The expression for the thyristor (chopper switch) current is given by I = (α 2 .Vs – αE)/R Find the value of firing angle α, for which the thyristor current is maximum.

To find the value of the firing angle ( alpha ) for which the thyristor current ( I ) is maximum, we start with the given expression:

[

I = frac{alpha^2 V_s – alpha E}{R}

]

To find the maximum current with respect to ( alpha ), we can take the derivative of ( I ) with respect to ( alpha ) and set it to zero:

[

frac{dI}{dalpha} = frac{2alpha V_s – E}{R} = 0

]

Setting the derivative equal to zero gives:

[

2alpha V_s – E = 0

]

Solving for ( alpha ) gives:

[

2alpha V_s = E implies alpha = frac{E}{2V_s}

]

Thus, the value of the firing angle ( alpha ) for which the thyristor current is maximum is:

[

alpha = frac{E}{2V_s}

]