Integration of Renewable Energy Sources in Power

The project focuses on topics related to the integration of renewable energy sources in power systems. Issues being investigated include: islanding detection, micro-grids, and electricity market operation with renewable energy sources.

First we focus on islanding detection of inverter based DG. Islanding is a condition in which a part of the utility system, which contains both load and generation, is isolated from the rest of the utility system and continues to operate. There are three main categories for islanding detection methods: passive, active, and communication based. Passive methods rely on monitoring a certain parameter and then setting thresholds on the selected parameter. Despite its simplicity and ease of implementation, passive methods suffer from large Non-detection Zones (NDZ). NDZ could be defined as the values of loading for which an islanding detection method would fail to detect islanding. The NDZ concept is commonly used for evaluating the performance of islanding detection methods. Active methods introduce deliberate changes or disturbances to the connected circuit and then monitor the response to determine an islanding condition. Active methods have smaller NDZ, but can degrade the power quality of the system. Communication based methods have negligible NDZ, but are much more expensive than the former methods.

The general task in this work is to study and analyze the DG islanding phenomenon for inverter based DG. Survey results showed that the majority of islanding detection methods either suffer from power quality problems or large NDZs. In addition, most of the islanding studies focus only on constant impedance loads. Thus, the primary and secondary research objectives are:

(*) Developing a new islanding detection method

The main goal of this part of the work is to develop a new islanding detection method that would combine the advantages of the previously proposed methods while avoiding disadvantages associated with these methods. The target is to develop the islanding detection method with the following characteristics:

(*) Simple and easy to implement
(*) Does not create any power quality problems
(*) Has negligible NDZ
(*) Testing islanding detection on various load models

Most islanding studies have been designed under the assumption that constant impedance loads create the hardest detectable case for an islanding detection method. In this work, we examine the validity of this assumption by taking into account different load models.

The studies reported are based on time-domain simulations conducted in the PSCAD/EMTDC environment. Mathematical analysis is provided to validate the simulation results.

One major accomplishment is the development of a new simple, easy to implement, and efficient islanding detection method for inverter based distributed generation. The IEEE Standards propose the use of constant impedance loads for testing islanding detection methods. A major finding is that constant impedance loads do not necessarily impose the hardest detectable condition for islanding detection methods. The load's frequency dependence is an important factor that should be taken into consideration when testing islanding detection methods.

The project team is currently developing an electricity market simulation model to examine price dynamics resulting from high penetrations of wind power in grids with active transmission constraints. A survey of demand response technologies and demand response aggregation techniques across different customer classes is also ongoing. Results from the demand response study will be used to incorporate price-elastic demand-side bidding in the electricity market model.