| How to absorb and utilize regenerative braking energy effectively has always been an important research problem in the field of traction power supply system in urban rail transit.The cost of traction power supply accounts for about 50% of the total electricity bill,while the power cost accounts for about 40% of the total operating cost of urban rail transit.With the development of the urban rail transit,energy saving of traction power supply has a great significance for reducing the operating cost of urban rail transit.At present,instead of the original consumption type,the way to recover the regenerative braking energy has changed into energy feedback type and energy storage type.However,the energy feedback system has the problem of returning power to the main substations,while the energy storage system has the problem of high cost under the same power.At present,the power supply system only uses a single type device,it is difficult to realize the complementary advantages of the two devices,so it is difficult to maximize the energy saving effect.Therefore,the urban rail power supply system with hybrid ground regenerative braking energy utilization devices is taken as the research object,the energy feedback devices and the energy storage devices are put into use in the system at the same time.Each part of the system is modeled,and the power supply calculation algorithm of the system is studied in this paper.The optimization model of the system is also studied in the paper,and the NSGA-Ⅱ with normal distribution crossover is used to optimize the design of the system.The structure of DC traction power supply system of urban rail transit is analyzed in this paper,and the power supply calculation model of traction substations in rectification mode,the three-layer ground network model of "catenary-rail-earth" related to the length of power supply zone,and the power supply calculation model of trains with on-board braking resistor during traction and braking periods are established.The topological model and working characteristics of the energy storage devices and the inverter feedback devices in the traction substations are studied and analyzed in this paper.When these two devices are used in the traction substations,the power supply calculation model under different operation modes are established.The conversion scheme between the operation modes is formulated,and the energy flow relationship between the devices in the traction substations and the trains is analyzed.Then,the dynamic adjustment strategy of the inverter feedback devices considering the duty cycle is established,and the power flow calculation algorithm of urban rail transit power supply system with hybrid ground regenerative braking energy utilization device is studied.By comparing with the measured data,it is concluded that the results of the improved algorithm are more consistent with the actual load process of the device.The influence of starting voltage of inverter feedback devices on energy consumption of power supply system is studied by the power supply calculation algorithm,and the influence of no-load voltage of rectifier units and number of the train departure on the selection of optimal starting voltage of inverter feedback devices is also studied in the paper.The results show that,when the starting voltage of inverter feedback devices is too high or too low,the energy saving effect of the devices on the system will be reduced;when the no-load voltage of the system is high or the number of the train departure is small,it is helpful to enhance the energy saving effect by properly reducing the starting voltage of the inverter feedback devices.Aiming at the urban rail power supply system with hybrid ground regenerative braking energy utilization device,the optimization model of power supply system with the lowest cost of the devices and the lowest energy consumption of the main substations is established.In order to solve the problem that the search space of simulated binary crossover operators used in conventional NSGA-Ⅱ optimization algorithm is not complete enough,this paper attempts to improve NSGA-II algorithm by using normal distribution crossover operator,and the solution method of the system optimization model combined with power supply calculation algorithm is given.The optimal design of installation position,installation type and installation capacity of regenerative braking energy utilization devices in the system is realized.The optimization results show that,the optimal solution set obtained by the improved algorithm is more complete.The optimization model of urban rail power supply system is solved by NSGA-II with normal distribution crossover.Taking the actual project as an example,the system is optimized and a set of optimal configuration schemes is obtained.An example of how to select an optimal solution from the optimal solution set in the actual design process is given,and it is verified that the urban rail power supply system optimization model solving method can be used for the optimization design of the actual subway project.The relationship between the cost of devices and the energy consumption of the system is discussed,for the urban rail power supply system,if the cost of regenerative braking energy utilization devices is higher,the energy consumption of the main substations will be smaller,but when the cost of the devices exceeds a certain number,with the increase of the cost,the reduction of the energy consumption of the system will slow down obviously,and the improvement effect of putting more devices into the system will be weakened.The optimization design of A-type vehicle and B-type vehicle is carried out respectively,the difference between the optimization results of the two systems is analyzed.The mechanism that how does the regenerative braking energy utilization devices save energy for the system is revealed,compared with the urban rail power supply system without regenerative braking energy utilization device,the electricity saved from the main substations after putting the devices into use is essentially the difference between the less energy consumed by the on-board braking resistance and the return power. |
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