| Electronics > Microcontrollers |
| Control and filtering algorithms on a MSP430 |
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| scrat:
There will be a probability that the load connected to the unpowered grid will absorb the reference current at a voltage near to the grid's nominal one (you must accept at least the grid voltage tolerance, 10% here in Italy). The reference will be provided by the inverter itself. Usually the current's harmonic content is limited by regulations, which leads to the use of a PLL for extracting the first harmonic's phase. Once at steady-state, there is the possibility that you will stay locked to the same voltage you're generating, at least for a certain time. One simple solution is to add (numerically) a periodical small frequency/phase shift as a disturb (into the PLL), and to see if a frequency drift follows. If there are many similar devices connected to the same grid (I was thinking of a gym with many bikes) I think it will be a mess. I hope not to discourage you, just to warn against some problems. I'm not directly involved into grid tie inverters, but my tutor does, so I know a little about these issues. |
| NiHaoMike:
It would source current in proportion to the output voltage, effectively behaving as a negative resistor. No PLL needed. From my research, the tolerance of the grid frequency is less than +-0.5Hz. It would be unlikely for a load to maintain that on its own. |
| scrat:
Monitoring frequency, that kind of control could be good, it seems to be inherently unstable when the grid is down, since noise will make the frequency drift away. Maybe it has some drawbacks on harmonic content and voltage-current phase, so they use more complex algorithms. |
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