Dynamic Breaking - FPGA Implementation of DCC

University essay from Lunds universitet/Industriell elektroteknik och automation

Abstract: In this thesis a Direct Current Control (DCC) is implemented for controlling a PMSM. The controller should be implemented in an already existing program. This program is used for testing electrical machines. The new testing method is called Dynamic braking, more information about this method can be read in the report "Performance and efficiency evaluation of FPGA controlled IPMSM under dynamic loading," by Y. Loayza, A. Reinap and M. Alaküla. The reason to implement a DCC is that the current PI-controller have problems with sudden changes in current reference. This has become a limitation of the speed due to the risk of damaging the inverter. With the characteristics of a DCC some of the problems that a PIcontroller can be neglected, for example the need of feedforwarding and overshoots. Also the simplicity of the DCC is an advantage. This comes with a cost which is that it demands high sampling frequency. But with the FPGA’s parallel execusion and possibility to high sampling frequency it is possible to use the DCC. The goal of this thesis is to make the DCC work in the existing project and also take care of the problem that the previous controller had. The implemented DCC was able to work in the existing project. A new problem has occurred, the switching frequency. Due to the fact that the DCC is switching when needed, the switching frequency can be too high , this limits the minimum size of the tolerance band. The things that has to be considered in the choise of tolerance band is the switching frequency against the control of the current. Smaller tolerance band gives better control to the cost of higher switching frequency. With the DCC the influence of cogging is reduced in the measurement and the control of the current is improved.

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