New Method for Detecting Instantaneous Reactive and Harmonic Currents in Single-phase Systems

In the control strategies for an active power filter(APF),the determination of harmonic and reactive components of the load current is the most important stage.And no perfect approaches have been brought forward so far for single-phase nonlinear loads such as electric traction loads.In this paper,a new method based on the orthogonality of sine is proposed in order to detect the harmonic and reactive currents in single-phase power systems,and it can detect the fundamental active currents and then compensate harmonic and reactive currents in the load currents accurately.Simulation studies illustrate the proposed method can provide the required signals for APF to perform compensation within a transient period of 2 to 3 cycles and the steady error is negligible,and it can realize real-time detection accurately.It is not necessary to adopt the phase lock loop(PLL) in it,and it overcomes the influence of the frequency fluctuation.It is simple and reliable and its hardware implementation is easy.The selection of low pass filter(LPF) is discussed in detail,it is concluded that the higher the LPF order is,the lower the cut-off frequency is,the better the steady accuracy becomes and the slower the rapidity of dynamic response becomes.