Complex Network Analysis of China National Standards for New Energy Vehicles

Abstract

Standards are technical measures to regulate and promote sustainability. China National Standards for new energy vehicles (NEV) are developing at an increasing rate. We explored the functions and citation network the China national standards from a complex-network perspective. Different types of standards were clustered and citation relationships were identified based on standards’ document analyses. In this paper, the evolution of standard nodes and citation links are presented, and implications for future standardization work are proposed. In total, 114 existing standards were identified through desktop research and network analysis by using the Gephi ForceAtlas2 algorithm. This study can be helpful for future standardization in areas such as autonomous driving and carbon-related standards based on citation-network analysis.

1. Introduction

China is the biggest new energy vehicle (NEV) market, followed by Europe and the United States. With fast market penetration, the quality attributes such as safety, performance and compatibility of NEV raised society and regulators’ concern, such as battery fire accident, battery range, charge time, compatible charging stations. There is fierce competition of NEV manufacturers to win consumer market. The product quality information needs to be based on public standards for fair competition, which is also important for protecting consumers’ rights. Also, standards provide technical guidance and requirements for sustainability issue, such as reduce emission, public infrastructure investment and energy consumption. There is a consensus that standards played important roles for consumers, governments, and industries.

From a consumer-adoption perspective, the safety, performance and compatibility attributes of NEVs are important quality factors on consumer-adoption willingness and behaviors such as battery safety, battery life, charging time, battery range, compatibility with the public charging station facility, etc. [1,2,3]. The quality attributes and standards are related to consumer utilities [4]. Standards are import factors that affect the consumer’s adoption of electric vehicles. The most critical standards related to NEVs include safety standards, performance standards and compatibility standards [5].

From a government perspective, standards are the technical basis for a government to regulate market competition and technical diffusion [6], protect consumer rights and the environment, facilitate trade [7] and reduce information asymmetry [8]. Standards also play key roles on sustainability issues such as pollutant and GHG (Greenhouse Gas) emissions, energy saving, recycling of materials and batteries and reduction in waste of charging stations, among others [9,10].

From an industry perspective, standards are also important factors for technology lock-in [11], with double-sided effects that can both promote and be barriers for technology diffusion with respect to the actual cases in which the standard could be favorable for the specified product or technology [12]. Standards can also play more important roles together with patents [13], especially in compatibility standards related to communication technology [14]. Indirect network effects such as charging infrastructure based on compatibility standards are also important factors that have an impact on the future technology diffusion of NEVs [15]. Patents and patent pools can have synergic effects on the standards in NEV diffusion [16].

However, the functions, evolution and citation network of the China national standards for NEVs are not clear in previous study, the research in this area can help understand the relationship and structure of the China National Standards of NEVs, and highlight the important standards and their clustering, which is also helpful for future standardization work. We were inspired by the literature [10] on Australian plastic standards, the air quality standard citation network and green technology patent data in the literature [17,18]. We used desktop research and the complex-network analysis software Gephi with ForceAtlas2 algorithm [13] to identify the most important standard clusters and links in the network and to understand the evolution of the standard network. Finally, we provide implications and suggestions for future standardization work in areas such as autonomous driving and carbon-related standards based on citation-network analysis.

2. Materials and Methods

Data were collected from China National Standard Database (https://openstd.samr.gov.cn), managed by State Administration for Market Regulation (SAMR) and National Technical Committee of Auto Standardization (http://www.catarc.org.cn). A total of 114 NEV national standards were selected (data collected on 25 October 2022).

As shown in Figure 1, we preprocessed the raw data according to the publication year, standard types and organizations that draft the standards, and we present the data from an evolutionary and sectional perspective. Then, the citation relationship matrix was manually extracted from the normative reference section of the standards’ text, as the database has no citation relationship. We built the citation table for citation-network analysis. Additionally, we segmented the standards into four major types, and, from an evolutionary perspective, we segmented the standards and analyzed the standard numbers, links and types based on publication year of each standard.

Gephi software was used to have trial runs with different algorithms such as Fruchterman–Reingold, OpenOrd, Yifan Hu etc. Finally, ForceAtlas2 algorithm was chosen for clustering analysis of the standard-citation network [13], which was found to be the most suitable clustering method among other toolkits. The clustering was comprehensively analyzed with standard-type and function analysis. The distribution and trend of standards were presented based on standard types (which were general standards, safety standards, performance standards and compatibility standards), to provide more insights regarding China’s NEV standards. Topological indexes such as degree centrality and betweenness centrality were used to identify the most important standards.

3. Results

3.1. Standard Publication Overview

China published national standards to regulate the safety requirements and performance claim, promote the compatibility of NEVs and increase environmental awareness and responsibility regarding NEVs, for example controlling emissions and reducing energy consumption.

As shown in Figure 2, the standard publication trend has been seeing fast-increasing sales of NEVs since 2010. The left axis is the number of published standards, while the right axis represents NEV sales. From 2001 to 2014, only a few standards were developed. This corresponds to the low market penetration of NEV products in China´s market. With the fast increase in NEV sales from 2015 to 2021, a significant number of standards were published between 2015 and 2021, averaging 14 NEV national standards per year (publication minimum: 6 standards in 2019; and maximum: 24 standards in 2021). The new rise of technical standards was formed as a basis to regulate and guide the technical diffusion, market claiming, market access and surveillance of NEVs.

China is recently undergoing a fast market penetration of NEVs and extensive standardization activities regarding NEVs.

3.2. Sectional Analysis of Standards

China National Standards consist of two types: GB standards, which are mandatory standards, and GB/T standards, which are recommended standards. Among NEV national standards, there are only five mandatory GB standards, as listed in

Table 1. GB standards of NEV.

Standard No.	Standard Name	Publication Year
GB 19755	Technical requirements and measurement methods for emissions from light-duty hybrid electric vehicles	2016
GB 22757.2	Energy consumption label for light-duty vehicles—Part 2: For off-vehicle-chargeable hybrid electric vehicles and pure electric vehicles	2017
GB 18384	Electric vehicles safety requirements	2020
GB 38031	Electric vehicles traction battery safety requirements	2020
GB 38032	Electric buses safety requirements	2020

. The other 109 standards are voluntary standards with the prefix GB/T. Among the GB standards, two standards were published in years 2016 and 2017: GB 19755 and GB 22757.2. They covered technical requirements and labeling requirements regarding emission and energy consumption (environmental and energy perspectives). Three safety standards were published in 2020 to cover the EV and its traction battery, and the electric bus. The mandatory standard highlighted the minimum quality requirements and the environmental and sustainability duties that EVs and battery manufacturers must consider before launching a product into China’s market.

According to GB/T 19596-2017 (Terminology of electric vehicles), the major types of EV can be the battery electric vehicle (BEV) and the hybrid electric vehicle (PHEV). As shown in

Table 2. Classification of GB standards according to target system.

Target System	GB/T Standard	GB Standard
Electric-drive system	4	0
General requirements	22	3
On-board energy system	18	1
Charge/replacement system and interface	30	0
Other system and component	6	0
Fuel-cell EV/systems	20	0
PHEV	6	1
BEV	9	0

, regarding EV battery types, there were 20 (17.5%) fuel-cell EV standards out of the total 114 standards, which indicated that fuel-cell EV standards were in the developing stage, while other cell types were covered in the majority of the standards. The charge/replacement system and interface were the major types of standards, while general-type standards targeted the system, and compatibility standards focused on compatibility/interface requirements. As the target-system matrix had a vertical and horizontal relationship, the statistic value of the standards partly overlapped (for example, general requirements can also cover partial standards of fuel-cell EV/system, PHEV and BEV).

Regarding standard types, we classified them according to the summary of [5,8] and adapted the classification according to the Chinese National Standards of EV. The four major types are general, safety, performance and compatibility standards.

• Safety standards: These standards can increase consumer confidence and facilitate trade. They are the basis for technical barriers to trade, and focus on safety requirements and test methods, such as the battery-overcharge or the short-circuit tests.
• Performance standards: These standards are the basis for the measurement of product performance and market claims, which can reduce information asymmetry, decrease purchasing search costs and facilitate trade. The target aspects can be battery range, charging time, endurance, etc.
• Compatibility standards: These standards can facilitate compatible charging of NEVs to increase the indirect network effect of the charging stations. They also include information-exchange formats such as V2X (vehicle-to-everything) communication.
• General standards: These standards target components or end products. They cover safety, performance and compatibility requirements for the targeted product. Terminology standards are also covered by this category.

As shown in Figure 3, in total, 50 (44%) standards were published from 2001 to 2021 (an average of 4 standards published each year). In total, there were 12 (11%) safety standards, 10 of them published in years 2020 and 2021. The other two standards were published in 2017 and 2018. A total of 32 (28%) performance standards were published during the period 2005–2021. The rest are 20 (18%) compatibility standards that were published from 2012 to 2021.

3.3. Citation Network and Cluster Analysis of Standards

Evolutionary stages are shown in Figure 4, Figure 5 and Figure 6. There were few standards before 2013, as shown in Figure 4, when only 12 standards were interlinked. The standardization and citation network developed rapidly after 2013, as shown in Figure 5. In 2017, more than 50 standards and five clusters were found in the network, then in 2021, a total of 114 standards and eight clusters were found in the network, as shown in Figure 6. Compared with Figure 5, there were more standards related to wireless charging systems, the recycling of batteries, battery swap and fuel-cell batteries, which reflected the standardization and technical diffusion trend at that time. Based on the historical-data analysis, it is also expected that, in future standards, a citation network will emerge regarding more innovative products, functions, components and quality perspectives.

Based on the data from 2021, a total of 114 Chinese national standards (including 5 GB standards and 109 GB/T standards) were analyzed using the Gephi ForceAtlas2 algorithm [19] and divided into 8 clusters, as shown in Figure 7. The notation of each cluster can be seen below.

In the figure, the notation of each cluster is described as follows:

• EVWPT—Electric-vehicle wireless power transfer
• FCEV—Fuel-cell electric vehicles
• EVTB—Electric-vehicle traction battery
• EVDM—Electric-vehicle drive motor
• EVRM—Electric-vehicle remote management
• EVSS—Electric-vehicle safety standards
• EVPS—Electric-vehicle performance standards
• EVCS—Electric-vehicle compatibility standards

The links with terminology standard GB/T 19596 are the basis of almost all NEV standards. Fuel-cell EV also has a large number of standards, while safety standards have less nodes but important roles in the network, (for example, in-degree of GB 18384 is the second most important node in the network. Compatibility standards GB/T 20234.1, GB/T 18487.1, GB/T 29317 and GB/T 27930 are all in the EVCS cluster. The total sum of in-degree of the four nodes is 41, which means the standards have important citations. As for the wireless power-transfer, remote-management, drive-motor and traction-battery standard clusters, there is an average of 3–5 standards in each cluster. These standard areas need to be further developed.

To identify the important nodes in the network, there exist typical measurements or indexes such as degree centrality and betweenness centrality [20]. The degree centrality is divided into in-degree and out-degree. In-degree, given by the expression $C_I\left(i\right)={\displaystyle \sum }_{i=1}^n{A}_{ij}$, refers to the total number of times the standard has been cited, and the higher the in-degree centrality, the more times the standard has been cited and the higher its status in the network. Out-degree, given by the expression $C_O\left(j\right)={\displaystyle \sum }_{j=1}^n{A}_{ij}$, refers to the total number of times a standard refers to other standards. The higher the out-degree centrality, the more times the standard refers to other standards and the stronger the absorption capacity.

Table 3. Top eight in-degree among China’s NEV standards.

Standard No.	Standard Name	In-Degree	Out-Degree
GB/T 19596	Terminology of electric vehicles	67	2
GB 18384	Electric-vehicle safety requirements	20	6
GB/T 24548	Fuel-Cell Electric Vehicles—Terminology	14	1
GB/T 20234.1	Connection set of conductive charging for electric vehicles—Part 1: General requirements	13	2
GB/T 18487.1	Electric-vehicle conductive charging system—Part 1: General requirements	11	7
GB/T 29317	Terminology of electric-vehicle charging/battery-swap infrastructure	9	0
GB/T 27930	Communication protocols between off-board conductive charger and battery-management system for electric vehicle	8	2
GB/T 24549	Fuel-cell electric vehicles—Safety requirements	8	4

summarizes the top eight national standards for new-energy vehicles.

From the in-degree distribution chart, we can find that the citation network roughly follows the power-law distribution of the scale-free network [21], which means a minority of standards have more citations, while other standards are seldom cited and can be ignored. In Figure 8, the y axis p(k) is the degree distribution, denoted as the probability of a node chosen uniformly at random to have a degree k. The x axis is the degree k.

Betweenness centrality, or, in brief, betweenness, is given by the expression $g\left(v\right)={\displaystyle \sum }_{s\ne v\ne t}\frac{{\sigma }_{st}\left(v\right)}{{\sigma }_{st}}$, where ${\sigma }_{st}$ denotes the total number of shortest paths from node s to node t and ${\sigma }_{st}\left(v\right)$ means the number of paths that pass through v. Betweenness centrality refers to the ratio of the number of paths passing through a standard node and connecting two other standard nodes to the shortest number of paths connected between these two standard nodes. It is used to measure the control of resources by nodes in the network.

Table 4. Top 10 nodes with highest betweenness in China’s NEV standards network.

Standard No.	Standard Name	Betweenness
GB 18384	Electric-vehicle safety requirements	341
GB/T 19596	Terminology of electric vehicles	247
GB/T 18487.1	Electric-vehicle conductive charging system—Part 1: General requirements	206
GB/T 20234.1	Connection set of conductive charging for electric vehicles—Part 1: General requirements	156
GB/T 24549	Fuel-cell electric vehicles—Safety requirements	141
GB/T 19836	Instrumentation for electric vehicles	85
GB/T 19752	Hybrid electric vehicles—Power performance—Test method	74
GB/T 24548	Fuel-Cell Electric Vehicles—Terminology	24
GB/T 37154	Fuel-cell electric vehicles—Test methods of hydrogen emission	22
GB/T 36288	Fuel-cell electric vehicles—Safety requirement of fuel-cell stack	21

lists the top 10 nodes with highest betweenness in China’s NEV standards network.

Among all standards, only 12 items have a betweenness of more than 20, and 70% of the standards have a betweenness centrality of 0, indicating that most standards have weak control over the entire network. Only a small number of standards have a high betweenness and occupy an important position; such standards are mainly basic standards and method standards. The highest betweenness reaches 340 with the GB 18384 standard (Electric-vehicle safety requirements), which is a national mandatory standard that has a strong control over the whole standard network. The second highest is GB 19596 (Terminology of electric vehicles), which reached 247.

As shown in

Table 5. Organizations that participated in GB standards of NEVs.

No	Organization	Type	Standards Amount
1	China Automotive Technology and Research Center	Research Institute	111
2	BYD	Enterprise	44
3	Beijing Electric VEHICLE Co., Ltd.	Enterprise	32
4	Pan Asia Technical Automotive Center	Enterprise	25
5	SAIC Motor Group	Enterprise	24
6	Chongqing Changan	Enterprise	23
7	China FAW Group	Enterprise	20
8	Dongfeng Motor Corporation	Enterprise	18
9	Potevio New Energy Co., Ltd.	Enterprise	18
10	Beijing Institute of Technology	Research Institute	18
11	SAIC GM Wuling Automobile	Enterprise	16
12	STATE GRID of China	Enterprise	14
13	Cheryev	Enterprise	14
14	Tsinghua University	Research Institute	14
15	NIO Shanghai	Enterprise	13

, among the organizations drafting standards, the top one is the China Automotive Technology and Research Center with a total of 111 standards, accounting for 97% of all standards, far ahead of other stakeholders, which indicates that the China Automotive Technology and Research Center has quite an extensive participation in the drafting of new-energy-vehicle standards.

Among the top 15 organizations involved in the drafting of the standards, 12 of them are enterprises, including established automobile companies with extensive resources, such as BYD, SAIC Motor Group, Dongfeng Motor, FAW, etc., as well as new start-ups, such as NIO, Potevio, etc. The other three are scientific research institutions, including the Tsinghua University and the Beijing Institute of Technology.

Among the standards with a high betweenness, the main drafting units are the China Automotive Technology and Research Center, BYD Automobile Industry Co., Ltd. and other companies that occupy important resources in the industry.

4. Discussion

Based on the number of published standards, citation links and clusters, the development of China’s NEV standards can be divided into three major stages. The first stage is from 2001 to 2014, when only a few standards were developed, corresponding to the low market penetration of NEV products in China’s market. With the fast increase in NEV sales from 2015 to 2018, a significant number of NEV standards were published during those 4 years, and five clusters entered the standard citation network. New standards related with wireless charging systems, the recycling of batteries, battery swap and fuel-cell batteries were established between 2019 and 2021. New clusters of technical standards were formed as a basis to regulate and guide technical diffusion, market claiming, market access and market surveillance.

The top three years with the highest number of standards published are 2021, 2017 and 2020, which indicates the high demands of standards and the fierce competition, which needs harmonized standards. It is expected that more standards will be developed regarding new types of NEVs, new functions and new components in the future, following new requirements and new test methods.

Compared with existing standards and technologies, the following gaps are expected to be filled: Safety standards related to crush tests, super capacitors, fuel-cell electric vehicle, functional safety of traction motor system, conduction charging system, etc. Performance standards for fuel-cell electric vehicle, such as test methods, energy-consumption measurements, recycling and battery echelon use, environmental tests and endurance tests of the critical components (such as the hydrogen circulation pump, the air compressor, the cooling pump, etc.). Compatibility standards regarding hydrogen systems, battery swap platforms, interface, vehicle-to-everything, etc. General standards related to critical components such as the engine, hybrid power sources, conductive on-board chargers, DC/DC inverters, heat management systems, etc., as well as new types of vehicles such as the PHEV bus and the BEV bus, etc. Additionally, the terminology of the existing standards is also expected to be updated to adapt to future technology and products.

The citation network of standards can be a reference for new-standard development and the modification of existing standards. for instance, to facilitate the research work on related standards by considering the citation map and to find the missing linkage. Moreover, the network can be utilized to explore more opportunities for new components and products—such as in the case of the FCEV cluster, which can be interlinked with EVSS, EVCS and EVPS regarding their corresponding safety, performance and compatibility standard requirements—or in the case of new standards being developed, to inversely trace back to the cited standards to check if new terminology shall be added or modified. If new risks and methods are adopted in the new standards, then other related standards could also be checked to decide whether the clauses or requirements should also be updated.

Considering the few enterprises that participated in the standards, more enterprises are encouraged to participate more actively in the standardization work, to broadly consider the different technology and test methods, harmonize the technology routes and keep the diversity of the technological options. Governments and policymakers are recommended to well balance the pay-off between sustainability requirements and economic benefits. As standards are technical measures to control and regulate the market and technology, the testing of components, systems and vehicles can raise the cost for manufacturers significantly. Too many standards and/or overlapping standards can pose an unnecessary burden to the industry, such as an increase in the manufacturing and compliance cost or an increase in the process complexity. The lack of a stringent level of requirements can lead to a social cost, such as a safety risk to consumers and harm to the environment. Therefore, policymakers and standardization bodies should pay attention to the architecture, structure and quality requirements of the standards to well balance the social benefits and the industrial constraints. The clustering, citation-relationship mapping can be referenced to identify overlapping nodes and links.

5. Conclusions

Standards are important technical measures for protecting consumer and society, regulating the industry, which have strategic impacts for the sustainability development. Regarding the China NEV market, in this paper, we explored the functions, evolutions, and citation network of the China national standards for NEVs, and provided implications for the governments and the industry. The history and current state of China’s NEV standards, following the technical diffusion of NEVs in China’s market, is analyzed from the perspective of a complex network. Based on the types of standards, the citation network is analyzed to find the standard clusters and most important standard nodes based on the ForceAtlas2 algorithm and the network topology index. Considered the existing standards and new technologies that entered the market, future standards on new technologies, regarding safety, performance and compatibility attributes are discussed. Also, the double-side effects of standards are discussed to balance the social benefits and industry constraints such as state-of-the-art technology and cost. The citation network can be a reference for future standardization work to find possible linkages, new standard nodes and backward implications for standard modification.

Nevertheless, future research work can be conducted in the following directions: Firstly, international standards and other national standards can be analyzed for comparison and harmonization. Secondly, considering that patents and standards are more and more closely interlinked, especially for standard essential patents and patent pools [22,23], a future patent and standard comprehensive analysis can be performed, especially for vehicle-to-everything V2X, 5G technology and autonomous-driving system applications in NEVs [24].