In rolling mill drives, often 200-300 of the base speed is used.

About 25 of the worlds electrical energy is consumed by electric motors in industrial applications.

Systems using VFDs can be more efficient than those using throttling control of fluid flow, such as in systems with pumps and damper control for fans.

However, the global market penetration for all applications of VFDs is relatively small.

Some types of single-phase motors or synchronous motors can be advantageous in some situations, but generally three-phase induction motors are preferred as the most economical.

Motors that are designed for fixed-speed operation are often used.

Elevated-voltage stresses imposed on induction motors that are supplied by VFDs require that such motors be designed for definite-purpose inverter-fed duty in accordance with such requirements as Part 31 of NEMA Standard MG-1.

Voltage-source inverter (VSI) drives (see Generic topologies sub-section below) are by far the most common type of drives.

Most drives are AC-AC drives in that they convert AC line input to AC inverter output.

However, in some applications such as common DC bus or solar applications, drives are configured as DC-AC drives.

The most basic rectifier converter for the VSI drive is configured as a three-phase, six-pulse, full-wave diode bridge.

In a VSI drive, the DC link consists of a capacitor which smooths out the converters DC output ripple and provides a stiff input to the inverter.

VSI drives provide higher power factor and lower harmonic distortion than phase-controlled current-source inverter (CSI) and load-commutated inverter (LCI) drives (see Generic topologies sub-section below).

The drive controller can also be configured as a phase converter having single-phase converter input and three-phase inverter output.

Introduced in 1983, 8 the insulated-gate bipolar transistor (IGBT) has in the past two decades come to dominate VFDs as an inverter switching device.

For example, for 460 V, 60 Hz motors, this linear VHz relationship is 46060 7.67 VHz.

While suitable in wide-ranging applications, VHz control is sub-optimal in high-performance applications involving low speed or demanding, dynamic speed regulation, positioning, and reversing load requirements.

Some VHz control drives can also operate in quadratic VHz mode or can even be programmed to suit special multi-point VHz paths.

With SPWM control (see Fig.

This is sometimes called field weakening and, for AC motors, means operating at less than rated VHz and above rated nameplate speed.

Permanent magnet synchronous motors have quite limited field-weakening speed range due to the constant magnet flux linkage.

Wound-rotor synchronous motors and induction motors have much wider speed range.

For example, a 100 HP, 460 V, 60 Hz, 1775 RPM (4-pole) induction motor supplied with 460 V, 75 Hz (6.134 VHz), would be limited to 6075 80 torque at 125 speed (2218.75 RPM) 100 power.

At higher speeds, the induction motor torque has to be limited further due to the lowering of the breakaway torque a of the motor.

Thus, rated power can be typically produced only up to 130-150 of the rated nameplate speed.

Wound-rotor synchronous motors can be run at even higher speeds.

Vfd Install Milling Machine