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A two-variable extremum seeking controller with application to self-tuned vibration energy harvesting

A new control strategy for sliding-mode extremum seeking in two-variables is proposed in this study. The controller converts the two-variable search problem into a single-variable problem in which the direction of changes on the two-dimensional phase plane is used as the sliding mode variable. Simulations are conducted to show that the proposed method is simpler, faster and more accurate than multi-variable sliding mode extremum seeking control methods in the current literature. The proposed controller is utilized for maximum power point tracking in vibration energy harvesters where both damping and stiffness of the harvester can be tuned using power electronic techniques. Experimental results show that the proposed controller is capable of tuning the variables for seeking the extremum point without using any model of the system.