Product category:
Industrial Drives/Controls
News Release from: Yaskawa Electric Europe | Subject: Inverters
Edited by the Engineeringtalk Editorial
Team on 05 March 2001
Inverter emergency braking without brake
resistors
Many inverter controlled, induction motor applications require the ability to stop quickly, and Yaskawa is proposing to achieve this by manipulating the commanded frequency
Many inverter controlled, induction motor applications require the ability to stop quickly These applications include emergency stops, quick stopping of fans, centrifuges, presses and so forth
This article was originally published on Engineeringtalk on 31 Jul 2001 at 8.00am (UK)
Related stories
Inverters aimed at machine tool spindle drives
Yaskawa Electric has launched the Varispeed-626M5 series, a range of high performance AC vector controlled inverter drives designed for machine tool spindle drive applications
Inverters take control of wire knitting
Tritex Design and Development produces machines to knit fine wire into circular tubes from 0.2 to 30in diameter, and selected Yaskawa VS Mini J7 single-phase inverters to control its motors.
A novel method being proposed by engineers at Yaskawa in collaboration with engineers at Yaskawa Electric Corporation, Japan, uses the concept of operating the induction motor under very poor efficiency condition by manipulating the commanded frequency.
This method causes most of the regenerative energy to be dissipated in the motor thereby achieving fast stopping times without the need for braking resistor units.
Though the heat dissipating capability of the motor limits the number of times this stopping method can be employed, eliminating the braking unit along with the brake resistor brings significant economic benefit to user.
Currently the two common stopping methods, coasting and decelerated stop, are currently available in most inverters without regenerative converters at the front end.
In the coasting method, the control signals for turning the output lGBTs of the inverter ON and OFF are turned to OFF, no voltage is provided to the motor and it coasts to a stop.
The time taken for the motor to come to rest depends on the inertia of the rotor-load combination and the load torque including mechanical friction.
In the decelerated stopping method, the motor is commanded to operate at a reduced frequency (speed).
The commanded frequency is gradually reduced to bring the motor to rest.
Due to the inertia of the rotor-load combination, the speed cannot be reduced instantaneously.
Since the commanded speed is lower than the actual rotating speed of the rotor, the motor starts behaving like an induction generator.
Decelerating torque is produced which corresponds to losses in the motor and inverter, which is responsible for bringing the motor to a stop The deceleration stopping method requires careful selection of the deceleration time to achieve optimum stopping performance.
The stopping time can be shortened if the user uses a brake unit across the DC bus.
The fastest stopping time achievable depends on the size of the brake unit.
The size and cost of the additional IGBT-resistor combination is an added burden to the end user.
• Yaskawa Electric Europe: contact details and other news
• Email this article to a colleague
• Register for the free Engineeringtalk email newsletter
• Engineeringtalk Home Page
