New RDC Method Using Trapezoidal Excitation Signal Considering Resolver Nonlinearity

The resolver is a kind of transformer that requires one excitation signal. Among numerous resolver-to-digital conversion (RDC) methods, the square wave excitation method has the advantage of being easy to demodulate and implement, but nonlinear problems may arise due to the high-frequency components in the square wave. These nonlinear problems distort the resolver output signals and make demodulation difficult. To minimize these nonlinear problems while maintaining the advantages of the square-wave excitation method, a new RDC method using a trapezoidal excitation signal is proposed in this article. The trapezoidal excitation signal is expressed through a Fourier series expansion to find the optimal point at which the total harmonic distortion (THD) along the length of the flat region is minimized. Additionally, a simple circuit for implementing trapezoidal excitation signals is also introduced. The effectiveness of the proposed method is verified through experiments.