17 ms·

This is correct, an added benefit is if the power poles are actually down then the communication over the powerlines would be down, but that’s fine as power cou

by bobbob1921 2y ago

This is correct, an added benefit is if the power poles are actually down then the communication over the powerlines would be down, but that’s fine as power couldn’t be sent over the lines anyway in that case. What I wonder about/have concerns in regards to, is as someone else mentioned the relays required to turn on and off backfeeding in terms of electrical Utility workers having to de-energize a line to perform work. I’m not too sure that these workers can entrust their lives to the reliability of various (multiple) relays to not sporadically switch back on once the line has been confirmed as de-energized (in other words depending on the relay not to malfunction and re-energized while the workers are working upon the line ) I assume there will be some types of tools to monitor / alarm the workers for exactly this scenario (ie something they can attach to the line while it is being worked on and if it becomes re-energized an alarm will sound).

Shog9 2y ago
Generally grid backfeed capability for these systems is predicated on the presence of a stable voltage and frequency already on the grid - this is both a safety measure and a practical necessity, as the inverter needs to synchronize with the grid frequency.
- crznp 2y ago
  Just to add the terms: a "grid following" matches the grid's voltage/frequency, so it only works when connected to the grid. A "grid forming" system can set its voltage/frequency independently and can only work off-grid It sounds like mauvehaus is talking about a hybrid system that has both grid following and grid forming capabilities: switching to grid-forming as it disconnects. But that means that you can't power your neighbors.
- screcth 2y ago
  I wonder why it is that real world systems don't use a GPS receiver to obtain a 1 Hz signal that's synchronized to the GPS clock and then generate a local 50/60 Hz clock for grid synchronization. I'm just an EE with no experience in real power systems, so this may be absurd to someone who knows how this stuff works.
  - burnished 2y ago
    I didn't take power systems either (EE that went CE), but even if your clock was accurate and the system was tuned wouldn't you still likely be out of phase? I don't remember enough about the whys (like, does the type of load modify the frequency? gone down the memory hole) but I remember a guest lecturer mentioning that the actual frequency frequently had small deviations from nominal, too
    - throwup238 2y ago
      Yeah that's what the synchronization is for - the precise frequency doesn't matter except for consumer devices that use it as a clock signal. If the hot line is at 120V and you're a quarter cycle out of phase at 0V, all of that energy is just going to flow directly to your circuit and destroy something. Since the frequency represents the spinning of large turbines, a power plant going online out of phase is essentially slamming their turbines into a massive external force (things go boom).
      - screcth 2y ago
        If you use GPS-based synchronization you have a reference of when zero crossings should occur. This does not mean that you have to output exactly that waveform. Once you have a reference you can use a control algorithm. like a PID, to adjust the phase of the grid that you are generating locally. If you sense that the grid is running out of phase from what your GPS clock says is the true reference you can increase/decrease your power output a bit to increase/decrease its frequency and catch up with the phase error. It would be analogous to a type 2 PLL. The 1 Hz GPS clock would be the reference clock, the 60 Hz grid would be the "PLL output" and the VCO would be the power turbine, or AC inverter.
        burnished 2y ago
        Ok, potentially stupid question, but if you're already using the grid as a control signal what do you need the external clock for?

Shog9 2y ago

Generally grid backfeed capability for these systems is predicated on the presence of a stable voltage and frequency already on the grid - this is both a safety measure and a practical necessity, as the inverter needs to synchronize with the grid frequency.

crznp 2y ago
Just to add the terms: a "grid following" matches the grid's voltage/frequency, so it only works when connected to the grid. A "grid forming" system can set its voltage/frequency independently and can only work off-grid It sounds like mauvehaus is talking about a hybrid system that has both grid following and grid forming capabilities: switching to grid-forming as it disconnects. But that means that you can't power your neighbors.
screcth 2y ago
I wonder why it is that real world systems don't use a GPS receiver to obtain a 1 Hz signal that's synchronized to the GPS clock and then generate a local 50/60 Hz clock for grid synchronization. I'm just an EE with no experience in real power systems, so this may be absurd to someone who knows how this stuff works.
- burnished 2y ago
  I didn't take power systems either (EE that went CE), but even if your clock was accurate and the system was tuned wouldn't you still likely be out of phase? I don't remember enough about the whys (like, does the type of load modify the frequency? gone down the memory hole) but I remember a guest lecturer mentioning that the actual frequency frequently had small deviations from nominal, too
  - throwup238 2y ago
    Yeah that's what the synchronization is for - the precise frequency doesn't matter except for consumer devices that use it as a clock signal. If the hot line is at 120V and you're a quarter cycle out of phase at 0V, all of that energy is just going to flow directly to your circuit and destroy something. Since the frequency represents the spinning of large turbines, a power plant going online out of phase is essentially slamming their turbines into a massive external force (things go boom).
    - screcth 2y ago
      If you use GPS-based synchronization you have a reference of when zero crossings should occur. This does not mean that you have to output exactly that waveform. Once you have a reference you can use a control algorithm. like a PID, to adjust the phase of the grid that you are generating locally. If you sense that the grid is running out of phase from what your GPS clock says is the true reference you can increase/decrease your power output a bit to increase/decrease its frequency and catch up with the phase error. It would be analogous to a type 2 PLL. The 1 Hz GPS clock would be the reference clock, the 60 Hz grid would be the "PLL output" and the VCO would be the power turbine, or AC inverter.
      - burnished 2y ago
        Ok, potentially stupid question, but if you're already using the grid as a control signal what do you need the external clock for?