The tokamak start-up is a very important phase during the process to obtain a suitable equalizing plasma, and its governing model can be described as a set of nonlinear ordinary differential equations (ODEs). In this paper, we first estimate the parameters in the original model and set up an accurate model to express how the variables change during the start-up phase, especially how the plasma current changes with respect to time and the loop voltage. Then, we apply the control parameterization method to obtain an approximate optimal parameters selection problem for the loop voltage design to achieve a desired plasma current target. Computational optimal control techniques such as the variational method and the costate method are employed to solve the problem, respectively. Finally, numerical simulations are performed and the results obtained via different methods are compared. Our numerical parameterization method and optimization procedure turn out to be effective.
The bidirectional converter in AC / DC hybrid microgrid is an important link to balance the power on both sides of AC and DC, Its control method is extremely important. This paper proposes an improved droop control strategy for bidirectional converter using DC-side power amount control. This control can autonomously and smoothly switch in rectifyer, inverter and idle modes. Utilizing DC-side power control avoids normalized calculations. Strategy meets two modes of island and grid connection, eliminating the need for multiple control strategy switches. Simulation results show that the DC bus voltage and AC frequency are near the rated value, which guarantees the stable operation of the AC-DC hybrid microgrid.
During the manufacturing process of the system-in-package, it has become susceptible to defects and internal residual stresses when dies, components, electric functionality and geometric complexity have increased. The mismatch of thermal expansion coefficient (CTE) among packaging materials and devices may lead to various failure modes during manufacturing processes, such as die broken, solder crack, substrate interface delamination. In this paper, the effect of underfill on the reliability of a system-in-package has been studied. A Bluetooth package is considered. The dimension of the package is 4.84 (L) × 6.15 (W) × 1.32 (H) mm. It contains an IC chip and several passive components such as crystals and filters. The substrate is NSMD type. Three underfill materials are considered. Materials were selected based on the numerical simulation. The causes of void formation during the underfill process have been investigated. In addition, the adhesion test of die passive material and PCB solder register was performed.
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