Hi,

I am trying to optimize operation of CHP with objective function to minimize economic costs.

I have binary variable y_CHP(t) which denotes if the CHP is on (y_CHP=1) or off (=0) at specific time.

I want to minimize the number of times it turns on/off by multiplying the change by some cost parameter:

(y_CHP(t-1)-y_CHP(t))*1000

The problem is when the state changes, y_CHP(t-1)-y_CHP(t)is either 1 or -1 and the cost is -1000 or 1000. So if I do this, the programm will try to have as many -1000 as possible which is not realistc. So I need to somehow make abs( y_CHP(t-1)-y_CHP(t) )*1000.

Any idea how this can be done?

Thanks!

asked 28 Apr '14, 04:52

cesnjak's gravatar image

cesnjak
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edited 28 Apr '14, 05:27


While I don't really see how the sum of two binary variables, y_CHP(t-1) + y_CHP(t) (w/ y_CHP in {0,1}), ever results in -1 ... @Paul Rubin has written a blog post for you (and me, and everyone who has had, still has or will have this question): http://orinanobworld.blogspot.com/2012/07/modeling-absolute-values.html

link

answered 28 Apr '14, 05:25

fbahr's gravatar image

fbahr ♦
4.6k716
accept rate: 13%

edited 28 Apr '14, 07:24

Sorry, It should say y_CHP(t-1)-y_CHP(t) everywhere. I will have a look at the link. Thanks!

(28 Apr '14, 05:28) cesnjak

Well, if you add an other variable z_t that models the cost from the transition 0 to 1 or 1 to 0, you can indeed add z_t to the minimize function with the following

z_t >= y_CHP(t-1)-y_CHP(t)
z_t >= y_CHP(t)-y_CHP(t-1)

You can see z_t as an upper bound to the absolute value, so minimizing z_t will let you automatically find the absolute value.

link

answered 28 Apr '14, 11:13

David's gravatar image

David
30616
accept rate: 12%

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Asked: 28 Apr '14, 04:52

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Last updated: 28 Apr '14, 11:13

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