Reseaech On Wideband Impedance Measurement For Train-Network System Of High-Speed Railway

By the end of 2021,the total operating mileages of high-speed railway in China has been over 40000 km.It is the country with the longest operating mileages,the largest construction scales and the largest number of high-speed trains in the world.Thus,it is important to ensure the safe and stable operation of high-speed railway.Four quadrant converter(4QC)is the core equipment of high-speed train for traction drive.Its mismatch with the “impedance characteristics” of the network side will lead to wideband oscillations,and wideband impedance measurement is an important scheme to analyse,prevent and solve these problems.Therefore,it is of great significance to study the wideband impedance measurement method of train-network system of high-speed railway.The traditional frequency-sweeping-based impedance measurement method has the following shortcomings: 1)Repeated harmonic injections,signal acquisitions,spectrum extractions and impedance calculations make the measurement process cumbersome and time-consuming;2)The actual system is time-varying,and the frequency-sweeping-based impedance measurement method can not obtain the wideband impedance characteristics of the measured system at the same time.Therefore,this paper studies the wideband-disturbance-based impedance measurement method to quickly obtain the wideband impedance characteristics of the train-network system by injecting wideband harmonic disturbance at one time.The main works of this paper can be summarized as follows:(1)For the wideband impedance measurement method of the network-side system,a one-time injection method of wideband disturbance based on pulse width modulation(PWM)is proposed.For the wider target frequency band,based on the piecewise measurement,a bilaterally controllable disturbance method based on chirp pulse width modulation(Chirp-PWM)is proposed.Secondly,for wideband data acquisition,according to the response waveform characteristics under different disturbances,the specific requirements for sampling frequency are put forward.Then,for wideband spectrum extraction,the spectrum leakage of the fast Fourier transform(FFT)result caused by the fundamental deviation of the tested system is studied and the countermeasures are put forward.Finally,the corresponding impedance calculation method is proposed.(2)For the frequency coupling interference of the wideband impedance measurement method of the train-side system,firstly,the topology and control of the 4QC and the frequency coupling phenomenon caused by its asymmetric control loops(voltage loop and phase-locked loop)are presented in detai.Secondly,the interference mechanism of 4QC frequency coupling phenomenon on wideband impedance measurement is analyzed,and an odd-even-frequency alternating injection method is proposed,which can avoid the frequency coupling interference under wideband disturbance.Then,for wideband data acquisition,combining the traditional dq transform with the proposed αβ-VEM-based dq transform method,the complete dq data can be collected.Finally,with the obtained dq data,combined with spectrum analysis and dq impedance calculation method,the wideband impedance characteristics of train-side 4QC can be obtained without frequency coupling interference.(3)For the train-side wideband disturbance injection device of train-network system,firstly,the hardware topology and overall control of the injection device based on cascade H-bridge(CHB)are proposed.Then,for the wideband harmonic disturbance control loop,the basic control strategy is derived by the internal model principle(IMP).On this basis,notch filter and repetitive controller are used to enhance the performance of wideband harmonic disturbance control loop.Finally,for the problem that the low-frequency current of the device affects the performance of the control system,a grid-side impedance optimization method based on RLC is proposed to improve the low-frequency output performance of the device.(4)The development and experiment of wideband impedance measurement device are carried out.According to the basic steps of wideband impedance measurement,four basic modules of the device are designed: 1)wideband disturbance control module;2)wideband harmonic disturbance module;3)wideband data acquisition module;4)spectrum extraction and impedance calculation module.For each module,the specific hardware/software development schemes are put forward.Taking the development of 10-kW wideband impedance measurement device for power network as an example,a device is developed to measure the wideband impedance of the 220-V power network in the lab,and the corresponding measurement results are obtained.The device can provide a technical reference for the development of high-power measurement device for high-speed railway.To realize the wideband impedance measurement of the train-network system of high-speed railway,this paper first presents the overall framework and basic steps of wideband impedance measurement.Then,the detailed wideband impedance measurement methods are studied according to the wideband impedance characteristics of network side and train side of train-network system.Finally,according to the established wideband impedance measurement theory and technical method,the development method of wideband impedance measurement device is designed.It can provide a complete reference scheme for the theory and application of wideband impedance measurement.