Grid Current Direct Control For Three-Phase Four-Wire APF

A variety of nonlinear load connected on the power grid may introduce harmonic pollution. Harmonic elimination becomes an important issue, active power filter (APF) is attracting more and more attention. This thesis investigates harmonics in a three-phase four-wire system with active power filter applications for harmonic elimination. A mathematical model of the three-phase four-wire APF and its control strategy is presented.APF principle and its typical configuration for a three-phase four-wire system is studied in detail in the thesis. A mathematical model of the three-phase four-wire active power filter is constructed in a-b-c stationary coordinate system, based on the switching current modeling methods. Forward-fed voltage decoupling and transformation onto d-q-0coordinate system were investigated in the APF design.The thesis studies the AC-DC inversion of the active power filter, and derives that grid current direct control is equivalent to traditional load current harmonic and reactive current control. The control strategy of the four-leg active power filter based on the grid current direct-control have been analyzed. The double-loop PI controllers and the controller parameters have been designed. Finally, MATLAB simulation has verified the effectiveness of the proposed APF grid current direct control.Because there are no precise APF system model parameters, obtained by PI controller is not a good engineering design to improve the performance of the APF compensation. On this basis, this thesis proposes an outer voltage controller parameters optimization method based on PSO algorithm, and is used to achieve voltage loop automatic parameters optimization, and by setting the dual function of the fitness function. MATLAB simulation was conducted to verify the effectiveness of the proposed method.An experimental prototype is built by using the dSPACE systems, test results have shown that the grid current direct control is feasible, demonstrates better harmonic compensation effect, and the proposed PSO algorithm is able to optimize the outer voltage loop parameters of the three-phase four-wire APF.