EV Charger Ground Equalization Prevents RCD Tripping
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Solution Overview
Problem
The existing charging systems for electric vehicles can trigger residual-current devices (RCDs) when the external charging power source is coupled to an internal, isolated energy storage system, leading to suspended charging due to equalization of electrical grounds, which is inconvenient for users.
Innovation Solution
A conductive charging system that includes a polyphase motor drive circuit with a switching assembly, a sensing circuit, and a common mode voltage driver to align the ground voltages and reduce residual currents by converting AC line voltage to a charging voltage, using a controller to manage the switching assembly and driver stages to minimize voltage differences and prevent RCD tripping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an isolated ground is used for the energy storage system to ensure safety, then user safety is improved, but residual current is generated during charging causing RCD tripping
Solution Approach 1:
The system performs preliminary voltage equalization between the isolated energy storage system ground and the AC charging system ground before initiating charging. This preliminary action prevents residual current generation by ensuring both grounds are at the same potential level before the charging connection is established.
Solution Approach 2:
The patent introduces an intermediary ground equalization circuit that mediates between the isolated energy storage system ground and the AC charging system ground. This intermediary mechanism transfers charge to equalize voltages without creating harmful residual currents through the RCD-protected circuit.
2Ease of operation
If the user plugs the EV into the wall socket and leaves, then user convenience is improved, but charging may be suspended due to RCD tripping without user awareness
Solution Approach 1:
The system performs preliminary ground voltage equalization automatically when the charging connector is engaged, before the user leaves. This preliminary action ensures charging will not be suspended due to RCD tripping, maintaining charging continuity without requiring user awareness or intervention.
Solution Approach 2:
The ground equalization process is fully automated and self-executing upon connector engagement. The system serves itself by automatically detecting voltage differences and equalizing grounds without user intervention, ensuring reliable charging operation while the user is away.
3Object-generated harmful factors
If a common mode voltage driver is added to equalize ground voltages, then residual current is reduced, but device complexity increases
Solution Approach 1:
The common mode voltage driver is integrated into the existing motor drive circuitry, allowing the same hardware to serve dual functions: motor control during vehicle operation and ground voltage equalization during charging. This multi-functionality reduces overall system complexity despite adding the equalization capability.
Solution Approach 2:
The system changes the operating parameters of existing driver stages to enable ground voltage equalization. By adjusting voltage levels and switching patterns of the common mode driver, the system achieves ground equalization without requiring fundamentally new hardware, thus limiting complexity increases.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system effectively reduces residual currents during charging, ensuring continuous operation and user convenience by preventing RCD tripping, even when the energy storage system has a large capacitance to chassis ground.
Implementation Method 1
a converter, coupled to the energy storage system and including a number N number of the plurality of driver stages
Implementation Method 2
a switching assembly, coupled between the plurality of driver stages and the line input voltage, controlling communication of the line voltage to the plurality of driver stages
Implementation Method 3
a sensing circuit, coupled to the line voltage and to the energy storage system, measuring an ESS common mode voltage of the energy storage system to a voltage reference and measuring a line common mode voltage of the line voltage to the voltage reference
Implementation Method 4
a common mode voltage driver, coupled to the energy storage system and to at least one driver stage of the plurality of driver stages, at least one driver stage not including one of the N number of driver stages and responsive to a second set of driver signals to match the ESS common mode voltage with the line common mode voltage
Data Source
AI summary
A charging system and method that accommodates and reduces potential residual or leakage current when electrical grounds of a charger and an energy storage system are equalized at the moment of initiating charging. The charging system using an alternating current (AC) line voltage for conductive charging of an energy storage system (ESS) coupled to a polyphase motor drive circuit communicated to a polyphase motor, and converting the line voltage to a charging voltage communicated to the energy storage system using a set of the plurality of driver stages.