Measurement of Instantaneous Active and Reactive Power with SRF Theory

Abstract

The advancements in power electronics has contributed towards development of power quality improvement devices. These devices include active filters, static VAR compensator, DVRs, UPQC, STATCOM etc. For the control of these devices, a common requirement is measurement of instantaneous voltage, current and power in appropriate frame of reference. For ease of control of three phase circuits, the three phase quantities are converter into three phase quantities using transformation. In this paper, a synchronous reference frame (SRF) theory often known as dq theory is deployed for measurement of instantaneous active and reactive power. By transforming three-phase voltages and currents into a rotating dq0 coordinate system aligned with the voltage vector, time-varying AC quantities are converted into steady DC components, simplifying power computation. The methodology employs Clark (α-β) and Park (dq0) transformations to derive instantaneous active power (P) and reactive power (Q) via direct relationships with the d- and q-axis currents. In this paper MATLAB simulation results are presented and the simulation results are validated with hardware prototype model.