Introduction to Variable Frequency Drives (VFDs)

Overview

RealPars promotion for PLC programming training.
Induction/AC electric motors rotate based on the number of poles and the supplied power frequency.
Frequency affects Revolutions Per Minute (RPM).

Frequency & RPM: Higher frequency = Higher RPM.
- In the US, standard frequency is 60 Hertz.
- Two-pole AC motor: 3600 RPM at 60 Hz.

Mechanical Speed Reducer
- Decreases output speed by increasing torque.
- Requires lubrication; not suitable for distant shafts; sensitive to vibration and noise.
Adding More Sets of Poles
- Reduces speed without electrical alteration.
- Transistor systems exist but lack fine control.
Variable Frequency Drive (VFD)
- Configurable for desired speed and voltage.
- Can adjust motor speed to meet changing requirements.

Industrial Applications: Controls for extruders, electric cranes, roller coasters, mechanical bulls, etc.
Commercial Applications: Used in pumps, HVAC for flow control, and volume regulation.

Current Transformers (T1, T2, T3)
- Measure current to detect discrepancies and ground faults.
Converter/Rectifier
- Converts three-phase AC to DC using diodes.
- Six-pulse rectifier allows current flow in one direction.
DC Filter & Buffer (DC Bus)
- Composed of capacitors and resistors.
- Pre-charge circuit prevents damage during power-up by limiting current flow.
- Capacitors charge through resistors; contact closes when fully charged to create a low-resistance path.
- Resistors ensure voltage division among capacitors.

Variable Frequency Drives:
- Allow precise motor speed control.
- Three Main Stages:
  1. Converter/Rectifier: Converts AC to DC.
  2. DC Link: Filters and buffers DC with capacitors and resistors.
  3. IGBT Module: Converts DC back to AC.
Next Steps: Part 2 will discuss the IGBT module and PWM for AC output and precise motor speed control.