Faults in power systems can induce oscillations in power flows in transmission lines. These oscillations can grow in magnitude within seconds if left un-damped or poorly damped. Ultimately this leads to loss of synchronisation between generators or possible voltage collapse and blackouts. To monitor and control the dynamics of generators, which cause such oscillations if they remain uncontrolled, the operating state needs to be estimated in real-time (Dynamic State Estimation).
Currently, Energy Management Systems (EMS) estimate the operating state of power systems using Static State Estimation (SSE), which estimates the state every 5 seconds, which is too slow.
Dynamic State Estimation (DSE) improves on this by estimating in real-time. Currently, DSE needs Phasor Measurement Units (PMUs) to measure magnitude and phase of current and voltage of a node in power system. The problem with PMUs is the lack of tolerance to error in current algorithms, which assume 0.1 %, but in reality PMU error is ~1 %. They also rely on GPS (global clock) for time-synchronisation.
Researchers from Imperial College London have developed a new algorithm that has several benefits over current DSE methods:
- Tolerates 10 % error in measurements (Figure 1)
- Only requires an analog measurement of the current and voltage of the generator to estimate its dynamic state.
- Does not need GPS for time-synchronisation between generator rotor angle and I/V phase angle - uses relative difference between the two instead of a reference angle provided by GPS.
The inputs for the DSE algorithm are: measurable time-varying quantities (voltage, current, and power of generator), measurable constants (resistance, reactance, inertia of generator), which are measured beforehand and used as parameters. Outputs from the algorithm are angle, speed, voltage, and flux of the rotating parts of the generator. The outputs can be used to control the generator and control oscillations in the power system.
The algorithm converts current and voltage sine waves to its magnitude and phase (phasor). Usually PMUs require a reference angle to the phase of the phasor using GPS synchronisation (which is a source of large error). This algorithm does not require the use of PMUs. Instead of estimating the absolute rotor angle it estimates the relative angle between the rotor and voltage/current phase, thus eliminating the need for GPS synchronisation.
Figure 1. Performance of the DSE without PMU (Imperial College IP) at 10% error in measurements compared to the DSE with PMU (prior art) at 3 % error in measurements.
This technology is protected by an international patent publication (WO2019016547A1).
Professor Bikash Pal, Professor of Power Systems, Electrical and Electronic Engineering, Imperial College.
Dr Abhinav Singh, Lecturer of Power Systems at the School of Electronics and Computer Science, University of Southampton.
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