The diploma thesis discusses reading the total load current value and sending this data to electricity end-users. It takes a look at the different options of reading and sending values.
We began the research by determining the possibility of using existing electricity meters. Such meters usually do not provide communication links that we could use. In the future, meters with the so-called P1 connector will be used for such purposes. During the research we used a standalone meter of electrical quantities, which is usually used to measure energy and to monitor other quantities, such as voltages, currents and other parameters. They typically support communication via the Modbus protocol and the RS485 connection. We assumed that we would not need a meter with the MID certificate to conduct our research. Such meters are used when precise energy measurements are required, as they are directly charged on the energy bill.
For data-sending purposes, we looked at the possibility of using the existing electrical and dedicated communication installations. We decided to start by examining the possibility of sending data via the electrical installations. We learnt the advantages and disadvantages of communicating via power lines. We chose the MQTT protocol as a good alternative; it is designed for the Internet of Things and can be implemented via wired Ethernet connections or wireless WiFi networks.
We prepared two desktop models to facilitate the problem-solving process.
The first model contains the required AC distribution, a three-phase meter, a microcontroller, a PLC interface, a power supply unit with a battery, and all other required equipment. The model also provided the option of connecting different single-phase loads, which were used to modify the total current or the total current value transmitted to end-users. One load was a 200 W incandescent lightbulb, while other loads were connected via a standard AC socket. Communication with the meter took place via the Modbus protocol.
In the second model we used only a PLC interface, a microcontroller and a battery. We decided on battery power supply so we could easily transport the model from room to room, thus changing the conditions for PLC communication.
We used the Raspberry PI microcontroller and the ES1642-C PLC interface in both desktop models. In both cases, communication between the two took place via a serial port; TTL levels were used. To control communication with the first model, we used a light-emitting diode (LED), which flashes every time a message about the total current value is successfully received.
When transmitting the total current value via PLC, we encountered a limited communication speed and size of transmitted packets. We chose the optimal transmission option by transmitting only one byte at a time with a period of one or more seconds. One byte meant that we had to optimally present the total current value between the values of 0 and 255; in some cases, the current could even be negative.
Afterwards, we tested the transmission via TCP/IP communication and the MQTT protocol. The thesis deals with the Internet of Things and MQTT was one of the most useful protocols for meeting our requirements.
Based on the tests using PLC and MQTT/TCP/IP communications, we were able to sum up the observed advantages and disadvantages of the first and second method of transmitting the total current value.
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