Yoshitaka Iwaji

Position-sensorless control method at low speed for permanent magnet synchronous motors using induced voltage caused by magnetic saturation

A new position-sensorless method has been developed for a permanent magnet synchronous motor (PMSM) drive at low speed. This method utilizes the induced voltage caused by magnetic saturation of PMSM. The rotor position can be detected by using the open phase voltage of a conventional 120-degree commutation. No harmonic injection is needed. This paper discusses the principle of the proposed method and the experimental results.

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.

Position Sensorless Vector Control of Permanent Magnet Synchronous Motors for Electrical Household Appliances

A position sensorless vector control for a permanent magnet synchronous motor (PMSM) suitable for electrical household appliance motor drives is described in this paper. As a position sensorless control, a simple position estimate equation is presented. The derivation of the equation is described. A simplified vector control method for position sensorless PMSMs is proposed. The proposed method does not employ any automatic speed regulator or automatic current regulator. However, since the motor supply voltage Vd and Vq are calculated on the control rotation axis, the drive performance of our method is almost the same as that of a conventional vector control under a steady-state condition, i.e. constant load and constant speed. Simulation and experimental results are shown. Finally, the authors applied the proposed method to a battery-driven cordless vacuum cleaner. By experiment, a stable drive of 50,000 min-1 was confirmed.

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).

Initial rotor position estimation of the interior permanent magnet synchronous motor

A new method of the rotor position estimation is proposed for interior permanent magnet synchronous motors. The proposed method for the initial rotor position estimation consists of two parts: one estimates the rotor position of the magnetic pole; the other determines the direction of the magnetization at the estimated position at the same period. The basic idea and the experimental results are discussed in this paper.

New vector controller for PM motors which modeled the cross-coupling magnetic flux saturation

A new magnetic-flux saturation model has been developed for permanent magnet synchronous motors. In the new model, simple first-order functions Φd(id, iq) and Φq(id, iq) express the relationships between d-q axis currents and each axis magnetic flux, considering magnetic saturation and cross-coupling effects. Taking advantage of these new features, we developed a current controller that introduced the precise inverse model of the motor using the above function. Furthermore, simulations of the proposed current controller were evaluated under ideal conditions without any modeling error. Moreover, it showed, in principle, that the ideal first-order lag characteristic without the current interference between d-q axes could be realized in the conditions of cross-coupling magnetic flux saturation.

Inductance measurement method for permanent magnet synchronous motors using AC with DC bias

We have developed a method that uses AC with a DC bias to measure the inductances (Ld, Lq) of permanent magnet synchronous motors (PMSMs). Such motors are widely used in electrical equipment because they are highly efficient. Our method can be used to measure nonlinear characteristics of a PMSM, such as magnetic flux and inductance with cross-magnetization. We have compared our method with a conventional method and the results of a finite-element method analysis. The comparisons with the finite-element method analysis revealed that our method can be used to accurately determine the inductances of PMSMs, which is necessary in some vector control strategies.

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.

A novel PWM pulse modifying method for reconstructing three-phase AC currents from DC bus currents of inverter

A novel PWM pulse modifying method for DC bus current detection has been developed to reduce acoustic noise and distortion. DC bus current detection needs wide pulse durations to reconstruct three AC currents. PWM pulse modifying methods have been proposed to expand short pulse durations at low modulation. However, harmonic currents caused by modification signals distort reconstructed currents and create a specific frequency. In this paper, several PWM modifying methods are examined. Moreover a method for modifying signals is proposed that prevents harmonic currents from distorting reconstructed currents and creating a low frequency. Simulated and experimental results show good performances of total harmonic distortion and a high frequency.