In this paper, a combined water treatment system that uses both reverse osmosis process (R.O.) and evaporationdistillation process (E.D.) sequentially is studied. The electrical supply of the process is a 1.1 kW battery-less photovoltaic system. One major problem here is the system’s inability due to start-up electric motors, which the largest one is an AC compressor. As a result, voltage of different parts of the system falls at compressor starting moment, leading to under-voltage lockout function to operate in power converters. This will make the power converter output shut down for a second. Eventually, the compressor will not start to run and the system may get totally unstable. This paper proposes a starting step-down power transformer to run the AC compressor, and pass the starting moment. The transformer turn ratio is determined so that the compressor start with the least possible voltage. This will prevent system instability and PV operating point hanging situation. After the start-up moment, a mechanical switch will trigger the compressor to the nominal voltage to reach the nominal torque and speed at steady state. The experimental results shows that using a starter transformer can effectively strict the compressor’s inrush current and prevent the PV-based system instability.
