Bruno Francois

Energy Management and Operational Planning of a Microgrid With a PV-Based Active Generator for Smart Grid Applications

The development of energy management tools for next-generation PhotoVoltaic (PV) installations, including storage units, provides flexibility to distribution system operators. In this paper, the aggregation and implementation of these determinist energy management methods for business customers in a microgrid power system are presented. This paper proposes a determinist energy management system for a microgrid, including advanced PV generators with embedded storage units and a gas microturbine. The system is organized according to different functions and is implemented in two parts: a central energy management of the microgrid and a local power management at the customer side. The power planning is designed according to the prediction for PV power production and the load forecasting. The central and local management systems exchange data and order through a communication network. According to received grid power references, additional functions are also designed to manage locally the power flows between the various sources. Application to the case of a hybrid supercapacitor battery-based PV active generator is presented.

Energy Management and Power Control of a Hybrid Active Wind Generator for Distributed Power Generation and Grid Integration

Classical wind energy conversion systems are usually passive generators. The generated power does not depend on the grid requirement but entirely on the fluctuant wind condition. A dc-coupled wind/hydrogen/supercapacitor hybrid power system is studied in this paper. The purpose of the control system is to coordinate these different sources, particularly their power exchange, in order to make controllable the generated power. As a result, an active wind generator can be built to provide some ancillary services to the grid. The control system should be adapted to integrate the power management strategies. Two power management strategies are presented and compared experimentally. We found that the “source-following” strategy has better performances on the grid power regulation than the “grid-following” strategy.

Power Control Design of a Battery Charger in a Hybrid Active PV Generator for Load-Following Applications

A hybrid generator with a photovoltaic energy conversion system is proposed with supercapacitors and lead-acid batteries in a dc-coupled structure. The objective of this system is to supply the prescribed reactive and active power to the grid. This paper focuses on the strategy, which makes it possible to ensure a high battery state of charge and overcharge security by designing a dedicated local control system. A continuous dynamic model and a control design of the power system studied are proposed in this paper. Simulation and experimental results illustrate the performances obtained.

Dynamic Frequency Control Support by Energy Storage to Reduce the Impact of Wind and Solar Generation on Isolated Power System's Inertia

In electrical islands, frequency excursions are sizeable and automatic load shedding is often required in response to disturbances. Moreover, the displacement of conventional generation with wind and solar plants, which usually do not provide inertial response, further weakens these power systems. Fast-acting storage, by injecting power within instants after the loss of a generating unit, can back up conventional generation assets during the activation of their primary reserve. This paper relies on dynamic simulations to study the provision of such a dynamic frequency control support by energy storage systems in the French island of Guadeloupe with large shares of wind or solar generation. The results show that fast-acting storage, by acting as a synthetic inertia, can mitigate the impact of these sources on the dynamic performance of the studied island grid in the case of a major generation outage. The other concerns raised by renewables (e.g., variability, forecast accuracy, low voltage ride-through, etc.) have not been addressed within this project.

High Wind Power Penetration in Isolated Power Systems—Assessment of Wind Inertial and Primary Frequency Responses

Grid operational challenges are significant to increase securely the wind penetration level. New embedded control functions are therefore required in order to make participate wind generators in power system management. In this paper the implementation of inertial response and primary frequency control in a wind turbine controller are investigated. Main factors affecting the performances of the frequency regulation are identified and characterized. The influence of control parameters and the turbine operating point on the inertial response are analyzed through obtained performances in an islanded power system. The combined control scheme using both controllers is also developed and the potential of the obtained grid service at partial load is discussed.

Control implementation of a five-leg AC-AC converter to supply a three-phase induction machine

A fault-tolerant ac-ac converter capable of supplying a three-phase induction machine from the grid with an unitary power factor has been proposed. With one faulted converter leg, two of the remaining five legs are connected to the grid, two legs are connected to the machine, and a common leg is shared by the grid and the machine. The previously developed control strategy required a too great computation time for practical implementation. In this paper, a new control strategy is suggested for this power converter. It enables an easier control implementation. Experimental results are provided.

DC Link Capacitor Voltage Balancing in a Three-Phase Diode Clamped Inverter Controlled by a Direct Space Vector of Line-to-Line Voltages

In this paper, the direct modulation strategy of a three-level inverter with self stabilization of the dc link voltage is extended to a five-level inverter. Therefore, a new modeling and control strategy of a five-level three-phase diode-clamped inverter (DCI) is presented. The obtained modeling shows that modulated multilevel voltages are obtained by combination of eight different three-level functions, which are called modulation functions. Therefore, a space-vector scheme without using a Park transform is explained. Based on this algorithm, the location of the reference voltage vector can be easily determined. Then, the voltage vectors are selected to generate corresponding levels and simultaneously their durations are calculated. More over, the redundancies of different switch configurations for the generation of intermediate voltages are used to limit the deviation of capacitor voltages. Experimental results are given to illustrate the proposed control strategy of the three-phase three-level diode clamped inverter. Then, obtained results for a five-level three-phase DCI with the extended version of the control strategy are presented to show the good performances of the proposed balancing modulation.

Improved Crowbar Control Strategy of DFIG Based Wind Turbines for Grid Fault Ride-Through

Nowadays, the most widely used variable speed machine for wind turbine above 1MW is the doubly fed induction generator (DFIG). As the wind power penetration continues to increase, wind turbines are required to provide Low Voltage Ride-Through (LVRT) capability. Crowbars are commonly used to protect the power converters during voltage dips. Its main drawback is that the DFIG absorbs reactive power from the grid during grid faults. This paper proposes an improved control strategy for the crowbar protection to reduce its operation time. And a simple demagnetization method is adopted to decrease the oscillations of the transient current. Moreover, reactive power can be provided to assist the recovery of the grid voltage. Simulation results show the effectiveness of the proposed control schemes.

Emission Reduction and Economical Optimization of an Urban Microgrid Operation Including Dispatched PV-Based Active Generators

In order to take full advantage of distributed generators, an evolution of the classical power system organization and management is also necessary. An aggregator of a residential urban electrical network can be considered by the distribution system operator as a stakeholder, which is able to control a cluster of local generators and loads with technical constraints for the connection with the remaining distribution grid and commercial contracts with outer electrical producers. This paper is focused on the design of the microgrid central energy management system which relies on a day-ahead operational planning and an online adjustment procedure during the operation. A dynamic programming-based algorithm is derived to solve the unit commitment problem with a multiobjective function in order to reduce the economic cost and CO2 equivalent emissions. The proposed energy management system is implemented into a supervisory control and data acquisition (SCADA) and tested by using a hardware-in-the-loop simulation of the urban network. Economic and environmental gains are evaluated.

Dynamic frequency control support: A virtual inertia provided by distributed energy storage to isolated power systems

In electrical islands, frequency excursions are sizeable and automatic load shedding is often required in response to disturbances. By injecting active power in the timeframe of hundreds of milliseconds up to a few seconds after the loss of a generating unit, fast-acting storage can support the conventional production assets during the activation of their primary reserve. Using dynamic and hardware-in-the-loop (realtime) simulations, the provision of such a dynamic frequency control support by distributed energy storage systems has been studied in the case of the French island of Guadeloupe. Dedicated control algorithms have been developed and tested on a small-scale ultracapacitor storage unit. By acting as a virtual inertia, it has been shown that fast storage systems can improve substantially the dynamic performances of electrical islands.