How can I obtain the negative sequence currents and voltages in the d and q axises for inverter control?

Hi! I understand that to convert a 3-phase signal into dq0 (positive sequence) I can use the abc/dq0 transformation block and use the angle theta from the PLL. Theoretically speaking, to obtain the dq0 negative sequence components I simply need to use -theta instead of +theta in the abc/dq0 transformation block, but doing this does not work. It creates a 2nd harmonic ripple that is difficult to filter out and still retain the normal behaviour on the inverter output. Any alternative ways to find Id negative, Iq negative, Vd negative, and Vq negative?

Answer 1

[MULI]

Hi Fater,

I understand that when you are using a negative angle for abc to dqo transformation you are getting 2nd order harmonics.

You can try the below alternative approach which transforms negative sequence to dq0 components.

• Use a sequence analyser to decompose the three-phase signals into positive, negative, and zero sequences and isolate the negative sequence.

https://www.mathworks.com/help/sps/ref/sequenceanalyzer.html

• Apply the abc/dq0 transformation to the isolated negative sequence using the normal angle. This method avoids the introduction of unwanted harmonics.

https://www.mathworks.com/help/sps/powersys/ref/abctodq0dq0toabc.html

• After transformation, use a low-pass filter to smooth out any residual oscillations in the dq0 negative sequence components.

https://www.mathworks.com/help/sps/ref/lowpassfilterdiscreteorcontinuous.html

Hope this answers your query!