Bi-directional grid-connected power converters - General and safety requirements
1Key Takeaways
This part of IEC 62909 specifies the general and safety aspects of bidirectional grid-connected power converters (GCPCs), which consist of a grid-side inverter and two or more types of DC power ports on the application side, with a system voltage not exceeding 1000V AC or 1500V DC. This document can also be used for sp…
2Expert Interpretation
An in-depth interpretation of the BS EN IEC 62909-1:2025 international standard for bidirectional grid-connected power converters, covering general specifications, safety requirements, performance testing, and implementation guidelines for GCPC equipment. It is suitable for new energy system integrators and power electronics equipment manufacturers.
Standard Background and Evolution Analysis
BS EN IEC 62909-1:2025 is the core international standard for bidirectional grid-connected power converters (GCPCs). As the UK national implementation of IEC 62909-1:2025, it replaces the 2018 version and will complete its transition period on September 30, 2028. Developed by IEC/TC 22/SC 22E, the "Regulated Power Supplies" subcommittee, this standard reflects the global technological needs to address climate change and fossil fuel depletion.
Key technical changes in the standard's evolution include the addition of "safety" to the title, the clarification of the scope of application of GCPCs, and the strengthening of safety requirements for multi-port systems. With the popularization of distributed energy systems, the importance of bidirectional inverters in residential and commercial energy management is becoming increasingly prominent. This standard provides a technical specification basis for optimizing electricity consumption and improving energy efficiency.
Core Terminology and Definition System
The standard establishes a complete GCPC terminology system, providing a unified technical language for the industry:
| Terms | Definition | Technical Points |
|---|---|---|
| Bidirectional Grid-Connected Power Converter | A power converter with multiple DC power ports connected to an AC distribution network | System voltage ≤1000V AC or 1500V DC |
| Bidirectional Inverter | Equipment capable of achieving AC to DC and DC to AC active power conversion | Supporting bidirectional energy flow |
| DC Link Interface | Internal system DC bus between the DC/DC converter and bidirectional inverter | Core node for system energy exchange |
| Grid Independent Operation | Supplying AC loads via the GCPC during grid isolation | Key modes for backup power functionality |
System Architecture and Operation Modes
GCPC The typical architecture includes multiple DC/DC converters, a DC link interface, a bidirectional inverter, and control functions. The standard defines four basic operation modes:
Mode I: Power is transferred from multiple distributed energy resources to the grid and/or AC loads, and may also include inter-energy charging. This mode is suitable for scenarios where surplus power is connected to the grid during peak PV generation periods.
Mode II: Power is transmitted from the grid to multiple distributed energy resources, suitable for charging energy storage devices during nighttime periods with low electricity prices.
Mode III: When the bidirectional inverter is inactive, power is transmitted between distributed energy resources to achieve optimal energy allocation.
Mode IV: With the grid operating independently, power is supplied from multiple distributed energy resources to AC loads, ensuring continuous power supply to critical loads.
Technical Specifications for Performance Requirements
DC Link Interface Voltage Range
The standard defines the voltage range of the DC link interface, including the rated voltage, nominal operating voltage range, allowable operating voltage range and withstand voltage:
| Voltage parameters | Definition | Technical requirements |
|---|---|---|
| Nominal operating voltage range | The DC link interface voltage range for normal operation of the power electronic converter | Specified by the manufacturer, taking into account factors such as modulation index and ripple voltage |
| Allowable operating voltage range | The voltage range that exceeds the nominal range but is still allowed to operate | When exceeding the range, operation must be stopped within the specified time |
| Withstand Voltage | The maximum withstand voltage to prevent damage to the equipment | Specified by the manufacturer in the documentation |
Key Converter Performance
DC/DC converters must be able to limit current when the DC link voltage suddenly changes, including short-circuit conditions. Bidirectional inverters must operate smoothly when the DC input voltage suddenly changes, ensuring that the system-side AC current transients are within the manufacturer's specified range.
Safety Requirements and Compliance Testing
The standard fully adopts the safety framework of IEC 62477-1:2022, covering hazard protection requirements, testing requirements, and information labeling requirements:
Hazard Protection: Manufacturers are required to conduct a specific risk analysis for multi-source systems connected to the grid, describing the protective measures implemented to mitigate risks. Refer to the risk assessment guidance in Annex R of IEC 62477-1:2022.
Grid-interactive inverter protection fault tolerance: The requirements of 4.4.4.15 of IEC 62109-2:2011 can be applied to ensure the safety of the equipment in the event of a protection system failure.
DC link interface protection: Manufacturers are required to specify the maximum short-circuit current rating in accordance with 4.3.2 of IEC 62477-1:2022 for coordination and selection of overcurrent protection devices.
Scope and Boundaries of the Standard
The standard clearly specifies the types of equipment that are applicable and inapplicable, providing clear guidance to avoid conflicts in standards:
| Equipment Type | Applicable Standard | Remarks |
|---|---|---|
| Multi-portGCPC | IEC 62909-1 | With battery, DER and CPT ports |
| Uninterruptible Power Supply Systems | IEC 62040 Series | Not included in the scope of this standard |
| Photovoltaic System Power Converter Equipment | IEC 62109 series | Covered by dedicated standards |
| Electric vehicle charging equipment | IEC 61851 series | Battery charging and discharging converters in charging stations |
Implementation recommendations and compliance paths
Design phase considerations
During the product design phase, manufacturers should focus on the following: DC link voltage range design, hot-swap transient management, multi-source system risk analysis, and protection mechanism design. Particular attention should be paid to determining the nominal operating voltage range, taking into account factors such as the upper and lower limits of the adjustable voltage range, transient range limits, voltage slew rate (dV/dt), ripple voltage range, and frequency.
Test Verification Requirements
Compliance testing must be performed in accordance with Clause 5 of IEC 62477-1:2022, including electrical type testing, protection function verification, and information marking integrity check. For the AC output characteristics in grid-independent operation mode, verification must be carried out in accordance with 6.4.2.3 and 6.4.2.10 of IEC 62040-3:2021 to ensure that the voltage waveform characteristics and dynamic output performance meet the declared requirements.
Documentation and Marking
The manufacturer must provide complete technical documentation, including: the rated voltage and nominal operating voltage range of the DC connection interface, the current limit of each PEC, the maximum starting current, the protection level, and the operating time. Equipment marking must comply with the requirements of Clause 6 of IEC 62477-1:2022 to ensure that installers and end users can correctly understand the capabilities and limitations of the equipment.
Transitional Arrangements
BS EN IEC 62909-1:2018 will be withdrawn on September 30, 2028. Manufacturers must complete product updates and certification conversions before this date. It is recommended that national standard implementation be completed before September 30, 2026 to ensure that products meet the latest safety requirements.
Technology Development Trends and Standard Outlook
With the rapid development of distributed energy systems and electric vehicles, the technical requirements for bidirectional grid-connected converters will continue to evolve. This standard provides an important technical foundation for the construction of future smart grids, virtual power plants, and energy internet. Manufacturers should pay attention to the development progress of the IEC 63285 series (Energy Storage Power Converter Subsystems for Electrical Energy Storage Systems) and updates to related standards to ensure continued product compliance.
The implementation of this standard will promote comprehensive improvements in the energy efficiency, safety, and interoperability of GCPC equipment, providing strong technical support for the global energy transition and the achievement of carbon neutrality goals.