MODELING AND INVESTIGATION OF STEADY-STATE OPERATING MODES OF A SELF-EXCITED AUTONOMOUS INDUCTION GENERATOR WITH CAPACITIVE EXCITATION

Abstract

This paper investigates the steady-state operating modes of an autonomous self-excited induction generator (SEIG) equipped with a capacitive excitation system and operating under active and active-inductive load conditions. The growing demand for autonomous and decentralized power generation systems based on renewable and alternative energy sources has significantly increased interest in induction generators due to their simplicity, reliability, low maintenance requirements, and absence of a separate excitation source. However, the operation of self-excited induction generators is characterized by substantial variations in output voltage and frequency depending on load magnitude and power factor, which complicates the analysis and design of such systems.

The objective of this study is to develop and validate an improved method for calculating the static characteristics of a low-power autonomous induction generator, taking into account the variation of generated voltage frequency under changing load conditions. Unlike many conventional calculation methods that assume constant output frequency or neglect its dependence on load, the proposed approach incorporates the actual influence of load-induced frequency changes. This consideration is particularly important for low-power induction generators, which typically exhibit higher rated slip values and are therefore more sensitive to variations in operating conditions.

The proposed mathematical model is based on the equivalent circuits of both the induction generator and the induction motor load. The analysis employs a system of electrical equilibrium equations that describe electromagnetic processes in the generator-load system. To simplify calculations, the induction motor load is represented by an equivalent RL circuit with parameters dependent on motor slip. The resulting mathematical formulation enables simultaneous determination of the generator magnetizing reactance and the relative frequency of the generated voltage. This approach allows accurate prediction of generator voltage, frequency, and loadability under various operating conditions.

Using the developed methodology, static characteristics were calculated for an induction generator based on a standard squirrel-cage induction machine of type AIR80A4SU2 with a rated power of 1.2 kW. The generator was analyzed under both resistive and active-inductive loading conditions. The results demonstrate that neglecting frequency variation leads to significant errors in estimating voltage regulation, overload capability, and stable operating limits. The discrepancy becomes especially pronounced when the generator supplies induction motor loads characterized by high starting currents and variable power factors.

To verify the adequacy of the proposed model, extensive experimental investigations were carried out using a laboratory test bench incorporating an induction generator, a DC drive motor, a configurable capacitor bank, and various types of electrical loads. Experimental measurements included generator voltage, load current, rotor speed, excitation capacitance, and output power. The obtained results demonstrated good agreement with theoretical predictions. Comparative analysis of calculated and measured characteristics showed that the deviation between experimental and theoretical data does not exceed 4–6%, confirming the validity and practical applicability of the developed calculation method.

Keywords: Self-Excited Induction Generator (SEIG); Autonomous Induction Generator; Capacitive Self-Excitation; Capacitor Bank; Static Characteristics; Steady-State Analysis; Frequency Variation; Voltage Regulation; Load Characteristics; Active-Inductive Load; Overload Capability.