PV Monitor #4 - The great pretender (2)

2. Delta Solivia protocol description

Messages on the RS485-bus look like this:

Let's now split the response

 

[02]	STX
[06]	RESPONSE
[01]	Inverter ID
[04]	Number of data bytes
[20][06]	Command and subcommand (the same of the request)
[00][1B]	16-bit value of the requested parameter
[3C][27]	CRC-16
[03]	ETX

​ 

UPDATE: I added some other data, namely the daily yield

 

 

which can be read by means of the following request

 

Request	Response	Value	Meaning
[02][05][01][02][13][03][21][0D][03]	[02][06][01][04][13][03][00][AE][E3][29][02]	0x00AE (174)	Daily yield (Wh)

 

To implement the Delta Solivia protocol, I started from this project. I had to make some changes to use python3 (the library was written to support python2) and to use the correct commands.

Here is a brief description of the functions involved

3.1 solivia_readData

This function reads a specific value from the Delta Solivia inverter (DC power, AC power, etc).  The only caveat here is that I had to add a check to remove some trailing 0xff characters that are probably mistakenly read by the USB-to-RS485 converter when inverter drives RS485 from RX to TX.

def solivia_readData(s):
    log.debug("Reading %s"%(s))

    cmd = solivia_inverter.getCmdStringFor(s)
    log.debug("Command: %s"%binascii.hexlify(cmd))
    solivia_connection.write(cmd)
    rawResponse = solivia_connection.read(100)

    cntr = 0
    while (cntr < len(rawResponse) and rawResponse[cntr] == 0xff):
       cntr += 1

    response = rawResponse[cntr:]

    floatValue = float("0")
    if response:
        log.debug("Received response %s\n"%binascii.hexlify(response))

        value = solivia_inverter.getValueFromResponse(response)
        #log.debug("Value %s"%value)
        if solivia_isFloat(value):
            floatValue = float(value)

    return floatValue 

The code leverages functions in the deltaInv.py file to extract a value as a floating point number from the inverter response

3.2 solivia_updateChannel

This function updates all the Modbus registers required to mimic one of Omega OM240 channels. The following Modbus registers are initialized

• 2 16-bits registers with the value
• 8 16-bits registers with the timestamp string
• 1 16-bits registers with the flags

Here is the code

def solivia_updateChannel(ch, value, ts):
    """ Registers are as follow
    0-1 Input A (IEE754)
    2-3 Input B
    4-5 Temperature
    6-14 Timestamp "dd/mm/yy hh:mm:ss"
    15  Flags
    """
    vHex = solivia_floatToHex(value)[2:]
    log.debug("value=%f, vHex=%s"%(value,vHex))
    stime = ts.strftime("%d/%m/%y %H:%M:%S").encode('utf-8').hex().ljust(36, '0')

    values = [int(vHex[0:4],16), int(vHex[4:8],16),
                 0, 0,
                 0, 0,
              int(stime[0:4],16), int(stime[4:8],16), int(stime[8:12],16), int(stime[12:16],16), int(stime[16:20],16), int(stime[20:24],16), int(stime[24:28],16), int(stime[28:32],16), int(stime[32:36],16),
                 3]
    return values 

3.3 solivia_reader

This functions reads all the measures and update the corresponding channels

def solivia_reader(a):
    """ A worker process that runs every so often and
    updates live values of the context. It should be noted
    that there is a race condition for the update.
    :param arguments: The input arguments to the call
    """
    log.info("Updating inverter data\n")

    dcVolts = solivia_readData('DC Volts1')
    dcCur = solivia_readData('DC Cur1')
    dcPow = solivia_readData('DC Pwr1')
    acVolts = solivia_readData('AC Volts')
    acCur = solivia_readData('AC Current')
    acPow = solivia_readData('AC Power')
    acTemp = solivia_readData('AC Temp')
    dcTemp = solivia_readData('DC Temp')

    context = a[0]
    register = 3
    slaveId = 0x00

    address = 0
    values = solivia_updateChannel(0, dcPow, datetime.now())
    context[slaveId].setValues(register, address, values)

    address = 16
    values = solivia_updateChannel(0, acPow, datetime.now())
    context[slaveId].setValues(register, address, values)

    address = 32
    values = solivia_updateChannel(0, acTemp, datetime.now())
    context[slaveId].setValues(register, address, values)

    address = 48
    values = solivia_updateChannel(0, dcTemp, datetime.now())
    context[slaveId].setValues(register, address, values)

    currDate = datetime.now().strftime("%d/%m/%y").encode('utf-8').hex().ljust(10, '0')
    currTime = datetime.now().strftime("%H:%M:%S").encode('utf-8').hex().ljust(8, '0')

    log.debug(currDate+"-"+currTime+" %.6f %.6f %.6f %.6f %.6f %.6f %.6f %.6f OK\n" %(dcVolts, dcCur, dcPow, acVolts, acCur, acPow, dcTemp, acTemp )) 

    log.info("Scheduling task")
    time = 5.0
    loop = LoopingCall(f=solivia_reader, a=(context,))
    loop.start(time, now=True)  # initially delay by time