基于开关频率调制的高频变压器励磁曲线测量方法及其电磁暂态模型

Measurement Method of Magnetization Curve of High-frequency Transformer Based on Switching Frequency Modulation and Its Electromagnetic Transient Model

高频变压器是双有源桥(dual active bridge, DAB)变换器的关键器件,在运行中可能出现直流偏磁,构建具备铁芯非线性表征能力的高频变压器模型,是准确分析直流偏磁及其他涉及铁芯饱和的电磁暂态特性的基础。模型的关键在于准确测量高频变压器的励磁曲线。该文通过开关频率调制使DAB产生等幅值变频方波电压,对中间高频变压器进行变磁链激励,通过端口电压电流测量和计算获得其磁滞回线簇和励磁曲线。该方法不需要新增任何交流激励电源,可在DAB变换器投运时通过开关调制实现高频变压器励磁曲线的测量,解决了高频变压器励磁曲线测量低效率和高成本的难题。以1台高频变压器为对象,对其励磁曲线进行测量并构建电磁暂态模型,搭建DAB测试平台,开展了额定频率过电压和直流偏磁试验及仿真,模型仿真误差均在7%以内,均方误差最大仅0.0027。结果表明:考虑励磁非线性的高频变压器电磁暂态模型能够大幅提高铁芯饱和工况的仿真精度,对DAB电磁暂态特性分析与控制具有重要意义。

The high-frequency transformer is a crucial device in a dual active bridge(DAB)converter.DC bias may occur during operations.Constructing a high-frequency transformer model with the capability to accurately represent the nonlinearity of the magnetic core is the basis to accurately analyze the electromagnetic transient characteristics involving core saturation,such as direct current(DC)bias.The key lies in accurately measuring the magnetization curve of the high-frequency transformer.In this paper,the DAB generates an equal amplitude variable frequency square wave voltage by switching frequency modulation,and the intermediate high-frequency transformer is excited by variable flux linkage.Magnetization curves and hysteresis loop clusters are obtained through calculations based on the voltage and current data measured at the port.This method does not need to add any AC excitation power supply,and can realize the measurement of magnetization curve of high frequency transformer by switching modulation when DAB converter is put into operation,which can solve the technological problems of inefficient and high-cost measurements for the magnetization curves of high-frequency transformers.A DAB platform is built to measure the magnetization curve of a test high-frequency transformer and its electromagnetic transient model is built.The rated frequency overvoltage and DC bias experiments and simulaitons are carried out.The model simulation errors are all within 7%,and the maximum mean square error(MSE)is only 0.0027.The results show that a high-frequency transformer electromagnetic transient model that considers excitation nonlinearity can greatly improve the simulation accuracy of core saturation conditions,and it is of great significance to the electromagnetic transient characteristics analysis and control of DAB.