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.

Power System Real-Time Monitoring by Using PMU-Based Robust State Estimation Method

Throughout the history of power system protection, researchers have strived to increase sensitivity and speed of apparatus protection systems without compromising security. With the significant technological advances in wide-area measurement systems, for transmission system protection, current differential protection scheme outscores alternatives like overcurrent and distance protection schemes. Therefore, in this paper, we address this challenge by proposing a methodology for adaptive control of the restraining region in a current differential plane. First an error analysis of conventional phasor approach for current differential protection is provided using the concept of dynamic phasor. Subsequently, we extend the methodology for protection of series compensated transmission lines. Finally, we also evaluate the speed versus accuracy conflict using phasorlets. Electromagnetic Transient Program simulations are used to substantiate the claims. The results demonstrate the utility of the proposed approach.

Adaptive Current Differential Protection Schemes for Transmission-Line Protection

This paper focuses on a multiagent-based distributed coordinated control for radial dc microgrid considering transmission time delays. First, a two-level multiagent system is constructed, where local control is formulated based on local states and executed by means of the first-level agent, and distributed coordinated control law is formulated based on wide-area information and executed by means of the secondary-level agent in order to improve the voltage control performances. Afterward, the research mainly focuses on designing the local controller and the distributed coordinated controller. For the purpose of robust stability, the local control is designed as local state-feedback-based $\text{H}_{\boldsymbol \infty }$ robust controller. It is worth mentioning that the distributed coordinated control consists of local state feedback control and decoupling coordinated control law that only come from adjacent distributed energy resource units. Moreover, the distributed coordinated controller is designed by means of delay-dependent $\text{H}_{\boldsymbol \infty }$ robust control method taking into account transmission time delays. Finally, the validity of the proposed control scheme is demonstrated by means of simulation results.

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Multiagent System-Based Distributed Coordinated Control for Radial DC Microgrid Considering Transmission Time Delays

The dynamic state estimation (DSE) applied to power systems with synchrophasor measurements would estimate the system's true state based on measurements and predictions. In this application, as phasor measurement units (PMUs) are not deployed at all power system buses, state predictions would enhance the redundancy of DSE input data. The significance of predicted and measured data in DSE is affected by their confidence levels, which are inversely proportional to the corresponding variances. In practice, power system states may undergo drastic changes during hourly load fluctuations, component outages, or network switchings. In such conditions, the inclusion of predicted values could degrade the power system state estimation. This paper presents a mixed-integer programming formulation of DSE that is capable of simultaneously discarding predicted values whenever sudden changes in the system state are detected. This feature enhances the DSE computation and will not require iterative executions. The proposed model accommodates system-wide synchronized measurements of PMUs, which could be of interest to smart grid applications in energy management systems. The voltage phasors at buses without PMUs are calculated via voltage and current measurements of adjacent buses, which are referred to as indirect measurements. The guide to the expression of uncertainty in measurement is used for computing the confidence level of indirect measurements based on uncertainties associated with PMU measurements as well as with transmission line parameters. Simulation studies are conducted on an illustrative three-bus example and the IEEE 57-bus power system, and the performance of the proposed model is thoroughly discussed.

Power System Dynamic State Estimation With Synchronized Phasor Measurements

Synchronized phasor measurement units (PMUs) are becoming a reality in more and more power sys- tems, mainly at the transmission level. This paper presents, in a tutorial manner, the benefits that existing and future State Estimators (SE) can achieve by incorporating these de- vices in the monitoring process. After a review of the rele- vant PMU technological aspects and the associated deploy- ment issues (observability, optimal location, etc.), the alter- native SE formulations in the presence of PMUs are revis- ited. Then, several application environments are separately addressed, regarding the enhancements potentially brought about by the use of PMUs.

On the use of PMUs in power system state estimation

This paper proposes a power system dynamic state estimation method (the improved fast-decoupled method) based on the phaser measurement unit (PMU) data and the SCADA data together, and points the shortage of the traditional state estimation methods This method forecasts the load flow data at the next time by the historical database, and combines the PMU data at the next time to dynamic state estimation for power systems. It indicates that this method not only shortens the computer time of the state estimation, but also increases the precision of the state estimation through analysis of example. This method is much more applied for the demand of the development of future power systems.

A Dynamic State Estimation method with PMU and SCADA measurement for power systems

Delay-independent decentralized stabilizer design for large interconnected power systems based on WAMS

This paper reports on the development of integrated protection for power system. The concept of integrated protection is introduced, in which a centralized protection system (or relay) provides the protection of multiple power plant or a substation. Examples are given of the protection schemes with the features of integrated protection which are currently under development. A novel integrated protection scheme for substation and network protection is described. The technique is based on the detection and processing of fault generated transient current signals, in which specially designed protection relays are installed at each substation of a network. The transient detection unit of the relay detects the fault generated transient current signals. The transient polarity identification algorithm is then applied to the transient signals to identify the polarity of the signal detected. The direction of a fault is determined by comparison of the polarity of the signals derived from all the line sections connected to the substation. The actual faulted section is identified by processing the directional information from various substations.

Integrated protection of power systems

This paper describes a new current differential relay. A current differential plane is presented firstly to depict different system statuses. Two traditional current differential protection schemes are discussed by plotting their operating and restraint region in the current-differential plane. A relay characteristic with more appropriate operating and restraint region is plotted in the plane by analyzing the tolerances a current differential relay has. Based on the analysis, a new scheme of current differential protection is designed. It is tolerant of channel delay asymmetry, power system impedance nonhomogeneity and CT saturation. Finally we prove the relay performance using simulations. It enhances current differential relay performance without a significant increase in cost.

A New Current Differential Protection Scheme for Two-Terminal Transmission Lines

This paper discusses the factors affecting interoperability between multi-vendor devices, the necessity for interoperability testing, and the types of interoperability should be conducted. It is recommended that proof-of-concept interoperability should be preformed before full scope integration, and it is crucial to adopt interoperability testing as part of site commissioning test. Interoperability testing is the next step forward after conformance test to ensure an IEC 61850 based substation automation system will interoperate as it is designed in the field. Conformance test can reduce the number of costly issues and problems during integration, site commissioning and operation. Devices passed conformance test may still subject to issues during integration, commissioning and operation. Conformance test does not mean interoperability test. Conformance testing cannot replace interoperability testing.

Zhi-qian Bo

Papers

A Dynamic State Estimation method with PMU and SCADA measurement for power systems

Delay-independent decentralized stabilizer design for large interconnected power systems based on WAMS

Integrated protection of power systems

A New Current Differential Protection Scheme for Two-Terminal Transmission Lines

The importance of IEC 61850 interoperability testing