The high-tech industry is pushing the motion system technology towards faster, more precise and more robust system. One of the keys to this growing demand is the advancement of motion control. To this day, Proportional-Integral-Derivative (PID) has been the workhorse for the industry system control. This is because PID is simple to design and implement and adapt to industrial loopshaping method. Nevertheless, PID suffers fundamental limitations of linear control. To deal with this, a nonlinear control should be utilized. Reset control is a nonlinear control that is still easy but can overcome the limitation of linear control and more importantly, loop shaping method can be used to reset control by using describing function analysis
which is pseudo-approximation of nonlinear system that based on the first harmonic. However, reset control also introduces higher order harmonics into the system that can negatively affect system performance. This is because these harmonics may cause some unwanted dynamics present in system response. Describing function which is the common tool to analyze and design reset control is not accurate enough since higher order harmonics are not considered. Recently, a tool to visualize higher order harmonics in frequency domain is developed. This open the possibilities to study the behavior of higher order harmonics and its effect to system performance.
This thesis focuses on a performance analysis and tuning of a novel reset element called ’Constant in Gain, Lead in Phase’(CgLp). It is shown by the literature that reset control is often utilized to provide phase lag reduction but CgLp has shown the use of reset control to provide phase compensation and this improves system performance. Since its introduction, no guidelines available in the literature to design and tune CgLp. Looking at its potential to be industry standard for motion control, finding guidelines to tune CgLp is an important step to achieve this goal. To do the optimal tuning of reset element, higher order harmonics should be considered so that the effect of unwanted response can be minimized while maintaining the advantage of reset control. Therefore, the work in this thesis is performed by doing performance analysis of CgLp through describing function and HOSIDF.
It is shown that while there is an improvement in tracking and steady state precision performance by using CgLp compared to normal PID, there is deterioration of the performance although describing function predicted an improvement. This is because there is a trade-off between improvement by CgLp and the rise of higher order harmonics gain. In this work, the higher order harmonics was considered at the bandwidth frequency and normalized over its first harmonic. It was observed that the optimal performance is achieved when the highest gain value of normalized 3rd harmonic is around half of maximum possible value of normalized 3rd harmonic.