Software

The Electrical Power System main functions are to extract, store and manage electrical energy. In order to achieve this, the module performs hardware and software tasks. These tasks are processed by a MSP430F6659 microcontroller placed in the EPS module. The main EPS tasks are described as follows:

1. Analog to digital conversion of variables, specially solar panel inputs

2. Battery voltage, current and state of charge monitoring

3. Task scheduling based on battery state of charge

4. Actuation on dc-dc converters

5. Actuation on MPPT integrated circuits

6. Communication with OBDH

7. Communication with Beacon

The main code is being developed following this flowchart:

EPS Data Frame

The data frame sent from EPS to OBDH is composed of the following data:

• Solar panel current - 12 bytes
• Solar panel voltage - 6 bytes
• Total voltage (MPPT output) - 2 bytes
• Bus voltage - 2 bytes
• MSP430 internal temperature sensors - 2 bytes
• Voltage reference generator temperature - 2 bytes
• Battery average current - 2 bytes
• Battery monitor temperature - 2 bytes
• Battery voltage - 4 bytes
• Battery current - 2 bytes
• Battery accumulated current - 2 bytes
• Protection register - 1 byte
• Status register - 1 byte
• Cycle counter register - 1 byte
• Remaining active absolute capacity - 1 byte
• Remaining standby absolute capacity - 1 byte
• Remaining active relative capacity - 1 byte
• Remaining standby relative capacity - 1 byte
• RTD temperature measurements - 21 bytes
• EPS status - 1 byte

Decoding

ADC Solar Panel Current

$V_{ADC} = ADC_{msb} << 8~ | ~ADC_{lsb}$

$I_{panel} = \frac{V_{ADC}\times6.1035\times10^{-4}}{50\times10^{-3}\times25\times10^{-6}\times1.65\times10^{3}} A$

ADC Solar Panel Voltage

$V_{ADC} = ADC_{msb} << 8~ | ~ADC_{lsb}$

$V_{panel} = \frac{V_{ADC}\times6.1035\times10^{-4}\times(100\times10^{3}+93\times10^{3})}{100\times10^{3}} V$

ADC Total Voltage

$V_{ADC} = ADC_{msb} << 8~ | ~ADC_{lsb}$

$V_{total} = \frac{V_{ADC}\times6.1035\times10^{-4}\times(100\times10^{3}+300\times10^{3})}{100\times10^{3}}V$

ADC Bus Voltage

$V_{ADC} = ADC_{msb} << 8~ | ~ADC_{lsb}$

$V_{bus} = \frac{V_{ADC}\times6.1035\times10^{-4}\times(100\times10^{3}+300\times10^{3})}{100\times10^{3}}V$

ADC Internal Temperature Sensor

$V_{ADC} = ADC_{msb} << 8~ | ~ADC_{lsb}$

$Internal\_Temperature = \frac{V_{ADC}\times6.1035\times10^{-4} - 0.986}{0.00355} ºC$

ADC Voltage Reference Temperature

$V_{ADC} = ADC_{msb} << 8~ | ~ADC_{lsb}$

$Reference\_Generator\_Temperature = \frac{V_{ADC}\times6.1035\times10^{-4} - 0.509}{2.64}ºC$

Battery Average Current

$signal = average\_current_{msb}~\&~0x80$, where & is the bitwise and operation.

if $signal = 0x00h$ then $V_{average\_current} = average\_current_{msb} << 8~ | ~average\_current_{lsb}$

if $signal = 0x80h$ then $V_{average\_current} = (\sim average\_current_{msb}) << 8~ | ~(\sim average\_current_{lsb} + 1)$, where ~ is the bitwise not operation.

$battery\_average\_current = \frac{V\_average\_current\times1.5625\times10^{-6}}{0.01}A$

Battery Monitor Temperature

$V{_battery\_monitor\_temperature} = battery\_monitor\_temperature_{msb} << 8~ | ~battery\_monitor\_temperature_{lsb}$

$battery\_monitor\_temperature = V_{battery\_monitor\_temperature}\times0.125~ºC$

Battery Voltage

$signal = battery\_voltage_{msb}~ \& ~0x80h$

if $signal = 0x00h$ then $V_{battery\_voltage} = (battery\_voltage_{msb} >> 5) << 8 | (battery\_voltage_{lsb} >> 5) | ((battery\_voltage_{msb} << 3) \& 0xf8))$

if $signal = 0x80h$ then $V_{battery\_voltage} = \sim((battery\_voltage_{msb} >> 5)<< 8)| \sim((battery\_voltage_{lsb} >> 5) | ((battery\_voltage_{msb} << 3)~\&~0xf8))) +1$

$battery\_voltage = V_{battery\_voltage}\times4.886\times10^{-3}V$

Battery Current

$signal = battery\_current_{msb}~ \& ~0x80h$

if $signal = 0x00h$ then $V_{battery\_current} = (battery\_current_{msb} << 8)~ |~battery\_current_{lsb}$

if $signal = 0x80h$ then $V_{battery\_current} = (\sim battery\_current\_msb)<< 8~ | ~\sim battery\_current\_lsb + 1$

$battery\_current = \frac{V_{battery\_current}\times1.5625\times10^{-6}}{0.01}A$

Battery Accumulated Current

$V_{battery\_accumulated\_current} = battery\_accumulated\_current_{msb} << 8~ | ~battery\_accumulated\_current_{lsb}$

$battery\_accumulated\_current = \frac{V{_battery\_accumulated\_current\times6.25}\times10^{-6}}{0.01}Ah$

Cycle Counter

$cycle\_counter = 2\times cycle\_counter\_register$

Remaining Active Absolute Capacity (RAAC)

$V_{RAAC} = RAAC_{MSB}<< 8~ | ~RAAC_{LSB}$

$RAAC = V_{RAAC}\times1.6~mAh$

Remaining Standby Absolute Capacity (RSAC)

$V_{RSAC} = RSAC_{MSB}<< 8~ | ~RSAC_{LSB}$

$RSAC = V_{RSAC}\times1.6~mAh$

Remaining Active Relative Capacity (RARC)

$RARC = RARC\_register~ \%$

Remaining Standby Relative Capacity (RSRC)

$RSRC = RSRC\_register~ \%$

RTD temperatures

$V_{temperature} = V_{temperature0} << 16~ | ~V_{temperature1}<< 8~ | ~V_{temperature2}$

$temperature = \frac{V_{temperature}\times0.0000139326 - 1000}{3.85} ºC$