A Single-phase Harmonic Compensation System Based On The Analog Circuits

In recent years, with the non-linear load devices widely applied in power system, electrical harmonic pollution is getting more and more serious.The Active Power Filter(APF) is an important equipment to compensate harmonic and reactive power current in electrical system. The key problem is to detect the harmonic current accurately in real-time mode.There exist many detection methods of reactive and harmonic currents.Especially, Instantaneous reactive power theory proposed by H. Akagi has the widely application.P-q calculating mode and ip-iq calculating mode are two harmonic current detecting methods on the basis of the theory of instantaneous reactive power.The principle is instantaneous voltages and currents in three-phase circuits can be transformed into two-phase components on orthogonal α-βcoordinates.By this way, the fundamental component current can be detected accurately in three-phase balanced system without distorted voltages.However, the detective error will be made because of limitations of this method such as direct application in three-phase four-wire system.Sorts of improvement have been done to overcome defects above.An implementation method without phase lock loop (PLL) is put forward. It will not be influenced when source voltages are distorted; the symmetrical component method is used to obtain the positive sequence component voltage, thus the detective influence of fundamental active current can be eliminated in asymmetrical three-phase voltage;it also can be successfully applied in asymmetrical three-phase four-wire system by zero sequence current selected unit.Furthermore, a new definition of generalized instantaneous reactive power theory makes it possible to detect characteristic harmonic current corresponding to fault.On this basis, a new method based on general theory of instantaneous reactive power for random harmonic current detection is investigated.Positive and negative sequence component of random harmonic current can be detected respectively by properly modifying the switch matrix which is based upon the traditional ip-iq method. The zero sequence current component can also be detected by equivalent triangle conversion. Finally, the detected sequences above can be summed up to obtain the random harmonic current.The results of simulation and spectrum analysis make it evident that this algorithm has a high precision and flexibility.