Research On Harmonic Detection Of APF And DC Side Ripple Voltage Control Based On HHT Transform

Active power filter(APF) can not only detect the system's harmonic, but also inhibit the flicker and compensate the reactive power. In APF, because of the inverter own's losses,and compensation current's time-varying characteristic, APF dc side capacitor voltage attenuation or large voltage fluctuation occurs, while a large ripple also accompanies them. Dc side capacitor voltage ripple depends on capacitance and harmonic distribution of compensation current. So it is essential to research the relationship between dc side capacitance and capacitor voltage ripple, harmonic detection, and stabilized controling voltage for improving the efficiency of APF harmonic compensation.Aiming to ripple voltage problem, the dissertation calculates and analyzes ripple voltage.The voltage loop controller takes improved PI control method to implement APF dc side voltage ripple control. The efficiency of this method is tested and verified by simulated analysis. For the voltage ripple caused by harmonic distribution, the Hilbert huang transform(HHT) method is applied to harmonic detection. And HHT is combined with Proportional Resonance(PR), which acts as a current control loop controller to achieve dc side voltage ripple control. And compared with the traditional method of instantaneous reactive power theory, simulation results show that this method has a better real-time performance. The main contents are below:(1) To study the application of HHT transform harmonic detecting method, the dissertation analyzes the transformation of HHT and explains it by constructing the presupposed signal. HHT transform harmonic detecting method is used to detect the harmonic wave, obtaining the instantaneous amplitude of each harmonic component instantaneous frequency and instantaneous phase.(2) The application of APF harmonic detection based on HHT transform is researched.The dissertation applies the HHT transformation method to harmonic detection module,carries on the empirical mode decomposition(EMD) to the input current signals to get each intrinsic mode function(IMF) and uses the Hilbert transformation to obtain harmonic components, then completes harmonic detection process.(3) The producing mechanism of dc side APF ripple voltage is studied, and the ripple voltage fluctuation rate and the instantaneous amplitude are calculated, after that the improved PI controller is used to realize ripple voltage control. The dissertation uses space vector pulse width modulation(SVPWM) method to control ripple voltage. The simulation results show that the improved PI control method improves the system of compensation effect and reduces the energy exchange of APF compared with the traditional PI control method.(4) Harmonic method based on HHT transform is studied in the application of the dc side APF ripple voltage control. By this method, it can detect the harmonic wave, observe the size of the dc side voltage ripple, and compare with the instantaneous reactive power theory.At the same time ripple voltage control is realized by using current loop PR controller. The simulated results demonstrate that the harmonic method based on HHT transform is a better way to track and get in time.