It's not so easy to communicate via RS232, the timing of sending commands is a bit critical. See the following part in the manual:
The data exchange is character based, synchronisation between the computer and the supply (input) is performed using echo. The data transfer to the computer (output) is asynchronous, breaks between two characters, programmable of the break time, allow the computer to receive and evaluate the incoming data. Break time is setting 3 ms at works.

We offer a Windows software for controlling the NHQ105M via RS232, see

www.fastcomtec.com/fwww/datashee/hv/dllhvc.pdf