Autonomous search and tracking of objects using model predictive control of unmanned aerial vehicle and gimbal: Hardware-in-the-loop simulation of payload and avionics

This paper describes the design of model predictive control (MPC) for an unmanned aerial vehicle (UAV) used to track objects of interest identified by a real-time camera vision (CV) module in a search and track (SAT) autonomous system. A fully functional UAV payload is introduced, which includes an infra-red (IR) camera installed in a two-axis gimbal system. Hardware-in-loop (HIL) simulations are performed to test the MPC's performance in the SAT system, where the gimbal attitude and the UAV's flight trajectory are optimized to place the object to be tracked in the center of the IR camera's image.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Management of harmonic propagation in a marine vessel by use of optimization

Advances in power electronics drive systems for variable speed operation has enabled extensive use of such solutions in the propulsion and thruster systems of marine vessels. These solutions however introduce current and voltage distortions that compromises the overall power quality of the onboard electrical system. This paper presents and discusses one approach for generating the harmonic current reference for an active filter based on optimization. Two relevant results are revealed by this study: 1) lower THD values are attained by performing system optimization compared to local compensation of one load, and 2) the lower THD values are achieved with a smaller active filter rating than the one required for local load compensation.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Optimal Compensation of Harmonic Propagation in a Multi-Bus Microgrid

This paper discusses how an Active Power Filter (APF) can be utilized for system-wide harmonic mitigation in a microgrid with multiple sources of harmonic distortion located at different buses. A two-bus microgrid system with independent nonlinear loads at both buses is first investigated analytically, and it is demonstrated that it is possible to derive a harmonic current injection from the APF that will minimize the harmonic distortion at both buses. However, analytical optimization of the APF current will be sensitive to parameter variations, will deteriorate when the APF reaches current saturation and cannot be easily extended to larger systems with many loads at different buses. A more practically applicable method for calculating the APF current references, by using the framework of Model Predictive Control (MPC) is instead proposed for the investigated system. Under realistic operating conditions, this approach can obtain further improvement in the system-level harmonic mitigation. The characteristics and performances that are obtained with the analytical solution and the MPC-based control are assessed by time domain simulations in the Matlab/Simulink environment. The results clearly indicate how an MPC-based system-oriented compensation can maximize the utilization of a single APF in a multi-bus Microgrid.© EA4EPQ. This is the authors’ accepted and refereed manuscript to the article

System-Wide Harmonic Mitigation in a Diesel Electric Ship by Model Predictive Control

Email Print Request Permissions This paper proposes a system-oriented approach for mitigating harmonic distortions by utilizing a single Active Power Filter (APF) in an electrical grid with multiple buses. Common practice for control of APFs is to locally compensate the load current harmonics or to mitigate voltage harmonics at a single bus. However, the operation of an APF in a multi-bus system will influence the voltages at neighboring buses. It is therefore possible to optimize the APF operation from a system perspective instead of considering only conventional local filtering strategies. For such purposes, Model Predictive Control (MPC) is proposed in this paper as a framework for generating APF current references that will minimize the harmonic distortions of the overall system within a given APF rating. A diesel-electric ship, with two buses supplying separate harmonic loads, with an APF located at one of the buses, is used as study case. The operation with on-line MPCbased optimization of the APF current references is compared to two benchmark methods based on conventional approaches for APF control. The results demonstrate that the MPC generates current references that better utilize the APF current capability for system-wide harmonic mitigation.2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other work

Optimization-based Control in Shipboard Electric Systems

With stringent, and globally sanctioned, environmental rules and regulations, dictating limits for allowed emissions of greenhouse gases and particle matter from combustion of fossil fuels, the marine vessel’s efficiency has recently received a lot of attention. At the same time, in addition to meet environmental requirements from multiple stakeholders, ship owners strive to enhance revenue in an economically challenged market by reducing operational costs and gain competitive advantages. Examples of such competitive advantages are reduced environmental footprints, increased vessel/operational platform efficiency, operational flexibility and reliability, and higher Environmental Regularity Numbers (ERN). To asses the marine vessel’s efficiency is complex and involves multiple disciplines. In this work, the main contributions are centered around the discipline automation and automatic control design, with the use of optimization-based control strategies to improve the (AC) shipboard power plant’s efficiency. Two topics are covered in this thesis: Optimal harmonic mitigation using Model Predictive Control (MPC), and optimization-based unit commitment as part of Energy Management Systems (EMS). These two topics, although intertwined, represents different levels of power system control and contribute both to the efficiency of the shipboard power plant. The thesis is divided into three parts. The first part, which is covered by Chapter 2, presents a review of the shipboard electrical power system’s evolution. From the first successful use of shipboard electricity, marked by the use of electricity in SS Columbia in 1880 for illumination purposes, to present day with all-electric vessels using batteries, the shipboard power system has transitioned from containing few single-purpose passive components to containing many multi-purpose active components that rely on automatic control. Thus, the discipline automation and automatic control design plays an important part in the present stage of the shipboard electrical power system’s evolution. Chapter 2 ends with a discussion of properties and challenges of the marine vessel’s power system, including, among others, AC vs DC, integrated power systems and grid design, power electronics, harmonic pollution and electrical stability, and the increasing level of software complexity. The second part of the thesis, which is covered by Chapter 3-5, addresses the problem of harmonic pollution and presents a novel harmonic mitigation strategy based on optimal control. The proposed method, which relies on a single, controllable Active Power Filter (APF), uses an MPC that (online) generates APF current references based on an optimization objective to minimize the total harmonic pollution in the whole power system – a system-level harmonic mitigation approach. Chapter 3 presents simulation results of the proposed method compared with two conventional APF control strategies using a two-bus shipboard power system with 6- and 12- pulse rectifier loads as test subject. The results demonstrate that the MPC is able to generate current references that better utilize the APF current capability for system-level harmonic mitigation, and is able to reduce the Total Harmonic Distortion (THD) beyond what is achieved with the conventional mitigation approaches. Chapter 4 introduces a system-level harmonic mitigation approach, also considering the control of a single APF, that is based on offline analytical optimization. The offline analytical optimization method is compared with the MPC in Chapter 3 and conventional mitigation strategies using a two-bus shipboard power system with 12-pulse rectifier loads as test subject. Non-idealities, such as parameter-mismatch and transformer saturation, are introduced in the simulation, and the results show that also in this case the MPC-based system-level harmonic mitigation method is superior compared to the offline analytical optimization and the conventional mitigation approaches. The last chapter in this part, Chapter 5, addresses an event-based system architecture with real-time implementation of a single-phase version of the MPC presented in Chapter 3 and 4 for system-level harmonic mitigation. Hardware-In-Loop (HIL) simulations using two desktop computers and a simulator demonstrate that the proposed system architecture and MPC implementation meet the real-time requirements for system-level harmonic mitigation. The last part of the thesis, which is covered by Chapter 6, addresses the problem of unit commitment in an Energy Management System (EMS). Real power system data from three different vessels in operation, a ferry, a Platform Supply Vessel (PSV) and a seismic survey vessel, are extracted and analyzed with regards to diesel-generator-set (genset) loadings and genset running hours to shed light on potential fuel efficiency improvements. As demonstrated by the extracted data, the gensets in all three vessels run with non-optimal loading conditions relative individual gensets’ Specific Fuel Oil Consumption (SFOC) curves. Two unit commitment methods, one based on Mixed-Integer Linear Programming (optimization) and one based on logics, are presented and discussed. Moreover, three power system configurations are proposed; i) four fixed-speed gensets, ii) three fixed-speed genset and one variable-speed genset, and iii) four fixed-speed gensets and an Energy Storage System (ESS). The two unit commitment methods are compared by simulation studies of the three proposed power system configurations, using the real load profiles extracted from the three vessels during operation. The simulation results indicate that optimal EMS algorithms in combination with a revised power system configuration can increase the operational efficiency, in terms of fuel savings and reduction in genset running hours. The last chapter in the thesis, Chapter 7, summarizes and concludes the work, and presents recommendations for future work

Tracking objects with fixed-wing UAV using model predictive control and machine vision

This thesis describes the development of an object tracking system for unmanned aerial vehicles (UAVs), intended to be used for search and rescue (SAR) missions. The UAV is equipped with a two-axis gimbal system, which houses an infrared (IR) camera used to detect and track objects of interest, and a lower level autopilot. An external computer vision (CV) module is assumed implemented and connected to the object tracking system, providing object positions and velocities to the control system. The realization of the object tracking system includes the design and assembly of the UAV s payload, the design and implementation of a model predictive controller (MPC), embedded in a larger control environment, and the design and implementation of a human machine interface (HMI). The HMI allows remote control of the object tracking system from a ground control station. A toolkit for realizing optimal control problems (OCP), MPC and moving horizon estimators (MHE), called ACADO, is used. To gain real-time communication between all system modules, an asynchronous multi-threaded running environment, with interface to external HMIs, the CV module, the autopilot and external control systems, was implemented. In addition to the IR camera, a color still camera is mounted in the payload, intended for capturing high definition images of objects of interest and relaying the images to the operator on the ground. By using the center of the IR camera image projected down on earth, together with the UAV s and the objects positions, the MPC is used to calculateway-points, path planning for the UAV, and gimbal attitude, which are used as control actions to the autopilot and the gimbal. Communication between the control system and the autopilot is handled by DUNE. If multiple objects are located and are to be tracked, the control system utilizes an object selection algorithm that determines which object to track depending on the distance between the UAV and each object. If multiple objects are clustered together, the object selection algorithm can choose to track all the clustered objects simultaneously. The object selection algorithm features dynamic object clustering, which is capable of tracking multiple moving objects. The system was tested in simulations, where suitable ACADO parameters were found through experimentation. Important requirements for the ACADO parameters are smooth gimbal control, an efficient UAV path and acceptable time consumption. The implemented HMI gives the operator access to live camera streams, the ability to alter system parameters and manually control the gimbal. The object tracking system was tested using hardware-in-loop (HIL) testing, and the results were encouraging. During the first flight of the UAV, without the payload on-board, the autopilot exhibited erroneous behavior and the UAV was grounded. A solution to the problem was not found in time to conduct any further flight tests during this thesis. A prototype for a three-axis stabilized brushless gimbal was designed and 3D printed. This was as a result of the two-axis gimbal system s limited stabilizationcapabilities, small range of movement and seemingly fragile construction. Out of a suspected need for damping to improve image quality from the still camera, the process of designing and prototyping a wire vibration isolator camera mount was started. Further work and testing is required to realize both the gimbal and dampened camera mount. The lack of flight tests prohibited the completion of the object tracking system.Keywords: object tracking system, unmanned aerial vehicle (UAV), search and rescue,two-axis gimbal system, infrared (IR) camera, computer vision (CV), model predictivecontrol (MPC), control environment, human machine interface (HMI), remote control, ground control, ACADO, real-time, asynchronous multi-threaded running environment, way-point, path planning, DUNE, dynamic object clustering, multiple moving objects, hardware-in-loop (HIL), three-axis stabilized brushless gimbal, wire vibration isolato

Handling system harmonic propagation in a diesel-electric ship with an active filter

Harmonic distortion is often a challenge in marine vessel power systems due to the presence of large motor drives containing diode or thyristor rectifiers. Governing standards impose requirements on bus voltage Total Harmonic Distortion (THD) which can be demanding to fulfil. An attractive measure to reduce THD is to use 12-pulse rectifiers, as they are known to cancel the 5th and the 7th harmonic. However, the added cost and space of this solution compared with standard 6-pulse rectifiers is significant. This paper proposes to base propulsion motor drives on 6-pulse rectifiers, and mitigate harmonic problems by means of power electronic based active filters. A detailed numeric simulation model is developed for evaluating the performance of the topology. A case study system is defined consisting of two propulsion motor drives and two synchronous generators. The active filter greatly improves the bus voltage THD in all defined simulation cases. The performance is also better than a corresponding system using 12-pulse rectifiers and no active filteracceptedVersion© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Extremum-Seeking Control for Harmonic Mitigation in Electrical Grids of Marine Vessels

This paper focuses on the minimization of the harmonic distortion in multibus electrical grids of marine vessels using a single active power filter. An active power filter is commonly used for local harmonic mitigation. However, local filtering may lead to a “whack-a-mole” effect, where the reduction of harmonic distortion at the point of installation is coupled to an increase of distortion in other grid nodes. The few existing filtering methods that consider system-wide mitigation are based on an accurate model of the power grid, which may not be available if the complexity and the scale of the grid are large. In this work, we investigate the use of an extremum-seeking control method to optimize the injection current of an active power filter for system-wide harmonic mitigation. Because the extremum-seeking control method is model-free, it can be used without knowledge of the electrical grid. Moreover, the method can be implemented on top of the existing approaches to combine the fast transient response of conventional harmonic-mitigation methods with the optimizing capabilities of extremum-seeking control

Optimized current reference generation for system-level harmonic mitigation in a diesel-electric ship using non-linear model predictive control

Non-linear optimal control using collocation and multiple shooting is investigated in this paper to generate the current reference signal for the lower level control of an active filter in a marine vessel with diesel-electric propulsion. The optimization objective is aimed at using the active filter for system-level minimization of Total Harmonics Distortion with the minimum rating of the active filter. The investigation of the different algorithms is oriented to the search of a solution that can offer a good compromise between accuracy and real-time implementation abilities. Results indicate that linear problem formulations are more suitable for real time implementation as they require less computational costs with minimal loss of flexibility. Non-linear problem formulations provide higher flexibility at the cost of higher computational efforts

Distributed control architecture for real-time model predictive control for system-level harmonic mitigation in power systems

It can be challenging to design and implement Model Predictive Control (MPC) schemes in systems with fast dynamics. As MPCs often introduce high computational loads, it can be hard to assure real-time properties required by the dynamic system. An understanding of the system’s behavior, to exploit system properties that can benefit real-time implementation is imperative. Moreover, MPC implementations on embedded local devices rarely allows flexibility to changes in model and control philosophy, due to increased complexity and computational loads. A change in control philosophy (run-time) can be quite relevant in power systems that can change from an integrated to a segregated state. This paper proposes a distributed control hierarchy with a real-time MPC implementation, designed as a higher-level control unit, to feed a lower-level control device with references. The higher-level control unit’s objective in this paper is to generate the control reference of an Active Power Filter for system-level harmonic mitigation. In particular, a novel system architecture, which incorporates the higher-level MPC control and handles distribution of control action to low-level controllers, as well as receiving measurements used by the MPC, is proposed to obtain the application’s real-time properties and control flexibility. The higher-level MPC control, which is designed as a distributed control node, can be swapped with another controller (or control philosophy) if the control objective or the dynamic system changes. A standard optimization framework and standard software and hardware technology is used, and the MPC is designed on the basis of repetitive and distributed control, which allows the use of relatively low control update rate. A simulator architecture is implemented with the aim of mimicking a Hardware-In-Loop (HIL) simulator test to evaluate the application’s real-time properties, as well as the application’s resource usage. The results demonstrates that the implementation of the harmonic mitigation application exhibits the real-time requirements of the application with acceptable resource usage