Distributed Generation (DG) use in distribution networks is propagating rapidly and the involved technology is advancing at a fast pace. This necessitates that engineers must be equipped with better tools to assess the impact of DG on their electrical networks. CYME has enhanced the functionality of its distribution analysis software CYMDIST in a significant way to meet the growing need.

CYMDIST provides the ability to model all types of DG including all electronically coupled DG such as wind turbines (synchronous or induction), gas turbine (high speed), energy storage, photovoltaic, etc. These enhanced DG models are used in power flow, short-circuit, and transient stability studies. CYMDIST also features a complete suite of DG models with their dynamic behavior, control functions and protection systems. The added DG resources are primarily electronically-interfaced DG resources and other conventional resources used in DG applications.

Islanded systems simulation and network reduction are now included in CYMDIST in order to evaluate the impact of DG.

These enhancements were implemented in CYMDIST in close coordination with Natural Resources Canada’s CANMET Energy Technology Centre—Varennes that provided their support in developing and testing the new models. http://cetc-varennes.nrcan.gc.ca

In CYMDIST the DG models are divided in three categories depending on how they are coupled with the electrical network:

• Synchronous generators that can be operated in three different modes: voltage control, fixed generation or swing.
• Induction generators that provide constant power.
• Inverter-based generators used with wind turbines (synchronous or induction), gas turbine (high speed), energy storage, photovoltaic source and fuel cells.

The dynamic models of electronically-interfaced DG resources include:

• Micro-turbine generation systems.
• Variable-speed wind energy conversion systems (WECS).
• Direct drive permanent magnet synchronous generators.
• Doubly-fed induction generators.
• Other inverter-based with simplified sources models such as: photovoltaic systems, fuel cell systems and battery energy storage systems.

The Impedances Estimation function provides typical values of the generator impedances if the data is not available to the user. It is based on standards for short-circuit calculations that provide a series of tables for different generator sizes and types. The estimation function provides the data that enables different “what-if” scenarios and that provides accurate results on the impact of DG.

When performing studies on a large distribution network that includes a number of DG sources, a reduced network is beneficial since it lessens the computational effort and simplifies the study, focusing only on the area of interest. The CYMDIST Network Reduction function allows reducing a large network into a much smaller equivalent network by keeping the area and equipments of interest. More importantly, this sophisticated equivalent model allows matching exactly the power flow and short-circuit results of the original detailed network.

The dynamic modeling of the converters interfaced takes into account the grid-side control functions. They include current/power control and voltage/ frequency control. Source-side control systems are also modeled to provide practical operation limits for DG units.

CYMDIST features the two most utilized Anti-Islanding protection functions:

• Passive approaches: over-/under voltage detection and over-/under frequency detection.
• Active approaches: voltage positive feedback and frequency positive feedback.

Protection functions of DG units themselves are also included.

Integration of DG technology creates networks that are fed by multiple sources. CYMDIST has been modified to allow modeling of islanding (network fed by DG’s only or both) and to provide the capability to set any DG as a swing for the network. Simulation algorithms and reports have been enhanced to view the new configuration and to report overloading of any DGs for any operating conditions.