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A phase-locked loop (PLL) is a closed-loop feedback control system that estimates the frequency as well as phase of an input signal. The most commonly deployed synchronization method in three-phase applications is a type-2 synchronous reference frame PLL. With pre/in-loop selective harmonic filtering stage, type-2 PLLs can obtain good detection speed, decent stability margins, and better disturbance rejection. However, it suffers from the finite steady-state phase error during ramp change in input signal frequency. To tackle this challenge type-3 PLLs have been developed recently, either by adding a feed-forward path to the PLL structure, or by using a second-order controller as the loop filter. However, recent analysis carried out of type-3 PLLs show that they aggravate stability problem and compromise the performance in terms of detection speed and disturbance rejection. A new concept of synchronization is proposed in this paper that obtains the performance of type-3 PLL but retains all the advantages associated with type-2 PLL. Extensive experimental results are provided to validate the proposed work. [ABSTRACT FROM AUTHOR]

Controllers based on fractional order calculus are gaining more and more interests from the control community. This type of controllers may involve fractional integration, fractional differentiation and/or fractional systems in their structure or implementation. They have been introduced in the control applications in a continuous effort to enhance the system control quality performances and robustness. In this study, a new scheme of fractional order adaptive controller via high‐gain output feedback for a class of linear, time‐invariant, minimum phase and single input‐single output systems of relative degree one is proposed. The basic idea of the new design is a further modification in the adaptive proportional control law by the introduction of a fractional integration besides of the regular one of the squared output of the system in the adaptation gain of the control strategy. An analytical stability proof of the feedback control system is presented. The control quality enhancement of the proposed control scheme compared with the classical one has been presented through the simulation results of an illustrative example. [ABSTRACT FROM AUTHOR]

The slotless permanent-magnet self-bearing motor (SBM) technology is used to fully provide radial bearing and motoring functionality simultaneously in a six degree-of-freedom magnetic actuator for potential precision pointing and tracking applications in space such as intersatellite laser communications. This novel precision magnetic actuator incorporates two SBMs to produce both radial bearing forces and motoring torque, and one active magnetic bearing to provide axial support, and thus allows for a complete electromagnetic suspension and precision noncontact pointing. An analytical representation of the overall dynamic system is presented for controller design. Six decoupled proportional-integral-derivative controllers are designed, and a feedback control system is implemented. The closed-loop performance confirms experimentally that the precision magnetic actuator is capable of smooth angular slewing while maintaining good stabilization. The most encouraging result is that the actuator achieves a high angular resolution of 754 nrad over a large azimuth range of ±45°. [ABSTRACT FROM PUBLISHER]

A prototype design of an inexpensive polymer-based tunneling accelerometer is described in this paper. Instead of silicon, polymethyl methacrylate (PMMA) is used as the mechanical material. By using silicon molds fabricated by conventional lithography and wet-etching techniques in hot embossing, PMMA structures can be replicated within 20 min. The performance of the tunneling sensor can be estimated and improved based on mechanical-level analysis by ANSYS and system-level analysis by MATLAB. The nonlinear tunneling mechanism and electrostatic actuation are linearized using small-signal approximation. To enhance the stability and broaden the bandwidth of the tunneling accelerometer system, a feedback control system with one zero and two poles is designed. The dynamic range of the system is greatly enhanced. The bandwidth of the closed-loop system is approximately 15 kHz. [ABSTRACT FROM PUBLISHER]

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