Fault Diagnosis And Fault-Tolerant Control Technology Of Railway Electrical Traction Converter

High-speed railway has experienced a rapid development during the last decade due to the high transport capacity, safety, comfort, all-weather transport advantages, environmental friendliness and sustainability. As of the end of 2015, China's high-speed railway mileage has reached 19,000 kilometers. As one of the key system of high-speed railway, power electrical traction drive system needs a high reliability to guarantee the safe and stable operation of high-speed train. However, it is shown in some statistical studies that as an important component of energy conversion in traction drive system, the electrical traction converter has a higher failure rate since it withstands major electric and thermal stresses during operation. Thus, it is a significant theoretical and engineering value to improve the traction drive system reliability and maintenance efficiency, reduce the failure impacts and losses, by deteceting the traction converter failure online and taking timely fault isolation and fault-tolerant control strategy.In this dissertation, the fault diagnosis and tolerant control technologies of the two level electrical traction converter in high-speed electrical multiple units (EMU) are studied, focusing on the single-phase pulsewidth modulation (PWM) rectifier, DC-link circuit, traction inverter and sensors. The details are as follows:Firstly, the normal and fault mathematical models of the electrical traction converter are established to obtain the fault features, compare and analyze the fault influences to the traction drive system, which providing the theoretical basis for studying the effective fault diagnosis and fault-tolerant control methods. The mathematical models include insulated gate bipolar transistor (IGBT) and bypass diode open-circuit fault models in single-phase PWM rectifier and traction inverter, LC resonant circuit open- and short-circuit fault models in DC-link circuit, and sensors gain fault, offset fault and constant fault models.Then, the fault diagnosis and fault-tolerant control methods of the traction converter are proposed according to the different fault features, respectively. For single-phase PWM rectifier, the model-based method is adopted to detect the IGBT open switch fault owing to the constant frequency control strategy, smaller power fluctuations, and less change of the model and control parameters. The basic idea of this method is via analyzing and evaluating the system residual, which is obtained by continuously comparing the actual system output with the one of the mathematical model. The residual is zero or within a small threshold when the svstem is normally operating. On the contrary, the amplitude of the system residual will increase sharply during a fault. It will be shown that this proposed method cannot only detect a faulty rectifier, but can also locate the faulty switch in a few milliseconds, without any additional hardware. Only the values of the catenary current, the DC-link voltage and the command signals from the TCU are needed to create the model.For Grid-side current sensor and DC-link voltage sensor, the state observer-based fault diagnosis and fault-tolerant approach is presented. The diagnosis method is based on residual generation, obtained by continuously comparing the actual system outputs with those of the state observers. And, the output of the faulty sensor is replaced by that of the staste observer after fault detection and isolation. The traction drive system will recover by using this reconfiguration strategy a few milliseconds.Moreover, the amplitude of the ripple voltage in DC-link increases a little when the resonant inductor is in short circuit fault, which is potential to, but not to shut down the system immediately. The ripple voltage could creat some low-frequency harmonic currents in traction motor, which may jeopardize the safety of the traction drive system. In this dissertation, the fault diagnosis method is by detecting and evaluating the amplitude of the ripple voltage. Then, the fault-tolerant control algorithm is enabled by compensating the traction motor stator frequency to eliminate the low-frequency harmonics after the fault detection.It is really difficult to obtain the accurate mathematical model of the traction motor, since its nonlinearity, strong coupling, and mutative parameters. Thus, the inverter IGBT open switch fault diagnosis is achieved by analyzing the amplitudes and symmetries of the three-phase stator currents in this dissertation. It can not only permit much more robust diagnostics of single-IGBT faults, make feasible the diagnostics of multiple-IGBT faults, but can also locate the faulty current sensor within one fundamental period. After fault dectection and isolation, the measurement redundancy of the system allows the fault-tolerant control by reconstructing the two healthy sensors.Finally, the digital simulation model based on Matlab/Simulink and Hardware-in-Loop experimental platform based on RT-lab emulator are created to verify the effectiveness and feasibility of the proposed fault diagnosis and fault-tolerant control algorithms. Proportional integrator (PI) controller in the external control loop and proportional resonant (PR) controller in the inner loop control are adopted in the rectifier side control to ensure a unity power factor operation and DC-link voltage regulation. Space vector pulse width modulation and direct field-oriented control are applied in the inverter-side control to achieve good dvnamic responses of motor speed. Both the simulation and experimental parameters are the same as that of the China Railway High-speed 3 (CRH3) EMU. The algorithms are tested in traction drive mode, regenerative braking mode, and grid voltage and load variation condition. Both simulation and experiment results show that the proposed fault diagnosis and fault-tolerant control algorithms are quite reliable, capable of fast diagnosis at a low computational requirement, lower cost without any additional hardware, which is very suitable for improving the reliability and the fault maintenance efficiency of the traction converters.