Xinyao Zhu

Bio: Xinyao Zhu is an academic researcher from Huazhong University of Science and Technology. The author has contributed to research in topics: Computer science & Power (physics). The author has an hindex of 2, co-authored 2 publications receiving 28 citations.

Improved Complex Torque Coefficient Method Using CPCM for Multi-Machine System SSR Analysis

Abstract: Calculation of the complex torque coefficient for multi-machine system subsynchronous resonance (SSR) assessment had been proven a hard task. In this paper the concept of complex frequency domain port-equivalence conductance matrix (CPCM) is introduced to model the individual system component which represents the relationship between the terminal voltage and current in frequency domain, and the model of the overall power system can be established easily. Thus the complex torque coefficients of the generator unit under investigation can be calculated for SSR assessment. The advantages of this proposed method are that it can take the shaft dynamics and the rotor angle interactions among the generator units into consideration for the multi-machine power system SSR analysis, as well as it can be used to analyze the effectiveness of SSR damping devices. The effectiveness of the proposed method has been verified by both the eigenvalue analysis and the time domain simulation.

Day-Ahead Optimal Operation Strategy of Distribution Network Based on Energy Consumption Characteristics of Data Centers and Guidance Price Mechanism

Abstract: With the increasing penetration of distributed generation and flexible load in the distribution network, power generation and consumption plans made by different stakeholders may lead to uneven distribution of power flow in space and overload of some lines. For the increasingly large data centers in the flexible load, this paper proposes a day-ahead optimal operation strategy of distribution network based on its energy consumption characteristics and guidance price mechanism. First of all, combined with the CPU dynamic frequency modulation technology, the energy consumption characteristics of the data center and the best working mode of the internal server are analyzed. On this basis, the principle of equal consumption micro-increase rate is promoted from the perspective of economy, and the guidance price is formulated according to the profit seeking behavior of the data center operators. Guide the data load and the data center energy consumption, and realize the optimal operation of the distribution network in the day-ahead through the information interaction between the grid company and the data center operators. Finally, the IEEE-33 bus distribution network system embedded with the data centers is used for simulation and analysis. The results eliminate part of the lines overload caused by the original data load plan, and verify the effectiveness of the proposed strategy.

VDCOL link optimization of HVDC system based on improved genetic algorithm

Abstract: The fault of the receiving-end AC power grid of the high voltage direct current (HVDC) transmission system may cause the HVDC subsequent commutation failures. In order to dynamically adjust the DC current command during the recovery process of the first HVDC commutation failure to achieve the purpose of suppressing the HVDC subsequent commutation failures, a new method is proposed based on improved genetic algorithm (IGA) of the voltage dependent current order limiter (VDCOL) link optimization method. This paper analyzes the influencing factors of HVDC subsequent commutation failures and the reactive power interaction between the inverter converter station and the external power grid. Taking VDCOL as the research object, the work principle and limitations of conventional VDCOL are introduced. In order to overcome the single linear defect of the conventional VDCOL link, an IGA was used to optimize the parameters of the multi-segment inflection point of the VDCOL link, which realized the dynamic reactive power demand adjustment of the inverter side converter station when the receiving-end AC power grid was faulty, and then suppress the HVDC subsequent commutation failures. Finally, the simulation results demonstrate the effectiveness of the proposed method.

Properties and physical interpretation of the dynamic interactions between voltage source converters and grid: electrical oscillation and its stability control

Abstract: Voltage source converters (VSCs) play an important role in the power conversion of renewable power generation (RPG) systems. Conventional power systems are considerably affected by power electronic devices in systems with a high percentage of RPG. Various abnormal interactions in the form of oscillations between VSCs and grid have been reported, whereas the mechanism at the core is still lacking understanding. In this study, the properties of interactions between the VSC and grid are investigated, and through an analytical model the mechanisms of electrical oscillations are revealed. First, a simple resistance-inductance-capacitance (RLC) equivalent to the small-signal model of VSC-grid system was derived based on the knowledge of virtual passive element effects of VSC. Then, an intrinsic oscillatory point in the RLC circuit was identified, the damping characteristics of the current controller and phase-locked-loop (PLL) at this point were analysed. Subsequently, a critical stability criterion for the determination of PLL bandwidth that may trigger oscillations was established. For the improvement of the overall damping, a VSC stabiliser was proposed. Finally, the mechanism analysis and analytical criteria were verified by time-domain simulations in PSCAD/EMTDC.

Sub‐synchronous interactions in power systems with wind turbines: a review

Abstract: The sub-synchronous interactions (SSIs) observed in wind power plants have gained attention in recent years. These oscillations are characterised by the diversity of wind power generation types, power grids and power electronic devices. Two pure electrical oscillations, namely induction generator effect (IGE) and sub-synchronous control interaction in wind farms, are firstly discussed on their different characteristics. Particularly, IGE normally falls into the category of sub-synchronous resonance. Then two major types of wind turbines: doubly fed induction generator and permanent magnet synchronous generator with respect to their participations in SSI are reviewed according to the current research status. Several typical analysis and mitigation techniques in existing literature are also expounded in regard to their advantages and disadvantages. Additionally, the research on a grid-connected voltage-source converter in combination with the phase-locked loop, which has caused instability issues including SSI, is briefly introduced. Conclusions are drawn and several perspectives on the future work are presented at the end of this study.

Modeling and stability analysis methods for investigating subsynchronous control interaction in large-scale wind power systems

Abstract: The subsynchronous control interaction (SSCI) occurs when the wind turbine converter (WTC) controls interact with the series-compensated or weak AC network. The mechanism and attributes of the emerging interaction phenomenon invilving wind turbine generators (WTGs) are quite different from the traditional subsynchronous resonance or oscillation (SSR/SSO) phenomenon in steam turbine-generators (STGs). The SSCI is characterized by various system-wide parameters, including the wind speed and its uneven distribution in a wind power plant, varying number of WTGs connected to the grid, type of the WTGs, parameters of the WTC controls, level of series compensation, stiffness of the grid, etc. Such system-wide parameters change over time and thus make the modeling and analysis rather challenging to conduct SSCI studies. An ideal modeling approach for the SSCI is expected to preserve the system topology as well as valid for a wide range of operating conditions and parameters of the system. On the other hand, an ideal stability analysis method is supposed to give key quantitative information, such as the magnitude, frequency, and origin of the oscillation, as well as the component level participation indices. This paper provides a comparative insight into the application of existing and emerging modeling and stability analysis approaches for SSCI investigations in large-scale wind farms. It highlights the strengths and weaknesses of various modeling methods and analysis criteria. Finally, the paper underlines the recent advancements and points out towards the research directions in small/large-signal impedance modeling and stability approaches for accurate and quantitative investigation of the SSCI.

Stability Assessment of DFIG Subsynchronous Oscillation Based on Energy Dissipation Intensity Analysis

Abstract: Concerning the subsynchronous oscillation caused by the integration of doubly-fed induction generator (DFIG) to the power grid via the series compensation circuit, a method to assess the stability of subsynchronous oscillation based on the dissipation intensity is proposed in this article. First, the transient energy that DFIG generates in one oscillation period is defined as the dynamic energy of DFIG, and the model of DFIG dynamic energy containing internal control and external networks is constructed. And then, according to the Lyapunov stability theory, the negative gradient of dynamic energy is defined as the dissipation intensity, which reflects the dissipation effect of DFIG on the energy generated during oscillation. On this basis, the effect of the series compensation degree, phase-locked loop, and converter control parameters on subsynchronous oscillation is assessed, and real-time assessment of the stability level of DFIG-integrated power system is realized. Finally, a simulation model is built in RT-LAB to verify the proposed method. Simulation results demonstrate that the stability level of the system can be assessed accurately according to the value of dissipation intensity. When the value of dissipation intensity is positive, system oscillation converges. When the dissipation intensity is zero, the system oscillates with constant-amplitude oscillation. When the value of dissipation intensity is negative, system oscillation diverges.

Mitigation of power system forced oscillations based on unified power flow controller

Abstract: Forced oscillations (FOs), or low-frequency oscillations (LFOs) caused by periodic, continuous, small power disturbances, threaten the security and stability of power systems. Flexible AC transmission system (FACTS) devices can effectively mitigate LFOs via stability control. We propose a novel method that mitigates FOs by shifting the resonant frequency. Based on the features of the linearized swing equation of a generator, a resonant frequency shift can be achieved by controlling the synchronous torque coefficient using a unified power flow controller (UPFC). Because of the resonance mechanism, the steady-state response of an FO can be effectively mitigated when the resonant frequency changes from the original one, which was close to the disturbance frequency. The principle is that a change in resonant frequency affects the resonance condition. Simulations are conducted in a single-machine infinite-bus (SMIB) system, and the simulation results verify that the method is straightforward to implement and can significantly mitigate FOs. The controller robustness when the resonant frequency is not accurately estimated is also analyzed in the simulations.