Condition Monitoring And Fault Diagnosis Of Power Device For Quadratic DC-DC Converter

With the development and application of new energy technologies such as solar photovoltaic power generation and wind power generation,higher requirements have been placed on the function and reliability of power converters.For example,the traditional DC-DC converters have been unable to adapt well to the high gain requirements of new energy power generation.In recent years,the quadratic DC-DC converters have been widely used in new energy power generation due to it high gain and simple structure.The cost is the same as the traditional DC-DC converter,the quadratic DC-DC converters only needs one power switch,but it can achieve the quadratic voltage gain and expand the input-output conversion range.However,the quadratic DC-DC converters are relatively less reliable than the traditional DC-DC converters.Power devices will withstand higher voltages and operating temperatures and are extremely prone to failure.Therefore,it condition monitoring and fault diagnosis are of great significance.In order to improve the reliability of the quadratic DC-DC converter,this paper develops the online condition monitoring method and fault diagnosis method of the power device of the quadratic DC-DC converter.The main contents are as follows:（1）The working principle and characteristics of the quadratic DC-DC converter are analyzed.Compared with the traditional DC-DC converter in terms of complexity,volume and conversion efficiency,the advantages are pointed out.Taking the CCM-CCM mode quadratic Boost converter as an example,the power device losses of the quadratic boost converter are calculated and the junction temperature simulation is performed.It is pointed out that compared with the traditional Boost converter,the power device losses and junction temperature increase greatly and easy to fail.The higher rate indicates the relationship between power loss and duty cycle,load resistance and power supply voltage.Using the PLECS platform,the model is established and the simulation results are given.（2）IGBT devices are more commonly used in the quadratic DC-DC converters due to the greater voltage and current stresses.Taking the IGBT device of the DC-DC converters as an example,a condition monitoring study based on saturation voltage drop was carried out.First,the failure mechanism of the IGBT device is analyzed,and the volt-ampere characteristics and temperature-sensitive characteristics of the saturation voltage drop are pointed out from the perspective of physical mechanism.The three-dimensional relationship of collector current I_C—saturation voltage drop U_CEsat—junction temperature T_jis studied.Then,in the DC-DC converter,the performance degradation state is reflected by obtaining the situation where the conduction voltage drop of the IGBT device at the current moment and the saturation voltage drop of the normal IGBT device under the same condition state.（3）For the power switch and the power diode in the quadratic DC-DC converter,a fault diagnosis method that can quickly diagnose the short circuit or open circuit of the switch or the diode is designed online.In this method,through in-depth study of the difference between the voltage and current signals of the switch or the diode during fault and normal operation,the characteristic electrical quantities,inductance voltages and PWM signals that are easily extracted in the converter are selected as fault diagnosis signals.Using simple logic combination can correctly determine the type of failure The test results are given to verify the effectiveness and feasibility of the proposed online fault diagnosis method.