Research On Adaptive Control Of Shunt Active Power Filter

Large quantities of non-linear loads and various kinds of electrical devices have been connected to the power grid in recent years with advanced developments in power electronic technology, which inevitably leads to the evident deterioration of power quality problems, such as harmonic disturbances and shortage of reactive power. However, the Active Power Filter(APF) that can efficiently suppress harmonics and conduct compensation of reactive power, become one of the most important ways to solve problems in regard to power quality. The output current of APF could vary rapidly and in a wide range. So it is clearly that the characteristic of APF output filter will definitely impact on compensation performance of an APF. Nevertheless, the inductance of output filter has strong non-linearity and differs apparently in light and heavy load condition because of the physical property of magnetic materials. This will absolutely affect results of APF’s digital controller. Therefore, fuzzy control is considered in this dissertation and the 3-phase-3-wire shunt APF is regarded as the research object. In addition, the current-loop adaptive control algorithms with conditions of verified output filter inductance are investigated.Firstly, mathematic model of shunt APF is established and non-linearity of output filter inductance is investigated. After analysis of APF working theory, main circuit model of shunt APF is obtained and modeling process is conducted under ABC stationary coordinate, stationary coordinate and dq synchronized rotary coordinate. Besides, the non-linearity characteristic of output filter inductance is analyzed by studying on features of magnetic materials and modeling in mathematical way. Furthermore, the inductance variation is simulated and investigated according to simulation results.Secondly, Fuzzy PI adaptive control algorithm of APF current loop is designed. The fundamentals of fuzzy controller are described firstly combining its composition with design procedures. The digital PI controller is designed under conditions of rated inductance and studies of inductance variation’s impact on control performance are also conducted. Hence, fuzzy control is considered in APF current loop control strategy. Similarly, simulation results of fuzzy PI adaptive control are investigated in this section.In the end, repetitive control is considered to enhance tracking precision of APF reference signal. The fundamentals of repetitive control are shown from the beginning of inner-model theory and analysis of repetitive control performance is conducted by aspects of stability, steady-state error and time of convergence. Similarly, an example of designing repetitive controller is introduced and its stability is verified. Respectively, simulations based on repetitive + PI and repetitive + Fuzzy PI are conducted and their waveforms are implemented to explain situations of control performance.