Open loop Boost converter modeling in Simulink

Ming Sun

Ming Sun / November 28, 2022

7 min read––– views

Block diagram

The Boost converter power stage block diagram is shown in Fig. 1.

Boost converter block diagram
Fig. 1Boost converter block diagram[1]

Equations

In order to create the model in Matlab, we have to derive equations first. For a Boost converter inductor, we have the following:

`L*{di_L}/{dt}=D*V_{text(in)}-D^'*(V_{text(in)}-V_{out})`
(1)

Where,

`D^' = 1-D`
(2)

Eq. 1 can be simplified as:

`L*{di_L}/{dt}=V_{text(in)}-D^'*V_{out} = V_{text(in)} - V_{SW}`
(3)

Where,

`V_{SW} = -D^'*V_{out}`
(4)

Eq. 4 can be rewritten as:

`{di_L}/{dt}=(V_{text(in)} - V_{SW})/L`
(5)

For the output capacitor, we have the following:

`C*(dV_{out})/dt = D^'*i_L - V_{out}/R`
(6)

Eq. 6 can be rewritten as:

`(dV_{out})/dt = 1/C*(D^'*i_L - V_{out}/R)`
(7)

The overall process to model the open loop Boost converter is similar as the open loop Buck converter modeling as described in Ref. [2].

  • First, let us import to integrator into the simulink cavans as shown in Fig. 2.
Import integrator and mark the signal
Fig. 2Import integrator and mark the signal
  • To mimic the switching behavior on the VSW net, we will use a switch. Fig. 2 shows the connections. Basically, when duty cycle D is greater than 0.1, VSW is connected to ground and while D is less than 0.1, VSW is connected to Vout. This is exactly the switching behavior for a Boost converter.
Use switch and pulse generator to mimic the VSW waveform
Fig. 3Use switch and pulse generator to mimic the VSW waveform

The setting of the pulse generator is as shown in Fig. 4.

pulse generator properties
Fig. 4pulse generator properties

Since the overall process to build this Boost converter open loop model is similar of the process for the Buck converter, please refer to Ref. [2] if you are not familiar with the process. The completed open loop Boost converter model in Simulink is as shown in Fig. 5.

Completed simulink model for open-loop Boost converter
Fig. 5Completed simulink model for open-loop Boost converter

Simulation results

We know for a given Boost converter with 5Vin and 20% duty cycle, its output can be calculated as:

`V_{out} = V_{text(in)}/D^' = (5V)/0.8=6.25V`
(8)

The simulation results from simulink are as shown in Fig. 6.

Open-loop Boost converter simulation results
Fig. 6Open-loop Boost converter simulation results

Fig. 7 shows the zoom-in waveforms. We can see that the Vout average voltage meets our expectation.

Open-loop Boost converter simulation results - zoom in
Fig. 7Open-loop Boost converter simulation results - zoom in

References and materials

[1] Fundamentals of power electronics - Chapter 2

[2] Simulation of open-loop Buck converter in Simulink

[3] Open-loop Boost converter model - pdf

[4] Open-loop Boost converter Simulink model - download


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