A systematic methodology for smooth connection of wind-turbine-driven doubly fed induction generators (DFIGs) to the grid is presented. Synchronization of the voltage induced in the DFIG open stator to that of the grid, which needs to be accomplished prior to connection, is thoroughly examined. A particular grid-voltage-oriented rotor control scheme is considered for this purpose. Generic tuning equations for the rotor current integralproportional (I-P) controllers involved in this scheme are also derived. Transition between the control configurations devoted to synchronization and normal operation-active power generation and reactive power interchange with the grid-at the instant of connection is studied in detail. Mainly due to the reference frame selected for synchronization, the greater part of this transition takes place naturally. However, given that the rotor current dynamics vary significantly depending on whether the DFIG stator is connected to the grid or not, the parameters of the I-P controllers involved in both schemes will accordingly be different. Consequently, a "bumpless" strategy is provided that preserves the smoothness of the connection. A simple method for initial rotor positioning, required when performing vector control based on an incremental encoder, is also suggested. The resulting overall methodology is validated on a 7-kW DFIG-based laboratory-scale test bench.Index Terms-Doubly fed induction generators (DFIGs), industrial power system control, initial rotor positioning, smooth connection, synchronization, vector control, wind power generation. NOMENCLATURE -Subscript. ı m s Stator magnetizing current space phasor. i r , i s Rotor and stator direct-or quadratureaxis current components, expressed in a particular reference frame. ı r , ı s Rotor and stator current space phasors, expressed in a particular reference frame. L m , L r , L s Magnetizing, rotor, and stator inductances. L rRotor transient inductance. P s , Q s Stator-side active and reactive powers.

Soft robotic systems have applications in industrial, medical, and security applications. Many applications require these robots to be small and lightweight. One challenge in developing a soft robotic system is to drive multiple degrees-of-freedom (DOF) with few actuators, thereby reducing system size and weight. This paper presents the analysis and design of an inchworm-like mobile robot that consists of multiple, independent thermally activated joints but is driven by a single actuator. To realize control of this under-actuated system, a solder-based locking mechanism has been developed to selectively activate individual joints without requiring additional actuators. The design and performance analysis of a prototype mobile robot that is capable of inchworm-like translational and steering motion is described. The design of novel "feet" with anisotropic friction properties is also described.

In this work we present a novel, inductance-based system to measure and control the motion of bellows-driven continuum joints in soft robots. The sensing system relies on coils of wire wrapped around the minor diameters of each bellows on the joint. As the bellows extend, these coils of wire become more distant, decreasing their mutual inductance. Measuring this change in mutual inductance allows us to measure the motion of the joint. By dividing the sensing of the joint into two sections and measuring the motion of each section independently, we are able to measure the overall deformation of the joint with a piece-wise constant-curvature approximation. This technique allows us to measure lateral displacements that would be otherwise unobservable. When measuring bending, the inductance sensors measured the joint orientation with an RMS error of 1.1 °. The inductance sensors were also successfully used as feedback to control the orientation of Correspondence to: Wyatt Felt. Disclosure of potential conflicts of interest. Authors Wyatt Felt and C. David Remy are listed as inventors on a patent application for inductance sensing on bellows actuators. The other authors are (or were) employed by Pneubotics and/or its parent organization, Otherlab. Each of them has an investment interest with the company, and each is listed as an inventor in patents related to this work.

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