Interactive inverters

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Interactive inverters

  1. 1. Interactive Inverters Maree
  2. 2. Inverters - a rehash part of a modern remote area power system DC (ELV) to AC(240 V) allows use of normal 240 V equipment two types: rotary inverters (mechanical) DC motor directly coupled to an AC alternator pure sine wave very good quality power high mechanical loses -> inefficient not common today electronic inverters (solid state) 240 V 50Hz AC output rapidly switch DC polarity to produce AC -> fed to a transformer to provide required output voltage transformer output is square wave - used directly or fed through a filter circuit to produce wave form more like sine wave -> filter process causes loses (inefficiencies) advances in inverter design allow for the production of true sine wave inverters which produce sine waves directly rather than filtering a square wave -> greater efficiencies.
  3. 3. Features of modern inverters Automatic stand-by mode when no load is connected saves on power consumption senses load usually between 5 - 20 watts Thermal and short circuit shut down protection against overload faults sometimes solid state protection, sometimes circuit breakers Reverse polarity protection protects unit against inadvertent reversal of input connections Over and under voltage shutdown protect from damage from supply voltage outside normal operating range protect battery against excessive discharge Quartz controlled output frequency accurate frequency control for devices that are frequency sensitive Regulated output voltage protects against variation in output voltage which may damage some appliances
  4. 4. Factors when selecting an inverter type of wave form required by load motors designed for sine wave -> heat, inefficiencies computers and some switching speed controllers need sine wave motors generally ok with square wave microwave ovens need sine wave output rating and efficiency -> size and cost one inverter for lot or square wave for most + smaller sine wave for PC, microwave. (sine wave inverters more expensive and have lower surge rating)
  5. 5. Inverter sizing generally specified in terms of continuous output in W or VA efficiency graph over a range of loads overload capacity also quoted as % or figures given for 5 minute or 1/2 hour overload capacities (generally 200-400% of continuous rating) look at continuous rating in relation to average load sizer and take into account peak load for surge capacity. Peak load generally far more than average load (genset may be more economic) daily load figure will need to be broken up into a profile in order to obtain a picture of power usage across the day to obtain a figure on which to base the continuous rating of inverter. Can be done by breaking up power usage into one hour blocks -> inverter continuous rating based on largest one hour block. Overload figures are for periods up to 1/2 hour, loads longer than 1/2 hour must be treated as continuous. inverter efficiency must be taken into account when sizing system. Modern inverters 80-90% from ~30-100% of rated output. Efficiencies fall off as load approaches zero or rises above continuous rating.
  6. 6. Factors when choosing an inverter Wattage - continuous, intermittent (1/2 hr) and surge rating Output wave shape - as mentioned previously Frequency and distortion - within .01% for frequency and < 4% harmonic distortion Autostart - standby mode when no load Minimum input current - 0.6 A Input voltage - 10-16 V Output voltage - maintain AC voltage 3-5% Efficiency - preferably have access to the full graph, not just "peak efficiency" figure Safety - AS 3100, AS 3108, C Tick, 'MEN' safety switch compatible Does it have all the displays you want; data download facility Warranty min 5 year and how hard is it to act on warranty?
  7. 7. Terminology It can be a little confusing... Grid-interactive inverters Interactive inverter / inverter charger Grid-feed inverters (one-way) Grid-tie (US)
  8. 8. Grid-interactive inverters Don't generate own frequency - synchronized to grid simpler than RAPS (no batteries) very strict standards re: voltage, frequency and wave form (harmonic content and radio interference) must be disconnected from grid if repairs are being carried out to grid safeguards built in if grid goes down or other faults occur (including anti- islanding protection - injecting small pulses that are slightly out of phase with the AC electrical system in order to cancel any stray resonances that may be present when the grid shuts down) usually specified by max output and PV array connected must have output V and current within limits of inverter input DC input about 150-400V / 134-286V max input current rating (-> size of modules or number of strings that can be connected)
  9. 9. Interactive inverter chargers Selectronic describes its off-grid/leasure inverters as either interactive inverter chargers or stand-alone inverters . "Selectronic Interactive Inverter Chargers use a battery to store energy for periods when power demand is low. When the demand is high, or when the battery requires recharging, the inverter automatically starts a generator."
  10. 10. Grid-interactive inverters vs grid-feed inverters Grid feed inverters send the power from solar PV panels direct to the grid. They do not use a battery bank and therefore they do not give you any power back up in the event of a grid power failure. Grid interactive inverters perform the same function as grid feed inverters, however they allow power to flow 'both ways'. They also incorporate a battery bank and have an automatic built in charger. This type of system gives you back up power in the event that the grid fails or goes out of tolerance in terms of its voltage and frequency.
  11. 11. Some manufacturers... Selectronic SMA (Sunnyboy) Fronius Xantrex Latronics Outback Power Systems Kaco

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