# LoRa Enabled Smart Inverters for Microgrid Scenarios with Widespread Elements
## 5 LoRa Enabled Smart Inverters
### Experimental Results  
These tests were performed to prove the inverters' active power levels can follow the remotely generated power references transmitted by a LoRa point-to-point communication architecture. These references were generated and transmitted once per minute. On the other hand, the transmissions of inverters power measurements took place every five seconds. Both the references and measurements, accompanied by their respected timestamps, were recorded on a local MQTT data logger subscribing to the relevant topics generated by previously introduced LoRa Node B. The tests were conducted for an indoor scenario (with obstacles) rather than a clear line-of-sight outdoor long-range situation. The two transceivers (Node A and Node B) were situated in two adjacent buildings with several concrete walls and doors in between. Their separation distance was approximately 100 m. This configuration demonstrated a typical LoRaWAN application, since it was well out of the range of conventional WiFi. As comprehensively explained in Section 3, the effect of utilizing different SFs is to sacrifice throughput for coverage and vice versa. In other words, by increasing the Time-on-Air, the probability of intercepting the message is increased, especially in messy environments. To visualize this effect, two tests have been conducted for SF 12 and SF 7,  
Figure 14: Uplink transmission flowchart. which are the upper and lower limits in the LoRa modulation. The results are illustrated in Figure 15.  
As it can be observed in Figure 15a, in the case of SF 12, a stable communication link was established since the measurements always follow their respected references. On the other hand, utilizing SF 7 as illustrated in Figure 15b, resulted in an unreliable communication system. For example, in the interval between seconds 60-180, the recorded measurements remain at 160 even though a new power reference has been created. Furthermore, no measurements were recorded for about a minute in the middle of this time interval. This clearly means a link loss has occurred and, as it can be observed, a newly generated reference was lost since it was not received and recognized by the inverter (LoRa Node A). The same problem repeatedly happened in other instances of the experiment period. In total, four power references are not received by the inverter which are highlighted in the figure. The irregularity observed in this case is due to the arbitrary variation of the link budget due to the passing of people and opening/closing of doors, since LoRa Node A was situated in an operational and busy office. Other electrical and thermal interferences were also present. Therefore, this situation can very well emulate a real-world scenario. Another set of tests were performed to illustrate the effect of transmission power on the stability and reliability of the LoRa communication link. The Tx power of the Pycom/Lopy4 devices is set to 14 dBm by default and this power level was used for the previous tests. At this point, the tests were conducted for two other power values of 15 dBm and 5 dBm (for both Node A and Node B), and the results are presented in Figure 16. It should be noted that in both of these tests SF 7 is used and both the transceivers are situated in the same laboratory in close proximity of about 10 m. The same as previous tests, ten power references are generated, one minute apart, and the inverters measurements sampling rates were set to every five seconds. Comparing Figure 16a with b visualizes the Tx power effect and as expected, in the case of lower transmission power, an unstable communication link is established where packet losses are observed in both measurements and references transmissions. More specifically, five power references fail to be received and recognized by the inverter, which are highlighted in the figure. On the other hand, Tx power of 15 dBm (approximately 30 milliwatts) guarantees a robust information exchange system.