Abstract
In this paper, a refined reference current generation algorithm based on instantaneous power (pq) theory is proposed, for operation of an indirect current controlled (ICC) three-level neutral-point diode clamped (NPC) inverter-based shunt active power filter (SAPF) under non-sinusoidal source voltage conditions. SAPF is recognized as one of the most effective solutions to current harmonics due to its flexibility in dealing with various power system conditions. As for its controller, pq theory has widely been applied to generate the desired reference current due to its simple implementation features. However, the conventional dependency on self-tuning filter (STF) in generating reference current has significantly limited mitigation performance of SAPF. Besides, the conventional STF-based pq theory algorithm is still considered to possess needless features which increase computational complexity. Furthermore, the conventional algorithm is mostly designed to suit operation of direct current controlled (DCC) SAPF which is incapable of handling switching ripples problems, thereby leading to inefficient mitigation performance. Therefore, three main improvements are performed which include replacement of STF with mathematical-based fundamental real power identifier, removal of redundant features, and generation of sinusoidal reference current. To validate effectiveness and feasibility of the proposed algorithm, simulation work in MATLAB-Simulink and laboratory test utilizing a TMS320F28335 digital signal processor (DSP) are performed. Both simulation and experimental findings demonstrate superiority of the proposed algorithm over the conventional algorithm.
Highlights
The widespread use of nonlinear loads has greatly degraded the quality of grid currents via generation of harmonic currents
The non-sinusoidal iinj,re f forces the subsequent pulse-width modulation (PWM) switching pulses S1−4 meant for controlling mitigation operation of Shunt Active Power Filter (SAPF), to be generated based on the direct current controlled (DCC) scheme which operates by requiring the measurement of the actual injection current iinj
Utilizing each reference current generation algorithm has successfully removed the harmonic currents generated by both nonlinear loads, resulting in total harmonics distortion (THD) values of far below 5%, complying with the limit set by IEEE Standard 519-2014 [36]
Summary
The widespread use of nonlinear loads has greatly degraded the quality of grid currents via generation of harmonic currents. In the context of SRF-based reference current generation algorithms, the STF algorithm has been applied to enhance the ability of phase-locked loops (PLLs) to work under non-sinusoidal source voltages [41] Like optimization algorithms, this algorithm is only evaluated under steady-state conditions. From [7,40,42], in order to achieve the best filtering performance of STF in extracting dc components of load currents, K2 is commonly set at a value between the range of 20 to 80, and f c is fixed at 50 Hz. Once the dc components of source voltage vSα(dc) and vSβ(dc) , and ac components of load current i Lα(ac) and i Lβ(ac) are computed, instantaneous complex power s is calculated as follows:. The non-sinusoidal iinj,re f forces the subsequent PWM switching pulses S1−4 meant for controlling mitigation operation of SAPF, to be generated based on the DCC scheme which operates by requiring the measurement of the actual injection current iinj
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