Harmonics reduction in standalone DFIG-DC system by shunt active filter controlled in stator flux reference frame

Abstract

The presence of diode rectifier in standalone Doubly Fed Induction Generator-Direct Current (DFIG-DC) system leads to considerable current, voltage and torque harmonics and requires reactive power from the machine. A unique shunt active filter arrangement is proposed for addressing these requirements. The DC Link of DFIG-DC itself acts as input to shunt active filter and there is no requirement of creating and regulating a separate one. Since the stator flux reference frame is known in FOC of DFIG-DC system; the same can be used as PLL for the generation of current references for harmonics and reactive compensation in active filter control scheme. Hence, the AC voltage sensing is not needed in the proposed active filter control. In this paper, it is shown that current, voltage and torque harmonics are reduced with the help of shunt active filter, which have lower rating compared to the rotor side converter. The proposed scheme is verified by detailed experiments on a 5.5 kW slip-ring induction machine.

Improved super‐twisting sliding mode control of a stand‐alone DFIG‐DC system with harmonic current suppression

“…With these results, the innovation of the proposed approach over the existing compensation method in [23] is illustrated. In [23], a shunt active filter is added in the stator side of DFIG to suppress the fifth and seventh stator current harmonics. Meanwhile, the torque ripples are reduced indirectly.…”

“…The primary objectives of dc power generation system are to keep dcbus voltage constant under stand-alone condition or to control stable power flow under grid-connected condition. In recent years, the regulation of DFIG-DC system is considered in [10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

“…In [22], a direct torque control strategy is proposed with a hysteresis controller for a DFIG-DC system controlled from the stator side. To further relax the influence of harmonics, a shunt active filter in the stator flux reference frame is added to reduce the harmonic current and torque ripple in [23]. However, the cost of the equipment is increased due to the additional converter.…”

“…The torque ripples are reduced to one‐third of that without compensation. Moreover, compared with [23], the shunt active filter is removed while keeping a similar suppression performance to harmonic currents and torque ripples. By removing the active filter, the cost is reduced obviously.…”