This module provides a standardized interface for software-based RTU implementations for interacting with different type of Power Grid Backends. These backends either can be physical components, local software implementations, or distributed Power Simulations for representing complex grids.

This module does not provide any simulative functionalities but serves the sole purpose of enabling exchangable RTU implementations and Power Grid Backends.

This document specifies the functionality provided by the RTU abstraction layer, implemented as RTUBackend interface. The main communication with datapoints attached to the RTU should be handled through this interface. Since both the simulation and RTU model will change how a RTU can and should be interacted with, some functions need to be implemented by the inheriting class. In the current design, it is expected that a class inheriting from the RTU backend implements all functionality specific to a combination of simulation and RTU model. We expect a specific RTU model to define a new RTU backend class that inherits from our interface and sets it as attribute of the main RTU object.

A RTU is initialised with information about all datapoints attached to it. Only changing the default cause of transmission for a datapoint is possible at a later point. The format of datapoints handed over may vary, we require:

• The datapoint is castable to a tuple
• The first four entires accessible as [0:5] represent [coa, ioa, type-ID, cot, related-ioa] (Information Object Adddress, Common Address, default ASDU-Type-ID, default Cause of Transmission, ioa of related datapoint then identified as (coa, related-ioa))
• coa, ioa, related-ioa types: int or str; their values are stored, retrieved, and compared against in a type-sensitive fashion!
• type-ID, cot type: int; cot in [1,47]; type-ID roughly in [1,127] (some values of the interval are undefined)
• the default cot will be chosen when a query is send and no new cot is given
• If cot == 1, the interface assumes periodic updates are send to the RTU as mentioned in IEC-104
• the [coa, ioa, type-ID, cot, related-ioa] combination is referred to primitive datapoint, its entire model-specific combination as complex datapoint
• any usage of the cot in the following is assumed to conform with IEC-104

If additional information, like Panda-DataFrame references, are necessary in your model, hand them over in all entries after the fifth.

Retrieving values from/ writing values to datapoints and any further communication is model-dependent and requires two functions to be implemented. The types COA and IOA are set to Union[int, str].

1. _build_IO_query(self, coa: COA, ioa: IOA, cot: int = 0, value=None)
   • construct an IO query in your model-specific format.
   • behaviour for coa-ioa combinations not referring to a datapoint attached the RTU is undefined
   • if cot==0, chooses the cot the backend was initialised with
   • if value is None, builds a get-query, otherwise a set-query
     • Resulting limitation: cannot set an IO to None
2. _send_query(self, query: Any)
   • sends the IO query based on your RTU-grid-simulation-model
   • return None if some error occured. non-None return may either signal correctly sent set-query or return value from get-query.
   • The respective return value is forwarded when retrieving/ setting IOs.

Neither of these functions is expected to be called directly by an operator.

The RTU backend pre-defines these functions:

1. __init__(self, coa: COA, datapoints: Iterable[Tuple[COA, IOA, int, int, ...]], autostart=False, logger=None, includes_relationship=False)

   • sets up datapoint storage
   • the datapoints need to be deterministcally castable to tuples in the datapoints section
   • coordination with other devices etc. can be started with autostart=True that calls function 2
   • inserts an empty-relationship after index [3] if includes_relationship=False
     • if includes_relationship=True, expects the value at [4] to be of type IOA and the same primitive datatype used for the ioas at the 2nd tuple-index
   • checks all relationships on correctness (see function 3)
   • raises RuntimeError if an invalid relationship is stored (see function 3)
   • ends by executing function 2 if austostart=True

2. wait_until_ready(self, timeout: Union[float, None]=None) -> None

   • terminates as soon as all model-dependent coordinations & start functions are completed
   • raises a TimeoutError if your model-dependent setups have not finished in the given timeout
   • timeout in [s] for numbers, never forces stop if timeout is None
   • may requires overwriting to conform with your RTU + simulator model

3. sanitise_check_relationships(self) -> bool:

   • checks if all datapoints storing a relationship link to an attached datapoint with the same coa and stored relation-ship.
   • raises a RuntimeError if an invalid relationship is found

4. _invalid_type_id(self, coa: COA, ioa: IOA, type_id: int) -> Union[bool, None, int]

   • checks if the type_id-argument and the datapoint's default type_id are command-query type_ids (in [45,69])
   • if True, returns defaulttype_id == type_id
   • reasoning: restrict allowed command-queries to those specified by the datapoint
   • returns None for unattached datapoint
   • returns 0 if either the handed over type_id or the type_id stored for the datapoint are not command-query-type_ids

5. get_IO(self, coa: COA, ioa: IOA, cot: int=0, type_id: int=0) -> Any

   • retrieve the IO based on the coa-ioa combination
   • returns None if the RTU has no such datapoint with a resp. IO attached to it or a type_id != 0 is given and which is invalid for this datapoint
   • if cot==0, chooses default cot stored

6. has_IO(self, coa: COA, ioa: IOA) -> bool

   • check if an IO with the given coa-ioa combination is attached to the RTU

7. set_IO(self, coa: COA, ioa: IOA, value, cot: int=0, type_id: int=0) -> Union[bool, None]

   • sets an IO on a datapoint
   • if cot==0 build query with default cot
   • returns the model-dependent query response for attached datapoints and None if the RTU does not know such an IO or type_id is given which is not valid for this datapoint
     • resulting limitation: cannot differentiate between the return of a None query response and a non-attached IO

8. get_related_IO(self, coa: COA, ioa: IOA, cot: int = 0) -> Any

   • performsget_IO but for the datapoint related to the (coa, ioa)-identified datapoint
   • also returns None if no relationship is stored

9. set_related_IO(self, coa: COA, ioa: IOA, value, cot: int = 0) -> Union[bool, None]

   • performs set_IO but for the datapoint related to the (coa, ioa)-identified datapoint
   • also returns None if no relationship is stored

10. get_periodic_ids(self) -> Set[Tuple[COA, IOA]]

    • returns all coa-ioa combinations the RTU expects periodic messages from (initialised with cot==1)

11. get_periodic_data_points(self) -> Set[Tuple[COA, IOA, int, int]]

    • returns all primitive datapoints the RTU expects periodic messages from

12. get_periodic_ioas(self, coa: COA = -1) -> Set[IOA] - returns all IOAs of periodicly updating datapoints with the given coa - if coa==-1, checks for all datapoints with the backend's coa

13. get_data_point(self, coa: COA, ioa: IOA, with_value=False) -> Union[None, Tuple, Tuple[Tuple, Any]]

    • retrieves the primitive datapoint corresponding to the coa-ioa combination
    • returns None if no such datapoint is known
    • adds the resp. IO if with_value=True

14. get_related_data_point(self, coa: COA, ioa: IOA, with_value=False) -> Union[None, Tuple, Tuple[Tuple, Any]]

    • performs get_data_point but on the related datapoint instead
    • also returns None if no relationship is stored

15. change_cause_of_transmission(self, coa: COA, ioa: IOA, new_cot: int) -> None

    • change the default-cot for a datapoint attached
    • if new_cot== 1 or default_cot==1 expects that a model-dependent command to the datapoint is send to update the periodic-update status
    • does not change if cot not in [1,47]

16. get_ioas(self, coa: COA = -1) -> Set[IOA]

    • retrieve all ioas from datapoints with the given coa attached to the RTU
    • if coa==-1, checks for the backend's coa

17. get_data_points(self) -> Set(Tuple[COA, IOA, int, int])

    • retrieves all primitive data points attached to the RTU

18. _get_complex_data_point(self, coa: COA, ioa: IOA, with_value=False) -> Union[None, Tuple, Tuple[Tuple, Any]]

    • retrieves the respective complex data point
    • also returns the IO if with_value=True

19. _get_complex_related_data_point(self, coa: COA, ioa: IOA, with_value=False) -> Union[None, Tuple, Tuple[Tuple, Any]]

    • performs _get_complex_data_point on the related datapoint
    • also returns None if no relationship is stored

The initialisation function should be overwritten if more objects/ data for the communication between RTU and simulation model needs to be provided to send or build queries. For instance, Julian Filter's pandapower model also simulates the communication with ZMQ. Corresponding wrappers and other metadata necessary to partially access, initialise and control the client would thus be necessary to be added by the inheriting backend. This may require overwriting wait_until_ready(...) as well.

The following attributes are defined upon initialisaton of the interface

1. data_store: Dict[COA, Dict[IOA, Tuple[COA, IOA, int, int, IOA, ...]]]
   • stores all complex datapoints for building the queries etc.
   • this format to ensure easy traversal and compability with all known models
2. datapoints: Set[Tuple[COA, IOA, int, int, IOA]]
   • stores all primitive datapoints
3. coa: COA
   • coa of the RTU
4. started: threading.Event
   • marks start-up & initialisation of all model-dependent clients etc.
5. logger: Union[sink_logger, logging.Logger]
   • logger to use if wanted
   • if no logger is handed over, a sink_logger that discards all messages is set-up, this cleans up logging behaviour as no checkup if a logger exists is necessary
   • the sink_logger only provides the main logging functions:
     • .critical(msg), .error(msg), .warning(msg), .info(msg), .debug(msg)
6. __inserted_relationship: Bool
   • marks whether insertion of empty relationships were necessary
   • mostly aimed at debugging

1. logging: If a non-sink logger is attached

Logging is assumed to be done through the logging package. The interface assumes the logger is already set up in regards to file handlers, etc. . The logger is assumed to be separate for each RTU or as it does not always repeat the backend's COA. A sink is connected that accepts all main logging messages stated above if no real logger is handed over. The interface logs the following data:

1. CRITICAL
   • the backend could not start clients etc. in wait_until_ready in the time-threshold given
2. WARNING
   • calling set_IO or get_IO on an unattached datapoint
   • executing get_related_IO or set_related_IO on a datapoint without a relationship
   • sending the query for set_IO, get_IO, or or its related-datapoint versions on an attached datapoint failed for some other reason
   • changing the cot for an unattached datapoint or trying to set it to an invalid value
   • trying to set/get IOs with an invalid type_id for the given datapoint or if the corresponding IO does not lie in the IEC104-range for this type_id
3. INFO
   • whenever the self.started status changes
   • time [s] it took to setup a client (if applicable)
   • whenever the periodicity of a datapoint was changed
4. DEBUG
   • str(query) send and its result

A model often needs to be constructable from exported data, e.g., pickle, yaml, or regular xml files. This is not strictly necessary, but encouraged and should be implemented through a static from_data(...) function.

1. stop(self) -> bool

   • stops all model-specific communicators (zmq-clients, etc.)
   • returns success of this operation (should only fail in special cases or raise exceptions instead)
   • clears the started Event

2. __del__(self)

   • stops all model-specific communicators (zmq-clients, etc.) safely

We encourage tests written with pytest. For several only indirectly or model-independent functions already fully defined by the backend, test-functions can be imported from RTU/tests/RTUs.py, denoted by a standard prefix. They only require the RTU or Backend + the datapoints initialised with as input. Example tests for a constant and pandapower-backend are defined there as well.

To our knowledge, many implementations use pandapower, panda DataFrames, and PPQueries in one way or another. There exist some test examples and corresponding Backend that use the following DataFrame input format:

• [coa, ioa, type-ID, cot, pp_table, pp_column, pp_index, others]
  • this does not include relationship-ioas and requires initialising the backend with includes_relationship=False!

and the following PPQuery format as named tuple:

• [table, column, index, value]

If you make your data frame fit to this format, you should be able to copy the _build_IO_query implementation from the PandapowerBackend example.

The interface requires a python version >=3.5. Some examples will require a higher python version due to other dependencies. If this is the case, it is clearly marked.

Examples are listed in the RTU/Backends.py file. A mini-RTU-simulation with a Backend is given in RTU/examples/RTUs.py.

Please let us know if any of the following specifications do not hold.

• the coa, ioa, relationship-ioas are not stored as integers/ strings; the cot/type-ID is not stored as integer in your model

• you believe other functionality is shared between the vast majority of RTU or simulation models and if implemented in this interface does not get in the way of those models the functionality is not shared with

• any other compability problem if this interface would be implemented for your RTU and simulation model

Or if the following any of these three do hold:

• your model requires the type-ID during IO-query construction/ sending
• your model allows IOs with a valid None value
  • since the send-query functions etc. return None for various errors
• a datapoint identified through (coa, ioa) needs to store a relationship to a datapoint with a different coa