Research on the Influence of Stray Parameters in the Circuit of the Hybrid Energy Storage
In the course of battery discharge in hybrid energy storage, overvoltage trends to appear at opposite ends of the IGBT (Insulated Gate Bipolar Transistor) when the IGBT is switched off, which is likely to cause overvoltage to damage the IGBT. To solve the problem, this paper has made analyses of the mechanism of capacitor when overvoltage caused by the IGBT failure, the stray inductance in the hybrid energy storage circuit and the inductance of switch-off current on the overvoltage. And the corresponding mathematical formula is derived. On the basis, a simulation model is established. The rational distribution and the addition of an absorption loop can reduce the peak value of overvoltage. It is found from simulations that the absorption circuit will lead to voltage oscillation in the main circuit. Aimed at this phenomenon, the design of the absorption loop is optimized. Simulations and experiments prove the proposed method to be effective.
A Novel Closed-Loop Control Method for Li-Ion Batteries Connected in Series Power Supply Based on the Time Sequences Recalculation Algorithm
The charging time of Li-ion batteries connected in series (LBCSs) power supply is the main concern in an electromagnetic propulsion system. However, the capacity loss of a Li-ion battery is inevitable due to the repetitive operation of LBCSs power supply, which leads to the decrease in the average current. Thus, the voltages of symmetrically distributed pulse capacitors of LBCSs power supply will not reach the setting value in the specified time. This paper proposes a novel closed-loop control method to solve the problem. By collecting the pulse capacitor voltage and the circuit current, the time sequences of Li-ion batteries are recalculated in real time in a closed-loop to increase the average current. The time-domain model of the circuit topology of the LBCSs power supply and an innovative closed-loop control method based on the time sequences recalculation algorithm are described first. Then, the circuit model is built in PSIM for simulation analyses. Finally, a series of experiments are conducted to confirm the effectiveness of the method on the megawatt LBCSs power supply platform. Both the simulation and experimental results validate that the proposed method not only shortens the charging time, but also increases the average current. In practical experiments, the charging time is shortened by 4.5% and the average current is increased by 4.8% using the proposed method at the capacity loss of 50 V.
Conductance of Solutions of Lithium tris(trifluoromethanesulfonyl) Methide in Water, Acetonitrile, Propylene Carbonate, N,N‐Dimethylformamide, and Nitromethane at 25°C
In order to determine the solution properties of lithium tris(trifluoromethanesulfonyl) methide (LiMe) in water and the aprotic solvents acetonitrile (AN), propylene carbonate (PC), N,N-dimethylformamide (DMF), and nitromethane (MeNO{sub 2}), conductance measurements have been carried out at 25 C. Molar conductivities at infinite dilution ({Lambda}{degree}) and ion pair association constants (K{sub a}) were obtained analyzing the experimental data with the Fuoss-Hsia conductance equation using the expansion of Fernandez-Prini and Justice with and without inclusion of the Chen effect. The results show that according to the ability of the solvents to solvate lithium ion, ion-pair formation is small or nonexistent in solvents with high donor number (water, PC, DMF, and AN) but fairly moderate in nitromethane. Single-ion molar conductivities at infinite dilution for ClO{sub 4}{sup {minus}}, AsF{sub 6}{sup {minus}}, PF{sub 6}{sup {minus}} CF{sub 3}SO{sub 3}{sup {minus}}, N(CF{sub 3}SO{sub 2}){sub 2}{sup {minus}}, and C(CF{sub 3}SO{sub 2}){sub 3}{sup {minus}} anions, obtained by combining these results with literature data, decrease as expected as the ionic radius increases, and with one exception are always greater than that of the lithium ion. This general trend does not, however, apply in water where the limiting ionic conductance of the lithium cation is greater than that of the methidemore » anion. This anomalous behavior is attributed to significant solvation of the methide ion in water. Voltammetric measurements indicate high electrochemical stability of methide anion. Such anodic stability and the increase in the transference number of lithium ion in LiMe solutions strongly support the use of this electrolyte in high energy, high voltage lithium batteries.« less