Lately by virtue of the appearance of the renewable energy sources, more and more local communities build their own power supply networks, which are local, decentralized and autonomous.
Normally they are able to provide the necessary energy. If energy- lack or excess occurs, then the appropriate amount of energy will be fed-in or out to the public network.
Characteristics of the these local networks are:
- they consist of a number of renewable energy sources, whose output power varies widely, and
- the consumer load varies also in a wide range
Therefore, these networks are generally unbalanced, respectively unstable and require special technical measures to ensure their normal operation. The solution to the problem is “SMART GRID”.
By definition, “SMART GRID” are non-homogenous/unbalanced networks which, through control systems, are brought into a “stable” state.
The liberalized energy market consists of a certain number of dealers offering various conditions for power supply to the consumers. Thus there are three sides on the market:
The producer supplies the dealer with a certain amount of energy for certain time periods. The dealer sells energy to his customers. In case of insufficient or overspend quantities the dealer is charged with penalties.
Usually the calculation period between dealer and supplier is one hour and it is the dealer’s interest to nullify his balance. Therefore dealers use their own supervision (and optional control) systems for monitoring (controlling) the in- and outgoing energy flows.
In order to be agile the dealer should rely on information about the energy flows within at least one order shorter period than his supplier – i.e. less than 5 minutes. Thus in between calculation times one could adjust the energy flow in order to obtain better balance at the end of the period.
In case of a few users with stable load the energy supervision could be done manually.
A problem occurs when the consumer count increases and the load varies. Then an derivative of the “SMART GRID” system – the Energy Management System – EMS is a necessity.
The main functions of the EMS system are:
- collect information from all consumer’s measuring devices – energy meters
- transfer information from the sources to the Central Station
- control of the communication processes in the system
- discovering of communication disturbances and/or losses
- recovering the data occurred during connection interruptions
- plausibility- and data completeness check of the information and its processing and analysis
- performing an energy balance for the last 5 minutes
- visualization of the analysis and balance calculation results in graphical and/or table form
- data archiving
- database consistency check
- in case of missing information appropriate requests for the missing data has to be created, send and fulfilled etc.
In offline state the system provides the user with the following options:
- configuration of the system
- configuration and changing settings of the communication channels by:
– communication environments
– communication networks
– communication protocols
– topology, etc.
- input of data for the customers
- input of data for the measuring devices
- generate and edit pictures, tables and etc.
Next problem is related with the user possibilities to react on the information delivered by the system.
1st case: The user has no means to control the energy flow. Then the user has to contact with consumers and ask them to reduce certain loads. It is clear that this approach is palliative.
2nd case: The user is able to act on the energy flow, i.e. has control and communication with devices of the client to adjust electric loads. This is much better scenario, but requires special technical and organizational prerequisites. In case those requirements are met, the system could expand its control capabilities to adapt client’s needs.
3rd case: The user is part of “balancing group” with capabilities to influence the power generators and switch devices. Using the system capabilities a “smart grid” can be created.
A power network, whose topology and load permanently varies in a wide range, is a non-homogeneous – unbalanced network. An unbalanced network, which by means of the control system can by balanced is defined as a “Smart Grid”.
In this case, besides standard EMS functions, the system is suited with additional functions like:
- topology calculation
- energy flows calculation
- state estimation etc.
This implies not only controlling the consumer’s energy network, but also balancing the power network of the “balancing group”.