In the present study, the simultaneous
and accurate determination
of liquid viscosity and surface tension of the n-alkanes n-hexane (n-C6H14), n-octane (n-C8H18), n-decane (n-C10H22), and n-hexadecane (n-C16H34) by surface light scattering (SLS)
in thermodynamic equilibrium is demonstrated. Measurements have been
performed over a wide temperature range from 283.15 K up to 473.15
K for n-C6H14, 523.15 K for n-C8H18, and 573.15 K for n-C10H22 and n-C16H34. The liquid dynamic viscosity and surface
tension data with average total measurement uncertainties (k = 2) of 2.0 and 1.7% agree with the available literature
and contribute to a new database at high temperatures. Over the entire
temperature range, a Vogel-type equation for the dynamic viscosity
and a modified van der Waals equation for the surface tension represent
the measured data for the four n-alkanes within experimental
uncertainties. By also considering our former SLS data for n-dodecane (n-C12H26) and n-octacosane (n-C28H58), empirical models for the liquid viscosity and surface
tension of n-alkanes were developed as a function
of temperature and carbon number covering values between 6 and 28.
Agreement between these models and reference correlations for additional
selected n-alkanes, which were not included in the
development procedure, was found.
This paper proposes an optimized and coordinated model predictive control (MPC) scheme for doublyfed induction generators (DFIGs) with DC-based converter system to improve the efficiency and dynamic performance in DC grids. In this configuration, the stator and rotor of the DFIG are connected to the DC bus via voltage source converters, namely, a rotor side converter (RSC) and a stator side converter (SSC). Optimized trajectories for rotor flux and stator current are proposed to minimize Joule losses of the DFIG, which is particularly advantageous at low and moderate torque. The coordinated MPC scheme is applied to overcome the weaknesses of the field-oriented control technique in the rotor flux-oriented frame, which makes the rotor flux stable and the stator current track its reference closely and quickly. Lastly, simulations and experiments are carried out to validate the feasibility of the control scheme and to analyze the steady-state and dynamic performance of the DFIG.
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