416 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 19, NO. 2, JUNE 2004 A Novel Hybrid Isolated Generating System Based on PV Fed Inverter-Assisted Wind-Driven Induction Generators S. Arul Daniel and N. AmmasaiGounden Abstract—Isolated renewable energy systems based on hybrid wind-solar sources are considered as feasible and reliable options instead of wind-diesel systems. An isolated hybrid scheme em- ploying a simple three-phase square-wave inverter to integrate a photovoltaic array with a wind-driven induction generator has been proposed for the first time. A dynamic mathematical model of the hybrid scheme with variables expressed in - synchronous reference frame has been developed. The model is implemented in the power system blockset platform and a comparison has been made between transients simulated and transients obtained in an experimental prototype. Close agreement between experimental and the simulated waveforms has been observed, which validates the model. Index Terms—Hybrid wind-solar system, inverter, photovoltaic array, wind-driven induction generator. NOMENCLATURE Thermal voltage (in volts). , Quadrature and direct-axis machine currents (in amps). Current at the operating point of the array (in amps). Reverse saturation current (in amps). Light-generated current (in amps). Short-circuit current (in amps). , Per phase inductances of stator, rotor (referred to the stator winding) [in henries]. Per phase magnetizing inductance (in henries). , Real power delivered by PV array and IG (in watts). Real power fed to the load (in watts). Series resistance of the array (in ohms). , Quadrature and direct-axis machine voltages (in volts). Open-circuit voltage of the array (in volts). Voltage at the operating point of the array (in volts). Load voltage per-phase (in volts). Load resistance (in ohms). , Resistances of stator, rotor (referred to the stator winding) [in ohms]. , Angular speeds of reference-frame and rotor (rad/s). Manuscript received December 4, 2002. The authors are with the Department of Electrical and Electronics Engi- neering, National Institute of Technology (formerly Regional Engineering College), Tiruchirappalli 620 015, India (e-mail: daniel@nitt.edu; ammas@ nitt.edu). Digital Object Identifier 10.1109/TEC.2004.827031 I. INTRODUCTION I T is well known that renewable energy sources are attractive options for providing power in places where a connection to the utility network is either impossible or unduly expensive. Photovoltaic (PV) generation systems and isolated wind-electric systems are considered among the renewable systems to be vi- able alternatives for the designer of such remote power supplies. Nevertheless, systems based on either wind or solar energy are unreliable due to seasonal and diurnal variations of these re- sources. Earlier, wind-diesel systems were employed to over- come the diluteness of the renewable resources, but the recur- ring need of the diesel oil and frequent maintenance requirement of the diesel-generators made such a system to be inappropriate for off-grid supplies [1]. The control of such a scheme is also far from straightforward, especially where there is a high wind penetration [2]. Furthermore, it decreases the advantage of clean and nonpollution energy achieved from the renewable sources. A system that is based fully on renewable resources but at the same time reliable is necessary and hybrid wind and solar sys- tems with a small battery storage meet these requirements. Recently, a hybrid scheme employing wind-turbine perma- nent-magnet (PM) alternator and PV array was proposed, in which the sources were connected in series through dc–dc con- verters [3]. Subsequently, a simpler configuration connecting the sources in parallel was attempted [4]. Further, for supplying ac loads in these hybrid wind-solar schemes, the varying amplitude varying frequency of the stator voltage of the PM alternator and the variable dc voltage of the PV array have to be suitably conditioned using complex power-electronic interfaces [5]–[7]. However, for any off-grid system, it is desirable to install components and their associated controls that are maintenance free and economical. In this situation, schemes employing wind-driven induction generators with a simple power-electronic interface have been attempted. Though induction machines are robust, inexpensive, require little maintenance and possess higher power-weight ratio over dc and PM alternators, wind-driven capacitor-excited induction generators are not preferred in remote power systems due to their unsatisfactory voltage regulation and frequency variation [8], [9]. To overcome these limitations, instead of providing reactive power using a three-phase capacitor bank, inverter-as- sisted induction generators (IGs) were proposed. Earlier, Enes et al. proposed IG schemes with PWM inverters where the excess energy was sent to the utility grid to maintain the stator voltage and frequency constant or a speed governor to control 0885-8969/04$20.00 © 2004 IEEE