CAPACITANCE REQUIREMENTS OF SELF-EXCITED INDUCTION GENERATORS

This paper presents a simple method for computing the minimum value of capacitance required for initiating voltage build-up in a three-phase self-excited induction generator. Based on the steady-state equivalent circuit model, a consideration of the circuit conductances yields a 6th-degree polynomial in the per-unit frequency. The polynomial can be solved for real roots, which enables the value of C(min) to be calculated. Critical values of load impedance and speed, below which the machine fails to self-excite irrespective of the capacitance used, are found to exist. Closed form solutions for C(min) are derived for no-load and inductive loads. Using the same numerical approach, an iterative procedure is also developed for predicting the capacitance required for maintaining the terminal voltage at a preset value when the generator is supplying load. Experimental results obtained on a 2 kW induction machine confirm the feasibility and accuracy of the proposed methods.