Research On The Key Issues And Application For The Quick Response Harmonic Mitigation Technique

In recent years, as part of the development strategy of the grid, the power quality issue has drawn more and more attention. The Shunt Active Power Filter(APF), as an effective advanced power electronic device to suppress harmonic current, is one of the effective measures to solve these problems. Although these years APF has become a hot research topic and the compensation performance of APF are also rising, there is still insufficient in the compensation effect of the Shunt Active Power Filter in some complex environment. Meanwhile, it also needs to analysis and research on these specific issues. For example, how to detect harmonic effectively in larger voltage distortion environment; how to achieve a better dynamic response and gain a good harmonic track effect; how to achieve better system parameter design, etc.. Therefore, according to the analysis above, this paper analyzes and studies the key technology and application of the harmonic mitigation.How to detect the harmonic current quickly and accurately is the foundation of achieving a good compensation effect for APF. After a variety of harmonic current detection algorithms are studied, the research finds it is difficult for most algorithms to track and detect the harmonic effectively and accurately when there is larger distortion or voltage frequency deviation in the grid voltage. Therefore, this paper analyzes the mathematical model of instantaneous voltage in normed space and puts forward the strategy that the standard voltage waveform is obtained through the application of variational method in function normed space, according to the minimum power consumption principle of the compensation system. Thereout, the standard positive sequence voltage signal and the distortion current component, as derivatives, are gained. Meanwhile, the extracting method of standard positive sequence voltage based on normed space can also be combined with a variety of current detection strategies to meet the demand of more detection and tracking requirements. In the end, the feasibility and effectiveness of this strategy is verified by comparing the simulation with the traditional harmonic current detection strategy.In order to achieve a better dynamic response and a better overall compensation effect, this paper puts forward a new kind of composite compensation current control strategy, combining the PI control with the improved dual repetitive control effectively. Firstly, the front adjust parameters and the PI control are added to the conventional repetitive control structure. The dynamic effect is improved and the astatic control is achieved through the specific analysis of the mathematical model and the regulation of parameters of the front and the limitation of the parameter range. And on this basis, the improved repetitive control structure is inserted in the feedback control in parallel to form a double mode repetitive controller. Moreover, detailed parameters optimization design and the calculation process are given. In the end of this paper, the effectiveness and feasibility of the compound control algorithm is checked through building sudden load simulation, the contrast verification experiment of dynamic characteristics and steady state tests. The simulation results and experiment waveforms manifest that the compound control algorithm has a very good dynamic response and a good overall compensation effect.That there are many switch states in the APF system of the three-phase four wire makes the voltage modulation complex, so the traditional two-dimensional modulation strategy is difficult to meet the demand. Its shortcomings reveals more apparently in the three-phase four-line system. Combining the space vector modulation strategy with the conventional control method has a good compensation effect. Therefore, this paper proposes the3D space vector modulation strategy based on the natural coordinate system (Three-dimensional space vector modulation,3D-SVM), analyzes and studies the tetrahedron decision process. The reference vector synthesis is made clear and intuitive by the classification combined with the pointer arithmetic. Moreover, the calculation of reference vector function time and the effective arrangement of time order are discussed. In order to avoid the same bridge arms of the switch connecting directly, which causes system faults and adds the dead time, this paper studies the influence of dead time effect on the overall compensation effect, and a set of strategies based on the prediction and compensation of dead time effect, which can effectively reduce the control error caused by the dead time and improve the accuracy of the overall compensation.This paper puts forward a method of designing practical LCL filter parameters applied to the shunt active power filter (SAPF). Firstly, the harmonic model of the application of the LCL filter parameters to the SAP is built. Secondly, the changing relationship between the filter parameters and the harmonic frequency is studied. Parameters are determined in accordance with the limited scope of LCL resonance frequency, the ratio of capacitor branch impedance parameters, the three-dimensional relation curve between the inductance parameter ratio and the resonant frequency as well as the attenuation performance requirements of low frequency and high frequency respectively. Thirdly, the effectiveness and feasibility of the parameter design method is verified by simulations and prototype tests.In order to achieve a faster dynamic response speed and a better overall compensation effect, this paper gives detailed analysis process of the prototype parameter design, including the main circuit topology structure analysis, the main circuit power component analysis, the analysis of the dc side voltage and dc side capacitor, etc.. And on this basis, the designs of the main control chip of the control system and each module circuit are studied. Finally, the control algorithms mentioned above are tested and analyzed by the laboratory prototype.