Motomichi Ohto

Analysis of permanent-magnet machine for sensorless control based on high-frequency signal injection

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.

Analysis of permanent magnet machine for sensorless control based on high frequency signal injection

This paper presents the analysis of the surface mounted permanent magnet (SMPM) machine for the sensorless control algorithm using the high frequency fluctuating voltage signal injection method. A simplified high frequency model of a SMPM machine in the estimated rotor reference frame is developed. Then, the impedances of a SMPM machine at high frequency are analyzed by finite element analysis (FEA) and is compared with impedance measurements using a pulse width modulation (PWM) inverter system under various injection conditions. The results of the FEA and high frequency impedance measurements are coincident with each other, and give physical insights in sensorless operation of the SMPM machine. The experimental results of speed control and position control using a commercial SMPM machine are presented based on the analysis of the SMPM machine for the sensorless control algorithm.

Design and selection of AC machines for saliency-based sensorless control

This paper presents a design method for introducing a measurable saliency in the spatial impedances of structurally symmetrical AC machines without any periodic modulation and considerations in selection of AC machines for saliency-based sensorless control. In the structurally symmetrical AC machines such as surface mounted permanent magnet synchronous machine (SMPMM) and induction machine (IM), the saliency in the spatial impedances is built by the spatial saturation on the leakage flux paths. It is explained by the machine model considering the spatial saturation, analyzed by finite element method, and verified experimentally on the test machines. In the design or the selection of AC machines, the consideration of this phenomenon can make any saliency-based sensorless control for zero or low speed operation viable. The selection of AC machines and the control accuracy assessment for saliency-based sensorless control are discussed.

Encoderless Servo Drive With Adequately Designed IPMSM for Pulse-Voltage-Injection-Based Position Detection

This paper presents a technology fusion of encoderless control technique and encoderless-specialized motor applied for servo drive applications. First, a fast encoderless control technique which employs a high-frequency pulsating signal injection method with square-wave pulse voltage at d -axis is proposed. The estimation principle is almost the same as that of a resolver, and the control technique includes a fast initial position estimation algorithm based on magnetic hysteresis phenomenon. Next, a prototype interior permanent-magnet synchronous motor is designed to act like a resolver. Then, evaluation results of the prototype encoderless drive system are reported. Finally, the prototype system is confirmed to fulfill major servo specifications of about 10-b net resolution of the position detection at standstill and more than 60-Hz speed control bandwidth in operation speed from 0 up to 1000 min-1 . In conclusion, the proposed encoderless drive system is verified to achieve major control performances almost comparable to those of encoder-assisted servo drive systems.

Harmonic Loss and Torque Analysis of High-Speed Induction Motors

In this paper, we investigate the harmonic losses and torque of high-speed induction motors from both results of measurements and calculations. The calculation method of harmonic core losses and torque has been developed from the viewpoint of practical and useful application to rotating machines. This method is based on the combination of 2-D and 1-D finite-element methods with approximated core loss modeling, which requires only few material constants obtained by Epstein frame tests. The frequency and the flux density dependence of the core loss are modeled by the 1-D analysis along the thickness direction of electrical steel sheets. Furthermore, the proposed method can decompose the total loss and torque into harmonic components because of its simple modeling. This decomposition reveals the main loss factors and the decrease in the torque of the high-speed induction motors due to the harmonic core losses. The validity of the calculation is confirmed by measurements. In addition, useful information for the design of high-speed induction motors is obtained by using the proposed method.

Equivalent circuit modeling of induction motors considering stray load loss and harmonic torques using finite element method

A novel equivalent circuit of induction motors is investigated by the finite element method in order to take into account effects of stray load loss and harmonic torques. The characteristics of the motor obtained by the proposed and conventional circuits are compared with the measured results in order to confirm the validity and usefulness of the proposed circuit. It is revealed that the result of the proposed circuit is more accurate than the direct solution of the finite element method because the circuit takes into account the effect of the iron loss, which is neglected in the equations of the finite element method.

Characteristics of a novel segment type switched reluctance motor using grain-oriented electric steel

The authors developed a novel segment type switched reluctance motor (SRM) as a rare earth less motor. The torque was increased by 40% and radial force was decreased by 76% compared with the same size VR type SRM. In this paper we propose a new type rotor using grain-oriented electric steel for the segment core. We compare the torque and efficiency characteristics with a non-oriented electric steel type by a finite element method and show effectiveness of the new type rotor

Design, Modeling, and Control of an IPMSM With an Asymmetric Rotor and Search Coils for Absolute Position Sensorless Drive

In this paper, a design methodology and control algorithms of an interior permanent-magnet synchronous machines (IPMSM) for absolute position sensorless drive are proposed. In conventional research on absolute position sensorless control, initial motion of the rotor was inevitable, which was not preferred in many applications. In order to eliminate the initial motion, an IPMSM with an asymmetric rotor and search coils is devised. In the proposed IPMSM, the information of the absolute position is included in the voltage signals at the search coils. By measuring and analyzing the search coil voltages, the absolute position can be estimated without any initial motion of the rotor. Overall performances of the proposed motor are evaluated through rigorous finite element analyses and experimental tests.

Harmonic loss analysis and air-gap optimization of high speed induction motors

The Air-gap width of high speed induction motors is optimized in order to improve the efficiency. First, the loss and torque of the conventional motor are calculated by the finite element method in order to separately estimate the harmonic components. It is revealed that the largest loss component at high speed conditions is the harmonic core losses by the stator and rotor slots. It is also revealed that these harmonics also cause considerable decrease in the torque of the motor at the high speed conditions. Next, the air-gap width of the motor is optimized by the finite element method. The optimized motor is manufactured and measured in order to verify the characteristics. It is clarified that the efficiency of the optimized motor is significantly improved by the decrease in the loss as well as the increase in the torque.

Encoderless servo drive with adequately designed IPMSM for saliency-based position detection

This paper presents a newly developed encoderless servo drive with an adequately designed interior permanent magnet synchronous motor (IPMSM). The motor for encoderless servo drive is designed to act like resolver incorporated with saliency-based position detection technique. The resolution of the position detection and sustainability against load are considered in the design. As the position detection a pulse voltage injection technique is employed to realize higher dynamics in the control performance than conventional technique. This paper mainly focuses on the technology fusion in between motor design and control design. Finally, the fast initial pole positioning, the high-dynamics performance in position and speed control, which are sufficient for servo drive applications, are shown in this paper. The net-resolution of the position detection is about 10 bits, and the accuracy of positioning is less than 1 mechanical degree in position control at steady state.