# A Review of Harmonic Detection, Suppression, Aggregation, and Estimation Techniques
## 4 Harmonic Aggregation  
Harmonic aggregation is a technique used to combine a signal's harmonic components to estimate the signal's fundamental frequency and overall harmonic content. This technique is widely used in various fields, such as audio signal processing, power system analysis, and communications systems. In recent years, researchers have been developing new methods for harmonic aggregation that are more robust and efficient than traditional methods; Figure 7 presents the overview of harmonic aggregation discussed in this section. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Method** & **Ref.** & **Advantage** & **Disadvantage** & **Applications** \\ \hline Passive Filters & [27; 28; 29; 30] & Low-cost, simple implementation & Performance affected by system frequency changes & Common in industrial power systems \\ \hline Active Power Filters & [31; 32; 33; 34; 35] & Suppresses dynamic harmonics, compensates reactive power & High hardware cost, complex circuit design & High-performance grid systems \\ \hline Hybrid Filters (Passive + Active PF) & [36; 37; 38; 39] & Balances cost and performance & Slight impact on device capacity & Modern power systems with budget constraints \\ \hline Dynamic Voltage & [41; 42] & Compensates for voltage sags/swells, mitigates harmonic distortion & Expensive and complex issues & Grid systems with voltage fluctuation issues \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Harmonic suppression methods. Figure 7: Harmonic aggregation overview. One part of evaluating the harmonics tolerated by a power system is estimating the total amount of harmonics coming from different sources. The assessment of harmonics is not precise or consistent because there can be unpredictable changes in the system's nonlinear sources and parameters that influence the total. The combination of various harmonic sources usually results in a sum that is less than the arithmetic total of the maximum values due to uncertainties in the magnitude and phase angle. Therefore, accurately estimating the resulting sum is difficult [43]. The accurate assessment of the harmonic combination from several non-linear sources operating at the same time is important because of the uncertainty in the magnitudes and phase angles of the harmonic currents injected into the transmission. The method used in [44] takes into account the system topology of the wind farms and the overall system. The harmonic currents injected for penetration are evaluated, and these alternative values are calculated and compared to the cumulative curves. This study indicates that estimates of harmonic aggregation using the IEC 61400-21-1 [45] methodology may lead to errors in the power system. In [46], the authors provide an overview of the work investigating the aggregation of multiple identical harmonic sources within a single renewable energy generator (REG) plant. REG investors can generate a wide range of harmonics; the magnitude of the error introduced is significant when harmonics from multiple sources are added arithmetically. The phenomenon of harmonic cancellation happens due to dispersion in harmonic phase angles. Variation of circuit parameters inside switch mode power supply (SMPS) is responsible for harmonic cancellation between same-type and mixed-type SMPS aggregate load [47]. Renewable sources are now a considerable part of modern power generation and distribution systems; due to variable speed turbines, large wind power plants (WPP) are sources of harmonics and inter-harmonics in voltage and current [48]. The model developed in [48] helps meet the challenges of wind power integration; harmonic aggregation and cancellation are some of these challenges. The aggregation of harmonics produced by the wind power plant is independent of the power generated; this is consistent with the findings in [49], which analyzed the accumulation of complex current harmonics and inter-harmonics.