The architecture design of a CCS2 V2G DC charging station involves the coordination of three layers: power hardware, control electronics and communication protocols. Below is a comprehensive technical framework for reference and further refinement.
1. Overall System Architecture
The system consists of four major functional modules:
- Power Conversion Module
- Control & Protection Module
- Communication Module
- HMI & Metering Module
2. Hardware Architecture (Power Stage)
A CCS2 DC charging station with V2G capability adopts a bidirectional, isolated power conversion link. Compared with conventional unidirectional charging piles, it adds an inverter (discharging) path and imposes stricter power quality control.
Key Design Points
- Front-stage 3-phase AC/DC (PFC Stage)
- Topology: Vienna rectifier is widely used for unidirectional applications, while V2G scenarios generally adopt bidirectional 3-level topologies, such as 3-phase voltage-type AC/DC with SiC MOSFETs for bidirectional power flow, or T-type 3-level bridge.
- Power Devices: SiC MOSFETs (650V / 1200V) are commonly used for power ratings above 30 kW, with switching frequency ranging from 20 kHz to 50 kHz to balance efficiency and magnetic component size.
- Functions: AC/DC rectification (G2V) + DC/AC inversion (V2G) + decoupled control of active and reactive power (for grid support, frequency regulation and voltage regulation scenarios).
- Power Quality: Complies with IEC 61000-3-12 (harmonics), EN 50549 (grid connection protection) and other standards. THD is typically required to be less than 5% during V2G discharging.
- Isolated Bidirectional DC-DC Stage
- Preferred topologies: CLLC resonant converter (symmetric bidirectional, high efficiency with soft switching, suitable for fixed or narrow voltage gain range) or Dual Active Bridge (DAB, superior dynamic response under wide voltage range, adaptable to vehicle battery voltage platforms of 150–1000V).
- The isolation transformer shall be designed per the highest insulation class to isolate vehicle potential from grid potential.
- This stage acts as the mandatory galvanic isolation point required by the CCS2 standard (GB/T 27930 and IEC 61851-23 both mandate galvanic isolation between vehicle and charger).
- DC Bus & Output Stage
- Bus capacitors + bus voltage/current sensors for V2G power loop control.
- DC contactors (one for positive and one for negative pole; some designs add pre-charge resistors and pre-charge contactors for soft start after CCS2 connector plug-in).
- HVIL (High-Voltage Interlock Loop): runs through the gun connector, DC bus and converter. Output will be cut off immediately once any segment is disconnected.
- IMD (Insulation Monitoring Device): continuously monitors insulation resistance of positive/negative bus to ground and triggers protection upon faults.
3. Communication Architecture
Communication for CCS2 DC V2G is divided into two layers: vehicle-charger communication (EVCC ↔ SECC) and charger-cloud communication (SECC ↔ CSMS). The former is critical to enable bidirectional V2G dispatch.
Detailed Communication Protocol Stack
- Vehicle-Charger Layer (EVCC ↔ SECC) — Core Enabler of V2G
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- On-board Charger Internal Bus (Main Controller ↔ Power Modules)
- Charger-Cloud Layer (SECC ↔ CSMS)
Safety & Compliance Points Specific to V2G
- Islanding Protection: During discharging mode, anti-islanding detection shall comply with IEC 62116 / UL 1741. Output must be disconnected within the required time upon grid outage.
- Bidirectional Metering: Metering ICs must support bidirectional energy metering with separate accounting for charging and discharging (different electricity tariffs).
- Power Factor & Harmonics: Discharging must also satisfy grid harmonic limits; power quality requirements cannot be relaxed merely because energy is fed back to the grid.
- Certification: For the European market, CE marking, EN 61851-23 (safety standard for DC charging stations) and EN 62477-1 (safety for power conversion systems) need to be considered.
