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Sensorless motor control is ‘as good as using an encoder’
Germany’s KEB Automation has developed and patented a sensorless method for controlling motors that, it claims, is “in no way inferior to operation with an encoder”. The field-oriented vector method can control permanent magnet synchronous, IPM (internal permanent magnet) and synchronous reluctance motors over their entire speed range, with less susceptibility to faults, reduced wiring effort and lower costs than encoder-based systems.
KEB suggests that the technique – which it calls Complex Vector Sensorless Control (CVSCL) – could be used in servodrive positioning applications where, for example, where high concentricity is required even at the lowest speeds. It could also be applied to flywheel energy storage systems that operate at the torque limit over their entire speed range.
“The new motor control method enables the determination of position, speed and electrical motor parameters,” explains Achim Schöke, KEB’s deputy head of electronics development. “Thanks to CVSCL, a speed-dependent selection of different encoderless control methods is not necessary. This would eliminate problematic switching processes, which can lead to instabilities due to transient processes.”
The encoderless control algorithm, which can also be used to adapt parameters can, in principle, be fed with any input signals. To demonstrate this free choice of injection signals for encoderless control, KEB has injected high-frequency signals into a motor via one if its Combivert F6 drives to create musical sounds. The injected voltages are first high-pass filtered and then superimposed on the setpoint voltages of the field-oriented control. The resulting voltages are then applied to the motor via the inverter’s power semiconductors.
The set-up is controlled using dSpace’s MicroLabBox development system. This real-time system provides high computing power and low I/O latencies.
“Frequently-used injections are pulsating and rotating signals,” Schöke explains. “Basically, pulsating signals can be represented by superimposing two signals that rotate at the same frequency in opposite directions.”
He adds that KEB plans to implement the new encoderless control concept in firmware for its drives. “For application areas where the drive must be operated safely in the lower speed range up to and including zero speed, or where high speeds must be reached quickly and safely from the start, CVSCL is a true enrichment.”
KEB Automation: LinkedIn
