Harmonic Filter Reduction of OffshoreWind Farms Connected with a Diode Based HVDC Link Report Noveltyand industrial relevance Even though LCC-HVDC links have benefitsin terms of efficiency, cost and power capacity, they are not used forconnecting large off-shore windfarms to mainland grid due to the requirement ofvery large filter banks. This paper shows that using the additional controlflexibility provided by using turbines having fully rated converters, thefilter bank size can be considerably reduced. Hence, making it a feasible,efficient, reliable and cost-effective solution for connecting off shore farmsto AC-grid. Summary In the system, consisting of off shoreparts (windfarm, ac grid, rectifier) and on shore parts (ac grid and inverters)each turbine has a fully rated back-to-back converter connected to a PMSG, effectivelycontrolling the frequency and voltage of the off shore grid using a distributedcontrol algorithm.
They also provide protection to the HVDC link and off shoregrid from short circuit. So, a controlled rectifier is no longer needed, thisenables us to replace the controlled SCR rectifier with uncontrolled dioderectifier. The need for large and heavy capacitor and filter banks (the MVArating being typically around 0.4-0.6 pu), to provide reactive power and reduceharmonics, makes the system bulky and expensive. Additionally, the filterdesign depends on the network harmonic impedance which requires lengthyanalysis of the network. Reactive power compensation can be provided by the turbinefrontend converter, thereby reducing the capacitor and filter banks to approximately0.
1 pu, which is one-fifth of its original size. As, the wind turbine front-endconverters are needed to produce 0.4pu reactive power, we need to increase thepower ratings of the converters and transformers by 7.7%. Filter bank reduction hasconsiderable effect on off shore ac currents and voltage. With the reduced 0.5pu capacitor and filter bank, the diode rectifier current harmonics increasemarginally as the distortion of windfarm ac voltage is small, below 0.
03 pu, withinplanned level specified in IEC-1000-3-6. Nonetheless, it has significant effecton current through the capacitor bank. The harmonics rise from 0.05 pu to a maxof 0.28 pu. This rise in distortion must be taken in consideration whiledefining capacitor bank’s ratings. The conduction loss at rated power of frontend converter increases by approx.
16% due to its increase in current rating by7.7%, The wind turbine transformer loss, consisting mainly of of and Eddy current lossesis increased to 0.605%( 0.1 pu bank) from 0.
6%, and the increase in harmonicloss is found to be negligible, 0.7%. To conclude, with the controlalgorithm we can use diode rectifier, with much reduced filter bankrequirements, causing only small effect on system losses.
The need forswitching filter banks according to the power transmitted is also eliminatedthereby, improving reliability and reducing costs. How the paper relates to H54PE2