12.5-kVA grid forming converter (RFPSC), with electromechanical grid model

This example simulates a grid forming controlled converter, which uses reference feedforward power synchronization control (RFPSC) method connected to a weak grid. The control system includes a power synchronization loop (PSL) to synchronize with the grid, an inner P_type current controller used to damp the current oscillations enhanced with a reference-feedforward term. The converter is connected to an AC grid with electromechanical dynamics through an LCL filter and an inductive impedance.

Imports.

import numpy as np
from gritulator import model, control
from gritulator import BaseValuesElectrical, plot_grid

# To check the computation time of the program
import time
start_time = time.time()

Compute base values based on the nominal values (just for figures).

base_values = BaseValuesElectrical(
    U_nom=400, I_nom=18, f_nom=50.0, P_nom=12.5e3)

Configure the system model (grid model).

grid_filter = model.LCLFilter(L_fc=3e-3, C_f=10e-6, L_fg=3e-3, L_g=20e-3)
grid_model = model.FlexSource(w_N=2*np.pi*50, S_grid=500e3, H_g=2, r_d = 0.05)
converter = model.Inverter(u_dc=650)

mdl = model.ac_grid.ACFlexSourceAndLCLFilterModel(
    grid_filter, grid_model, converter)

pars = control.grid_forming.PSCCtrlPars(
        L_f=3e-3,
        f_sw = 5e3,
        T_s = 1/(10e3),
        on_rf=True,
        on_v_dc=False,
        i_max = 1.5*base_values.i,
        w_0_cc = 2*np.pi*5,
        R_a = .2*base_values.Z)
ctrl = control.grid_forming.PSCCtrl(pars)

Set the time-dependent reference and disturbance signals.

# Set the active power reference
ctrl.p_g_ref = lambda t: ((t > .2)*(6.25e3))

# AC-voltage magnitude (to simulate voltage dips or short-circuits)
e_g_abs_var =  lambda t: np.sqrt(2/3)*400
mdl.grid_model.e_g_abs = e_g_abs_var # grid voltage magnitude

# AC grid electromechanical model
mdl.grid_model.p_e = lambda t: (t > .4)*50e3 # load disturbance in the AC grid
mdl.grid_model.p_m_ref = lambda t: 0 # mechanical power reference

# Create the simulation object and simulate it
sim = model.Simulation(mdl, ctrl, pwm=False)
sim.simulate(t_stop = 6)

# Print the execution time
print('\nExecution time: {:.2f} s'.format((time.time() - start_time)))

Execution time: 29.79 s

Plot results in SI or per unit values.

plot_grid(sim, base=base_values, plot_pcc_voltage=True, plot_w=True)

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