Question on DRM021 ACIM V/Hz Control Using 56F80x

[sandrom]

Greetings all,

I'm struggling on a old Variable Frequency Drive project with uC 56F8023 (i cannot change micro). For better understand how to develop it, I found a 2002 C example project (from Motorola) that can be created from "CW 8.3 for DSC56800/E" (build 091203).

With it you can create a project from "File => New... => Processor Expert Examples Stationery => DemoApplications => MotorControl => 56F8023 => 3ph_ACIM_VectorControl". 

This project refers (I suppose) to the Designer Reference Manual in subject.

It is a very good point to start from, but I can't found detailed documentation of the code.

Do anybody have some more information about it?

The stuff I can't figure out is at the start of main header file:

/* Application maximum values used for scaling */
/* maximal voltage (dc-bus) measurable by ADC 407.0 V = 100 % */
#define APP_VOLT_MAX 407.0 /* [V] */
/* maximal output frequency of generated sinewaves [Hz] 128.0 Hz = 100 % */
#define APP_OMEGA_MAX 128.0 /* [Hz] */‍‍‍‍‍‍‍‍‍‍

I understood that the 407.0 depends on HW design (as described in comment), but I don't understand where the 128.0 Hz come from!

Can anyone help me understand this? My big problem is that I don't have the demo board and other HW described in the DRM, so I can't do "reverse engineering" for better understand the example project.

Thanks in advance!

Sandro

[xiangjun_rong]

Hi, Sandro,

This is the maximum frequency the code can express. as you know that the DSC is fixed point processor, it can only handle fixed point data. All variable must be expressed in Frac16 format.

For example,

50HZ     50/128=0.390625                  0.390625*32767=12799    in memory in Frac16 format

60HZ     60/128=0.46875                    0.46875*32767=15359    in memory in Frac16 format

120HZ  120/128=0.9375                    0.9375*32767=30719

It is the same as #define APP_VOLT_MAX 407.0, all voltage is expressed as (voltage/APP_VOLT_MAX)*32767 in memory.


Hope it can help you

BR

Xiangjun Rong

[sandrom]

Hello Xiangjun,

thank you for the answer, I understand this expression mode, but the thing that I don't understand is: why 128.0? Why not 200.0 Hz or any other value? Is it an arbitrary value?

APP_VOLT_MAX I deduced depends on hardware design (resistive divider from DC-Bus in input to ADC converter, I suppose...), but I can't figure out the 128.0 value.

I hope you can help me,

thanks again for helping me!

Sandro

[xiangjun_rong]

Hi, Sandro

Frankly speaking, i do not know why it is 128, but the frequency must be greater than 50, 60,...which are most ACIM nominated frequency.

BR

Xiangjun Rong

[sandrom]

Hello Xiangjun,

continuing testing and trying, we ended at your same consideration, I think there is no reason for that 128, probably simply a value that can fit project-related work frequencies.

Hoping that this is the truth :smileyhappy:

Thanks a lot Xiangjun for helping me in a so old project!

Best regards,

Sandro