Xiaoxin Zhou

Bio: Xiaoxin Zhou is an academic researcher from Electric Power Research Institute. The author has contributed to research in topics: Electric power system & AC power. The author has an hindex of 13, co-authored 39 publications receiving 459 citations.

Analysis and design of vector control for VSC-HVDC connected to weak grids

Abstract: Voltage source converter based high voltage direct current transmission (VSC-HVDC) is considered one of the most suitable technologies to integrate renewable energies. However, connecting VSC to a weak grid is challenging since traditional vector control tends to become unstable under high power demand conditions. In this paper, an improved vector control method is proposed wherein a feed forward branch based on steady state and small signal analysis of the VSC system is added under weak grid situations. The feed forward branch promotes faster reactive power response, thus enhancing the stability of the VSC system. Since the improved vector control uses the same inner loop as traditional vector control, the proposed method allows for the ability to retain fault current suppression capabilities. Furthermore, the control parameters of the outer loop of the improved vector control need not vary according to the variation of the operating points, which makes it easy to implement. The feed forward branch is implemented by solving a nonlinear equation or through use of a look-up table. The influence of the estimation errors of short circuit ratio (SCR) on the control performance is also studied. The effectiveness of the improved vector control is demonstrated through small signal model analysis and time domain simulations.

Robust observer-based nonlinear control of multimachine power systems

Abstract: A novel robust observer-based nonlinear controller (RONC) for excitation control of synchronous generators interconnected in a multimachine power system is presented. The RONC is developed based on a feedback linearising control strategy for nonlinear systems and it employs estimation of system states and perturbation. A sliding-mode observer is designed to estimate system states and perturbation which encompasses all the system nonlinearities and uncertainties. The successful estimates of states and perturbation are involved in the feedback control law, which enables a real-time compensation of system nonlinearities, to realise the feedback linearisation of the nonlinear power system. The RONC is robust in performance as its design does not require the exact knowledge of the power system. Moreover, the RONC is easy to implement as only one state is measured. The simulation study is carried out based on a three-machine power system. The results show that the RONC has better performance and robustness, under variations of power system operation conditions and disturbances, in comparison with a conventional nonlinear state feedback linearising controller (NFLC).

Analysis of low frequency oscillation and source location in power systems

Abstract: The major problem in current online diagnosis and analysis for power system oscillation is mainly concerned with finding the oscillation source in a fast and correct way using the data collected by the Wide Area Measurement System (WAMS). This paper for the first time proposes a scheme of cut set energy based on WAMS. Independent of accurate parameters, the scheme can make full use of WAMS data based on cut set energy construction and fast calculation to locate the source during oscillation. Afterwards, a scheme of torque decomposition is proposed, based on which the controller's torque can be divided into damping torque and synchronous torque by calculation through WAMS data, and this paper puts forward the abnormal response and simulation models calibration of influential controllers. Analysis of an oscillation case shows how the cut set energy scheme and the torque decomposition scheme are applied in a real-world power system, and the schemes are proven to be reliable and practical in identifying and locating oscillation sources.

World energy outlook

Abstract: This chapter discusses leading problems linked to energy that the world is now confronting and to propose some ideas concerning possible solutions. Oil deserves special attention among all energy sources. Since the beginning of 1981, it has merely been continuing and enhancing the downward movement in consumption and prices caused by excessive rises, especially for light crudes such as those from Africa, and the slowing down of worldwide economic growth. Densely-populated oil-producing countries need to produce to live, to pay for their food and their equipment. If the economic growth of the industrialized countries were to be 4%, even if investment in the rational use of energy were pushed to the limit and the development of nonpetroleum energy sources were also pursued actively, it would be extremely difficult to prevent a sharp rise in prices. It is evident that it is absolutely necessary to pursue actively the development of coal, natural gas, and nuclear power if a physical shortage of energy is not to block economic growth.

Comparison of particle swarm optimization and genetic algorithm for FACTS-based controller design

Abstract: Recently, genetic algorithms (GA) and particle swarm optimization (PSO) technique have attracted considerable attention among various modern heuristic optimization techniques. The GA has been popular in academia and the industry mainly because of its intuitiveness, ease of implementation, and the ability to effectively solve highly non-linear, mixed integer optimization problems that are typical of complex engineering systems. PSO technique is a relatively recent heuristic search method whose mechanics are inspired by the swarming or collaborative behavior of biological populations. Since the two approaches are supposed to find a solution to a given objective function but employ different strategies and computational effort, it is appropriate to compare their performance. This paper presents the application and performance comparison of PSO and GA optimization techniques, for flexible ac transmission system (FACTS)-based controller design. The design objective is to enhance the power system stability. The design problem of the FACTS-based controller is formulated as an optimization problem and both PSO and GA optimization techniques are employed to search for optimal controller parameters. The performance of both optimization techniques in terms of computational effort, computational time and convergence rate is compared. Further, the optimized controllers are tested on a weakly connected power system subjected to different disturbances over a wide range of loading conditions and parameter variations and their performance is compared with the conventional power system stabilizer (CPSS). The eigenvalue analysis and non-linear simulation results are presented and compared to show the effectiveness of both the techniques in designing a FACTS-based controller, to enhance power system stability.

The gas transmission problem solved by an extension of the simplex algorithm

Abstract: The problem of distributing gas through a network of pipelines is formulated as a cost minimization subject to nonlinear flow-pressure relations, material balances, and pressure bounds. The solution method is based on piecewise linear approximations of the nonlinear flow-pressure relations. The approximated problem is solved by an extension of the Simplex method. The solution method is tested on real-world data and compared with alternative solution methods.

Energy storage system: Current studies on batteries and power condition system

Abstract: To maximize the introduction of renewable energy, introducing grid energy storage systems are essential. Electrochemical energy storage system, i.e., battery system, exhibits high potential for grid energy storage application. A battery energy storage system is comprised of a battery module and a power conversion module. This paper starts by reviewing several potential battery systems, as well as an advanced aluminum-ion battery that currently has promising prospects in the electrochemical energy storage system. The characteristics of the batteries are reviewed and compared, including the materials, electrochemistry, performance and costs. The application prospect of the batteries is discussed. The paper summarizes the features of current and future grid energy storage battery, lists the advantages and disadvantages of different types of batteries, and points out that the performance and capacity of large-scale battery energy storage system depend on battery and power condition system (PCS). The power conversion system determines the operational condition of the entire energy storage system. The new generation wide bandgap semiconductor for power electronic technology is discussed from the perspective of performance, topology, model and non-linearity and is compared to the traditional silicon-based semiconductor. Finally, the application prospect of the new generation semiconductor technology in the energy storage system is indicated. This paper concludes the application status of the energy storage system in the renewable energy power generation and indicates the critical problems that need to be addressed during the construction and operation of the storage system.