best value public electric car charging stations engineering technology

1. Construction mode of electric vehicle charging and swapping station

1.1. Government-led model

The government or public institution is the main body for the construction and operation of charging stations, and power suppliers, charging device R&D and manufacturing enterprises or other social forces participate together. The outstanding feature of the government-led model is that the central and local governments support the construction, operation and development of electric vehicle charging stations through “direct investment, government ownership”. According to different government construction and operation methods, this model can have two specific operation methods:

(1) Direct-dominant approach, that is, the construction of electric vehicle charging stations is directly funded by the government, and the relevant government departments are responsible for operation and management after completion.
(2) The indirect leading method, that is, the construction of electric vehicle charging stations is funded by the government, and then handed over to state-owned enterprises for operation and management after completion, or entrusted to professional institutions for operation and management.

The advantages of the government-led model: the government invests in the construction of charging stations, and the government organizes the operation, and the losses are borne by the finances, which can promote the implementation and development of the commercial operation of electric vehicles, and lead and promote the orderly development of the construction of electric vehicles and charging stations; Unified planning and intensive development of electric vehicle charging stations.

Disadvantages of the government-led model: increased financial pressure on the government, low operational efficiency, and is not conducive to the large-scale and intensive construction and operation of electric vehicle charging stations. With the expansion of the scale and area of ​​commercial operation of electric vehicles, the investment demand increases, making it difficult for the government’s financial capacity to support, and the government’s financing pressure cannot be relieved.

1.2. Enterprise-led model

By investing and operating electric vehicle charging stations as market entities, enterprises investing in electric vehicle charging stations can gradually transform traditional energy enterprises into new energy enterprises. Power grid companies incorporate the construction of electric vehicle charging stations into an integral part of the smart grid, which can not only promote energy storage technology, but also promote the development of clean energy, and realize the saving and efficient use of power resources.
The advantages of the enterprise-led model: it broadens the investment channels and reduces the financial pressure of the government; it can ensure the capital investment required for the construction of electric vehicle charging stations; it can effectively improve the operating efficiency and management level of charging stations.

Disadvantages of the enterprise-led model: easily lead to disorderly development of charging station construction; influence or restrict the development of the electric vehicle industry; lack of coordination with related fields. In the electric vehicle demonstration operation stage, the fixed asset investment of charging station operators in a single operation area cannot continue to maximize benefits after the demonstration operation period expires.

According to the different organization and management methods of the construction subject for the commercial operation of charging station projects, the charging station affiliated enterprise-led type can be divided into three types: direct-led type, entrusted operation type and integrated operation type:

(1) Directly dominant type. The direct-dominant type is characterized by the construction of charging stations by one or more power supply departments, or production enterprises that research, develop and manufacture charging devices, and these enterprises are jointly responsible for the commercial operation of charging stations.

(2) Entrusted operation type. The characteristic of the entrusted operation type is that the charging station affiliates invest in the construction of the charging station, but commission a professional enterprise to carry out the commercial operation of the charging station, and put forward operation requirements and specifications. The main body of the construction itself generally provides technical personnel to participate in the commercial operation.

(3) Integrated operation type. The integrated operation type is characterized in that the affiliated enterprises of the charging station and the main body of the commercial operation of electric vehicles unite to jointly build and operate the charging station, such as the power supply department and the bus company responsible for the operation of electric vehicles or with the official vehicle and commercial vehicle departments. Or jointly build and operate charging stations between enterprises, so as to facilitate the commercial operation of electric vehicle charging stations by the main body of electric vehicle operators.

1.3. User-led mode

Electric vehicle users invest in the construction of electric vehicle charging stations in order to meet their own vehicle operation needs. The charging station invested and constructed by electric vehicle users is regarded as a supporting facility for electric vehicles, so as to avoid being restricted by external charging stations and thus adversely and inconveniently affecting the operation of electric vehicles. The advantage of the user-led model is that electric vehicle users can build charging facilities according to their own needs, so as to realize the effective connection between charging facilities and their own electric vehicles. The disadvantage is that electric vehicle users not only have to bear the high cost of construction and operation of charging facilities, but also lead to low utilization rate of charging facilities and repeated construction.

1.4. Scope of application of different operation modes of charging stations

The scope of application of the different operation modes of the charging station is as follows:
(1) The government-led model is suitable for the small-scale commercial operation of electric vehicles, or in the early stage of electric vehicle development, and companies need to be encouraged to engage in the construction of electric vehicle charging infrastructure, or when the government has strong economic strength, this model can be used. Demonstrate government support.

(2) The charging station affiliated enterprise-led model is suitable for power supply enterprises that urgently need to expand the power market, improve the quality and performance of charging products, have government support, have strong enterprise strength, and have long-term planning in the operating area.

(3) The social enterprise-led model is suitable for large-scale commercial operation of electric vehicles, large passenger flow, large charging demand, weak government financial capacity, good market environment and market mechanism, and relatively smooth financing channels.

(4) Electric vehicle user-led charging infrastructure construction In order to meet the user’s own operation needs, with the gradual expansion and maturity of the electric vehicle market, there is a trend of commercial operation.

The above four modes have their own characteristics. The selection of the commercial operation mode of electric vehicles should be based on the actual situation, so as to reflect the division of labor and cooperation between the government and the market in the market economy, and to reflect the professional division of labor and cooperation between different enterprises and institutions based on core competitiveness. The optimal allocation of market resources is the criterion.

2. Electric vehicle charging station workflow

2.1. Workflow of battery replacement method

When the electric vehicle enters the charging station, it enters the energy supply program according to the demand of the electric vehicle. The process of replacing the battery is shown in Figure 1.

The specific workflow of replacing the battery of an electric vehicle is as follows:
(1) Replacement application. In order to replace the battery of electric vehicles more quickly, the vehicle that needs to replace the battery should apply to the charging station for battery replacement before entering the station, so that the platform can arrange the parking location, notify the battery storage room to prepare for battery replacement, and transport the battery to the battery replacement area. , prepare to uninstall the device. (For more battery information visit Tycorun Battery)

(2) The vehicle enters the replacement area. After the vehicle that has made a replacement request enters the station, drive the vehicle to the exact position of the battery replacement area according to the dispatch instruction, and prepare to replace the battery.
(3) Fault diagnosis. Before replacing the battery, you must carefully read the fault records of the on-board monitoring device to check whether the on-board battery is faulty during operation. If there is a fault record, record the fault information (including the fault location and type), distinguish the faulty battery from the non-faulty battery, and then clear the fault record.

(4) Replace the battery. First disconnect the high and low voltage power supply of the electric vehicle, and then unload the battery. When unloading the battery, separate the faulty battery from the non-faulty battery; after unloading, load the prepared battery into the vehicle.

(5) Fault diagnosis. After the fully charged battery is loaded into the vehicle, turn on the high and low voltage power supply of the electric vehicle, and perform another fault diagnosis to ensure that the electric vehicle after replacing the battery is running normally. Step (7); if the failure still occurs, go to step (6).

(6) Troubleshooting. Read the fault diagnosis results of the vehicle monitoring carefully to find the cause of the fault. If it is a fault that can be eliminated immediately, such as the connection cable is not connected, go to step (5) after troubleshooting; Fault information (including fault location and type), then clear the fault record, and return to step (4) after receiving the backup battery.

(7) Treatment after battery replacement. Send the faulty battery to the battery maintenance area of ​​the storage tank; send the faultless battery box to the charging area for charging.

1) Workflow of battery charging
After the unloaded battery is screened and maintained, it must be charged. The operation steps are:
(1) Transport the trouble-free battery unloaded from the vehicle to the charging platform.
(2) Connect all the connectors on the charging platform, including the battery management system plug connectors (with the power cord and the internal communication line of the battery management system).
(3) Connect the connector between the charger and the charging platform.
(4) Close the power switch.
(5) Power on the charger control power supply.
(6) The communication between the charger, the battery management system and the monitoring PC is established.
(7) Set the charging parameters after confirming that the battery is normal. After the parameter settings are returned successfully, start the charger to start charging.

(8) If everything is normal, after the charging is over, the charger will notify the monitoring room that the charging is over and request to turn off the charger. If a malfunction occurs during operation, the malfunction must be eliminated before operation. And notify the monitoring room that there is a fault in the charging process and request processing. The charging fault and charger control strategy are shown in Table 1. After shutdown, check the fault code to find the cause of the fault. If the first three kinds of faults in Table 1 occur during the charging process, after the shutdown, remove the faulty battery box, record the fault location and fault type, and send it to the battery maintenance area, and then restart the charger according to the above steps to continue charging.

2) Workflow of battery maintenance
The maintenance of the electric vehicle power battery is similar to the primary maintenance and secondary maintenance of the fuel vehicle, and the battery of the electric vehicle also needs regular maintenance. There are no standards to refer to in this regard, and no ready-made data are available.

Although the single power battery has a long working life, due to the large difference between the battery cells and the different aging speed of the battery, the possibility of overcharge and overdischarge of the battery is greatly increased. It cannot provide effective dynamic data of battery operation and provide basis for battery maintenance. Therefore, it is very necessary to start from the development of battery management system and gradually improve the maintenance of electric vehicle batteries. The work of the battery distribution center is to control the capacity balance within the index, and the index is determined according to the use requirements.

The core of battery maintenance work is to control the balance of battery capacity, adjust and control the use state, and provide reasonable environmental conditions for the battery. The BMS used for electric vehicles now has the function of automatic capacity balancing. The designers all claim that the “energy transfer” method can be used to achieve the function of automatically balancing the cells of the battery pack. In fact, it is impossible to use the function of this external circuit to change the electrochemical performance of the battery itself, and this function is bound to increase the complexity of the battery management system, and even cause a significant drop in reliability. BMS exacerbates the aging of the battery pack.

At present, the battery management system of electric vehicles can only undertake the detection function, and does not have the function of balancing the capacity of the battery pack. The core problem of the operation quality of the battery is to control the balance of the capacity of the battery pack. The imbalance of the battery is absolute, the balance is relative, and the imbalance of the battery pack always develops in the direction of increasing automatically. Maintenance is all about keeping the balance within a “reasonable” range. The criterion for “reasonableness” is to look at the proportion of the investment required to pursue those indicators and to obtain them.

The control of battery capacity balance must be manually adjusted and controlled according to the actual operating state. When charging, the battery management system detects that a battery has reached the upper limit of charging, and will reduce the charging current; when discharging, it detects that a battery has reached the lower limit, and restricts continued discharge, which makes the capacity of a part of the battery unusable. Through manual maintenance, the unevenness of its structural capacity is compressed to a small range.

The maintenance of the battery is carried out in the battery maintenance area, as shown in Figure 2. The main task of the battery maintenance area is to select and maintain the faulty battery. The battery maintenance area is equipped with battery testing and testing instruments to provide data support for battery diagnosis and screening. After the battery screening is completed, the batteries that can no longer be used should be properly disposed of, the batteries that can be used should be fully charged after necessary maintenance, and then the batteries will be sent to the battery storage room for assembly and initialization.

When the electric vehicle power battery reaches a certain number of times of replacement, operation period, or is damaged or faulty, it should be handed over to the relevant departments for routine maintenance or fault repair, including the development of the secondary circuit of the battery box, cell performance, insulation, and connectors. Maintenance and repair of appearance and parts. Power battery repairs include planned repairs, unplanned breakdown repairs, and accident repairs.

2.2. Workflow of vehicle charging mode

The electric vehicle enters the charging station and enters the energy supply program according to the demand. If the vehicle is charging, connect the vehicle charging system. The system performs fault diagnosis, issues a condition detection report, and enters the charging procedure according to different conditions (the vehicle charged by the whole vehicle can be supplemented daily by the whole vehicle, or it can be used for emergency quick charging of the whole vehicle when temporary charging is required). After the vehicle charging system enters the charging program, the charger communicates with the vehicle battery management system to transmit the battery data to the charger monitoring network host. The specific workflow of the vehicle using the vehicle charging method is as follows:

(1) After plugging in the charging plug, the on-board equipment (including on-board monitoring and battery management systems) will automatically supply power and operate normally.
(2) Close the control power supply of the charger.
(3) Confirm that the CAN network between the monitoring room and the charger, vehicle monitoring, and vehicle battery management system has been established.
(4) After confirming that the battery is in a normal state, set the charging parameters. After the parameter settings are returned successfully, start the charger to start charging.
If a fault occurs during operation, the fault must be eliminated before continuing to operate.

2.3. Battery charging working state transition
The whole charging process of the battery includes four stages: the charging handshake stage, the charging parameter configuration stage, the charging stage and the charging end stage. The overall process of battery charging is shown in Figure 3.

1) Charging handshake stage
After the battery management system and the charger are physically connected and powered on, the battery management system and the charger enter the charging handshake stage. At this stage, both parties shake hands and confirm information about electric vehicles and batteries. The flowchart of the charging handshake phase is shown in Figure 4. The purpose of the message in the charging handshake phase is as follows:

(1) PCN256 charger identification message (CRM) Purpose: to provide charger identification information to the battery management system. After the battery management system and the charger are physically connected and powered on, the charger sends a charger identification message with SPN2562 = 00 to the battery management system every 20ms. If the battery management system identification information is still not received after sending 3 frames of identification messages in succession, the charger determines that the charging connection is abnormal, and at the same time automatically cuts off the power supply circuit and sends an overtime message.

(2) PCN512 battery pack identity code information message (BRM) Purpose: to provide battery pack identity code information to the charger. After the battery management system receives the charger identification message of SPN2562-00, it sends it to the charger every 20ms. When the data field length exceeds 8 bytes, it needs to use the transmission protocol function to transmit, and the sending interval is 10ms. If the SPN2562-01 charger identification message has not been received in the 3-frame identification message, the battery management system judges that the charging connection is abnormal, and at the same time automatically cuts off the charging circuit and issues an overtime message.

(3) PGN768BMS version information message (BVM) Purpose: To confirm the version information of the communication protocol of the battery management system. After the battery management system receives the SPN2562 = 01 charger identification message, it sends the communication protocol version information to the charger.

(4) PGN1024 charging handshake phase error code (CEI) Purpose: The error code that occurs in the charging handshake phase.

2) Charging parameter configuration stage
After the charging handshake phase is completed, the battery management system and the charger enter the charging parameter configuration phase. At this stage, the battery management system sends detailed charging parameters of the battery to the charger, and the charger sends information such as the maximum output level of the charger to the battery management system. stage (Figure 5).

The purpose of the message in the charging parameter configuration phase is as follows:
(1) PGN1280 charging parameter configuration stage error code (CE2) date. Error code that occurred during the charging parameter configuration phase.

(2) Purpose of PGN1536 battery charging parameter message (BCP). In the charging parameter configuration stage, the battery management system sends the charging parameters of the battery to the charger (the maximum allowable charging voltage of the battery module, the maximum allowable charging current of the battery, the maximum allowable charging capacity of the battery, the maximum allowable total charging voltage of the battery, and the maximum allowable temperature of the battery) .

(3) Purpose of PGN1792 battery parameter #1 message (BPI). In the charging parameter configuration stage, the battery management system sends the battery physical parameter 1 to the charger (vehicle number, number of battery modules in series, number of battery modules in parallel, and estimated remaining capacity of the vehicle battery).

(4) The purpose of PCN2048 Song Battery Parameter #2 message (BP2). In the charging parameter configuration stage, the battery management system sends the battery physical parameters 2 to the charger (battery charging current, battery charging voltage, battery supplier code, battery group number, and the number of batteries in each group).

(5) The purpose of PGN2304 charger to send time synchronization information message (CTS). In the charging parameter configuration stage, the time synchronization information sent by the charger to the battery management system.
(6) The purpose of the maximum output level message (CML) of the PGN2560 charger. In the charging parameter configuration stage, the charger sends the maximum output level of the charger to the battery management system in order to estimate the charging time.

(7) Purpose of PCN2816 battery charging ready message (BRO). In the charging parameter configuration stage, the battery management system sends the battery charging ready message to the charger to let the charger confirm that the battery is ready to be charged.

(8) PGN3072 charger output ready message (CRO) purpose. In the charging parameter configuration stage, the charger sends a ready message to the battery management system of the charger to let the battery confirm that the charger is ready to output.

3) Charging stage
After the charging parameter configuration phase is completed, the battery management system and the charger enter the charging phase. The battery management system sends the battery charging level requirement and battery charging status to the charger in real time. According to the charging level of the battery, the charger needs to adjust the charging voltage and current and monitor the charging process. The flowchart of the charging stage is shown in Figure 6.

The purpose of the message in the charging phase is as follows:
(1) Purpose of PGN4096 battery charge level message (BCL). Let the charger update the charge level of the battery in real time. In the constant voltage charging mode, the output voltage of the charger should meet the voltage demand value, and the output current should not exceed the current demand value; in the constant current charging mode, the output current of the charger should meet the current demand value, and the output voltage should not exceed the current demand value. Voltage demand value; in constant power charging mode, the output power of the charger should meet the power demand value, and the output voltage cannot exceed the voltage demand value.

(2) Purpose of PGN4352 battery charge status message (BCS). Let the charger determine the current state of charge and remaining charge time of the battery.
(3) The purpose of PGN4608 battery management system to send battery status information message (BSI). During the charging phase, the battery management system sends battery status information to the charger.
(4) The purpose of PCN4864 battery management system to send battery status information message (BS2). During the charging phase, the battery management system sends battery status information to the charger.

(5) The purpose of PCN5120 charger charging status message (CCS). Let the battery management system confirm the current charging status and accumulated charging time of the charger.
(6) The purpose of the voltage message (BMV) of each module of the PGN5376 battery pack. The voltage value of each module of the battery pack. The length of the data field exceeds 8 bytes and needs to be transmitted using the transmission protocol function.

(7) Purpose of PGN5632 battery pack temperature message (BMT). Battery pack temperature. When the data length exceeds 8 bytes, it needs to use the transmission protocol function to transmit.
(8) Purpose of PGN5888 battery charge capacity SOC value message (BSOC). The value of the charge capacity of the battery pack. When the length of the data field exceeds 8 bytes, the transmission protocol function needs to be used for transmission.

(9) The purpose of PCN6144 battery pack average module voltage value message (BAV). The average module voltage of each battery pack.
When the length of the data field exceeds 8 bytes, the transmission protocol function needs to be used for transmission.
(10) PCN6400 battery management system terminates the charging message (BST) purpose. Let the charger confirm that the battery management system will send a termination message to end the charging process and the reason for ending the charging.

(11) The PCN6656 charger terminates the charging message (CST) purpose. Let the battery management system confirm that the charger is about to end charging and the reason for the end of charging.
(12) PCN6912 Charge Phase Error Code (CE3) Purpose. Charge phase error code.

4) Charging end stage
After one of the battery management system and the charger ends the charging phase, the charging end phase is entered. At this stage, the battery management system and the charger send each other their respective statistical data during the entire charging process. The flowchart of the charging end stage is shown in Figure 7. The purpose of the message in the charging end phase is as follows:

(1) PCN7168 battery management system statistical data message (BSD) Purpose: to let the charger confirm the specific statistical data of this charging process.
(2) PCN7424 Charger Statistical Data Message (CSD) Purpose: To let the battery management system confirm the specific statistical data of the charger about this charging process.
(3) PCN7680 Charge End Stage Error Code (CE4): Error code at the end of charge stage.

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