For hardware review of V2G systems, start by locating the bidirectional power converter, then verify main current measurement, residual current detection, insulation monitoring and fault disconnection respectively. Referencing real‑world equipment and manufacturer circuit diagrams, this document illustrates the differences between AC V2G and DC V2G, and describes how communication states can be validated via local current, voltage and disconnection feedback.

ISO 15118‑20:2022/Amd 1:2026 was formally released on 13 July 2026. The 2022 edition already defines communication messages and timings for bidirectional power transfer. This amendment adds AC DER services and MCS services and improves safety concepts, further aligning AC bidirectional charging‑discharging operations with distributed energy resource (DER) requirements.

Domestic Chinese standards are also being rapidly implemented.
GB/T 46148‑2025 Technical Specification for Smart Electric‑Vehicle Charging‑Discharging Equipment came into force on 1 March 2026, covering grid‑tied Mode‑4 DC charging‑discharging equipment and Mode‑3 connection Type‑C AC charging‑discharging equipment.
NB/T 11867‑2025 Test Requirements for Off‑Board DC Electric‑Vehicle Charging‑Discharging Devices was implemented on 28 March 2026. Meanwhile, dedicated control and interaction communication guidelines for AC V2G are still under development.
The No. 1 Modification Sheet for GB/T 43332‑2023 Safety Requirements for Conductive Charging‑Discharging of Electric Vehicles was published on 30 July 2026 and will take effect on 1 November 2026; as of this document date, it is in published‑pending‑implementation status.
The No. 1 Modification Sheet for GB/T 18487.1‑2023 was released and implemented on 25 May 2026 and shall also be checked for engineering references.

These regulatory changes mean V2G capability can no longer be judged merely by “supporting reverse discharge”. Engineers must first distinguish AC‑ and DC‑based architectures, identify the location of power converters, trace current flow paths, and map possible return paths for ground leakage / fault currents. Scheduling commands, vehicle‑charger communications and local measurements should be linked within one unified validation chain.

1. Standard Updates and Hardware Validation

ISO 15118‑20 defines layer‑2 network and application‑layer communication between the EV Communication Controller (EVCC) and Supply Equipment Communication Controller (SECC). Its 2022 release already includes bidirectional power transfer services such as AC_BPT and DC_BPT. Therefore the claim that “ISO only added V2G support in 2026” is incorrect.

Hardware engineering teams should pay close attention to the AC DER service introduced in the 2026 amendment. When an electric vehicle operates as an AC‑side distributed energy resource, it must handle service entry, energy‑export shutdown, disturbance response and recovery in addition to its charging‑discharging capacity. Communication services express operational intent, yet actual grid‑interconnection behaviour must comply with applicable grid codes. Adoption of ISO 15118‑20 alone does not guarantee full grid‑code compliance for the complete equipment.

For hardware design, operating states must be provable via physical measurements. For example, zero active‑power output does not inherently mean all currents drop to zero instantaneously. Protocol‑level trip or stop states cannot independently prove physical disconnection of the main power circuit. Local measurements of current, voltage, insulation and contact feedback must collectively confirm equipment status.

Table 1 Status and engineering focus of relevant standards

2. Key Focus Points of Selected International and Domestic Standards

The ISO 15118 series specified herein focuses on high‑level communication between vehicles and charging infrastructure. Corresponding Chinese domestic documents cover equipment technical requirements, safety requirements, communication protocols and test methodologies. Comparisons between these standard sets illustrate division‑of‑work, and should not be interpreted as a ranking of V2G technical maturity. International projects likewise require supporting electrical‑safety and grid‑interconnection standards.

For DC‑V2G in China, a well‑defined framework combining “equipment specifications — communication protocols — test requirements” has been established. GB/T 27930‑2023 extends CAN‑bus communication coverage to charging‑discharging machines, while NB/T 11867‑2025 provides dedicated test validation for grid‑tied off‑board DC charging‑discharging devices defined in NB/T 33021‑2024.

AC V2G is at a different development stage. Although GB/T 46148‑2025 includes AC charging‑discharging equipment within smart charging‑discharging‑equipment scope, dedicated national guidance documents for AC‑V2G control and interactive communication are still under drafting. Engineering projects must clearly demarcate boundaries among enforced published standards, project‑specific agreements and draft documents under development. Draft standards shall not be treated as compliance criteria.

Application‑level deployments are also advancing. On 13 March 2025, four Chinese government authorities issued the Notice on Announcing the First Batch of Large‑Scale Vehicle‑to‑Grid Demonstration Pilots, publicly released 2 April 2025. Nine cities and thirty projects were selected for the pilot programme, mandating pilot‑site construction together with grid‑connection, metering and dispatching support.

3. From Equipment Form‑Factor to Power‑Converter Location

A frequently misunderstood statement in V2G discussions is “current reversal”. AC current naturally reverses instantaneous direction every mains cycle. What V2G actually reverses is the direction of average active power. For DC circuits with fixed voltage polarity definition, charging and discharging manifest directly as reversal of current sign.

Two typical hardware form‑factors are presented below. The Mobilize PowerBox Verso (left) is an AC‑V2G‑capable unit requiring a bidirectional‑AC‑V2G‑enabled EV and supporting services. The Fermata Energy FE‑20 (right) is a bidirectional DC‑V2G device with a maximum DC power rating of 20 kW according to CHAdeMO documentation. Both feature compact enclosures. Differentiate AC vs DC V2G by vehicle‑side interface and power‑converter location, not by physical size or mounting configuration.

Figure 1 Comparison of AC and DC V2G Device Appearance

Table 2 Core architectural differences between AC V2G and DC V2G

3.1 AC V2G: Bidirectional Conversion Performed by On‑Board OBC

In typical AC‑V2G implementations, charging infrastructure delivers grid AC power to the vehicle, and the on‑board bidirectional OBC executes AC‑DC conversion and power regulation. During reverse discharge, the OBC converts battery DC back into grid‑compliant AC power. The AC charging unit itself performs connection, metering, communication and protective functions.

Conventional AC charging piles paired with unidirectional OBCs cannot realise V2G automatically. The on‑board converter must support reverse operation, together with matching vehicle‑charger communication, protection and grid‑interconnection controls.

Therefore judging whether a vehicle is drawing power or feeding power back to the grid in AC systems cannot rely solely on instantaneous current polarity. Synchronous sampling of voltage and current is required for active‑power computation. For single‑phase systems, average power p(t)=u(t)i(t) computed over one or more mains cycles determines power direction. For three‑phase systems, phase‑wise active power values are summed. Where reactive‑power exchange occurs, RMS current may remain substantial even when active power approaches zero.

Figure 2 Structure of CLLLC Isolated DC/DC Stage inside Bidirectional OBC

Source: Texas Instruments, TIDM-02013 User's Guide TIDUF18A, Figure 2-1 on Page 4

3.2 DC V2G: Bidirectional Conversion Performed by Off‑Board Hardware

In DC‑V2G systems, the vehicle presents a high‑voltage DC interface. Bidirectional power conversion between the utility grid and traction battery is primarily accomplished inside off‑board charging‑discharging equipment. Hardware generally comprises a grid‑side bidirectional AC‑DC stage, DC‑link bus and optionally bidirectional DC‑DC stages according to topology requirements. Consequently grid‑side current, internal converter‑stage currents and DC‑output current each constitute independent measurement points for control and protection.

Vehicle‑charger digital communication for Chinese DC‑V2G deployments is clearly defined by GB/T 27930‑2023, specifying CAN‑based signalling between SECC and EVCC applicable to Mode‑4 charging / charging‑discharging equipment. Class‑B systems correspond to charging‑discharging systems referenced in GB/T 18487.1‑2023.

Figure 3 AFE and DAB Power Topology of Off-board DC Charging Equipment

Source: Infineon, REF-EV50KW2SICKIT User Guide, Figure 2 on Page 6

3.3 Division of Responsibilities: Main‑Current Sensing, Residual‑Current Detection and Insulation Monitoring

Clarifying architecture makes current‑sensing boundaries unambiguous. In AC‑V2G, operating current flows bidirectionally between grid and on‑board OBC; power direction is derived from combined voltage‑and‑current measurements. In DC‑V2G with fixed voltage polarity, charge / discharge states correspond directly to DC‑current sign reversal. Meanwhile ground‑leakage / fault‑current paths differ from main operating‑current paths. Residual‑current detection and Insulation‑Monitoring‑Devices (IMD) fulfil distinct functional roles.

Table 3 Functional division: main‑current measurement, residual‑current detection and insulation monitoring

4. Scheduling Links and Vehicle‑Charger Communication Links

V2G systems implement at least two disjoint communication channels.

1. Communication between upper‑layer dispatch / aggregation platforms and charging‑discharging equipment: conveys permit‑to‑discharge setpoints, target power levels and stop‑discharge scheduling intent.

2. Vehicle‑EVCC to equipment‑SECC vehicle‑charger communication: exchanges EV capability reports, service selection, charge‑discharge parameters, operational status and session termination.

Within the ISO framework, ISO 15118‑20 governs network‑layer and application‑layer interaction between EVCC and SECC. A typical workflow proceeds as: establish communication session → service discovery & selection → capability‑and‑boundary exchange → power‑transfer activation → continuous status / parameter reporting → service stop or resume. The 2022 edition’s AC_BPT / DC_BPT implement bidirectional power‑transfer services; the 2026 amendment’s AC_DER adds DER‑oriented service semantics and control parameters.

In Chinese DC‑V2G implementations, GB/T 27930‑2023 uses CAN‑bus signalling covering handshaking, parameter negotiation, charge‑discharge preparation, energy transfer and session termination. For AC V2G, GB/T 46148‑2025 mandates digital‑communication and dispatch‑response capabilities, yet dedicated AC‑V2G interaction guidelines remain under drafting. Real‑world projects must follow published standards plus project‑specific interface agreements.

One fundamental principle applies across all communication stacks: fast fault responses for severe over‑current, short‑circuit and insulation‑failure events must execute via local closed‑loop detection. Fault protection shall not depend on round‑trip communication latency. Communications may request power shutdown, but local measurements and protection hardware must verify that power flow has indeed ceased.

Table 4 Responsibilities of Communication and Local Protection

5. Normal Operating Current versus Ground‑Related Current

As summarised in Table 3, main‑current sensors measure magnitude, direction and rate‑of‑change within power‑circuit loops. Residual‑current detection evaluates the instantaneous algebraic sum of currents across all monitored live conductors. Insulation‑Monitoring‑Devices assess insulation‑to‑earth resistance for unearthed high‑voltage circuits. None of these functions can substitute for one another.

For AC V2G, nominal operating current flows between utility grid and on‑board OBC across phase and neutral (or three‑phase) conductors. Under ideal conditions, the vector sum of all live‑conductor currents passing through a residual‑current sensor approximates zero. Imbalance arises where current returns via insulation defects, EMI Y‑capacitors, vehicle chassis or PE protective‑earth paths. High‑frequency PWM induced dv/dt also creates displacement currents through parasitic capacitances. Measured ground‑referenced current therefore comprises both genuine insulation‑fault components and capacitive leakage inherent to normal operation. For through‑core residual‑current sensors, all monitored live conductors shall pass together through the magnetic core; PE protective‑earth conductor must not pass through the same core, to avoid cancelling the target imbalance signal.

DC‑V2G scenarios are more complex. Where the vehicle‑side high‑voltage DC circuit is unearthed or galvanically isolated, a first insulation degradation fault may not generate sufficient continuous fault‑current to trigger residual‑current protection immediately. Hence “low residual‑current” cannot be interpreted as “good insulation condition”. This motivates the functional separation between IMD and residual‑current detection. IEC 61557‑8 specifies IMD requirements for IT‑type power systems. Where both vehicle‑end and charger‑end IMD units are fitted, measurement timing and signal‑injection schemes must be coordinated to prevent mutual interference between monitoring devices.

Sensor design must also address performance around the zero‑current crossing point. V2G power‑regulation and charge‑discharge transitions frequently operate near zero current. Zero‑offset drift, thermal drift and measurement noise can corrupt power‑flow‑direction judgement. As an illustrative example: for an 800 V DC system, a mere 0.1 A current offset introduces approximately 80 W power‑estimation error (ignoring voltage measurement error). This is not a formal standard limit; it demonstrates how small current‑sensor offset translates to meaningful power inaccuracy in high‑voltage systems.

6. Validation of Isolation and Fault Interruption

Bidirectional power systems contain at least three distinct energy sources: utility grid, vehicle traction battery and internal equipment energy storage. Even after PWM gate signals are disabled, DC‑link capacitors retain substantial stored energy. Intrinsic diode conduction within power semiconductors can sustain residual current for short periods following command‑based shutdown. Therefore these events must be verified independently: power‑stop command, power‑semiconductor turn‑off, galvanic disconnection of main circuit, and decay of residual voltage down to safe levels.

Isolation itself covers multiple distinct requirements: galvanic isolation of power circuits, primary‑to‑secondary signal isolation for sensors, control‑supply isolation and insulation‑to‑earth monitoring each answer separate technical questions. Current‑flow reversal in V2G does not automatically increase creepage distance or clearances. Insulation coordination must be calculated according to operating voltage, transient over‑voltage, pollution degree, material group, altitude and high‑frequency voltage stress, following the frameworks defined in IEC 60664‑1:2020+AMD1:2025 and IEC 60664‑4.

Fast fault protection must remain decoupled from communication signalling. Controlled normal shutdown may ramp power close to zero prior to contactor opening. Severe short‑circuit faults require fast local detection and semiconductor‑based protection actions according to permissible fault‑energy limits; fuses, circuit‑breakers or other validated disconnection hardware perform subsequent physical isolation. For insulation anomalies, alarm, power‑derating or tripping strategies are determined by system earthing topology and applicable standards. Following any fault event, critical node current and voltage shall be re‑measured to confirm elimination of sustained energy‑feed paths. Re‑activation shall be prohibited until safe conditions are restored.

7. MAGTRON Technology Enables V2G Current‑Control and Safety Sensing

V2G systems require high measurement stability, fast dynamic response and high integration density, for charge‑discharge transition current feedback as well as AC‑side residual‑current protection. MAGTRON combines fluxgate sensing technology, proprietary IC chips and modular hardware design to deliver high‑performance, easy‑to‑integrate components for equipment developers.

Figure 4 MAGTRON main‑current and residual‑current‑detection products
Left: MCSC‑200S/P; Right: RCMU101SM1‑2EI‑K

7.1 MCSC‑200S/P Series: Low‑Drift, High‑Bandwidth for Bidirectional Current Control

The MAGTRON MCSC‑200S/P leverages proprietary Closed‑loop iFluxgate® closed‑loop fluxgate technology. It offers 200 A rated current, 450 A full‑scale measurement range and 200 kHz signal bandwidth, featuring ultra‑low zero‑point drift, low thermal drift and fast transient response.

Suited to frequent power‑level adjustment and charge‑discharge direction reversals in V2G applications, low drift minimises measurement bias near zero‑current crossings, while high bandwidth captures rapid current transients and delivers timely, stable current feedback to system controllers.

From an integration perspective, the compact PCB‑mount plug‑form‑factor reduces board‑space occupation and simplifies mechanical assembly for power‑control‑board integration. Low insertion loss and high noise immunity make it well‑suited for power‑electronic current‑measurement tasks. Combined with synchronous voltage sampling and active‑power computation, it provides the measurement foundation for bidirectional power regulation while optimising hardware layout efficiency.

7.2 RCMU101 Series: Proprietary SoC and Built‑In Self‑Test Simplify Detection Design

Tailored for residual‑current‑detection requirements of charging infrastructure, the MAGTRON RCMU101 series merges iFluxgate® fluxgate sensing with in‑house system‑on‑chip processing hardware. The RCMU101SM1‑2EI‑K example uses a highly integrated proprietary SoC solution embedding self‑test diagnostics, decision logic and logic‑level output within a compact module.

On‑chip integration reduces external peripheral‑circuit complexity. Digital logic‑level output interfaces enable straightforward status reading by host controllers and lower overall system‑integration workload. Built‑in self‑diagnostic capability allows continuous health‑checking of the detection chain, supporting verifiable protection‑loop implementation for end‑equipment.

Powered from a single 5 V supply, it features small footprint ideal for space‑constrained compact charger hardware. For AC‑V2G protection schemes, select appropriate RCMU model matched to conductor rating and protection requirements. When coordinated with host controllers and disconnection actuators, it implements complete residual‑current protection functions and translates component‑level integration benefits into simplified hardware design and system validation.

8. Conclusion

V2G technology enables electric vehicles to operate as distributed energy resources for utility grids. The fundamental distinction between AC V2G and DC V2G lies in bidirectional‑power‑converter location: converters are normally located onboard the vehicle for AC‑V2G, while DC‑V2G power conversion resides predominantly within off‑board equipment. Measurement points, vehicle‑charger communication and fault‑current pathways must all be analysed in the context of the specific hardware topology.

Hardware design reviews should follow this workflow:
Standard & operational‑state review → AC/DC topology analysis → dispatch & vehicle‑charger communication assessment → main‑current measurement review → residual‑current / insulation‑monitoring validation → local fault‑protection verification → post‑fault status re‑confirmation

Only when protocol‑reported states can be cross‑validated against real‑world measured current, voltage and insulation parameters can a robust, verifiable safety closed‑loop be achieved for V2G systems.

References

1. ISO 15118‑20:2022/Amd 1:2026, AC DER, MCS and enhanced safety concepts, published 13 July 2026

2. ISO 15118‑20:2022, Second‑generation network‑layer and application‑layer requirements for vehicle‑to‑grid communication

3. National Standards Information Public Service Platform, GB/T 46148‑2025, implemented 1 March 2026

4. National Standards Information Public Service Platform, NB/T 11867‑2025, implemented 28 March 2026

5. Full‑Text National‑Standard Publication System, GB/T 27930‑2023, implemented 1 April 2024

6. National Standards Information Public Service Platform, GB/T 18487.1‑2023 plus its No. 1 Modification Sheet, modification sheet implemented 25 May 2026

7. Joint notice by four PRC government authorities: Notice on Announcing the First Batch of Large‑Scale Vehicle‑to‑Grid Demonstration Pilots, issued 13 March 2025, public release 2 April 2025

8. National Standards Information Public Service Platform, GB/T 43332‑2023 No. 1 Modification Sheet, published 30 July 2026, effective 1 November 2026

9. National Standards Information Public Service Platform, Project 20261987‑Z‑524, AC‑V2G control & interaction communication guideline (under drafting)

10. IEC 60664‑1:2020+AMD1:2025 and IEC 60664 series catalogue, insulation‑coordination standards

11. IEC 61557‑8:2014, Insulation‑monitoring‑devices for IT power‑distribution systems

12. Mobilize official product documentation, PowerBox series hardware overview and Verso bidirectional‑V2G feature description

13. CHAdeMO Association, Fermata Energy FE‑20 V2X Charger technical datasheet

14. Texas Instruments, TIDUF18A Rev 02, 7.4‑kW Bidirectional On‑Board Charger Reference‑Design (GaN‑based), February 2024, Page 4 Figure 2‑1

15. Infineon, REF‑EV50KW2SICKIT User Guide Rev 1.0, June 2024, Page 6 Figure 2 and bidirectional‑test constraints