DC/DC converter

DC/DC buck/boost control functions.

High-level functions to control the DC/DC converter. This module does not directly access any hardware. The PWM signal for the half bridge is generated in a separate module.

Enums

enum DcdcOperationMode

DC/DC operation mode

Defines which type of device is connected to the high side and low side ports

Values:

enumerator DCDC_MODE_OFF: DC/DC converter switched off

enumerator DCDC_MODE_BUCK

Buck converter mode

Solar panel at high side port, battery / load at low side port (typical MPPT).

enumerator DCDC_MODE_BOOST

Boost converter mode

Battery at high side port, solar panel at low side (e.g. e-bike charging).

enumerator DCDC_MODE_AUTO

Automatic mode selection

Boost or buck mode is automatically chosen based on high-side and low-side port settings.

May be used in nanogrid applications: Accept input power (if available and need for charging) or provide output power (if no other power source available on the grid and battery charged)

enum DcdcControlState

DC/DC control state

Allows to determine the current control state (off, CC, CV and MPPT)

Values:

enumerator DCDC_CONTROL_OFF: DC/DC switched off (low input power or actively disabled)

enumerator DCDC_CONTROL_MPPT: Maximum Power Point Tracking.

enumerator DCDC_CONTROL_CC_LS: Constant-Current control at low-side.

enumerator DCDC_CONTROL_CV_LS: Constant-Voltage control at low-side.

enumerator DCDC_CONTROL_CC_HS: Constant-Current control at high-side.

enumerator DCDC_CONTROL_CV_HS: Constant-Voltage control at high-side.

enumerator DCDC_CONTROL_DERATING: Hardware-limits (current or temperature) reached.

Functions

void dcdc_low_level_controller()

Low-level control function

Implement this function e.g. for cycle-by-cylce current limitation.

It is called from the DMA after each new current reading, i.e. it runs in ISR context with high frequency and must be VERY fast!

class Dcdc

#include <dcdc.h>

DC/DC class

Contains all data belonging to the DC/DC sub-component of the PCB, incl. actual measurements and calibration parameters.

Public Functions

Dcdc(DcBus *high, DcBus *low, DcdcOperationMode mode)

Initialize DC/DC and DC/DC port structs

See http://libre.solar/docs/dcdc_control for detailed information

Parameters:

high – High voltage bus (e.g. solar input for MPPT buck)
low – Low voltage bus (e.g. battery output for MPPT buck)
mode – Operation mode (buck, boost or nanogrid)

DcdcOperationMode check_start_conditions()

Check for valid start conditions of the DC/DC converter

Returns:: operation mode that is valid for starting up

void control()

Main control function for the DC/DC converter

If DC/DC is off, this function checks start conditions and starts conversion if possible.

void test(): Test mode for DC/DC, ramping up/down to 50% duty cycle

void stop()

Fast stop function (bypassing control loop)

May be called from an ISR which detected overvoltage / overcurrent conditions.

DC/DC will be restarted automatically from control function if condtions are valid.

void fuse_destruction()

Prevent overcharging of battery in case of shorted HS MOSFET

This function switches the LS MOSFET continuously on to blow the battery input fuse. The reason for self destruction should be logged and stored to EEPROM prior to calling this function, as the charge controller power supply will be cut after the fuse is destroyed.

Public Members

DcdcOperationMode mode: DC/DC mode (buck, boost or nanogrid)

bool enable: Can be used to disable the DC/DC power stage.

uint16_t state: Control state (off / MPPT / CC / CV)

DcBus *hvb: Pointer to DC bus at high voltage side.

DcBus *lvb: Pointer to DC bus at low voltage (inductor) side.

float inductor_current: Inductor current.

float power: Low-side power.

float temp_mosfets: MOSFET temperature measurement (if existing)

float power_prev: Stores previous conversion power (set via dcdc_control)

int32_t pwm_direction: Direction of PWM change for MPPT.

int32_t off_timestamp: Last time the DC/DC was switched off.

int32_t power_good_timestamp: Last time the DC/DC reached above minimum output power.

float inductor_current_max = 0: Maximum low-side (inductor) current.

float hs_voltage_max = 0: Maximum high-side voltage.

float ls_voltage_max: Maximum low-side voltage.

float ls_voltage_min: Minimum low-side voltage, e.g. for driver supply.

float output_power_min: Minimum output power (if lower, DC/DC is switched off)

uint32_t restart_interval: Restart interval (s): When should we retry to start charging after low output power cut-off?

Private Functions

void perturb_observe_buck()

MPPT perturb & observe control (buck mode)

Returns:: calculated pwm duty cycle delta or 0 if the DC/DC should be stopped

void perturb_observe_boost()

MPPT perturb & observe control (boost mode)

Returns:: calculated pwm duty cycle delta or 0 if the DC/DC should be stopped

void output_hvs_enable(): If manual control of the reverse polarity MOSFET on the high-side is available, this function enables it to use the high voltage side as output.

void output_hvs_disable(): Disable the reverse polarity MOSFET on the high-side (if option available)

bool check_hs_mosfet_short(): Check if the high-side MOSFET is shorted

bool startup_inhibit(bool reset = false)

Check if we need to wait for voltages to settle before starting the DC/DC

Parameters:: reset – Reset the inhibit counter if set to true
Returns:: true if we need to wait