Adaptive Notch Filter for Stable Reference Signals
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Solution Overview
Problem
Modern power systems with low-inertia sources, such as those connected through inverters, pose challenges for intelligent electronic devices (IEDs) in accurately tracking changes in polarizing quantities, leading to potential misoperations during faults due to step changes in voltage parameters.
Innovation Solution
IEDs employ an adaptive notch filter and additional inertia to accurately estimate angular frequency, transforming A-phase, B-phase, and C-phase measurements into d and q components, reducing double frequency components and adding inertia to the estimated angular frequency to generate a more stable reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional polarizing quantity tracking methods are used in power systems with low-inertia sources, then the system responds quickly to changes, but the polarizing signal becomes unstable and causes misoperations of protection relays
Solution Approach 1:
The patent applies beforehand cushioning by adding artificial inertia to the polarizing quantity before it is used by protection elements. The modified synchronous reference frame phase-locked loop (MSRF-PLL) incorporates inertia simulation that cushions abrupt changes in polarizing signals, preventing misoperations while maintaining accurate fault detection. This is achieved through the inertia coefficient that smooths transient responses.
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting the inertia coefficient based on system conditions. The inertia coefficient is modified according to the rate of change of frequency and other system parameters, allowing the polarizing quantity to adapt its response characteristics. This enables the system to maintain reliability under varying operating conditions while preserving necessary responsiveness.
2Stability of the object's composition
If inertia is added to the polarizing quantity to prevent misoperations, then the stability of the polarizing signal improves, but the response speed to actual faults may be reduced
Solution Approach 1:
The patent applies dynamics by making the inertia coefficient dynamic rather than fixed. The inertia coefficient is adjusted in real-time based on system frequency deviations and rate of change of frequency. During actual faults with significant frequency deviations, the effective inertia is reduced to maintain fast response, while during normal operations with small variations, higher inertia is applied to ensure signal stability and prevent misoperations.
Solution Approach 2:
The patent implements parameter changes by modifying the inertia coefficient as a variable parameter that changes with system conditions. The coefficient is increased during stable operations to smooth the polarizing signal and decreased during transient fault conditions to maintain responsiveness. This dynamic parameter adjustment resolves the contradiction between stability and response speed.
3Measurement precision
If the polarizing quantity tracks voltage parameter changes rapidly, then accurate fault detection is achieved, but step changes cause misoperations of protection relays
Solution Approach 1:
The patent applies beforehand cushioning by incorporating an inertia simulation mechanism in the MSRF-PLL that cushions step changes in the polarizing quantity before they reach protection elements. The inertia coefficient is specifically designed to attenuate abrupt changes while preserving the tracking accuracy of genuine fault conditions, preventing relay misoperations caused by transient voltage variations.
Solution Approach 2:
The patent implements feedback through the closed-loop structure of the modified synchronous reference frame phase-locked loop. The system continuously monitors voltage parameters and adjusts the polarizing quantity with feedback control, while the inertia mechanism provides damping feedback that prevents oscillations and misoperations. This feedback mechanism ensures both accurate tracking and reliable operation.
Data Source
AI summary
The present disclosure relates to generating reference signals for distance and directional elements in power systems. For example, an intelligent electronic device (IED) may receive A-phase, B-phase, and C-phase electrical measurements of a power system. The IED may transform the A-phase, B-phase, and C-phase measurements to a d-component, a q-component, and a 0-component. The IED may include an adaptive notch filter that reduces or eliminates a double frequency component that may be present when step changes of frequency and/or amplitude occur and/or when the A-phase, B-phase, and C-phase measurements have different amplitudes. By reducing the double frequency component, the IED may generate a more accurate ω which may allow for more accurately tracking changes to the polarizing source. Further, the IED may separately add inertia to the estimated angular frequency used in generating a reference signal.