In permanent magnet synchronous machine (PMSM) design, a limited number of stator and rotor slots distorts the air-gap flux distribution and its effective length. It causes machine parameters to vary with the rotor position. The rotor flux linkage harmonics introduce non-sinusoidal back-EMF, which causes current harmonics when conventional PI current controller is adopted. Those machines suffer from high frequency torque ripple due to air-gap flux harmonics in low speed region. However, in high speed region, where the torque ripple is filtered out by the mechanical system, the torque ripple may be disregarded. In this case, torque-ripple suppression methods and the associated harmonic current components generate losses. Therefore, a sinusoidal current control is required to reduce undesired harmonic losses. In this manner, this paper focuses on the sinusoidal current control strategy based on harmonic voltage injection, which requires knowledge of rotor magnet flux linkage harmonics. This paper also proposes both offline and online schemes for identification of rotor magnet flux linkage harmonics. These methods do not require any proprietary machine design details such as the shape of stator or rotor for finite element analysis (FEA). Commonly used PI plus resonant (PIR) controller is also designed and its disadvantages in terms of speed-dependent gain and stability, in comparison to the proposed scheme, are highlighted. Finally, experimental results are presented to compare the proposed scheme with the conventional method at different operating conditions.

This article proposes a new maximum torque per ampere (MTPA) control strategy for an induction motor (IM) controlled by the scalar ( v / f ) method. In scalar control, constant air-gap flux control is generally adopted for IM drives to provide the same torque capability in all operating ranges. However, this control method results in poor motor efficiency due to excessive stator current at light loads. This work proposes a new MTPA control method to minimize the stator current amplitude based on reactive power without measuring the rotor mechanical speed, resulting in improved system efficiency at light loads. In addition, this method proposes an online machine parameter compensation method. Thus, this proposed method is robust to parameter variations. Simulation and experimental results are provided to verify the performance of this MTPA control strategy.

This paper presents a simple discontinuous pulse width modulation (DPWM) switching scheme to reduce the switching loss of a single DC-link dual two-level inverter fed an open-end winding (OW) induction motor (IM). The dual inverter system is attractive in many applications due to higher DC-link voltage utilization. Additionally, the OW motor has the potential fault-tolerant capability. However, the use of the dual inverter results in reduced system efficiency due to increased power losses in the inverter. Moreover, an OW motor inherently suffers from a zero-sequence current (ZSC) issue because the open neutral point of the stator windings provides the ZSC path. The ZSC causes negative effects in the system, such as an additional power loss and total harmonic distortion (THD). Thus, this work proposes an optimal DPWM scheme to reduce the inverter loss while suppressing the ZSC. Additionally, this work proposes a strategy to make the average power loss of each inverter equal. The performance of the proposed method is discussed in terms of switching power loss reduction and ZSC suppression. Simulation and experimental results are provided to verify the effectiveness of the proposed DPWM scheme.

In vector-controlled drive systems, a position sensorless drive with a single current sensor (SD-SCS) is an attractive system due to the minimum number of sensors. However, when the saliency-based SD-SCS is applied, the position estimation accuracy is deteriorated due to the errors in the injected pulsewidth-modulated voltage and the reconstructed current. This article proposes a current-derivative-based sensorless control using a three active vector pulsewidth modulation (TAVPWM) to enhance the saliency-based SD-SCS. First, the TAVPWM scheme, which eliminates the current reconstruction dead zone in the low-modulation region, is adopted to improve the low-speed drive. Next, the derivatives of the phase currents are utilized and analyzed to minimize the position estimation error in the overall operating regions. Finally, the transition strategy with respect to the speed is proposed for the full-speed sensorless drive. Owing to the proposed method, the switching frequency increases up to 16 kHz and the audible noise is virtually eliminated in the saliency-based SD-SCS. Furthermore, the enhanced dynamic performance is verified by various experimental results.

This study proposes a novel pulsewidth modulation (PWM) strategy in high modulation index (MI) regions for the open-end winding permanent magnet synchronous motor fed by the dual inverter with the common dc bus. The dual-inverter system is getting attention due to the higher voltage utilization and the potential fault-tolerant capability. However, the dual-inverter system inherently suffers from the zero-sequence current (ZSC) flowing due to the opened neutral point of the stator windings and the common dc bus. This ZSC causes negative effects, such as power loss and torque ripple. Various PWM schemes have been proposed to suppress the ZSC. However, the conventional methods focus on a linear MI region and have performance degradation due to the limited voltage modulation margin. This study proposes simple PWM schemes for the ZSC control in the overmodulation and six-step regions. The proposed method can suppress the ZSC while maximizing the voltage utilization with minimum switching loss increase. Simulation and experimental results are provided to verify the performance of the proposed PWM strategy.

In this paper, a new maximum torque per ampere (MTPA) control method for surface permanent magnet synchronous motors (SPMSMs) controlled by the scalar control (v/f) method is proposed. The scalar control is a sensorless method that controls only the magnitude and the frequency of the stator voltage vector without the information of the rotor position. This method suggests the injection of the high frequency voltage signal in the stator current vector reference frame, which can be calculated from the measured phase currents, to avoid the use of rotor position information. In addition, this method adjusts only the magnitude of the stator voltage to minimize the stator current based on the calculated input power. Another merit of this method is the robustness of the MTPA control to machine parameter errors or variations. With this proposed method, the stator current can be minimized in the whole speed-torque range and the drive efficiency can be improved. Simulation and experimental results are provided to verify the performance of this control strategy.