## 1 Introduction  
The Electric Vehicle (EV) is gaining popularity as an alternative transportation means due to its environmental friendliness. The EV market is rapidly growing, led by the U.S.A., Japan and France. Governments are actively supporting EV consumers in America and Europe, as well as Asian countries. In particular, many countries have set strategies for the growth of the EV market: France aims to sell two million EVs by 2020, Germany one million EVs by 2020 and China five million EVs by 2020 [1].  
EV is powered by electricity, and the EV charger, called the EV Supply Equipment (EVSE), plays the main role in the EV charging infrastructure. Without interoperability, however, EV technology cannot become a practical solution for future transportation. Different EV, EVSE and back-end system manufacturers will release their products to the market, but these will not necessarily be compatible with each other. To address this problem, standard bodies have been working on relevant standards [2], such as ISO/IEC 15118 [3; 4; 5], IEC 61851 [6; 7] and IEC 61850-90-8 [8], as well as CHAdeMO (CHArge de MOve) [9] and DIN (Deutsches Institut fur Normung; in english, German Institute for Standardization) [10]. At the center of standardization efforts for EV charging is ISO/IEC 15118. This standard defines the use cases (Part 1 [3]) and the communication interface between EV and EVSE from the physical layer to the application layer under the OSI (Open System Interconnection) seven-layer model (Parts 2 [4] and 3 [5]); in particular, the standard adopted HPGP (HomePlug Green PHY\({}^{TM}\)) [11] PLC (Power Line Communication) for the physical communication medium. Related standards will be discussed in Section 2.  
Some studies investigated the technology around the EV charging standards. [PERSON] and [PERSON] [PERSON] and [PERSON] (2012) investigated the efficiency of ISO/IEC 15118 message exchange, and [PERSON] _et al._[PERSON] _et al._ (2013) evaluated the performance of PLC over the IEC 61851 control pilot signal and suggested improvements of the standard. [PERSON] _et al._[PERSON] _et al._ (2014) also discussed how the communication between EV and EVSE can be integrated with the smart grid communication.  
While the standards provide guidelines to interoperable implementation, interoperability cannot be guaranteed. Explicit testing for the standard conformance is necessary to provide an authorized verification on the interoperability of an implementation. In the same light, ISO/IEC 15118 Parts 4 ([PERSON] _et al._, 2015) and 5 ([PERSON] _et al._, 2016) define testing methodologies, but they are still under development. Meanwhile, [PERSON] _et al._[PERSON] _et al._ (2017) and [PERSON] _et al._[PERSON] _et al._ (2018) described approaches for interoperability testing of vehicle to grid communication interfaces based on ISO/IEC 15118. On the other hand, [PERSON] _et al._[PERSON] _et al._ (2019, 20) and [PERSON] _et al._[PERSON] _et al._ (2018) built a testing system for EV charging based on CAN (Controller Area Network) communication ([PERSON] _et al._, 2018).  
In this paper, we present our test system according to ISO/IEC 15118, IEC 61850-90-8, IEC 61851 and HPGP. We use the TTCN-3 testing framework for the maximum flexibility of the test system to support various testing scenarios. Our contribution is as follows:  
* (i) We built a test system for EVSE in accordance with relevant standards, including ISO/IEC 15118, IEC 61851, IEC 61850-90-8 and HPGP.
* (ii) We built the first conformance test system for ISO/IEC 15118 that can test the communication between EVSE and the operator.
* (iii) We developed a reference EV charger that implements IEC-61850-90-8.  
The paper is organized as follows. In Section 2, we describe the technologies related to EV charging. In Section 3, we illustrate the design and implementation of the test system, and in Section 4, we evaluate the test system. We conclude in Section 5.