Dear Idris Musa, As far as I know version 4.1 explicitly allows more than one slack bus (bus it still cannot deal the situation when the Q output of any slack bus reach its limit). 'pfsoln.m' defined how to distribute the generations. From it we know Matpower assigned all active network loss undertaken by each slack bus to its first generator (version 4.1 make this available for all slack buses). I agree with you that the situation you mentioned is not physically meaningful. Thus, as my opinion: Firstly, with the grid connected you can define the PCC bus only as the slack bus, while without the connection, define the generator bus in this island as slack bus (the reason to define only one slack bus is that the electrical connection between PCC and the other slack bus is usually not weak enough, so setting their voltage angles both as given conditions is usually not reasonable -- how do you know the proper angles difference between the two slack buses? Absorbing P may be a sign that the setting angle of the slack bus is too small.); Secondly, if the P loss is large and you don't think assigning it to the first generator is sound, you can change the code of 'pfsoln.m', distribute P loss equally to each generator on the slack bus; Thirdly, the premise of that your slack bus P generation is reasonable, is that all other generators' P settings are proper. Negative P generation may imply others' P settings don't fit the real sistuation. Especially when you consider the island re-connect to the grid, I think decreasing the P generations in the island is quite normal.
Shiyang, Li -----邮件原件----- 发件人: [email protected] [mailto:[email protected]] 代表 Idris Musa 发送时间: 2012年1月10日 20:15 收件人: 'MATPOWER discussion forum' 主题: AC power flow for multiple generators Dear all, I want run AC power flow, considering multiple generators with possibility of Islanding using MATPOWER 4.1. In addition to the grid supply I have five generators of equal output capacity at particular bus location. I defined this bus location as slack bus. This means I have two slack buses (including the grid supply). When I run MATPOWER AC power flow, with the grid connected, one of the generators (the first generator of the five connected) is taking care of system losses, showing that the chosen generator has unlimited capacity and is also absorbing negative active power. I am assuming a distributed generator (which could be synchronous generator, fuel cell etc) is this physically feasible? I had expected the grid supply been the first slack bus to take care of the system losses and provide other support for the network. I would be glad if someone could advice on how to go about it. Idris Musa
