Fault Tolerant And Coupling Characteristics Analysis For Multiphase Parallel Interleaved Inverter

Multiphase parallel interleaved inverter technology has received more and more attention after extensive research and mature application of two-phase parallel interleaved inverter,with the development of power electronics technology.It can increase capacity in parallel,achieve output multilevel through carrier interleaving,and high equivalent switching frequency.It also has the potential for redundancy and modular design.Although the increase in the number of interleaved parallel phases can bring about these benefits,it also causes many new problems,including coupling inductance,filter inductance,controller design,and fault-tolerant operation strategies.This paper first analyzes the circuit characteristics of multi-phase parallel interleaved inverters and designs the coupled inductors.Then,the paper analyzes the soft saturation characteristics of magnetic powder filter inductors,that is,the inductance vary with the value of current,and proposes a corresponding compensation strategy.Then,the paper analyzes the control problem of low control frequency and high equivalent switching frequency,and proposes a controller bandwidth extension method.Finally,this paper analyzes and designs a fault-tolerant operation strategy based on coil short-circuit for multi-phase interleaved parallel inverters.The main research content of this article is as follows:The multi-phase parallel interleaved inverter has the advantages of multi-level output and high equivalent switching frequency.Then,as the number of interleaved parallel phases increases,will the number of output levels always increase,is there a limit? This paper analyzes the circuit characteristics of multi-phase interleaved parallel inverters.Based on the relationship between the modulation ratio and the number of interleaved shunt phases,the maximum number of interleaved parallel phases is deduced.In this paper,coupling inductors are chosen to connect each switch arm.Coupling inductance without air gap can greatly reduce the volume of the magnetic core element,but at the same time,it also has the problem of saturation,which is harmful to the reliable operation of the inverter.This paper analyzes the magnetic characteristics of the key device coupled inductors of a multiphase interleaved parallel inverter.According to the relevant conclusions,the design principle of enhancing the anti-saturation capability of the coupled inductor is proposed,and several coupled inductors suitable for different application requirements are designed.Multi-phase interleaved parallel inverters have multi-level outputs and high equivalent switching frequencies,and conventional inductor design methods are no longer applicable.In addition,the high frequency characteristics of magnetic powder core is better than that of silicon steel sheet,which is more suitable as the material of the filter inductance of the multi-phase interleaved parallel inverter.However,magnetic powder core material inductors have soft saturation characteristics,and the magnetic permeability decreases with the increase of the magnetic field strength.The external performance is that the inductance value decreases as the current increases.This affects the inverter’s current ripple characteristics,harmonic characteristics,and controller bandwidth.This paper investigates the relationship between the output current ripple and the number of interleaved shunt phases and the switching frequency of a multiphase interleaved shunt inverter.Based on this,an inductance design method for multi-phase interleaved parallel inverters is proposed.According to the soft saturation characteristics of the magnetic powder core,the model based on the Fourier series expansion was established and its influence mechanism on the inverter was analyzed.According to the law of current ripple variation,the principle of inductor design that adapts to the soft saturation characteristics of magnetic powder core is proposed,and smaller and more accurate inductor design results can be obtained than conventional methods.According to the mechanism of magnetic powder core inductance,a compensation control strategy is proposed to effectively improve the performance of the inverter.Finally,the experimental results verify the correctness of the analysis and the effectiveness of the proposed method.In a multi-phase interleaved parallel-connected inverter,the equivalent switching frequency is high and the inductance of the filter inductance is small.On the other hand,the frequency of digital control is limited by the digital implementation process,which is usually up to twice the switching frequency.This situation where the equivalent switching frequency is much higher than the control frequency is different from the conventional inverter,and there are new problems.This paper analyzes the effect of high equivalent switching frequency on inverter performance and controller design,and compares the advantages and disadvantages of several different control strategies.Then a controller bandwidth expansion method based on phase margin compensation is proposed.With this method,the initial controller bandwidth is increased by 13%,which significantly improves the dynamic response characteristics of the inverter.In a multi-phase interleaved parallel-connected inverter,the number of switching devices is large and there is a relatively large risk of failure.However,when the coupled inductor is in fault of the inverter,there is a saturation problem,which seriously affects the fault-tolerant operation capability of the multi-phase interleaved parallel inverter.In addition,when designing a fault-tolerant operation strategy and coupling inductance,it is necessary to couple the key parameters such as the voltage and current of the inductor coil and the circulation of the bridge arm.The number of magnetic poles in the coupled inductor is large,and the magnetic flux coupling relationship is complex,which makes it difficult to solve these parameters.This paper analyzes the magnetic properties of a coupled inductor under fault conditions and the principle of a fault-tolerant operation strategy based on the short circuit of the winding.Based on this,a set of methods for calculating the proposed key parameters was proposed.The results can be used to guide fault-tolerant operation strategies and the design of coupled inductors.Finally,the experimental results verify the correctness of the analysis and the effectiveness of the proposed method.