An Audio-Based Iterative Controller for Soft Landing of Electromechanical Relays

TL;DR

The study addresses reducing switching impacts in electromechanical relays by introducing an audio-based soft-landing controller. It combines a real-time flux-tracking loop, a differential-flatness-based feedforward to generate a flux reference, and a learning-type run-to-run adaptation that optimizes model parameters using a microphone signal with a Nelder–Mead search, yielding a robust, modular control framework. Experimental results on ten relays show reduced acoustic noise and lower variability, including robustness to an induced resistance change that mimics temperature effects, with the flux-based feedforward outperforming a voltage-based alternative. Overall, the approach offers a practical, adaptable solution that preserves relay advantages while enhancing soft-landing performance.

Abstract

Electromechanical relays and contactors suffer from strong collisions at the end of the switching operations. This causes several undesirable phenomena, such as clicking, mechanical wear and contact bounce. Thus, there is great interest in mitigating these switching impacts while keeping the advantageous features of these devices. This paper proposes a complete control strategy for soft landing. The control structure includes three main components. The first one is a real-time flux-tracking feedback controller, which presents several advantages over voltage or current control. The second one is a feedforward controller, which computes the flux reference signal based on a proposed dynamical model and the desired position trajectory for the switching operations. Lastly, the third control component is a learning-type run-to-run adaptation law that iteratively adapts the model parameters based on an audio signal. It exploits the repetitive nature of these devices in order to circumvent modeling discrepancies due to unit-to-unit variability or small changes between operations. The effectiveness of the proposed control is demonstrated through various experiments.

Figures (10)

• Figure 1: Electromechanical relay. (a) Photo. (b) Schematic diagram.
• Figure 2: Schematic diagram of the different stages during the armature movement. (a) Only the armature and the plastic component are in motion. (b) The plastic component pushes and deforms the moving contact. (c) The moving contact is already touching the normally open contact, but can still be deformed.
• Figure 3: Control diagram. The superscript $n$ is used to denote the variables of the $n$th operation. The inner loop (blocks in orange) is the real-time flux-tracking controller. The flux linkage reference $\lambda_\mathrm{d}$ is provided in real time by the feedforward controller (in green) which is fed with the desired position trajectory $\theta _\mathrm{d}$. The run-to-run adaptation law (in blue) uses the audio signal $v_\mathrm{audio}$ to update the parameter set $p$ of the feedforward controller only once per operation.
• Figure 4: Desired position trajectory based on two concatenated $5$th-degree polynomial trajectories.
• Figure 5: Experimental setup.