H-Infinity Speed Controller Design for Vibratory Drive Trains with Low Mass Ratio

Variable frequency drives in industrial speed-controlled applications with high reduction gear ratios – which are often used in case the driven process demands for high torques – are prone to extensive and lightly damped mechanical oscillations. This is due to the low process-side inertia and notable gear play, which both encourage excitation of the lowest mechanical resonance frequency. Moreover, it is well known, that a significant active damping contribution is hardly realizable through tuning of a classical PI speed controller. Due to multifaceted requirements with respect to control objectives and mandatory robustness properties, ℋ∞ theory appears to be a promising instrument for the design of an advanced speed controller for such systems. Therefore, this paper presents a ℋ∞ theory-based speed control design methodology. A drive system example with very low load-side inertia is chosen in order to demonstrate the effectiveness of the presented control approach.