Research On Control And Protection Technology Of Low Voltage DC Power Distribution System

The development of power electronics technology,the increase of DC loads,the large number of applications of distributed power,and my country’s "carbon neutral" goal all indicate that the low-voltage DC power distribution systems has great development potential.The low-voltage DC power distribution system has different control and protection strategies under different voltage changes.So,a voltage division strategy is proposed.The equipment can adjust the control strategy according to the bus voltage without centralized control,making the control and protection of the system simple and reliable.The voltage is divided into over-voltage protection zone,normal working zone,under-voltage protection zone and short-circuit protection zone,and the range of the voltage interval is determined by referring to the existing DC voltage standard.Complete the design of control and protection schemes for different voltage ranges with the goals of different voltage ranges.In the normal working area,the system should maintain the stability of the bus voltage,reserve sufficient power margin,enhance the dynamic performance of the power supply equipment,and prevent the system from entering the voltage protection zone.First,select the droop control strategy by comparing the commonly used coordinated control strategy of bus voltage.And the design of the droop curve of the system was completed in the project.Secondly,because the low-voltage DC power distribution system has diverse equipment and complex working conditions,it is difficult to clarify the power margin of power distribution system.For this,a system power margin evaluation method is proposed to facilitate the upper scheduling system to evaluate the power margin of power distribution system.Finally,combined with simulation,the feasibility of the control strategy in the normal working area is verified.In the voltage protection zone,part of the equipment in the system should be cut off,and the output power of the power supply equipment should be increased,so that the power margin of the system could increase.Considering the influence of the voltage deviation caused by the line impedance and the requirements of the short-circuit protection zone,the voltage protection configuration scheme of the system is completed.Combined with the simulation model,the feasibility of the protection strategy of the voltage protection zone is verified.In the short-circuit protection zone,the short-circuit characteristics of the equipment are analyzed,and the equipment converters are divided into controllable converters and uncontrollable converters according to their ability to control short-circuit current.The short-circuit process of the equipment is divided into the capacitor discharge phase and the power/inductor discharge phase.Then the calculations of short-circuit current of different phases for the equipment are completed,and the characteristics of short-circuit current for the system are analyzed in the project.For scenarios with high power supply reliability requirements,the protection scheme of relying only on the cooperation of the circuit breaker and the equipment’s own protection cannot meet the line selection requirements.With reference to the AC system,fault ride-through requirements are proposed.Finally,combined with simulation,the effects and deficiencies of fault ride-through are verified.