Power Network Frequency Research Articles

Analysis Method of Primary Frequency Modulation Capability of Power System Based on GRNN

One of the most important key parameters in power network operation is power frequency. The power network will be affected by various disturbances in operation, and the frequency of the power network will show different fluctuations under different disturbances. Once the frequency of the power network deviates from the normal operation level, the power quality of the power network will decrease, and the power equipment will be in an abnormal operation state. With the development of power network, the scale of distributed microgrid with high uncertainty such as new energy is expanding increasingly, the proportion of UHVDC transmission lines is increasing, and the structure of power network is changing, which makes the regulation of power network frequency facing greater challenges. In this paper, relying on the mechanism of integrated load of power network and the participation of generator set in primary frequency modulation, the primary frequency modulation capability of 60 s power network under different frequency disturbance conditions is analysed, and the training and simulation prediction of GRNN generalized regression neural network prediction model are completed by using MATLAB software. By predicting of the generator set under different disturbances, the parameters related to the primary frequency modulation capability of the power network, such as the maximum amplitude of the active power fluctuation, the time when the maximum amplitude occurs and the time when the power network is restored to stability, are obtained to provide more accurate dispatching support for the dispatching side.

Subsynchronous Resonance in Independent Energo with Distributed Semiconductoring Load

A subsynchronous eleсtromechanical resonance in autonomous power systems is caused by the coincidence of the natural frequency of power network and one of the natural frequencies of turbogenerator unit in the electrical power plant. The occurrence and development of subsynchronous resonance causes subsynchronous oscillations of generators rotors, which are dangerous for shaft elements of turbogenerator units. Besides that, load angle oscillations having small amplitude under frequencies of 10-15 Hz create radial vibrations in bearing supports of turbogenerator units. The vibrations cause the emergency disconnection by vibration protection. In this paper the feature of subsynchronous resonance development in autonomous power system is present in the load power uncontrolled asynchronous motors and a large amount of similar frequency-controlled asynchronous various power drives through numerical simulations are discussed.

Study on Asynchronous Sampling in Digital Electrical Energy Metering Based on IEC61850

Technical issues regarding asynchronous sampling for digital electrical energy metering based on IEC 61850 are studied. Asynchronous sampling is inevitable when the power network frequency fluctuates. The additional metering error caused by asynchronous sampling is simulated and discussed. The additional error can be as big as 2% under typical conditions, which is unacceptable. Quasi-synchronous sampling algorithm is employed to reduce the error. Simulation result shows that it can reduce the error to an ignorable level. The error under extreme conditions is also simulated and discussed.

A Vector Decomposion FFT Algorithm to Improve Power Network Frequency

The measurement of power network running frequency is an important part of power quality test. For a variety of disturbances, anti-interfering and accuracy are required for the algorithm for frequency detecting. Benefited from FFT and efficient DSP chips, the Fourier transform algorithm can be used for reliable and efficient analysis of power network frequency. However, the spectrum leakage of FFT causes impact on the frequency detection accuracy, and the DSP's processing capacity is also limited. Therefore, vector decomposition window-added FFT algorithm based on fixed sampling rate and FFT points is discussed in this paper to handle the problem of impact caused by frequency leakage and to improve frequency detection accuracy. Good results can be achieved by using this algorithm as shown in the experiment.

Nonlinear Control of a Variable Speed Wind Generator

we are considering the problem of controlling wind turbine synchronous generators driven through AC/DC rectifiers and DC/AC inverters. The control objectives are threefold: (i) forcing the turbine speed to track a reference signal, (ii) regulating the DC Link voltage, (iii) enforcing power factor correction (PFC) with respect to the power network. First, a nonlinear model of the whole controlled system is developed in the Park-coordinates. Then, a nonlinear multi-loop controller is synthesized using the backstepping design technique. A formal analysis based on Lyapunov stability and average theory is developed to describe the control system performances. In addition to closed-loop global asymptotic stability, it is proved that all control objectives (turbine speed tracking, DC link voltage regulation, and unitary power factor) are asymptotically achieved up to small harmonic errors (ripples). The amplitudes of these harmonic errors depend on the power network frequency: the larger the power net frequency the smaller the error amplitudes. The above results are confirmed by simulations which, besides, show that the proposed regulator is quite robust with respect to uncertain changes of wind speed.