Antoneta Iuliana Bratcu

State of art of optimization methods for assembly line design

The problem of optimal design of the assembly lines is considered. The paper is especially focused on the line balancing and resource planning step for the preliminary design stage. A survey of existing methods is given.

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.

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.

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.

A survey of the self-balancing production lines (“bucket brigades”)

The purpose of this paper is to present the main idea and rules of the “bucket brigades” and to analyse the modelling approaches and some real case studies reported in the literature. The “bucket brigades” represent a new concept of organising the flow line activities. This principle, first time implemented at Toyota, requires a considerably reduced design and supervision effort as regards the traditional assembly lines. The simple functioning protocol yields the spontaneous line balancing, due to a decentralised control strategy. So, for instance, it is no longer need to solve the Assembly Line Balancing (ALB) problem, which is NP-hard. In this paper, the main theoretical results are summed up, emphasizing the advantages and disadvantages of implementing the bucket brigades and identifying the still open problems. It seems that the bucket brigades have some strong points versus the classical solutions, including, but not limited to: decentralisation, flexibility, adaptability. This study will allow to generally concluding on some new trends in the production systems design and management.

Power optimization strategy for cascaded DC-DC converter architectures of photovoltaic modules

This paper proposes a control strategy aiming at operating cascaded DC-DC converter architectures of photovoltaic (PV) modules at maximum power irrespective of the irradiance conditions, meanwhile meeting constraints of voltage-limitation type. The global optimum of cascaded connections of PV modules is generally equivalent with operating all the modules at maximum power point tracking (MPPT). The most important disturbance occurs when the irradiance levels of modules are sensibly different because of various reasons - in this case, voltage-limitation requirements may be broken. The proposed supervising strategy then attempts to establish the best suboptimal power regime. MATLAB®/Simulink® numerical simulation results are presented in the case of a monophased grid-connected PV system, where individual MPPTs have been implemented by extremum seeking control (ESC).

Hardware-in-the-loop testing of PV control systems using RT-Lab simulator

This paper presents a testing system for power converters control units. A hardware-in-the-loop test bench is designed for assessing control unit performances. A photovoltaic generator, coupled with a boost circuit, is software-simulated within a real-time environment, RT-Lab and coupled in closed loop with the physical control unit to be tested.

Frequency-separation-based energy management control strategy of power flows within electric vehicles using ultracapacitors

This paper deals with a frequency-based energy sharing method between batteries and ultracapacitors (UC) as power sources within an electric vehicle (EV). A frequency splitter is used for routing the low-frequency content of power demand into the battery and its high frequencies into the UC system, taking profit from the UC as a peak power unit. The autonomy may thus be increased while also preserving the battery life. Real-time experiments on a dedicated test rig validate the proposed energy management approach.

Management and Control of Operating Regimes of Cross-Flow Water Turbines

This paper deals with a generation system based on cross-flow water turbines (CFWTs) operating in a river stream. It is equipped with a permanent-magnet synchronous generator and can feed a power grid or an insulated load through a back-to-back power electronics converter. This paper concerns the control of these two operating regimes with focus on the manner of achieving a soft switching between them, in order to ensure the balance between the generated and the provided power and to alleviate transients. The control laws and the switching sequences have been experimentally validated on a real-time CFWT simulator equipped with the same type of generator and power electronics converter. This paper aims at offering a synthetic vision of how the CFWT-based generation system should be controlled across the main operating regimes in order to preserve its continuity of service.

Some new results on the analysis and simulation of bucket brigades (self-balancing production lines)

The bucket brigades are self-balancing production lines where each human operator can move from one station to the next to continue working on a given part. When workers finish their job, they walk back to take over the ongoing work of their predecessor. For the bucket brigades, the line balancing emerges spontaneously. Several mathematical models have been proposed in literature for the analysis of bucket brigades, often where the basic assumptions seem to be too constraining. This paper analyses the behaviour of these lines when relaxing some of the usual restrictive assumptions. Two approaches are developed: analysis and simulation. An original analytical model is suggested and using this model, the sufficient condition of self-balancing for a finite backward velocity is studied. Then, a novel technique for the simulation of bucket brigades is proposed. This model uses the software Matlab/Simulink™. The results of simulation study are reported and analysed. The simulation model is flexible and easily extensible, in order to allow further embedding of complex dynamics which have not yet been considered.