Abstract
Harmonic amplification for doubly-fed induction generator wind turbine systems (DFIG WTSs) will occur due to the existence of non-linear loads and reactive power compensation installation, and grid voltage and total grid current at the point of common coupling (PCC) will be distorted. An impedance model is established to analyze the interaction between DFIG WTS, non-linear loads and weak grids. Harmonic current impact factor and harmonic voltage impact factor is proposed to analyze the impact of harmonic current source on total grid current and voltage at the PCC with different control strategies. A virtual harmonic resistor and capacitor method is adopted to reduce the harmonic voltage. An impedance-based analysis method is adopted to analyze the stability of the DFIG system. To achieve optimal control of harmonic voltage and harmonic current, a coordination factor is proposed to adjust the dynamic allocation for harmonic voltage and harmonic current at PCC. The experimental results demonstrate the effectiveness of the proposed control strategy.
Highlights
Renewable energy technologies, especially wind power technology, have won widespread attention and seen rapid development due to the grim energy and environmental issues, and DFIG wind power systems are the most widely used [1,2,3,4,5,6]
Using a grid-side converter (GSC) and rotor-side converter (RSC) together, one can achieve the stable operation of control DFIG, and the converter only accounts for 30% of the total power-generating capacity
DFIG control has been maturely researched under the ideal grid voltage conditions, but non-linear loads are often linked to the grid, which will inject harmonics into the grid, especially when parallel capacitors and line impedance are contained in weak grids, and a harmonic amplification will occur in double-fed wind power systems due to their interaction with the DFIG impedance, this leads to distortion in the total grid current and voltage at the point of common coupling (PCC)
Summary
Especially wind power technology, have won widespread attention and seen rapid development due to the grim energy and environmental issues, and DFIG wind power systems are the most widely used [1,2,3,4,5,6]. If a conventional control strategy is adopted, distorted stator and rotor currents, fluctuating stator active and reactive power and torque are produced, which is harmful for the DFIG WTS and the grid [12,13]. In [15,16], an integrated mathematical model of DFIG was presented in a positive synchronous reference fame (d-q frame) under distorted grid voltage conditions, where the pulsations of electromagnetic torque and instantaneous stator active/reactive powers were fully described. The total grid harmonic current is suppressed with the PIR regulator in the GSC and RSC adopts a closed-loop control strategy of stator harmonic current based on the rotor current loop with a PIR regulator, respectively.
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