Load Characteristic Model: LDEV1
Added in September 22, 2025 Simulator 24 patch
LDEV1 is based on the model developed by EPRI summarized in the November 2022 report entitled
"A Positive Sequence Model for Aggregated Representation Electric Vehicle Chargers"
EPRI Project 1-116982
written by L. Sundaresh and P. Matra
Description of the LDEV1 model
This model was developed by EPRI for use as an electric vehicle charger model. However, this model can be used to represent any aggregation of a large number of power electronic loads. Examples would be an electrical vehicle charging station, a large number of computers such as a data center, a crypto-currency mining facility, a large number of variable frequency drives, and so on.
The values MWinit and Mvarinit on the left of the block diagram below are calculated as part of the stability simulation initialization routine. MWInit is set equal to the initial MW of the load. When this model is used inside the CompLoad component-based load structure, then the parameter QPRatio is used to calculate the Mvarinit value and any extra Mvars are assigned as done with the CompLoad. When this model is used as a stand-alone model as part of a LoadModelGroup, Load, Bus, Area, etc. then the QPRatio is ignored and the Mvarinit is set equal to the load's initial Mvar. If a simple event occurs in the simulation and the final voltage returns to the initial voltage and the cease and reconnect logic is never engaged during the simulation, then this model will bring the MW and Mvar back to the same as the initial condition. The top half of the block diagram below represents the real power (MW) response of the load while the bottom half of the block diagram represents the reactive power (Mvar) response.
The dynamic portion of this model is described in the left side of the block diagram by the dynamic states 1 - 6 . The washout blocks (Kvp/Tvp and Kvq/Tvq parameters) model a response where the model load will decrease when a decreasing voltage is encountered (such as after and during a fault) and the load will then increase when the voltage is increasing (during fault recovery). This is meant to model a device such as a variable frequency drive which may reduce the electrical power during a fault, but then after the fault clears an additional amount of load will be seen to re-accelerate the mechanical load that the VFD is driving. This model is not simulating any characteristics of the mechanical load or the control system that causes this behavior, but is using the simple washout blocks to approximation the behavior. The MW control path also includes a simple frequency droop with deadband response that the load may have. After this the lead lag blocks are used to model any other transient response of the real and reactive loads. This leads to States 1 and 2 in the block diagram below which represent the model's request for a per unit power based on the initial voltage Vinit.
After this, both the real power and reactive portions of this model are split into 4 independent paths determined by the fractions FrA, FrB, FrC, and a fourth path with a fraction (1 - FrA - FrB - FrC). Each of these control paths have a user input which is the exponent of the voltage relationship relative to the initial voltage. Any value of nPA and nQA is allowed, but it is useful to realize that nPA = 0 indicates a path that acts as a constant power at steady state, nPA = 1 indicates constant current, and nPA = 2 indicates constant impedance. After the exponent is modeled, each path then divides by per unit voltage to convert to a current signal. The limits Ipmax/Ipmin or Iqmax/Iqmin are then used. Next the fractional amount of the path (FrA) is applied and then this amount is multiplied by a value FracOnA which represents the fraction of a particular path that remains connected to the system. The FracOnA models the Cease and Reconnect logic of the path. Paths A, B, and C have such logic, while Path D does not have fractional cease and reconnect logic. For each, if the filtered voltage is less than VcA for more than TcA seconds, then a decision to cease a portion of the load. Then after an an additional delay of TdelayA seconds, the FracOnA is reduced to a value of (1 - FcA). Then the system will wait to see if the filtered voltage goes above VrA for more than TrA seconds at which time it will begin ramping the FracOnA value back up to 1.0 over a time of Tramp seconds. Additional detail is included below to describe how these timers are reset and how a voltage drops after the model begins to ramping is handled. See the pseud-code and diagrams below for more details.
Finally, the output of each path goes through a delay block using the Tnum time constant to result a final desired current for each path. The currents from the 4 paths are then summed to give a total real current (Ipmw) and total reactive current (Iqmvar) for the load. The treatment of this model in the algebraic network boundary equations is then a constant current.
Model Equations and/or Block Diagrams
Modified in Version 24 patch on February 11, 2026. Added the initialization feature Iqextra when the model is used as a stand-alone model.
Parameters:
| Lfm | Loading
factor used to calculate MVAbase of model as MWinit/Lfm. Lfm<0.001 is treated as a 1.00. |
| Tfltr | Voltage measurement time
constant [s] (values less than 2*TimeStep are treated as 0, values less than 4*timestep are treated as 4*Timestep) |
| Dbd | Deadband on frequency response [pu] (>= 0, absolute value will be used) |
| Kdroop | Frequency droop [per unit] |
| Kvp | Proportional constant for active power washout |
| Tvp | Time constant for active power washout [seconds] (<= 2*TimeStep will result in washout block being ignored) |
| QPratio | Q/P ratio for MvarInit computation from MWInit. MvarInit = QPRatio*MWInit |
| Kvq | Proportional constant for reactive power washout |
| Tvq | Time constant for reactive power washout [seconds] (<= 2*TimeStep will result in washout block being ignored) |
| Ta | Lead time constant [seconds] |
| Tb | Lag time constant [seconds] (<= 2*TimeStep will result in lead lag block being ignored) |
| FrA | Fraction of Type A (If FrA + FrB + FrC > 1.0 they are normalized to sum to 1.0) |
| FrB | Fraction of Type B (If FrA + FrB + FrC > 1.0 they are normalized to sum to 1.0) |
| FrC | Fraction of Type C (If FrA + FrB + FrC > 1.0 they are normalized to sum to 1.0) |
| nPA | Active Power Exponential for Type A |
| nQA | Reactive Power Exponential for Type A |
| nPB | Active Power Exponential for Type B |
| nQB | Reactive Power Exponential for Type B |
| nPC | Active Power Exponential for Type C |
| nQC | Reactive Power Exponential for Type C |
| nPD | Active Power Exponential for Type D |
| nQD | Reactive Power Exponential for Type D |
| FcA | Fraction that will cease for Type A (0<=FcA<=1) |
| VcA | Voltage threshold for cease logic for Type A [per unit] |
| TcA | Time delay for cease logic to be initiated for Type A [seconds] |
| TdelayA | Time delay to cease after detection for Type A [seconds] |
| VrA | Voltage threshold to initiate power ramp logic for Type A [per unit] |
| TrA | Time delay for ramp up reconnection logic to be initiated for Type A [seconds] |
| TrampA | Ramp up time for Type A [seconds] |
| FcB | Fraction that will cease for Type B (0<=FcB<=1) |
| VcB | Voltage threshold for cease logic for Type B [per unit] |
| TcB | Time delay for cease logic to be initiated for Type B [seconds] |
| TdelayB | Time delay to cease after detection for Type B [seconds] |
| VrB | Voltage threshold to initiate power ramp logic for Type B [per unit] |
| TrB | Time delay for ramp up reconnection logic to be initiated for Type B [seconds] |
| TrampB | Ramp up time for Type B [seconds] |
| FcC | Fraction that will cease for Type C (0<=FcC<=1) |
| VcC | Voltage threshold for cease logic for Type C [per unit] |
| TcC | Time delay for cease logic to be initiated for Type C [seconds] |
| TdelayC | Time delay to cease after detection for Type C [seconds] |
| VrC | Voltage threshold to initiate power ramp logic for Type C [per unit] |
| TrC | Time delay for ramp up reconnection logic to be initiated for Type C [seconds] |
| TrampC | Ramp up time for Type C [seconds] |
| Ipmax | Maximum Ip [per unit] |
| Ipmin | Minimum Ip [per unit] |
| Iqmax | Maximum Iq [per unit] |
| Iqmin | Minimum Iq [per unit] |
| ndelt | Time step subdivision factor (not used by PowerWorld) |
| Tnum | Time delay for outputs [seconds] (If < 4*TimeStep are treated as 4*TimeStep) |
