| At present,the railway system actively responds to the slogan of “resolutely fight for pollution prevention and”.How to comprehensively and effectively save energy,reduce emissions and reduce consumption,especially reducing the energy consumption of traction,has become a major point in railway construction.In recent years,our country has increased the construction of a series of western railway lines such as the "Sichuan-Tibet Railway".A large number of long ramps have further highlighted the problem of power quality management.At the same time,huge energy will be generated when the train is regeneratively braked.Railway Power Conditioner(RPC)can effectively solve power quality.Compared with the RPC composed of the traditional voltage source converter,the RPC composed by the Modular Multilevel Converter(MMC)has the advantages of simple structure,lower construction cost and energy consumption,and high quality of commutation power.In view of the advantages of rich photovoltaic energy in the western region,the integration of photovoltaic power generation into the traction power supply system,as an important part of the horizontal multi-source complementation in the traction power supply system,will help promote the energy saving and emission reduction of the railway system and the nearby consumption of photovoltaic power.Combining the negative sequence and harmonic control of the railway traction power supply system,and considering the reasonable utilization of regenerative braking energy,this paper proposes a photovoltaic power generation and energy storage system based on MMC-RPC and its control strategy for electrified railways.The two-arm MMC-RPC performs control to compensate for the negative sequence and harmonic currents generated by the traction load,while absorbing photovoltaic energy nearby,and rationally using the train’s regenerative braking energy to cut peaks and fill valleys.The main work of this paper is as follows:(1)The modeling,control and analysis of the traction power supply system MMC-RPC were carried out.First introduced the basic structure of the traction power supply system,studied the basic structure and working principle of the modular multilevel converter MMC and MMC-RPC,and then further studied the control method of MMC-RPC to manage the power quality of the traction power supply system,including The calculation of the negative sequence and harmonic compensation current,the MMC-RPC voltage and current double loop control mode and the carrier phase shift sinusoidal pulse width modulation strategy,design the main circuit parameters.Finally,MATLAB/Simulink is used to build a simulation model of the MMC-RPC system.Through the operation of electric locomotives in traction and regenerative braking modes,it is verified that MMC-RPC has a good compensation on negative sequence and harmonic currents in the traction power supply system.(2)Analyze the basic principles of photovoltaic power generation,including the equivalent model of photovoltaic cells,the mathematical model of photovoltaic cell output,and the output characteristics of photovoltaic cells.Subsequently,the maximum power point tracking control technology in photovoltaic power generation is analyzed.After comparing various methods,the admittance incremental method is adopted,and the maximum power point tracking is performed based on the Boost circuit.The photovoltaic module model is built on MATLAB/Simulink.Simulation experiments verify the effectiveness of the technology.Then,the photovoltaic power generation is connected to MMC-RPC,that is,photovoltaic components are connected to the DC bus of MMC-RPC through a DC/DC converter to output photovoltaic power,and then photovoltaic power generation energy is supplied to electric locomotives through MMC-RPC.The system operation results before and after photovoltaic power connection show that the system of photovoltaic power generation MMC-RPC still has a good compensation capability on negative sequence and harmonic currents.At the same time,photovoltaic energy is an important part among the horizontal multi-source complementation in the traction power supply system,which reduces the power consumption of the traction station and turns into a powerful supplement to the energy supply of the railway system.(3)On the basis of the negative sequence and harmonic currents compensation of the traction power supply system MMC-RPC,further realize the absorption of photovoltaic power,rationally use the regenerative braking energy of electric locomotives,and achieve the purpose of peak reduction and valley filling.This chapter proposes the power supply scheme of MMC-RPC connected with photovoltaic power generation system and energy storage device,and the working principle of MMC-RPC with photovoltaic and energy storage is analyzed.Then based on the state of charge of the super capacitor energy storage,the capacity,charge and discharge power,etc.are analyzed and calculated.And the power distribution and energy management of the MMC-RPC system including photovoltaic and energy storage are designed considering various working conditions.Finally,a model was built on MATLAB/Simulink for simulation verification.Under a variety of typical operating conditions,the operating status of the traction substation,photovoltaics,and super capacitors in the system meets the feasibility of the power distribution and energy management scheme,and achieves the functions of absorbing photovoltaic energy,cutting peaks and filling valleys.Under boundary conditions,the standby mode,discharge mode,and charge mode of super capacitors also meet the requirements of power and capacity.Compared with the previous two chapters,the system still has the ability to solve power quality problem. |
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