Suppression of Current Fluctuations and the Brake Torque for PMSM Shutoff in Electric Vehicles

Abstract

When a safety-related fault in the motor controller is detected, the torque output of the motor cannot be effectively shut off in time and an overcurrent occurs at the moment of switching. The advantages and disadvantages of the open circuit and active short-circuit methods are analyzed. Combining the advantages of these two operations, this paper proposes a new mixed voltage modulation method. It introduces a voltage modulation ratio that represents the duty cycle of the open circuit operation during a PWM period. This ratio is first set to a fixed value and gradually reduced to zero. The inverter is switched at a mixed operation and finally remains in the active short-circuit mode. The current can be quickly converged by a freewheeling diode of open circuit. After switching to active circuit, the brake torque is safety. The effectiveness of this shutoff method was verified by simulations and experiments. It shows that current fluctuations are suppressed and the torque output is also within a safety range. In addition, this shutoff method does not require any additional sensor information and is simple to implement.

IGBT Junction Temperature Measurement Under Active-Short-Circuit and Locked-Rotor Modes in New Energy Vehicles

“…In this case, the coolant temperature is estimated by means of the thermal model between the NTC and coolant, since the temperature of equipped NTC temperature sensor can be real-time obtained. The coolant temperature can be obtained according to (21) based on the NTC temperature. IGBT, FWD and half bridge, respectively.…”

“…In the past research, more attention has been paid to thermal stresses on IGBT modules under the normal operating applications. However, the common abnormal operation in electric drive system such as active-short-circuit (ASC) [21]and locked-rotor(LR) modes [22] should be investigated, since large energies will be involved and the operations can drive the semiconductor chips into destruction immediately when reaching the thermal limit.…”

“…With respect to the ASC mode, it serves as a protection mechanism according to the functional safety standards for vehicle ISO 26262 [23,24]. Three high-side IGBTs or three low-side IGBTs are switched on during the ASC operation and the three phases of the motor are short circuited via the high-side IGBTs or the low-side IGBTs, respectively [21]. In this case, either the high-side or low-side IGBTs are switched, resulting in asymmetric operation of the inverter.…”

Safe Turn-Off Strategy for Electric Drives in Automotive Applications

“…In [5], both the short-and open-circuit strategies are compared and evaluated in case of a single-phase open-circuit fault in the electric machine. Lu et al [6] proposed a hybrid approach by varying the switching signals between FW and ASC. The selection of the safe state depends on the operating point of the electric machine and the type of electric machine used.…”