MTS Systems Series TBF-R User Manual download pdf (Page 10)

2.3 Principle of the Amplifier

The three-phase servo amplifiers of Series TBF are based on the principle of the speed

control with secondary current control loop. In addition to that the current-mode logic

controls the commutation of the electronically commutated servo amplifier (brushless). The

signal flow of this functional group is shown in the following figure.

S pe e d C on tro lle r

Cu rren t-m o de

co ntrol

Re so lve r

Co n diiton in g

nnom

–

Figure 1: Principle of the Amplifier

The speed control loop consists of speed controller, circuit, motor and speed

measurement. The nominal speed value is externally given, e.g. through potentiometer, NC

control or something similar. The actual speed value is determined at the motor shaft by a

resolver. The difference between nominal value and actual value is formed at the summing

point and transmitted to the speed controller. The speed controller then defines the

required current set value.

The current control loop consists of the current controllers, the amplifier stage, the current

measurement and the motor windings. The current set values available at the output of the

current controller, control the six power switches of the inverter through a pulse-width

modulator. With a PWM frequency of 9.5kHz this leads, due to the special activation, to a

current ripple of 19kHz and consequently to a merely audible clock noise.

This secondary control loop (current) under another one (speed) guarantees a stable

control with good dynamics and high rigidity of the drive. This even allows the easy

realization of current limitations, necessary to protect the motor and the amplifier, just by

limiting the output voltage of the speed controller (current set value).

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MTS Systems Series TBF-R User Manual Page 10