Scalability evaluation of a Modbus TCP control and monitoring system for Distributed Energy Resources

Abstract

Modbus TCP is a communication protocol widely used in industrial applications and to communicate with energy assets such as inverters or data loggers. The communications technologies involved in the management of distributed energy resources (DER) should prove their ability to include new units in the operation while fulfilling functional requirements.This paper studies the scalability performance of Modbus TCP protocol over Ethernet to monitor and control DER in a positive energy district (PED) environment. This use case is part of an Innovative Element (IE) being demonstrated in the city of Dijon within the RESPONSE project. The analysis was carried out considering different bit error ratios (BER) and number of servers. As performance indicator, the time spent by the client to poll all the servers (i.e., polling time) was measured, as it is the most restrictive functional requirement in the use case analysed, requiring it to be one minute.Results from simulations show how increasing BER and the number of devices in the network impact the total polling time. Despite the average polling time complied with the required one in most cases, its standard deviation significantly increased with BER. If the transmission medium presents a low BER, Modbus TCP has a great scalability potential to control and monitor devices that require data exchanges every minute. In addition, the maximum number of devices to keep a good performance is considered appropriate for its application in a PED environment. Future works may assess the impact of distance or topology on use case’s performance.