Wave Energy Converter’s Slack and Stiff Connection: Study of Absorbed Power in Irregular Waves

Two different concepts of wave energy converter coupled to the novel C-GEN linear generator have been studied numerically, including the evaluation of different buoy sizes. The first concept has a slack connection between the buoy and the generator on the seabed. Another concept is based on a stiff connection between the buoy and the generator placed on an offshore platform. Three different approaches to calculate the damping force have been utilized within this study: the optimal damping coefficient, R-load, and RC-load. R-load is a model for the load applied to a grid-connected generator with passive rectification. RC-load is a model for a phase angle compensation applied to a system with active rectification. The radiation forces originating from the oscillatory motion of the buoy have been approximated using the transfer function in the frequency domain and the vector fitting algorithm. A comparison of the approximation methods is presented, and their accuracy has been evaluated. The advantage of the vector fitting method has been shown, especially for higher approximation orders which fit the transfer function with high accuracy. The study’s final results are shown in terms of the absorbed power for the sea states of March 2018 at Wave Hub, UK.

Nonlinear Analytical Model of Localized Sub-THz and THz Rectifications in FET Power Detectors

<div>A nonlinear analytical model for THz FET power detectors based on their distributed RC network is presented. This empirical model works well for both drain-unbiased and drain-biased THz FET responses. The physics-based analysis reveals that localized THz rectifications in long channel transistors may be mathematically expressed in the same way as regular RF frequency rectifications of a single lumped device. However, the one lumped FET model can’t work properly at THz frequencies without correct definitions of THz signals on its terminals and independently considers localized rectifications on the source and drain sides. An improved compact one lumped THz FET power detector model with additional Schottky diodes at the source and drain terminals is presented. THz FET detector can also perform a simultaneous self-amplification (active rectification) of the localized THz rectified dc signal when operates in the saturation regime beyond its unity gain frequency. A novel analytical expression for the localized THz dc rectified response is developed for FETs operating in the saturation regime. The presented physics-based model agrees excellently with the measured experimental results of GaAs HEMT transistors at 1.6THz under arbitrary biasing conditions. Many novel electronic designs can be implemented for Millimeter-wave and THz technologies based on the physical FET's nonlinear nature in this frequency range</div>

Nonlinear Analytical Model of Localized Sub-THz and THz Rectifications in FET Power Detectors

<div>A nonlinear analytical model for THz FET power detectors based on their distributed RC network is presented. This empirical model works well for both drain-unbiased and drain-biased THz FET responses. The physics-based analysis reveals that localized THz rectifications in long channel transistors may be mathematically expressed in the same way as regular RF frequency rectifications of a single lumped device. However, the one lumped FET model can’t work properly at THz frequencies without correct definitions of THz signals on its terminals and independently considers localized rectifications on the source and drain sides. An improved compact one lumped THz FET power detector model with additional Schottky diodes at the source and drain terminals is presented. THz FET detector can also perform a simultaneous self-amplification (active rectification) of the localized THz rectified dc signal when operates in the saturation regime beyond its unity gain frequency. A novel analytical expression for the localized THz dc rectified response is developed for FETs operating in the saturation regime. The presented physics-based model agrees excellently with the measured experimental results of GaAs HEMT transistors at 1.6THz under arbitrary biasing conditions. Many novel electronic designs can be implemented for Millimeter-wave and THz technologies based on the physical FET's nonlinear nature in this frequency range</div>

Impedance-Based Synchronization of Active Rectifier in Inductive Power Transfer Systems

Active rectification is a common option for improving efficiency and impedance matching in inductive power transfer systems. One of the technical challenges in active rectification is the synchronization of phase angle. In this work, the rectifier input impedance, which is calculated from the AC current and AC voltage, is used as the control objective during phase synchronization. When the impedance angle matches the target value, synchronization of phase is automatically fulfilled. The details of a PI-controller-based phase synchronization algorithm is introduced, and the PI coefficients are manually optimized. Experimental results demonstrate the good performance of the proposed phase synchronization method. <br>

Impedance-Based Synchronization of Active Rectifier in Inductive Power Transfer Systems

Active rectification is a common option for improving efficiency and impedance matching in inductive power transfer systems. One of the technical challenges in active rectification is the synchronization of phase angle. In this work, the rectifier input impedance, which is calculated from the AC current and AC voltage, is used as the control objective during phase synchronization. When the impedance angle matches the target value, synchronization of phase is automatically fulfilled. The details of a PI-controller-based phase synchronization algorithm is introduced, and the PI coefficients are manually optimized. Experimental results demonstrate the good performance of the proposed phase synchronization method. <br>

Research on an axial-mounted dual magnetostrictive material rods-based electro-hydrostatic actuator

In this paper, an electro-hydrostatic actuator driven by dual axial-mounted magnetostrictive material rods-based pumps (MMPs) with a new type of active rectification valve is designed in the current study. Based on flow distribution of the active rectification valve and driving energy provided by two MMPs, the actuator can output continuous and bidirectional displacement. By establishing a mathematical model of the actuating system, using simulation techniques, the change rule of hydraulic cylinder’s motion state caused by different driving signals are studied and analyzed. Test equipment platform is constructed in the laboratory to test the output characteristics and confirm the feasibility of the new concept. The experimental results indicate that the maximum flow rate can reach approximately 2.7 L·min−1, while the operating frequency is 180 Hz.