Abstract
The integration of renewable power sources with power grids presents many challenges, such as synchronization with the grid, power quality problems and so on. The shunt active power filter (SAPF) can be a solution to address the issue while suppressing the grid-end current harmonics and distortions. Nonetheless, available SAPFs work somewhat unpredictably in practice. This is attributed to the dependency of the SAPF controller on nonlinear complicated equations and two distorted variables, such as load current and voltage, to produce the current reference. This condition will worsen when the plant includes wind turbines which inherently produce 3rd, 5th, 7th and 11th voltage harmonics. Moreover, the inability of the typical phase locked loop (PLL) used to synchronize the SAPF reference with the power grid also disrupts SAPF operation. This paper proposes an improved synchronous reference frame (SRF) which is equipped with a wavelet-based PLL to control the SAPF, using one variable such as load current. Firstly the fundamental positive sequence of the source voltage, obtained using a wavelet, is used as the input signal of the PLL through an orthogonal signal generator process. Then, the generated orthogonal signals are applied through the SRF-based compensation algorithm to synchronize the SAPF’s reference with power grid. To further force the remained uncompensated grid current harmonics to pass through the SAPF, an improved series filter (SF) equipped with a current harmonic suppression loop is proposed. Concurrent operation of the improved SAPF and SF is coordinated through a unified power quality conditioner (UPQC). The DC-link capacitor of the proposed UPQC, used to interconnect a photovoltaic (PV) system to the power grid, is regulated by an adaptive controller. Matlab/Simulink results confirm that the proposed wavelet-based UPQC results in purely sinusoidal grid-end currents with total harmonic distortion (THD) = 1.29%, which leads to high electrical efficiency of a grid-connected PV system.
Highlights
With the increasingly energy crisis and environmental pollution, the use of renewable green energy sources, such as wind and solar, has been becoming popular worldwide
Depending on only one variable, namely the load current, to generate the current reference of the shunt active power filter (SAPF), a wavelet-based synchronous reference frame (SRF) theory is suggested to direct the control of the SAPF
Reference of the SAPF, a wavelet-based SRF theory is suggested to direct the control of the SAPF
Summary
With the increasingly energy crisis and environmental pollution, the use of renewable green energy sources, such as wind and solar, has been becoming popular worldwide. In [10], a compensation algorithm based on the advanced generalized theory of instantaneous power (A-GTIP) is proposed to control the shunt active power filter (SAPF) in presence of non-linear loads. A-GTIP method is used to integrate a photovoltaic (PV) system into the power grid [22] This method, like other compensation algorithms including current’s physical component [11] and conservative power theory [12], depends on two variables, namely load-terminal currents and voltages, to calculate the oscillated active and inactive powers. In [25], a synchronous reference frame (SRF)-based compensation algorithm is introduced to extract the SAPF’s references This method only needs the information of one variable, namely the load-terminal current.
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