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REQUIREMENT
*** WORKING DRAFT ***
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Application Concept
The purpose for developing a secondary controller object is to enable the redispatch of setpoints during a simulation to return frequency to its nominal value.
Use Case
The following use cases/research questions are of potential interest. They are each labeled for reference in further discussion.
- (U0) The secondary controller will first of all simply enable a dynamic simulation to run for longer while maintaining realistic results, i.e. nominal frequency and voltage.
- (U1) What are potential issues in the interaction of various generators (Grid Forming, Grid Following, Rotating) via a secondary controller.
Requirements
- (1) The secondary controller should be able to interact with any object that has an active and/or reactive power setpoint ( Diesel, Inverters, loads, etc.) and can participate in both Delta mode and QSTS.
- As some control models require the adjustment from the secondary controller to be the full schedule and not just a delta, the controller object must be able to see all participating object's schedules.
- (2) The secondary controller should be able to but not have to control all compatible objects from the previous point.
- (3) Each participant in secondary control should be assigned a participation factor indicating what part of the power mismatch is mapped to this unit
- participation factors should be alterable over the course of the simulation.
- participation factors for active power and reactive power need not be the same.
- (4) The secondary controller should implement a PID control that will ensure zero frequency error in the steady-state, as well as a voltage profile within tolerance bounds (U0).
- (5) The time interval at which secondary control signals are sent should be allowed to vary.
- There should be an ability to "discretize" the output signal, i.e. receiving unit only get an update every x seconds.
- There should also be an ability to slew the output signal to specific generators (e.g. integral control) in order to avoid excessive setpoint jumps.
- (6) The capacity available to the secondary controller need not be the same as the full capacity of the object in question.
- (7) The secondary controller must respect object limits for the quantities it is regulating. If a limit is reached, that object's participation must be redistributed among the remaining units.
- (8) All gains/parameters in the secondary control should be alterable to allow for higher level EMS/Microgrid Controller, etc. to adjust to varying system conditions.
Performance and Validation Tests
- (P0) Simulate load coming online without secondary control. Frequency should stabilize but not at nominal.
- (P1) Repeat P0 but with secondary control. Does frequency return to nominal?
- (P2) Repeat P0, but instead of secondary control allow one unit to operate in isochronous mode. How is the response different w.r.t P1?
- (P3) Simulate a long feeder section coming on without secondary control, resulting in voltage voltage violations.
- (P4) Repeat P3 but with secondary control. Does the voltage stabilize inside the appropriate band.
Open Questions and Future Work
Future expansion could address the following questions via these scenarios:
- (U2) How might secondary control be "stacked" and interact with each other for interaction in networked microgrids.
- The secondary controller object would be able to itself participate in secondary control
- (U3) Can secondary control be "expanded" to consider other objectives:
- This will require somehow capturing the "interface" through which regions interact, i.e. inter-ties/PCC and the scheduled export/import power via these objects.
- Classical inclusions in Secondary Control (i.e. AGC):
- Resource allocation, i.e. "optimal" (however that is defined).
- Maintain intertie flows (also relevant for networked microgrids).
- Some additional aspects may include:
- Reserves considerations
- Inertia, etc.
- Participation factors will be function dependent. That means that a generator might for example have a participation factor for frequency control, a different one for VAR control, etc.
- (U4) How should the secondary controller be altered during contingency events to reallocate factors, potentially adjust gains, etc.
- (U5) This controller is modeled explicitly as a centralized entity. Future work could consider distributed solutions, although the object structure would likely need to change so much that a new implementation will be necessary.