# Grid connected transistor bridge inverter

1. Mar 7, 2013

### Samtheguy

1. The problem statement, all variables and given/known data

Hi there. I was just wondering if anyone can conform that my method for this problem is correct so far?

The transistor-bridge converter shown below is being used to connect a PV array to the grid.
For the purpose of this coursework, you may assume that:
• The PV array behaves as an ideal DC voltage source.
• The grid is an ideal sinusoidal voltage source at 50 Hz.
• The components are ideal and lossless.
• Bipolar switching is used.

The DC voltage (Vdc) is 458 V.
The inverter switches at 1800 Hz and its output inductor is 4 mH.
The modulation index is 0.59 at angle of 15 degrees relative to the grid voltage.
The AC grid voltage is 217 V.

Question - Calculate Vi (Magnitude and angle)

3. The attempt at a solution

The modulation index is defined as: Mi = Vi peak (of the fundamental component) / Vdc
Therefore; Vi = Mi x Vdc
Vi = 0.59 x 458
Vi = 270.22V

However this is a peak voltage. Hence the rms voltage is; 270.22/sqrt(2)
So Vi = 191.074 V (rms)

Since it is at an angle of 15 degrees to the grid voltage, use the sine rule to obtain the total length of the Vi phasor.

Vi / sin(90) = 191.074 / sin(75)
Vi = 197.814V

So we'll say Vi = 198V at an angle of 15 degrees to the grid voltage.
Is that correct??

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Last edited: Mar 7, 2013
2. Mar 8, 2013

### rude man

Looks right to me. I assume Vi is the square-wave voltage on the left-hand side of the inductor.

3. Mar 9, 2013