Calculation of Inductance of chokes to be used for the paralleling of the Inverters - LS Workshop
##### Calculation of Inductance of chokes to be used for the paralleling of the Inverters

For the calculation of the Inductance of the chokes to be used to parallel the two inverters, we take into consideration the following two possibilities:-

1. The corresponding parallel arms +ve & -ve are connected directly to one another (i.e. using busbars) as a result of which the inductance at the input is negligible.

2. The corresponding paralllel arms +ve & -ve are both connected to the output of the bridge rectifier as a result of which the inductance of these connections must be taken into consideration.

In the diagrams, for clarity, only one arm of each inverter has been shown and the possible connection of the DC busbars at the inut of each arm. It must be understood that for the entire system, there would be 3 such arms per inverter, giving therefore the 3-phase output.

Case 1

Direction connection of DC Inputs of paralleled Inverters

Here we have,

maximum value of Vdc = 850V

maximum delay between switching OFF of one TOP IGBT and switching ON of one BOT IGBT, Dt = 125 ns (i.e. the maximum possible time delay between the control pulse being received at the IGBTs and the IGBTs switching as a result)

say, maximum allowed DiSC = 10 A

Therefore,

Lac = 850 /(2 x 10)x 0.125 µH
= 42.5 * 0.125 µH
= 5.3125 µH
Lac = approx 5 µH

Case 2
Connection of Inputs of paralleled Inverters to Input bridge rectifier.

In this case, the additional inductance at the outputs of the bridge recifier will serve another purpose i.e. to smoothen the ripples in the output of the bridge circuit.