Digital Control of Negative Imaginary Systems Using Discrete-Time Multi-HIGS: Application to a Dual-Stage MEMS Force Sensor

A team of researchers from UNSW Canberra and the University of Texas at Dallas has published a breakthrough in control systems engineering. Their paper, "Digital Control of Negative Imaginary Systems Using Discrete-Time Multi-HIGS: Application to a Dual-Stage MEMS Force Sensor," introduces a novel digital controller designed for complex systems with inherent stability challenges. The core innovation is the Discrete-Time Multi-Hybrid Integrator-Gain System (Multi-HIGS), a nonlinear controller that combines multiple HIGS elements in parallel. The team mathematically proved that their bimodal and trimodal HIGS configurations retain the crucial Negative Imaginary (NI) property, enabling them to asymptotically stabilize linear NI systems—a significant theoretical advancement for digital control frameworks.

The practical application demonstrates the controller's power. The researchers implemented their discrete-time Multi-HIGS on a two-input, two-output dual-stage micro-electromechanical systems (MEMS) force sensor. This type of sensor is notoriously difficult to control due to its lightly damped resonant modes, which can cause instability and poor performance. By evaluating the closed-loop system in both time and frequency domains, the experiments confirmed that the Multi-HIGS controller effectively suppresses these problematic resonances. Crucially, it does so while preserving favorable phase characteristics, a key requirement for robust performance. This result highlights the method's potential as a go-to, robust nonlinear controller for digitally managing a wide array of NI systems, from advanced sensors to precision actuators.