Vector Strategy of Formation of the Compensating Current of Shunt Active Filter In Sliding Mode

Abstract

A space-vector strategy for controlling of a three-phase shunt active power filter (SAPF), which is connected to a utility grid in which there is a nonlinear load, is proposed. The filter consists of a semiconductor voltage inverter with fully controlled switches, a capacitive storage and a single-link output RL filter. The DC voltage of the storage capacitor is stabilized by a second-order sliding mode, which is based on the implementation of a finite double-twisting algorithm. To form the compensation current, an indirect control strategy and a space-vector algorithm for tracking the instantaneous value of the current of the "parallelogram" type are used. Space-vector method avoids ambiguity in the choice of vectors of the output voltage of the inverter under the solution of the problem of current tracking. The proposed algorithm uses the methods of projective geometry to determine the relative position of the spatial vectors of voltages and currents of the power supply system, so it does not contain the difficult mathematical operations for calculating inverse trigonometric functions. The selection of the appropriate output voltage vector of the SAPF inverter on the location of the end of the current error vector relative to some switching lines is based. Switching lines from the projections of the two-dimensional sliding surface on the plane α-β are formed. These projections are subject to further linear transformation, the matrix of which is non-degenerate. Linear transformation of projections of these sliding surfaces includes sequential operations of rotation at a fixed angle, parallel movement and application of the rotation matrix. This rotation matrix has constant coefficients, which change abruply at some points in time. The classical method of equivalent control is applied. The transition from one group of coefficients to another occurs based on the spatial location of the equivalent control vector, the coordinates of which are calculated in real time. The choice of the rotation matrix provides unambiguous determination of the spatial position and the choice of the corresponding output voltage vector of the SAPF inverter. A simulation model of the power supply system with a two-dimensional sliding mode and taking into account the features that are inherent in the real-time sliding mode is built, and the simulation results are analyzed. The "switching freeze" method to eliminate chattering was used. The proposed strategy with the traditional three-channels hysteresis algorithm of the compensation current tracking according to the criteria of the number of switches is compared.