2–8

Basic System Description

Basic System Description

A motor control system will obviously include a motor and inverter, as well as a breaker or fuses for safety. If you are connecting a motor to the inverter on a test bench just to get started, that’s all you may need for now. But a system can also have a variety of additional components. Some can be for noise suppression, while others may enhance the inverter’s braking performance. The figure and table below show a system with all the optional components you may need in your finished application.

Inverter Mounting

and Installation

 

 

From power supply

Breaker,

MCCB or

GFI

L1

L2

L3

 

 

+1

+

Inverter

RB

GND

T1 T2 T3

Motor

Thermal

switch

Name

Function

 

 

 

 

Breaker / discon-

A molded-case circuit breaker (MCCB), ground fault

nect

interrupter (GFI), or a fused disconnect device. NOTE:

 

The installer must refer to the NEC and local codes to

 

ensure safety and compliance.

 

 

Input-side

This is useful in suppressing harmonics induced on the

AC Reactor

power supply lines and for improving the power factor.

 

WARNING: Some applications must use an input-

 

side AC reactor to prevent inverter damage. See

 

Warning on next page.

 

 

Radio noise filter

Electrical noise interference may occur on nearby

 

equipment such as a radio receiver. This magnetic

 

choke filter helps reduce radiated noise (can also be

 

used on output).

 

 

EMI filter (for

Reduces the conducted noise on the power supply

CE applications,

wiring between the inverter and the power distribution

see Appendix D)

system. Connect to the inverter primary (input side).

 

 

Radio noise filter

This capacitive filter reduces radiated noise from the

(use in non-CE

main power wires in the inverter input side.

applications)

 

 

 

DC link choke

Suppresses harmonics generated by the inverter.

 

However, it will not protect the input diode bridge

 

rectifier.

 

 

Braking resistor

This is useful for increasing the inverter’s control

 

torque for high duty-cycle (ON-OFF) applications, and

 

improving the decelerating capability.

 

 

Radio noise filter

Electrical noise interference may occur on nearby

 

equipment such as a radio receiver. This magnetic

 

choke filter helps reduce radiated noise (can also be

 

used on input).

 

 

Output-side

This reactor reduces the vibrations in the motor caused

AC reactor

by the inverter’s switching waveforms, by smoothing

 

the waveform to approximate commercial power

 

quality. It is also useful to reduce harmonics when

 

wiring from the inverter to the motor is more than 10m

 

in length.

 

 

LCR filter

Sine wave shaping filter for output side.

 

 

NOTE: Note that some components are required for regulatory agency compliance (see Chapter 5 and Appendix D).