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This paper focuses on the modelling of the series resonant converter proposed as a DC/DC converter for DC wind turbines. The closed-loop control design based on the discrete time domain modelling technique for the converter (named SRC#) operated in continuous-conduction mode (CCM) is investigated. To facilitate dynamic analysis and design of control structure, the design process includes derivation of linearized state-space equations, design of closed-loop control structure, and design of gain scheduling controller. The analytical results of system are verified in z-domain by comparison of circuit simulator response (in PLECS™) to changes in pulse frequency and disturbances in input and output voltages and show a good agreement. Furthermore, the test results also give enough supporting arguments to proposed control design.

6.5kV IGBT power modules and line frequency press-pack diodes are proposed for a new mega-watt, medium voltage, resonant converter intended for DC wind turbines. The challenge of characterizing losses in softswitching semiconductors - without building the full circuit - is overcome by a proposed test circuit and procedure that minimizes cost and complexity, yet subjects the device under test to similar use as in the target application. The paper describes the test method, and results obtained with it.

Offshore HVDC-connected wind farms promise reduced electrical losses, lower bill-of material cost and undiminished functionality with the condition the wind plant MV collection network becomes DC, rather than MVAC. One dearly missed building block that would enable the transition to a DC voltage collection, is the DC/DC converter for high power & high voltage (megawatss and kilovolts).The main objective of this thesis was investigation and development of a turbine DC/DC converter proof of concept. The selected topology is based on a single phase series resonant converter, operated with a new modulation scheme, which permits regulation of power from nominal level to zero, in presence of variable input and output DC voltage levels. The circuit was rearranged so that the LC tank is located on the rectifier side of thehigh-turns ration transformer combined with frequency control and phase shifted inverter modulation. The modulation scheme was entitled pulse removal technique and it keeps the transformer flux constant from nominal frequency down to DC, always in sub-resonant continuous or discontinuous conduction mode. A design guide line, suitable for a given range of specifications, in the megawatt (5 to 15 MW), kilovolt (_35 to _50 kV) and kilohertz (0.5 to 5.0 kHz) range is introduced, while medium voltage experimental setups are implemented for characterization of losses, control and voltage sharing.

Offshore HVDC-connected wind farms can with advantage let the wind plant powercollection network become DC, rather than AC, promising reduced electrical losses, lowerbill-of-material cost and undimished functionality. However, no standards exist for anoffshore medium-voltage DC power collection cable-based system, routing power fromMVDC wind turbines all the way to the HVDC export cable. To progress, it is thereforeimportant to establish some common reference for the design and performance of thecomponents needed in an MVDC collection network. Any suggested MVDC collectionsolution must be possible to characterise and evaluate through a series of case studies. Thispaper proposes a methodology to simulate the MVDC collection network and thereby findsuitable ratings of its components. The methodology is intended to allow studies on anyconfiguration of the MVDC power collection, regardless of choice of turbine converter circuit,MVDC cable configuration, use of DC circuit breakers, substation converter circuit, controland protection. The paper will present the necessary list of studies, and include examples ofsimulation results for an examplary MVDC wind power plant. Offshore HVDC-connected wind farms where the wind plant power collection network becomes DC, rather than AC, offer reduced electrical losses, lower equipment ratings potentially leading to lower bill-of-material cost, and undiminished functionality. However, no standards exist for an offshore medium-voltage DC power collection cable-based system, routing power from MVDC wind turbines all the way to the HVDC export cable. To progress, it is therefore important to establish some common reference for the design and performance of the components needed in an MVDC collection network. Any suggested MVDC collection solution must be possible to characterize and evaluate through a series of case studies. This paper proposes a methodology to simulate the MVDC collection network and thereby find suitable ratings of its components. The methodology is intended to allow studies on any configuration of the MVDC power collection, regardless of choice of turbine converter circuit, MVDC cable configuration, use of DC circuit breakers, substation converter circuit, control and protection. The paper presents the necessary list of studies, and includes examples of simulation results for an exemplary MVDC wind power plant.

For a DC wind turbine, a single phase series-resonant converter for unidirectional power is studied. This paper aims to identify and compare impact on electrical losses and component ratings from the choice of three candidate control strategies. The evaluation is purely based on circuit simulations and offline post-processing of losses. The initial findings indicate that lower losses are obtained in discontinuous current mode (DCM) conditions, with drawbacks on transformer design.