Hello I am using  VFD-EL series drive of Delta. My application requires setting of VFD speed through HMI. The PLC i am using is Jazz model T17 of Unitronics. What are the various ways we can achieve it

it can be done with modbus.

You can use Modbus RTU Or Ethernet/RS485 converter card.

You can also use 4 - 20/-10-10 ma/dc via PLC to your hmi.. Be careful when using communication as you need to consider drive state when communication fails..

Please stay away from Modbus as Modbus usually does not have good communication status information out of the box.....

Yes..I agree with Wellington...the VFD-EL supports modbus by default and the HMI/PLC unit (Jazz) supports modbus via an add-on module. I'd prefer to use a 4-20mA output from the Jazz to the VFD, but the T17 does not seem to support analog outputs...I don't see how else this can be easily done by using the equipment that you specified.

As to Ian's comment.. "No Analog Output" You can use 2 digital outputs to drive 2 programmed inputs on the drive. The first drive inputs will be programmed as "Increase Speed" the other as "decrease speed". You would then use the outputs to increase or decrease speed. No need for analog out on the PLC.

Thank you for your help.

Only as a very, very last resort, as your existing equipment seems so limited.
You could take a R2R resistor ladder and drive it with dry contact outputs,
or digital sink/source outputs driving relays to get the dry contacts. If you are real
creative you can see how it would be possible to get 64 different voltage
divider combinations, driving 0-10V input or the 4-20ma analog for 64 drive speed
references, from only 8 discrete dry contact outputs configured as a mux
switch array selecting the resistor you will develop the O/P voltage off,
or the 4-20 thru, whatever the case.

(I have used 4 dry O/P's on a dumb omron shoebox plc to drive 8 drive speeds,
thru the 0-10v speed ref into the drive. I used 8 pots instead of fixed resistors
so you get 8 different fully adjustable "dials" speeds from 4 O/P's only of the PLC)

good way is 0-10v control for el drive or any vfd control signal. i nothing knows about ur plc Jazz. but mostly plc r using analog out module for vfd operation. it is simple way to drive vfd.