Abstract

Powerline Communications is the proposed ISO/OSI layer 1 and 2 technology of the ISO/IEC 15118 joint working group for the Vehicle-to-Grid Communication Interface in case of conductive charging. This work introduces a test bed for analyzing PLC in the context of V2G communication. It presents measurement results and first experiences being made for broadband and narrowband PLC over the control pilot line of the charging cable. The analysis focuses on available application layer data rates, the time domain of the control pilot signal and PLC’s impact on the resulting reliability of the charging state recognition according to IEC 61851-1. It is shown that with the investigated narrowband PLC module the corresponding IEC 61851-1 charging states of the electric vehicle cannot be detected reliably with current standard compliant supply equipment charge controllers. The application of such narrowband PLC would therefore necessitate the application of additional low-pass filters in the IEC 61851 controller which in turn increases its EV state recognition lag. Therefore we propose the application of the analyzed broadband PLC technology for the Vehicle-to-Grid Communication Interface due to less interference.

Index Terms

Electric Mobility; IEC 61851; PLC Interference

I. INTRODUCTION

CCORDING to IEC 61851-1 [1] conductive charging of Electric Vehicles (EVs) in Mode 3 requires additional digital communication for grid compatibility. Such digital communication is currently being specified as part of the Vehicle-to-Grid Communication Interface (V2GCI) in the ISO/IEC 15118 joint working group. This work presents a

testbed for investigating the ISO/OSI layer 1 and 2 characteristics of the proposed digital communication between EVs and EV Supply Equipments (EVSEs). For conductive charging PLC is the proposed layer 1 and 2 technology being applied on the control pilot line of the charging cable. Our test bed enables analysis of PLC communication between EVSE and EV over normal phases of the charging cable and over the control pilot line. According to IEC 61851-1 [1] the EVSE also

applies a Pulse Width Modulation (PWM) signal on the control pilot line signaling its maximum charging power being available by adapting the PWM duty cycle. The calculation of the duty cycle dc can be seen in Table 1. E.g., a maximum EVSE output current of 30A results in a duty cycle of 50%. A special duty cycle for triggering digital communication according to ISO/IEC 15118 [2] will be 5%. Next to the maximum output current of the EVSE the PWM also signalizes the state of the EV. Figure 1 introduces the possible states which are defined by the positive amplitude of the PWM signal. If the charging plug is not connected, the vehicle is in state A, which means that it is not connected to the EVSE. As soon as the plug is

connected on EV side, the EV signalizes state B by decreasing the positive voltage to 9V. This means that the EV is connected but not ready for charging. When the EV is ready for charging it can either signalize state C (6V) or state D (3V) for optional ventilation. For reliable detection of the states a variance of ±1V is allowed for the voltage levels. When these boundaries are exceeded, the EVSE charge controller will stop the charging process. In state C and state D the PLC communication can be activated and charging parameters are negotiated via ISO/IEC 15118. Hence, Section III analyzes the PLC communication over the control pilot line for all possible states regarding data rate and interferences in the time

Performance Evaluation of PLC over the IEC 61851 Control Pilot Signal

Christian Lewandowski, Sven Gröning, Jens Schmutzler, Christian Wietfeld Communication Networks Institute, TU Dortmund University,

Dortmund, Germany

Email: {christian.lewandowski, sven.groening, jens.schmutzler, christian.wietfeld}@tu-dortmund.de

A

State A

State B

State C

State D

12V

9V

6V

3V

0V

-12.0V

. . .

t

-11.4V

-12.6V State A:State B:

EV not connectedEV connected, not ready

State C:State D:

EV connected, ready, no ventilation required EV connected, ready, ventilation required

Figure 1 IEC 61851 EV states with PWM signal

domain. Additionally the reliability of a charging process is analyzed with different PLC technologies to ensure interoperability between the PWM and the V2GCI.

Available line current Nominal Duty Cycle provided by EVSE (Tolerance ± 1 percentage point)

Digital communication will be used to control an off-board DC charger or communicate available line current for an on-board charger.

5% duty cycle

Current from 6 A to 51 A: (% duty cycle) = current[A] / 0,6

10 % ≤ duty cycle ≤ 85 %

Current from 51 A to 80 A: (% duty cycle) = (current[A] / 2,5) + 64

85 % < duty cycle ≤ 96 %

Table 1 Pilot Duty Cycle provided by EVSE [1]

II. ELECTRIC MOBILITY TEST BED

In the proposed test bed for evaluating PLC technologies (see Figure 2) the EV is interconnected to the EVSE with a charging cable. The EVSE provides two charge points. One is equipped with Smart Message Language (SML) and the other with Device Language Message Specification (DLMS) metering technologies as well as an Uninterrupted Power Supply (UPS) for the EVSE Communication Controller (EVSECC) and the IEC 61851 communication unit, which is based on the Siemens SIPLUS ECC2000 CM-230 controller. The PWM of IEC 61851 is transmitted over the control pilot of the

type 2 charging plug to the EV, where an analog circuit indicates the charging state of the vehicle. Each charge point is equipped with a power socket for a PLC modem in order to evaluate different narrow- and broadband technologies. EVSE and EV also contain a PLC over IEC 61851 Control Pilot Coupling Device, which modulates the HF PLC Signal on the control pilot. For analyzing the Electromagnetic Interferences (EMI), it is also possible to connect EMI test receiver or a spectrum analyzer. Furthermore, an Additive White Gaussian Noise (AWGN) signal can be superposed to analyze the robustness of the applied PLC technology.

III. EVALUATION RESULTS OF PLC OVER IEC 61851 CONTROL PILOT

For the evaluation of PLC over the control pilot line, a narrowband and a broadband technology have been chosen. The narrowband technology allows communication on the different CENELEC (9 kHz – 148.5 kHz) frequency bands [5] as well as on the ARIB (10 kHz – 450 kHz, Japan) and FCC (10 kHz – 490 kHz, USA) bands. The broadband technology Homeplug AV [3] is similar to Homeplug GreenPHY [4], which is currently discussed as a promising candidate for the V2GCI. Simulative analyses of Homeplug GreenPHY in charging processes have been made in [6]. Measurements with the test bed to determine the achievable control pilot data rate for Homeplug AV have been accomplished with Iperf [7]. Figure 3 depicts the results for a 30 minutes measurement. The mean application layer data rate of PLC over normal phases is 49.92 Mbit/s independent from the EV charging state. In case of communication over the control pilot the application layer data rate varies between different states. In state B, a mean data rate of 32.64 Mbit/s has been measured in the range of 28.18 Mbit/s and 37.138 Mbit/s. In state C the mean data rate decreases to 22.67 Mbit/s and in state D to 4.18 Mbit/s.

Exchangable PLC technologies Connection ofmulti phase loads

PLC overControl Pilot

Coupling Device

I/O modulefor IEC 61851

communication

Type 2 charging plug

Chargingequipment

12V

EVSE chargecontroller CM-230

EV Communication

Controller

Figure 2 PLC communication test bed for electric mobility

0

10

20

30

40

50

60

Phase State B State C State D

Dat

a ra

te [

Mb

it/s

]

Figure 3 Data rate of Homeplug AV

over Phase and Control Pilot

Figure 4 shows exemplary results for the control pilot PWM signal in state C which indicates, that the EV is ready for charging. Without PLC communication the PWM Signal has a small standard deviation of 0.092V. This state was chosen for evaluation, because the ISO/IEC 15118 application layer communication processes are initiated in this state and the PLC signal is added to the control pilot. In case Homeplug AV is applied to the control pilot the standard deviation increases to 0.265V

and a few outliers with minimum of -13.28V and maximum of 7.27V exceed the voltage boundaries. However, the tested EVSE charge controller is still able to detect the EV state correctly. The reason might be a lower sample rate, so that the outliers will not be detected by the EVSE charge controller. Unlikely, the narrowband PLC signal is applied to the control pilot. To demonstrate the possible interferences that can occur, the CENELEC BC band with a transmit power of +6dB was chosen for communication. At approximately 1075µs, a high deviation of ± 6V can be seen so that the charge controller is not able to detect the vehicle state correctly resulting in a charging error state. Using other frequency ranges and transmit power levels reduce the problem but does not resolve it. A low pass filter at the control pilot output connector of the EVSE charge controller could reduce the interferences of the PLC signal, which in turn increases an EV state recognition lag due to increased rise time of the PWM edges. Therefore we propose to use the investigated broadband PLC technology for the V2GCI to ensure reliable charging processes.

IV. CONCLUSION

This work presented a test bed containing an EVSE and an EV for evaluation of PLC technologies for electric mobility. To meet requirements from current trends in international standardization, PLC over the control pilot line was realized. The correct functionality of a standard charge controller was proven for Homeplug AV, although the voltage boundaries are exceeded by outliers due to higher standard deviation of the PWM signal. For the narrowband technology high deviations of ± 6V can be observed and the standard charge controller is not able to work correctly anymore. The integration of a low pass filter can reduce the interferences caused by PLC communication, but results in a state recognition lag. Hence, we propose the application of the broadband PLC technology for reliable charging processes within the V2GCI. In future work different narrowband and broadband PLC technologies need to be analyzed for V2G communication in order to ensure the interoperability between the IEC 61851 PWM signal and the V2GCI. Furthermore their robustness is tested by applying systematic interference signals.

ACKNOWLEDGMENT

The work in this paper was funded by the German Federal Ministry of Economics and Technology (BMWi) as part of the e-mobility project with reference number 01ME09012. The authors would like to thank the project partners RWE, SAP Research, Ewald & Günter, TU-Berlin and TU-Dortmund for fruitful discussions during the project.

REFERENCES [1] IEC TC 69 IS 61851-1:2010 Ed. 2.0 – Electric Vehicle conductive charging system; Part 1: General requirements. [2] ISO/IEC TC/SC 69 JWG1 CD 15118-1:2011 - Vehicle to grid communication interface – Part 1: General information and use-case definition,

Geneva, Switzerland. [3] HomePlug PowerLine Alliance, “HomePlug AV baseline specification”, Version 1.0.00, Dec. 2005. [4] HomePlug GREEN PHY Specification, Release Version 1.00, 14-June 2010 [5] DIN EN 50065-1:2010, Signaling on low-voltage electrical installations in the frequency range 3 kHz to 148.5 kHz - Part 1: General requirements,

frequency bands and electromagnetic disturbances. [6] Lewandowski, C., Haendeler, S. and Wietfeld, C., "Performance Evaluation of Large-Scale Charge Point Networks for Electric Mobility Services",

International Conference on Systems and Networks Communications (ICSNC 2011), Barcelona, Spain, Oct 2011. [7] Iperf: http://sourceforge.net/projects/iperf

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-10

-5

0

5

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15

0 200 400 600 800 1000 1200 1400 1600 1800 2000

Vol

tage

[V

]

Time [µs]

Narrowband PLC Homeplug AV No PLC

Figure 4 IEC 61851 PWM Signal with narrow- and broadband

PLC communication