A Modular Multiple DC Transformer Based DC Transmission System for PMSG Based Offshore Wind Farm Integration

Abstract

In this paper, a modular multiple DC (MMDC) transformer based DC transmission system, which is used for permanent magnetic synchronous generator (PMSG) based offshore wind farm grid connection, is proposed. The MMDC transformer is composed of input-parallel output-series (IPOS) DC/DC submodule groups, each of which consists of several input-series output-series (ISOS) LLC resonant converters (i.e., submodules). In the offshore wind farm, the electrical power generated by PMSG is converted to DC power by diode rectifier. Compared with the existing offshore wind farm grid-connection schemes, the proposed system has advantages of fewer conversion stages, higher efficiency and lower cost. The mathematical relationship of the system is studied, and then one kind of control strategy is proposed. Furthermore, a detailed DC transmission system simulation model containing a 160 submodules (LLC resonant converters) based MMDC transformer is built in PSCAD/EMTDC. Finally, a down-scaled experimental prototype of the DC system, which includes 9 submodules, is presented. Both simulation and experimental results validate the feasibility of the proposed DC system and effectiveness of the control strategy. INDEX TERMS Offshore DC wind farm, modular multiple DC transformer, HVDC, input-parallel outputseries, input-series output-series.

Modular Combined DC-DC Autotransformer for Offshore Wind Power Integration with DC Collection

“…According to (10), α H,N (or α H,N+1 ) is largest in the HVM and supposed to be calculated particularly. U vacH,N , U vdcH,N , and P MMCH,N are described as [11]:…”

“…With the help of the AC transformers, isolated topologies could achieve the requirement of the high stepping ratio and galvanic isolation, but they show characteristics of high cost and large operation losses. Non-isolated topologies require less power semiconductor devices and no need for a transformer or the transformer which does not have to be rated for the full power of the DC-DC converter [11]. Compared with isolated topologies, non-isolated topologies have a smaller footprint and less operation losses and reduce the footprint of an offshore platform which is the major part of the total cost in an OWF [12].…”

Recent developments in offshore wind energy systems: Technologies and practices

“…This was accomplished by exploring the distance ranges with respect to offshore and remote onshore wind energy systems. A modular multiple DC transformer-based DC transmission system was described in detail by Hu et al [18]. This system employed a permanent magnetic synchronous generator based offshore wind farm grid connection.…”

Distributed model predictive control of all‐dc offshore wind farm for short‐term frequency support

“…In terms of transmission, the high‐voltage direct‐current (HVDC) is recognized as the most suitable, technical, and economical solution to this problem [4]. In terms of power collection, within a large OWF, using the dc collection grid would lead to a substantial reduction in the weight of the cables and the size of offshore platforms [5]. Considering these two facts, a dc‐grid OWF with an HVDC connection, which is also known as HVDC‐connected all‐dc OWF, is the future trend for offshore wind energy applications.…”