1 Description
- 1.1 Secondary Control Loop – Voltage
- 1.2 Secondary Control Loop – Frequency
2 Mask and Parameters
3 Inputs, Outputs, and Signals Available for Monitoring
- 3.1 Inputs
- 3.2 Output
4 Intellectual Property Disclaimer

Grid-forming converters pose a steady state error in voltage and frequency due to the operation of the primary controller and the secondary controller provides setpoints to the primary controller to compensate for such deviations. The controller measures the RMS value of the voltage and frequency at the point of interest and estimates the adjusted references for voltage and angular frequency for the Primary control loop. To keep the system safe from abnormal deviation of voltage and frequency, limits have been added for both parameters in this control block. In addition, the rate of change for voltage and frequency can also be controlled in the Secondary controller.

Description

The block contains secondary control loops for voltage and frequency adjustments. Brief descriptions of the adopted Outer Control Loop approaches are as follows.

Secondary Control Loop – Voltage

This loop takes the RMS value of the measured voltage and compares it with the reference. The error signal is then passed to a PI controller. To keep the system safe from abnormal deviation of voltage, a rate limiter and a saturation block are used. The control architecture of the Secondary Control Loop for Voltage control is shown below.

Secondary Control Loop – Frequency

This loop takes the measured frequency and compares it with the reference. The error signal is then passed to a PI controller. To keep the system safe from abnormal deviation of frequency, a rate limiter and a saturation block are used. The control architecture of the Secondary Control Loop for Frequency control is below.

Mask and Parameters

The following information is required by the configuration mask of the Reference Generation block:

Parameter	Description	Units
Nominal Operating Voltage	Nominal line-to-line RMS voltage of the grid-forming converter	V
Nominal Frequency	Nominal frequency of the grid-forming converter	Hz
Voltage Proportional Gain	Proportional Gain of the Secondary Voltage Control Loop	pu
Voltage Integral Gain	Integral Gain of the Secondary Voltage Control Loop	pu/s
Frequency Proportional Gain	Proportional Gain of the Secondary Frequency Control Loop	pu
Frequency Integral Gain	Integral Gain of the Secondary Frequency Control Loop	pu/s
Upper Voltage Limit	Maximum Limit of the Voltage (L-L, RMS). The secondary controller saturates to this value	V
Lower Voltage Limit	Minimum Limit of the Voltage (L-L, RMS). The secondary controller saturates to this value	V
Upper Frequency Limit	Maximum Limit of the frequency. The secondary controller saturates to this value	Hz
Lower Frequency Limit	Minimum Limit of the frequency. The secondary controller saturates to this value	Hz
Maximum Rate of Frequency Change	Maximum rate at which the secondary controller can change the Frequency reference	pu/s
Maximum Rate of Voltage Change	Maximum rate at which the secondary controller can change the voltage reference	pu/s

Inputs, Outputs, and Signals Available for Monitoring

Inputs

Parameter	Description	UNITS
Frequency	Measured System frequency	pu
Voltage	Measured RMS voltage at the Point of Interest	pu
Reset	Reset Signal	pu

Output

Parameter	Description	UNITS
Vref	Reference Voltage for the primary control loop	pu
Omega_ref	Reference Angular frequency for the primary control loop	pu

Intellectual Property Disclaimer

Natural Resources Canada owns all intellectual property rights in the Smart Inverter Modelling Toolbox software and related products.

HYPERSIM Documentation

GFM Secondary Control Three-Phase