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Variable-frequency inverter types

There are three common types of frequency inverter. Current source inversion (CSI) has been successfully used in signal processing and industrial power applications. CSI frequency inverter are the only type that has regenerative power capability. In other words, they can absorb power flow back from the motor into the power supply. CSI frequency inverter give a very clean current waveform but require large, expensive inductors in their construction and cause cogging (pulsating movement during rotation) below 6 Hz.

Voltage source inversion (VSI) drives have poor power factor, can cause motor cogging below 6 Hz, and are non-regenerative. Consequently, CSI and VSI drives have not been widely used.

Pulse-width modulation (PWM) frequency inverter are most commonly used in industry because of excellent input power factor due to fixed DC bus voltage, no motor cogging, higher efficiencies, and lower cost. A PWM frequency inverter uses a series of voltage pulses of different lengths to simulate a sinusoidal wave. Ideally, the pulses are timed so that the time average integral of the drive yields a perfect sinusoid. The current method of choice to produce this waveform runs a triangle wave and sine wave through a comparator, and outputs a voltage pulse whenever the sine wave's value is greater than the triangle wave. The current electric component of choice to generate the voltage pulse is the insulated gate bipolar transistor (IGBT), although silicon-controlled rectifiers (SCRs) can work as well. In the near future, injection-enhanced gate transistors (IEGTs) will be used to perform this task. Much more long term, memristors will probably become the component of choice for this task.

Memristors are the fourth passive circuit element, linking electric charge and magnetic flux. Memristors have been hypothesized to exist for more than 30 years, but were not fabricated until April 2008 by Hewlett Packard Labs. Hewlett Packard hopes to use these devices as a passive transistor, reducing their heat generation compared to other types of memory. Regardless of the component used to form the sine wave, the switching action causes problems.

This article comes from ecmweb edit released

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