Riassunto analitico
In modern electric drives for traction applications the inverter is the heart of the system.
It provides AC current starting from a DC source using switches.
In the lasts years a lot of effort was put into increasing switching frequency in order to improve electric drive energy efficiency, to reduce torque ripples and motor noise.
However, this trend also has some shortcomings: every switching operation corresponds to a step-like voltage input in the machine winding, that generates overvoltage waves.
The overvoltage waves create an uneven voltage distribution in wires that could take into insulating failure due to partial discharge phenomena.
This phenomenon depends also on system properties, such as feeder cable length and impedance, motor coil arrangements, insulant material dielectric constant…
For these reasons, the estimation of voltage distribution during these transients is very important also in the design phase, to correctly design all aspects of the electric drive system, in order to avoid undesired short life of insulant material once it is put in operation.
A complete literature review is reported in this work, trying also to categorize the different methods and to extract practical information that are not reported but that can be useful for the modelling techniques evaluation.
The survey shows that there is not an overall best method, but every method is most suitable for being used in a specific phase of development.
The most accurate methods are the ones that consider the frequency dependency of electrical parameters, but they are more complex to be developed and more time consuming, thus they could be useful once the concept is almost fixed and a very precise voltage estimation is needed for an optimal design.
Other simplified methods, instead, could be useful in the early design phase, since even if their accuracy is not the best, they are very fast and can be used for sensitivity analysis.
Experimental measures for validation are reported in the thesis, since it is not possible to develop a reliable model without having feedback from the real word.
In the last chapter 2 modelling techniques were selected and replicated according to the tools and the capability of the working team, in order to understand if they could be useful for the needs of the company.
The first is multiconductor transmission line simplified circuit solved in SIMSCAPE electrical with electrical parameters, evaluated using electromagnetic FEM software.
The second is a “multidomain simulation” completely developed in an electromagnetic FEM software, able to also consider frequency dependency.
Since it is only a preliminary analysis some simplifications have been made during modelling activities: nevertheless, the results obtained are already acceptable and the two techniques will be considered for further investigations.
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Abstract
In modern electric drives for traction applications the inverter is the heart of the system.
It provides AC current starting from a DC source using switches.
In the lasts years a lot of effort was put into increasing switching frequency in order to improve electric drive energy efficiency, to reduce torque ripples and motor noise.
However, this trend also has some shortcomings: every switching operation corresponds to a step-like voltage input in the machine winding, that generates overvoltage waves.
The overvoltage waves create an uneven voltage distribution in wires that could take into insulating failure due to partial discharge phenomena.
This phenomenon depends also on system properties, such as feeder cable length and impedance, motor coil arrangements, insulant material dielectric constant…
For these reasons, the estimation of voltage distribution during these transients is very important also in the design phase, to correctly design all aspects of the electric drive system, in order to avoid undesired short life of insulant material once it is put in operation.
A complete literature review is reported in this work, trying also to categorize the different methods and to extract practical information that are not reported but that can be useful for the modelling techniques evaluation.
The survey shows that there is not an overall best method, but every method is most suitable for being used in a specific phase of development.
The most accurate methods are the ones that consider the frequency dependency of electrical parameters, but they are more complex to be developed and more time consuming, thus they could be useful once the concept is almost fixed and a very precise voltage estimation is needed for an optimal design.
Other simplified methods, instead, could be useful in the early design phase, since even if their accuracy is not the best, they are very fast and can be used for sensitivity analysis.
Experimental measures for validation are reported in the thesis, since it is not possible to develop a reliable model without having feedback from the real word.
In the last chapter 2 modelling techniques were selected and replicated according to the tools and the capability of the working team, in order to understand if they could be useful for the needs of the company.
The first is multiconductor transmission line simplified circuit solved in SIMSCAPE electrical with electrical parameters, evaluated using electromagnetic FEM software.
The second is a “multidomain simulation” completely developed in an electromagnetic FEM software, able to also consider frequency dependency.
Since it is only a preliminary analysis some simplifications have been made during modelling activities: nevertheless, the results obtained are already acceptable and the two techniques will be considered for further investigations.
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