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Description

The Renewable Energy Electrical Controller – Type A (REEC_A) is a WECC standard dynamic model used to represent the electrical control of inverter-based resources (IBRs) such as photovoltaic (PV) plants, wind power plants (Type 3/4), and battery energy storage systems (BESS) in positive-sequence stability studies. It regulates current, voltage, and reactive power using measurements at the Point of Measurement (POM), while tracking voltage and reactive power objectives defined at the Point of Interconnection (POI). The block model mainly contains three parts:

• Active current controls, which generate the active current command Ipcmd

• Reactive current controls, which generate the reactive current command Iqcmd

• The converter current limit logic, which limits the active and reactive current to within the ratings of the converter

Active power control

The control path is relatively simple. It is essentially a straight pass through from the upstream plant controller through the electrical controls to the generator/converter. There is a single time constant and a set of limits to emulate the control delay and limits. The only other aspect is the flag PFlag. PFlag = 0 or PFlag = 1, the selection of the flag depends on whether the input connected to the controller is power or torque.

Reactive Power Control

There are several options for reactive power control:

In addition to the above, there is a separate proportional, with deadband, current injection control, which can be used either as proportional voltage control during a voltage dip (deadband set to zero) or a proportional current injection with deadband during a voltage dip. To disable this path, Kqv can be set to zero, or Vup and Vdip set to, for example, 2 and 0, respectively.

The parameters Iqfrz and Thld can be used in association with this current injection loop to create various state transitions, as shown in the following figure.

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State transitions in the REEC_A

It is noted that Thld could be either zero, or less than zero, or greater than zero.

• If Thld > 0, then once voltage_dip (voltage_dip is a flag which is set and reset in the model. Voltage_dip is 0 if the Vdip<VT<Vup, else it is 1) becomes 0, Iqinj is held at Iqfrz for Thld seconds.

• If Thld < 0, then once voltage_dip goes to 0, Iqinj remains state (equal to Iqv) for Thld seconds.

• If Thld = 0, then Iqinj goes back to zero as soon as Voltage_dip becomes 0.

There is also a parameter, Thld2, when set to a non-zero value, will hold the Ipmax command at the value it has been frozen at during a voltage dip, after the fault clears. That is, after voltage_dip returns to 0 following clearing a fault, then Ipmax calculated during the fault remains fixed for Thld2 seconds. Then, the Ipmax calculation continues normally.

Current limit logic

In its most basic form, the current limit is a semicircle around quadrants 1 and 4. That is, only positive active current is allowed (Ipmin = 0) since this is a model for a generator, and the total current must be less than or equal to Imax. The selection of the Pqflag determines whether priority is given to active or reactive current [1].

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Mask and Parameters

General Parameters

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REEC_A diagram

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Voltage, Q and PF Control

Reactive Current Injection During Voltage Dips

Active Power Control

Current Limit Logic

Voltage-dependent Limits

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The VDL1 and VDL2 characteristics are defined by 4 pairs of Vq-Iq points (pu voltage versus reactive current) and Vp-Ip points (pu voltage versus active current).

Initial Values

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Inputs, Outputs and Signal Available for Monitoring

Inputs

Outputs

Acknowledgements

The development of the REEC_A block in the Smart Inverter Control Library is a contribution of CanmetENERGY at Natural Resource Canada.

Reference

[1]   Model User Guide for Generic Renewable Energy System Models, EPRI, October 2023.