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Ac current source follower

In this example you need to have a first Twist with the Grid Forming example.

Schematic p2p

The parameters are:

  • \(U_{DC} = 40 V\)
  • \(R_{LOAD} = 15 \Omega\).

In the second Twist we use a software phase locked loop ( "PLL" ). By this way we are synchronised with the grid voltage and we can then inject current with a power factor of one. The current is regulated using a proportional resonant ("PR") regulator.

Software overview

Import a library

the "pll" and "pr" are provided by the OwnTech control library which must be included in the file platfomio.ini.

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

Define a regulator

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 = 0.2F;
static float32_t Kr = 3000.0F;
static float32_t Ts = control_task_period * 1.0e-6F;
static float32_t w0 = 2.0 * PI * 50.0;   // pulsation

Configure the PLL

You have to define a PLL: 

static PllSinus pll;
static PllDatas pll_datas;

Then initialize it: 

float32_t rise_time = 50e-3;
pll.init(Ts, Vgrid_amplitude, f0, rise_time);

and use it: 

pll_datas = pll.calculateWithReturn(V1_low_value - V2_low_value);

The calculation return a structure with 3 fields:

  1. the pulsation w in [rad/s]
  2. the angle angle in [rad]
  3. the angle error error in [rad/s]

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

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

Retrieve recorded datas

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.