Abstract
In order to obtain accurate angular position and velocity from resolver signals, Resolver-to-Digital Conversion (RDC) is necessary. However, there are inevitable harmonics in resolver signals, which will deteriorate RDC accuracy seriously. Although the harmonics of resolver signals can be suppressed by using low-pass filters (LPFs), the phase lag of LPFs will result in additional errors in RDC, especially for the suppression of lower-order harmonics. In this paper, a novel filtering strategy is proposed for resolver signals by combining two complementary filters (CFs) with a frequency locked loop (FLL). Firstly, CFs are designed for the sinusoidal and cosinusoidal channels by using the natural orthogonality in the resolver signals. Each CF consists of two LPFs assisted by the estimated frequency from FLL with a frequency discriminator and a second-order observer. Secondly, a frequency discriminator is designed to detect the frequency error between the resolver signals before and after CFs. Thirdly, a second-order observer is designed to estimate the signal frequency by regulating the frequency error. Compared with conventional LPFs, FLL based CFs can suppress the low-frequency harmonics without phase lags and can improve RDC accuracy. Simulation and experimental results demonstrate the effectiveness of the proposed strategy.
Highlights
As a kind of shaft angle transducers with high accuracy, strong reliability, and great ruggedness, resolvers have been widely used in many harsh environments, such as aerospace, navigation, ordnance, industrial robots, and electric vehicles, etc. [1]-[5]
Since resolvers can only output two orthogonal signals modulated by high-frequency excitation, resolver-todigital conversion (RDC) is necessary to obtain rotor position and velocity [6]
The accuracy of RDC depends on the quality of resolver signals, which are usually disturbed by many unexpected factors, such as amplitude asymmetry, DC offsets, quadrature error, and harmonics [8]
Summary
As a kind of shaft angle transducers with high accuracy, strong reliability, and great ruggedness, resolvers have been widely used in many harsh environments, such as aerospace, navigation, ordnance, industrial robots, and electric vehicles, etc. [1]-[5]. Low-pass filter (LPF) is the most common solution to suppress harmonics in resolver signals. In [16] and [17], low-pass FIR filters were used to suppress harmonics and noises in resolver signals. These filters have fixed cutoff frequency which design is a dilemma in applications. If the harmonic frequency to be filtered is very low, only a lower cutoff frequency can be selected, which will cause a large phase lag in the fundamental component of resolver signals. By using FLL based CFs, the low-frequency harmonics can be suppressed in revolver signals without phase delay.
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