Bogdan Otomega

Model Predictive Control to Alleviate Thermal Overloads

An approach inspired by model predictive control is proposed to determine a sequence of control actions aimed at alleviating thermal overloads. The algorithm brings the line currents below their limits in the time interval left by protections while accounting for constraints on control changes at each step. Its closed-loop nature allows to compensate for model inaccuracies.

Reverse-logic control of load tap changers in emergency voltage conditions

This papers deals with the emergency control of load tap changers (LTCs) to face low transmission voltages or voltage instability situations. The proposed simple control logic consists in reverting the tap movements once the voltage at a monitored transmission bus falls below some threshold. A deadband on this voltage allows the system to settle down in between the normal and reverse logic modes. In order to control a large number of LTCs, the latter are divided into clusters, each with its own monitored voltage. The paper also considers the control of two levels of LTCs in cascade, where proper coordination is required between the two levels. The proposed scheme has been tested on a detailed EHV-HV-MV planning model of the Western region of the French transmission system operated by RTE. Long-term time responses to major disturbances are shown to illustrate the performance of the proposed scheme.

Distributed Undervoltage Load Shedding

A new design of load shedding against long-term voltage instability is proposed. It uses a set of distributed controllers, each monitoring a transmission voltage, controlling a group of loads, acting in closed-loop, and adjusting its action to the voltage evolution. The whole system operates without information exchange between controllers.

Coordination of distributed generators through the virtual power plant concept

In this paper the authors propose a market strategy of a microgrid incorporating a virtual power plant. For exemplification, a configuration consisting of different types of distributed generators and a lumped load are considered. The aim of the virtual power plant is to maximize the profit by minimization of the total cost involved for electrical energy generation by the distributed generators that are part of the virtual power plant.

Power transfer capacity enhancement using SVC

This paper presents the results of a feasibility study for installing FACTS devices in the South-Eastern part of Romanian power grid (Dobrogea - a peninsular area), to increase the transfer capacity to the rest of the grid. This study assumed, on one hand, the scheduled increase in generated power in the area, mainly due to two new units in the Cernavod ă nuclear power plant (1400 MW installed power) and wind generation with an estimated installed power of over 1600 MW. On the other hand, the scenarios considered the present topology and future developments of the transmission network. The increase in generated power in the S-E part of the power grid may lead to changes in the power market schedules, causing generation decrease or even shut down of other generators, leading to power flow changes and power system stability problems.

Market strategy of distributed generation through the virtual power plant concept

In this paper the authors propose a market strategy of a microgrid incorporating a virtual power plant. For exemplification, a configuration consisting of different types of distributed generators are considered. The aim of the virtual power plant is to maximize the profit by appropriate bidding strategy on the electricity market and optimal use of the sources.

A load shedding scheme against both short- and long-term voltage instabilities in the presence of induction motors

In the presence of induction motors in loads, long-term voltage instability may result in sharp voltage decreases, once the generators supporting transmission voltages have their field currents limited. Furthermore, after a fault, induction motors may fail re-accelerating and their stalling leads to short-term voltage instability. This paper investigates the ability of the load shedding scheme, previously proposed by the authors, to deal with both short and long-term voltage instabilities. The scheme is distributed with minimal amount of information exchange. It is also shown that the selectivity of this protection scheme can be increased by prioritizing in time the various controllers. Detailed time simulations of a test system are reported.

Local vs. wide-area undervoltage load shedding in the presence of induction motor loads

In the presence of induction motor loads, long-term voltage instability may end up in a sharp voltage decrease, which makes the tuning of undervoltage load shedding more delicate. This paper first investigates the ability of a purely distributed load shedding scheme, previously proposed by the authors, to cope with these situations. Owing to difficulties to reconcile dependability and security, an alternative wide-area protection is considered. The latter consists of generators sending overexcitation signals to the load shedding controllers in order to allow the latter to act faster. Detailed time simulations of a test system are reported.

Distributed load interruption and shedding against voltage delayed recovery or instability

This paper deals with a two-part system integrity protection scheme to be installed in distribution networks, to counteract fault-induced delayed voltage recovery or even short-term voltage instability due to induction motors. The first part consists of a fast triggered but temporary reduction of some loads to facilitate motor re-acceleration after fault clearing. The second part resorts to load shedding, as a back-up. The scheme relies on purely distributed controllers; each of them measures a bus voltage and interrupts/disconnects load at the same bus. Tests have been performed on a generic MV/LV system. They illustrate the benefit of load interruption and the selectivity of the proposed scheme.

A purely distributed implementation of undervoltage load shedding

A new design of load shedding against long-term voltage instability is proposed. It uses a set of distributed controllers, each monitoring a transmission voltage and controlling a group of loads. Each controller acts in closed-loop, shedding amounts that vary in magnitude and time according to the evolution of its monitored voltage. The whole system operates without information exchange between controllers, the latter being implicitly coordinated through network voltages. The operation, design and robustness of the proposed scheme are illustrated through a small but realistic example.