10-kVA grid following converter, dc-bus voltage control

This example simulates a grid following controlled converter connected to a strong grid and regulating the dc-bus voltage at the same time. The control system includes a DC-bus voltage controller, a phase-locked loop (PLL) to synchronize with the grid, a current reference generatior and a PI-based current controller.

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=14.5, f_nom=50.0, P_nom=10e3)

Create the system model.

# grid impedance and filter model
grid_filter = model.LFilter(L_f=10e-3, L_g=0, R_g=0)
# AC grid model (either constant frequency or dynamic electromechanical model)
grid_model = model.StiffSource(w_N=2*np.pi*50)
# DC-bus dynamic model
dc_model = model.dc_bus.DCBus(C_dc = 1e-3, u_dc0=600, G_dc=0)
converter = model.Inverter(u_dc=600)

# if you do not want to simulate any DC bus dynamics, you should define:
# dc_model = None
# This would make the DC voltage constant, using the value given from the
# converter model. Do not forget to deactivate the dc-bus control in this case.

if dc_model == None:
    mdl = model.ac_grid.StiffSourceAndLFilterModel(
        grid_filter, grid_model, converter)
else:
    mdl = model.dc_bus.DCBusAndLFilterModel(
        grid_filter, grid_model, dc_model, converter)

Configure the control system.

# Control parameters
pars = control.grid_following.GridFollowingCtrlPars(
            L_f=10e-3,
            C_dc = 1e-3,
            f_sw = 8e3,
            T_s = 1/(16e3),
            on_v_dc=True,
            i_max = 1.5*base_values.i,
            p_max = base_values.p,
            )
ctrl = control.grid_following.GridFollowingCtrl(pars)

Set the time-dependent reference and disturbance signals.

# Set the reactive power reference
ctrl.q_g_ref = lambda t: (t > .04)*(4e3)

# DC-bus external current disturbance
if dc_model != None:
    mdl.dc_model.i_ext = lambda t: (t > .06)*(10)

# 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

# DC voltage reference
ctrl.u_dc_ref = lambda t: 600 + (t > .02)*(50)

Create the simulation object and simulate it.

sim = model.Simulation(mdl, ctrl, pwm=False)
sim.simulate(t_stop = .1)

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

Execution time: 0.98 s

Plot results in SI or per unit values.

plot_grid(sim, base=None)

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