Jung-Ik Ha

Sensorless drive of surface-mounted permanent-magnet motor by high-frequency signal injection based on magnetic saliency

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.

Sensorless field orientation control of an induction machine by high frequency signal injection

This paper describes a new scheme to find the rotor flux angle from stator voltages and currents by injecting a high-frequency signal. The signal is not a rotating one but a fluctuating one at a reference frame rotating synchronously to the fundamental stator frequency. When the estimated rotor flux angle coincides with the actual angle, the proposed method makes virtually no ripple torque, no vibration and less audible noise caused by the injected signal. The difference of impedances between the flux axis and the quadrature axis at high-frequency signal injection on the rotor flux angle is explained by the equivalent circuit equation of the induction machine. The difference is verified by experiments on test motors under various testing conditions. A sensorless field orientation algorithm is proposed and experimental results clarify the satisfactory operation of the algorithm with one hundred and fifty percent load torque at zero stator frequency.

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.

Position controlled synchronous reluctance motor without rotational transducer

This paper presents a position sensorless control scheme of synchronous reluctance motor combining a high frequency current injection in a low speed region and the flux estimation based on the stator voltages in a high speed region. The rotor has inherent saliency and its angle is estimated from d-axis stator current injection and the appropriate signal demodulation in a low speed region. In a high speed region, the rotor angle is 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 synchronous reluctance motor are given to verify the proposed scheme.

PWM Switching Frequency Signal Injection Sensorless Method in IPMSM

This paper describes how to extract the rotor position information using a PWM switching frequency voltage signal injection without position sensor in Interior Permanent Magnet Synchronous Machine (IPMSM). The frequency of injected voltage signal is increased to PWM switching frequency, and the dynamics of the sensorless control can be improved. Compared to conventional heterodyning process, the proposed method is simple to implement and appropriate for PWM switching frequency signal injection. The high frequency voltage signal can be injected in the stationary reference frame or in the estimated rotor reference frame. In this paper, two sensorless methods are proposed according to the injection reference frame. To verify the proposed methods, 5kHz voltage signal injection with 5kHz PWM switching frequency inverter system in both reference frames were implemented. The experimental results confirm the effectiveness of the proposed method.

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.

Physical understanding of high frequency injection method to sensorless drives of an induction machine

This paper presents a physical understanding of a high frequency signal injection method to sensorless drives of an induction machine and proposes a sensorless algorithm based on it for zero or low stator frequency operation. The fluctuating high frequency signal at a synchronously rotating reference frame with the fundamental stator frequency generates an asymmetry of the spatial impedances in an induction machine. The difference of impedances between the flux axis and the quadrature axis at high frequency signal injection on the rotor flux angle is explained by the equivalent circuit equation of the induction machine. And the physical phenomenon due to the injected signal is analyzed and examined by finite element method under various operating conditions. The difference is also verified experimentally on the test motors. An algorithm to estimate the rotor flux angle and the rotor speed utilizing the physical phenomena without any speed transducer is proposed. It contains a scheme extracting the high frequency impedance components related to the rotor flux position. The experimental results clarify the satisfactory operation of the algorithm with heavy load torque at zero stator frequency or zero speed regardless of operation mode-generating or motoring.

Sensorless position control and initial position estimation of an interior permanent magnet motor

This paper describes a torque, speed or position control method at the stand still and low speed in the interior permanent magnet (IPM) motor drive system without any rotational transducer. While IPM motors originally have 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 the starting from an arbitrary rotor position is also proposed. It can distinguish the north magnetic pole position from the south one in several tens of milliseconds. The proposed scheme enables position control of a transducerless or position-sensorless IPM motor. The experimental results clarify the satisfactory operation of the proposed position control algorithm under any load condition.

Sensorless drive of SMPM motor by high frequency signal injection

This paper represents a new sensorless control scheme of surface mounted permanent magnet (SMPM) motors. To estimate the rotor position of the SMPM motor, a high frequency voltage signal is injected and the resultant injected frequency current signal is used. In the SMPM motor, due to the flux of the permanent magnet, the stator core around the q-axis winding is saturated. This saturation effect makes some magnetic saliency of the SMPM motor. In this paper, to estimate the rotor position using this magnetic saliency, the high frequency model of the SMPM motor is developed 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 at low and zero speed operation even under heavy load conditions. The experimental results verify the performance of the proposed sensorless 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.