ABSTRACT
The capacitance model suitable for the non-circular cross-section plasma is studied based on the capacitance model of the circular cross-section plasma. The coaxial elliptic-torus capacitor property is further derived and used to determine the capacity of non-circular cross-section tokamak plasma, such as EAST (Experimental Advanced Superconducting Tokamak). By testing all the physical terms in this model, we find that the capacitance [Formula: see text]) is increasing exponentially with the increase of elongation ratio (k2/k1), while the minor radius ratio (a2/a1) is just reversed at the flat-top of plasma current, and the capacitance property is implicitly included in the H-mode study during the L-H transition. It is noted that Cp-H mode is the least and Cp-I mode is approximately equal to Cp-L mode under the L-mode, I-mode and H-mode regimes based on this capacitance model in EAST. Consequently, it may be integrated into an equivalent circuit of the tokamak transformer or transport computer code of the edge plasma for use in precise simulations of fusion plasma behavior in the future, such as ITER (International Tokamak Experimental Reactor) or BEST (Burning-plasma Experimental Superconducting Tokamak) in China.
ABSTRACT
The B-dot sensor is a type of Rogowski coil widely used in the measurement of current. However, the accuracy of the B-dot for measuring aircraft high-frequency lightning current is greatly affected by factors such as numerical integration drift, high-frequency oscillation, and calibration. In this study, a new design and optimization for improving the B-dot measuring accuracy was carried out. To correct the drift of the numerical integral of the measurement signal in differential mode, the measuring current was reconstructed based on the nonlinear least squares method. The sensor was then optimized by isolating the sampling resistance and matching the impedance with a voltage follower. A low-cost coaxial loop calibration system was also designed to calibrate the high frequency and strong magnetic fields more accurately. Finally, the optimized B-dot sensor accuracy was greatly improved with a measuring range of 30 kA/m, an error of 3.1%, and a high-frequency response of 50 MHz. Our study greatly increases the accuracy of measuring aircraft high-frequency lightning current.
ABSTRACT
The accurate state of charge (SOC) estimation can protect the battery from overcharging and over-discharging, and it is useful to make an effective dispatching strategy. The extended Kalman filter (EKF) method is used to estimate SOC widely. But it does not consider the SOC constraints. Moreover, the convergence is influenced by the uncertain initial SOC, which may lead to false alarm, unwanted operation of protection, error dispatching and poor robustness of the system. This paper presents an improved extended Kalman filter (IEKF) method to estimate SOC for vanadium redox battery (VRB) by introducing a gain factor. It can be adjusted automatically according to the output error and SOC boundary. To implement IEKF estimator, a VRB state space model is established and its parameters are identified by recursive least square (RLS) method. Then a VRB of 5kW/30kWh experimental platform is built. Finally, the IEKF method is validated and compared with EKF against unknown initial value through the experiments. The results have shown that IEKF method is superior to EKF in terms of accuracy, convergence speed and robustness. And the estimated SOC remains bounded by using IEKF method. It is more suitable for SOC estimation than EKF algorithm in the industrial applications.
