Seddik Bacha

Optimal Power Flow Management for Grid Connected PV Systems With Batteries

This paper presents an optimal power management mechanism for grid connected photovoltaic (PV) systems with storage. The objective is to help intensive penetration of PV production into the grid by proposing peak shaving service at the lowest cost. The structure of a power supervisor based on an optimal predictive power scheduling algorithm is proposed. Optimization is performed using Dynamic Programming and is compared with a simple ruled-based management. The particularity of this study remains first in the consideration of batteries ageing into the optimization process and second in the “day-ahead” approach of power management. Simulations and real conditions application are carried out over one exemplary day. In simulation, it points out that peak shaving is realized with the minimal cost, but especially that power fluctuations on the grid are reduced which matches with the initial objective of helping PV penetration into the grid. In real conditions, efficiency of the predictive schedule depends on accuracy of the forecasts, which leads to future works about optimal reactive power management.

Cascaded DC–DC Converter Photovoltaic Systems: Power Optimization Issues

This paper investigates the issues of ensuring global power optimization for cascaded dc-dc converter architectures of photovoltaic (PV) generators irrespective of the irradiance conditions. The global optimum of such connections of PV modules is generally equivalent with performing the maximum power point tracking (MPPT) on all the modules. The most important disturbance occurs when the irradiance levels of modules happen to be sensibly different from a module to another - in this case, voltage-limitation requirements may be broken. The proposed supervisory algorithm then attempts to establish the best suboptimal power regime. Validation has been achieved by MATLAB/Simulink numerical simulation in the case of a single-phase grid-connected PV system, where individual MPPTs have been implemented by an extremum-seeking control, a robust and less-knowledge-demanding perturb-and-observe method.

New Optimized PWM VSC Control Structures and Strategies Under Unbalanced Voltage Transients

Control structures and strategies have a critical influence on a power electronic converters behavior during disturbances. Most of the previous works in the field of pulsewidth modulation voltage-source converter (VSC) operation under unbalanced conditions propose dual vector controllers with dc bus voltage optimization strategies, which have been proven to be well adapted for rectifier applications. In this paper, two major contributions are made. On the one hand, a new optimized operation strategy based on exchanged power maximization is proposed for vector control structures, which permits the extension of optimized operation to other VSC applications (e.g., flexible alternating current transmission system and distributed generation interfaces). On the other hand, a scalar control structure is proposed based on resonant controllers, together with three adapted optimized operation strategies, namely: 1) dc bus voltage optimization; 2) power exchange maximization; and 3) a hybrid strategy (an intermediary mode between the other two strategies). Their main advantage is their simplicity and the lack of real-time symmetrical component extraction techniques. This scalar controller and the proposed optimized operation strategies are compared to conventional vector controllers. It is proven through experimental analysis that the proposed scalar controller offers very good performances with simpler structures and bigger flexibility in terms of operation modes.

Real-Time Analysis of the Transient Response Improvement of Fixed-Speed Wind Farms by Using a Reduced-Scale STATCOM Prototype

As the total number of installed wind farms is far from being negligible, an upgrading of their technology is essential to fulfil new interconnection requirements. Power electronics are considered to be a key technology to accomplish this task. In this paper the use of a STATCOM for the improvement of the ride-through capability of fixed-speed wind farms is analyzed. Critical aspects like STATCOM rating and control are analyzed. A modified STATCOM controller is proposed, based on the series combination of a power factor control loop and a voltage regulation loop, which permits an optimized behavior of the wind farm both in normal and fault conditions. The contribution of the STATCOM is analyzed by means of Hybrid real-time tests (with a reduced-scale physical prototype) and offline (full scale) simulations in PSCAD/EMTDC. The study highlights the great contribution of STATCOMs to the transient behavior of fixed-speed wind farms and the importance of an appropriate control strategy choice on the performance and rating of the device

Maximizing the Power Output of Partially Shaded Photovoltaic Plants Through Optimization of the Interconnections Among Its Modules

Photovoltaic applications worldwide have reported problems with shading. Passing clouds, the moving shade of a neighbors chimney or a nearby tree, can completely compromise the power production of such plants despite their size or sophistication. In order to address this issue, this paper makes an exhaustive study of the available interconnections among the modules of a shaded photovoltaic field and how they impact power production. As a result, a clear relationship between the interconnections of the PV modules and their power output is proposed through empirical connection laws.

A Single Synchronous Frame Hybrid (SSFH) Multifrequency Controller for Power Active Filters

Conventional integration-based controllers, such as the multisynchronous PI and the multiresonant controllers, are well adapted for multifrequency-current-control applications. The first controller involves multiple reference frames, while the second one operates in a static frame using multiple resonant regulators. This paper presents a hybrid type of controller, called a single synchronous frame hybrid (SSFH) controller, which combines both features: It operates in an SSF mixing conventional PI and resonant controllers. A detailed design criterion for the SSFH controller is presented based on a frequency-response approach. Digital-implementation aspects (such as computation delays) and the phase margin of the system are taken into consideration during the design process. The SSFH and the multiresonant controllers are compared considering various criteria such as the computational load and the performances in terms of transient and steady-state response. It is concluded that the SSFH controller is a very interesting and execution time-saving structure for heavily distorted multifrequency applications, which is especially adapted for balanced or slightly unbalanced cases

Energy-Reliability Optimization of Wind Energy Conversion Systems by Sliding Mode Control

This paper describes a manner in which the energy-reliability optimization of wind energy conversion systemspsila operation can be achieved by means of the sliding mode control. The proposed approach aims at designing a tradeoff between maximizing the power harvested from wind by a horizontal-axis-grid-connected variable-speed doubly-fed-induction-generator-based wind power system and minimizing its mechanical stress. An appropriate sliding surface has been found in the speed-power plane, which allows the operation more or less close to the optimal regimes characteristic. Thus, by torque controlling the generator, an energy-reliability optimization of the wind turbine behavior is performed. The proposed control law is validated by both off-line and real-time simulation; the latter on a dedicated experimental rig, based upon the hardware-in-the-loop simulation concept. The results show that the control objective is fully accomplished.

Space Vector Method for Voltage Dips and Swells Analysis

A new method for voltage dips and swells analysis is presented in this paper. This method is based on the space vector representation in the complex plane and the zero-sequence voltage. Indeed, in the case of nonfaulted system voltages, the space vector follows a circle in the complex plane with a radius equal to the nominal voltage. It follows the same shape for balanced dips, but with a smaller radius. For unbalanced dips, this shape becomes an ellipse with parameters depending on the phase(s) in drop, dip magnitude and phase angle shift. For swells the space vector shape is not modified, though the zero-sequence voltage presents significant changes in its phase and magnitude and can be used for swells analysis. The changes in the space vector and the zero-sequence voltage are used to determine the dip/swell time occurrence, to classify and finally characterize the measured power-quality disturbance. Algorithms are developed for each step of this automatic voltage dips and swells analysis (segmentation, classification, and characterization) and are validated on real measurement data.

Low-Voltage Transformer Loss-of-Life Assessments for a High Penetration of Plug-In Hybrid Electric Vehicles (PHEVs)

In the coming years, plug-in hybrid electric vehicles (PHEVs) will strongly penetrate the French car fleet. Their impact on each element of the electric distribution grid needs to be estimated. In this paper, the impact of PHEVs on the life duration of the medium-voltage/low-voltage (LV) transformer using a thermal model to estimate the hot-spot temperature is studied. Based on probabilistic algorithms, three penetration rates of PHEVs are studied. A stochastic method is applied to construct domestic daily load profiles of houses constituting an LV residential electric grid supplied by the transformer. Correlated with the initial load rate (without PHEVs) of the transformer, two indices are proposed; the DTR_PHEV_X and VTR_PHEV_X to calculate, respectively, the life duration and aging rate of transformer in the presence of PHEVs. It is shown that the aging rate of the transformer is quadratic in the presence of PHEVs.

Hardware-in-the-Loop-based Simulator for a Class of Variable-speed Wind Energy Conversion Systems: Design and Performance Assessment

This paper focuses on the design, building, error evaluation, and performance assessment of a physical simulator for a variable-speed wind energy conversion system (WECS). Such simulator, dedicated to control algorithms validation, must replicate the dynamical behavior of the WECS physically in real time. To this end, software parts, which model subsystems of the plant, and hardware parts, taken as they are from the plant, are closed-loop connected, thus implementing a hardware-in-the-loop (HIL) simulator. The simulator interacts with a software-simulated environment-in this case, the wind velocity-in order to run experiments under controllable conditions. Controllers to be tested interact directly with the hardware part of the simulator, thus better approaching the behavior of the real-world WECS. A complete grid-connected generation chain employing a horizontal-axis fixed-pitch three-bladed rotor permanent-magnet-synchronous-generator-based WECS is chosen as example for the design and performance assessment of an HIL simulator, both in frequency and time domain.