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Ac Voltage Source

In this example we build an AC voltage source using a Twist and supply a resistor.

Schematic p2p

The parameters are:

  • \(U_{DC} = 40 V\)
  • \(R_{LOAD} = 30 \Omega\).

Software overview

Import libraries

This example depends on two libraries:

  1. control_library
  2. ScopeMimicry

To use them, you have to add the following lines in platformio.ini file: 

lib_deps=
    control_library = https://github.com/owntech-foundation/control_library.git
    scope = https://github.com/owntech-foundation/scopemimicry.git

Define a regulator

The voltage regulation will be done by a proportional resonant regulator. This component is provided by the OwnTech control library control_lib.

The Proportional Resonant regulator is initialized with the lines above:

PrParams params = PrParams(Ts, Kp, Kr, w0, 0.0F, -Udc, Udc);
prop_res.init(params);

The parameters are defined with these values:

static Pr prop_res; // controller instanciation. 
static float32_t Kp = 0.02F;
static float32_t Kr = 4000.0F;
static float32_t Ts = control_task_period * 1.0e-6F;
static float32_t w0 = 2.0 * PI * 50.0;   // pulsation
static float32_t Udc = 40.0F;

3. Run the example.

Tip

To capture the current ripple you have to follow these steps: - press the p key to go in POWER_MODE - press the t key to activate the trigger of the ScopeMimicry instance. - press the i key to come back in IDLE_MODE - press the r key to retrieve the data.

After these steps you should see in your directory a new folder called Data_records appear. Within it you will find three files with the following naming convention :

  • Year-month-day-hour-minute-second.txt - a raw data file
  • Year-month-day-hour-minute-second.csv - a post-treated csv file
  • Year-month-day-hour-minute-second.png - an automatically generated png file

As an example here are two acquisitions:

data records
Figure 1: data records

In the code there's some parameters you can change: - num_trig_ration_point: it sets the number of trig_ratio value will be sweep between begin_trig_ratio and end_trig_ratio - begin_trig_ratio : beginning value of the sweep. - end_trig_ratio: end value of the sweep.

To view some variables.

After stop i.e. in IDLE mode you can retrieve some data by pressing 'r'. It calls a function dump_scope_datas() which send to the console variables recorded during the power flow phase.

The voltage source is defined by the voltage difference: \(U_{12} = V_{1low} - V_{2low}\).

Link with the duty cycle:

  • The leg1 is fixed in buck mode then: \(V_{1low} = \alpha_1 . U_{DC}\)
  • The leg2 is fixed in boost mode then: \(V_{2low} = (1-\alpha_2) . U_{DC}\)

We change at the same time \(\alpha_1\) and \(\alpha_2\), then we have : \(\alpha_1 = \alpha_2 = \alpha\).
And then: \(U_{12} = (2.\alpha - 1).U_{DC}\)

\(\alpha = \dfrac{U_{12}}{2.U_{DC}} + 0.5\)