Synchronized phasor measurements have become a mature technology with several international manufacturers offering commercial phasor measurement units (PMUs) which meet the prevailing industry ...standard for synchrophasors. With the occurrence of major blackouts in many power systems around the world, the value of data provided by PMUs has been recognized, and installation of PMUs on power transmission networks of most major power systems has become an important current activity. This paper provides a brief introduction to the PMU and wide-area measurement system (WAMS) technology and discusses the uses of these measurements for improved monitoring, protection, and control of power networks.
Doubly fed induction generator (DFIG) wind turbines with virtual inertia control are coupled to power system in dynamic characteristics, and the control input of virtual inertia control is directly ...affected by the tracking ability of phase-locked loop (PLL). Thus, it is urgent to study the impact of DFIG wind turbines with virtual inertia control on power system small-signal stability considering the effects of PLL. First, based on DFIG operation characteristic and control strategy, a small-signal model of interconnected system with DFIG integration considering PLL and virtual inertial control is established. Second, the attenuation time constants of DFIG state variables are calculated, and according to the attenuation speeds of different state variables and the coupling between them, it is found out that PLL and virtual inertia are the main factors that affect the coupling between DFIG and synchronous generators. And then, considering that both PLL and virtual inertia control will affect the oscillation modes of synchronous generators, analytical method is used to reveal system small-signal stability under the joint effects of the two factors quantitatively. Analysis results show that, for DFIG wind turbines with virtual inertial control, PLL affects system damping mainly by affecting the participation of virtual inertia in the system. The smaller the PI parameters of PLL are, the smaller the participation factor of virtual inertia control state variables in the interarea oscillation mode is, and the bigger the electromechanical oscillation mode damping ratio is. Simulation results verify the reasonableness of the established model and the possibility that virtual inertia control may cause system small-signal stability to deteriorate in multimachine system.
Uncalibrated instrument transformers present at the inputs of phasor measurement units (PMUs) can significantly degrade their outputs. This also causes problems in downstream applications that use ...PMU data. This paper presents a method for calibrating voltage transformers online using synchrophasor measurements. The proposed approach aims to find the optimal locations where good quality measurements must be added in order to bring the calibration error of all the measurements below a predefined threshold. The IEEE 118-bus system, the IEEE 300-bus system, and a 2383-bus Polish system have been used as the test systems for this analysis. The advantage of the proposed approach is its effectiveness and robustness.
In view of the time delay and potential information loss problem in wide-area data acquisition, a wide-area backup protection algorithm based on the distance protection fitting factor is proposed in ...this paper. First, the contribution of the distance protection operating information to fault identification is defined as the distance protection contribution degree. Second, the protection fitness function and protection fitness expectation function are constructed using the distance protection contribution degree as the weight. And then, the distance protection fitting factor is gained by calculating the division of the protection fitness function by the protection fitness expectation function. Thus, the fault line can be identified. Finally, simulation tests on the IEEE 10-machine 39-bus system and Guizhou Duyun real-time digital simulator verify that the proposed method is not affected by the time delay in wide-area data acquisition and is able to identify the fault line correctly even when a large amount of distance protection operating information is lost or in error. Meanwhile, the uncertainty problem in traditional weight setting due to reliance on subjective experience is avoided. Besides, being small in computation amount, the proposed method is easy to implement in engineering practice.
Utilities across the world are seeing increased penetration of inverter-based renewable generation (RG) in their systems. These RGs have ride through curves programmed in them which define operating ...conditions that need to be satisfied during electrical disturbances. If they are violated, the RGs are tripped offline. In systems with large amounts of RGs tightly coupled electrically, there can be disturbances that cause sudden loss of a large number of RGs, which will then considerably exacerbate the stability of the system. Such a phenomenon is not captured by the existing direct methods for TSA. In this paper, by treating RG-rich systems as non-linear switched systems as opposed to the traditional approach of treating this tripping phenomenon as an instability, an approach utilizing multiple low voltage ride through constrained stability regions (CSRs) is proposed for capturing unstable fault clearing times. The CSRs are estimated through Lyapunov functions found using sum of squares programming. The effectiveness of the proposed technique is demonstrated using a three-machine system.
•The method is well adaptable to different operation modes.•The method is strongly immune to the transition resistance.•Unaffected by the weak feed characteristics of the wind generator collector ...system.•The method is not affected by fault on the adjacent line.
In view of the sensitivity and selectivity problems in DFIG (doubly-fed induction generator) wind farm collector line protection, a new adaptive distance protection scheme is proposed. First, according to the geometric distribution characteristics of the collector line voltage and current, the equation of voltage drop from the relaying point to the fault point is established and the adaptive setting coefficient is calculated. On this basis, a new adaptive distance protection criterion is formed according to the phase relationship between the fault current and the measured current. Wind farm simulation tests on RTDS verify that, the proposed method is well adaptable to different operation modes, strongly immune to the fault resistance and unaffected by the weak feed characteristics of the wind generator collector system.
Concerning the stochastic excitation caused by wind power fluctuation and the stochastic parameter of virtual inertia caused by wind speed uncertainty, a power system stability analysis method ...considering the Wiener noise is proposed in this paper. First, based on the reduced-order model of DFIG retaining virtual inertia control and phase-locked loop (phase-locked loop) dynamics, the analytic function relationship between stochastic parameters and elements in the state matrix is derived using the sensitivity analysis method; thus, the model of interconnected system with stochastic parameters considering the Wiener noise is established. And by constructing the Lyapunov functional containing the model of stochastic parameters, the linear matrix inequality (LMI) that satisfies the robust stochastic stability criterion is derived. Furthermore, by transforming the solving of LMI to a feasibility problem, the stability of system is identified. And then, by calculating online system instability probability under the current operating condition, the probability stability analysis method is proposed. On this basis, a system stochastic stability degree index is defined in this paper, which quantifies the effect of stochastic parameters on system small-signal stability, and could provide more effective information for the safe and stable operation of power system. Simulation tests on the IEEE four-generator two-area system and the New England 10-machine 39-bus system verify that the proposed method could effectively identify the small-signal stability of power system under the joint influence of stochastic parameter and stochastic external excitation, and is applicable to complex system with multiple generators.
Based on the boundary characteristic of a dc transmission line, the response of transient harmonic current in the line-commutated converter HVDC transmission system is analyzed under various fault ...conditions in this paper. A new transient harmonic current protection scheme is proposed. The discrete Fourier transform is used to extract transient harmonic currents at both terminals of the dc transmission line and the type of fault can be identified by the transient harmonic currents. Two main factors including fault resistance and fault location that affect performance of the protection are also discussed in this study. The test system is modeled based on the CIGRE benchmark including distributed parameters of the dc transmission line. Comprehensive test studies show that the performance of the transient harmonic current protection scheme is encouraging. It can not only identify internal faults and external faults correctly and quickly, but also can respond to high ground resistance faults.
In view of the problem that the detailed model of doubly-fed induction generator (DFIG) considering virtual inertia control is high ordered and difficult to analyse, a reduced-order model for DFIG ...that is applicable to small-signal stability analysis is presented. First, according to the attenuating speed of each state variable, the dynamic characteristics of different components of DFIG are explored from the time scale perspective. On this basis, considering the electromechanical coupling characteristic of DFIG, the third-order simplified model retaining the dynamic of virtual inertia control and phase-locked loop is derived. Moreover then, the dynamic model of inter-connected system with reduced-order model integration is established. Finally, the attenuation time constant of each state variable of DFIG detailed model is calculated. Simulation tests on the New England 10-generator 39-bus test system verify that compared with detailed model of DFIG, the presented reduced-order model could reflect the dynamic characteristics of power system under small-signal disturbance more accurately, with greatly reduced computation amount.
This paper presents an algorithm for better phasor estimation at off-nominal frequencies. The sampling rate remains unchanged, but instead the amplitude of the sample values within a buffer is ...altered in order to give a signal of the same amplitude but different frequency. The re-calculation of the samples is done by second order spline interpolation. The effect is that the signal frequency appears to be changed to nominal. The algorithm requires knowledge of the frequency, which has to be determined by other means. It can only be used for filters with a finite window length, such as finite-impulse response filters. The proposed algorithm gives a maximum magnitude error of less than 0.1% for frequency deviations up to 10% from nominal. The proposed algorithm does not need any over-sampling and re-sampling to a lower sampling rate. It helps preserve the desired frequency characteristics of filters at off-nominal frequencies. This paper presents a simulation example, which uses an off-nominal test signal of 55 Hz with a 10% second harmonic. The result indicates that this test signal might cause problems for some phasor algorithms, but the proposed sample value adjustment algorithm handles this test case efficiently and complies with Level 1 of IEEE Standard C37.118-2005.
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