Power System State Estimation Using Phasor Reference Frame Transformation
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Solution Overview
Problem
The integration of phasor measurements in electrical power system state estimation is challenging due to the need for synchronizing measurements across a common reference frame, making the system vulnerable to signal loss from the reference PMU, which complicates the reconciliation of phasor measurement and state estimator reference frames.
Innovation Solution
A method and apparatus for estimating the state of an electrical power system using phasor measurement data referenced to a phasor measurement reference frame, with techniques such as generating pseudo-measurements for angular differences or treating the reference angle as an additional state variable to reconcile the reference frames, allowing for robust state estimation even in the presence of signal loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference PMU is placed at the location of the slack bus to reconcile reference frames, then the state estimation can be performed accurately, but the system becomes vulnerable to signal loss from the reference PMU
Solution Approach 1:
The patent introduces an intermediary approach by using multiple reference frames and transformation matrices to reconcile phasor measurement reference frame with state estimator reference frame. Instead of relying on a single reference PMU at the slack bus, the system uses measurement data from multiple locations and applies coordinate transformations to align reference frames, thereby eliminating the single point of failure vulnerability.
Solution Approach 2:
The patent changes the reference frame parameters by allowing the state estimator to operate in a reference frame that is rotated relative to the phasor measurement reference frame. This is achieved through reference frame transformation matrices that can be adjusted based on system conditions, enabling the system to maintain accuracy even when the traditional reference PMU signal is lost.
2Measurement precision
If phasor measurements are synchronized to UTC reference frame, then time-synchronized measurements can be provided across the network, but the reference frame reconciliation process becomes complex and time-consuming
Solution Approach 1:
The patent applies preliminary action by pre-establishing the relationship between UTC reference frame and state estimator reference frame through systematic development of transformation matrices and reference frame alignment procedures. This preliminary setup allows the system to automatically reconcile reference frames during normal operation without complex real-time calculations, reducing operational complexity while maintaining synchronization accuracy.
3Ease of operation
If traditional non-phasor measurements are used for state estimation, then the estimation can be performed without reference frame reconciliation, but the measurement information is insufficient and less accurate
Solution Approach 1:
The patent merges traditional non-phasor measurements with phasor measurements from multiple locations into a unified state estimation framework. By combining these measurement types and using reference frame transformation to align them properly, the system achieves both the simplicity of traditional estimation methods and the enhanced accuracy provided by phasor measurements, without requiring complex reference frame reconciliation during operation.
Data Source
AI summary
Phasor measurement units (108) provide phasor data from various locations (102) in an electrical power system. The phasor data is referenced to a common timing signal. Non-phasor measurement data is also obtained at various locations in the power system. A phasor assisted state estimator (120) uses the phasor data and the non-phasor data to determine the power system state.