Smart Grid Scorecard suggestions: Would your design measure up?

A method of inverter control and anti-islanding. A robust and reliable method of grid interactive inverter control and anti-islanding: 1. Avoids the frequency tracking, potential instability, and drift problems. 2. Allows the power authority more flexibility and control of grid operation. 3. Imposes few if any performance compromises. 4. Has no scalability limits. 5. Relatively inexpensive. 6. Facilitates greater reliability of supply. 7. Offers several other potential benefits. By introducing a low bit rate signal modulated on a set of low frequency carriers, injected by the power authority into the grid at certain places, so equipped grid connected inverters would receive this signal shut down or isolate their output from the grid if the signal falls below a certain threshold, or carries a shutdown command, or is corrupted for more than a short period. The information carried by this signal should include: 1. A signal identification keyword 2. A phase synchronization reference 3. An error detection word 4. Time and date 5. Commands to reduce or increase power output or to retard or advance phase angle 6. Tariff information. With signal injectors at suitable places in the grid, this method would be highly fail safe since almost any fault which will cause the grid to fail in an area will also automatically cut off the signal to that same area, since it would be carried by the same wires, transformers, etc. as the power, and will thereby cause all affected inverters to shut down. In any case the signal injectors would be under the control of the power authority, which could switch any one or more of them off at any time it chooses such as during repair of power distribution faults. The method would be economical since the receiver circuit for the signal could be fairly simple and only a small proportion of the cost of an inverter, and the signal injectors, although more expensive, would only be required in small numbers, since each one could serve a large number of premises and inverters. The signal would not cause any interference since the frequencies used are all well below the radio bands and at a much lower power than the mains fundamental and at a similar or lower level than typical existing mains noise, and would be thoroughly filtered out by the power supplies of electronic equipment. Another important benefit is that the signal could carry a mains phase (and frequency) reference. Currently it seems that grid interactive inverters generally use the mains 60 Hz fundamental waveform to control the phase of their power output. A major problem with this approach is that since their output is feeding the mains, they are interfering with and altering the very thing they use as a reference, in a way which is not fully predictable or practical to compensate for. This problem is likely to get worse, and probably unmanageable, unless a better approach is adopted. There need not be any concern that noise or interference might "look like" or be mistaken for the correct signal, since the probability of this occurring, even transiently, could easily be kept to insignificant levels by a suitable, and quite practical packet length or signal identification keyword, and by use of an error detection word. The use of a power output control command field in the signal would allow the power authority much better control of inverters during power disruptions and restorations and minimize surges and transients. Suggested signal format for improved inverter control, anti-islanding, etc. To minimize the number of signal injectors required, the signal carrier frequencies can propagate long distances over the grid without excessive attenuation, without causing radio interference, and without being excessively subject to interference from external sources. The data rate required is only a few tens of bits per second. These requirements are probably best satisfied by a signal with carriers of a few hundred Hertz. Since most of the noise on the grid is harmonics of the fundamental, to minimize interference with the signal by using carrier frequencies midway between the first few harmonics. Some higher carriers might be used for some optional or less important information. The carriers could easily and efficiently be filtered by the FFT (Fast Fourier Transform), preferably synchronized to the mains fundamental. The modulation should be phase shift keying, with 180° shifts, and the modulation rate for each carrier should not be greater than about 30 Baud. It may be desirable for the two carriers in each of the pairs formed to be modulated with the same data and be 180° out of phase with each other at the zero crossings of the (ideal or reference) mains cycle. It would be possible, and may be desirable for reasons of redundancy and noise immunity, for a number of the carrier pairs to be modulated with the same information. These carriers can also be used (while simultaneously carrying data) to provide an accurate and reliable phase (and frequency) reference for the mains 60 Hz fundamental. This might best be achieved if all of the carriers have a zero crossing at the same time as one of the two zero crossings of the (ideal or reference) mains cycle.