Inverter-fed induction motors (IMs) contain a serious of current harmonics, which become severer under stator and rotor faults. The resultant fault components in the currents affect the monitoring of the motor status. With this background, the fault components in the electromagnetic torque under stator faults considering harmonics are derived in this paper, and the fault components in current harmonics under rotor faults are analyzed. More importantly, the monitoring based on the fault characteristics (both in the torque and current) is proposed to provide reliable stator and rotor fault diagnosis. Specifically, the fault components induced by stator faults in the electromagnetic torque are discussed in this paper, and then, fault components are characterized in the torque spectrum to identify stator faults. To achieve so, a full-order flux observer is adopted to calculate the torque. On the other hand, under rotor faults, the sidebands caused by time and space harmonics in the current are analyzed and exploited to recognize rotor faults, being the motor current signature analysis (MCSA). Experimental tests are performed on an inverter-fed 2.2 kW/380 V/50 Hz IM, which verifies the analysis and the effectiveness of the proposed fault diagnosis methods of inverter-fed IMs.
The speed range of the rail transit traction system is very wide and mostly uses the hybrid pulse width modulation. The traditional hybrid pulse width modulation requires different types of modulation strategies to cooperate in switching, which inevitably leads to current and torque ripple and complicates the modulation strategy. In order to solve this problem, this paper proposed an advanced synchronous SVPWM overmodulation method, which can greatly simplify the entire modulation strategy. The modulation method is theoretically analyzed and its detailed mathematical expressions are obtained in this paper. Based on the mathematical expression, this paper analyzed the harmonics of the advanced synchronous SVPWM overmodulation strategy and compared it with that of SHE-PWM. Finally, the simulation and experimental verification of the modulation method are carried out, which proves that the method has simple and efficient and excellent harmonic characteristic.
Aiming at the high-frequency resonance (HFR) and low-frequency oscillation (LFO) phenomena in high-speed railways, a comprehensive suppression method named voltage constant transient active oscillation compensation (VCT-AOC) is proposed. This method is optimized on the basis of AOC, and the adjustment time is shortened by the VCT suppression measure. When serious HFR happens, the system can be quickly restored and stabilized by completely removing the network voltage oscillation in the control part, thereby avoiding the transient overvoltage and overcurrent damage to the system. According to the characteristics of AOC and VCT, the VCT-AOC comprehensive suppression method is proposed, and the specific implementation scheme of this method is given. This paper established the train-network impedance model with AOC and VCT suppression methods. The Generalized Nyquist Analysis (GNA) method and the dominant pole analysis method are used to analyze the effect of VCT and AOC on the system. Finally, the effectiveness of suppression methods is verified by simulations and experiments.
INDEX TERMSVoltage constant transient active oscillation compensation, high-frequency resonance, lowfrequency oscillation, suppression method, train-network power supply system.
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