Shigehisa Aoyagi

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.

A simplified sensorless vector control based on the average of the DC bus current

This paper describes a simplified sensorless vector control for permanent magnet synchronous motors (PMSM) using the average of the DC bus current. This method sets up the drive control system at relatively inexpensive because the micro controller does not need to have a precise timer and the calculation load is slight. The proposed method effectively changes two different current estimation methods in accordance with the operation mode. First, the controller estimates d-axis current and identifies back-EMF parameter in synchronous operation mode at the low speed region. The identification error of back-EMF parameter affects efficiency of the proposed system, so it needs to be zero. Second, the controller estimates q-axis current in vector control mode. The identified parameter and q-axis current define voltage reference to realize high efficiency drive. Experimental results confirm the effectiveness of proposed method.

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.

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.

Motor drive system using nonlinear mathematical model for permanent magnet synchronous motors

We have developed a mathematical model for permanent magnet synchronous motors (PMSMs). The nonlinear characteristics of this model are expressed using a total of eight constants. The magnet flux characteristics of PMSMs can be obtained by using this simplified model. This model can also be transformed into a reverse function, and motor drive simulation including nonlinear characteristics can easily be implemented. Here, we present the simulation results using our nonlinear model. We also demonstrated the effectiveness of the model by simulating estimates of rotor positions based on magnet flux nonlinear characteristics.

Analysis of RMS current on DC-link capacitor with single-shunt current sensing system

A single-shunt current sensing technique is widely used in industrial system to reduce the cost and mounting space of current sensors in an inverter. In addition, a pulse shift control technique, which maintains the pulse duration and achieves reliable current detection, is used in a single-shunt current sensing system. In this paper, the RMS current on the DC-link capacitor with a pulse shift control technique was analyzed. The analysis results showed that the RMS current on the DC-link capacitor in the single-shunt current sensing system increases over 50% compared to a conventional three-phase current sensing system, in case of a low modulation factor. In addition, the rise in temperature of the DC-link capacitor with or without the single-shunt current sensing was verified by examination. An advanced single-shunt current sensing technique for a redundant inverter system to reduce the RMS current on the DC-link capacitor and the audible noise is also proposed in this paper.

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.