FEATURE Drives & Controly

Drive controllers and fi lters minimise power losses in high-speed machine tool

spindles and turbo blowers HF motor chokes, input/output filters and sinusoidal filters based on the latest core materials ensure a long operating life of CNC main spindles and high-speed compressors


ew drive controllers and motor fi lters for high frequency (HF) applications from KEB Automation are helping

customers develop highly-effi cient machine concepts for turbo blowers and CNC machine tool spindles. The objective is to increase performance and protect the motor windings at output frequencies up to 2,000Hz.

A powerful drive

“For industrial high-speed applications, we have developed particularly powerful drive controllers, which our customers are using to operate all common high-frequency spindles and high-speed motor types,” said Fabian Fischer, Team Leader Application Sales at KEB Automation.

The associated motor fi lter technology is an important part of the drive package. HF motor chokes, input/output fi lters and sinusoidal fi lters based on the latest core materials, ensure the long operating life of CNC main spindles and high-speed compressors. The two main features are based on the winding protection and the stabilisation of the thermal balance of the HF motors. As Fischer states: “By using a specially-designed HF motor choke, both the voltage level in the winding and the rate of voltage rise [dU/dt] can be reduced to below 500V/µs.” Both are main factors that aff ect the lifetime of the insulation. In addition, there is noticeable reduction in the high frequency

A high-speed spindle (photo copyright Alfred Jager GmbH)

motor side are not signifi cantly reduced, we start at two points: fi rstly, through our own fi lter development, production and EMC test environment and, secondly, through additional control routines in the drive controllers,” said Fischer.

Asynchronous motor – without and with different types of motor choke vs power losses

spectrum and therefore an improvement in the power loss balance in the motor.

For highly thermally-sensitive systems, such as air bearing spindles or the electromagnetic bearing of the rotor in blower motors, both the current and the phase voltage must be reduced to the torque-forming fundamental frequency. This requires a sine fi lter. By using a motor fi lter, the physical

properties and therefore the equivalent circuit diagram of the motor are signifi cantly changed due to the fi lter’s own inductance. “In order to adjust the components in the system in such a way that control dynamics, torque and shaft power on the

Resonance-free operation For correct operation of the sine fi lter, the output circuit can be checked for natural frequency, and the fi lter-internal components can be dimensioned for resonance-free operation. For large series, it is possible to tune an application-specifi c sine fi lter to the operating point of the customer’s machine. “Here, the power loss balance can be optimised in a way that would not be possible with any currently-known modulation method and none of the common power stage topologies on the inverter side,” said Fischer. In addition, the motor/sinusoidal

fi lter output network can be adjusted in such a way that the power loss balance is improved by increasing the voltage at the motor terminals, achieving an increase in power at the motor shaft. The COMBIVERT F6 and S6 drive

controllers from KEB feature software notch fi lters that generate resonance-free modulation for all speed-controlled operating modes, whether with or without an encoder.



Comparison – switching frequency and filter technique vs power losses Synchronous motor – with/without sine filter July/August 2020 | Automation 15

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