Max Power Output

Two ideal AC voltage sources V S = 10 e j π / 6 V_S = 10 e^{j \pi/6} and V R = 10 e j 0 V_R = 10 e^{j 0} are connected across an impedance Z = 1 + j X Z = 1 + j X , where X 0 X \geq 0 . What value of X X maximizes the active power outputted by V S V_S ?

Note: The quantity j j is the imaginary unit


The answer is 0.7673.

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1 solution

Steven Chase
Sep 4, 2020

Current out of source V S V_S :

I S = V S V R 1 + j X I_S = \frac{V_S - V_R}{1 + j X}

Active power out of source V S V_S :

P S = R e ( V S I S ) P_S = Re(V_S I_S^*)

Sweep X X over a range and find the maximum value of P S P_S . This occurs when X 0.7673 X \approx 0.7673 .

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import math

VSmag = 10.0
VRmag = 10.0

VSang = math.pi/6.0
VRang = 0.0

VS = complex(VSmag*math.cos(VSang),VSmag*math.sin(VSang))
VR = complex(VRmag*math.cos(VRang),VRmag*math.sin(VRang))

R = 1.0

##################################################################

dX = 10.0**(-2.0)

PSmax = 0.0
X_store = 0.0

X = 0.0

while X <= 20.0:

    Z = complex(R,X)

    IS = (VS - VR)/Z

    ISconj = complex(IS.real,-IS.imag)

    SS = VS*ISconj

    PS = SS.real

    if PS > PSmax:
        PSmax = PS
        X_store = X

    #print X,PS

    X = X + dX

print ""
print ""
print dX
print X_store

##################################################################

#>>> 
#0.0001
#0.7673
#>>> ================================ RESTART ================================
#>>> 
#1e-05
#0.767329999999
#>>> ================================ RESTART ================================
#>>> 
#1e-06
#0.767327000001
#>>> 

@Steven Chase how to solve it analytically?

Talulah Riley - 9 months, 1 week ago

I'd like to post a solution, but I can't find "Add your explanation" field for some reason... Could it be because I missed the right answer 3 times?

Novak Radivojević - 9 months, 1 week ago

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@Novak Radivojević Yes sir, if you missed the right answer 3 times, then it means you are not solver of this problem therefore you don't have right to post the solution.
No matter after 3 wrong tries, if you get the correct answer then also.
No problem post you solution here in the comments.
It will be helpfull.


Talulah Riley - 9 months, 1 week ago

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Well, my solution involves drawing a phasor diagram, so I had to do it on paper and take a picture of it, but it seems that i can't upload images from here, unfortunately. But if you're interested in what's the exact solution, it's tan(5*pi/24).

Novak Radivojević - 9 months, 1 week ago

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@Novak Radivojević @Novak Radivojević hey bro you still upload.

Talulah Riley - 9 months, 1 week ago

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@Talulah Riley @Novak Radivojević Go to community. In posting problem
Use gallery feature from there
Now use that link here
And that photo wil be uploaded here.

Talulah Riley - 9 months, 1 week ago

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@Talulah Riley Cool trick, thanks! Here's the solution :)

Novak Radivojević - 9 months, 1 week ago

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@Novak Radivojević Just open the image in new tab and it will be more clear

Novak Radivojević - 9 months, 1 week ago

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