Research On Control Strategies And Engineering Application Of High-power Harmonic Eliminating In Power Station

The paper discussed the harmonic detecting, eliminating and the reactive power compensation for the power station. It lucubrated the main technologies of the high-power Shunt Hybrid Active Power Filter (SHAPF), which includes its harmonic detecting method, working performances, optimal controlling strategy and its practical realization.Firstly, the paper proposed a new method which based on the ip-iq theorem to detect the individual harmonics and the 1st reactive current. Compared to the ip-iq theorem, it leaves out the conversations between the 3-phase coordinate and 2-phase coordinate. It can also apply directly to the single-phase power systems, 3-phase-3-line power systems and 3-phase-4-line power systems. And for the low-pass filter which is used in detecting harmonics, the paper proposed a new method which used synthetically the ButterWorth Filter and the Average Low-pass Filter to reduce the detecting error which exists when only a ButterWorth Filter were adopted and to restrain the fluctuation of the detected harmonics in the condition of the 1st current changing greatly when only a Average Low-pass Filter were adopted. In the novel method, a novel idea was proposed to evaluate the harmonic detecting method according to the output of the low-pass filter and considering the facts such that the 1st current is much more than the harmonic currents and the 1~st current and the harmonic currents are changing all the time.Secondly, the paper built a model for the Hybrid Active Power Filter and the performance of the SHAPF is inferred based on this model. It extended the proportion factor to the planar form and proposed that the fluctuation of the parameters of the power net and the tendency of the controller's work point should be considered when the performance of the hybrid active power filter was evaluated. Some rules were found about the influence of the performance of the HAPF when the parameters of the power net were changed. The paper discussed the factors those possibly weaken the performance of the SHAPF including the fluctuation of the harmonic current of the loads, the fluctuation of the harmonic voltage ofthe loads, the fluctuation of the reactance of the power net and the fluctuation of the frequency of the power net. Comparing the influence of these factors in different control strategies, a conclusion was drawn that the SHAPF has different resistive capacity to these factors in different control strategies.Thirdly, a decision-making system based on the fuzzy expert control is proposed to decide which control strategies should be adopted. The decision-making system considered the preliminary Work Points near the current Work Point of the SHAPF and 4 influencing factors and 5 control strategies. It can identify automatically the parameters of the power net and select a best control strategy according to the performance to resist the influence in the preliminary Work Points and the current Work Point. On the other hand, the intelligent self-adaptive control methods, such as the Single Nerve PID and the Self-Adaptive ANN, were adopted to improve the control precision and dynamical performance.Finally, the paper proposed a Multi-Object Fuzzy Optimized scheme to decide the parameters of the reactive power filter and the output low-pass filter. After considering the fixed reactive power compensation and the dynamic reactive power compensation, it optimized the parameters to get the minimum harmonic capacity of the active power filter and the minimum price of the whole system. And then the paper analysis the mutual inductance among the three phase inductions, the result shows that it get best effect when the three phase inductions were placed in a regular triangle in a horizontal level. The paper discussed the design of the IGBT inverter and its snubber circuits. In succession, the dead time and it influence in inverter was discussed and a approximate none dead time SPWM is introduce to reduce the influence of the dead time. The practice proved the good performance of the SHAPF designed referring to this paper.