Linear optimization for active distribution systems operation considering demand response mismatch

Abstract

Active distribution system (ADS) is defined as distribution networks with systems in place to control a combination of distributed energy resources (DERs), including distributed generators (DGs), energy storage systems (EES), demand response (DR), etc. Recently, high penetration of DERs especially for stochastic and variant renewable resources transforms the distribution system from the traditional "passive" unidirectional flow operation approach to "active" bi-directional flow operation approach. This situation has posed critical challenges for the Distribution System Operators (DSOs) to accommodate renewable energy, reduce network loss and assure power quality by optimal scheduling of DGs, EES, and DR. This paper proposes a linear optimization model for the coordination of active and reactive power dispatch in ADS, considering the stochastic of renewable energy and demand response. The objective is to maximize the profit of DSO constrained by the security and power quality. Current practices for optimal operation of ADS treat load as constant power model regardless of its voltage dependency. The voltages of feeders, however, show more significant variability in ADS, making the constant power model less accurate. The ZIP model should be adopted. The concept of demand response mismatch (DRM) is proposed to stress the necessity of accounting for the load reactive power and load's voltage dependency. DRM is taken into consideration in this paper. On the other hand, when the demand decreases at the beginning, it may rebound later. We also formulate the "Pay-back effect" of load in this paper. Inspired by a novel DC power flow method with reactive power consideration, this paper originally introduces this method into ADS, in order to reduce the complexity of the model while ensuring the accuracy of model. This method deals with all the power flow equations by introducing a novel parameter called 'modified phase angle' and in this way the power flow equations can be transformed into linear forms. That means that no further iteration is needed and the calculation will be much faster. The effectiveness of the method is verified by numerical cases.