Skip to content

Use the software Phase Locked Loop.

Introduction

The PllSinus is used to track sinusoid and extract angle and pulsation. It is included in the filters.cpp module.

pll block diagram

block diagram of software phase locked loop

Parameters:

  • We set \(f_0\) the frequency of the signal to track linked with \(\omega_0=2.\pi.f_0\).
  • \(\Delta \omega\) has been arbitrarily fixed to be 20% of \(\omega_0\).
  • \(K_p, T_i\) parameters are computed using the rise_time of the closed loop, which fix the dynamic of the PLL and we have also to take into account of the amplitude of the signal.

Use of the PllSinus filter.

The use of the `PllSinus is based on 3 steps.

  1. Object instanciation (declaration).
  2. Initialisation.
  3. Execution.

Example

We define constants used to initialize the parameter structure. 

#include "filters.h"

static float32_t amplitude = 16.0F; // amplitude of the voltage sinus to track.
static float32_t f0 = 50.0;               // frequency assumed of the signal to track [Hz]
static float32_t rise_time = 50.e-3F;     // dynamic of the loop [s].
static float32_t Ts = 100.0e-6F;          // sampling time [s]

We define the variable pll which is an instance of PllSinus object. 

static PllSinus pll;

In the setup_routine() of the OwnTech Power API, you must initialize the PllSinus with its parameters.

pll.init(Ts, amplitude, f0, rise_time);

In the loop_critical_task() you can call the method calculateWithReturn()

pll_datas = pll.calculateWithReturn(signal_to_track);

pll_datas is a structure which kept the results of the PllSinus calculation for one step.

the PllData structure has 3 fields: 

struct PllDatas {
    float32_t w;     // estimated pulsation [rad/s]
    float32_t angle; // estimated angle [rad]
    float32_t error; // angle error [rad]
};

Note

Remind that the loop_critical_task() is called at the sampling time you define and must be equal to \(T_s\).

Example

You can find a pll use with the grid following example which requires a synchronisation to inject current in parallel with a voltage source.