Verification by simulation of power management strategies for 4Q-load

Abstract

Diesel generators in small electricity grids are mostly not used in a very efficient way. The reason for this is twofold. First of all the efficiency of a diesel generator is dependent on the ratio between the average power and the peak power of the generator. The smaller this ratio, the lower the efficiency. Furthermore some loads can regenerate energy. In small grids this energy is mostly not needed elsewhere and should be dissipated. A solution solving both above mentioned problems is using an energy storage device in the system. This storage can be used for peak shaving and storing regenerated energy. In this paper for six defined power management strategies, simulation models are developed. These strategies are: Only Generator, Peak Power Shaving, Dynamic Solution, Max On or Off, Average Power and Only Storage. In this paper a system based on a Li-ion HP battery is under consideration. Two models for the a Li-ion HP battery are compared: the simple model and the Thévenin model. It is shown that the Thévenin battery model gives the best results. Simulation results for all power management strategies are given. From this it can be concluded that the model for the Only Generator method is too simple if the voltage is under concern. For the other methods the simulation models seems to be appropriate. One problem can be observed when scaled models are used: the internal resistance of a battery doesn¿t scale with the same factor as the energy content. So the observations made are only an indication if a scaled model is used. From the simulations it is concluded that the power management strategies are correct.