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This paper presents a comprehensive evaluation of several direct torque control (DTC) strategies for permanent magnet synchronous machines (PMSMs), namely DTC, model predictive DTC, and duty ratio modulated DTC. Moreover, field-oriented control is also included in this study. The aforementioned control strategies are reviewed and their control performances are analyzed and compared. The comparison is carried out through simulation, finite-element analysis, and experimental results of a PMSM fed by a two-level voltage source inverter. With the intent to fully reveal the advantages and disadvantages of each control strategy, critical evaluation has been conducted on the basis of several criteria: Torque ripple, stator flux ripple, switching frequency of inverter, steady-state control performance, dynamic response, machine losses, parameter sensitivity, algorithm complexity, and stator current total harmonic distortion.

In this paper, the effectiveness of a simplified characterization method for permanent magnet machines is evaluated through performance sensitivity analysis. Performance sensitivity analysis is a novel way to evaluate the effectiveness of any identification method, as it investigates the effects of parametric errors upon the output performance of a machine. Parametric errors are due to inaccuracies during the identification process. This evaluation tool was validated using a 10-kW SmCo interior permanent magnet machine characterized using two different identification methods. A detailed identification procedure is used as the basis for evaluating a simplified method. The performance experimental data were collected using torque controllers based on the parameters extracted with both approaches. This information is used to perform the sensitivity analysis over the operating range of the machine. Finally, the results are compared and analyzed to determine the effectiveness of the simplified characterization method and its implications on the control performance.

Partial demagnetization is studied in detail in this paper to understand its effects and develop a robust detection method. The voltage and current harmonics can be used to indicate that a fault exists but this method cannot always differentiate demagnetization from eccentricity. The inductance characteristics of the direct rotor oriented axis are used to verify the harmonic-based detection findings. The detection of partial demagnetization is improved by determining the incremental inductance over a range of direct axis currents; this way secondary ‘knees’ caused by asymmetrical rotor saturation are found. This asymmetrical saturation can be determined with the inductance. A detailed discussion and observation of the effect of partial demagnetization is novel compared to the literature. Three types of demagnetization are discussed in this paper: uniform demagnetization, partial demagnetization of one magnet and removal of three magnets from the rotor. Finite elements analysis is used to simulate the changes in the incremental inductance waveforms under each type of demagnetization. Experimental data is introduced in this paper to validate the incremental inductance results for the removal of three magnets.

This paper introduces a detailed nonlinearity characterization technique for insulated-gate bipolar transistor inverters in a drive system which is able to measure device nonlinearities. Methods are derived from measurements of the voltage on the inverter phases. These measurements are obtained while applying a set of direct currents to an electrical machine. These methods are then applied to tests using alternating current. The study of inverter nonlinearities is useful in order to improve controller accuracy, implement sensorless controllers, and conduct condition monitoring. These methods fulfill the need to characterize each device in an inverter. In addition to characterizing every device using either AC or DC current, the method is resistant to noise; for these reasons the method is applicable in the field. Simulations and experimental work demonstrate the benefits and applicability of the methods.

High performance operation of interior permanent magnet machines relies heavily upon machine characteristics or parameters. Thus the performance of the control is heavily tied to this determination of machine parameters, and any errors therein can degrade performance. Proper characterization can help towards the goal of the highest performance controller, but knowing the effects of parameter variation can allow the control designer to predict what variations will have the largest negative effect upon performance. This method uses the most accurate characterization methods to date, and finds the effects of variation of these found parameters. This analysis can be used to develop controllers sensitive to parametric change. Once the actual parameters are found, the effect of parameter variation upon output performance is determined.

This paper presents a simplified experimental method to accurately estimate the parameters of a permanent magnet synchronous machine. It accounts for the self and cross saturation effects over the entire operation range of the machine. Experimentally, the procedure is performed only using the components typically used in a traction drive system, such as current sensors, a position encoder, a DC link voltage sensor and a digital signal processor. AC voltage sensors, analog filtering hardware and additional measuring equipment are not required. With fewer components, the method is suitable for machine commissioning in the field. Therefore, the process of characterization is no longer confined to a laboratory environment. The method was experimentally verified using a 10-kW SmCo and a 125-kW NdFeB interior permanent magnet machine.