Spec:sync check

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= Overview = The synchronization check capability in GridLAB-D will be implemented to perform paralleling for two independent power grids. This could be used to parallel two separate power systems, or to reconnect a microgrid to the bulk power system. In the simulation, the frequency and voltage metrics are checked. When conditions are satisfied, the sync_check object sends a closure command to its parent switch_object.

= Published properties (i.e., GLM inputs) =

The mapping between the properties and variables is listed in Table 1. The sync_check object will inherit all standard Object_(directive) values as well. The variable definitions are presented in Table 2 of the next section "Variable definitions". Note that the properties listed here represent two different modes for calculating the from/to voltage conditions - MAG_DIFF and SEP_DIFF. Notes are included as to which property is used for which mode.

Two sample sync_check objects defined in the glm file are shown as follows.

Using only the difference of the overall magnitude:

object sync_check {   name sc_m12; parent swt_01; armed true; volt_compare_mode MAG_DIFF; frequency_tolerance 0.6 Hz; voltage_tolerance 0.01; //Unit: pu   metrics_period 5 s;    delta_trigger_mult 2.0; }

Using the difference of the voltage magnitudes and angles separately:

object sync_check {   name sc_m12; parent swt_01; armed true; volt_compare_mode SEP_DIFF; frequency_tolerance 0.6 Hz; voltage_magnitude_tolerance 0.01; //Unit: pu   voltage_angle_tolerance 5 deg; metrics_period 5 s;   delta_trigger_mult 2.0; }

= Variable definitions = Variables of the sync_check functionality are defined as follows:

= Methodology =

Quasi-Steady State Time Series (QSTS)
In QSTS mode, the sync_check object will check current voltage and frequency metrics against the appropriate tolerance values, but multiplied by the deltamode_trigger_mult variable. If they are within this expanded range and the sync_check is armed, deltamode will be triggered.

Deltamode
Paralleling will only occur when the grid-alignment conditions are met. While the voltage and frequency metrics are within the multiple of deltamode_trigger_mult and the appropriate tolerances, deltamode will continue to be requested (SM_DELTA). e.g., if in MAG_DIFF mode, the sync_check is armed, and the magnitude of the voltage difference is less than deltamode_trigger_mult * eps_volt, a request to stay in deltamode will be sent.

The pseudocode of the sync_check method is shown as follows. It is run in each step of the deltamode.

algorithm sync_check is input: freq_m1, freq_m2, volt_m1, volt_m2 output: Flag swt_cmd such that swt_cmd is true for sending the closure command, false for monitoring freq_diff ← abs(freq_m1 - freq_m2) if (volt_comare_mode == MAG_DIFF) do volt_diff ← abs(volt_m1 - volt_m2) volt_diff_pu ← volt_diff/volt_norm if (freq_diff_pu <= eps_freq) and (volt_diff_pu <= eps_volt) do t_sat ← t_sat + dt_dm else do t_sat ← 0 else do volt_diff_mag ← abs(abs(volt_m1) - abs(volt_m2)) volt_diff_mag_pu ← volt_diff_mag/volt_norm volt_diff_ang ← abs(angle(volt_m1) - angle(volt_m2)) if (freq_diff_pu <= eps_freq) and (volt_diff_mag_pu <= eps_mag_volt) and (volt_diff_ang <= eps_ang_volt) do t_sat ← t_sat + dt_dm else do t_sat ← 0 if (t_sat >= t_ud) do swt_cmd ← true else do swt_cmd ← false return swt_cmd

= Validation =

This subsection provides an outline on how the sync_check object will be tested to ensure its functionality. The current plan is to use two 4-node test systems interconnected through a sync_check object, which is open initially. The frequency and voltage values measured at the 'from' and 'to' nodes of the sync_check object are initialized in different values. The deviations must be larger than the user defined tolerances. The frequency and voltage of the 'from' node of its parent switch object are manipulated by a player towards the measurements of the 'to' node. Once the deviations are both within the tolerance longer than the user defined period, a 'closure' command should be sent to close its parent switch object. This sample use case will be included in the autotest for the sync_check object.

= See also =
 * Requirements
 * Implementation
 * sync_ctrl
 * IEEE Std C50.13TM-2014