Mohd A. Alhamadi

A high precision resolver-to-DC converter

A newly developed resolver converter, providing a pseudolinear voltage proportional to the shaft angle, is presented. This converter is based on a new concept involving the absolute values of the demodulated sine and cosine resolver signals together with a dedicated linearization technique. The converter enables instantaneous determination of the mechanical angle with a theoretical error of nonlinearity below 0.011/spl deg/ over the 360/spl deg/ range. The practical performance of this converter is compared to that of a 10/sup 5/ pulses per revolution optical encoder arrangement. The theory of operation, computer simulation, full circuit details, and experimental results are given.

A novel resolver-to-360/spl deg/ linearized converter

A novel and simple resolver-to-dc converter is presented. It is shown that by appropriate processing of the sine and cosine resolver signals, the proposed converter may produce an output voltage proportional to the shaft angle. A dedicated compensation method is applied to produce an almost perfectly linear output. This enables determination of the angle with reasonable accuracy without a processor and/or a look-up table. The tests carried out under various operating conditions are satisfactory and in good agreement with theory. This paper gives the theoretical analysis, the computer simulation, the full circuit details, and experimental results of the proposed scheme.

A Resolver Angle Estimator Based on Its Excitation Signal

A resolver generates a pair of signals proportional to the sine and cosine of the angular position of its shaft. A new low-cost method for converting the amplitudes of these sine/cosine transducer signals into a measure of the input angle without using lookup tables is proposed. The new method takes advantage of the components used to operate the resolver, the excitation (carrier) signal in particular. This is a feedforward method based on comparing the amplitudes of the resolver signals to those of the excitation signal together with another shifted by pi/2. A simple method is then used to estimate the shaft angle through this comparison technique. The poor precision of comparison of the signals around their highly nonlinear peak regions is avoided by using a simple technique that relies only on the alternating pseudolinear segments of the signals. This results in a better overall accuracy of the converter. Beside simplicity of implementation, the proposed scheme offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal.

A New Low Cost Linear Resolver Converter

A new low cost converter topology is proposed for sinusoidal position encoders. The converter enables determination of the angle from the sine and cosine signals of the encoder. When used with resolvers, the implementation of the present scheme takes advantage of the available excitation signal used to operate the device. This trigonometric reference signal is optimally used to generate an analogue signal equivalent to a digital look-up table (LUT). This enables determination of the mechanical angle without using LUT, A/D, and D/A converters. The scheme is optimized in order to achieve highest possible precision. Beside simplicity of its implementation, the proposed converter offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal. The converter was implemented using ordinary low-cost analog components. The theory of operation, computer simulation, and experimental results are given.

Three-dimensional finite element analysis of permanent magnet brushless DC motor drives-status of the state of the art

This paper reviews advances in the state of the art of applying three-dimensional finite-element (3-D-FE) magnetic field computation techniques to the analysis and quantification of parameters and performance of permanent magnet (PM) brushless DC motors as components of brushless DC drives. The application of the powerful 3-D-FE formulation based on the coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) concept to a case study PM brushless DC motor with skewed permanent magnet mounts is reviewed and summarized. This large-scale simulation of such a motor drive system is shown to be successfully implementable using workstation type computer environments.

A new iterative learning control method for PWM inverter current regulation

AC servomotor speed or current controller based on PI control and/or optimal control, can not eliminate the cyclical fluctuations of speed or current when subject to periodic disturbances. PWM inverters output waveforms are distorted by dead-time effect, which is cyclical type disturbances. Conventional dead-time compensation methods based on feedforward techniques, using current reference polarity, do not resolve these effects around zero current crossing area. A new current regulation method based on iterative learning control technique is proposed in order to reduce the distortions caused by both the dead-time and the zero crossing problems.

A Novel Converter for Sinusoidal Encoders

The paper presents a novel and low cost method for determining the angle from sine and cosine signals generated by angular position sensors such as resolvers and sinusoidal encoders. The proposed scheme is based upon the use of the pseudo-linearity of sinusoidal signals around zero crossings. By inputting the transducer signals to a programmable weighted summer, and using simple trigonometry, an analog output made up of 16 pseudo-linear segments may be generated. These segments cover the full 360deg range of input angle, and are identifiable using a set of 4 generated binary outputs. The binary outputs enable crude measurement of the angle with a step of 22.5deg, while the analog output refines measurement by enabling precise determination of the angle with an overall theoretical error of 0.018deg. The converter was built using basic analog components. Experimental results generated with a revolver showed excellent agreement with theory and simulation.

Optimization of the skew angle of rotor magnetic poles in permanent magnet machines based on the inverse problem method

This paper presents optimization of the skew angle of rotor magnetic poles in permanent magnet class of machines. The skew angle optimization is achieved using the gradient based inverse problem methodology. The paper introduces the armature winding flux linkages and associated induced EMFs for the first time as the object function. In the mean time, this object function involves the use of stored energy and excitation perturbation techniques. An example 1.2 HP permanent magnet brushless DC machine is used to demonstrate the validity and usefulness of the method.

A resolver converter based upon a novel open-loop technique

The paper presents a novel technique for the determination of the angle from slowly-varying quadrature co- sinusoidal signals produced, for example, by position sensors. In the presented scheme applied to a resolver, the separately generated constant-frequency sine wave used for exciting the resolver together with an additional cosine wave are used as reference against which the amplitudes of the angle-dependent demodulated resolver sine and cosine signals are compared. At the instant equality between respective amplitudes of the signals are detected, two sample and hold circuits sample a voltage proportional to the angle of the shaft of the resolver from a triangular waveform generated from the reference signals. In theory, the sample and hold devices produce identical output voltages proportional to the unknown angle of the transducer. In order to improve the precision of the proposed converter, the two sample and hold circuits outputs are fed into a multiplexer to produce a single output that takes full advantage of the accurate comparison outside the peak regions of the signals. With this method, the validated output is obtained from the accurate comparisons involving the alternating pseudo-linear segments of the trigonometric signals. Another important feature of this converter is its robustness to amplitude fluctuations in the trigonometric reference signals which are used for the excitation of the resolver. A converter based on this technique has been successfully implemented using basic electronic components. Theory of operation, computer simulation and experimental results are given.

An open-loop technique for angle determination from position encoders

The paper presents a novel technique for the determination of the angle from low-frequency quadrature cosinusoidal signals produced, for example, by position sensors. In the presented scheme applied to a resolver, the separately generated constant-frequency sine wave used for exciting the resolver together with an additional cosine wave are used as reference against which the amplitudes of the angle-dependent demodulated resolver sine and cosine signals are compared. At the instant equality between amplitudes of respective signals are detected, a sample and hold circuit samples a voltage proportional to the angle of the shaft of the resolver from a triangular waveform generated from the reference signals. This is a feed-forward method, which is an analog equivalent to digital look up table techniques. In order to improve the precision of the proposed converter, a new technique is used to take full advantage of the alternating pseudo-linear segments of the trigonometric signals. With this method, the sampling relies only on the accurate comparison outside the peak regions of the signals. A converter based on this technique has been successfully implemented using basic electronic components. Theory of operation, computer simulation and experimental results are given.