Choosing the right optimization model is critical for balancing accuracy, computational speed, and analysis goals. This guide helps you select among ED, UC, DC-OPF, and AC-OPF.
Feature | ED | UC | DC-OPF | AC-OPF |
|---|---|---|---|---|
Problem Type | LP/QP | MIP | LP/QP | NLP |
Network Model | None | None | DC (linearized) | AC (full) |
Time Periods | Single | Multiple (24+) | Single | Single |
Commitment Decisions | ✗ | ✓ Binary | ✗ | ✗ |
Transmission Limits | ✗ | ✗ | ✓ | ✓ |
Voltage Constraints | ✗ | ✗ | ✗ | ✓ |
Reactive Power | ✗ | ✗ | ✗ | ✓ |
Transmission Losses | ✗ | ✗ | ✗ | ✓ |
Startup Costs | ✗ | ✓ | ✗ | ✗ |
Ramping Limits | ✗ | ✓ | ✗ | ✗ |
Min Up/Down Time | ✗ | ✓ | ✗ | ✗ |
Reserve Requirements | ✗ | ✓ | ✗ | ✗ |
Solving Speed | Fastest | Slow | Fast | Medium |
Strengths:
Fastest solving speed
Convex formulation
Easy to understand
Good for teaching
Merit order analysis
Weaknesses:
No network constraints
May be infeasible in reality
Cost is lower bound only
No temporal dynamics
Best for:
Screening studies
Fuel cost sensitivity
Technology comparisons
Educational purposes
Strengths:
Realistic scheduling
Startup/shutdown costs
Temporal constraints
Reserve provision
Day-ahead markets
Weaknesses:
No network constraints
Slow (MIP)
May not be AC feasible
High memory usage
Best for:
Day-ahead planning
Generator scheduling
Cycling cost analysis
Reserve studies
Strengths:
Network-aware
Fast (LP)
Locational prices (LMPs)
Congestion analysis
Always converges
Weaknesses:
Voltage fixed
No reactive power
Ignores losses
DC approximation errors
Best for:
Market clearing
LMP calculation
Congestion studies
Large-scale analysis
Strengths:
Complete physics
Voltage and reactive
Accurate losses
True feasibility
Highest accuracy
Weaknesses:
Slower (NLP)
May not converge
Local optima possible
Sensitive to initialization
Best for:
Feasibility validation
Voltage studies
Reactive planning
Detailed operations
Decarbonization Studies
Primary: UC (capture cycling costs)
Secondary: DC-OPF (transmission needs)
Validation: AC-OPF (feasibility check)
Renewable Integration
Primary: UC (ramping, reserves)
Secondary: DC-OPF (congestion from variable generation)
Detailed: AC-OPF (voltage impact)
Transmission Planning
Primary: DC-OPF (congestion, LMPs)
Validation: AC-OPF (true flow limits)
Optional: UC (temporal patterns)
Market Design
Primary: DC-OPF (locational pricing)
UC: Day-ahead commitment
Validation: AC-OPF (deliverability)
Day-Ahead Markets
Stage 1: UC (commitment schedule)
Stage 2: DC-OPF (dispatch + LMPs)
Post-analysis: AC-OPF (feasibility)
Congestion Management
Primary: DC-OPF (identify constraints)
Validation: AC-OPF (verify relief)
Questions ED can answer:
What is the minimum possible generation cost?
Which generators should run based on merit order?
What is the system marginal price?
How do fuel prices affect dispatch?
Questions ED cannot answer:
Is the dispatch AC feasible?
Are transmission lines overloaded?
What are the locational prices?
How should units be scheduled over time?
Questions UC can answer:
Which units should be online each hour?
When should units start up and shut down?
What are the total cycling costs?
Are reserve requirements met?
How much ramping capability is needed?
Questions UC cannot answer:
Are there transmission constraints?
What are locational prices?
Is reactive power adequate?
Are voltages within limits?
Questions DC-OPF can answer:
Which transmission lines are congested?
What are locational marginal prices?
Where should new transmission be built?
How much does congestion cost?
What is the optimal dispatch with network?
Questions DC-OPF cannot answer:
Are voltages acceptable?
Is reactive power sufficient?
What are the transmission losses?
How should units be scheduled over time?
Questions AC-OPF can answer:
Is the dispatch truly feasible?
What are the actual voltages?
How much reactive power is needed?
What are the transmission losses?
Are generator capability curves violated?
Questions AC-OPF cannot answer:
How should units be scheduled? (single period)
What are startup costs? (no commitment)
Time horizon?
Single period → OPF
Multiple periods → UC
Network important?
No → ED/UC
Yes → DC-OPF/AC-OPF
Voltage critical?
No → DC-OPF
Yes → AC-OPF
Speed requirement?
Fast → ED/DC-OPF
Moderate → AC-OPF
Can wait → UC
Accuracy need?
Approximate → ED/DC-OPF
High → AC-OPF
Complete → UC + AC-OPF
Progressive refinement:
Start simple (ED or DC-OPF)
Check if results reasonable
Add complexity if needed
Validate with more accurate model
Iterate until confidence achieved
Learn each model:
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