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VOLTAGE ORIENTED CONTROL – SIMULATION

3.9 Grid connected converter simulation

This section shows the simulations results of the complete system built with (Figure 3.49) : A DISCRETE block Sampling system (sample and hold block) PLL Decoupled controller

PWM block (sinusoidal PWM) An asymmetric PWM is used here, as we saw in the section “2.4.1 Sinusoidal PWM”, we have .

Grid and rectifier model We are now using the model presented in the previous part “3.8 Grid modeling” with small

unknown grid impedance

and a switch (beaker)

the output as we can see in Figure 3.48.

. We also add a second switch in

Figure 3.48 : Single phase schematic

Simulation steps, Simulink block diagram 3.9.1 SIMULATION STEPS

The simulation is composed by three steps. In the step I : SW1 and SW2 are open, step II : SW1 closed and SW2 open, step III : SW1 and SW2 closed.

¬ Step : Synchronization

  • SW1 and SW2 are open.

  • The voltage

is sent to the PLL and the voltage angle

is calculated.

  • All IGBTs are OFF (the rectifier becomes a simple three phase diode rectifier). No current is

flowing into the rectifier.

The controller is in standby mode. All discrete integrators are disabled. All integrators should be disabled when all IGBTs are OFF. Otherwise, the integrator part of the controller will try to set the error to zero but since there are no switches activated, the error cannot be set to

zero. The integrator value will increase. DC link link capacitor is charged to the reference value

(in the simulation, this action

is done by setting the Initial Condition to

into the integrator of the DC link model).

ATTENTION, the value

should respect the condition explain in “2.2.3 Limitations” :

where

is the Line to Neutral amplitude of

.

55

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