Closed loop voltage mode - owntech-foundation/Tutorials GitHub Wiki
The goal of this tutorial is to use the TWIST in order to lower the output voltage. This is made with a closed-loop control.
Required Hardware
- TWIST v_1_3 or later
- PC 64-bits (windows or linux)
- DC power supply (48 V, 2 A)
- Resistive load
- Oscilloscope or multimeter
Required Software
- Git
- Visual code studio
- Ownplot
Step-by-step implementation
0 - Owntech.ini
First, go to the platformio.ini file on the root, near the LICENSE file and uncomment line 45. As shown in the image below. It will automatically download the pid library that will be used in this tutorial.
- Use the following main.cpp code to deploy your closed loop voltage source.
//-------------OWNTECH DRIVERS-------------------
#include "SpinAPI.h"
#include "TaskAPI.h"
#include "TwistAPI.h"
#include "DataAPI.h"
#include "opalib_control_pid.h"
//------------ZEPHYR DRIVERS----------------------
#include "console/console.h"
//--------------SETUP FUNCTIONS DECLARATION-------------------
void setup_routine(); // Setups the hardware and software of the system
//--------------LOOP FUNCTIONS DECLARATION--------------------
void loop_application_task(); // Code to be executed in the background task
void loop_communication_task(); // Code to be executed in the background task
void loop_control_task(); // Code to be executed in real time in the critical task
enum serial_interface_menu_mode //LIST OF POSSIBLE MODES FOR THE OWNTECH CONVERTER
{
IDLEMODE =0,
SERIALMODE,
POWERMODE,
BUCKMODE,
};
uint8_t received_serial_char;
uint8_t mode = IDLEMODE;
//--------------USER VARIABLES DECLARATIONS----------------------
static float32_t duty_cycle = 0.5; //[-] duty cycle (comm task)
static float32_t duty_cycle_step = 0.05; //[-] duty cycle step (comm task)
static bool pwm_enable = false; //[bool] state of the PWM (ctrl task)
static uint32_t control_task_period = 50; //[us] period of the control task
//Measurement data
static float32_t V1_low_value; //store value of V1_low (app task)
static float32_t V2_low_value; //store value of V2_low (app task)
static float32_t V_high_value; //store value of Vhigh (app task)
static float32_t I1_low_value; //store value of i1_low (app task)
static float32_t I2_low_value; //store value of i2_low (app task)
static float32_t I_high_value; //store value of ihigh (app task)
static float32_t meas_data; //temp storage meas value (ctrl task)
//
static float32_t voltage_reference = 10; //voltage reference (app task)
static int cpt_step = 0; //counter for voltage reference (app task)
static float32_t kp = 0.000215;
static float32_t ki = 2.86;
static float32_t kd = 0.0;
//---------------SETUP FUNCTIONS----------------------------------
void setup_routine()
{
data.enableTwistDefaultChannels();
spin.version.setBoardVersion(SPIN_v_0_9);
twist.setVersion(shield_TWIST_V1_3);
twist.initLegBuck(LEG1);
twist.initLegBuck(LEG2);
float32_t GV1 = 0.044301359147286994;
float32_t OV1 = -89.8291125470221;
float32_t GV2 = 0.043891466731813246;
float32_t OV2 = -89.01321095039089;
float32_t GVH = 0.029777494874229947;
float32_t OVH = 0.12805533844297656;
float32_t GI1 = 0.005510045850270965;
float32_t OI1 = -11.298753103344417;
float32_t GI2 = 0.005569903739753797;
float32_t OI2 = -11.47851441455354;
float32_t GIH = 0.0052774398156665;
float32_t OIH = -10.864400298536168;
data.setParameters(V1_LOW, GV1, OV1);
data.setParameters(V2_LOW, GV2, OV2);
data.setParameters(V_HIGH, GVH, OVH);
data.setParameters(I1_LOW, GI1, OI1);
data.setParameters(I2_LOW, GI2, OI2);
data.setParameters(I_HIGH, GIH, OIH);
uint8_t AppTask_num = task.createBackground(loop_application_task);
uint8_t CommTask_num = task.createBackground(loop_communication_task);
task.createCritical(&loop_control_task, control_task_period);
opalib_control_init_leg1_pid(kp, ki, kd, control_task_period);
opalib_control_init_leg2_pid(kp, ki, kd, control_task_period);
task.startBackground(AppTask_num);
task.startBackground(CommTask_num);
task.startCritical();
}
//---------------LOOP FUNCTIONS----------------------------------
void loop_communication_task()
{
received_serial_char = console_getchar();
switch (received_serial_char) {
case 'h':
//----------SERIAL INTERFACE MENU-----------------------
printk(" ________________________________________\n");
printk("| ------- MENU --------- |\n");
printk("| press i : idle mode |\n");
printk("| press s : serial mode |\n");
printk("| press p : power mode |\n");
printk("| press u : duty cycle UP |\n");
printk("| press d : duty cycle DOWN |\n");
printk("| press b : closed-loop buck mode |\n");
printk("|________________________________________|\n\n");
//------------------------------------------------------
break;
case 'i':
printk("idle mode\n");
mode = IDLEMODE;
break;
case 's':
printk("serial mode\n");
mode = SERIALMODE;
break;
case 'p':
printk("power mode\n");
mode = POWERMODE;
break;
case 'u':
printk("duty cycle UP: %f\n", duty_cycle);
duty_cycle = duty_cycle + duty_cycle_step;
if(duty_cycle>1.0) duty_cycle = 1.0;
break;
case 'd':
printk("duty cycle DOWN: %f\n", duty_cycle);
duty_cycle = duty_cycle - duty_cycle_step;
if(duty_cycle<0.0) duty_cycle = 0.0;
break;
case 'b':
printk("closed-loop buck mode\n");
mode = BUCKMODE;
break;
default:
break;
}
}
void loop_application_task()
{
if(mode==IDLEMODE) {
spin.led.turnOff();
}else if(mode==SERIALMODE) {
spin.led.turnOn();
}else if(mode==POWERMODE) {
spin.led.toggle();
}else if(mode==BUCKMODE) {
spin.led.turnOn();
if(cpt_step==10) voltage_reference = 15;
if(cpt_step==20) {
voltage_reference = 10;
cpt_step=0;
}
cpt_step ++;
}
printk("%f:", duty_cycle);
printk("%f:", V_high_value);
printk("%f:", V1_low_value);
printk("%f:", V2_low_value);
printk("%f:", I_high_value);
printk("%f:", I1_low_value);
printk("%f\n", I2_low_value);
task.suspendBackgroundMs(100);
}
void loop_control_task()
{
meas_data = data.getLatest(V1_LOW);
if (meas_data != NO_VALUE)
V1_low_value = meas_data;
meas_data = data.getLatest(V2_LOW);
if (meas_data != NO_VALUE)
V2_low_value = meas_data;
meas_data = data.getLatest(V_HIGH);
if (meas_data != NO_VALUE)
V_high_value = meas_data;
meas_data = data.getLatest(I1_LOW);
if (meas_data != NO_VALUE)
I1_low_value = meas_data;
meas_data = data.getLatest(I2_LOW);
if (meas_data != NO_VALUE)
I2_low_value = meas_data;
meas_data = data.getLatest(I_HIGH);
if (meas_data != NO_VALUE)
I_high_value = meas_data;
if(mode==IDLEMODE || mode==SERIALMODE) {
pwm_enable = false;
twist.stopAll();
}else if(mode==POWERMODE || mode==BUCKMODE) {
if(!pwm_enable) {
pwm_enable = true;
twist.startAll();
}
if(mode==BUCKMODE){
duty_cycle = opalib_control_leg1_pid_calculation(voltage_reference, V1_low_value);
}
//Sends the PWM to the switches
twist.setAllDutyCycle(duty_cycle);
}
}
/**
* This is the main function of this example
* This function is generic and does not need editing.
*/
void main(void)
{
setup_routine();
}
Code explanation
- Drivers
- The Owntech drivers allows you to use our power API and all-made up libraries.
- The Zephyr libraries use the API from the Real-Time OS (RTOS) we are using to manage tasks on the microcontroller
-
Declaration To setup hardware, software, functions and different power mode we will use.
-
User variable description
- The 'voltage_reference' is the output voltage you are willing
- The 'cpt-step' is a counter used for creating a step on the voltage reference
- duty_cycle & duty-cycle_step : they define the parameters for the closed loop control of the power converter.
- The measurement data are used to visualize your voltage and current data. The 'high' postfix refers to your input voltage or current. The 'high' postfix refers to your output voltage or current.
- Setup functions
- 'spin.version.setBoardVersion(SPIN_v_0_9);' to setup your spin version.
twist.setVersion(shield_TWIST_V1_3);does the same for the twist board. - 'twist.initAllBuck()' to setup that your power legs will be used in an interleaved mode to lower your output voltage.
- data.enableTwistDefaultChannels will enable the default channel configuration of the twist board as covered in the Measurements tutorial
- 'console_init()' initializes serial communication
- 'data.setParameters(V1_LOW, GV1, OV1);' to setup gain and offset for each measurement of the board.
- The 'meas_data' variable is used to verify that the measurement has succeeded.
- Here will be defined our power usage. The power conversion defined above will be started here with
twist.startAll()function, depending on the mode choosen (BUCKMODEorPOWERMODE). - In the buck mode, our duty cycle is calculated by one our librairies. The duty cycle is calculated regarding the input voltage and the reference output voltage with the 'opalib_control_interleaved_pid_calculation()' function.
- The control task then send the duty cycle value to all the switches with the 'set.setAllDutyCycle(duty_cycle)' function.
Convert your power
- Now we will connect your TWIST board to the power supply and to the PC via the USBC.
- Connect the pins Vhigh and GND of the TWIST to the DC power supply (set its current limitation at 1 A).
- Connect the pins VLow1, Vlow2 and GND of the TWIST to a resistive load.
- Connect the USB-C connector of the SPIN to the PC thanks via an USB cable.
- Switch ON the DC power supply. Choose a voltage between 0 and 48 V.
-
Build
and Upload 
-
Use OwnPlot or Serial Monitor to visualize the data and control your power.