Showing papers by "Jihong Wang published in 2016"

A review on compressed air energy storage – A pathway for smart grid and polygeneration

Abstract: The increase in energy demand and reduction in resources for conventional energy production along with various environmental impacts, promote the use of renewable energy for electricity generation and other energy-need applications around the world. Wind power has emerged as the biggest renewable energy source in the world, whose potential, when employed properly, serves to provide the best power output. In order to achieve self-sustenance in energy supply and to match the critical needs of impoverished and developing regions, wind power has proven to be the best solution. However, wind power is intermittent and unstable in nature and hence creates lot of grid integration and power fluctuation issues, which ultimately disturb the stability of the grid. In such cases, energy storage technologies are highly essential and researchers turned their attention to find efficient ways of storing energy to achieve maximum utilization. The use of batteries to store wind energy is very expensive and not practical for wind applications. Compressed Air Energy Storage (CAES) is found to be a viable solution to store energy generated from wind and other renewable energy systems. A detailed review on various aspects of a CAES system has been made and presented in this paper which includes the thermodynamic analysis, modeling and simulation analysis, experimental investigation, various control strategies, some case studies and economic evaluation with the role of energy storage towards smart grid and poly-generation.

Predictive control strategy of a gas turbine for improvement of combined cycle power plant dynamic performance and efficiency.

Abstract: This paper presents a novel strategy for implementing model predictive control (MPC) to a large gas turbine power plant as a part of our research progress in order to improve plant thermal efficiency and load–frequency control performance. A generalized state space model for a large gas turbine covering the whole steady operational range is designed according to subspace identification method with closed loop data as input to the identification algorithm. Then the model is used in developing a MPC and integrated into the plant existing control strategy. The strategy principle is based on feeding the reference signals of the pilot valve, natural gas valve, and the compressor pressure ratio controller with the optimized decisions given by the MPC instead of direct application of the control signals. If the set points for the compressor controller and turbine valves are sent in a timely manner, there will be more kinetic energy in the plant to release faster responses on the output and the overall system efficiency is improved. Simulation results have illustrated the feasibility of the proposed application that has achieved significant improvement in the frequency variations and load following capability which are also translated to be improvements in the overall combined cycle thermal efficiency of around 1.1 % compared to the existing one.

Delay-dependent stability of LFC in Microgrid with varying time delays

Abstract: Load frequency control systems used to rely on dedicated communication links. The deregulation of the electricity market and the emergence of the Microgrids and Smartgrids made the open communication infrastructure an exigent need for future power system. In this case the load frequency control signals will be exchanged through communication network. The communication network is characterized by variable time delay which may lead to system instability. This paper investigates the stability of load frequency control system in islanded micro-grid with the presence of the time delay. The stability analysis is based on solving a set of linear matrix inequalities. Also, the effects of the controller gains and time delay variation rate on the maximum allowable delay bound are investigated.

Mathematical Modeling and Control of a Cost Effective AC Voltage Stabilizer

Abstract: AC voltage regulation is required in both the domestic and industrial sectors to avoid undesired effects from random voltage variations of the power supply. The paper introduces an ac voltage stabilizer/converter (ACVS) that is based on a controllable autotransformer technology. The proposed ACVS offers a specified strategy of voltage regulation, less harmonics, and low cost. The paper explains the operating principle of the ACVS and derives its nonlinear mathematical model. To ensure the desired performance of the ACVS while it is subject to uncertain input voltage and load variations, an optimal control strategy is designed. It is achieved via transforming the ACVS model extending with fictive axis emulation into a rotating reference frame and the linearization of the model via specific orientation of the reference frame and introducing a linear control action. Operation of the ACVS is simulated under different disturbances due to load and grid voltage changes, and compared to voltage stabilization with application of I and PI controllers. Experimental results are presented to demonstrate the voltage regulation technology.

A combined MTPA and maximum efficiency control strategy for IPMSM motor drive systems

Abstract: For electric vehicle applications, it is desirable to achieve maximum torque output of the traction motor for fast acceleration and minimize electrical losses, from energy saving point of view, which is achieved by Maximum Torque Per Ampere (MTPA) and Maximum Efficiency (ME) control methods, respectively. This paper introduces a compromise solution between MTPA and ME approaches obtained for Interior Permanent Magnet Synchronous Motor (IPMSM) drive, smoothly combining them and yielding a desired priority of the maximum torque or efficiency depending on the operating conditions. The proposed approach does not require switching between the methods which can worsen the dynamic performance of the system, and it is easy in implementation. The paper demonstrates an application of the proposed methodology with respect to the referred torque profile. For lower torques, the system is closer to the MTPA control which is useful for the fast dynamics. For higher torques, where power losses are higher, the system is closer to the ME approach providing almost the minimum of electric energy losses, which is useful for preventing battery discharge. The methodology is justified analytically and verified via simulations of steady state and dynamic characteristics of a torque vector control system.

Delay-dependent stability of DC Microgrid with time-varying delay

Abstract: In order to optimize the efficiency of renewable energy sources they are connected in a form of AC and DC Microgrids. Furthermore the increased number of DC loads has shifted the view to DC Microgrids. This paper presents the stability and maximum time delay calculation for a DC Microgrid implementing master-slave control strategy. The communication between the master and the slave is achieved through communication network which makes the DC Microgrid a time delay system. A stability criterion based on Lyapunov-Krasovskii functional and replacing the delay term by Newton-Leibnitz formula is used to derive a set of linear matrix inequalities. The binary iteration algorithm is used to solve the set of linear matrix inequalities and to calculate the maximum allowable delay bound. The effects of the voltage controller gains on the maximum allowable delay bound are also investigated. Further, the relation between the maximum allowable delay bound and the time delay variation rate is studied. The results are tested through simulation using Matlab/Simulink.

Modelling of the whole process of a university campus CHP power plant and dynamic performance study

Abstract: Combined heat and power (CHP) refers to a process/system designed to utilize the waste or residual heat from a power generation process. Thus, a CHP plant can produce both electricity and heat. The nature of such a combination makes the process more complex than any single power generation process or boiler heating system. The paper focuses on modelling study and analysis of energy efficiency of the University of Warwick micro-CHP power plant. In this CHP modelling study, a gas turbine module is built to provide driving power and methane is used as fuel gas. Heat recovery system and auxiliary boiler modules are developed for thermal power generation. All the sub-systems are validated by comparing the simulation results with the operating data collected from the CHP plant. The dynamic performance of the key CHP process outputs is studied with respect to the variation of the input syngas stream, including electricity generation, thermal power output and water output temperature. Simplified controllers are also applied to the gas engineheat recovery subsystem and auxiliary boiler. Simulation results with/without feedback control are both analyzed. The study has highlighted the key factors which influence the plant performance and suggested the strategy for potential energy efficiency improvement.

Networked control of parallel DC/DC converters over CAN bus

Abstract: The rapid development and the low cost of the communication networks made them a viable alternative to conventional wiring in distributed energy systems. Closing the feedback through a communication network forms a networked control system which is characterized by time delay and packet loss. However, exchanging the control signals over communication networks reduces the complexity in the wiring and enhances the reliability, the induced time delay and data loss could lead to system instability. The most widely approach for modeling the time delay and the packet loss is through using Markov chains. The paper addresses the stability of parallel DC/DC Buck converters over CAN bus. The networked converters system is formulated as standard Markovian Jump System. The stochastic stability of the parallel DC/DC converters controlled through the CAN is investigated in the paper. The resulting stability problem is in the form of Linear Matrix Inequality. The range of the controller parameter that achieve the stochastic stability of the system over the CAN is calculated.

Feasibility Study of a Scroll Expander for Recycling Low-Pressure Exhaust Gas Energy from a Vehicle Gasoline Engine System

Abstract: The growing number of vehicles on the road has led to a rapid increase in fuel consumption and toxic gas emissions, so the challenges in fuel efficiency improvement and reduction of CO2 and NOx emissions have always been on the top agenda of the automotive industry. The paper presents a feasibility study of recovering the low-pressure exhaust gas energy via by-pass connection of a scroll expander to the engine system exhaust. The paper starts with the description of the proposed new exhaust energy recycling scheme and the mathematical modelling of the system. A feasibility study is carried out to investigate whether this new scheme can work with the engine operation conditions specified by the engine test data. The initial study indicated that the scroll expander structure needs to be modified; otherwise, it cannot be used for exhaust energy recovery. The experimental test and simulation results presented in this paper indicate that it is feasible to recover the low-pressure exhaust gas energy using a scroll expander with a modified structure. The proposed energy recovery system has the potential to produce over 400 W power output with over 90% of engine exhaust flow recycling.

Stability of parallel DC/DC converters with time varying delay

Abstract: The rapid development in communication networks made them very attractive to replace conventional wiring in distributed power electronic systems. Parallel DC/DC converters are one of the important distributed power electronic systems. Conventionally, the controllers exchange the control signals through wires. This reduces the reliability and increases the system cost and complexity. Replacing them with communication network will introduce a time delay that may lead to system instability. The paper addresses the stability of parallel DC converters controlled over communication networks. The network is represented as variable time delay. A theorem based on solving a set of linear matrix inequalities is used to investigate the delay-dependent stability of the system. The effects of the voltage controller parameters on the maximum allowable delay bound are investigated. Furthermore the effect of the time delay variation rate on the maximum allowable delay bound is discussed.

Modelling of one-dimensional noisy dynamical systems with a Frobenius-Perron solution

Abstract: Energy storage plays an important role in maintaining energy balance for the future power network. A novel solution by learning human body energy system is explored aiming to determine the best ratio between the energy storage and generation capacity with variations of mixed energy sources. The fluctuation process of energy storage in human body and power network can be approximately represented by a one-dimensional noisy dynamical system. This paper develops a new approach to inferring a piecewise linear semi-Markov transformation of a one-dimensional discrete time dynamical system that is subjected to additive stochastic noise, based on sequences of probability density functions observed from the noisy dynamical system. The reconstructed map that approximates the underlying transformation can be used to predict the amount of stable fat/energy storage, and to achieve the bio-inspired three-point (generation, load and storage) balance structure. A numerical example is used to demonstrate the applicability of the derived algorithm and robustness with respect to additive stochastic noise.