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The paper presents a novel approach to detect magnet faults such as local demagnetization in brushless permanent-magnet motors. We have developed a new form of analytical model that solves the Laplacian/quasi-Poissonian field equations in the machine's air-gap and magnet element regions. We verified the model by using finite-element software in which demagnetization faults were simulated and electromotive force was calculated as a function of rotor position. We then introduced the numerical data of electromotive force into a gradient-based algorithm that uses the analytical model to locate demagnetized regions in the magnet as simulated in the finite-element package. The fast and accurate convergence of the algorithm makes the model useful in magnet fault diagnostics.