Key Control Techniques Research On Diode Clamped Split Capacitor Three Level APF

With the continuous development of modern society, a series of nonlinear loads such as power electronic load has been widely used in power grid. However, these nonlinear loads will inject a large amount of harmonic and reactive power into the power grid, which will affect the normal operation of the grid connected devices. Therefore, the power electronic devices as active filter harmonic and reactive compensation, has attracted wide attention. Compared to the traditional two level active power filter, three level structure has high quality of output voltage, low switching loss, low switching devices stress, cost savings and other advantages. Due to the three-phase four wire power supply system used in our country, three level APF has become a research hotpoint in the field of power quality control.In this paper, the practical significance of this topic is discussed, and the research status of three level active power filter domestic and abroad is analyzed.Secondly, in this paper, the two topology of three-level diode clamped three-phase four wire APF were briefly introduced, analysis of the diode clamp split capacitor active power filter control procedure and specific three-level converter working mode. Based on the theoretical analysis, the mathematical models of the abc coordinate system and of the dqO coordinate system are established.Thirdly, the key technologies of the diode clamped three level split capacitor active filter include three aspects, which are the harmonic detection technology, the PWM modulation technique and the neutral point balancing control strategy. Based on the harmonic detection method of traditional three-phase three line system, a detailed analysis of ip-iq-iO detection method and p-q-r method based on three-phase four wire system is presented. According to the inherent defects of the DC filter LPF,this paper proposes a improved type of DC link filter under balanced and unbalanced situation, which remarkably reduces the filter link delay and overshoot, and verified by simulation.Based on the traditional two level SVPWM modulation technology, the principle and implementation process of the three level space voltage SVPWM modulation are analyzed, the simulation model and the simulation waveforms are given and analyzed. In addition, an analysis of the causes of neutral point potential unbalance is introduced. Based on the three-level SVPWM modulation technology, the influence long and short vector on the neutral point potential is analyzed, and the control method of the neutral point potential is proposed by adjusting the action time of the positive and negative short vectors, and the Simulink simulation model is set up to verify the method.Finally, on the basis of principle analysis and simulation verify the design three-level split capacitor three-phase four-wire APF prototype, describing in detail the working principle of the main circuit of the hardware, parameter design and component selection are prensented.System control module function and work principle is introduced. Then introduced the system software design, work flow and so on. The test prototype and the experimental equipment are introduced, and the experimental waveforms are analyzed in detail. The accuracy of the proposed method is verified.