Fig. 7 Flowchart for iterative solving process of core temperature and ESR. Capacitor Lifetime The capacitor lifetime is influenced by the capacitor core temperature and the ripple current and is given [17] for both kinds of capacitors by: where is the capacitor lifetime under its maximum temperature and commonly given by Lb manufacturer datasheets. denotes the allowable maximum ripple current at a given I0 frequency, also given in data sheets, and denotes the actual ripple current value. The is a I K constant, which is typically assigned a value of 2 []. Battery ripple current analysis Studies show that ripple current affects battery lifetime due to the internal temperature rise []. Therefore, the battery ripple current should be maintained under a certain limit to avoid the harmful effect. The dc-link capacitor is represented by an equivalent circuit including Rc, Lc and as shown in . The switching frequency is 20 kHz, and that the of battery pack and Cc, ESR interconnects can be neglected since the impedance of interconnects is dominated by the inductance component, shown as in . It includes the inductance introduced by the battery L1 pack and interconnects between the battery pack and the inverter. The battery ripple current can be obtained as according to the equivalent circuit shown in Fig. 8. Fig. 8 Equivalent AC circuit of the EV inverter for the battery ripple current analysis. The reference values of inductance (L1b) are assigned to 10 µH considering the practical component layout and the parameters of interconnects. The battery ripple current in RMS
Fig. 7 Flowchart for iterative solving process of core temperature and ESR. Capacitor Lifetime The capacitor lifetime is influenced by the capacitor core temperature and the ripple current and is given [17] for both kinds of capacitors by: where Lb is the capacitor lifetime under its maximum temperature and commonly given by manufacturer datasheets. I0 denotes the allowable maximum ripple current at a given frequency, also given in data sheets, and I denotes the actual ripple current value. The K is a constant, which is typically assigned a value of 2 []. Battery ripple current analysis Studies show that ripple current affects battery lifetime due to the internal temperature rise []. Therefore, the battery ripple current should be maintained under a certain limit to avoid the harmful effect. The dc-link capacitor is represented by an equivalent circuit including Rc, Lc and Cc, as shown in . The switching frequency is 20 kHz, and that the ESR of battery pack and interconnects can be neglected since the impedance of interconnects is dominated by the inductance component, shown as L1 in . It includes the inductance introduced by the battery pack and interconnects between the battery pack and the inverter. The battery ripple current can be obtained as according to the equivalent circuit shown in Fig. 8. Fig. 8 Equivalent AC circuit of the EV inverter for the battery ripple current analysis. The reference values of inductance (L1b) are assigned to 10 µH considering the practical component layout and the parameters of interconnects. The RMS battery ripple current in