The following paper presents a novel, empirical approach to gate charge control of a MOSFET used in low-side drive applications such as found in dc motor drives during turn-OFF, using pulsewidth modulation (PWM) based on ideal expressions of MOSFET behavior during turn-OFF. Without gate charge control, ringing and overshoot caused by dv/dt effects during the turn-OFF can result in an increase in electromagnetic interference as well as an increased power dissipation. The ringing can be difficult to suppress through the addition of suppression components as they add cost and bulk to the motor controller. Previous work has focused on the observation of dv/dt, feed-forward, or openloop means. Although complex gate charge solutions exist in dedicated application-specific integrated circuits (ASICs), a simple, cost-effective solution is proposed in this paper. This solution differs from previous solutions, making use of the ideal relationship between the drain-to-source and gate-to-source voltage of the MOS-FET on turn-OFF to determine the region of high dv/dt to control a two-staged gate charge removal scheme. This solution can be readily implemented in microprocessor-based control schemes used to control motor drives and switch-mode power supplies utilizing lowside MOSFET switching. Circuit operation and advantages are presented and supported by simulation and experimental results.
With the proliferation of electronic devices in automobiles, an emphasis has been placed on EMC issues for among others reasons, safety. The EMC design cycle can be lengthy, with the mitigation of conducted RFI emissions still largely a trial and error process. The use of a virtual motor and drive model can be used to shorten this process. In the modeling of conducted RFI emissions, an accurate model of motor and drive is necessary. Furthermore, a representative method of characterizing the conducted RFI spectrum is required. A virtual motor model for an electronically commutated engine cooling fan motor and drive is presented to predict conducted RFI emissions up to 30 MHz. This model forms the basis of a method that may be used to predict conducted RFI emissions on other motor and drive types.
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