Adjustable Speed Drives ASDs

Adjustable speed drives (ASDs) are commonly used in industrial applications because of their efficiency, but they are often susceptible to power fluctuations and interruptions. Disruptions in industrial settings are highly undesirable, and down time of a machine in a continuously running process can cause significant monetary losses. Adjustable speed drives that can ride-through power supply disturbances are valuable tools for industry. 

The major reasons for ASD shutdown are transients, interruptions, sags (under-voltages), swells (over-voltages), waveform distortions, voltage fluctuations, and frequency variations [11-13]. These problems can cause ADS symptoms such as premature trips or shuts down, resets and restarts, frequent repairs and replacements, erratic control of process parameters, unexplained fuse blowing and/or component failures, and frequent motor overheating trips and/or continuous operation of motor cooling systems. 

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Adjustable speed drives (ASDs) produce noise signals that are very often troublesome. The noise frequency generated by the ASDs is typically higher than the harmonic frequencies of the fundamental voltage. Because of this, the noise could find its way into sensitive data and signal circuits unless such circuits are sufficiently isolated from the ASD power lines. 

In a newspaper printing facility, two adjustable speed drives (ASDs) were installed as part of a new conveyor system to transport the finished product to the shipping area. The ASDs were shutting themselves off periodically, causing papers to back up on the conveyor and disrupting production. 

ES application areas include power electronics, memory protection, battery enhancement, portable energy sources, power quality improvement, adjustable speed drives (ASDs), high power actuators, hybrid electric vehicles, renewable and off-peak energy storage, and military and aerospace applications. All these application areas will be discussed in this chapter. 

FIGURE 4.14 Adjustable speed drive input current for a smaller motor operating at 50 Hz (ASD with input line inductors). 

The capacitor bank and the transformer form a parallel resonant circuit with the seventh harmonic current from the ASDs acting as the harmonic source. This condition is represented in Figure 4.19. Two adjustable speed drives typically draw a current of 550 A each, for a total load of 1100 A. If the seventh harmonic current is 5.0% of the fundamental (which is typical in drive applications), the seventh harmonic current seen by the parallel resonant circuit is 55 A = /7. 

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