Compact multifunctional filter

An electrical filter comprised of a parallel passive filter, a parallel active filter and at least one varistor;

• the filter is installed in parallel to an electrical network after consumption meters, wherein the filter is compact and low-cost for installation near unbalanced loads;
• the electrical network supplies at least one unbalanced load;
• the parallel passive filter is further comprised of a capacitor, a resistor and an inductor;
• the parallel passive filter is sized to attenuate an unwanted harmonic present in the electrical network, between about 60 Hz to 1140 Hz, where the passive filter diverts the unwanted harmonic from the electrical network;
• the parallel active filter is further comprised of a pulse width modulation inverter and digital signal processor;
• the digital signal processor reads a current and voltage on the electrical network and the digital signal processor determines a pulse width modulation signal;
• the pulse width modulation inverter uses insulated gate bipolar transistors (IGBT) to generate a sinusoidal signal with harmonics;
• the parallel active filter injects the sinusoidal signal into the electrical network thereby canceling a remaining harmonic in the electrical network;
• wherein the at least one varistor functions as a surge protection device up to 680 Vac;
• and
• wherein the filter avoids interfering with installed power of the electrical network, selectively cancels impedance between the electrical network and ground for frequencies other than 60 Hz, and stabilizes frequency variations to maintain 60 Hz operation.