Reference signal generating method for distance and directional protection elements
View Patent ↗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.
1. An intelligent electronic device (IED), comprising:
one or more inputs configured to receive at least an A-phase measurement, a B-phase measurement, and a C-phase measurement of an electric power system; and
processing circuitry configured to:
transform, via an abc/dq0 transform, the A-phase measurement, the B-phase measurement, and the C-phase measurement into at least a d-component signal and a q-component signal;
determine an estimated angular frequency, based at least in part on the q-component signal, to be used by the abc/dq0 transform;
add additional inertia to the estimated angular frequency separately from determining the estimated angular frequency; and
provide one or more reference signals based on the estimated angular frequency with the additional inertia added;
detect a fault in the electric power system using the one or more reference signals; and
perform an operation upon detecting the fault.
2. The IED of claim 1 , wherein the processing circuitry comprises:
a proportional-integral (PI) controller configured to provide an integral signal and a proportional signal; and
a notch filter, between the PI controller and the abc/dq0 transform, configured to receive the q-component signal and to provide a filtered q-component signal that reduces an oscillating component of the q signal that occurs during asymmetry in the A-phase measurement, the B-phase measurement, the C-phase measurement, or any combination thereof.
3. The IED of claim 2 , wherein the notch filter comprises a first adaptive notch filter configured to receive the integral signal, corresponding to estimated system frequency, and to adapt coefficients used in filtering the q-component signal based on the frequency.
4. The IED of claim 3 , wherein the processing circuitry comprises a second adaptive notch filter configured to receive the integral signal, corresponding to estimated system frequency, and to adapt coefficients used in filtering the d-component signal based on the frequency.
5. The IED of claim 4 , wherein the processing circuitry comprises a second low pass filter configured to reduce transient oscillations of the filtered d-component signal provided by the second adaptive notch filter.
6. The IED of claim 3 , wherein the processing circuitry comprises a first low pass filter configured to reduce transient oscillations of the filtered q-component signal provided by the first adaptive notch filter.
7. The IED of claim 1 , wherein the processing circuitry is configured to add inertia to the estimated angular frequency using an arcsin function, a low pass filter, and a saturation block.
8. The IED of claim 7 , wherein the saturation block limits delay caused by the low pass filter.
9. A method, comprising:
receiving an A-phase measurement, a B-phase measurement, and a C-phase measurement of an electrical power system;
transforming the A-phase measurement, the B-phase measurement, and the C-phase measurement to at least a d-component and a q-component;
determining an estimated angular frequency based at least in part on the q-component;
adding additional inertia to the estimated angular frequency separately from determining the estimated angular frequency;
providing a reference signal based on the estimated angular frequency with the additional inertia added; and
performing a protection operation on the electrical power system based at least in part on the reference signal.
10. The method of claim 9 , comprising determining, via an adaptive notch filter, the estimated angular frequency using the q-component and an adaptation signal corresponding to the system frequency.
11. The method of claim 10 , comprising determining, via a proportional-integral (PI) controller, a proportional output signal and an integral output signal, wherein the integral signal is used as the adaptation signal corresponding to the system frequency.
12. The method of claim 11 , wherein the PI controller combines the proportional output signal and the integral output signal into a combined signal, integrates the combined signal, and delays the integrated combined signal to determine the estimated angular frequency.
13. The method of claim 9 , comprising filtering the d-component and the q-component with respective adaptive notch filters and respective low-pass filters.
14. The method of claim 9 , comprising:
determining an arcsin signal of the q-component;
delaying and filtering the arcsin signal using a low pass filter (LPF) to obtain a filtered signal;
limiting delay of the filtered signal; and
adding the filtered signal with the limited delay to the estimated angular frequency as the additional inertia.
15. A system, comprising:
an input configured to receive at least an A-phase measurement, a B-phase measurement, and a C-phase measurement of an electric power system;
memory; and
a processor operatively coupled to the memory, wherein the processor is configured to execute instructions stored in the memory to cause the processor to:
transform the A-phase measurement, the B-phase measurement, and the C-phase measurement into at least a d-component and a q-component;
determine an estimated angular frequency based at least in part on the q-component;
add additional inertia to the estimated angular frequency separately from determining the estimated angular frequency; and
provide a reference signal based on the estimated angular frequency with the additional inertia added;
detect a fault in the electric power system based at least in part on the reference signal; and
determine a fault distance, fault direction, or both, upon detecting the fault.
16. The system of claim 15 , wherein the processor is configured to determine the estimated angular frequency using a synchronous reference frame phase-locked loop.
17. The system of claim 15 , wherein the processor is configured to filter the q-component via an adaptive notch filter, wherein the adaptive notch filter is adapted based on an adaptation signal corresponding to system frequency.
18. The system of claim 15 , wherein the processor is configured to:
determine positive sequence voltage based on the reference signal;
determine the fault distance, the fault direction, or both, using the positive sequence voltage.
19. The system of claim 18 , wherein the processor is configured to send a signal to a circuit breaker to open the circuit breaker upon detection of the fault.
20. The system of claim 15 , wherein the processor is configured to transform, using the estimated angular frequency, the d-component, the q-component, and a 0-component signal to a reference signal comprising an A-phase voltage, a B-phase voltage, and a C-phase voltage.