Voltage Phase Angle Difference Research Articles

A new four‐step method to identify the parameters of transmission line based on SCADA data

Accurate parameters of transmission line (ParTL) are the basis of power system analysis. For high-voltage transmission line (TL), remote terminal units (RTUs) are widely installed to provide supervisory control and data acquisition (SCADA) measurements. Based on multiple snapshots of SCADA data at both ends of the TL, a four-step method to identify ParTL is proposed in this paper. In detail, based on the π-model of TL, the relationship between voltage phase angle difference (VPADs) and parameter identification is presented. And then, the general estimation formulation for VPADs is established. Furthermore, four steps to simplify and solve the formulation are detailed, that is, firstly after the approximated relationship between VPADs and reactance are derived, the estimation of VPADs at multiple snapshots is converted into the optimal problem with reactance of TL, just one variable, and the VPADs are estimated roughly; secondly based on the median estimation, the ParTL are identified roughly; thirdly, combined with Taylor series expansions and the alternating current power flow model, the VPADs are estimated accurately; fourthly, the ParTL are identified accurately. Finally, the results with simulated and field data verify the effectiveness and practicality of the proposed method.

Research on the Unstable Branch Screening Method for Power System With High-Proportion Wind Power

The sooner the system instability is predicted and the unstable branches are screened, the timelier emergency control can be implemented for a wind power system. In this paper, aiming at the problem that the existing unstable branch screening methods are lack prejudgment, an unstable branch screening method for power system with high-proportion wind power is proposed. Firstly, the equivalent external characteristics model of the wind farm was deduced. And based on this, the out-of-step oscillation characteristics of the power system with high proportion wind power was analyzed. Secondly, based on the oscillation characteristics, line weak-connection index (LWcI) was proposed to quantify the stability margin of a branch. Then an instability prediction method and an unstable branch screening method were proposed based on LWcI and voltage phase angle difference. Finally, the rapidity and effectiveness of the proposed method are verified through the simulation analysis of IEEE-118 system.

Islanding Detection Using a Micro-Synchrophasor for Distribution Systems with Distributed Generation

Distributed Generation (DG) has changed the power generation system to small-scale instead of large-scale generation. The demanding issue with the interconnection of DG is the detection of unintended islanding in a network. Several methods proposed in the literature show drawbacks such as high non-detection zones (NDZ) and higher tripping time. In this paper, the IEEE 13 bus distribution network with DGs like wind and solar power plants is integrated at two buses. Islanding is detected by utilizing data from a micro-synchrophasor located at the distribution grid and the DG. The micro-synchrophasor-based unintended islanding detection algorithm is based on parameters such as voltage, rate of change of voltage, frequency, rate of change of frequency, voltage phase angle difference and the rate of change of the voltage phase angle difference between the utility and the islanded grid. The proposed islanding detection algorithm discriminates between islanding and non-islanding conditions and is highly efficient under zero power mismatch conditions. The proposed method has null NDZ and satisfies the IEEE 1547 standard for DG tripping time. The effectiveness of the proposed IDM was verified when there are multiple DGs in the islanded grid. Also, the proposed method does not require additional hardware as it can be incorporated in digital relays with synchrophasor functionality.

Analysis of Unified Power Flow Controller Steady-State Power Flow Regulation Capability and Its Key Factors

As the latest generation of flexible AC transmission system (FACTS) devices, the unified power flow controller (UPFC) has comprehensive control capability and has played an important role in modern power systems. Research on UPFC steady-state power flow regulation capability is valuable for the design and operation of UPFC projects. To analyze the UPFC regulation capability, in this paper, the interaction between the UPFC and the external system is studied and the key factors of UPFC regulation capability are analyzed. It is demonstrated that the changes in the voltage magnitude and phase angle difference of UPFC-embedded line terminals will hinder the UPFC from regulating the power flow and decrease the UPFC regulation capability. Therefore, the UPFC power flow regulation capability is not only related to the parameters of the UPFC and its installation line, but also related to grid parameters. To analyze the UPFC active power flow regulation capability in practical power grids, the relationship between the UPFC regulation capability and grid parameters is deduced, and an estimation method is proposed to calculate the regulation range. Then, the estimation method is applied in the Chuxiong Power Grid and compared with power flow calculations. The results verify the UPFC power flow regulation characteristics given by the analysis and the effectiveness of the estimation method. Besides, it is shown that the estimation method can lower the requirements for the power flow calculation program, and reduce computation load.

Characteristics of PMU Phase Angle Difference Induced by Frequency Deviation of Crystal Oscillator and its Detection Method

Phasor measurement unit (PMU), which could provide high-frequency phasors including the amplitude and phase angle synchronized with Global Positioning System (GPS)/BeiDou Navigation Satellite System (BDS) signal, plays a vital role in dynamic monitoring of power systems. However, if the GPS/BDS signal could not be received, the time of PMU, which depends on the crystal oscillator (CO), would cause measurement deviation due to frequency shifts of CO, and then the PMU data would engage deviations and deteriorate the relevant applications. In recognizing the above problems, this article proposes a method to detect the frequency deviation of the crystal oscillator (FDCO) based on the correlation coefficient, according to its relation with the characteristic of the voltage phase angle difference (VPAD) between the two ends of the line. In detail, firstly, the quality of the VPAD of PMU between the two ends of the line is analyzed and the related problem is stated. Secondly, the characteristics of PMU data, when FDCO exists, are derived and analyzed, especially the VPAD between the line, and the suitability of the data for detecting the FDCO is discussed. Thirdly, the ideas and specific methods of detecting the FDCO in case of malfunction of GPS/BDS signal are proposed. Furthermore, the validity of the proposed method with simulation data and modified measured data is presented. Finally, the conjectures on the reasons for the approximately constant VPAD deviation in the previous section are discussed.

Assessment of PMU‐based wide‐area angle criterion for fault detection in microgrid

The penetration of distributed generation in the power distribution system has increased significantly in recent years, bringing serious protection challenges. Hence, it is mandated to develop effective and reliable fault detection scheme for present-day microgrid environment. This study presents a phasor measurement unit-based (PMU) wide-area phase angle criterion for building a protection system for the microgrid. The absolute value of the rate of change of voltage phase angle difference between the point of common coupling and the bus closest to the fault point is utilised for fault detection in grid connected as well as in the islanded modes of operation. C37.118.1 complied PMUs are employed at the appropriate locations for accurate and faithful measurement of voltage phase angle and the rate of angle difference (RAD) for detecting faulted conditions. PMUs are connected to phasor data concentrator, which receives the time synchronised phasor data and acts as a centralised processing unit. The proposed protection index has been extensively validated on MATLAB/Simulink environment as well as the real-time digital simulator with external PMUs. The test results show that the proposed RAD is a potential candidate for providing effective fault detection measure for microgrid including large variations in operating conditions.

Linear Approximations for the Influence of Phasor Angle Difference Errors on Line Parameter Calculation

Phase angle measurements from phasor measurement units (PMUs) may have errors that can significantly affect line parameter calculation. In this paper, approximate expressions for the influence of phase angle difference errors on line parameter calculation are derived. Specifically, first the PMU phase angle error at both ends of a line is analyzed and an equivalent synchronization error is defined; second, approximated expressions for the influence of current and voltage phase angle difference error on the line parameters are derived. The voltage amplitude ratio on the relative error of line reactance, resistance, and capacitance measurement through the π-type equivalent model are considered. The influence of voltage and current phase angle difference error on reactance and resistance is shown from the perspective of relative sensitivity. The relative sensitivity expressions in active power form are given and the identifiable conditions of line reactance parameters based on PMU data are given. In addition, this paper presents the influence mechanism of voltage magnitude and discusses the case of synchronization issue. Finally, the accuracy of the sensitivity equations is verified by simulations, and the influence of the voltage amplitude ratio and the line flow on the identification result is quantitatively analyzed.

Effect of the approximation of voltage angle difference on the OPF algorithms in the power network

In real-time applications involving power flow equations, measuring of voltage phase angle difference of the connected buses is essential. However, it needs special techniques to measure voltage angle difference, which may enlarge the computational burden of the working controller and hence, may make the control process slow. In this paper, authors investigate the approximation of angle difference to zero and its effects on the convergence speed and optimal solutions of a distributed algorithm. To test this approximation, a distributed nonlinear algorithm is proposed to optimize the multi-objective function which includes power loss, voltage deviation and cost of reactive power generation, by controlling the reactive power generations from distributed generators. Authors investigate the reasons which may outlaw making this approximation and finally, propose a condition to make such approximation. Importance of making this approximation in terms of fast convergence of the algorithms is also illustrated.

Distributed Enforcement of Phase-Cohesiveness for Frequency Control of Islanded Inverter-Based Microgrids

In this paper, we propose a frequency controller for lossless microgrids which achieves a desired active power load sharing while regulating system frequency to some nominal value. The control scheme is based on the slow readjustment of the active power reference of each inverter, i.e., each inverter aims to track a slowly-varying reference that is set sufficiently close to its actual active power injection and moved slowly to reach some desired injection value. This way, the control enforces the trajectory to satisfy the so-called phase-cohesiveness property, i.e., the absolute value of the voltage phase angle difference across electrical lines is smaller than $\frac{\pi}{2}$ , which ensures that the system remains stable at all times and the actual active power injections track the slowly-varying reference. We also propose a distributed method to find desired injections, which satisfy the phase-cohesiveness property for tree networks as well as for some cyclic networks. We also discuss implementation aspects of the proposed control scheme and demonstrate its feasibility using a 9-bus microgrid.

Enhancement of power system damping using VSC-based series connected FACTS controllers

An equivalent model is proposed to analyse the capabilities of voltage source converter (VSC)-based series connected flexible AC transmission system (FACTS) controllers of various types to damp power system oscillations. A universal control strategy using a fuzzy logic method is developed for controlling these VSC-based series connected FACTS controllers. Only the magnitude of the injected voltage needs to be controlled, along with its phase angle which is always set to be constant at π/2 with respect to different reference voltage vectors for the different controllers. Local measurable signal — voltage phase angle difference between two local buses — is selected as an input base. Two inputs, namely the speed rate and acceleration, derived from the phase angle difference, are required for the fuzzy controller, which is robust and easy to tune, to damp power system oscillations. Case studies for a single machine infinite bus (SMIB) and two-machine test systems are conducted at the switch level using the well-established PSCAD/EMTDC software package.