Baldor: Digital drive for resolver-based ac brushless servo motors

A new model of Baldor Electric’s MicroFlex family extends servo drive applications to ac brushless servo motors using resolver feedback—likely opening added applications with a feedback device that’s more electrically robust than encoders.

By Control Engineering Staff July 28, 2005
New Baldor MicroFlex drive offers a choice of 3, 6, and 9 Amp continuous power ratings to simplify application matching, and it accommodates peak currents of 200%.

A new model of Baldor Electric ’s MicroFlex family extends servo drive applications to ac brushless servo motors using resolver feedback—likely opening added applications with a feedback device that’s more electrically robust than encoders. The drive also is said to give users a cost-effective way to maximize performance of existing automation systems (increase speed and smoothness), via digital signal processor (DSP) technology that minimizes cost, without having to replace the servo motor.

New MicroFlex resolver input model uses a resolver-to-digital-converter (RDC) IC to convert analog motor feedback signals into digital data just prior to processing. With the DSP, users can set up software-configurable anti-resonance filters to optimize dynamic performance and minimize settling times. This contrasts to setting “soft” servo-loop gains to eliminate noise and vibration by detuning the system, which is a common compromise when retrofitting a drive to an existing installation, says Baldor.

Switching losses and harmonics are significantly reduced by advanced space-vector modulation (SVM) methods used to control transistor power devices in the drive’s output stage. MicroFlex enables servo motors to run more smoothly and up to 15% faster, compared to conventional drives with pulse-width modulated (PWM) output stage.

MicroFlex drive operates in either torque or velocity control mode from single- or three-phase 50/60 Hz supply in the 115-230 V ac range. It generates a nominal bus supply of 160-325 V dc. The drive incorporates dc bus undervoltage and overvoltage monitoring, and includes overcurrent, overtemperature, and motor short-circuit protection. A built-in regenerative braking IGBT, along with an external dump resistor, handles braking energy dissipation.
MicroFlex drives are configured using Baldor’s Microsoft Windows software environment—Mint WorkBench. This tool is used across the company’s various servo drives and motion controllers.

—Frank J. Bartos, executive editor, Control Engineering, fbartos@reedbusiness.com