This paper presents a centralized control scheme to regulate distribution network voltages in the presence of high penetration of distributed generation. The approach is inspired of Model Predictive Control in order to compensate for modeling inaccuracies and measurement noise. The control actions, calculated from a multi-step optimization, are updated and corrected by real-time measurements. The proposed controller uses a linear model to predict the behavior of the system and the optimization is solved using quadratic programming. The proposed corrective control has been tested in a 11-kV distribution network including 75 nodes and hosting 22 distributed generating units.

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Model Predictive Control of Voltages in Active Distribution Networks

This paper presents a detailed comparative analysis between synchronous and induction machines for distributed generation applications. The impacts of these generators on the distribution network performance are determined and compared by using computational simulations. The technical factors analyzed are steady-state voltage profile, electrical power losses, voltage stability, transient stability, voltage sags during unbalanced faults, and short-circuit currents. The results showed that the best technical choice depends on the network characteristics, i.e., the main factors that may limit the penetration level of distributed generation.

/pdf/comparative-analysis-between-synchronous-and-induction-1qzwm5ognp.pdf

Comparative analysis between synchronous and induction machines for distributed generation applications

A two-level real-time voltage control scheme is proposed to keep voltages within specified limits in distribution grids using distributed generation units (DGUs). It combines a local and a centralized control of their reactive powers. The local control provides fast response after a disturbance, reducing its impact and enhancing voltage quality. The centralized control uses measurements collected throughout the network to bring the voltages inside tighter limits and balance the various DGU contributions. To this purpose, it adjusts in a coordinated way their reactive power set points, taking into account the local controls. This discrete control solves at each time step a multitime-step constrained optimization inspired of model predictive control. The method effectiveness is demonstrated on a 75-bus test system hosting 22 DGUs.

/pdf/combined-local-and-centralized-voltage-control-in-active-3lc7yd8rn0.pdf

Combined Local and Centralized Voltage Control in Active Distribution Networks

This paper presents experience with testing of gas turbine plants for NERC and WSCC compliance. Testing has been performed on older analog-electronic and new digital-electronic units. The level of detail used in modeling and model availability in simulation programs are ongoing issues. Temperature limits and outer-loop controls such as PF/VAr controls and load sharing have been seen to dominate plant performance.

Utility experience with gas turbine testing and modeling

The growing environmental concern and various benefits of distributed generation (DG) have resulted in significant penetration of DG in many distribution systems worldwide. One of the major expected benefits of DG is the improvement in the reliability of power supply by supplying load during power outage by operating in an island mode. However, there are many challenges to overcome before islanding operation of a distribution system with DG can become a viable solution in future. This paper reviews some of the major challenges with islanding operation and explores some possible solutions to overcome those challenges.

Review on islanding operation of distribution system with distributed generation

The trend toward automation of today's power stations has prompted an increased demand for excitation systems having voltage regulators with the ability to automatically regulate generator reactive power (VAr) output or power factor (PF). While not really a new type of control, automatic VAr and PF controllers are appearing in the specifications of more and more power plants and generator voltage regulators. This paper provides a functional description of voltage, VAr, and PF controllers and regulators, along with an example demonstrating the superior steady-state voltage support performance on a transmission system by regulating voltage, rather than VArs or PF. The paper concludes that VAr/PF controllers or regulators should generally not be specified or utilized on excitation controls for voltage supporting generator applications.

J.D. Hurley

Papers

The adverse effects of excitation system VAr and power factor controllers