Ryoichi Takahata

Position sensorless control method at zero speed region for permanent magnet synchronous motors based on block commutation drive

A new position sensor-less method has been developed for permanent magnet synchronous motor (PMSM) drives in zero speed regions. This method utilizes the induced voltage caused by magnetic saturation (IVMS) of PMSM. The rotor position can be detected by IVMS. Furthermore, we introduce a bi-polar pulse modulation to the zero-speed region. By this modulation, both the normal and reversal direction IVMS can be detected and the bi-direction drive achieved. The principle of the proposed method and the experimental results are discussed in this paper.

Minimum Current Start-Up Method by Combined Use of Two Position-Sensorless Controls

A start-up method for reducing the start-up current of a permanent-magnet synchronous motor (PMSM) is proposed. Minimum current start-up is achieved by combining two position-sensorless control methods that require no harmonic injection. Position-sensorless control for low-speed regions utilizes induced voltage caused by the magnetic saturation of a PMSM with a conventional block commutation drive. During acceleration of the rotor, the position-sensorless control is switched to the second method, which is based on back electromotive force with a sinusoidal commutation drive. Since unconsidered switching may result in start-up failure when the proposed start-up method is used in applications with periodic load properties, a method to determine the correct timing to change the position-sensorless control in consideration of load variation is also proposed. The proposed methods are validated in start-up tests using a reciprocating compressor with a large periodic load torque.

Low-speed position sensorless drive for highly efficient permanent magnet synchronous motor without rare-earth metals

In this paper, we discuss a position sensorless drive for an axial structure motor without rare-earth metals in a low-speed region. Since this motor has no saliency, a conventional position sensorless drive using harmonic injection cannot be applied. Therefore, we apply a position sensorless drive based on Induced Voltage caused by Magnetic Saturation (IVMS) to this motor. As IVMS becomes very small for motors without saliency, we introduce a differential amplifier and adjust its gain appropriately. We implemented this method by using a microcomputer and an analog circuit. As a result, excellent drive performance in a low-speed region was obtained in experiments for the motor (200V/11kW).

Analysis of rotor eccentricity on permanent magnet synchronous motor characteristics

This paper describes the influence of rotor eccentricity on permanent magnet synchronous motor characteristics by a magnetic field analysis and several experiments. The rotor eccentricity unbalances the magnetic force and thus increases the mechanical loss. Furthermore, a circulating current generated in two three-phase windings connected in parallel results in an increase of electric power loss in the permanent magnet synchronous motor. Therefore, we presented that the flux barrier rotor is effective to reduce the harmful effect of the rotor eccentricity.

Fast calculation of load conditions of permanent magnet synchronous machines using finite elements

This paper proposes a method of characteristics calculation for permanent magnet synchronous machines (PMSMs) using static finite element analysis (FEA) and steady-state dq-axis equations. The method calculates characteristics such as torque, voltage, current, inductances, etc. under any balanced steady-state load conditions. Various types of input condition can be selected to identify the load condition. For example, the characteristics are calculated at the load condition that has the smallest current amplitude and the inputted torque and frequency. The computing time of the method is small because the FEA is static. The calculated results of a 750-watt PMSM under minimum-current control and field-weakening control have agreed well with the measurements. The method is useful in PMSM development and design.

All-speed-range drive for surface permanent magnet synchronous motors by combined use of two position sensorless methods

A new position sensorless method is proposed for surface permanent magnet synchronous motors in all speed regions. In this method, two sensorless methods are switched in accordance with the rotating speed. In low speed regions, an Induced Voltage caused by a Magnetic Saturation (IVMS) based method is used. This method is switched to a back EMF based sinusoidal current method at a medium or high speed. Some control blocks are commonly used for both methods. Therefore, the methods can be switched smoothly and rapidly. The basic idea and the experimental results are described.

Position sensorless control method at zero speed region for permanent magnet synchronous motors using the neutral point voltage of stator windings

A new sensorless control method that uses the neutral point voltage from stator windings is proposed. Each inductance of the three phase coils of the permanent magnet synchronous motor (PMSM) is slightly affected by the rotor magnet flux. As a result, the neutral point voltage also changes depending on the rotor position. The rotor position can be estimated by detecting the neutral point voltage even in the zero-speed regions based on this principle. In addition to this, this method can be applied to nonsaliency PMSMs. This paper presents the principle and the experimental results when using a small-capacity PMSM without saliency.

Energy saving start-up method by combined use of two position sensorless controls

This paper proposes a start-up method for reducing electrical energy at starting periods. Minimum current startup is achieved by combining two position sensorless control methods that require no harmonic injection. Position sensorless control for low-speed regions utilizes the induced voltage caused by the magnetic saturation of a permanent magnet synchronous motor with conventional block commutation drive. At acceleration, the position sensorless control is changed to the second method based on back-EMF with sinusoidal commutation drive. This paper also addresses when to change the control, as unconsidered switching may result in start-up failure when used with applications that have periodic load properties. A simple yet powerful method to identify the most suitable timing considering load variation is proposed. The proposed methods are validated using a reciprocating compressor with a large periodic load torque.

Influences of rotor eccentricity on permanent magnet synchronous motor characteristics

This paper describes the influence of rotor eccentricity on permanent magnet synchronous motor characteristics. Specifically, we studied the influence of rotor eccentricity on permanent magnet synchronous motor characteristics by conducting a magnetic field analysis and several experiments. The rotor eccentricity unbalances the magnetic force and thus increases the mechanical loss. Furthermore, a circulating current generated in two three-phase windings connected in parallel results in an increase in electric power loss in the permanent magnet synchronous motor.