Resonant Controller for Higher Harmonics Compensation in PWM rectifiers
Rising content of higher harmonic in grid voltage become a serious problem of powersystems. Main source of higher harmonics are non linear loads connected to grid system, like diode rectifi ers, cyclo converters or power packs. Non linear loads consume nonsinusoidal current, what leads to occurring of higher harmonics in voltage signal. Th ere are several methods to deal with high harmonic content. Th e easiest and most popular are passive fi lters, which are made from capacitance and inductance elements. LC circuit is tuned to exact harmonic, which is supposed to be minimized. Passive fi lters are widely applied places where many non linear loads are connected to grid voltage, high quality of voltage s obligatory, in UPS systems, etc. Th e main disadvantage of passive fi lters is variation of parameters due to temperature and humidity, high cost and losses. Th e second well known approach to harmonic mitigation is active fi lter. Active fi lters, also known as harmonic compensators, are circuits made by power electronic elements [1] Active compensator are employed in industrial companies or commercial energy systems to avoid paying high penalties for adding disturbances to grid voltage. Main advantages of active compensators are high effi ciency and reliability, which are occupied by high cost of harmonic compensators. Active fi lters, according to topology, are divided into two groups: shunt and series compensators. Shunt active fi lters [2] produce current in opposite phase to higher current harmonics generated by non linear loads. Harmonic signals, generated by compensator, are added to grid current, which leads to harmonic cancellation. Series active compensators [3] eliminate unwanted harmonics by setting high impedance to all signals except fundamental 50 Hz harmonic. Combination of passive and active fi lters are very expensive hybrid fi lters, which join high functionality and effi ciency. Other known methods of harmonic compensation are galvanic separation, special transformer connection, etc. In this article, harmonic mitigation algorithm implemented in control structure of grid converter operating with non linear load, is described. In this case, no additional passive or active elements are necessary. All compensation is made by digital implementation in control algorithm of rectifi er.