Research And Design On Multi-winding High Frequency Transformer

The HVDC transmission technology is being widely applied to offshore wind farms.For the key component of DC-DC converter in HVDC system,multi-winding high-frequency transformer can be used to realize the balance of power and voltage of each module in order to simplify system design.Light-weighted high-frequency transformer can reduce the costs of offshore platform construction because it’s smaller and lighter than low-frequency transformer with identical capacity.There are several key problems in the research on high-frequency transformer.The high-frequency eddy current effects cause a reduction in leakage inductance.In addition,the skin and proximity effects,as well as the high-speed magnetization and demagnetization of the magnetic cores under non-sinusoidal excitations have made the calculation of transformer winding and core losses more complicated.Furthermore,the cooling system must be able to transfer higher heating quantity in per unit volume.This paper proposes a design methodology of multi-winding high-frequency transformer.The finite element models of multi-physical field of transformer are established to study the magnetic field distribution and power loss characteristics of high frequency transformer.This paper gives an analysis of the high-frequency leakage inductance and the calculation for leakage inductance of multi-winding transformer by FEM.The winding and core losses calculation under non-sinusoidal excitation is simplified by the introduction of the equivalent frequency.Two solutions of multi-winding structure design are studied and one of them is chosen to design a 1MW high-power multi-winding single-phase transformer with rated frequency of 20 k Hz.An effective cooling system is built on the basis of the heating power and location of main power loss components.The efficiency is 99.67% with transformer losses and rated inputs of cooling devices taken into consideration.