charge_controller_v7/cc_cv_charging.c

/*
* MIN_VOLTAGE_MV, MAXIMUM_VOLTAGE will be replaced by the value a slot gets from Pi
* Article referred: 
* https://www.monolithicpower.com/learning/resources/battery-charger-fundamentals
* https://www.instructables.com/Programming-a-Lithium-ion-Battery-Charger-Using-a-/
*/

#include "cc_cv_charging.h"
#include "battery.h"
#include "dac.h"
#include "adc.h"
#include "ti/devices/msp/m0p/mspm0g350x.h"
#include "ti/driverlib/dl_gpio.h"
#include <stdio.h>

//#define BATTERY_CAPACITY_MAH (2000)
#define MAX_VOLTAGE_MV (4200)
#define MIN_VOLTAGE_MV (3000)
#define CC_CURRENT_LIMIT_MA (500)
#define CUTOFF_CURRENT_MA (50)
#define MAX_CYCLES (2)
#define CONSTANT_VALUE (1)
#define SHUNT_RESISTOR (0.1)

//********** Not used **************************
// if the battery is deeply discharged then 50mA of trickle charge is given for a set timer
//#define TRICKLE_CHARGE_CURRENT_MA (50)
//#define TRICKLE_CHARGE_VOLTAGE_MV (2100)
//#define TRICKLE_CHARGE_TIMEOUT_MS (5000) //5 mseconds


//Pre Charge

//#define PRE_CHARGE_CURRENT_MA (BATTERY_CAPACITY_MAH/ 10)
static ChargingState charging_state= STATE_PRE_CHARGE;
static uint16_t cycle_count= 0;
static uint32_t pre_charge_start_time= 0;

//Functions for Charging and Discharging

void CC_CV_UpdateChargingState(uint8_t slot_id){
    uint16_t batt_voltage= batteries[slot_id].voltage;
    int16_t batt_current= batteries[slot_id].current;
    if(batt_voltage < MIN_VOLTAGE_MV){
        charging_state= STATE_PRE_CHARGE;
    }

    else if(batt_voltage >= MIN_VOLTAGE_MV && batt_voltage < MAX_VOLTAGE_MV - BATTERY_THRESHOLD){
        charging_state= STATE_CC_CHARGING;
    }

    else if(batt_voltage >= MAX_VOLTAGE_MV - BATTERY_THRESHOLD){
        charging_state= STATE_CV_CHARGING;
    }

    else if(charging_state == STATE_CV_CHARGING && batt_current <= CUTOFF_CURRENT_MA + BATTERY_THRESHOLD){

        if(cycle_count < MAX_CYCLES){
            charging_state= STATE_DISCHARGING;
        }
        else{
            charging_state = STATE_FINAL_DISCHARGE;
        }
        
    }

    else if(charging_state == STATE_DISCHARGING && batt_voltage <= MIN_VOLTAGE_MV + BATTERY_THRESHOLD) {
        charging_state= STATE_CC_CHARGING;      
    }
  
    else{
        charging_state= STATE_ERROR;
    }
}

/*
Function for Battery Charging and Discharging:
Trickle Charge: Only used when the battery voltage < ~2.1 V. 
    - In this state, the batteries internal protection may have been previously disconnected.
Pre Charge: Once the battery is in discharged state, pre-charging begins.
    - Starts charging safely with a typically low current C/10
Constant Current: Continues until the battery voltage has reached the "full" or floating voltage level
Constant Voltage: CV volatge starts once the maximum voltage threshold is obtained
*/

void CC_CV_ControlCharging(uint8_t slot_id){
    //Calling function to get all the conditional states
    CC_CV_UpdateChargingState(slot_id);
    uint16_t batt_voltage= batteries[slot_id].voltage;
    int16_t batt_current= batteries[slot_id].current;
    uint16_t batt_cutoff_current= batteries[slot_id].cut_off_current;
    uint16_t charge_current_mA= (batteries[slot_id].capacitance * batteries[slot_id].charge_fraction)/100;
    int16_t dac_channel_VoutA;

    switch(charging_state){
        
        case STATE_PRE_CHARGE:
            DL_GPIO_setPins(GPIO_Battery_Charging_PORT, GPIO_Battery_Charging_PIN_PB4_PIN);
            uint16_t pre_charge_current_limit_ma = charge_current_mA/10;
            DAC_fastWrite(pre_charge_current_limit_ma);
            printf("[CC-CV] Pre Charging: Slot %d at %d mA.\n", slot_id, pre_charge_current_limit_ma);
            break;
        
        case STATE_CC_CHARGING:
            DL_GPIO_setPins(GPIO_Battery_Charging_PORT, GPIO_Battery_Charging_PIN_PB4_PIN);
            DAC_fastWrite(charge_current_mA);
            printf("[CC-CV] CC Charging: Slot %d at %d mA.\n", slot_id, CC_CURRENT_LIMIT_MA);
            break;
        
        case STATE_CV_CHARGING:
            DL_GPIO_setPins(GPIO_Battery_Charging_PORT, GPIO_Battery_Charging_PIN_PB4_PIN);
            if(batt_current >= batt_cutoff_current+BATTERY_THRESHOLD){
                //Reducing by 5%
                dac_channel_VoutA= (batt_current - (batt_current-0.05));
            }
            else{
                dac_channel_VoutA= 0;
                charging_state= STATE_FINAL_DISCHARGE;
            }
            DAC_fastWrite(dac_channel_VoutA);
            printf("[CC-CV] CV Charging: Slot %d at %d mA.\n", slot_id, CUTOFF_CURRENT_MA);
            break;
        
        case STATE_DISCHARGING:
            DL_GPIO_clearPins(GPIO_Battery_Charging_PORT, GPIO_Battery_Charging_PIN_PB4_PIN);
            DL_GPIO_setPins(GPIO_Battery_Discharging_PORT, GPIO_Battery_Discharging_PIN_PB12_PIN);
            //still unsure about the value for channel VoutA:
            DAC_fastWrite(batt_voltage);
            printf("[CC-CV] Discharging: Slot %d at %d mA.\n", slot_id, batt_voltage);
            break;

        case STATE_FINAL_DISCHARGE:
            DL_GPIO_clearPins(GPIO_Battery_Charging_PORT, GPIO_Battery_Charging_PIN_PB4_PIN);
            DL_GPIO_clearPins(GPIO_Battery_Discharging_PORT, GPIO_Battery_Discharging_PIN_PB12_PIN);
            printf("[CC-CV] Final Discharge: Slot %d..\n", slot_id);
            DAC_fastWrite(0);
        
        case STATE_ERROR:
            DL_GPIO_clearPins(GPIO_Battery_Charging_PORT, GPIO_Battery_Charging_PIN_PB4_PIN);
            DL_GPIO_clearPins(GPIO_Battery_Discharging_PORT, GPIO_Battery_Discharging_PIN_PB12_PIN);
            printf("[CC-CV] Error: Slot %d.\n", slot_id);

        default:
            break;
        }
    
}