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1 Mask and Parameters
2 Inputs, Outputs, and Signals Available for Monitoring
- 2.1 Inputs
- 2.2 Outputs
3 Description
- 3.1 Single Loop Control
  - 3.1.1 Virtual Impedance
- 3.2 Double Loop Control
4 Comparison between the Inner Control Loop Methods
5 References
6 Intellectual Property Disclaimer

The Inner Control Loop block generates the reference control signal for the Reference Generation Block in the d-q coordinate. The inner Control Loop block responds according to the angular frequency, phase angle, and magnitude of the virtual voltage source set by the outer control loop. Two inner control loop structures for grid forming (GFM) converter, i.e., single-loop control and Double-loop control, have been included in the Inner Control Loop block. The fundamental difference between the single-loop and the Double-loop control structure is that the former controls the angular frequency and magnitude of the inverter’s virtual internal voltage source, whereas the latter controls the angular frequency and the magnitude of the filter’s capacitor voltage. Another crucial difference is that Single-loop control includes only the voltage control loop, whereas Double-loop control includes both the voltage and current control loops. Due to the absence of a current control loop, Single Loop Control may flow excessive current during larger disturbances. Virtual impedance has been integrated with the Single Loop Control approach to limit the current flow. On the contrary, Double Loop Control adopts the Current saturation technique to limit the current flow.

Mask and Parameters

Mask Parameters vary with the selection of Inner Control Loop Type. For Single Loop Inner Control Loop, following information are required by the configuration mask of the Inner Control Loop block.

Parameter	Description	Units
Voltage Loop Integral Gain	Integral Gain of the Voltage control Loop	pu/s
Virtual Impedance Gain	Virtual impedance gain. This parameter limits the inverter current during fault.	pu
Threshold Current	Maximum Current Limit	pu
Sample Time	Input sampling period	sec

If Double Loop Control is chosen as the Inner Control Loop, the following information is required by the configuration mask of the Inner Control Loop block.

Parameter	Description	Units
Nominal Power	Nominal Capacity of the Inverter	VA
Nominal Operating Voltage	Nominal Line-to-Line RMS voltage of the inverter	V
Nominal Frequency	Nominal Operating frequency of the Inverter	Hz
Voltage Loop Gains (Kp)	Proportional Gain of the Voltage Control Loop	pu
Voltage Loop Gains (Ki)	Integral Gain of the Voltage Control Loop	pu/s
Current Loop Gains (Kp)	Proportional Gain of the Current Control Loop	pu
Current Loop Gains (Ki)	Integral Gain of the Current Control Loop	pu/s
Output Current Feed Forward Gain	Current Feed Forward gain of the voltage control Loop	pu
Filtering Inductance	Total Inductance of the filter	H
Internal Resistance of the Filtering Inductor	Total Intrinsic resistance of the filtering Inductor	Ohm
Filtering Capacitance	Total Capacitance of the Filter	F
Current Limit	Maximum Current limit	pu
Sample Time	Input sampling period	sec

Inputs, Outputs, and Signals Available for Monitoring

Inputs

Parameter	Description	UNITS
Vdref	d-axis reference magnitude of the virtual voltage source. For single Loop Control, this is the reference voltage at the inverter terminal; for Double-loop Control, this is the reference voltage across the capacitor of the filter.	Pu
Iodq	Direct and Quadrature axis current at the output	Pu
Vodq	Direct and Quadrature axis voltage at the output	Pu
Omega	Angular Velocity	Pu
Iinvdq	Direct and Quadrature axis current at the inverter side inductor of the filter	pu
Reset	Reset Signal	-

Outputs

Parameter	Description	UNITS
Vdq_ref	Direct and Quadrature axis Reference Control Signal	pu

Description

The Inner Control Loop contains two conventionally adopted Inner Control Loop approaches, i.e., single-loop control and Double-Loop Control. Brief descriptions of the adopted Inner Control Loop approaches are as follows.