With the development of electrified railway, harmonic resonance accidents occur from time to time. Based on the mechanism of resonance, a harmonic resonance suppression radical method by impedance reshaping is proposed. Thus, the equivalent impedance of the train position is significantly reduced. Compared with the traditional method of improving harmonic current, this method of impedance reshaping can not only suppress the resonance caused by its own harmonic, but also suppress the resonance caused by other trains or other unknown harmonic sources. Harmonic impedance of the train in the resonant frequency is reshaped by detecting the resonance voltage and controlling the auxiliary converter harmonic current. The resonance identification and parameter settings of the impedance reshaping control are also discussed. The proposed harmonic resonance suppression strategy is fully tested with an auxiliary converter control in a simulation trains-network system model. The performance of the proposed strategy is further evaluated on the experimental platform. Both the results verify the effectiveness and feasibility of the proposed strategy. The application of SiC devices makes it effective to suppress the resonance of thousands of hertz. The experiment was validated in two cases. One is the resonance caused by the harmonic current of the train itself. The second is the resonance caused by the harmonic current of trains in other locations. In both cases, the train using impedance reshaping method can ensure that the resonance of its position is effectively suppressed.
In railway traction drive systems, six-step operation is widely used for motors in a flux-weakening region. Traditional vector control algorithms in six-step operation cannot work effectively due to the limitation of a single degree of freedom. This paper analyses the dq current coupling relationship when voltage amplitude is limited and applies a current closed-loop control strategy in six-step operation. This paper proposes a proper switching control strategy to achieve a dualmode control for induction motors in a full-speed region. The accuracy of field orientation is affected by changes in motor parameters and plays a key role in current control precision. This paper analyses the effect of field orientation error on motor six-step operation. It is found that the proposed current closed-loop control strategy can correct the field orientation error and guarantee the motor current to track the reference precisely. A case study of a 5.5 kW experimental platform is presented to validate the control schemes. Nomenclature , d-axis and q-axis stator voltage , d-axis and q-axis stator current Stator resistance Stator self-inductance Total leakage factor Stator angular velocity Maximum stator current vector amplitude Maximum stator voltage vector amplitude Inverter DC-link voltage Rotor flux Electromagnetic torque Rotor time constant Rotor self-inductance Mutual inductance Motor pole pairs Differential operator. Rated d-axis current _ Feed-forward compensatory d-axis voltage _ Feed-forward compensatory q-axis voltage Stator voltage vector Rotor angular velocity Motor base angular velocity Stator current vector amplitude δ Field orientation angle * Subscript denotes instruction value ^ Subscript denotes estimated value
Central 60° synchronous modulation is an easy pulse-width modulation (PWM) method to implement for the traction inverters of urban rail trains at a very low switching frequency. Unfortunately, its switching patterns are determined by a Fourier analysis of assumed steady-state voltages. As a result, its transient responses are not very good with over-currents and high instantaneous torque pulses. In the proposed solution, the switching patterns of the conventional central 60° modulation are modified according to the dynamic error between the target and actual stator flux. Then, the specific trajectory of the stator flux and current vector can be guaranteed, which leads to better system transients. In addition, stator flux control is introduced to get smooth mode switching between the central 60° modulation and the other PWMs in this paper. A detailed flow chart of the control signal transmission is given. The target flux is obtained by an integral of the target voltage. The actual PMSM flux is estimated by a minimum order flux state observer based on the extended flux model. Based on a two-level inverter model, improved rules in the α-β stationary coordinate system and equations of the switching patterns amendment are proposed. The proposed method is verified by simulation and experimental results.
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