Search

In this paper, an accurate high-frequency modeling methodology for a permanent magnet synchronous motor (PMSM) in a vehicular electrical braking system is presented, which is suitable for analyzing various electromagnetic interference problems caused by a motor drive system. The proposed modeling approach is established according to the vector fitting technique and based on the S-parameter measurements of the PMSM. The equivalent circuit model of the PMSM converted from a measured S-parameter matrix can better describe the impedance characteristics of the three-phase PMSM under study compared to the existing equivalent circuit models because the imbalances inside the motor are taken into account in the proposed modeling process. The proposed PMSM model exhibits high accuracy in the range from 100 kHz to 120 MHz in comparison with the common-mode and differential-mode characteristics of the PMSM, which are measured using the conventional setups.

This paper presents a method for the reduction of mode conversion from differential-mode (DM) noise to common-mode (CM) noise in an unbalanced EMI filter. The unbalanced nature in the EMI filter is a result of not incorporating all the required filter components due to space and cost constraints or due to the parasitic impedances of a printed circuit board (PCB). It is demonstrated that the reduction of mode conversion from DM noise to CM noise can be achieved by modifying the current path on the ground (GND) layer of the PCB of the unbalanced EMI filter. The currents on the GND layer are guided to take a longer route by introducing a "cutout" to the ground plane in the PCB, which increases the impedance of the current path on the GND layer. This approach does not require additional components to the EMI filter for the reduction of CM noise due to the mode conversion. Simulations show that the cutout decreases the CM noise converted from the DM noise by at least 4 dB in the AM radio frequency band (530 kHz – 1.8 MHz).

In electric vehicles, the pulse width modulation scheme is widely used in three-phase motor drive systems for its high performance. However, the fast switching of semiconductor devices may induce excessively high dv/dt and di/dt, which can cause electromagnetic interference (EMI) issues, making it difficult to satisfy electromagnetic compatibility standards. In this paper, the current conducted emission test for a three-phase motor drive system is performed based on CISPR 25 component-level testing setup for AM radio frequency band, which is from 530 kHz to 1.8 MHz. Under these conditions, common-mode (CM) noise generation mechanisms of the motor drive system are identified through measurements. It is found that the dominant mechanism is the mode conversion from differential mode (DM) switching current of the three-phase PWM inverter to CM current through the cable harness due to the imbalances in the PCB structure and EMI filter network which are at the dc input side of the three-phase inverter. Based on this finding, ground (GND) bridges are added between the digital signal and power GND nets to reduce the CM noise. The GND bridge effect on the reduction of CM noise in AM band is experimentally verified and further studied using circuit simulations.

In this paper, a modeling method for predicting the conducted emission with a current probe method is presented for a motor-drive braking system. The proposed model considers the motor driving circuit components and the measurement environment. The models of motor driving circuit component include PWM inverter circuits, 3-phase motor, PCB, heatsink, bus bars, and motor casing. The models of measurement environment involve the current probe, test table including ground plane, harness cable, and LISN. To reflect the accurate path of common and differential mode current of the motor drive system, co-simulation is proposed with the equivalent circuit and SPICE model. Co-simulation is eventually conducted by using EMC Studio of EMCoS Ltd. for the calculation of electromagnetic coupling around the circuit, and the high-frequency parameters of the motor driving circuit are calculated through ANSYS Inc.'s Q3D. For the model validation, the measurement and simulation results are compared, and the results of the conducted emission of those agree well in the range of 100 kHz up to 108 MHz.

Self-assembled InAs/GaAs quantum dots (QDs) were grown by molecular-beam epitaxy and their structure and strain characteristics were studied by using transmission electron microscopy (TEM). TEM investigations were performed by conventional bright field TEM, high-resolution electron microscopy (HREM), annular dark field (ADF) and high angle annular dark filed (HAADF)-STEM techniques. In addition, strain analysis was performed on an atomic-length scale by measuring the space of lattices in HREM. Compressive strain was induced to uncapped QDs from GaAs substrate and the strain increased more than 3.5 % after GaAs cap layer growth. On the other hand, tensile strain by capped QDs was induced to GaAs up to 10 nm over the QDs, i.e. 15 nm over the wetting layer. It was also confirmed that the tensile strain extension resulted in aligned QD growth with 15 nm thick spacers