Characterization, analysis and simulation of Electro Magnetic Interference (EMI) in HVAC motors
Variable speed motors are used in HVAC systems (furnaces, heat pumps and air conditioners) to condition the air in a residential/commercial space. The speed of the motor is adjusted to provide an efficient system operation in an air conditioned space. The motor speed is adjusted by controlling the power applied by means of precise electronic control. The power electronics components and the switched voltage and currents produce Electro Magnetic Interference (EMI) in the system. To mitigate EMI, filters are integrated at the front end of the electronic controller in order to achieve compliance with FCC and CISPR22 class B standard . However, the increased switching frequency, together with the increased current and voltage slew rates, di/dt and dv/dt, have detrimental effects on the Electro Magnetic compatibility (EMC) performance of the system. At the same time, EMI filters typically have a degraded attenuation due to parasitic elements at high frequencies, and will be less effective in filtering out the high frequency EMI noises generated from the power circuits. This thesis describes a modeling approach of an electric drive system with device level components, with emphasis on the study of EMI performance. The multi-domain system software Ansoft Simplorer is used to characterize and model the passive and semiconductor components in the control board. The passive components are characterized by using the measured results obtained from an impedance analyzer where the models are presented as equivalent circuits, which is sufficient in the frequency range of conducted emission (0.15 - 30 MHz). To characterize and validate the semiconductor components, several models are imported from Pspice and predefined libraries of Ansoft Simplorer. The EMI levels of the electronic drive are measured by using a Line impedance stabilization network (LISN) device connected between the power supply and the control board (electronic drive) where the drive operates a motor which is modeled as an RL load. The measured EMI results are compared to the simulated EMI results. The impact of the parasitics on the EMI and also the improvements in the EMI filter to reduce the EMI has been simulated and analyzed.
Pomalaza Raez, Purdue University.
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