Modeling PV for unbalanced, dynamic and quasistatic distribution system analysis

Multi-grounded neutral distribution feeders, which are typical in North America, have unbalanced loads and voltage control components. They have been designed for radial overcurrent protection, assuming only one source at the utility substation. Variable power sources on the feeder, such as distributed PV units, may interact with tap changers and switched capacitor banks on the feeder. Current injections from distributed PV can affect overcurrent device coordination, ground fault detection by utility devices, and possibly create overvoltages during ground faults. The simulation model has to be unbalanced, typically using phase coordinates rather than symmetrical components. It also has to operate in dynamic mode for short circuit calculations, typically at 1-cycle time steps, and in quasistatic mode for voltage control simulation, typically at 1-second time steps. These features are sometimes called “unbalanced RMS simulation”. The PV model needs to include an appropriate level of detail, while protecting the technology vendor´s proprietary information. To achieve this goal, a Simulink transient model of the PV unit has been interfaced to an open-source unbalanced RMS simulator called OpenDSS.