| In recent years,urban rail transit has been developing rapidly in major cities in China.The stable operation of subway trains and traction networks is the key to ensure passenger's safety and urban traffic order.Therefore,the stability of subway traction drive systems has become a hot topic in recent years and has received much attention.With dc-ac converter structure,stable dc power is the key to high performance traction drive system.However,due to limitations in space,weight,harmonic suppression,and other factors of the vehicle,the value of the DC-side filter inductor and the supporting capacitor,which serve as a regulated filter,is often difficult to meet the needs of system stability.Besides,the negative impedance caused by the vector control greatly attenuates the damping of the system which makes the system susceptible to DC-side oscillations under external excitation.Therefore,it is of great theoretical and engineering significance to study the instability phenomenon and explore its mechanism and propose suppression methods.The contents of this article is as follows:Firstly,the main circuit of the traction drive system of subway is introduced.Its operation mechanism and topological structure are analyzed.At the same time,the basic mathematic model of three-phase asynchronous motor is introduced.The principle of indirect vector control of rotor orientation based on coordinate transformation is described.Secondly,combining the simplify equivalent circuit of the system,the reason of LC oscillation in the traction drive system are analyzed,and the possible topology which would existence oscillation is discussed in connection with the main circuit of the train and the traction network.On this basis,the impedance ratio criterion was analyzed and combined with the small signal modeling method,the traction drive system impedance model based on the vector control scheme was constructed.And after that,the impedance ratio criterion was also constructed based on the input and output impedance of the system.At the same time,with the impedance ratio criterion and stability theories,the stability of the system under different operating conditions is discussed,and the factors including input power and parameters of LC filter which will have great influence on the stability of the system are also analyzed.Besides,according to the idea of damping compensation,three damping circuits are introduced and the formulas for calculating the parameters of each damping circuit are given.So based on these parameters,each damping circuit were discussed through simulations.After that,an active damping method which based on the feedforward compensation is described,and the method for compensation parameter selection with minimum disturbance is analyzed.At the same time,a power balance control method is proposed for compensating over-modulation situation that may be caused by voltage compensation in high-speed region and the stability control of the system in the full-speed domain is realized.Finally,a hardware-in-loop test platform based on the OP5600/RT-LAB and the DSP-TMS320F28335 controller was built.With this platform,the modeling of the traction drive system and the design of the vector control program and damping algorithm were completed.The computer simulation and test results in hardware-in-loop platform verify the effectiveness of the proposed oscillation suppression algorithm. |
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