Pulse-width modulation (PWM) variable-frequency drive projects started in the 1960s at Strömberg in Finland. Martti Harmoinen (fi) is regarded as the inventor of this technology. Strömberg managed to sell the idea of PWM drive to Helsinki Metro in 1973 and in 1982 the first PWM drive SAMI10 were operational. OverviewA variable-frequency drive (VFD, or adjustable-frequency drive, adjustable-speed drive, variable-speed drive, AC drive, micro drive, inverter drive, variable voltage variable frequency drive, or drive) is a type of. . A variable-frequency drive is a device used in a drive system consisting of the following three main sub-systems: AC motor, main drive assembly, and drive/operator interface. The AC ele. . Most VFDs allow auto-starting, which will drive the output to a designated frequency after a power cycle, after a fault has been cleared, or after the emergency stop signal has been restored (generally emergency stops are a.
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