Motor Integrated Variable Speed Drives

Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

Abstract

A new trend in the variable speed drives (VSDs) is to develop fully integrated systems, which lead to low-cost products with shorter design cycles. Motor Integrated design of VSDs will reduce cable length to connect drive with machine windings and installation time for end user. The electric drives are expected to have minimum effect on grid and motor connected to it, i.e. currents drawn from grid should be within specified limits and currents injecting in to machine should not overheat the machine windings to avoid insulation failure due to harmonics. It is also necessary that electric drives should not disturb other loads connected to the point of common coupling (PCC). Diode rectifier followed by a voltage source inverter (VSI) is well accepted by the industry, and it has low losses and high reliability, but it requires big and bulky passive elements to ensure total harmonic distortions (THDs) in input currents to be within specified limits of present standards. Improving the quality of input currents of a three-phase-fed VSD is a requirement that needs cheap and competitive solutions for implementation. High efficiency, small volume and low cost are nowadays basically the first three aspects mentioned when it comes to the development of any kind of power converter topology for power electronic applications. Concerning the use of a power converter in motor integrated VSDs, the first two mentioned aspects receive an even greater im-portance. Power converter design for integrated drives poses a host of significant challenges that originate both from the limitations on available space and the need to adapt the power converter to the thermal, vibration, and electromagnetic field stresses inside the motor housing. Losses in the motor can heat up the motor environment to a significant temperature above ambient. The high operating temperature of the power electronics in integrated drives seriously limits the power they can dissipate, which decreases the power handling capability of the converter. In motor integrated VSDs, the main challenge, as mentioned above, is to reduce the power converter losses and its size so it can fit inside the motor housing. Weight and volume of a filter inductor has to come down drastically to make it a suitable power converter for motor integrated variable speed drives. Introduction of active power electronic switches can ensure very high performance and small size of such an inductor. Such an arrangement is usually referred to as “Electronic Smoothing” techniques. The electronic smoothing inductor (ESI) based converter is easy to integrate in the existing power circuit of a VSD and does not demand too many changes either in the power circuit or in the control. Volume and weight of these drives with ESI are smaller and it is very much suitable for integration with an electrical motor. Converter topologies with reduced size of passive components will provide a compact power converter for integrated drives. In research, efforts have been made to replace the traditional limited-lifetime electrolytic capacitors with film capacitors. The voltage source inverter (VSI) with a small dc-link capacitor is getting more and more attention from the research community and industry. Impact on the utility of VSI with smaller DC link filter and standard three phase diode bridge rectifier at the front end is presented in this thesis and requirements of a buffer stage in the form of ESI is explained in detail. An equivalent circuit and linear model are developed to give the transfer function and control of the ESI based three-phase rectifier. In this thesis a power converter with ESI is designed and tested with standard induction motor to verify functionality of a working drive. One modified version of the ESI based converter has also been looked into to reduce losses of converter, but because of difficulties in reducing the bus-bar inductance in that design, further investigation was not carried out. The ESI based converter successfully brought down total harmonic distortions (THDs) in grid current to 31% level and improved power factor to 0.95 by employing a small converter with estimated losses of 23W for a 4kW system. Hence, there is a significant improvement in the performance of the drive.
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Detaljer

A new trend in the variable speed drives (VSDs) is to develop fully integrated systems, which lead to low-cost products with shorter design cycles. Motor Integrated design of VSDs will reduce cable length to connect drive with machine windings and installation time for end user. The electric drives are expected to have minimum effect on grid and motor connected to it, i.e. currents drawn from grid should be within specified limits and currents injecting in to machine should not overheat the machine windings to avoid insulation failure due to harmonics. It is also necessary that electric drives should not disturb other loads connected to the point of common coupling (PCC). Diode rectifier followed by a voltage source inverter (VSI) is well accepted by the industry, and it has low losses and high reliability, but it requires big and bulky passive elements to ensure total harmonic distortions (THDs) in input currents to be within specified limits of present standards. Improving the quality of input currents of a three-phase-fed VSD is a requirement that needs cheap and competitive solutions for implementation. High efficiency, small volume and low cost are nowadays basically the first three aspects mentioned when it comes to the development of any kind of power converter topology for power electronic applications. Concerning the use of a power converter in motor integrated VSDs, the first two mentioned aspects receive an even greater im-portance. Power converter design for integrated drives poses a host of significant challenges that originate both from the limitations on available space and the need to adapt the power converter to the thermal, vibration, and electromagnetic field stresses inside the motor housing. Losses in the motor can heat up the motor environment to a significant temperature above ambient. The high operating temperature of the power electronics in integrated drives seriously limits the power they can dissipate, which decreases the power handling capability of the converter. In motor integrated VSDs, the main challenge, as mentioned above, is to reduce the power converter losses and its size so it can fit inside the motor housing. Weight and volume of a filter inductor has to come down drastically to make it a suitable power converter for motor integrated variable speed drives. Introduction of active power electronic switches can ensure very high performance and small size of such an inductor. Such an arrangement is usually referred to as “Electronic Smoothing” techniques. The electronic smoothing inductor (ESI) based converter is easy to integrate in the existing power circuit of a VSD and does not demand too many changes either in the power circuit or in the control. Volume and weight of these drives with ESI are smaller and it is very much suitable for integration with an electrical motor. Converter topologies with reduced size of passive components will provide a compact power converter for integrated drives. In research, efforts have been made to replace the traditional limited-lifetime electrolytic capacitors with film capacitors. The voltage source inverter (VSI) with a small dc-link capacitor is getting more and more attention from the research community and industry. Impact on the utility of VSI with smaller DC link filter and standard three phase diode bridge rectifier at the front end is presented in this thesis and requirements of a buffer stage in the form of ESI is explained in detail. An equivalent circuit and linear model are developed to give the transfer function and control of the ESI based three-phase rectifier. In this thesis a power converter with ESI is designed and tested with standard induction motor to verify functionality of a working drive. One modified version of the ESI based converter has also been looked into to reduce losses of converter, but because of difficulties in reducing the bus-bar inductance in that design, further investigation was not carried out. The ESI based converter successfully brought down total harmonic distortions (THDs) in grid current to 31% level and improved power factor to 0.95 by employing a small converter with estimated losses of 23W for a 4kW system. Hence, there is a significant improvement in the performance of the drive.
OriginalsprogEngelsk
ForlagDepartment of Energy Technology, Aalborg University
Antal sider191
StatusUdgivet - 2015
PublikationsartForskning

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