Improving the SRF method to compensate low-order harmonics under nonsinusoidal network voltages

Abstract

Increasing the application of power in electronic devices has increased the harmonics in power systems. Numerous methods like the synchronous reference frame (SRF) and the p-q-based method have been suggested to overcome the effects of these harmonics. The conventional SRF method provides acceptable results in harmonic compensation of high-order harmonics (higher than the fourth order), but the transient response time will be drastically increased in the presence of low-order harmonics due to the existence of a conventional low-pass filter. Furthermore, if the load terminal voltages are distorted, then the conventional SRF method will become unable to implement load current compensation. This research has used wavelet transform to overcome these difficulties. The proposed method is not only faster than conventional SRF, but it can also compensate the load currents if the load terminal voltages are also distorted. The simulation and experimental results are performed using MATLAB/Simulink and digital signal processor TMS320F28335 to verify the proposed method.

A Wavelet-Based Unified Power Quality Conditioner to Eliminate Wind Turbine Non-Ideality Consequences on Grid-Connected Photovoltaic Systems

“…Figure 15a compares the power grid voltages before and after compensation by the SF. Figure 15c compares the grid-end currents compensated for by the proposed wavelet-based SRF method and another compensation method suggested in [29]. Figure 15b,c also show that the grid-end current is in the reverse phase with the instant load current.…”

“…Moreover, the employed PLL method was highly susceptible to noise. [29]. Figure 16 summarizes the THD of the simulated grid-end currents and load-terminal voltages compensated for by the proposed method under different gains for K, i.e., gain of the current harmonic suppression loop.…”

“…The first is the disability to compensate for the load currents under the distorted load-terminal voltages, due to the inaccuracy of the PLLs used in this method to extract and synchronize the SAPF reference [29,31]. The second is the SRF-based compensation algorithm performs unexpectedly when a non-linear load shows a very low impedance in some frequency components (see load impedance (ZL) in Figure 2).…”

“…[10] SRF method THD = 32.75% [29] The inaccuracy of the SRF-based method proposed in [29] is attributed to the inability of that method to compensate for the neutral source-end current. Moreover, the employed PLL method was highly susceptible to noise.…”

Proposing Wavelet-Based Low-Pass Filter and Input Filter to Improve Transient Response of Grid-Connected Photovoltaic Systems

“…Accordingly, the active filter's reaction time also worsens the transient response of an integrated PV unit to the power system. Meanwhile, when the grid-end current contains low-order harmonics, the conventional second-order low-pass filter is unable to fully separate the positive-sequence component of grid-end active power [5]. This additionally results in the malfunction of employed active filter.…”