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Load Modelling Mode

When OpenDSS solves a power flow, it needs to know how each load behaves when voltage rises or falls. A resistive heater draws less power at lower voltage, while some industrial equipment maintains roughly constant power draw across a wide range. loadModel lets you choose which behaviour best represents the loads in your network, and affects both the accuracy of results and how reliably the model converges on networks with voltage stress. It is set in the Work Package Configuration Options.

loadModel applies to customer loads, EV charging units and battery units modelled as loads. It does not apply to generation: generators are always modelled with OpenDSS generator Model 7, PV systems use the model from their advanced PV profile (see Advanced PV), and storage elements stay constant power.

Voltage Windows​

loadVMinPu, loadVMaxPu, genVMinPu and genVMaxPu set the per-unit voltage range in which the selected model behaves as intended. Outside it, OpenDSS moves towards constant impedance behaviour to keep the solution stable, without any warning.

  • loadVMinPu and loadVMaxPu apply to loads and storage elements. genVMinPu and genVMaxPu apply to generators and PV systems.
  • For a constant power load (Mode 1), a load above the maximum becomes constant impedance and draws more than its specified power. Below the minimum it blends towards constant impedance, reaching it at 0.5 pu, and draws less. For example, with loadVMinPu=0.9, a load bus solving at 0.85 pu draws less than specified.
  • genVMinPu also sets the generator's upper current limit. With genVMinPu=0.9, the limit is 1/0.9, or 111% of rated.

Wider windows let the selected model apply across more network conditions. Narrower windows cause more loads to fall back to constant impedance on stressed networks.

Modes​

Mode 1 - Constant Power (Default)

The load draws its specified kW and kVAr regardless of voltage, within the voltage window. This is the standard choice when load data comes from measured consumption such as smart meter interval data, as it uses those values directly. Check solved voltages across the network: buses outside the window deliver less load than specified if below it, and more if above it.

Mode 2 - Constant Impedance

Power scales with voltage squared, so a 10% voltage drop produces roughly a 19% reduction in power draw. This suits purely resistive loads such as electric water heaters and ovens, and is the most numerically stable mode. It is a reliable fallback if Mode 1 causes convergence difficulties, though it underestimates consumption in voltage-stressed areas. The loadVMinPu and loadVMaxPu window has no practical effect in this mode.

Modes 3 to 7

These are for specialist studies and are unlikely to be needed for standard hosting capacity analysis. The OpenDSS defaults are used for any mode parameters, as they cannot be set in the work package configuration. See the OpenDSS documentation for details.

  • Mode 3: constant P, quadratic Q
  • Mode 4: linear P, quadratic Q
  • Mode 5: constant current magnitude
  • Mode 6: constant P, fixed Q
  • Mode 7: constant P, with Q from a fixed impedance

Which mode should I use?​

For most Hosting Capacity studies, use Mode 1, as it directly honours your input load data. If you have convergence problems on heavily loaded or low-voltage feeders, widen loadVMinPu and loadVMaxPu first, as this extends the range over which Mode 1 behaves as intended. If problems persist, Mode 2 is a reliable fallback, with results slightly conservative in stressed areas.