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Interleaved operation

Overview

In the case of a two-phase interleaved buck converter, the term "interleaved" implies that there are two power stages operating, and they are out of phase by 180 degrees. This means that while one power stage is in its on-state (conducting), the other is in its off-state (non-conducting), and vice versa.

The 180-degree phase shift ensures that there is always at least one power stage active, reducing the overall ripple and improving the efficiency of the buck converter. The interleaved operation helps distribute the load more evenly, minimizing the stress on individual components and resulting in a more efficient power conversion process.

The image below shows two legs being connected for interleaving.

circuit
Figure 1: circuit

The waveform below shows how each switch in the image above operates and their associated current waveforms. Note that the frequency of the ripple in the output current is twice that of each current, and that its amplitude is divided by 2.

waveform
Figure 2: waveform

This example will implement interleaved operation using the two legs of the TWIST.

!!! attention Are you ready to start ? Before you can run this example, you must have successfully gone through our getting started.

Hardware setup and requirements

schema
Figure 3: schema

Warning

You will need : - 1 TWIST - A dc power supply (20-60V) - A resistor (or a dc electronic load)

Software setup

Software setup

Locate your platformio.ini file in your working folder.

platformio.ini location
Figure 4: platformio.ini location

We will import control_library in platformio.ini by decommenting the line :

lib_deps=
    #control_lib = https://github.com/owntech-foundation/control_library.git
It should look like this: 
lib_deps=
    control_lib = https://github.com/owntech-foundation/control_library.git

We can use this library to initialize a PID control with the function :

pid.init(pid_params);

the initial parameters are defined using the following lines :

static Pid pid; // define a pid controller.

static float32_t Ts = control_task_period * 1.e-6F;
static float32_t kp = 0.000215;
static float32_t Ti = 7.5175e-5;
static float32_t Td = 0.0;
static float32_t N = 0.0;
static float32_t upper_bound = 1.0F;
static float32_t lower_bound = 0.0F;
static PidParams pid_params(Ts, kp, Ti, Td, N, lower_bound, upper_bound);

Expected results

This code will control the output voltage to have 15V, you can control the output voltage with platformio serial monitor. The image below shows your a snippet of the window and the button to press.

serial monitor button
Figure 5: serial monitor button

When opening it for the first time, the serial monitor will give you an initialization message regarding the parameteres of the ADCs as shown below.

serial monitor initialization
Figure 6: serial monitor initialization

Tip

  • press u to increase the voltage
  • press d to decrease the voltage
  • press h to show the help menu

Here's sequence when the help menu is activated with h, the power mode is then activated with p and finally the Twist converter is put in idle with the i.

serial monitor working
Figure 7: serial monitor working

Note

When you send p the Twist board will send you back a stream of data on the following format: 

I1:V1:I2:V2:IH:VH
Where: - I1 is the current in LEG1 of the LOW side - V1 is the voltage in LEG1 of the LOW side - I2 is the current in LEG1 of the LOW side - V2 is the voltage in LEG2 of the LOW side - IH is the current in LEG2 of the LOW side - VH is the voltage on the HIGH side

For instance when you reveive this: 

1.44:14.80:0.13:16.14:1.14:22.82:

It means that I1 = 1.46 A, V1 = 14.80 V and so on.