Power System Analysis (Slides)

This panel session contains the following presentations:
1. Transient Stability Assessment and Dynamic Security Region in Power Electronics Dominated Power Systems
Transient stability accidents induced by converter based resources have been emerging frequently around the world. In this paper, the transient stability of the grid-tied voltage source converter (VSC) system is studied through estimating the basin of attraction (BOA) based on the hyperplane or hypersurface method. Meanwhile, fault critical clearing times are estimated, based on the approximated BOA and numerical fault trajectory. Further, the dynamic security region (DSR), an important index in traditional power systems, is extended to power electronics-dominated power systems in this paper. The DSR of VSC is defined in the space composed of active current references. Based on the estimated BOA, the single-VSC-infinite-bus system is taken as an example and its DSR is evaluated. Finally, all these analytical results are well verified by several numerical simulations in MATLAB/Simulink.
2. Transient Instability Mechanism of Droop-Controlled Inverter and Synchronous Generator-Interacted in an Islanded Microgrid
Transient instability mechanism of a mixed source islanded microgrid consisting of heterogeneous droop controlled inverter (DI) and synchronous generator (SG) is analyzed and verified. The analysis uses a simple DI-SG two-generator system, and then a second-order nonlinear dynamic oscillator is developed. Through the oscillator, time-variant damping is found to be cosine function of phase angle between the heterogeneous generators. When the islanded microgrid is subjected large disturbance, the damping approaches to smaller or even negative values. This finding reveals the root cause of transient instability of mixed source microgrid. Then, case studies of a simple test microgrid are performed to conduct the stability region estimation and time-domain simulations. Comparisons of different scenarios verify the findings of the transient instability mechanism.
3. Research on Data-Driven Transient Voltage Stability Assessment Considering Uncertainty
In order to evaluate the transient stability of renewable energy grid more effectively and measuring the epistemic uncertainty of the evaluation results, a power system transient voltage stability assessment method based on temporal convolution stochastic differential equation network (SDE-TCN) is proposed. The network takes the time series of the basic physical quantity measurement data of the power system as the input. Temporal residual convolution block based stochastic differential equation network is employed to extract the time series features. Meanwhile, the proposed method introduces the focal loss function to eliminate the imbalance of the samples and improve the accuracy of transient stability assessment. The drift network for learning prediction of stability and the diffusion network for learning uncertainty measurement in SDE-TCN network are trained respectively. As a result, test results on IEEE 39 bus system shows that this method can not only accurately evaluate the voltage transient stability of new energy power system, but also effectively quantify the uncertainty of stability evaluation..
4. Digital-Analog Hybrid Simulation of Renewable Energy Sent to Large-Scale AC Power Grid Through Zhangbei VSC-HVDC System
Zhangbei demonstration project is a typical case of large-scale renewable energy sending out through VSC-HVDC. It provides a feasible way for the transmission and utilization of renewable energy in Zhangbei area. Considering the large number of power electronic equipment in renewable energy power plants and VSC-HVDC systems, the potential risks of various types of oscillations exist. Previous studies have mostly focused on the renewable energy side. The research on the dynamic stability characteristics of large-scale power grid at the receiving end is relatively few. According to the operation data of North China Power Grid in 2021, a detailed EMT real-time simulation model of Zhangbei flexible DC transmission grid is built based on HYPERSIM, including renewable energy base, Zhangbei VSC-HVDC transmission project and large-scale AC power grid. Taking the super parallel computer SGI as the core equipment, the actual control and protection devices same as the project site is connected to the proposed model. Detailed simulation is carried out, for the faults near the renewable energy base, VSC-HVDC grid and AC power grid respectively. The AC / DC response in the process of fault and recovery is studied. Especially, a safety and stability control measure is taken for some AC side faults with poor recovery characteristics to ensure the safty and stability of the receiving power grid. The simulation results provided technical support for the commissioning test during operation.
5. Exploratory Study of Grid-Connected Photo-Voltaic System Operational Impacts on a Real Utility MV Distribution Network
The nature of the modern grid is rapidly changing with the increasing penetration of PV at MV and LV levels. This rising penetration reduces the dependency on conventional energy resources and leads to several issues that have not been seen by distribution system operators (DSOs) previously. This paper presents an exploratory study to investigate the impact of PV integration on an actual utility MV distribution feeder. \textcolor{black}{The impact of PV integration on power quality is studied using measurements from the power quality analyzers placed at different substations.} Moreover, the feeder simulation model is developed and validated with real PQA and SCADA data under similar loading conditions. Finally, the impact of PV on the network voltages and currents has been studied using the developed simulation model under various operating conditions to analyze the effect of PV integration on the distribution network.