In this paper,a new flux-weakening control method based on rotor flux orientation is presented to improve the current tracking capability and output characteristics of the motor torque,and the method is implemented in digital ac spindle driver system.Using Labview virtual oscilloscope to observe the real-time experimental data,the experimental results show that the method can effectively improve the dynamic response of motor as well as the output characteristics of the motor torque.

Maximum Torque Control of an Induction Machine in the Field Weakening Region

The multiphase machines present a lot of advantages when compared to the traditional three-phase machines, as example, for the same power, they operate with lower bus voltage and lower current per phase, present higher fault tolerance, and more specifically when it comes to concentrated windings machines, the harmonic current injection may be used to increase the torque production. Taking advantage of this last feature, in this work is developed the IFOC (indirect field oriented control) with current harmonic injection for a concentrated windings nine-phase induction motor drive, what confers the variable-speed machine operation with flux waveform optimization, reducing its peak value, giving better use to the iron core and allowing power density improvement.

IFOC for a Nine-phase Induction Motor Drive with Current Harmonic Injection

The performance of a sensor-based rotor flux-oriented vector control induction machine drive is highly influenced by the estimated value of the rotor time constant/rotor resistance which varies continuously with temperature when it is driven with the variable loads. Therefore, to achieve accurate torque control, online tunning of the rotor time constant is necessary. This article proposes a novel and simple adaption technique to estimate the rotor time constant. In this proposed method, the reference model of the rotor flux vector is derived using the voltage model of the induction machine, which is independent of the rotor time constant. The current controller uses the model of the rotor flux vector that is derived using the current model of the induction machine. This current model is dependent on the rotor time constant. The error between the rotor flux vectors derived using the current model and the voltage model is minimized using the least-squares method. In this process, the rotor time constant is always tuned to its actual value. The article also presents a simple approach to estimate the parameters of induction machine like the stator resistance, the net leakage inductance, and the initial value of the rotor time constant in an offline mode at a standstill condition. To validate the proposed algorithm, two experimental prototypes are developed for two different power ratings of 3.7 and 67 kW. Experimental results from these prototypes confirm the effectiveness, reliability, and stability of the proposed algorithm both in the motoring and regenerative modes of operation. This method of the adaptation of the rotor time constant is simple and, therefore, useful for practicing engineers.

Parameter Estimation and Online Adaptation of Rotor Time Constant for Induction Motor Drive

The performance of a sensor-based rotor flux-oriented vector control induction machine drive is highly influenced by the estimated value of the rotor time constant/rotor resistance which varies continuously with temperature when it is driven with the variable loads. Therefore, to achieve accurate torque control, online tunning of the rotor time constant is necessary. This article proposes a novel and simple adaption technique to estimate the rotor time constant. In this proposed method, the reference model of the rotor flux vector is derived using the voltage model of the induction machine, which is independent of the rotor time constant. The current controller uses the model of the rotor flux vector that is derived using the current model of the induction machine. This current model is dependent on the rotor time constant. The error between the rotor flux vectors derived using the current model and the voltage model is minimized using the least-squares method. In this process, the rotor time constant is always tuned to its actual value. The article also presents a simple approach to estimate the parameters of induction machine like the stator resistance, the net leakage inductance, and the initial value of the rotor time constant in an offline mode at a standstill condition. To validate the proposed algorithm, two experimental prototypes are developed for two different power ratings of 3.7 and 67 kW. Experimental results from these prototypes confirm the effectiveness, reliability, and stability of the proposed algorithm both in the motoring and regenerative modes of operation. This method of the adaptation of the rotor time constant is simple and, therefore, useful for practicing engineers. 

The Paper presents verification of induction motor control and its characteristics using indirect field-oriented control (IFOC) through a Typhoon Hardware-in-loop (HIL) simulation package with HIL604 configuration for both testbench control and real-time simulation. With field-oriented control, the angle and the magnitude of each phase’s voltage and current are controlled. Typically, torque control is accomplished by modulating the armature with a constant field current. The Field Weakening is used to boost the speed beyond its base value. To decouple the motor torque and flux, a d-q reference frame locked to the rotor flux vector is employed. Therefore, they can be independently controlled by the stator's quadrature-axis current and direct-axis current, respectively. Using the PI controller and SVPWM approach, satisfactory performance is realized. The rotor flux and magnetizing current are obtained using the proposed control strategy. To control the physical testbench, real-time control signals are amplified using PONOVO voltage and current amplifiers, which also make the output signal from the physical motor return at analog input ports of Typhoon. A dynamometer is used to measure the speed and torque of the induction motor. Software and hardware results are compared, and finally, efficiency is calculated. 

Field-Oriented Control Strategy Verification Based on Power Hardware in Loop Simulation Technology

Indirect rotor field oriented control (IRFOC) plays an important role in the high performance induction machine drives. In the indirect rotor field oriented control — based induction machine adjustable speed control system, the rotor field angle is usually obtained by the rotor angular velocity and the slip angular velocity. The rotor angular velocity can be sensed by an encoder with sufficient accuracy. However, the slip angular velocity is affected by the rotor parameters variations and the current control performance degradation especially in the field-weakening region. Therefore, the field angle used in the indirect rotor field oriented control may have considerable error. In the paper, the angle error caused by rotor resistance variation is analyzed and the impact on the output torque and the rotor field intensity of the induction machine is studied. Simulations and experimental verification in base-speed region and field-weakening region are presented.

Analysis of indirect rotor field oriented control-based induction machine performance under inaccurate field-oriented condition

Capacitive DC links provide the only low-impedance current path connected with an input source during the start-up of many voltage source converters. A soft-start circuit is usually implemented to limit the inrush current. A two-terminal active capacitor is recently proposed which can directly replace conventional passive capacitors in DC links, with reduced cost or size for a given application. The active capacitor has the same level of convenience with two power terminals only as a passive capacitor. This paper proposes two start-up schemes for the active capacitor to overcome the drawbacks of existing methods previously widely used for passive capacitors. One scheme is based on a trade-off design between the start-up performance and the component sizing of the active capacitor. The other scheme is based on either an additional bypass switch together with the existing soft-start circuit in the DC bus or a start-up circuit fully integrated in the active capacitor. The theoretical analyses and experiments are presented. A case study on a single-phase full-bridge rectifier demonstrates the effectiveness of the implemented start-up schemes.

Geng Tao

Papers

Analysis of indirect rotor field oriented control-based induction machine performance under inaccurate field-oriented condition

Practical considerations of the start-up procedure for an active capacitor