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This article proposes an online maximum torque-per-Ampere (MTPA) control of an interior permanent-magnet synchronous motor (IPMSM) based on the square-wave voltage signal injection. Because the proposed method does not rely on a position sensor, it is applicable to sensorless IPMSMs. The proposed algorithm consists of a dynamic inductance estimator, frequency-adaptive flux observer, and an MTPA tracking controller. The proposed inductance estimation utilizes the pulsating square-wave voltage injection, which can maximize the injection frequency, and the dynamic performance can be preserved during the signal injection. Through the online flux and inductance estimation, the magnetic saturation of the IPMSM and the temperature variation can be fully considered in the MTPA control. The conventional rotor position estimator is replaced with the MTPA tracking controller, which does not rely on offline commissioning parameters. The proposed algorithm can operate under both the torque control and speed control mode, and accurate torque control on MTPA curve can be achieved. The simulation and experimental results demonstrate that the proposed method accurately tracks the MTPA point up to 200% of the rated torque in the mid- and high-speed region. [ABSTRACT FROM AUTHOR]

For stable and efficient drives of interior permanent-magnet synchronous machines (IPMSMs), stator flux should be observed across a wide speed range. However, distortions such as a dc offset and low-order harmonics are contained in the estimated flux due to various reasons. In this paper, a distortion-minimizing flux observer is proposed to suppress the effects of dc offset and harmonics by implementing frequency-adaptive observers. The proposed frequency-adaptive flux observer is designed to extract a fundamental flux while keeping a simple structure even if the rotating speed of the IPMSM varies. The fundamental flux could be estimated by the proposed current- and voltage-model based flux observer, which is implemented with the frequency-adaptive observer and harmonic extractors. Moreover, parameter sensitivity and model transition are discussed to improve the performance of the proposed observers. The validity and effectiveness of the proposed methods are verified with simulation and experimental results. [ABSTRACT FROM AUTHOR]

This paper addresses the inverter nonlinearity of a three-level T-type inverter. The main causes of the nonlinearity are pulse shaping, pulse skipping due to narrow pulses for the dead time, and voltage drop of the switching devices. Although the same causes have existed in two-level inverters, the pulse skipping phenomenon and results are quite different in the case of the three-level T-type inverter. The effects of pulse shaping and skipping have been investigated and discussed. In addition, the voltage drop of the switching devices has been considered in conjunction with the conduction path of the T-type inverter. Compensation methods based on the pulse width modulation (PWM) of T-type inverter to alleviate the inverter nonlinearity have been proposed from research results. The proposed methods could be easily implemented by adding appropriate offset voltages to the voltage references of the inverter in PWM. Furthermore, a neutral voltage balancing method of a three-level T-type inverter has been proposed in conjunction with the proposed PWM methods using offset voltage. Through extensive experimental tests, the fifth- and seventh-harmonic components of the current are conspicuously reduced along with the even harmonics. The neutral voltage of the inverter can be balanced effectively with the proposed offset voltage adjustments as well. [ABSTRACT FROM AUTHOR]