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Re: [TRNSYS-users] Errors when using Powell's method for iteration

Chun Kwong,
  You have to be a bit careful when using the Powell's Method solver to make sure that the controller models that you are using (Type2, etc.) are set up to accomodate that solver and are in the appropriate mode for that solver. The idea of the Powell's Method solver is that if the system that you are trying to control has very nearly no capacitance (in other words no ability to store energy anywhere) then the system is going to react so quickly to changes in controller output that the Successive Substitution solver will not be able to converge. A good example is a PV panel and a resistive load. If the thermal capacitance of the PV panel is neglected then the combination of those two components may have difficulty converging on an operating point. The Powell's Method solver seeks to remedy the problem; my limited understanding of it is that it wiggles the inputs to each component by a little bit and it looks to see if the outputs wiggle a lot or a little. If they wiggle only a little, the system is said to be stable and converged. If they wiggle a lot, the solver tries to find a different discrete control state that is a better solution.  99 times out of 100, convergence problems in a successive substitution simulation are the result of oversimplification of the system (neglecting the piping, choosing models that have no thermal capacitance, tolerances too loose, timestep too big) and will not really be helped at all by switching to the Powell's Method controller.
Kind regards,
 David


a8304506@graduate.hku.hk wrote: 
Hello, Trnsys users.

I try to perform a simulation using the Powell's method for iteration, but with
errors "inconsistency in the input data" found for some components.  However,
when I switch back to the successive method, there is no error.  Do anyone know
how to rectify the problems?  Your reply is appreciated.  Thank you!

Best Regards
LEE, Chun Kwong
Research assistant
Division of Building Science and Technology
City University of Hong Kong




  

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