Review of wind farm power collection schemes

Abstract

The main development trend of wind power generation systems is large offshore wind farms (OWFs) with grid connection. However offshore wind farms have grown rapidly due to much better wind conditions. Hence, several large scale offshore wind farms are planned to be built and installed at distances greater than 100 km from the coast. Traditionally, an AC collector scheme collects energy from the wind farm and step up the voltages by power transformers and transmit power via AC submarine cables to the onshore substation. However, this is suitable for shorter distances about 50 km. When the distances are greater the AC transmission of bulk power from the wind farm to the onshore grid via undersea cables is not viable due the reactive power issues. Therefore HVDC transmission is now being considered for the grid connection of wind farms. However as wind farms constitute weak systems Line commutated converter (LCC) based HVDC is not viable and newer Modular Multilevel Converter (MMC) based Voltage Source Converters(VSC) are needed for AC-DC conversion. Opting for dc systems for both power collection and transmission pose a number of technical challenges in terms of developing HVDC breakers and DC -DC converters.

A Compact DC-DC Converter for Offshore Wind Farm Application

“…The middle circuit comprises a number of IGBT switches, capacitors, and diodes D (1)(2)(3)(4)(5)(6)(7)(8) . The number of capacitors denoted by "n" is set to 5 to create a voltage amplification of 5.…”

“…The number of capacitors denoted by "n" is set to 5 to create a voltage amplification of 5. The capacitances in the 5 sub-modules are indicated by C n , where n= (1,5). The switching The output circuit consists of an output diode D out connected in series with the output inductor L out , and one output capacitor C out.…”

“…Due to the increasing distances of renewable and embedded generation in transmission and distribution systems, it is expected that the use of High Voltage Direct Current HVDC transmission and Medium Voltage Direct Current (MVDC) distribution systems for the grid integration of windfarms will grow worldwide [1]. One of the key components in such systems is the DC-DC converter, required to act as the interface between the generation, transmission and distribution voltage levels.…”

High voltage cascaded step-up DC-DC Marx converter for offshore wind energy systems

“…Due to the increased distances to off shore windfarms from the shore, it is expected that the use of High Voltage Direct Current (HVDC) transmission and Medium Voltage Direct Current (MVDC) distribution systems for the grid integration of windfarms will grow worldwide. One of the key components in such systems is the DC-DC converter, required to act as the interface between the generation, transmission and distribution voltage levels [1]. Well-established DC-to-DC converters based on pulse width modulated (PWM) converters, which require high frequency switching, are not suitable.…”

“…Some converter topologies, which are suitable for high-voltage operation, have been proposed in the literature. Laird [3] and Alagab [1] have proposed suitable step-up converters. The drawback of these converters is the limited voltage gain.…”