Novel Hybrid Cascade H-bridge Active Power Filter with Star Configuration for Nonlinear Powerful Industrial Loads

Powerful DC thyristor converters of arc furnaces and rolling mills are widely used in industrial production. Transformerless compensating devices capable of actively filtering higher harmonics are used to eliminate such harmonics and to compensate reactive power. Modern active filter control systems have to solve two problems: reactive power compensation and elimination of the most significant harmonics in the load node. Note that the problem of balancing voltages at H-bridge capacitors has not been paid due attention so far. This paper proposes efficient ways to solve this problem. Balancing in reactive power compensation cells is done by altering the phase whereas the cells responsible for eliminating higher harmonics are balanced by altering the pulse width. Matlab/Simulink modeling has proven these solutions feasible and efficient. The main parameters to control (THDI, THDU, and capacitor voltage difference) are within acceptable levels. Active filtering has reduced the 11th and the 13th harmonic to the levels several times lower than the acceptable thresholds.