Study Of Total Supply Capability For Distribution Systems Based On Power Flow Calculation

The accuracy of Total Supply Capability(TSC) for Distribution Systems has important theoretical significance and application value. The methods of TSC calculating don't take into account the network loss and voltage drop, this paper will introduce the power flow to TSC theory. This paper proposed a new model and calculating method of TSC based on the power flow.First, this paper proposes a method to evaluate the accuracy of TSC. Based on traditional N-1 security guideline, the N-1 verification method which considers power flow is more serious and accurate. This evaluating method of TSC consists of two parts. The first part is based on the transformer and feeder N-1 security guideline, this part can decide the TSC operational point is accurate or not. The second part increases load of each node by a little, then uses the N-1 verification method to evaluate it again. If all of them don't pass, then it's TSC and the model is accurate.Secondly, this paper proposes TSC model based on power flow, which is formulated as maximizing the load of distribution system(ignoring loss), subject to the transform capacity, feeder capacity and voltage constraints. This model considers the network loss and voltage drop under the normal state and N-1 state. This paper presents an approximate model which has only single load node on each feeder, and an accurate model which has many load nodes. The approximate model assumes that the feeder load is only one load node at the root of feeder. It's applied to distribution system planning and optimization because of calculating fast. The accurate model calculates the power flow according to the real load profile. It's more accurate and applied to actual network. It's difficult to calculate the TSC model which is nonlinear programming problem.Both models are solved by general reduced gradient algorithm of Lingo for nonlinear programming problem, backward/forward sweep algorithm for iterative problems. For high-dimensional and large-scale of accurate model, the use of sparse matrix techniques is used for storage and model in order to reduce the problem complexity.Finally, a RBTS expended case and a large-scale actual case are used to verify the correctness of algorithms. And the differences between the two algorithms are compared through the two cases. At the same time the difference between the old TSC model, which isn't based on power flow, and the TSC model of this paper is compared too. Through the verification and comparison, the TSC model based on the power flow is accurate.