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Chance-Constrained Optimization for Incremental Volt/Var Control in Distribution Networks with High Renewable Integration


Kernekoncepter
The core message of this article is to design an incremental Volt/Var control scheme for distribution networks with high integration of inverter-interfaced distributed generation, such as photovoltaic systems. The control scheme is implemented by solving a chance-constrained optimization problem to minimize reactive power usage while maintaining voltages within safe limits sufficiently often.
Resumé

The article presents an incremental Volt/Var control scheme for distribution systems with high integration of inverter-interfaced distributed generation (such as photovoltaic systems). The key highlights are:

  1. The incremental Volt/Var controller is designed to minimize reactive power usage while maintaining voltages within safe limits sufficiently often. This is achieved by solving a chance-constrained optimization problem, where constraints are designed to ensure that voltage violations do not occur more often than a pre-specified probability.

  2. The chance-constrained optimization problem is solved using a successive convex approximation method. The resulting controller gains are then broadcast to the inverters, and the control is implemented locally at the inverters without the need for additional communication.

  3. The proposed method is tested on a low-voltage 42-node network and compared to benchmark methods. The results show that the chance-constrained approach leads to cost savings in a controlled, predictable way, while still avoiding significant over- or under-voltage issues.

  4. The article also discusses the stability analysis of the incremental Volt/Var controller and how the proposed framework can be extended to handle unplanned network topology changes.

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Statistik
The low-voltage 42-node network used in the simulations has photovoltaic power plants placed at each node, with inverter-rated sizes randomly chosen among {20, 25, 31} kVA. The load and PV production profiles have a granularity of 1 second, and the time horizon for the optimization is 1 hour. The forecast update interval is set to 30 minutes, and the reactive power setpoints are updated every 100 ms.
Citater
"The incremental Volt/Var controller is implemented with the objective of minimizing reactive power usage while maintaining voltages within safe limits sufficiently often." "To this end, the parameters of the incremental Volt/Var controller are obtained by solving a chance-constrained optimization problem, where constraints are designed to ensure that voltage violations do not occur more often than a pre-specified probability." "Once the gains are broadcast to the inverters, no additional communication is required since the controller is implemented locally at the inverters."

Dybere Forespørgsler

How can the proposed framework be extended to handle unplanned network topology changes in a more robust manner

To handle unplanned network topology changes in a more robust manner, the proposed framework can be extended by incorporating a real-time monitoring and adaptation mechanism. This would involve implementing a continuous monitoring system that can detect any sudden changes in the network topology. Once a change is detected, the system can trigger a reevaluation of the controller gains to adapt to the new network configuration. This adaptation process can be automated to ensure a timely response to any unplanned changes. Additionally, the framework can be enhanced with machine learning algorithms that can learn and adapt to new network topologies based on historical data and real-time measurements. By integrating these adaptive and learning capabilities, the framework can become more resilient to unplanned network topology changes.

What are the potential trade-offs between the choice of the probability threshold (ϵ) and the overall system performance in terms of reactive power usage, active power curtailment, and voltage regulation

The choice of the probability threshold (ϵ) in the proposed framework can have significant implications on the overall system performance. A lower ϵ value indicates a more stringent constraint on voltage violations, leading to a higher level of voltage regulation but potentially increasing reactive power usage and active power curtailment. On the other hand, a higher ϵ value allows for more flexibility in voltage regulation, reducing reactive power usage and active power curtailment but potentially leading to more frequent and longer voltage violations. The trade-offs between the choice of ϵ and system performance need to be carefully considered based on the specific requirements and priorities of the distribution network. For example, in a network where voltage stability is critical, a lower ϵ value may be preferred to ensure strict voltage regulation despite higher reactive power usage. Conversely, in a network where minimizing active power curtailment is a priority, a higher ϵ value may be chosen to allow for more flexibility in voltage regulation. Balancing these trade-offs requires a thorough analysis of the network characteristics, operational constraints, and performance objectives.

How can the proposed incremental Volt/Var control scheme be combined with other traditional voltage regulation methods, such as on-load tap changers or switched capacitor banks, to achieve an optimal coordination of slow and fast-acting controllers

The proposed incremental Volt/Var control scheme can be effectively combined with other traditional voltage regulation methods, such as on-load tap changers (OLTC) or switched capacitor banks, to achieve an optimal coordination of slow and fast-acting controllers. By integrating these different control strategies, the network can benefit from the strengths of each approach, leading to improved overall voltage regulation and system performance. One approach to combining these control methods is to use a hierarchical control structure, where the incremental Volt/Var control scheme operates at a faster timescale to provide real-time voltage regulation based on local measurements. The OLTC and switched capacitor banks can then operate at a slower timescale to make larger adjustments to the voltage profile based on system-wide measurements and network conditions. This hierarchical approach allows for a coordinated and efficient control strategy that leverages the strengths of both fast-acting and slow-acting controllers. Additionally, advanced coordination algorithms can be implemented to ensure seamless interaction between the different control devices. These algorithms can optimize the setpoints and operation of each controller based on the overall system objectives, such as minimizing losses, maximizing efficiency, and ensuring voltage stability. By integrating incremental Volt/Var control with traditional voltage regulation methods, the distribution network can achieve optimal performance and reliability.
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