Research On Fault Tolerant Shunt Active Power Filter

Abstract:Electrical energy plays an important role in the economic development and people's lives. With the rapid development of power electrical technologies and widely used high power switch devices, non-linear loads in the grid are widely increased, which causes harmonic pollution and energy losses. Meanwhile, voltage fluctuation and voltage flicker caused by the impulsive load and reactive power variation have greatly disturbed the industrial production and people's lives. It also makes the electrical system have problems such as heavy reactive power compensation and harmonic suppression. Active power filter has good well-known performance on reactive power compensation and harmonic suppression. But there are many problems for APF to be researched and improved. It is still an important task for APF on the field of power electrical applying technology. For example, it is under non-ideal operation condition how to keep APF running effectively, even when the inverter in APF has fault.This paper proposes the structure of fault tolerant parallel active power filter, named APF operating with fault tolerant, to improve the safe performance for APF. The relative theories and methods of fault tolerant APF are researched. The working mechanism, mathematical model, instructing current extracting method, control method, pulse modulating method and so on are researched in the paper. The basic researching method and technical proposal of fault tolerant APF are formed. The emphasis and achievement of the paper mainly manifests in the following aspects.(1) According to the characteristic of inverter fault, a structure of fault tolerant parallel APF is proposed. The possible fault types of inverter are given first. The structure of fault tolerant parallel APF is analyzed. Several operating models and corresponding primaries under fault condition are discussed.(2) The regular pattern outputting voltages and currents of three-phase four-switch inverter is analyzed. The influence caused by the DC-linked voltage fluctuation of three-phase four-switch inverter is also analyzed. That is the offset of the output voltage space vector of three-phase four-switch inverter. Comparing the structure with the three-phase six-switch structure without fault, the theory evidence of parameter design is provided.(3) The instructing current extracting method for fault tolerant parallel APF is proposed. The positive order fundamental active current can be obtained by the method even under unbalance load condition. The method is test and verified with simulation. The instructing current can be gotten under different bad condition.(4) Combining the structure characteristic of fault tolerant parallel APF, the controlling aim of DC-link capacitor voltage is illustrated. The method to stabilize the DC-link total voltage and the method to detect the DC-link current are proposed. The corresponding controlling strategy is put forward. The simulation is done. Simulating results show that the fault tolerant parallel APF can suppress the harmonic currents effectively. APF can work normally when the inverter is fault. The DC-link total voltage is kept stable and two capacitor voltages are kept balance.(5) The modulating method of SVPWM for fault tolerant APF is proposed. The traditional SVPWM method is given first, which needs a great deal of irrational number and trigonometric function operations. A lot of operating time is cost. The computing error is unavoidably is led into at the same time. On the other hand, due to the angle difference between the voltage space vector and the ?? coordinate system, it is complicate to judge sector. An improved SVPWM method for three-phase four-switch inverter is proposed in the paper. Using new coordinate transformation matrix, the computation of space voltage vector working time and the judgement of sector are simplified, which need not the irrational number and trigonometric function operations. However, the method works under the condition of DC-link voltage balance.(6) A SVPWM method with DC-link voltage unbalance is proposed. A method composing zero voltage space vectors is put forward with the DC-link voltage unbalance. The methods of computing the working time of voltage space vector and the judgment of sector are provided. The DC-link voltage unbalance is greatly restrained by the proposed SVPWM method.According to the background of power quality control and the improvement of operating safety for APF, the fault tolerant parallel APF is proposed in the paper. The fault schematic design for engineering application can be popularized to the other design and application in the field of power electrical systems. It is beneficial to push on the practical application for the power electrical systems.