Power inverter

[4] Technical standards for commercial power distribution grids require less than 3% THD in the wave shape at the customer's point of connection.

The second method converts DC to AC at battery level and uses a line-frequency transformer to create the output voltage.

[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.

The standard electric utility provides a sine wave, typically with minor imperfections but sometimes with significant distortion.

The lowest THD for a three-step modified sine wave is 30% when the pulses are at 130 degrees width of each electrical cycle.

[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).

[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.

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.

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.

Smaller popular consumer and commercial devices designed to mimic line power typically range from 150 to 3000 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.

Inverter circuits designed to produce a variable output voltage range are often used within motor speed controllers.

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.

Solar inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection.

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.

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.

This type of electromechanical inverter switch, called a vibrator or buzzer, was once used in vacuum tube automobile radios.

As they became available with adequate power ratings, transistors, and various other types of semiconductor switches have been incorporated into inverter circuit designs.

SCRs provide large power handling capability in a semiconductor device, and can readily be controlled over a variable firing range.

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.

Fourier 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.

Multiple pulse-width or carrier based PWM control schemes produce waveforms that are composed of many narrow pulses.

Typically there are several series- and parallel-resonant LC circuits, each tuned to a different harmonic of the power line frequency.

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.

Although inverters are usually combined for the purpose of achieving increased voltage or current ratings, the quality of the waveform is improved as well.

In 2014, 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.

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.

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.

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 1970 predominantly used mercury-arc valves.