Holomorphic Embedding Load-flow method: Difference between revisions

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The '''Holomorphic Embedding Load-flow Method''' ('''HELM'''<ref group="note">HELM is a trademark of Gridquant Inc.</ref>) is a solution method for the [[Power flow study|power flow]] equations of electrical power systems. Its main features are that it is [[Direct method (computational mathematics)|direct]] (that is, non-iterative) and that it mathematically guarantees a consistent selection of the correct operative branch of the multivalued problem, also signalling the condition of voltage collapse when there is no solution. These properties are relevant not only for the reliability of existing off-line and real-time applications, but also because they enable new types of analytical tools that would be impossible to build with existing iterative load flows (due to their convergence problems). An example of this would be [[decision support software|decision-support tools]] providing validated action plans in real time.

[[Direct method (computational mathematics)|direct]] (that is, non-iterative) and that it mathematically guarantees a consistent

selection of the correct operative branch of the multivalued problem, also signalling the condition of voltage collapse when there is no solution. These properties are relevant not only for the reliability of existing off-line and real-time applications, but also because they enable new types of analytical tools that would be impossible to build with existing iterative load flows (due to their convergence problems). An example of this would be decision-support tools providing validated action plans in real time.

The HELM load flow algorithm was invented by Antonio Trias and has been granted two US Patents.<ref>

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the injections are zero and this case has a well known and simple operational solution: all voltages are equal and all flow intensities are zero. Therefore, this choice for the embedding provides at s=0 a well known operational solution.

Now using classical techniques for variable elimination in polynomial systems<ref>B. Sturmfels, "Solving Systems of Polynomial Equations”, CBMS Regional Conference Series in Mathematics 97, AMS, 2002.</ref> (results from the theory of [[Resultants]] and [[GroebnerGröbner basis#Elimination property|Gröbner basis]] it can be proven that equations ({{EquationNote|1}}) do in fact define {{math|<var>V(s)</var>}} as holomorphic functions. More significantly, they define {{math|<var>V(s)</var>}} as [[algebraic curves]]. It is this specific fact, which becomes true because the embedding is holomorphic that guarantees the uniqueness of the result. The solution at {{math|<var>s</var>{{=}}0}} determines uniquely the solution everywhere (except on a finite number of branch cuts), thus getting rid of the multi-valuedness of the load-flow problem.

The technique to obtain the coefficients for the power series expansion (on {{math|<var>s</var>{{=}}0}}) of voltages {{math|<var>V</var>}} is quite straightforward, once one realizes that equations ({{EquationNote|2}}) can be used to obtain them order after order. Consider the power series expansion for <math>\textstyle V(s)=\sum_{n = 0}^\infty a[n] s^n</math> and <math>\textstyle 1/V(s)=\sum_{n = 0}^\infty b[n] s^n</math>. By substitution into equations ({{EquationNote|1}}) and identifying terms at each order in {{math|<var>sⁿ</var>}}, one obtains: