Introduction:
The Adjustable Speed Drives (ADS) are generally used in industry. In most drives AC motors are applied. The standard in those drives are Induction Motors (IM) and recently also Permanent Magnet Synchronous Motors (PMSM) are offered.
Variable speed drives are widely used in application such as pumps, fans, elevators, electrical vehicles, heating, ventilation and air-conditioning (HVAC), robotics, wind generation systems, ship propulsion, etc.
Previously, DC machines were preferred for variable speed drives. However, DC motors have disadvantages of higher cost, higher rotor inertia and maintenance problem with commutators and brushes. In addition they cannot operate in dirty and explosive environments. The AC motors do not have the disadvantages of DC machines.
Therefore, in last three decades the DC motors are progressively replaced by AC drives. The responsible for those result are development of modern semiconductor devices, especially power Insulated Gate Bipolar Transistor (IGBT) and Digital Signal Processor (DSP) technologies.
The most economical IM speed control methods are realized by using frequency converters. Many different topologies of frequency converters are proposed and investigated in a literature. However, a converter consisting of a diode rectifier, a dc-link and a Pulse Width Modulated (PWM) voltage inverter is the most applied used in industry (see section 2.3).
The high-performance frequency controlled PWM inverter – fed IM drive should be characterized by:
• fast flux and torque response,
• available maximum output torque in wide range of speed operation region,
• constant switching frequency,
• uni-polar voltage PWM,
• low flux and torque ripple,
• robustness for parameter variation,
• four-quadrant operation
These features depend on the applied control strategy. The main goal of the chosen control method is to provide the best possible parameters of drive. Additionally, a very important requirement regarding control method is simplicity (simple algorithm, simple tuning and operation with small controller dimension leads to low price of final product).
Source: Warsaw University of Technology
Author: Marcin Żelechowski
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