The monitoring and control of the energy in a production plant

Abstract

The increase in energy prices experienced by the industrial sector has enticed consumers to invest in renewable energy sources such as solar photovoltaic systems to meet their energy demand and hence reduce their energy costs. However, in the occurrence of a power outage or unstable grid conditions the grid-tied photovoltaic (PV) systems cannot be utilised since the utility grid is unavailable. Therefore, to continue with their production, industrial consumers use diesel-powered generators known to be significantly more expensive to operate when compared to the utility grid. Therefore, the aim of the project is to design and implement a system that in the event of a power outage, automatically synchronises the PV systems with the back-up diesel generator and thus reducing fuel costs. The main problem with synchronising PV systems with a generator was that due to its poor frequency regulation, the PV inverters would not connect due to their anti-islanding protection. Therefore, two possible solutions to address this problem were designed and implemented. The first system consisted of a master/slave inverter topology, which provided a solution that respected the grid code standards and also allowed the operation with the diesel generator. This system also maintains the overall power stability of the microgrid by switching the PV inverters on and off as required. The second solution approached the problem differently. A flywheel energy storage system (FESS) was designed to mitigate the frequency variations that occurred when an impulse load was applied to the electrical system. The aim was to keep the frequency variations within limits defined in the inverters’ grid standard, thus enabling parallel operation with the generator. The test results of the two systems showed that for successful synchronisation of the grid-tied photovoltaic inverters with a diesel generator, the master/slave inverter system should be primarily used for the microgrid operation to ensure that power stability is maintained. Additionally, the FESS can be used to regulate the system frequency when optimal frequency regulation is required by certain types of equipment used in the industry.