Wenshan Hu

Networked Predictive Control of Systems With Random Network Delays in Both Forward and Feedback Channels

The design problem of networked control systems (NCS) with constant and random network delay in the forward and feedback channels, respectively, is considered in this paper. A novel networked predictive control (NPC) scheme is proposed to overcome the effects of network delay and data dropout. Stability criteria of closed-loop NPC systems are presented. The necessary and sufficient conditions for the stability of closed-loop NCS with constant time delay are given. Furthermore, it is shown that a closed-loop NPC system with bounded random network delay is stable if its corresponding switched system is stable. Both simulation study and practical experiments show the effectiveness of the control scheme

Design and Stability Criteria of Networked Predictive Control Systems With Random Network Delay in the Feedback Channel

This paper is concerned with the design of networked control systems (NCSs) with random network delay in the feedback channel and gives stability criteria of closed-loop networked predictive control systems. The principle of predictive control is adopted to overcome the effects of network time delay. The necessary and sufficient conditions on the stability of the closed-loop NCS are derived, which provides useful analytical stability criteria. The closed-loop networked predictive control system with bounded random network delay is stable if the corresponding switched system is stable. Simulation and real-time results give an illustration of the proposed control strategies

Droop-Based Distributed Cooperative Control for Microgrids With Time-Varying Delays

This paper develops a droop-based distributed cooperative control scheme for microgrids under a switching communication network with non-uniform time-varying delays. We first design a pinning-based frequency/voltage controller containing a distributed voltage observer and then design a consensus-based active/reactive power controller, which are employed into the secondary control stage to generate the nominal set points used in the primary control stage for different distributed generators (DGs). By this approach, the frequencies and the weighted average value of all DGs’ voltages can be pinned to the desired values while maintaining the precise active and reactive power sharing. With the proposed scheme, each DG only needs to communicate with its neighbors intermittently, even if their communication networks are local and time-varying, and their variant delays may be non-uniform. Sufficient conditions on the requirements for the network connectivity and the delay upper bound that guarantee the stability and reliability of the microgrid are presented. The effectiveness of the proposed control scheme is verified by the simulation of a microgrid test system.

Design and Implementation of Web-Based Control Laboratory for Test Rigs in Geographically Diverse Locations

This paper compares current remote laboratories and describes the design and implementation of the Networked Control System Laboratory (NCSLab) in the University of Glamorgan on http://www/ncslab.net, which provides a unified and flexible Web-based interface to access test rigs located in different countries of the world. All the test rigs are connected and managed together by the NCSLab system. They are well cataloged by their characteristics, and their geographical locations are not necessarily known to the users. A three-layer structure, which consists of the main server, subservers, and test rigs, is adopted to organize the distributed facilities. All the control algorithms for the test rigs are generated by using the Matlab Real-time Workshop. Users can design and implement their own control algorithms for the test rigs. The Web interface is designed using Java JSP/Servlet technology which gives the users great flexibility, including remote tuning, remote monitoring (both data and videos), and remote control logics. In order to manage the massive information and support concurrent access, MySQL database is also integrated into the system.

Web-Based 3-D Control Laboratory for Remote Real-Time Experimentation

The design and implementation of Networked Control System Laboratory (NCSLab) 3-D which is a web-based 3-D control laboratory for remote real-time experimentation are introduced in this paper. NCSLab 3-D is built based on the NCSLab framework which supports the structure that the test rigs are located diversely in different parts of the world. In NCSLab 3-D, the test rigs are cataloged into several sublaboratories according to their functionalities. The laboratory building, sublaboratories, and test rigs are modeled in 3-D and reconstructed in a web-based interface using Flash 3-D engines. Users can “walk into” these laboratories and pick up the test rigs in a virtual reality environment similar to what they do in hands-on laboratories. During the remote experiments, the 3-D models are synchronized with the real test rigs through the network data links. Users are able to zoom in, zoom out, and rotate the 3-D models freely. Therefore, the real-time experiments can be watched from any angles. NCSLab 3-D has been applied to the control engineering education in Wuhan University, China. The results of the teaching practice show that NCSLab 3-D are able to bring great convenience to both users and maintenance personnel and improve the efficiency of the laboratory equipment significantly.

System modeling and optimization of microgrid using genetic algorithm

Microgrid has caused increasing attention for its high efficiency and low emissions. In this article a microgrid including a wind turbine, pv array and a CHP system consisting of fuel cells and a microturbine is studied and then the modeling of various DERs is conducted and the objective functions and constraints are developed. In the end the generic algorithm is employed to solved the optimal model and an operation scheme is achieved while meeting various constraints on the basis of tariff details, equipment performance, weather conditions and forecasts, load details and forecasts and other necessary information and then the economic costs and environmental impacts are analyzed and a conclusion that the multi-objective model can achieve high environmental benefits and spend as low operation cost as possible.

Frequency-Dependent Resistance of Litz-Wire Square Solenoid Coils and Quality Factor Optimization for Wireless Power Transfer

In order to achieve the highest efficiency of wireless power transfer (WPT) systems, the quality factor of the resonant coil should be as high as possible. Due to the skin effect and the proximity effect, the coil resistance increases with the increase in the frequency. The highest quality factor exists for the optimal frequency together with the corresponding frequency-dependent inductor resistance. This paper employs the Biot-Savart law to calculate the magnetic field strength, which results in the proximity-effect resistance in single-layer litz-wire square solenoid coils without a magnetic core. A strand-number coefficient is introduced to reflect the influence of the strand number inside the wire bundle on the proximity-effect resistance. The coefficient is obtained through simple inductor resistance measurements for various numbers of litz-wire strands. The optimal frequency for the highest quality factor is derived based on the resistance evaluation. Several prototype coils were manufactured to verify the resistance analysis. Two 50 cm × 50 cm square coils were employed to construct a WPT prototype. The maximum dc-dc efficiency of this WPT was about 75% at 100-cm distance.

Design and implementation of networked predictive control systems based on round trip time delay measurement

There are two random network transmission delays in networked control systems: forward and backward channel delays, which degrade the control performance significantly and even make the system unstable. In this paper, a predictive control method is presented to compensate the random delays. By using Diophantine equation, future control sequences for every possible time delay are generated, which are transmitted to the plant side in a single packet. The prediction is not based on individual forward and backward delays which are difficult to measure separately in a practical system but the round trip time (RTT) delay which is the sum of forward and backward delays, and is easy to measure. An active plant side and an event-driven controller are also introduced to achieve the aim. To illustrate the control performance improvement of the proposed control scheme, the results of off-line and real-time simulations and experiments for a practical servo control system are presented

Networked Predictive Control System with Data Compression

Random time delay and frequency data dropout can degrade the performance of networked control systems and even cause system instability. Liu et al. (2004) introduced a networked model based predictive control scheme to tackle this problem. In his method, a set of control sequences for every possible delay time are packed together and sent to the plant side, and on the plant side the relevant control signal corresponding to the measured time delay is selected. It is an effective method to compensate for the network delay. However, it raises a new problem that it would increase the network traffic, because a sequence requires more transmitting time than a single value. To solve this problem, this paper consider a least square method which is applied to compress the control sequence before it is send to the network.feedback control system

Modelling and practical implementation of 2-coil wireless power transfer systems

Wireless power transfer (WPT) based on inductive coupling could be potentially applied in many practical applications. It has attracted a lot of research interests in the last few years. In this paper, the modelling, design, and implementation of a 2-coil WPT system are represented. The prototype system can be implemented using conventional power electronic devices such as MOSFETs with very low costs as it works in relative low frequency range (less than 1MHz). In order to find out about the optimal working area for the WPT system, the circuit model based on the practical parameters from the prototype is built. The relationships between the exciting frequency, coupling, and output power are analyzed based on the circuit and magnetic principles. Apart from the theoretic study, the detailed implementation of the WPT prototype including the coil design, digital frequency generation, and high frequency power electronics is also introduced in this paper. Experiments are conducted to verify the effectiveness of the circuit analysis. By carefully tuning the circuit parameters, the prototype is able to deliver 20 W power through 2.2 meter distance with 20-30% efficiency.