Load Transfer Operation Research Articles

Two-Stage Optimization Model Based on Neo4j-Dueling Deep Q Network

To alleviate the power flow congestion in active distribution networks (ADNs), this paper proposes a two-stage load transfer optimization model based on Neo4j-Dueling DQN. First, the Neo4j graph model was established as the training environment for Dueling DQN. Meanwhile, the power supply paths from the congestion point to the power source point were obtained using the Cypher language built into Neo4j, forming a load transfer space that served as the action space. Secondly, based on various constraints in the load transfer process, a reward and penalty function was formulated to establish the Dueling DQN training model. Finally, according to the ε−greedy action selection strategy, actions were selected from the action space and interacted with the Neo4j environment, resulting in the optimal load transfer operation sequence. In this paper, Python was used as the programming language, TensorFlow open-source software library was used to form a deep reinforcement network, and Py2neo toolkit was used to complete the linkage between the python platform and Neo4j. We conducted experiments on a real 79-node system, using three power flow congestion scenarios for validation. Under the three power flow congestion scenarios, the time required to obtain the results was 2.87 s, 4.37 s and 3.45 s, respectively. For scenario 1 before and after load transfer, the line loss, voltage deviation and line load rate were reduced by about 56.0%, 76.0% and 55.7%, respectively. For scenario 2 before and after load transfer, the line loss, voltage deviation and line load rate were reduced by 41.7%, 72.9% and 56.7%, respectively. For scenario 3 before and after load transfer, the line loss, voltage deviation and line load rate were reduced by 13.6%, 47.1% and 37.7%, respectively. The experimental results show that the trained model can quickly and accurately derive the optimal load transfer operation sequence under different power flow congestion conditions, thereby validating the effectiveness of the proposed model.

Dynamic response analysis of load transfer of topsides from T-barge onto twin-barge in floatover installation

The twin-barge floatover method is a promising approach in the topsides installation of the offshore platform. However, the topsides transfer onto the twin-barge is a challenging task and is seldom investigated. This study focuses on the floatover load transfer operation of the topsides onto the twin-barge by a T-shaped barge and investigates the dynamic responses of the three proximate barges in the operation. The floatover mating process was experimentally simulated by three representative intermediate stages, including 0%, 50%, and 100% stages. The barge and topsides motions, the relative motions of mating points, the contact loads on mating units, tether forces, and mooring forces at various environmental conditions were analyzed. The three floating barges experienced large surge drift motions as well as the sway and yaw drift motions in head seas because of the unsymmetrical configurations. Although a relative radial distance between mating points occurred and exceeded the capture radius of the mating unit at limited instants, the relative motions were to a great extent within the capture radius, indicating the feasibility of the twin-barge floatover method. Comparisons of the loads at the three stages show that the mating units and the tether lines were subjected to larger impact impulse loads at the 0% stage than the 100% stage.

A Novel Method for Seamless Closed-Loop Load Transfer in Radial Distribution Networks

Closed-loop load transfer is an effective measure to improve the power supply reliability of radial distribution networks. However, the traditional closed-loop load transfer mode is passive for operators: the loop closing operation relies on complex network models and calculation methods, which is feasible for the distribution network with many sensors, but it is not practical for the low-voltage distribution network with a complex structure. The field operation is still based on the experience of operators, resulting in uncertainty of the loop closing and large loop-closing current. Besides, the coordination of multiple power sources for guaranteeing power supply can not guarantee the power quality and the economic cost is high, in which the adopted closed-loop device is not movable and has poor reusability. This article presents an active loop-closing mode: a seamless closed-loop load transfer system (SLTS), which can not only realize uninterrupted load transfer but also eliminate loop closing surge current and expand the application range of closed-loop load transfer. In the proposed system configuration, a series compensation voltage source is connected to two substations. Therefore, closed-loop current can be controlled flexibly by regulating this voltage source. The proposed system can be applied to adjacent substations to carry out closed-loop load transfer operations during equipment maintenance. Besides, it can be installed between two radial feeders to achieve seamless fault seal-healing. The control strategy of seamless closed-loop load transfer and fault seamless self-healing are proposed, respectively. The effectiveness of the proposed SLTS and the designed control strategy are validated via MATLAB/Simulink.

Numerical modeling of nonstationary hydrodynamic forces and induced motions of a coupled offshore floating installation system

Offshore installations always involve multi-body systems in which the hydrodynamic and mechanical interactions are complicated for the properties keep changing under certain operation procedures. Float-over deck (FOD) installation is a typical example, where the draft of barge continuously varies during the load transfer operation. Numerical analysis of such continuous operation is crucial to identify the extreme responses, but it's difficult to model the nonstationary properties involved in the hydrodynamic loads and motions and contact loads of the system. In the study, a numerical modeling methodology is developed to calculate these nonstationary hydrodynamic forces and induced responses, considering an active update of the hydrodynamic properties with the time varying body boundary conditions. The effects of time varying body boundary conditions on hydrodynamic forces and induced nonstationary motions and contact loads of a FOD installation system is studied. The results indicate that the dynamic analysis of the continuous load transfer operation could be effectively carried out with one update of hydrodynamic forces at the end of the operation. The barge roll motions and its natural period are the most affected. The proposed method could be used in intensive simulation of offshore multi-body systems with obvious draft variation during operations.

Experimental analysis of dynamic response of floatover installation using rapid transfer technique in continuous load transfer process

This study presents the experimental analysis of an innovative floatover installation method with the rapid transfer technique, in which the topside loads can be transferred fast and safely. In the rapid transfer process, 30% loads were firstly transferred onto the jackets within only 1 min using the jacking system. Then both the ballast system and the jacking system were employed to gradually transfer the loads onto the jackets. After 70% topside loads were transferred, the jacking system quickly offloads the remaining 30% loads within 1 min. The continuous load transfer operation was simulated in model tests. The complex motions of the barge and the topside as well as the loads on the Deck Support Unite (DSU) and the Leg Mating Unite (LMU) were analyzed. The maximum and minimum motions of the barge and the topside were statistically analyzed as well as DSU and LMU loads. Results indicate the barge pitch motions largely synchronize with the topside pitch before the second jack-down operation. The barge moved forward a little distance after twice jack-down operations. Results indicate DSU loads varied significantly during the jack-down operations and the jacking system should be designed to provide lateral restraints equivalent to 20% of the topside weight.

Load transfer operations for a dynamic vehicle routing problem with mixed backhauls

We consider a dynamic vehicle routing problem with mixed backhauls (DVRPMB) that seeks to plan, in the most efficient way, the delivery of dynamic pickup orders that arrive in real time, while a predefined plan of serving static delivery orders is being executed. Maintaining the original assignment of delivery orders to vehicles may limit system performance, since the changes in the system state caused by the arriving dynamic orders may grant re-assignments of such orders advantageous. Thus, in this paper, we introduce and solve a variant of DVRPMB that allows orders to be transferred between vehicles during plan implementation. We refer to this problem as the DVRPMB with load transfers (DVRPMB-LT). Since the problem is solved with periodic re-optimization, we focus on the underlying optimization problem, develop an appropriate model using an arc-based formulation, and compare the exact solutions to the ones of the corresponding problem that does not allow transfers. Furthermore, we develop a practical heuristic framework to address the complexity of DVRPMB-LT and solve cases of practical relevance. Subsequently, we employ the proposed framework to solve and analyze the full dynamic problem.

Self-Configuration of Waypoints for Docking Maneuvers of Flexible Automated Guided Vehicles

We study the problem of automatic configuration of the initial position, the so-called waypoint, from which to initiate a robust and accurate docking maneuver using nonholonomic (car-like) robotic forklifts in the context of automated manufacturing. The proper selection of these positions is of paramount importance to operate with the industrial grade of accuracy, repeatability, and reliability required by load transfer operations in industrial settings. An unconstrained optimization method coupled with probabilistic techniques is proposed to solve this problem. The proposed method permits to increase significantly the flexibility and adaptability of the autonomous robotic forklifts.

A Comparison of Control Techniques for Robust Docking Maneuvers of an AGV

This work addresses the path tracking problem of industrial guidance systems used by automated guided vehicles (AGVs) in load transfer operations. We focus on the control law that permits to AGVs to operate tracking a predefined route with industrial grade of accuracy, repeatability and reliability. One of the main issues of this problem is related to the important weight variation of AGVs when transporting a load, which induces slipping and skidding effects. Besides, localization error of the guidance system should be taken into account because position estimation is typically performed at a low sample rate. Other key point is that control law oscillations can knock down the load, which gives rise to safety and performance problems. Three control techniques - fuzzy, vector pursuit and flatness-based control - are compared in order to evaluate how they can deal with these problems and satisfy the robustness requirements of such an industrial application.

Autonomous Overhead Crane System Using a Fuzzy Logic Controller

This paper pertains to advanced automation of the load transfer process using overhead cranes. Overhead cranes are widely used in various areas of industry, including manufacturing, construction, shipping, etc. Load transfer operations using overhead cranes have to be performed fast and safely. As such, these operations are handled by expert operators however, the demand for an automatic consistent and reliable crane operation is on the rise. The crane–load system is highly nonlinear and time-varying, hence, solutions considering model-base approaches may lead to a complicated controller structure. Such a controller may require accurate estimation of the crane system parameters. In this paper we present a new fuzzy logic controller for overhead crane operation. The fuzzy controller is designed based on knowledge of an expert crane operator, and does not require any parameter estimation. It mimics the operator behavior by using the same crane–load system states that are realized by the operator. These states are the trolley position error and the load sway angle. The fuzzy controller action, on the other hand, is the desired trolley speed. The proposed controller is implemented and tested on a small-scale overhead crane. Experimental results show robust operation of the fuzzy controller as compared with that of a conventional controller.

Algorithm for improving the restorability of power supply in distribution systems

In this paper, a new concept of restorability of power supply (RPS) and the corresponding performance indices are suggested. Load transfer algorithm is used for enhancing the RPS of distribution systems. Feeder incidence diagram (FID) is proposed for analyzing the rules for load transfer. The performance indices, maximal interrupted power (MIP), and maximal number of interrupted customers (MNIC), is calculated before the restoration operation or apparatus maintenance. These indices can serve for evaluating the operation status of feeders, estimating the impact of load transfer and switch operation, and assessing the RPS. They can also be used to optimize the allocation of tie-breakers in a meshed network. The work is of great significance in distribution system reconstruction in China.

Distribution network reconfiguration for load balancing with a coloured Petri net algorithm

A rule-based expert system with a coloured Petri net (CPN) algorithm is developed for load balancing of distribution systems. CPN models of the distribution components such as four-way line switches are proposed to derive the proper switching operations. In this way, the loads on transformers and feeders will become more balanced. Heuristic rules based on the standard load transfer operation procedures of the Taipower distribution system are included in the best first search of the CPN to obtain the desired switching operations for load balancing. For the overload contingency during the summer peak season, load shedding is also considered in the CPN models, to provide service to as many key customers and loads as possible. The priority indices of each feeder and service zone are determined in advance according to the key customers within the service territory. A Taipower distribution system with 68 feeders is selected for computer simulation to demonstrate the effectiveness of the proposed methodology. It is found that load balancing of the distribution system can be obtained very efficiently and the risk of overloads can be reduced by applying the proposed CPN model to determine the optimal switching operation.

Rule-based approach to load transfer to alternate supplies based on the phase of the residual voltage on the disconnected busbar

Transfer techniques and a rule-based approach to an in-phase load transfer scheme for secondary selective substations are developed. The transfer scheme, with its developed transfer techniques and rule based algorithm, integrates into a microcontroller-based in-phase transfer controller to maintain the continuity of power supply to process loads. The rule sets initiating conditions, blocking transfer criteria, load shedding schedules and possible events. It provides a safe and successful bus transfer system. Operations of the load transfer scheme with simulated load conditions have been tested through the in-phase transfer controller. The results of computer simulation and test measurements show that the load transfer operation is performed successfully. The inrush current, transient torque and service reliability can also be improved by using this transfer scheme.

Control of a dynamic platform for offshore applications

An original concept of providing a dynamic platform system (DPS) for offshore load transfer operations in adverse weather conditions is discussed in this paper. The object here is to control the deck of the DPS to remain stationary in the presence of external disturbances. These disturbances are in the form of base motion disturbance and any unmeasurable disturbances acting directly on the deck. Two control methods based on the principle of invariance are used here on an experimental rig to investigate the disturbance isolation of the DPS. Good results have been obtained.