PID control action for AC reference of variable amplitude and frequency.

i have seen example of controlling output dc voltage of DC to DC buck converter using PID controller. I want to implement DC to AC converter. I tried using PID controller. Since i am comparing output AC signal(continuously varying) with reference sinusoidal signal, PID controller is not providing expected output. In case of DC to DC, both reference signal was constant. In my case, it is continuously varying sine wave. Can anyone suggest any way to get accurate DC to AC conversion? i changed kp and ki parameters to get needed response. it is working well. but, when i change frequency of input reference signal, output signal amplitude drops and again i have to change PID parameters. P.S. when i change frequency of input reference signal, again i have to change PID gain parameters. Can PID controller work with continuously varying reference signal(in terms of amplitude and frequency both) ?

Answer 1

[Sebastian Castro]

You need to do the PID control on a frame that rotates with the AC waveform. In other words, you need to find a way to measure your output signal and transform it to components either in phase or out of phase with the target sinusoid. This is commonly known as a d-q (direct-quadrature) transform.

Once you have these values, which should not oscillate at the AC frequency, you can use PID control. Then, you have to convert back to the oscillating frame to generate your inverter pulses.

The following paper might have way too much detail, but it's the best I found:

http://scholar.lib.vt.edu/theses/available/etd-06242007-205343/unrestricted/Armani_ETD.pdf

- Sebastian

[ashish ahir]

Is there any simulink example model available for understanding? It will be very helpful.

[ashish ahir]

An example showing D-Q transform for single phase will be very helpful.

[Sebastian Castro]

Sorry, didn't see the first comment.

I would start by looking at the power_bridges example ( link here). The voltage regulator performs the transformations I mentioned above and has a PID controller as well. It's three-phase, but you can just replace the PWM generator to deal with a single phase if needed.

Note: Make sure you look under the mask of the Voltage Regulator block. That's where all the good stuff is. To do this, click the little arrow icon on the block or right-click it and select "Mask > Look Under Mask".

- Sebastian

[Muhammad Armghan Mehmood]

This link is not working.

[Gordon]

You could have just used the rms block to take the rms as the reference instead of the varying sine wave.