The purpose of VVC is the coordinated control of reactive power and voltage and will optimize user-selectable objective functions subject to user-configurable constraints. SmartDMS VVC makes the following feasible:
- Volt/Var control can be optimal at the system level rather than just at the local level (as when local controllers are used).
- A network-based solution can handle a wider variety of different system conditions than a rule-based algorithm.
- The operator can easily choose from various objectives to be achieved.
Survalent VVC contains a number of built-in objectives that can be selected by the operator:
- Loss Minimization This objective minimizes total losses (transformer losses at the substation and line losses along the feeders).
- Energy Conservation This objective reduces load by minimizing voltage throughout the network without violating constraints.
- Revenue Maximization This objective maximizes the difference between energy sales (price of energy delivered to customers) and cost (cost of production or purchase). Voltage is raised until increased losses start to outweigh increased sales. Where this point falls depends on the actual mix of load types (constant current, constant impedance and constant power).
For the selected objective, the VVC program seeks an optimal solution that satisfies the following user-settable constraints:
- Acceptable feeder voltage profile (upper and lower limits on line voltages)
- Feeder load limits (upper limits on line currents)
- Power factor limits (at the substation and along the feeder)
Operating the system without violating these constraints is in fact the primary objective of VVC. They are generally treated as hard constraints, and are softened only if no other solution is possible. The softening process, which consists of adding penalty functions to the objective function, is under the user’s control.
VVC performs an optimization, and issues controls, at the top of every hour. VVC makes use of the following controls at both the substation and feeder level:
- Under-load tap changers (ULTCs)
- Shunt capacitors
The search algorithm of VVC is designed to lead to using the least number of control operations for each hour. Moreover, at each hour, VVC seeks a solution that will work for not just for the current hour, but also for the next hour (by using a projection of the substation and feeder injections from samples taken during the previous hour). This means that each hour’s solution is good for the full hour, not just right now. It also further serves to reduce controls required over the course of the day.
VVC can be operated in either automatic mode or semi-automatic mode:
- In automatic mode, VVC issues controls automatically. A priority zero alarm is raised to indicate that VVC operated. Results may be viewed in the VVC Log.
- In semi-automatic mode, VVC only raises a priority zero alarm without executing any controls. The operator may view the recommendations of VVC in the VVC Log.
VVC can be enabled or disabled globally as well as on a per substation basis. Where enabled, VVC can be set to automatic or semi-automatic mode on a per substation basis.
At each hour’s operation, VVC generates a log of its calculations and decision-making process. The log can be viewed as a DMS softcopy report, which may be printed if desired.
The VVC log includes the value of the objective function, both total and at each substation, both before and after optimization. This gives you an estimate of the calculated benefit of each VVC operation.
The VVC log also contains a list of the controls that were executed (if in automatic mode) or controls that VVC recommended to be executed (if in semi-automatic mode). In the case of the latter, the log contains a pushbutton that the dispatcher can use to instruct VVC to execute its recommendation. There’s a separate pushbutton for each substation that is in semi-automatic mode, so the dispatcher can choose to execute the recommendations for some substations and not others.
Optimal Feeder Reconfiguration (OFR)
The OFR (Optimal Feeder Reconfiguration) function finds the best choice of open (tie) points in a radial network. Survalent OFR is integrated with VVC in order to provide a coordinated solution. When OFR is enabled, it works with VVC to optimize the same objectives as VVC, plus Load Balancing.