Use a fixed sinewave lookup table, and regulate the incoming dc bus to the PWM stage independently.
Its then much easier to regulate the dc bus with a pretty fast analog control loop to keep the dc voltage constant.
This may or may not be real-life behavior, but in simulations I have seen a few cycles need to go by after I change some parameter, which causes output voltage to go up and down a few times.
Therefore it's not always useful to start applying feedback again right away after a change. Allow settling time or else the feedback can produce oscillating behavior, and increasingly large voltage swings.
True, but most of us typically have refrigeration and air conditioning cycling on and off.If you operate your inverter with constant load, there won't be any flicker.
Yes. I didn't suggest to omit voltage control, just to evaluate the inverter behavior systematically.True, but most of us typically have refrigeration and air conditioning cycling on and off.
First step to understand the system behavior would be to run a control characteristic without feedback to verify that the duty cycle variation is working correctly.
Secondly verify that your output voltage measurement is accurate and stable enough.
Finally implement a suitable control algorithm. It would be rather a PID-like or deadbeat compensating controller than an up/down ramp algorithm.
The basic measurement problem is sampling being asynchronous to output voltage period. Integrating (averaging) the samples over a full or at least half cycle is suggested. Addition low pass filtering to suppress pwm frequent residuals.
Dead beat is a digital controller algorithm that ideally cancels a perturbation (e.g. a load step) completely after e.g. two discrete time steps.
I have defined an extended look-up table to set the output voltage (from 33% to 97% of the maximum amplitude in steps of 0.5%). Thus I have a bidimensional array with 129 rows (the above mentioned attenuation) and 100 cols (samples per half wave).
Finally implement a suitable control algorithm. It would be rather a PID-like or deadbeat compensating controller than an up/down ramp algorithm.
Output is varied within a range of 5-6 volts. But it is not flickering. When the load is varied causing the output vary beyond 5-6 volts, the output frisks a bit only.
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