pure electric bus charging new choice

Background

In recent years, with the gradual growth of urban population in China, the pressure of urban public transport is also increasing year by year. At the same time, with the popularity of cars in large and medium-sized cities, the proportion of exhaust emissions in exhaust emissions is getting higher and higher, causing serious environmental problems and traffic jams in cities. Therefore, vigorously developing public transportation systems such as subway, light rail, tram, and pure electric bus driven by pure electric energy has become an urgent task for urban modernization. Classified from the capacity of public transport:

Large capacity Public transport

subway, light rail. Large passenger capacity and high operating speed; The construction period is very long, generally about 5 years; The investment cost is very high, about 0.6 billion yuan ~ 1 billion yuan/km;

Medium Capacity Public Transport

1) Modern tram. Medium passenger capacity and medium operating speed; long construction period, generally about 2 years; high investment cost, about 0.1 billion yuan/km; but there is a dispute between trams and other vehicles on the ground.
2) Dual-source trackless BRT trams. The passenger capacity is medium, the operation speed is medium; the construction period is short, generally within 1 year; the investment cost is low, about 10 million yuan/km; and the original ground road resources can be used.

Ordinary capacity Public transport

pure electric bus. Small passenger capacity and low operating speed. The construction period of supporting charging facilities is short, generally within 1 year; it completely shares road resources with the original bus without further investment.
From the above classification, it can be seen that different capacity modes of transportation have different positions in urban public transportation: subways and light rails can solve the transportation of urban trunk transportation, and trams and dual-source trackless BRT can be used as a powerful supplement to subways and light rails, which can alleviate regional transportation problems. The pure electric bus with ordinary capacity is responsible for the "last kilometer" of urban public transport, which can transport a large number of passengers to the final destination.
For ordinary pure electric buses, battery problems and charging problems have always been the main reasons that plague their development: the battery counterweight is too large and the carrying efficiency is low; the charging station and charging pile occupy a large area, the construction cost is high, and the power supply capacity utilization rate Low; the vehicle charging time is long, and it cannot move during the charging process, which affects the scheduling and parking of vehicles in the field.
In order to solve the above problems, the pure electric bus using the new lithium titanate battery can realize the rapid charging of the battery, and the cycle life of the battery can also fully meet the requirements of the pure electric bus. The battery of this type of pure electric bus configuration is about 46kWh, and it can run about 30km on a single charge, which can meet the operating mileage requirements of most urban bus lines. The charging facilities of the vehicle can adopt the mode of "mini skid-mounted substation + charging line network", combined with the intelligent charger integrated on the vehicle, which can not only provide large-capacity, flexible and fast charging services for the vehicle, but also bring the greatest savings in the floor area and construction cost of the charging facilities.

Mini Skid-mounted Flexible Charging Station for Pure Electric Bus

In order to provide a safe, large-capacity and high-density charging power supply for the new pure electric bus, Suzhou Wanlong Electric Group Co., Ltd. has specially developed a "mini-skid-mounted pure electric bus flexible charging station" for this application ". The main technical features of the charging station are as follows:

Flexible Charging Based on Intelligent Cloud Platform

the effective parking area of urban public transport parking lot is very important to the rational layout and line configuration of urban public transport. The mini skid-mounted flexible charging station for pure electric bus adopts the design idea of high power density to provide fast charging service for pure electric bus. Taking the 3-way DC 750V output DC feeder as an example, it covers an area of only 32 square meters and can provide a rated 600kW and a maximum 1200kW charging power for pure electric buses. The charging station can be produced and assembled in advance by the manufacturer, and can be directly transported to the site to complete the installation, with short engineering cycle and low comprehensive cost.
A charger is integrated on the new pure electric bus, and the intelligent charging cloud platform can send charging commands to the charger of the vehicle through a wireless channel to realize simultaneous charging of multiple electric buses under the charging line network. Since the charger is controllable, the charging power output by the DC feeder can be flexibly distributed to the vehicles under the DC feeder according to relevant instructions to realize flexible charging. Take the vehicle equipped with 46KWh battery as an example. After the vehicle travels 30 kilometers, 25% ~ 35% of the electricity is left, and the electric energy is quickly replenished into the parking lot. The rated power of the vehicle configuration is 150kW. The charger is flexibly charged through the charging line network, and the battery can be fully charged in about ten minutes, which can fully meet the application requirements of the public transportation industry. In this way, on-demand charging can be combined with battery power and status, vehicle operating conditions, charging station operating power and other charging conditions, charging resources can be reasonably allocated, and the charging power provided by the power station can be fully utilized to provide safe and fast charging services for vehicles.

charging system six security

The charging safety of pure electric buses has always been the focus of the public transport industry. The new charging station must not only closely monitor its own safety, but also evaluate the safety of the entire DC charging system in real time. To this end, the "mini-skid-mounted pure electric bus flexible charging station" integrates six major security technologies:
◆ Electrical safety protection of charging line network
◆ High current short circuit fault quick removal
◆ Intelligent fault detection
◆ Instantaneous fault quickly restore power supply
◆ Insulation monitoring of charging system
◆ Temperature monitoring of key nodes

Through the above technology, the charging network in the DC charging system can be protected to prevent the charging network from being damaged due to overload. For metallic high current short circuit, the DC fast circuit breaker and DC protection in the charging station can act quickly and cut off the fault current within ten milliseconds to ensure the safety of the equipment. The intelligent fault detection function can also identify whether there is a short circuit in the power supply system. If it is a transient short circuit, the power supply can be automatically closed and quickly restored without manual intervention. The insulation monitoring of DC charging system can monitor the changes of ground impedance of charging station, underground cable, charging line network and vehicle in real time, and evaluate the insulation health status between charging system and ground according to the changes of impedance. The temperature sensor in the station can monitor the connection reliability of key connection points in the charging station in real time to avoid temperature rise or fire caused by large current passing through.

Remote operation monitoring and maintenance management

"mini skid-mounted pure electric bus flexible charging station" adopts a highly integrated design, which integrates digital sensing technology, digital protection measurement and control technology, field bus technology and network communication technology on the basis of a new generation of electrical technology. It is mainly composed of high-voltage AC switch cabinet equipment, rectifier unit equipment, DC switch cabinet equipment, auxiliary power supply equipment, data management system, automatic fire protection system, integrated auxiliary system (access control, environment and video) and other modules.
The new charging station can complete in-station data acquisition, command issuance and other operations through the remote cloud platform. Managers can realize real-time monitoring of charging stations through the remote cloud management platform, and can quickly understand various faults and alarms in the station, and isolate related faults. That is, it can guarantee the reliability of the charging station operation, and can achieve the purpose of quickly restoring power supply, and truly realize "intelligent unattended".
Due to the unattended operation mode, the health status of the internal equipment of the charging station can be obtained through the remote cloud platform. The remote maintenance management terminal can know the health status of the equipment in the station in real time through the cloud platform. Through the analysis of various types of faults, alarms, status and other operating information, the working conditions of the equipment can be identified in time to achieve "equipment predictive maintenance". It not only reduces the number of operation and maintenance personnel, but also greatly reduces the cost of equipment operation and maintenance.

Mini Skid-mounted Pure Electric Bus Flexible Charging Station
WDQXB series intelligent box-type substation designed by Suzhou Wanlong Electric Group Co., Ltd. is a new generation of charging stations suitable for new pure electric buses. Its main parameters are as follows (take 3-way DC charging circuit as an example):

Typical parameters

■ Rated output power 600kW, maximum output power 1200kW
■ 3-way DC charging circuit
■ Input voltage AC 12kV
■ Output voltage DC 750V
■ Rated output DC 800A

■ Overall dimension L * W * H(mm)= 8000*4000*3500

Typical system primary scheme

According to the primary scheme of WDQXB series intelligent box-type substation system (single unit, as shown in Figure 1), its high-voltage AC switchgear equipment adopts HXGN15-12 series SF6 ring network switchgear with 10kV dual power supply. Rectifier unit adopts 12-pulse rectifier unit equipment with rated capacity of 630kVA and load grade V. DC switchgear equipment adopts WDQ series DC switchgear (DC750V), the DC system ensures emergency recovery of power supply in the fault circuit through standby feeder circuit, standby bus and bypass knife; the station auxiliary power equipment is equipped with 30kVA transformer and 32Ah DC power supply panel.
WDQ series DC switch cabinet adopts interchangeable circuit breaker handcart structure, fast circuit breaker adopts QDS8 series DC fast circuit breaker with high performance and high reliability (Icu = Ics = 30kA, small arcing distance, small volume and simple structure), relay protection device adopts ST700 series DC microcomputer comprehensive protection device, which makes up for the deficiency of traditional DC fast circuit breaker direct high current trip protection, protection and control functions such as over-current quick-break, over-current delay, thermal overload, line test, automatic reclosing, fault recording, etc. are added to improve the protection and control functions of the DC power supply system. In addition, the system is also equipped with insulation detection, temperature monitoring and other functions, which can monitor and evaluate the insulation status of the DC power supply system in real time and the connection reliability of the key connection points in the station.

Figure 1 WDQXB series intelligent box-type substation primary system diagram

Typical Remote Monitoring and Management System

In order to meet the data interaction between charging station, remote cloud platform and management service terminal, WDQXB series intelligent box substation is equipped with WKS-DTMS2000 intelligent DC traction electrical monitoring and management system.
The system consists of station control layer, communication management layer and spacer layer. TCP/IP Ethernet network communication is adopted between the station control layer and the communication management layer. According to the requirements of the secondary system protection security zone I of the power system, the network data must be encrypted to ensure the security of the data network. A fieldbus communication network is used between the communication management layer and the interval. The system takes the "WKS-DAS1000 data management system" in each intelligent box-type substation as the core, and realizes the remote monitoring and management of the entire box-type substation based on the intelligent terminal equipment such as "DC microcomputer integrated protection device", "intelligent measurement and control instrument", "temperature monitoring device", "insulation monitoring device" and "intelligent I/O module" through field bus communication technology. The system network topology is shown in FIG. 2.

Figure 2 WKS-DTMS2000 intelligent DC traction electrical monitoring and management system topology

Typical Charging System Topology

, from the current ordinary pure electric bus charging process, the charging facility is only a simple power supply equipment. The charging process mainly depends on the on-board battery management system and requires manual operation. Since the charger is installed in the charging pile, there are certain compatibility problems when charging different types of pure electric buses.
The charging system of the new pure electric bus combines the charging station, vehicle, remote cloud platform and various management service terminals to complete the charging process.
As shown in Figure 3, the topology of the new pure electric bus charging system, wherein the pure electric bus remote cloud management platform can obtain information such as vehicle battery status, vehicle position, remaining power, charging current and the like in real time through the communication link. The charging station remote cloud management platform can obtain charging station power information, charging loop current, various alarms and fault information through the communication link. The vehicle information management terminal and the charging integration management terminal can integrate the information of the vehicle and the electric quantity information of the charging station and the charging line network, and guide the vehicle to the appropriate charging line network for charging. The charging management terminal can also control the charging current through the on-board charger to meet the charging requirements of different vehicles (fast charging, slow charging, etc.). Throughout the charging process, various cloud platforms and management terminals integrate relevant information of vehicles and charging stations to rationally allocate charging resources and flexibly charge.
The remote maintenance and early warning terminal of the charging station can obtain various data in the station from the remote cloud management platform of the charging station, evaluate the health status of the charging station, and achieve "timely discovery and timely resolution" for abnormalities or alarms that occur during the use of the equipment ".

Fig.3 Topology of new pure electric bus charging system

engineering case
Since 2012, Beijing Tram Company has selected the "Intelligent DC Traction Electrical System Integration Solution" provided by Suzhou Wanlong Electric Group Co., Ltd. in accordance with relevant operation planning requirements. The equipment of more than 10 station-type dual-source pure electric bus DC traction stations such as Fuchengmen Station, Zizhuyuan Station and Maliandao Station has been intelligently upgraded and transformed, and more than 30 intelligent box-type DC traction substations have been newly built, for more than 1000 dual-source pure electric buses in Beijing to provide power for operation and charging. All DC traction stations are monitored and managed through a remote cloud platform, and ultimately unattended traction stations are realized.
Among them, the Longtan Park bus parking lot uses WDQXB series intelligent box-type substation to supply power to the parking lot's internal network and provide charging services for about 30 pure electric buses in the parking lot. The pure electric bus can be charged offline through the collector rod, and the vehicle runs through the power provided by the on-board battery after the charging is completed. as shown in Figure 4.

Figure 4 Beijing Longtan charging station and pure electric bus

figure 5 is the remote cloud platform management center station of the power supply station of Beijing tram company, which runs the "WKS-DTMS2000 intelligent DC traction electrical monitoring and management system" provided by Suzhou wanlong electric group co., ltd ". In terms of access capacity, the management system can access more than 200 substations. At present, the system has realized the remote monitoring and management of more than 40 intelligent DC traction substations.

Figure 5 Remote cloud platform management center