Abstract
Micro phasor measurement units (μPMU) installed in active distribution networks are very useful for improving observability by acquiring system real-time data. However, three-phase imbalance and harmonic power flows adversely impact the accuracy of synchronous measurements, which implies the importance of phasor estimation errors. This paper proposes a new phasor estimation algorithm for μPMU in active distribution networks that uses a conditional maximum likelihood (CML) estimation method. Firstly, the signal model of three-phase, three-wire and four-wire imbalance systems is established. Then, the probability distributions of the magnitude and phase angles are derived from the geometric characteristics of the CML method by solving the geometric equation. Simulation results show that the proposed CML based method is effective for estimating phasor and impedance models of active distribution networks by using μPMU measurement data.
Highlights
With the increasing popularity of distributed energy sources in power systems, the operation of distribution systems becomes more complex [1]
The performance of conditional maximum likelihood (CML) is estimated by Matlab, and the mean square error (MSE)
The performance of CML is verified by MSE, and the signals under harmonic, noise and frequency offset are tested
Summary
With the increasing popularity of distributed energy sources in power systems, the operation of distribution systems becomes more complex [1]. The proposed method is based on the knowledge that PV units generate minimum negative-sequence currents (even for different inverter controls), but under high-level noise conditions, the results have slightly increased location errors. Most of the traditional phasor measurement algorithms are based on the single-phase steady state signal model, which could be severely disturbed by three-phase imbalance, frequency fluctuations, and harmonic waves; as a consequence, the dynamic measurement results are not accurate. From the viewpoint of signal processing, a new algorithm for single-phase phasor measurement using conditional maximum likelihood estimation is proposed in [12]. The contribution of this paper is that the CML estimator has a simple closed-form expression determined from geometrical properties, applicable to the accurate measurement for the impedance of three-phase distribution networks.
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