WECC Distributed and Small PV Plants Generic Model (PVD1)

Author: WECC REMTF^[1]

Dynamic representation of large-scale PV plants requires the use of three renewable energy (RE) modules:

• REGC_A – Generator/Converter (inverter) interface with the grid.
• REEC_B – module, used to represent the Electrical Controls of the inverters. It acts on the active and reactive power reference from the REPC_A module, with feedback of terminal voltage and generator power output, and provides real and reactive current commands to the REGC_A module.
• REPC_A – Plant Controller.

These modules, in addition to others, are also used to represent wind and PV power plants.

Dynamic representation of distribution-connected small PV plants or multiple PV plants requires the use of one renewable energy (RE) modules:

• PVD1 – module, is recommended to represent distribution-connected small PV plants or multiple PV plants aggregated at a high voltage bus that is represented in power flow.

Key Modeling Assumptions

Unlike central station PV plants, distributed PV systems are connected at the distribution level, and thus are under state jurisdiction. Reliability and interconnection requirements, while varying from state to state, tend to reflect the requirements outlined in IEEE Standard 1547. In contrast with NERC and WECC central station reliability requirements, distributed PV systems at this time normally do not participate in steady state voltage regulation, and tighter bounds on operation for off-nominal voltage and frequency conditions result in significantly different fault ride-through capability.

In the near term, it is anticipated that the PV inverters applied in distributed systems will continue to comply with IEEE 1547, and will operate under constant power factor or constant reactive power modes of operation. The elimination of the closed-loop voltage regulator dynamics, along with the elimination of the DC dynamics, allows for substantial simplification of the model with respect to that of the large-scale PV plants. However, unlike a large-scale PV plant, the terminal voltages seen by the individual inverters within the composite load in the bulk system dynamic model are likely to vary substantially. A different protection model is used to capture the effect of the diverse terminal conditions on the aggregate generation.

PVD1 Input Parameters, Internal Variables, and Output Channels

PVD1 Input Parameters
Name	Description	Typical Values
igreg	Remote bus number for droop response (0 = generator terminal bus)	0
qmx	Maximum reactive power command (pu on mbase)	0.33
qmn	Minimum reactive power command (pu on mbase)	-0.33
v0	Lower limit of deadband for voltage droop response (pu)	–
v1	Upper limit of deadband for voltage droop response (pu)	–
dqdv	Voltage droop response characteristic	–
ialim	Apparent current limit (pu on mbase)	1.0 to 1.3
vt0	Voltage tripping response curve point 0 (pu)	0.88
vt1	Voltage tripping response curve point 1 (pu)	0.90
vt2	Voltage tripping response curve point 2 (pu)	1.1
vt3	Voltage tripping response curve point 3 (pu)	1.2
vrflag	Voltage tripping is latching (0) or partially self-resetting (>0 and ≤1)	0
ft0	Frequency tripping response curve point 0 (pu)	59.5
ft1	Frequency tripping response curve point 1 (pu)	59.7
ft2	Frequency tripping response curve point 2 (pu)	60.3
ft3	Frequency tripping response curve point 3 (pu)	60.5
frflag	Frequency trip ping is latching (0) or partially self-resetting (>0 and ≤1)	0
tip	Inverter active current lag time constant (s)	0.02
tiq	Inverter reactive current lag time constant (s)	0.02
PVD1 Internal Variables
Name	Description
vterm	Terminal voltage (pu, from network solution)
pref	Initial active power (pu on mbase, from power flow)
fterm	Terminal frequency deviation (pu, from network solution)
qref	Initial reactive power (pu on mbase, from power flow)
ipmax	Dynamic active current limit (pu on mbase)
iqmax	Dynamic reactive current limit (pu on mbase)
iqmin	Dynamic reactive current limit (pu on mbase, = -iqmax)
iqcmd	Desired reactive current (pu on mbase)
ipcmd	Desired active current (pu on mbase)

References