using a separate inverter for each string or panel, one DC output from the combiner connects to the central inverter, which converts DC to AC and delivers to your home and the utility grid from a single output.
Central inverters are typically deployed in large solar power systems in the 5kW – 100MW range.
(Source: Penn State)
Off-grid solar power systems operate independently of the utility grid and rely on battery storage to function during hours when there’s little to no sunlight.
Solar energy is intermittent by nature. Electricity production diminishes on cloudy days, and solar panels don’t work at night.
Grid-tied systems don’t require storage because they toggle between utility and solar electricity automatically. However, on-grid systems without solar batteries don’t work during a blackout.
For more information, please visit residential inverter.
Off-grid systems of sufficient size offer complete home energy security, and solar batteries are an essential component.
Unlike grid-tied systems without storage, the first stop for electricity after it’s produced by solar panels isn’t an inverter. Instead, a solar charge controller is first in the chain.
There are two types of solar charge controllers: Maximum Power Point Tracking (MPPT) and Pulse Width Modulation (PWM). Both alternate between supplying DC electricity to a solar battery for storage or to an inverter for conversion to AC.
The term “hybrid” can refer to several different types of residential solar power systems, including installations that utilize wind power in addition to PV-generated electricity.
Here, we’ll focus on hybrid solar power + storage systems that can also tap into on-grid — and even gas generator — power.
A grid-tied solar power system without storage offers benefits like lower electricity bills and a reduced carbon footprint.
However, on-grid PV systems without storage don’t supply power during a blackout.
Because a grid-tied system both transmits and consumes electricity from the power grid, it shuts down automatically during a blackout.
Otherwise, electricity sent from a PV system could injure or kill workers trying to restore power and cause further damage to utility infrastructure.
A hybrid solar system — like EcoFlow DELTA Pro Ultra offers all the benefits of a grid-tied PV system with the added energy security that comes with off-grid electricity storage.
EcoFlow DELTA Pro Ultra is a hybrid solar and whole-home backup power solution.
Fully maxed out, EcoFlow DELTA Pro Ultra provides:
What makes EcoFlow DELTA Pro Ultra a “hybrid” is the ease with which you can integrate on-grid electricity and gas generators.
You get seven charging options in total, including solar panels.
EcoFlow Smart Home Panel 2 integrates the DELTA Pro Ultra with your home circuit board and on-grid electricity for seamless hybrid power.
You can also plug EcoFlow DELTA Pro Ultra into a standard household outlet, but you’ll only get W of AC input, meaning it will take longer to recharge the battery.
Integration with EcoFlow Smart Home Panel 2 or your home Electric Vehicle pile is a simple job for a licensed electrician.
EcoFlow DELTA Pro Ultra doesn’t transmit electricity to the power company like grid-tied solar systems.
Instead, you get uninterrupted power during extended outages and up to a month of off-grid power.
A power optimizer is a DC-to-DC converter designed to maximize electricity production from photovoltaic modules and wind turbines.
In residential solar panel systems, power optimizers utilize maximum power point tracking (MPPT) to condition the electricity of an entire array and optimize inverter performance.
A power optimizer isn’t a solar inverter per se. Instead, it converts the DC electricity produced by solar panels to an optimal voltage for maximizing solar inverter performance.
One way to classify solar inverters by type is to divide them into grid-tied, off-grid, and hybrid systems.
The solar inverter types outlined above, such as string, central, and microinverter, can be utilized in different ways by all three systems.
Here are brief definitions of each.
(Source: longmontcolorado. gov)
In a grid-tied system, DC electricity from photovoltaic modules like solar panels is transmitted through cables directly to a solar inverter. The solar inverter converts DC to AC electricity for consumption in your home and transmission to the utility grid.
(Source: Penn State)
Off-grid solar power systems use solar batteries to store electricity to solve the problem of intermittency.
Because off-grid systems operate independently of the utility grid, electricity must be stored for use at night or at other times when your household consumes more power than your solar panels produce.
In an off-grid system, solar panels transmit DC electricity to a solar charge controller, which distributes power to a solar battery or solar inverter, depending on whether the priority is consumption or storage.
However, many off-grid systems can only be charged using solar panels and don’t give you the option to auto-switch between utility or fossil fuel generator power.
In some ways, a hybrid system offers the best of both worlds.
It allows you to toggle automatically or manually between the utility grid and solar power, depending on the parameters you set.
Crucially, a hybrid solar + storage system provides electricity during a blackout.
Depending on your solar battery capacity and electricity production potential, you can have power even during extended outages — or indefinitely.
There are several essential factors to consider when choosing a solar inverter.
Don’t make a purchase decision without taking the following into account.
The type of inverter you need depends on whether you purchase a grid-tied system, go off-grid, or combine the two by opting for hybrid solar + storage.
In an on-grid system, solar panels transmit DC electricity directly to a solar inverter that converts the current into AC power for immediate consumption or transmission back to the grid.
In off-grid and hybrid systems, DC from photovoltaic modules is sent to a solar charge controller, which routes the power to a solar battery or a solar inverter, depending on the parameters you specify.
The type of solar inverter best suited to your application is mostly determined by the amount of electricity the system must generate.
String inverters are suitable for relatively small systems, while central and microinverters are better equipped to handle high-wattage applications.
Inverters can be standalone components or built into devices like solar generators.
No matter which setup you choose, it’s essential to ensure compatibility between your photovoltaic modules and the solar inverter and ensure the solar input is higher than the maximum electricity production potential of your solar panel array.
Also, confirm that your solar inverter is compatible with other balance of system components and your utility provider (for grid-tied systems).
If you use a string or central inverter, your entire system will cease operating if your solar inverter fails.
One advantage of some microinverters is that by dedicating an inverter to each individual PV panel, the balance of the array should continue to work when the inverter on one or more panels fails.
Evaluating the warranty is one way of determining how confident a manufacturer is in the durability and longevity of its products.
Remember, if your inverter fails, your entire system will be offline.
Insist on a 5-year warranty at minimum.
The electricity production of string and central inverters can be impacted more negatively by factors like shade and debris obscuring individual panels in an array than alternatives like microinverters.
Carefully evaluate the environmental factors that exist in your installation area and do your best to position your photovoltaic panels to receive the maximum amount of peak sunlight.
Last but not least, the type of residential solar power system you purchase must fit your budget.
But that doesn’t mean you should go for the cheapest option.
Thanks to government incentives like the 30% Federal Solar Tax Credit and low-to-no-interest financing options direct from manufacturers, you have more freedom to make the wisest long-term investment.
(Source: Electrical Technology)
There are three different methods of stringing solar panels together and connecting them to the solar inverter or charge controller (for off-grid and hybrid systems.)
(Source: Alternative Energy Tutorials)
Connecting Solar Panels of the Same Model and Rated Power in Series
To connect your solar panels in series, wire the positive terminal to the negative terminal of each panel in the array. At the end, you’ll have a single positive/negative connection that will plug into your balance of system.
By wiring your solar panels in series, the output voltage of the array accumulates. In the diagram above, the output voltage of each panel is 6 volts. At the end of the series, the cumulative output is 18V (3 panels x 6V = 18V).
What’s crucial to note is that while the voltage output increases with each panel added to the series, the amperage remains the same.
Series connections are typically used for grid-tied systems that require a voltage of 24V or more.
Voltage Accumulation: If your installation requires high voltage to operate — standard with on-grid systems — series or hybrid series/parallel wiring is probably essential. Even if it’s not if your application is best served by higher voltage rather than amperage, a series connection is your best choice.
Efficiency and Performance: Without considering other factors, series connections will output slightly more electricity from the PV panel array than other wiring methods. There is less power lost delivering electricity over distance to your balance system in a series connection.
Thinner Cables: A relatively minor consideration, but parallel connections require higher gauge wiring due to how the electricity is transmitted. Series connections may cost slightly less to wire the same number of panels.
Better for Distance: Depending on the total surface area of your installation and how long the cables must be to connect to your balance of system, series connections may deliver an additional benefit. Voltage travels more efficiently than amperage over long distances.
Obstruction and Shading: The most significant disadvantage of wiring solar panels in series is that the output of the entire array is dependent on the individual production of each module.
If you have 20 solar panels with a rated voltage of 6V each, the maximum potential output during peak sun hours is 120V. However, if just one module is in the shade (or damaged) and only produces 4V, the array’s output will be reduced to 4V per panel. Instead of 120V of production, your panels will output 80V. If part of your installation area suffers from significant shade during peak sun hours, you should consider parallel or hybrid connections instead.
Danger: High Voltage: There are many benefits to increasing the voltage output of your solar panel array. However, high voltage can be dangerous or deadly if improperly used. Working with high voltage also dramatically increases the risk for the person doing the installation. If you decide to proceed with a series connection, it’s best to hire a
professional installer.
(Source: Alternative Energy Tutorials)
Connecting Solar Panels of the Same Model and Rated Power in Parallel
To wire solar panels in parallel, connect each panel’s positive terminals together. You also connect all the negative terminals to one another. Parallel wiring results in amperage accumulating and voltage remaining the same. The exact opposite effect of series wiring.
Again, using the same panels in the series example above, if the amperage per panel is 3V and you have 3 identical panels, your total output will be 9 amps (9A) and 6 volts (6V). The formula looks like this:
3A x 3 PV panels = 9A total output
Voltage doesn’t increase — the output remains 6V no matter how many solar panels you connect. If you have a 20-panel array connected in parallel with 6V/3A of rated power output, your maximum electricity production capacity is 6V/60A.
Cumulative Increase in Current: Each PV panel you add to an array connected in parallel adds its direct current output to the system’s total output.
Less Overall Vulnerability to Shade: Unlike the voltage produced by series connections, the increased amperage (current) produced by parallel connections is not dependent on the performance of individual panels. If one PV panel is covered in shade for part of the day, the performance of the entire array is not affected. Shaded panels will contribute less current to the total output, but the maximum output of the panels receiving direct sunlight remains the same.
For example, if you have 20 panels that output 3A of current in peak sunlight, but two are covered in shade, reducing their output to 2A, the cumulative output of your array will be reduced by 2A. The total (theoretical) output is 58A instead of 60A because each shaded panel produces 1A less.
For many rooftop installations, the advantage of parallel wiring is obvious. Depending on your location and roof structure, substantial portions of your solar panel array may be regularly shaded by obstructions like trees and neighbouring buildings for part of the day.
But they may produce their full rated power at regular intervals, depending on the earth’s rotation around the sun.
If the panel’s positioning means it never or rarely gets direct sunlight, you should move it.
Solar panels still produce electricity from ambient sunlight on overcast days. However, PV panels do not always produce their full-rated power.
Why?
PV panel performance depends entirely on the amount of solar irradiance (sunlight) it receives.
That’s why solar panels don’t “work” at night.
Investing in a mounted solar panel you know will consistently be in the shade makes little sense.
Constant Voltage: Unlike series connections, you can add additional PV panels without increasing the voltage. This makes parallel connections invaluable in applications that require 12V power input, like many motorhome and recreational vehicle systems.
Similarly, solar inverters have a maximum voltage capacity. You can add more PV panels to your array and continue using the same inverter. If you wired the same array in series and exceed the voltage capacity of your inverter, it will either shut down or permanently damage the component.
Less Efficient: The larger your solar panel array, the more power you will lose to inefficiency. Parallel wiring leaks more energy over long distances than series connections.
Less Resistant to Heat: Believe it or not, solar panels suffer in the heat. Direct sun exposure is optimal for electricity production, but solar panel efficiency declines rapidly as the temperature rises above 25°C.
That’s because the photovoltaic effect used by solar cells captures energy from sunlight, not from heat.
All solar inverters and balance of system components like PWM or MPPT charge controllers have minimum voltage requirements. If heat (or other factors) hinder solar panel efficiency to the degree that voltage output decreases below the minimum requirement, adding more PV panels wired in parallel will not solve the problem.
Thicker, More Expensive Cables: Amperage (current) flows through wires in a similar way to how water flows through a hose. The more current (water) you want to output, the bigger the cable (hose) has to be. Larger gauge wires are also less efficient at moving current over long distances. Parallel connections are typically better suited to smaller installations.
Connecting solar panels in series or parallel each has its pros and cons.
Can you have the best of both worlds?
Yes, many professionally installed solar panel installations combine series and parallel wiring in one array to maximize the product of each group of panels.
It’s possible to strike the optimal balance between series and parallel wiring by carefully planning the wiring based on the location of the panels on the roof relative to the sun and obstacles that obstruct sunlight at certain times of day.
Typically, the goal is to achieve the right balance of producing volts and producing amps by wiring panels together in series and in parallel — not either/or.
If your residential solar installation will have more than 3 or 4 PV panels, it’s best to work with a professional installer. It will cost you more upfront but should substantially increase your return on investment and shorten your solar payback period.
For safety and performance reasons, we highly recommend that you DO NOT attempt hybrid series-parallel wiring of your solar panels on your own. Work with a reputable installer to achieve optimal results.
Some of the factors a solar power professional will consider when developing a wiring plan include.
Involving an experienced installer in the process before buying your PV panels and balance of system can be an even better idea than just having them connect everything together.
The right installer can help you make an informed purchase decision and avoid common mistakes like buying too many solar panels or incompatible components.
Trying to choose an inverter and other components can become confusing. You can never be quite sure about compatibility between solar panels, batteries, inverters, and charge controllers. That’s why some companies have put together convenient all-in-one off-grid power solutions.
The EcoFlow Power Kits are an excellent example of a plug-and-play off-grid solar power system. They are perfect for cabins, tiny homes, and RVs.
The Power Hub includes all of the essential converters, outlets, and chargers for an off-grid system, including:
With an all-in-one system, you don’t need to worry about compatibility and whether the inverter is the right type for your solar power system. The Power Kits also work with all models of EcoFlow solar panels (rigid, portable, and flexible) and panels from other manufacturers.
A DC-DC step-down converter takes the high voltage of PV panels (often 50+ volts) and steps it down to the 48V that the EcoFlow Power Kit batteries expect.
The DC-DC battery charger with MPPT (multi-power point tracking) allows the battery bank to be charged directly by other DC power sources, such as a car alternator or a service battery.
An MPPT is especially useful in RV and other mobile applications. The technology allows for high-efficiency charging and is superior to similar chargers that use PWM (pulse width modulation) chargers.
The integrated MPPT charge controller allows for safe, efficient charging of your battery bank using the power generated by your solar array.
The inverter charger allows your system to charge and function using AC power. For example, with an RV installation, you can connect directly to shore power at campgrounds.
In short, you can’t have a residential or portable solar power system without at least one solar inverter.
The DC electricity produced by photovoltaic modules like solar panels won’t operate your home’s appliances and systems without being converted to AC electricity by a solar inverter.
If you’re looking for a whole home solar power system with no compatibility headaches and the ability to function using utility electricity or off-grid, check out the hybrid EcoFlow DELTA Pro Ultra inverter and solar battery system today.
Whether you’re shopping for portable power to-go or complete energy independence, EcoFlow has a solar power solution for you.
For more solar inverter manufacturerinformation, please contact us. We will provide professional answers.