Harmonic mitigation methods in large wind power plants

03.03.2014 00:00
Sunset Gunfleet Sands

Wind turbine generators (WTGs) are nowadays mainly connected via a widespread collector-system network of medium-voltage (MV) subsea cables. The voltage is then stepped up, and the wind power plant (WPP) is connected to the power grid through long high-voltage (HV) cables, which can be either a high-voltage alternating current (HVAC) or a high-voltage direct current (HVDC) transmission system. This grid connection system is still challenging to the industry from a harmonic generation, propagation and stability perspective.

Therefore, it is of great importance to investigate how a certain WTG or a group of WTGs interacts with the various elements of the WPP grid connection system, including the MV cable network, park transformer, HVAC export cable and shunt components such as the capacitor banks, shunt reactors, static VAR compensator (SVC), static synchronous compensators (STATCOMs), etc.

This paper presents potential harmonic problems and the various sources of such problems in large WPPs, as well as shows optimised harmonic mitigation methods. The harmonic problems (see Figure 1), such as harmonic resonances and emission sources as well as harmonic stability, are identified. Also, modern preventive and remedial harmonic mitigation methods (see Figure 2), in terms of passive and active filtering, are described.

It is shown that WPP grid connection system components, such as long HVAC cables and park transformers, can introduce low-frequency resonances, which can affect WTG control system operation and overall WPP stability as well as excitation of resonant circuits within the WPP grid connection system, causing significant harmonic distortion.
 
It is emphasised that there is a potential in terms of active filtering in modern power converters, eg in WTGs, STATCOMs or HVDC stations utilised in large, modern WPPs. It is also emphasised that the grid-side converter controller should be characterised by sufficient harmonic/noise rejection and adjusted depending on the WPP to which it is connected.