Main-circuit considerations of power coverters for integral motors

Sammanfattning: This thesis deals with different converter topologies for a 15kW permanent magnet (PM) integral motor. An integral motor combines the motor and the power electronics in one unit. The main objective is to find suitable converter alternatives for an integral motor. A suitable converter for an integral motor must be highly efficient and small in volume because the space for the power electronics is limited and the cooling capability of such a motor is reduced.It was shown that a 10uF polypropylene DC link capacitor is sufficient for the converter topology with a simple diode rectifier for a 15kW integral motor. The work includes a detailed analytical evaluation of the DC link voltage which leads to an equation of the maximum ripple in this voltage, depending on the motor power, the DC link capacitance and the switching frequency. Experiments were performed which validate the results of the simulations.As the diode rectifier does not provide line currents which fulfill the EMC standards given by the IEC, alternative switch-mode rectifiers are investigated in this thesis. Included are the Vienna Rectifier, the diode boost rectifier and the full-bridge switch-mode rectifier. Simulations with the software package PSCAD/EMTDC were performed for the mentioned converter topologies. All converters were designed in such a way that the harmonic emission of the line currents were in accordance with the EMC standards.A loss estimation method is presented which calculates the losses of the power devices by using both the simulation results and the loss data specified in the data-sheets for certain devices.It was found that the Vienna Rectifier with a tolerance band control is the most suitable alternative for the use in an integral motor. Measurements on prototype converters utilizing both the diode and the Vienna Rectifier are performed and the simulation and loss estimation results are confirmed. Furthermore, it was shown that the integral motor system performs well even under asymmetrical supply conditions despite the use of comparably small energy storage elements.A new model for the calculation of high-frequency losses in the corner coils of the presented type of integral motor is described as well. It is shown that the expected additional losses(especially eddy current losses) should not be neglected and need to be taken into account in future motor designs.