In a large battery-storage system, the rated output voltage of a battery string

Question

In a large battery-storage system, the rated output voltage of a battery string is 650 V (dc) and the rated current is 1,200 A. The voltage can vary in a range from 500V to 800V. This output voltage is boosted to 900V (dc), as an input to an inverter that interfaces with the three-phase utility grid. A switching power-pole with a bi-directional power capability is used. The switching frequency is selected to be 50 kHz, and the inductor value is selected such that the peak-to-peak ripple in the inductor current is less than 10% of the rated battery current, with the battery voltage at its rated value.

(a)  Calculate the inductance value.

(b)  Calculate the peak-to-peak ripple in the inductor current if operating at the

rated current but the battery voltage is at its minimum.

(c)  Repeat part (b) if the battery voltage is at its maximum.

Explanation / Answer

1) L = Vrated/(0.1*I rated*2*pi*f) = 17*10^-6 H

2) peak to peak ripple in current = Vmin/(2*pi*f*L) = 92.3 Amp

3) peak to peak ripple in current = Vmax/(2*pi*f*L) = 147.7 Amp

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