Application Of Modal Analysis On Harmonic Resonance Problem And Its Sensitivity Analysis In Power System

In this study, the cause, harm, current domestic and foreign research situation, as well as restraining approaches on harmonic resonance were discussed. In addition, both theoretical and experimental analysis methods were developed and studied.Harmonic resonance mainly manifests as overvoltage and overcurrent in power system. When harmonic resonance takes place, waveform distortion of voltage and current will be caused, which damages the power electric devices and even disturbs the normal operation of system. In our study, it was found that such resonance phenomenon is associated with the singularity of the network admittance matrix or loop impedance matrix. Thus, our research concentrates on harmonic resonance problems and analysis methods for parallel harmonic resonance, series harmonic resonance, Micro-grid harmonic resonance in power system. Also, the harmonic resonance sensitivity analysis was assessed.For the analysis of parallel harmonic resonance, the mathematical models of parallel harmonic resonance were established, and then frequency scan analysis and modal analysis processes were used to solve the parallel harmonic resonance problems. The characteristics of these two algorithms were also compared and analyzed. In addition, case study results confirm that more mechanic information of the parallel harmonic resonance can be achieved by modal analysis method. IEEE14-node and 30-node standard system was selected as an example and the results further illustrated the efficiency of the modal analysis method. In this test macro, the diagonal eigenvalue matrix and the left/right eigenvector matrices can be achieved through eigenvalue technique to analyze the node admittance matrix. Exact resonance frequency can be then obtained by analyzing the diagonal eigenvalue matrix, as well as the left and right eigenvector matrices show the potential to characterize the highest excitability and observability bus location, which is significant for the network programming and design in electrical power system.In another aspect of the analysis for parallel harmonic resonance of the system with branches containing independent constant voltage source, an improved modal analysis method combining modified nodal method with modal analysis was proposed to construct nodal matrix of the network. In this experiment,9-node system was used as a test system and the results demonstrated the efficiency and superiority of this improved modal analysis method in the field of harmonic resonance with branches containing independent constant voltage source.In the aspect of series harmonic resonance analysis, the characteristics of series harmonic resonance was initially analyzed and then loop impedance modal analysis method was developed to solve the series harmonic resonance problems. Based on the fundamental principle of modal analysis and mathematical model of series harmonic resonance, loop impedance modal analysis was used in test system. Compared with the traditional frequency scan result and the dummy branch method presented recently, the conclusion of the series harmonic resonance was reached.In addition, series harmonic resonance sensitivity analysis was evaluated according to eigenvalue theory and sensitivity analysis theory. In this sensitivity analysis, an analytical method was deduced and applied to determine which network components contribute significantly to a harmonic resonance phenomenon by calculating and comparing the sensitivities of each network component parameter under this resonance circumstance. Case study results further confirm the theoretical correctness. Moreover, our proposed method was applied in a practical industrial system which illustrated its validity and effectiveness. Thus, this practical method not only provides significant measures for harmonic resonance manage, but also support theoretical and experimental bases for the component parameter design.Finally, basing on the features of Micro-grid, modal analysis based harmonic resonance assessment method was introduced in harmonic resonance study in Micro-grid, and the assessment results revealing the frequencies where harmonic resonance existed and presented by clear index affecting area of the critical resonance. Beside, assessment results give guidelines for relieving and voiding harmonic resonance. The simulations tests results approve the analysis method is rational and effective.