Driving synchronous machines requires early and accurate knowledge of the absolute position of the rotor; current solutions based on resolvers, sin-cos or absolute encoders are complex, bulky and costly. Hence, in this work two variants of absolute rotary encoder based on Vernier method are analyzed. One, already discussed in the literature, displays the Vernier scale across the whole circumference (full-Vernier), the other shows half Vernier traces over the entire perimeter (half-Vernier), which is an original feature. Both implementations are characterized by only two tracks and as many sensors: the proposed conditioning algorithms provide the absolute angular position as a function of the time delays between the wave edges generated by the two traces, thus being of easy implementation on low-cost MCUs. The Vernier encoders are also compared with state-of-the-art absolute and relative solutions, i.e. incremental, binary and Graycode encoders. Experimental tests are carried out to assess the accuracy of the proposed sensors. The investigation shows that (i) the full-Vernier cannot provide, in practice, a reliable estimate of the direction of rotation and of the actual angular sector without resorting to a third sensor; (ii) the half-Vernier produces a trusty measurement of the absolute angle and velocity and (iii) can give a reliable position result with less than 30°shaft turn, but (iv) it can suffer from marginal performance degradation at low velocities in conjunction with high accelerations. Compared to the Gray encoder, the half-Vernier provides a simpler and more compact hardware for a given resolution, similar to that of an incremental encoder, at the expense of a small accuracy reduction at low speed.
There exist some modular mechanical systems that exhibit inherent synchronization capabilities. Among these, arrays of pendula connected to the same moving platform, under some particular conditions that are analyzed in this work, tend to approach the synchronous in-phase or antiphase motion. Such an appealing behavior can be replicated within modular electronic circuits equipped with multiple power converters to achieve the coordination of all units. The approach consists in recasting the mechanical equations of motion of interconnected pendula to the equivalent electrical circuit by impedance or mobility analogy. This allows obtaining a self-synchronizing network without the need of explicit communication between the modules. The effectiveness of the proposed distributed controller is assessed through experimental tests. Therefore, the fundamental points of novelty are the derivation of two (series and parallel) self-synchronizing electrical linear circuits through analogy with mechanical models and the introduction of a distributed voltage-source controller for parallel operation of converters based on a fully linear model. The proposed methodology is effective for both parallel-output converters with independent inputs (as in microgrid applications) and parallel-input and paralleloutput converters (as in high-current applications).
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