Discussions on Stability of Induction Machines System Using Photovoltaic Arrays and Its Maximum Power Tracking Scheme.

The electric power generated from a photovoltaic array (PVA) is generally utilized by interacting with the utility line through a utility-interactive inverter. This method, however, debases the power quality of the utility line and causes electromagnetic interference without a bulky power filter. On the other hand, the electric power from a PVA is utilized to drive a motor of a heat pump and so on. But the conventional pumping system can not generate a constant mechanical power since the solar power depends on weather conditions.The authors have proposed a new pumping system which is composed of two coupled induction machines. One induction machine is related to a PVA through a general-purpose inverter and the other is interacted to the utility line. This system can generate a desired mechanical power all day and supply the surplus electric power of the PVA to the utility line. This paper discusses the stability of the proposed two induction machines system in order to get a desired mechanical power from variable power of a PVA. It proves that the stability of this system is assured although the PVA is a non-constant voltage source. In addition, this paper proposes the use of a twin stator induction machine instead of two coupled induction machines construction. This new system can be implemented compactly. It is shown by experiments that the system can easily and stably generate a desired mechanical power under the condition of tracking the maximum power operating point of the PVA without measuring the operating voltage and a mechanical load demand.