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Bus Type Switching to Reduce Bound Violations in AC Power Flow

Anna Van Boven, Kyri Baker

TL;DR

The paper addresses the gap where DC-based market clears and NR-ACPF solutions may violate AC constraints on $Q$, $V$, and line limits. It proposes an analytical augmentation to NR-ACPF by introducing two new bus types, $P$ and $PQV$, enabling strategic bus-type switching to move degrees of freedom and enforce AC feasibility without changing market-setpoints. Across IEEE 14-, 57-, and 300-bus benchmarks, the P-PQV (and P-PQV') approaches substantially reduce voltage and reactive-power violations, increasing AC-feasible outcomes in many cases, though with added computational load. This method yields an interpretable, post-processing mechanism that can be integrated with existing NR-ACPF solvers to provide AC-feasible setpoints without operational disruptions.

Abstract

Wholesale power markets often use linear approximations of power system constraints. Because it does not consider inequality constraints, using AC power flow for feasibility post-processing can violate bounds on reactive power, voltage magnitudes, or thermal limits. There remains a need for a streamlined analytical approach that can guarantee AC feasibility while adhering to variable bounds. This paper suggests an augmented implementation of AC power flow that uses an additional two bus types (PQV and P) to help resolve voltage bound violations present in the traditional approach. The proposed method sacrifices the voltage setpoint at a generator in exchange for fixing the voltage at a load bus, thereby moving a degree of freedom around the network. Results on the IEEE 14-bus, 57-bus, and 300-bus test cases demonstrate how switching bus types can reduce overall network violations and help find feasible power system setpoints.

Bus Type Switching to Reduce Bound Violations in AC Power Flow

TL;DR

The paper addresses the gap where DC-based market clears and NR-ACPF solutions may violate AC constraints on , , and line limits. It proposes an analytical augmentation to NR-ACPF by introducing two new bus types, and , enabling strategic bus-type switching to move degrees of freedom and enforce AC feasibility without changing market-setpoints. Across IEEE 14-, 57-, and 300-bus benchmarks, the P-PQV (and P-PQV') approaches substantially reduce voltage and reactive-power violations, increasing AC-feasible outcomes in many cases, though with added computational load. This method yields an interpretable, post-processing mechanism that can be integrated with existing NR-ACPF solvers to provide AC-feasible setpoints without operational disruptions.

Abstract

Wholesale power markets often use linear approximations of power system constraints. Because it does not consider inequality constraints, using AC power flow for feasibility post-processing can violate bounds on reactive power, voltage magnitudes, or thermal limits. There remains a need for a streamlined analytical approach that can guarantee AC feasibility while adhering to variable bounds. This paper suggests an augmented implementation of AC power flow that uses an additional two bus types (PQV and P) to help resolve voltage bound violations present in the traditional approach. The proposed method sacrifices the voltage setpoint at a generator in exchange for fixing the voltage at a load bus, thereby moving a degree of freedom around the network. Results on the IEEE 14-bus, 57-bus, and 300-bus test cases demonstrate how switching bus types can reduce overall network violations and help find feasible power system setpoints.

Paper Structure

This paper contains 11 sections, 1 equation, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Background
  3. Baseline AC Power Flow with Newton-Raphson
  4. Methodology
  5. AC Power Flow with Bus Type Switching
  6. Flow Diagram
  7. Results
  8. Violation Comparison by AC-PF Approach
  9. Example of the P-PQV Approach
  10. Voltage Violation Distribution
  11. Discussion and Conclusion

Figures (4)

  • Figure 1: Assumed information flow for power grid operational procedures.
  • Figure 2: Proposed bus type switching algorithm.
  • Figure 3: An example on the IEEE 14-bus test case. With normal NR-ACPF, 9 bound violations occurred after power flow. With the proposed algorithm, only one violation remains.
  • Figure 4: Distribution of the total magnitude of voltage violations in the IEEE 14-bus, 57-bus and 300-bus test cases.