Shaft Voltage Reduction Method Using Carrier Wave Phase Shift in IPMSM

Common-Mode Voltage (CMV) induces shaft voltage and bearing current due to the electrical interaction with the parasitic capacitance of the motor. CMV, shaft voltage, and bearing current are considered the major causes of bearing fault. Motor fault in a traction system poses a risk of accidents. Therefore, it is necessary to reduce the CMV and the shaft voltage to ensure the reliability of the bearing. However, some existing CMV reduction methods are based on asynchronized space vector pulse width modulation (SVPWM), which will cause unacceptable harmonic distortion at a low switching frequency. Alternatively, some CMV reduction methods based on synchronized SVPWM burden the processor because they require a lot of calculation. In this paper, the method to reduce CMV and shaft voltage is proposed using carrier wave phase shift in SVPWM. CMV is explained in traditional SVPWM, and CMV is reduced by shifting the carrier wave phase of one phase. The simulation model is constructed through MATLAB/SIMULINK and Maxwell 2D/Twin Builder. Considering the proposed method, CMV, shaft voltage, and bearing current are analyzed by an equivalent circuit model. Moreover, the output torque behaviors with different input currents are analyzed through the simulation.

Common Mode Current Effects and Challenges for Wind Turbine Generator Application

Operation of the generator with full converter and long tower cables leads to common mode and bearing current in the wind turbine. Common mode and bearing current are almost always present in such systems, due to the harmonics reflections within large tower cables. An electrical system should be carefully designed to perform in such environments. Bearing insulation thickness should be carefully chosen to minimize the impact of bearing current. Ideally these currents should flow through the dedicated path within the nacelle and pass through the tower to the ground. Due to complex structure of the nacelle in the onshore geared turbine and dealing with a very high frequency current, this is usually not the case. A complex cable routing and formation of different conducting path leads the common mode current to flows into an unexpected direction. It is the part of a good system design to monitor the path and evaluate the potential impact on the sensitive components to avoid potential failure in the field. A higher downtime of the turbine corresponds to a less reliable turbine, this is also closely associated with the levelized cost of electricity. This paper presents an overview of the system for the preferred common mode current routing and recommend various method by which formation of unwanted grounding loops can be avoided.

Modified Slot Opening for Reducing Shaft-to-Frame Voltage of AC Motors

This paper presents a method to reduce the winding-to-rotor capacitance of electrical machines for the purpose of suppressing shaft-to-frame voltage, which causes reliability issues, such as electromagnetic interference (EMI) and bearing current. The proposed method is based on the modification of slot opening shape of the stator core, including the variation of slot opening width and the use of oblique slot opening. For the verification of the suggested method, six different slot opening shapes, including a reference design, are analyzed and compared using finite element analysis, and the results show that the proposed method can reduce the shaft-to-frame voltage by 98%, compared to the reference design.