Research On The Application Of Bridge-Connected Statically Controlled Energy Storage Devices In Power System Stability Control

Since the21st century, the new energy revolution, which aims at replacing fossil fueled energy with renewable and other new energy sources, has been gradually arising. Along with the new energy revolution, the energy storage technology has also drawn unprecedented attention and has been developed rapidly. Among various energy storage devices, bridge-connected statically controlled energy storage device (BSCESD) connected to the grid by power electronic circuit has the capability of exchanging the active and the reactive power with the grid independently, quickly and accurately. As a result, the BSCESD is a more powerful and flexible new measure to improve the power system stability. Therefore, the research on the application of BSCESD in power system stability control has great significance.This thesis begins with the extended linearized model of the single-machine infinite-bus (SMIB) system with BSCESD. The two methods including the torque method and the state space method are utilized to elaborate the mechanism of how to influence the power system dynamic characteristic with BSCESD. Then, by taking the practical requirements into consideration, the system layer controller of the BSCESD, which is designed to increase the damping and to enhance transient stability of the power system, is thoroughly studied.The main works and achievements of the thesis include:(1) Taking superconducting magnetic energy storage system (SMES) for an example, per unit model of BSCESD’s main circuit is built. Using the built model, the method of tuning the controllers’ parameters is developed systematically and comprehensively. Further the high-power expansion method is also investigated. Both methods are developed for the power condition system (PCS). It is demonstrated that a BSCESD can be equivalent to a first order element, whether the power orders of PCS are tracked by open-loop control with current signal feedback or by closed-loop control with power signal feedback. Further, the quantitative relationship between the time constant of the equivalent first order element and PCS controller parameters is derived. Then, the control problem of the multi-phase chopper designed for high-power voltage source converter based PCS is studied intensively, and a new control method for the multi-phase chopper used in SMES is proposed. In this method, the switching of voltage control vectors is utilized to maintain the DC bus voltage and its high anti-disturbance ability is assured. The current equality function of the multi-phase chopper.is achieved by switching the switch elements’ state combinations.(2) The mechanism of how to influence the power system dynamic characteristic with BSCESD is explained in detail. The differences between active and reactive power regulation using BSCESD to influence the power system dynamic characteristic and the impact of excitation control and amortisseurs on the effect of BSCESD are investigated deeply. In order to obtain the transfer function of perturbed electromagnetic torque to power regulations of BSCESD, an approximate method based on the residues of perturbed rotor angular speed to power regulations of BSCESD to is proposed.(3) The research on the design of damping controller to meet the requirements of field application is carried out from the following aspects, structure of the controllers, parameters’ adjustment, feedback inputs selection and robustness analysis. A simplified method of the damping controller design with the consideration of amortisseurs’ effect is presented and its validity is tested with the help of root locus analysis. Meanwhile, the conclusions which have practical values for the SMIB system with BSCESD are drawn as follows:Firstly, when controlled by the damping controller utilizing△ω or-△Pg as input, BSCESD is able to increase the damping of the power system effectively. However, when controlled by the damping controller utilizing△Pg as input to increase the damping of the power system, BSCESD is prone to induce the instability of the controller mode or the excitation mode, which restricts the BSCESD to improve the stability of the power system. Secondly, when BSCESD utilizes both active and reactive power regulation to improve the power system damping, the damping improvement of BSCESD is robust to any change in the grid reactance or operating point.(4) By segmenting the power system large-disturbance transient process properly and considering the effect of the excitation control, a segmentation-based controller which meets the practical requirement is proposed. Being controlled by the proposed controller, the BSCESD coordinates with the excitation control and improves both damping and transient stability of the power system. Therefore, the segmentation-based controller is capable to utilize the potential of BSCESD as much as possible.(5) As an important participant, the author takes part in the development of "150kJ/100kW high temperature superconducting magnetic energy storage system", and is mainly responsible for the design, calculation, simulation, development and debugging of PCS and monitoring system, as well as the design, implementation and data analysis of experiments. During the project, the power orders tracking experiments, laboratory experiments and field tests were carried out. The experimental results align pretty much with the theoretical analysis, which verifies the outcome of the thesis, including the study of the control techniques of PCS, the mechanism analysis of BSCESD, the comparison among different feedback inputs, and etc.