Application of UI in urban rail transit

Rail transit UI power supply is an important equipment to provide continuous, stable and uninterrupted power supply. UI device should be used in the main power supply of urban rail transit electromechanical system to ensure the normal operation of power supply. This paper analyzes the redundant power supply mode and capacity calculation of UI in urban rail transit.
In recent years, with the rapid development of urban rail transit, the electromechanical systems are platforms for rail transit operation command, enterprise management, passenger service and information transmission, ensuring safe and efficient train operation and providing high-quality services for passengers. Among them, the reliability of power supply equipment has become the top priority. There are various loads in the city power grid, which cause interference and pollution to the power grid, worsen the quality of power supply and affect the normal operation of the load. The construction purpose of UI power supply system is to provide high-quality, uninterrupted power supply for electrical equipment of electromechanical system through UI power supply system, so as to ensure the normal operation of electrical equipment.
Types of UI
UI is mainly composed of rectifier, battery, inverter and static switch.
UI is divided into the following types:
One
On line UI
UI has always made its inverter work. It first converts the external AC into DC through the circuit, and then converts the DC to AC through the inverter and outputs it to the load. In case of power failure, the standby DC power supply (battery pack) is used to supply power to the inverter. Since the inverter has been working all the time, there is no problem of switching time, which is suitable for occasions with strict requirements on power supply;
Two
Backup UI
Usually in the state of battery charging, the inverter switches to the working state in case of power failure, which transforms the DC power provided by the battery into stable AC output, so the backup UI is also called offline UI;
Three
Online Interactive UI
This is an intelligent UI. When the input power is normal, the UI inverter is in reverse working to charge the battery pack. When the mains power is abnormal, the inverter will immediately put into operation to convert the battery voltage to AC output. Therefore, Online Interactive UI has conversion time. In the urban rail transit system, the load of each electromechanical system requires high reliability of power supply, so the main power supply UI of each electromechanical system is generally online to improve the reliability and stability of the whole system.
Power supply mode of redundant backup
The UI of rail transit electromechanical system works in redundant backup mode. From the perspective of redundancy configuration scheme, there are the following modes: master-slave hot standby power supply mode; direct parallel redundant power supply mode;
Dual bus redundant power supply mode.
Master slave hot backup power supply mode
The hot standby redundancy mode is two UI series switching. During normal operation, only the main UI supplies power to the critical load, while the other UI is in no-load state. If the main UI fails to operate, it will switch to the bypass, and the standby UI will automatically take over after about 2-8 Ms. This structure is economical in price, but there are many single points of failure. If the main UI fails, the other one must take over the whole load, which means that the other must increase the power supply from 0 to 100% within about 8 ms. the defect of this method is that the standby UI is in no-load state for a long time, its battery life will be shortened and its capacity will be reduced, and the standby UI must have step load carrying capacity without capacity expansion. Because it is very difficult for people to know whether there are faults or hidden dangers in each part of the standby UI in real time, when the standby machine is to be started, it may not work normally.
Direct parallel redundant power supply mode
N + 1 type UI redundant parallel power supply scheme is to ensure that the output voltage amplitude of each single UI is the same, and the output frequency and phase are the same, the output terminals of N + 1 UI with the same output power are connected in parallel to supply power to the load with output power of n single UI. In normal operation, N + 1 UI share the load current averagely. When a UI fails, the remaining N UI will continue to supply power while automatically offline under the control of parallel control signal.
Dual bus redundant power supply mode
In UI power supply system, there are distribution cabinet and circuit breaker between the output terminal and the load. In case of maintenance or failure, the above configuration will cause load power failure, that is, although the failure rate of the system is reduced, the maintainability has not been completely solved. Therefore, dual bus redundancy configuration can be adopted. Two sets of UI system 1 and UI system 2 are set up in this scheme. In rail transit, the dual bus redundant power supply mode is adopted for each electromechanical system to increase the stability and reliability of the system, eliminate the single point bottleneck fault hidden trouble that may appear between the UI output terminal and the load end of the final subway user, and improve the fault tolerance function of the output power supply system. The practical application of UI in urban rail transit electromechanical system, UI equipment in the station, depot and control center are applied. Two sets of communication system are set in the station, which are dedicated system UI and public equipment UI; one set is set in the control center to supply power for central level equipment; one set is set for training and maintenance and switch equipment; the station signal system adopts large capacity UI, while the control center and depot have small capacity UI; The integrated monitoring system is composed of three subsystems: equipment monitoring, disaster prevention alarm and power monitoring. In general, one set is set in the main control equipment room of the station, one set is set up in the control center for the equipment power of the integrated monitoring system, one set is set for the power supply of large screen equipment, and one set is set for the depot; the UI equipment of bas is set in the station, and the UI equipment of bas is set in the depot; one set of UI is set in the station PSD control room. There are two kinds of UI power supply: distributed power supply and centralized power supply. In the power supply system of urban rail transit, centralized power supply has become a trend. The overall cost of centralized power supply is lower than that of decentralized power supply, and the unit capacity cost is reduced with the increase of UI capacity; Centralized power supply is convenient for installation, maintenance and management. Decentralized power supply requires a lot of installation space, and wiring lacks planning. Centralized power supply system can monitor and manage UI on a PC through background monitoring software,

The centralized power supply system can monitor and manage the UI on a PC through the background monitoring software, and the decentralized power supply system can achieve the same effect with more investment. In Shenzhen line 3, centralized power supply mode has been adopted, and many newly designed lines are also adopting centralized power supply mode. However, there are many motor loads in the PSD system, and there will be a large impact current when starting, which will impact the UI inverter, resulting in overload or bypass. Therefore, it is generally recommended to supply power separately. The capacity of UI is determined according to the total load capacity, which can be generally selected according to the following formula: UI capacity ≥ load capacity / 0.8, that is, the load capacity is less than 80% of the rated capacity of UI. The selection of 80% load is mainly based on the load starting impulse current and the need for future expansion. When configuring UI batteries, it should be noted that since UI usually uses a large number of battery packs as backup power supply, with many batteries and heavy weight, the calculation of load should be concerned in the design room. Users can calculate the type and weight of batteries according to the required UI capacity, and propose structural load-bearing reinforcement with the builder or designer or use scattered racks when preparing for the construction and decoration of the computer room. If the UI capacity is very small, then There is no need to consider. The bearing capacity of the UI system installation floor must be considered when installing. The UI battery cabinet should be installed on the ground floor or load beam. It is concluded that end urban rail transit project is a century old project and people's livelihood project. Reasonable use of UI structure and power supply mode will have a great impact on the safety and economy of rail transit electromechanical system.