Overview
2.2 Introduction
Product User Manual
Operating Instructions, Version AE 12/2009, A5E01454341C
21
often generate square-wave-shaped line currents. This can lead to harmonics and other
associated resonance problems.
The Perfect Harmony series draws nearly perfect sinusoidal input currents having a power
factor that exceeds 94% throughout the entire output frequency range without the use of
external power factor correction capacitors. This eliminates utility penalties for power factor
and demand charges, and improves voltage regulation. In addition, feeders, breakers, and
transformers are not overloaded with reactive power. Low speed applications specifically
benefit from the Perfect Harmony series, since a high and stable power factor is maintained
throughout the entire output range using standard induction motors.
Figure "Comparison of Perfect harmony and a typical Phase-Controlled SCR Drive"
compares graphs of power factor versus percent speed for the Perfect Harmony series and a
typical phase-controlled SCR drive.
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Figure 2-3 Comparison of Perfect harmony and a typical Phase-Controlled SCR Drive
2.2.3 Nearly Perfect Sinusoidal Output Voltages
The Robicon Perfect Harmony series of Medium Voltage (MV) Pulse Width Modulated
(PWM), Variable Frequency Motor Drives (VFD) are designed and manufactured by
Siemens LD-A, New Kensington, PA, USA with additional manufacturing facilities in Europe,
Asia, and South America. The Harmony VFD is intended for use with standard medium-
voltage three-phase AC induction, synchronous, wound rotor, permanent magnet, or super
conducting motors. When any of these types of motor is connected to a utility supply at a
fixed frequency (i.e., 60 or 50 Hz), the motor runs at a single speed. The Harmony series of
drives allow variable speed motor operation, without sacrificing any of the desirable
properties of the motor.
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