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This paper presents a voltage injection method for reconstructing phase currents from current signals measured on single current-shunt circuits with cost-effective and high-performance configurations in the pulsewidth modulation (PWM) inverters that are used for digital appliances. This method involves the injection of voltage signals at the carrier frequency for reconstructing the phase currents in PWM inverters using a single current sensor in the dc-link. It uses minimum signals to reduce the voltage and current harmonics caused by the injected signals. The vector of the injected voltage is at a minimum distance from the original reference to ensure the measurement time in the reconstruction of the phase currents. An injection sequence control method is also proposed to avoid an abrupt change in the injection signals. A PWM scheme for splitting phase voltages is proposed to reduce any audible noise, especially in low-speed operation. The proposed method reconstructs the phase currents with signals from a single current sensor and minimizes the amplitude of the injected signals to reduce the harmonics at audible noise frequencies in the injection signals. Experimental results showed the effectiveness of the proposed method. Index Terms--AC motor drives, current reconstruction, noise, pulsewidth modulated (PWM) inverters.

This paper presents an analysis of inherent position sensors in ac machines. In ac machine drives, the attachment of a mechanical transducer or a structural modification is necessary for zero or low speed operation where the back electromotive force (EMF) is zero or low. However, designs for introducing a measurable saliency in the spatial impedances of structurally symmetrical ac machines without any periodic modulation will make it possible to build sensorless drives at zero or low speed. Thin bridges in the core slots of a stator or rotor take the role of inherent magnetic sensors in ac machines. In structurally symmetric ac machines, such as a surface mounted permanent magnet synchronous machine (SMPMM) or induction machine (IM), the saliency in the spatial impedances is built by the spatial saturation on the leakage flux paths. This can be explained by a machine model that considers the spatial saturation, analyzed by the finite element method, and verified experimentally on test machines. Employing this phenomenon in the design or selection of symmetric ac machines will enable zero- or low-speed operation in sensorless drives. Index Terms--AC machines, ac motor drives, magnetic analysis, transducers.

This paper proposes a hybrid speed estimator that gives the synergetic effect between the model- and the saliency-based field orientations for induction motor drives. The model-based field orientation consists of a flux observer with an adaptive speed estimator that has unstable regions at zero frequency and zero speed. Saliency-based flux orientation utilizes magnetic saliencies caused by saturation and high-frequency injection that causes the torque ripples due to the chattering. The chattering is caused by the higher cutoff frequency of the flux-angle estimation to keep its high dynamics. The proposed method compensates both faults and realizes complete speed estimation from zero to high-speed condition including zero stator frequency. Index Terms--Flux observer, high-frequency voltage injection, hybrid speed estimator, induction motor drives.

This paper presents the analysis of a surface-mounted permanent-magnet (SMPM) machine for the sensorless control scheme based on the high-frequency fluctuating voltage signal injection method. A simplified high-frequency model of an SMPM machine in the estimated rotor reference frame is developed and a sensorless rotor position and speed estimation algorithm is described. To support this, the high-frequency impedances of an SMPM machine are analyzed by finite-element analysis (FEA) and compared with measurement results using a pulsewidth-modulation (PWM) inverter system under various injection conditions. The results of the FEA and measurements are coincident with each other with some errors due to the nonlinear behavior of the PWM inverter and the SMPM machine. The analysis results give physical insights into selecting the injection conditions for sensorless operation of the SMPM machine even though adjustments considering nonlinear behaviors of PWM inverters are required in the actual operation for the desired performance. The experimental results of speed and position control using a commercial SMPM machine are presented based on the analysis of the SMPM machine for the sensorless control algorithm. Index Terms--High-frequency signal injection, sensorless operation, surface-mounted permanent-magnet (SMPM) machine.

This paper presents a new sensorless control scheme of a surface-mounted permanent-magnet (SMPM) motor using high-frequency voltage signal injection method based on the high-frequency impedance difference. In the SMPM motor, due to the flux of the permanent magnet, the stator core around the q-axis winding is saturated. This makes the magnetic saliency in the motor. This magnetic saliency has the information about the rotor position. The high-frequency voltage signal is injected into the motor in order to detect the magnetic saliency and estimate the rotor position. In this paper, the relationship between the high-frequency voltages and high-frequency currents is developed using the voltage equations at the high frequency, and the high-frequency impedance characteristics are analyzed experimentally under various conditions. The proposed sensorless control scheme makes it possible to drive the SMPM motor in the low-speed region including zero speed, even under heavy load conditions. The experimental results verify the performance of the proposed sensorless algorithm. Index Terms--High-frequency signal injection, sensorless drive, surface-mounted permanent-magnet (SMPM) motor.

This paper describes a torque, speed, or position control method at standstill and low speed in the interior permanent-magnet motor (IPMM) drive system without any rotational transducer. While IPMMs have originally magnetic saliency, it varies according to the load conditions and the control performance can be easily degraded. In this paper, the saliency or impedance difference is used as the conventional methods and, nevertheless, in order to amplify the difference containing the information of the rotor angle and to maintain a reasonable performance under any load condition a high-frequency injection scheme is proposed. A speed and position estimation scheme based on the characteristics of the high-frequency impedance is proposed. The scheme extracts the high-frequency impedance components related to the rotor position. An initial angle estimation scheme for starting from an arbitrary rotor position is also proposed. It can distinguish the north magnetic pole position from the south one in several decade milliseconds. The proposed scheme enables position control of a transducerless or position-sensorless IPMM. The experimental results clarify the satisfactory operation of the proposed position control algorithm under any load condition. Index Terms--Motor drives, position estimation, sensorless control.

A harmonic injection-based algorithm is proposed for a digitally controlled inverter. Named sensorless field-orientation algorithm, its implementation only needs an adjustment in the software of the inverter without requiring changes in the existing hardware. Its use, on the other hand, provides reasonable torque control capability at zero and low stator frequency. Even during heavily loaded conditions, there is no vibration and minimal audible noise.

This paper presents a position sensorless control scheme of a synchronous reluctance motor (SynRM) combining a high-frequency current injection method in the low-speed region and the flux estimation method based on the stator voltages in the high-speed region. The rotor has inherent saliency, and its angle can be estimated from d-axis stator current injection and the appropriate signal demodulation in a low-speed region. In the high-speed region, the rotor angle can be estimated by the stator flux from the voltage information. This scheme gives a robust and dynamic estimation of the rotor angle independent of the operating conditions, including speed and load conditions. Experimental results of closed-loop speed and position control with a 3.75-kW axially laminated SynRM are given to verify the proposed scheme. Index Terms--Current injection method, sensorless control, synchronous reluctance motor.