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Flow chart of the implementation steps of the p-q Theory where filters are used to separate instantaneous real power into oscillating (˜ p) and average (¯ p) components. The imaginary power (q) is not separated if entirely compensated. 

Flow chart of the implementation steps of the p-q Theory where filters are used to separate instantaneous real power into oscillating (˜ p) and average (¯ p) components. The imaginary power (q) is not separated if entirely compensated. 

Source publication
Conference Paper
Full-text available
The paper addresses the impact that time varying angular frequencies observed in electrical signals can have on the calculation and separation of components from the instantaneous electric power signal. Instantaneous power theories provide various methods for calculating the instantaneous power components in an electrical network. These methods are...

Contexts in source publication

Context 1
... ON P-Q THEORY Figure 3 shows a flow chart indicating the necessary steps for the separation of average and oscillating power components from the calculated instantaneous power in a three phase power system. The separation of these components is usually done by using linear filters, as indicated by the green box in the figure. ...
Context 2
... The second one, also a synthetic signal, shows a step function with a superimposed sine wave on the instantaneous power and the last one is a field measurement of voltages and currents, of a marine vessel microgrid during sea voyage dynamic operation. The instantaneous power for this case was calculated according to the p-q Theory sketched in fig. ...
Context 3
... aim of the filter in the p-q theory sketched in fig. 3 is to extract or separate the higher frequency oscillation from the instantaneous power signal, so that the mean power value p mean(t) equals the low frequency oscillation component or effective power. As the EMD Filter separates the two harmonics into two separate IMFs, the mathematical mean value is approached with computational ...

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Citations

... The low inertia in such systems requires properly implemented controllers in order to maintain satisfying operation conditions. However, also the advanced inverter control may produce time-varying oscillations in conditions with varying load demand [1]. Hitherto, data acquisition-and measurement system have generally been based on the basic assumption of constant fundamental frequency and harmonics that are integer multiples of the fundamental frequency [2,3]. ...
... An extensive study of IEC Standard 6100-4-7 measuring methods states that these methods do not produce accurate results in environments with timevarying angular frequency [4]. Keeping the aforementioned problems of nonlinearities and time-varying quantities in mind, measurements and estimation in isolated microgrids should rather be based on instantaneous amplitude and frequency rather than the usage of average values [1,5]. With improved data acquisition-and measurement tools, the supervisory control systems in isolated microgrids may perform better actions, and earlier hidden distortions may be revealed. ...
... 13: Wavelet Spectrum of v(t) from[7] 14: Hilbert Spectrum of v(t) from[1] ...
Thesis
Full-text available
Modern electrical systems have introduced distributed generations and power converters. This brings out different issues such as low inertia of the grids and an increasing number of harmonics and non linear distortions injected. However, the fluctuations of instantaneous frequency are arguably the most characteristic feature of microgrids. Frequency drift during step load change as well all quasi-periodic fluctuation has an impact on various conditions as generators’ prime movers and governor’s characteristic. Quasi periodic frequency fluctuations can have besides detrimental effect on electrical receivers’ work, especially electric motors will be affected. The thesis aims at providing a deep insight into the phenomena of non-constant instantaneous frequency. Origin of instantaneous frequency fluctuations are analyzed, tools for the phenomenon identification are proposed. These considerations are based on careful analysis of data from the Norwegian power system and behavior of three real marine systems onboard of a ro-ro ship with shaft generator, research-training ship during work of auxiliary generating sets as well as integrated power system of ship with electrical propulsion. For each ship, the cases of rough and calm sea are compared. To analyze data, the empirical mode decomposition algorithm and the Hilbert transform implemented in Matlab will be used.
... The low inertia in such systems requires properly implemented controllers in order to maintain satisfying operation. In addition to the harmonic pollution, advanced inverter control may produce time-varying oscillations in conditions with varying load demand [1]. The role of these invertes are to serve as an interface between the generation source and the loads. ...
... The role of these invertes are to serve as an interface between the generation source and the loads. "Static" power electronics equipment such as the inverter is a means of inverting DC power to AC power in the cases where the generation source is not rotating, e.g solar panels, fuel cells or battery banks supplying DC power [1]. Hitherto, data acquisition-and measurement systems have generally been based on average value calculations and harmonics that are integer multiples of a constant fundamental frequency [2,3]. ...
... After an extensive study of IEC Standard 61000-4-7 measuring methods, [4] states that these methods do not produce accurate results in environments with time-varying angular frequency. Keeping the aforementioned problems of nonlinearities and time-varying quantities in mind, measurements and estimation in isolated microgrids should rather be based on instantaneous amplitude and frequency rather than the usage of average values [1,5]. With improved data acquisition-and measurement tools, the supervisory control systems in isolated microgrids may perform better actions, and earlier hidden distortions may be revealed. ...
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Several cases with time varying frequencies have been reported in isolated electrical systems such as stand-alone microgrids and marine vessel power systems. This thesis studies the use of several types of Kalman filters (KF), Hilbert-Huang Transform (HHT) and the proposed method of merging empirical mode decomposition (EMD) and KF for the purpose of tracking instantaneous values of voltage- and current waveforms in isolated microgrids with the aforementioned challenges. Both synthetic signals and real measurements from a marine vessel power system were used to validate the methods. The algorithms and methods were implemented in Matlab and Simulink. In varying degrees, the methods did all prove to be viable options for tracking of the fundamental frequency on the marine vessel. The proposed method turned out to be particularly powerful to decompose multicomponent signals consisting of several time-varying monocomponents, and track their instantaneous amplitude and frequency.