NB/T 11488-2024General specification for power conversion system of flow battery energy storage system (English PDF)

Foreword

This document was issued on 24 May 2024 by the National Energy Administration of the PRC and takes effect on 24 November 2024.

It is a NB/T standard: recommended rather than compulsory, but it is the text a Chinese reviewer applies when assessing a submission.

It is classified under ICS 29.220.01, Chinese classification K 84.

This document was drafted in accordance with the rules given in GB/T 1.1-2020 Directives for standardization - Part 1: Rules for the structure and drafting of standardizing documents.

Please note that some of the content of this document may be the subject of patent rights. The issuing body of this document assumes no responsibility for identifying patents.

This document was proposed by, and is under the administration of, the energy storage standardization technical committee of the energy industry.

This document is issued for the first time.

1 Scope

NB/T 11488-2024 is the Chinese specification for the power conversion system - the PCS - of a flow battery energy storage installation. It exists because the flow battery is the technology China is building for storage measured in hours, and because the converter, not the battery, is what the grid actually sees. The stacks and the vanadium tanks store the energy, but every ampere entering or leaving them passes through the PCS, and it is the PCS that decides whether the plant behaves as an asset the system operator can rely on or as a liability that trips off at the worst moment. A flow battery also makes demands a lithium converter does not: its terminal voltage swings widely with state of charge, the pumps have to keep running, and constant current and constant voltage charging both have to be held precisely, which is why this document defines stabilized current precision and stabilized voltage precision as measured quantities rather than marketing terms. The requirements that matter most are the grid ones. The converter has to ride through faults rather than disconnect: low voltage ride through when the system voltage dips, high voltage ride through when it rises, and frequency ride through, each within a specified range and time. It has to provide primary frequency modulation, with the response time defined as reaching 90 percent of the commanded power change and the settling time as the point after which the error never again exceeds 5 percent. It has to provide inertia response, adjusting active power according to the rate of change of frequency to slow it. And it has to have anti-islanding protection so it cannot energise a dead network. Around those, the document sets the classification by grid connection and by voltage level, the normal service conditions for grid-connected and stand-alone operation, twelve basic functions from zero-voltage start-up and pre-charging through mode switching to data storage, and the full performance requirements for electrical, safety, mechanical and electromagnetic compatibility, together with the auxiliary cooling and supply systems. Half the document is test method: six clauses of testing and six annexes, including the normative safety item requirements, the test apparatus, the verification method for the hardware-in-the-loop simulation model of the converter, and the method of determining active power control response time, settling time and deviation. It applies to converters up to 1 kV AC at 50 Hz with battery side voltage up to 1 500 V DC. It was issued on 24 May 2024 by the National Energy Administration and took effect on 24 November 2024.

This document specifies the normal service conditions, the basic functions, and the performance requirements for the electrical performance, the safety performance, the mechanical performance and the auxiliary systems of the power conversion system of a flow battery energy storage system, hereinafter referred to as the energy storage converter, and sets out the requirements for the inspection rules, the test methods, the marking, the packaging, the transport and the storage.

This document applies to three-phase and single-phase converters that use an electrochemical flow battery as the storage medium.

This document applies to converters whose alternating current side voltage is 1 kV and below, whose alternating current side frequency is 50 Hz, and whose battery side direct current voltage is 1 500 V and below. Energy storage system converters connected through a transformer to an alternating current side above 1 kV may use it for reference.

The direct current converters (DC/DC) of a flow battery energy storage system, and the integrated photovoltaic and storage converters with a PV port, may also use it for reference.

2 Normative references

The contents of the following documents constitute indispensable provisions of this document through normative reference in the text. For dated references, only the edition corresponding to that date applies to this document. For undated references, the latest edition, including all amendments, applies to this document.

GB/T 34120 Technical specification for power conversion system of electrochemical energy storage system

GB/T 34133 Technical specification for testing of power conversion system for energy storage

GB/T 3859.23 Semiconductor converters - General requirements and line commutated converters - Part 1-2: Application guide

GB/T 2423.3 Environmental testing - Part 2: Test methods - Test Cab: Damp heat, steady state

GB/T 2423.4 Environmental testing for electric and electronic products - Part 2: Test methods - Test Db: Damp heat, cyclic

GB/T 7251.1 Low-voltage switchgear and controlgear assemblies - Part 1: General rules

GB/T 12325 Power quality - Deviation of supply voltage

GB/T 12326 Power quality - Voltage fluctuation and flicker

GB/T 13384 General specifications for packing of mechanical and electrical products

GB/T 14549 Power quality - Harmonics in public supply network

GB/T 15543 Power quality - Three-phase voltage unbalance

GB/T 15945 Power quality - Frequency deviation for power system

GB/T 17045 Protection against electric shock - Common aspects for installation and equipment

GB/T 17626.2 Electromagnetic compatibility - Electrostatic discharge immunity test

GB/T 17626.4 Electromagnetic compatibility - Electrical fast transient and burst immunity test

GB/T 17626.6 Electromagnetic compatibility - Immunity to conducted disturbances induced by radio-frequency fields

GB/T 191 Packaging - Pictorial marking for handling of goods

GB/T 20626.1 Special environmental conditions - Electric and electronic products for high altitude - Part 1: General technical requirements

GB/T 24337 Power quality - Interharmonics in public supply network

GB/T 4208 Degrees of protection provided by enclosure (IP code)

GB/T 40595 Technical requirements and test guide for primary frequency modulation of grid-connected power sources

NB/T 31016 Technical specification for the converter of the battery energy storage power control system

NB/T 42089 Technical specification for the power conversion system of an electrochemical energy storage station

DL/T 860 (all parts) Communication networks and systems for power utility automation

3 Terms and definitions

The following terms and definitions apply to this document.

3.1 flow battery energy storage system

An equipment system that uses a flow battery as the storage medium and that stores and releases electrical energy cyclically by means of a converter.

3.2 power conversion system, PCS

The device that carries out bidirectional energy conversion between the storage battery and the alternating current grid; abbreviated to PCS.

3.3 AC terminal

The terminal of the energy storage converter used to connect the power-frequency alternating current.

3.4 DC terminal

The terminal of the energy storage converter used to connect the battery stack or the direct current bus of the battery array.

3.5 grid-connected mode

The operating mode in which the energy storage converter is normally connected to the grid through the alternating current terminal and can exchange energy with the grid.

3.6 stand-alone mode

The operating mode in which the energy storage converter is disconnected from the grid at the alternating current terminal or on the grid side, establishes voltage and frequency independently, and supplies or exchanges energy with the load and with other equipment.

3.7 stabilized current precision

The degree of stability of the output current of the direct current terminal of the energy storage converter when, in the constant current charging state, that current is held stable at any value within its rated range.

3.8 stabilized voltage precision

The degree of stability of the output voltage when, in the constant voltage charging state, the output current of the direct current terminal varies within its rated range and the output voltage is held stable at any value within the adjustable range.

3.9 fault ride through

The ability of the energy storage converter, when a power system fault or disturbance causes the voltage or frequency at its alternating current terminal to deviate from the normal operating range, to continue stable operation without disconnecting from the grid within the specified ranges of voltage and frequency variation and within the specified time interval. Fault ride through generally comprises voltage fault ride through and frequency fault ride through; voltage fault ride through generally comprises low voltage ride through and high voltage ride through.

3.10 low voltage ride through

The ability of the energy storage converter, when a power system fault or disturbance causes the voltage at its alternating current terminal to dip, to continue stable operation without disconnecting from the grid within the specified voltage dip range and time interval.

3.11 high voltage ride through

The ability of the energy storage converter, when a power system fault or disturbance causes the voltage at its alternating current terminal to rise, to continue operation without disconnecting from the grid within the specified voltage rise range and time interval.

3.12 primary frequency modulation

The control function by which the energy storage converter adjusts its own active power, when the power system frequency deviates from the target frequency, so as to reduce the system frequency deviation. [GB/T 40595-2021, definition 3.1, modified]

3.13 response time of primary frequency modulation

The time required, from the moment the frequency at the alternating current terminal of the energy storage converter leaves the primary frequency modulation dead band, for the change in the active power output of the converter to reach 90 percent of the difference between the active power target value and the initial value. [GB/T 40595-2021, definition 3.11, modified]

3.14 settling time of primary frequency modulation

The shortest time, from the moment the frequency at the alternating current terminal leaves the primary frequency modulation dead band, after which the absolute value of the difference between the active power output of the converter and the target value never again exceeds 5 percent of the difference between the active power target value and the initial value. [GB/T 40595-2021, definition 3.12, modified]

3.15 inertia response

The control characteristic by which the energy storage converter, when the power system frequency changes rapidly, adjusts its own active power according to the rate of change of frequency so as to slow that rapid change.

3.16 anti-islanding protection

The protection that prevents an unplanned islanding condition from arising.

3.17 touch current

The current passing through the body of a person or of livestock when they touch one or more accessible parts of an electrical installation or of electrical equipment. [GB/T 17045-2020, definition 3.9]

4 Classification and coding

4.1 Product classification

4.1.1 Classification by the connection relationship with the grid

Energy storage converters may be divided, according to their connection relationship with the grid, into: converters that switch between grid-connected and stand-alone operation; grid-connected converters; and stand-alone converters.

4.1.2 Classification by the voltage level of connection

Energy storage converters may be divided, according to the voltage level at which they are connected, into class A1 converters, applied in energy storage stations connected to the grid at 10 (6) kV and above and whose converter alternating current terminal voltage is not greater than 1 000 V; and class A2 converters, applied in energy storage stations connected to the grid at 10 (6) kV and above whose converter alternating current terminal voltage is above 1 000 V.