Introduction
Residual Current Operated Protective Devices (RCD) is a leakage protection device, which is widely used in low-voltage power distribution systems. It has been widely used in low-voltage power grids. With the continuous improvement of my country’s economic development level Application of residual current action protector in electric vehicle charging system the number of automobiles continues to rise; vigorously developing electric vehicles can speed up fuel substitution and reduce automobile exhaust emissions; it is of great significance to ensure energy security, promote energy conservation and emission reduction, and prevent air pollution. In order to ensure the safety of people and charging equipment during the charging process of electric vehicles, RCD has also been used in the field of electric vehicle charging. New application.
1. RCD Function and Classification
1.1 Basic Functions of RCD
There are two basic conditions for electric shock hazard protection:
- Fault protection (indirect contact) The main function or basic function of RCD is to provide fault protection, but RCD with sufficient sensitivity (such as residual operating current does not exceed 30mA) When other protective measures fail, it can still provide direct contact electric shock protection for users and livestock in direct contact with live conductive parts. RCDs whose rated residual operating current does not exceed 300mA can also protect against overcurrent protection appliances that do not operate for a long time. Provides protection against fire hazards caused by ground fault currents.
- Basic protection (direct contact) The residual current device (rcd) is used to detect earth fault currents and to interrupt supply if an earth current flows. The main application is to prevent electrocution but RCDs can also be used to protect equipment, especially against fire. The earth fault currents that operate a rcd can range from 5mA up to many amperes.
1.2 Classification
There are many different RCD types available, each being suitable for different equipment types.
- Type AC: AC type RCD must be used for protection against AC earth leakage current.
- Type A: A Type RCD must be used for protection against AC and pulsating DC (rectified AC) earth leakage current. It must be installed in any circuit where the main supply is likely to be rectified. Some examples of applications where this would apply are motor speed controllers (drives) and power tools.
- Type B: B Type RCD must be used for alternating and/or pulsating current with DC components and continuous fault current. B Type RCDs are recommended for use with drives and inverters for supplying motors for pumps, lifts, textile machines, machine tools, etc since they recognize a continuous fault current with a low-level ripple.
- Type F: F Type RCD is a special variant of type A with altered frequency characteristics, considering sensitivity to high frequencies. This type is only encountered since the introduction of IEC/EN 62423 but the solution is not completely new. The predecessor is type U, which was introduced to the market many years ago when the definition of properties of type F was not yet available.
AC type, A type, F type and B type RCD can respectively control the phase control, pulse control, single-phase half-wave, double-pulse bridge, double-pulse bridge/half-wave phase control, inverters using double-pulse bridge, Single-phase half-wave band filtering, inverter with double-pulse bridge with PFC, double-pulse bridge between phases, inverter with double-pulse bridge between phases, three-phase star, six-pulse bridge, and six-pulse bridge Protects against ground faults in the circuit of the inverter.
2. Electric Vehicle Charging Facilities
2.1 Overview Electric Vehicle Charging Infrastructure
Mainly includes various centralized charging (exchange) stations and decentralized charging piles. A sound charging infrastructure standard system is an important guarantee for the popularization of electric vehicles. The electric vehicle charging infrastructure standard system includes general requirements, equipment interfaces
The five main standards involved include:
GB/T18487.1-2015 “Electric Vehicle Conductive Charging System Part 1: General Requirements”;
GB/T20234.1-2015 “Electric Vehicle Conductive Charging Connection Device No. 1”
Part 1: General Requirements”; GB/T20234.2-2015 “Connecting Devices for Conductive Charging of Electric Vehicles
Part 2: AC Charging Interface”; GB/T20234.3-2015 “Connecting Devices for Conductive Charging of Electric Vehicles
Part 3: “DC Charging Interface”; GB/T27930-2015 “Communication Protocol between Off-Board Conductive Charger and Battery Management System for Electric Vehicles”.
Among them, the four charging modes in GB/T18487.1-2015 standard are respectively proposed for the application of RCD. Basic requirements
2.2 GB/T18487.1—2015 Standard Analysis
2.2.1 Electric vehicle charging mode usage conditions:
Charging Mode 1:
- Charging system uses standard sockets and plugs.
- Single-phase AC power supply should be used during energy transmission, and it is not allowed to exceed 8A and 250V.
- Plugs and sockets that meet the requirements of GB2099.1 and GB1002 should be used on the power supply side.
- The phase, neutral and protective earth conductors are used on the power supply side, and a residual current protection device is used on the power supply side.
- A protective earth conductor should be provided from the standard socket to the electric vehicle.
Charging Mode 2: Charging system uses standard sockets, and single-phase AC power supply should be used in the energy transmission process. When the power supply side uses a 16A plug and socket that meets the requirements of GB2099.1 and GB1002, the output cannot exceed 13A; the power supply side uses GB2099.1. The output cannot exceed 8A when it is in the 10A plug and socket required by GB1002. The phase line, neutral line and protective earth conductor are used on the power supply side, and an on-cable control and protection device (IC-CPD) is used to connect the power supply to the electric vehicle.
Charging mode 3: Mode 3 should have residual current protection function. Connection modes A, B, and C are suitable for modes 3. When using single-phase power supply, the current is not more than 32A. When using three-phase power supply and the current is more than 32A, connection method C should be used
Charging Mode 4: Mode 4 is used when the electric vehicle is connected to a DC-powered device, and is used for devices that are permanently connected to the grid (power supply) and devices that are connected to the grid (power supply) through cables to supply power. Mode 4 can be directly connected to AC grid or DC grid. Only connection method C applies to mode 4.
2.2.2 Charging connection method: the electric vehicle charging connection methods are divided into connection method A, connection method B and connection method C. The electric vehicle charging connection methods are shown in Table 1. Table 1 gives the definitions and connection diagrams of the three connection methods.
2.2.3 Requirements for RCD in the structure of electric vehicle power supply equipment: The AC power supply equipment of electric vehicles should adopt A-type or B-type RCD, which meets the relevant requirements of GB14048.2-2008, GB16916.1-2014 and GB22794-2008. When the AC power supply equipment has a power supply socket or vehicle that meets the requirements of GB/T20234 When the plug is connected, there should be protective measures against fault current: Type B RCD, or Type A RCD, or related devices that meet the residual current protection function of Type A
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Application of 3-RCD in Electric Vehicle Charging System
In order to realize the safe and reliable connection of electric vehicles to the power supply system, for all charging modes, GB/T18487.1-2015 and IEC60364-7-722:2015 stipulate that when the basic protection and/or fault protection fails, at least the Type A RCDs provide protection against electric shock.
According to the definition of mode 2 charging in GB/T18487.1-2015, electricity can be drawn from any socket in the building installation. Since it cannot be guaranteed that all existing building installations are equipped with the necessary protection measures such as RCD, electric vehicle mode 2 charging cable The upper control and protection device (IC-CPD) is used for the necessary part of electric vehicle charging to enter the power supply network safely and to protect against electric shock during the charging process. In addition to the residual current protection function of IC-CPD; In case of unsafe conditions that may be caused by high-impedance PE, the contacts are not allowed to close; IC-CPD also has a control and guidance function.
According to the requirements of GB/T18487.1-2015 electric vehicle mode 3 charging, residual DC current monitoring device (RDCMD), which has an internal or external mechanical switching device and is permanently connected to the AC electric vehicle charging station. The rated voltage of RDCMD does not exceed AC440V, rated frequency 50Hz, 60Hz or 50/60Hz, rated current does not exceed 63A. RDCMD is expected to disconnect the monitoring circuit when detecting smooth residual DC current of 6mA and above. Type B RCD itself can detect residual smooth DC current; type A The RCD needs to be connected in series with the RDCMD to avoid the incorrect operation of the A-type RCD caused by the drift of the operation characteristics of the A-type RCD caused by the residual smooth DC current of the load being greater than 6mA.
According to the requirements of GB/T18487.1-2015 electric vehicle mode 4 charging, DC RCD can provide fault protection for the lower end of the DC charging system, and can also provide direct contact protection. Therefore, according to the market demand of the electric vehicle industry, the project has been established internationally. Formulate the DC residual RCD (DC-RCD) standard, the reserved standard number is IEC/TS63053, and the formulation of this standard is expected to be completed in 2018.
To sum up, the four charging modes require the installation of different types of RCDs, as shown in Table 2.
Table 2 Charging Mode and Required RCD
| Charging Mode | Power Supply Equipment’s RCD Type | Product Type |
| Charging Mode 1 | Type A RCD is installed at the front end of the building Socket | SPE – PRCD |
| Charging Mode 2 | Type B RCD is installed at the end of the building Socket | IC – CPD |
| Charging Mode 3 type A RCD + RDCMD ( Under study ) | Type A RCD is installed at the front end of the building Socket | |
| Charging Mode 4 (Under Study) | DC Charging Pile or charging Station installation (DC – RCD) |
Conclusion
With the vigorous development of emerging fields, the application and development of RCDs have become more and more extensive. RCDs have not only been popularized in traditional household, commercial, rural and industrial fields, but have also begun to be used in electric vehicle charging systems. It is used in photovoltaic electrical installations, data centers, telecommunications centers, etc., to provide effective protection against electric shock accidents, electrical equipment leakage damage and electrical fires, and will play a greater role in personal safety and property safety.
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