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Abstract-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.

Abstract-In this paper, the overvoltage problems that might arise from the integration of photovoltaic panels into low-voltage distribution networks is addressed. A distributed scheme is proposed that adjusts the reactive and active power output of inverters to prevent or alleviate such problems. The proposed scheme is model-free and makes use of limited communication between the controllers, in the form of a distress signal, only during emergency conditions. It prioritizes the use of reactive power, while active power curtailment is performed only as a last resort. The behavior of the scheme is studied using dynamic simulations on a single low-voltage feeder and on a larger network composed of 14 low-voltage feeders. Its performance is compared to a centralized scheme based on the solution of an Optimal Power Flow problem, whose objective function is to minimize the active power curtailment. The proposed scheme successfully mitigates overvoltage situations due to high photovoltaic penetration and performs almost as well as the Optimal Power Flow based solution with significantly less information and communication requirements.Index Terms-low-voltage photovoltaic systems, active distribution network management, voltage control

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Abstract-This two-part paper deals with the early detection of an impending voltage instability from the system states provided by synchronized phasor measurements. Recognizing that voltage instability detection requires assessing a multi-dimensional system, the method fits a set of algebraic equations to the sampled states, and performs an efficient sensitivity computation in order to identify when a combination of load powers has passed through a maximum. The important effects of overexcitation limiters are accounted for. The approach does not require any load model. This first part of the paper is devoted to theoretical foundations of sensitivity calculation along the system trajectory, derivation of the algebraic model, and illustration on a simple 5-bus system involving the long-term dynamics of a load tap changer and a field current limiter.

The problem of defining and classifying power system stability has been addressed by several previous CIGRE and IEEE Task Force reports. These earlier efforts, however, do not completely reflect current industry needs, experiences and understanding. In particular, the definitions are not precise and the classifications do not encompass all practical instability scenarios.This report developed by a Task Force, set up jointly by the CIGRE Study Committee 38 and the IEEE Power System Dynamic Performance Committee, addresses the issue of stability definition and classification in power systems from a fundamental viewpoint and closely examines the practical ramifications. The report aims to define power system stability more precisely, provide a systematic basis for its classification, and discuss linkages to related issues such as power system reliability and security.

Abstract-This paper provides a methodology to restore transient stability. It relies on a well-behaved optimal power flow model with embedded transient stability constraints. The proposed methodology can be used for both dispatching and redispatching. In addition to power flow constraints and limits, the resulting optimal power flow model includes discrete time equations describing the time evolution of all machines in the system. Transient stability constraints are formulated by reducing the initial multi-machine model to a one-machine infinite-bus equivalent. This equivalent allows imposing angle bounds that ensure transient stability. The proposed optimal power flow model is tested and analyzed using an illustrative nine-bus system, the well-known New England 39-bus system, a ten-machine system, and a real-world 1228-bus system with 292 synchronous machines.