Approach to Enhance the Robustness on PMU-Based Power System Dynamic Equivalent Modeling

In order to avoid detailed active distribution network modeling in the context of stability analysis, complexity-reduced equivalent dynamic models, which reproduce substantial dynamic behavior of the detailed network, are applied. The Sensitivity-Technology-Control-Clustered Approach has been introduced in previous work as a method for creating equivalent dynamic models under proper consideration of dispersed generation, in particular also covering grid forming converters, which emulate inertia. However, the resulting equivalent dynamic model is parameterized according to one specific operating point of the corresponding detailed network. This work analyses the generalizability of this equivalent dynamic model with respect to changes in the corresponding detailed network’s operating point. Also, an update of the equivalent dynamic model to new operating points is proposed. To this end, the equivalent dynamic model derived from a base scenario is validated against the detailed network at different operating points and for different faults. Additionally, relevant parameters are identified, whose re-parameterization adapts the equivalent model to new operating points. We show that the equivalent model stays valid for small changes of the operating point of the detailed network and an update of relevant parameters of the equivalent model allows for a simplified adaptation to new operating points.

Fault recorders can track the transients in the power system during a fault. However, they cannot provide a wide area picture of the power system operating condition. The provision to track the transients is of great interest for the power system operators. In this paper, a two-stage state estimator (SE), based on both conventional and phasor measurement unit (PMU) measurements, is presented. The estimator is able to track the dynamics of the power system states during a fault. The advantage of the proposed SE is that it does not require full power system observability by the PMU measurements. The two-stage SE was successfully tested on the IEEE 14 and 118 bus systems.

This paper presents a novel coordinated algorithm, Fast Distributed State Estimation with Linear Coordination (FDSELC), considering Phasor Measurement Units (PMUs) measurements at both subsystem and coordination levels. At the subsystem level, the estimators apply augmented Fast Decoupled State Estimation algorithm to reduce the computational time at the first step. At the coordination level, linear estimators based on PMUs measurements are able to coordinate the voltage states of boundary buses, which lead to the further improvement of computational performance. Tests on the IEEE 118-bus system demonstrate the performance of the novel FDSELC algorithms. The results are compared with centralized and other distributed state estimation algorithms in terms of both the estimation quality and computational cost. In addition, the proposed FDSELC algorithm with the distributed control architecture is suitable for future smart grids. In this situation, a large power grid can be decomposed into subsystems, and those subsystems can be estimated, monitored and controlled separately.

Synchrophasor technology contributes significantly to the power system transformation into smart grid since it enables the wide area monitoring and control concept. At the same time, its integration to the smart grid imposes new cyber security challenges in these cyber-physical systems. The key element of the synchrophasor technology is the Phasor Measurement Unit (PMU) which provides synchronized measurements to the control center with a fast reporting rate. The PMU measurements are kept in a Phasor Data Concentrator (PDC) which collects and time aligns measurements from different PMUs. The communication between PMUs and PDC is defined by the synchrophasor communication standard, C37.118.2-2011, which lacks security mechanisms and hence it is vulnerable to cyber-attacks. Consequently, an intrusion detection system (IDS) that can detect PMU measurement manipulation is necessary to maintain the integrity and reliability of the PMU measurements. In this paper, a Synchrophasor Specific Intrusion Detection System that utilizes a PMU's behavioral model to detect data manipulation attacks against PMU measurements is proposed. The proposed IDS approach is tested and validated using a hardware in the loop setup for power systems considering an actual PMU.

Phasor measurement units (PMUs) are being deployed in incremental fashion in power systems. While PMUs may improve the quality of the state estimator (SE), the limited number of PMUs installed may not ensure complete observability of the system. Hybrid state estimator (HSE), considering PMU as well as conventional measurements, is therefore still needed for monitoring the power system. This article proposes a new algorithm belonging to the group of HSEs. Even in case of incomplete observability with PMUs, a two-step state estimation algorithm is presented to optimally utilize the PMU measurements, along with the conventional measurements from supervisory control and data acquisition (SCADA) system. A projection statistic based robust SE is used, when both SCADA and PMU measurements are available. During the interval between two successive arrivals of SCADA measurements, a linear SE is proposed, to exploit the available PMU measurements. The particular advantage of the proposed algorithm is its robustness and insensitivity to bad data. The proposed methods are successfully tested on IEEE-14 bus, 118 bus, and NRPG Indian 246 bus systems.

This paper proposes an online identification method utilizing phasor measurement unit (PMU) measurements, symmetric dot pattern (SDP) graphs, and the ResNet50‐L1 M model to facilitate the rapid identification of metering relative errors among interconnected capacitor voltage transformers (CVTs) in wide‐area substations within power systems. First, PMUs measured the three‐phase voltage data from interconnected CVTs across wide‐area substations. The amplitude differences of the three‐phase voltages were converted into Euclidean distances, which were then transformed into SDP graphs, with each type of metering relative error corresponding to a distinct SDP graph. The ResNet50‐L1 M model was established by integrating an L1 norm‐based attention mechanism into the ResNet50 architecture. This model was then trained on CVT SDP graphs representing various error states to develop an online error identification system. The effectiveness of the proposed method was evaluated based on data from the “Houshou transmission line” in Ningxia province, which connects the 330 kV Niushoushan substation and the 330 kV Houqiao substation operated by the State Grid Corporation of China. With 16 different error states tested, the model achieved an identification accuracy rate of 89.39%, demonstrating a notable improvement over other methods in comparative tests.

With the UHV (Ultra High Voltage) power grid construction and the interconnection of regional power grids, the scale of power grids in China is increasing rapidly. At the same time, significant uncertainty and variability is being introduced into power grid operation with the integration of large-scale renewable energy in power systems. All of these pose an enormous challenge to the operation control of power systems in China. For a long time, online static security analysis, as an important part of EMS (Energy Management System), has been an effective tool for power grid operation. However, it is increasingly difficult for traditional static security analysis in serial computing mode to be online applied in bulk power grids in China. A new practical parallel approach for online static security analysis is put forward in this paper. A multithread parallelism is introduced into contingency screening, detailed contingency evaluation and decision support for reducing the execution time. By employing the multithread technology, the hardware resources of multi-processor/multi-core computer can be fully used and the program can be speeded up effectively. The performance of the parallel static security analysis is demonstrated by tests on two large-scale power systems. The test results show that the proposed method can be online applied in real bulk power grids.

Summary Low-frequency oscillations (LFOs) are inherent phenomena of modern interconnected electrical power systems, essentially caused by the continuous exchange of momentum among rotating masses. It is widely recognized that LFOs can be induced by both the occurrence of multiple disturbances and the existence of periodic disturbance sources. LFOs can be classified into negative damped oscillations and forced power oscillations. The former can be suppressed by standard controllers (e.g., power system stabilizers). The latter cannot be eliminated until the disturbance source is removed or isolated. Thus, locating the forced disturbance source promptly and accurately is crucial. In this paper, a traditional energy function, simplified and improved, with a new decomposition way to show the direction of energy flow is proposed. Energy associated with the LFO is decomposed into oscillating component and quasi-steady component at the aim of analyzing the inducing multiple disturbances. The branch energy is hence decomposed into periodic and aperiodic components. By identifying the direction along which the aperiodic component is propagated and dissipated, the periodic forced disturbance source could be located rapidly and accurately. The proposed energy decomposition method provides a novel idea to judge the direction along which the dissipated energy flows. The effectiveness and feasibility of the proposed method were verified by simulation results obtained on an actual large-scale interconnected power grid in China. Copyright © 2015 John Wiley & Sons, Ltd.

The subject of the article is the technique for determination of the automatic excitation controller (AEC) parameters based on measurements from phasor measurement units (PMU). This paper shows the possibility of using PMU measurements for determining the synchronous generator AEC parameters. The article considers the type of the AEC which is ARV-MT of the Russian production. By using the simulation in the hardware and software system RTDS (Real-Time Digital Simulator), PMU measurements have been obtained for different modes of the AEC operation. Processing of the results has been carried out in MATLAB. The developed technique is based on the processing of obtained measurements by optimization algorithm. As a result of the comparative analysis, the most suitable type of optimization has been chosen. The possibility of PMU measurements use for determining the AEC parameters in different modes of its operation is shown. Also, the results of application of the technique for cases of a different power level noise in the circuit is investigated. The developed technique determines the AEC parameters with a sufficient accuracy by using PMU measurements. Thus, the technique allows one to extend the field of PMU application, and, being further developed, will allow one to monitor the AEC and calculate its parameters in real time.

Accurate real-time states provided by the state estimator are critical for power system reliable operation and control. This paper proposes a novel phasor measurement unit (PMU)-based robust state estimation method (PRSEM) to real-time monitor a power system under different operation conditions. To be specific, an adaptive weight assignment function to dynamically adjust the measurement weight based on the distance of big unwanted disturbances from the PMU measurements is proposed to increase algorithm robustness. Furthermore, a statistical test-based interpolation matrix ${H}$ updating judgment strategy is proposed. The processed and resynced PMU information are used as priori information and incorporated to the modified weighted least square estimation to address the measurements imperfect synchronization between supervisory control and data acquisition and PMU measurements. Finally, the innovation analysis-based bad data (BD) detection method, which can handle the smearing effect and critical measurement errors, is presented. We evaluate PRSEM by using IEEE benchmark test systems and a realistic utility system. The numerical results indicate that, in short computation time, PRSEM can effectively track the system real-time states with good robustness and can address several kinds of BD.

With the increase of the running time of the power grid, the equipment is old and damaged inevitably. When the old equipment is replaced, some components of the new equipment may be inconsistent with the old equipment. For example, the value of the line circuit breaker closing resistor will cause the difference in the resistance value of the three-phase closing resistor. There are few studies on the influence of different closing resistor values on overvoltage of three-phase circuit breaker. It is necessary to analyze the possible overvoltage risk in the process of line closing operation in this case. Taking the 750kV power grid in China as an example, combined with the value of the closing resistor in the actual power grid, the overvoltage of line energizing and single-phase reclosing are calculated and analyzed under 570/500/425Ω, 425/425/570Ω, 425/570/1500Ω three circuit breaker closing resistor configuration schemes. The influence of different value of three-phase closing resistor on overvoltage is presented. The research results can provide technical basis for optimized configuration of circuit breakers and the safe operation of the project.

Letters to the Editor on the paper ‘Dynamic Wavelet and Equivalent Models’ by O.M. Boaghe and S.A. Billings

This paper presents an adaptive wide-area control strategy based on energy function. The proposed method enhances the post-fault oscillation damping capability of Static Var Compensators (SVC) by incorporating load dynamics in the wide-area controller design that adapts to load variations. The load dynamics are obtained using Phasor Measurement Units (PMU) through load power and voltage data measurements, which are used to estimate a Moving Average (MA) dynamic load model. The obtained load model is then integrated into the wide-area controller to obtain the required SVC supplementary control action which modulates the load power in response to a disturbance based on inter-area dynamics obtained by employing a nonlinear Kalman filter and PMU measurements. The performance of the proposed strategy is evaluated on the simplified 14 generator model of the southeast Australian power system by using composite load models comprised of induction motor loads of various sizes and combinations. The obtained results show significant improvements in the system stability when the proposed control strategy is applied.

Based on an analysis of the misunderstanding and problems concerning wind power development, this paper summarizes the experiences of coordinated development of wind power and power grids in typical countries, proposes the principles and strategies for the coordinated development of wind power and power grids in China. Technically, bidirectional friendly technologies should be deployed to ensure the security of power system. In regulatory term, a complete and standardized regulatory strategy is key to harmonious interaction among different stakeholders concerning wind development. Incentive policies should be comprehensive, foreseeable and sustainable. Related measures and suggestions for large scale development of wind power in China are put forward.

In this paper, we investigate a design method for a cable-driven snake arm maintainer (SAM) and its dynamics modelling. A SAM can provide redundant degrees of freedom and high structural stiffness, as well as high load capacity and a simplified structure ideal for various narrow and extreme working environments, such as nuclear power plants. However, their serial-parallel configuration and cable drive system make the dynamics of a SAM strongly coupled, which is not conducive to accurate control. In this paper, we propose an equivalent dynamics modelling method for the strongly coupled dynamic characteristics of each joint cable. The cable traction dynamics are forcibly decoupled using force analysis and joint torque equivalent transformation. Then, the forcibly equivalent dynamic model is obtained based on traditional series robot dynamic modelling methods (Lagrangian method, etc.). To verify the correctness of the equivalent dynamics, a simple model-based controller is established. In addition, a SAM prototype is produced to collect joint angles and cable forces at different trajectories. Finally, the results of the equivalent dynamics control simulation and the prototype tests demonstrate the validity of the SAM structural design and the equivalent dynamics model.