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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;

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.

But before running, you have to add one line in the file platfomio.ini

monitor_filters = recorded_datas

And you have to put the python script filter_datas_recorded.py in a monitor directory which must be in you parent project directory. Then the script should capture the console stream to put it in a txt file named year-month-day_hour_minutes_secondes_record.txt.

These files can be plotted using the plot_data.py python script if you have the matplotlib and numpy modules installed.

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: \(U_{12} = (2.\alpha - 1).U_{DC}\)

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