I need occasionally drive watergate with gear box (e.g. http://www.servomech.com/main/screw-jacks.htm). Because location is far away from 220V I suppose powering from SLA 12V battery charged from solar panel. Battery capacity 7-20Ah. Required motor power is 50-100W (torque I think >0.2Nm). Because of outdoor usage I need IP66 or so. Price is also essential.
I did not find any 12V DC motors and seems that 3 phase AC motor (e.g. SIEMENS 1LA7063-6AB, 0.09kW,870 rev/min) produced in large quantities is the only option.
I can use power inverter 12V-DC/220V-AC and 3 phase frequency changer (e.g. Sinamics G110) to power motor even with trapezoidal profile. Expected efficiency 85%*95%. It could be assembled from stock products and it should work. I don't think it's worth to do it as home-made application.
I wonder if I can do it much simpler when I make simple inverter (IRS2153+current sensing IR2127+FETs+toroid transformer 2x12V/220V) and connect to 3 phase motor using Steinmetz method. Output of inverter is rectangular 220V voltage with adjustable frequency (easy to implement IRS2153 has option to force switching frequency from MCU).
The questions are:
1) Steinmetz decrease motor power to 70% and starting torque to 50%. But I believe efficiency remains unchanged, i.e. in other words I can use stronger motor without power loss compared to regular 3-phase triangle connection. Is it true ?
2) Is it possible to regulate motor revolutions via changing of inverter output freqeuncy (i.e. apply trapezoidal profile) ? I'm uncertain how Steinmetz capacitor value (70uF/1kW) is related to voltage frequency (50Hz).
3) how motor copes with rectangular AC waveform? I think it may affect insulation bacause of voltage peaks.