The Research Of Detection And Management Framework Of Harmonic In The Environment Of Smart Grid

With the development of smart grid, new types of devices are allowed to connected to the grid. But Most of these devices have a negative impact on power quality. Because of the optimization features, smart grid has higher and stricter demands on power quality. Also in today’s "low-carbon economy" of the electricity market model, a comprehensive power quality management system should be established to scientifically manage the control and the influence of power generators, power suppliers and electricity users, which can achieve the goal of energy saving and green power. According to the new requirements of smart grid, this paper focuses on the harmonics, which are very important for power quality. The research of power quality detection and management framework is completed with harmonic detection, harmonic losses calculation, harmonic source localization and harmonic responsibility quantization.Due to the application of electronic transformers and merging units in the digital substation, data acquisition mode is changed and the original harmonic detection algorithm is no longer applicable. A correction algorithm is used in this paper, by which the amplitudes of harmonics can be estimated from the two neighboring spectral lines. As the input waveform is a square wave with50%duty cycle, harmonic distortion is calculated respectively by correction algorithm and uncorrected algorithm. After compared with the theoretical values, the results prove that correction algorithm is more accurate than uncorrected algorithm, which can satisfy the requirements of the merging unit.Harmonic power increases the loss of power system, and understanding the harmonic loss ratio of the power network has guiding significance for the power company to draw up conserve energy measure. This paper uses equivalent resistance method to estimate harmonic loss in low-voltage distribution network with the measured data, which proves that harmonic losse will cause a great economic loss. Then this paper proposed a method by using harmonic distortion and the loss rate of platform area method based on measured loss to estimate harmonic loss, which is more suitable for the power quality monitoring system.In order to create a fair and reasonable electricity market environment, harmonic source localization problem in the power grid has become a technical issue to be sovled urgently. In this paper, the problem of the harmonic source localization based on harmonic impedance is deeply researched. After comparing a various kinds of methods for harmonic impedance calculation, we choose the binary linear regression method. The simulation model is set up and programmed with Matlab. According to the voltage and current of the point of common coupling, harmonic impedance can be estimated. Then the customers’ harmonic emission level can be calculated. The error between the estimated value of harmonic impedance and the set value is very small, which proves the accuracy of this method.However, there is not only one harmonic source in the power system. So it is necessary to effectively distinguish the responsibility of each harmonic source. After derivating the formulas of harmonic voltage, harmonic current and harmonic power apportioned by the system side and the user side, it proves that purely relying on harmonic current or voltage is not accurate for harmonic responsibility quantization. This paper chooses harmonic power to quantity harmonic responsibility and simulates a situation that two nonlinear users connected to the electricity grid with Matlab. The harmonic power apportioned by the system side and the user side proves the feasibility of this method.