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We have developed a pure-integration-based flux acquisition method for ac adjustable-speed drives. Based on the current-measurement-error analysis, a simple resonant-type observer is utilized to eliminate the drift or dc offset that originated in the current acquisition process. All the processes in correcting the problem do not rely on motor parameters and do not interfere with other higher frequency contents such as inverter non-linearity and motor cogging effects. The proposed technique further contains a residual error compensator to completely correct the initial value error and to eliminate miscellaneous dc offset errors of the integrator. The acquisition accuracy of the flux is significantly improved through pure integration by restraining the error of the flux magnitude and phase angle at a low stator frequency. Since the proposed scheme is based on a two-phase current measurement system, it is suitable for retrofitting ac drives, where two current sensors are commonly used. Index Terms--Current measurement error, pure-integration-based flux acquisition, residual error compensator, resonant-type observer (RTO).

This paper analyzes a high-frequency (HF) voltage-injection-based rotor winding temperature estimation method for current-regulated squirrel-cage induction motors (IMs). We develop a theoretical I-IF model of the rotor bar and then first provide an analysis of relevant HF model-based estimation aspects, such as the dependence of the rotor leakage inductance on the temperature and the relationship between the rotor resistance and rotor leakage inductance. We also include an analysis of magnetic saturation to improve the estimation accuracy, as well as an analysis of the phase delay effect resulting from the drive that significantly affects the HF signal precision. Then, a specialized offline commissioning scheme is proposed to compensate for the effect of the phase delay and magnetic saturation. The estimation technique and sensitivity analysis are verified by means of experiments performed on an inverter-fed 1.5-kW IM. Index Terms--High-frequency (HF) model of rotor bar, high-frequency (HF) voltage injection, inverter-fed induction motor (IM), phase delay resulting from the drive, rotor winding temperature estimation.

In this paper, we propose an injection-based axis switching (IAS) sensorless control scheme using a pulsating high-frequency (HF) signal to minimize position detection error and velocity estimation ripple resulting from the zero-current-clamping (ZCC) effect for surface-mounted permanent-magnet motors. When a pulsating carrier-signal voltage is injected in an estimated synchronous frame, the envelope of the resulting HF current measured in the stationary reference frame follows an amplitade-modulated pattern. Using this information, the IAS technique allows one to avoid multiple zero crossings of HF currents by adjusting the current phase angle according to the load condition. At no-load condition, the pulsating voltage is injected only on the d-axis, while the d-axis current is controlled to a certain nonzero value. Under a load condition, the injection voltage is switched to the q-axis, while the d-axis current drops back to zero. Thus, the proposed sensorless control enforces a much better estimation performance in a region of ZCC without a predefined offline commissioning test than the standard pulsating injection scheme. Experiments illustrate the effectiveness of the proposed method in suppressing the estimation error caused by the ZCC disturbance and in extending the system bandwidth. Index Terms--Estimated position error and velocity ripple, injection-based axis switching (IAS) sensorless control, pulsating high-frequency (HF) signal injection, zero-current-clamping (ZCC) effect.

This paper presents an online-correction method for current measurement errors for a pure-integration-based flux estimation down to a stator frequency of 1 Hz. A measurement-disturbance-observer (MDO)-based approach is taken as one possible solution for eliminating the dc offset and the additional negative-sequence component due to unbalanced current measurement gains in the synchronous coordinate. From the motor parameter sensitivity analysis, an MDO gain selection method is proposed to remove the estimation error resulting from a parameter mismatch. At the same time, the positive-sequence component estimation is performed by creating an error signal between a motor model reference and an estimated q-axis rotor flux established by a permanent magnet in the synchronous coordinate. The compensator utilizes a PI controller that controls the error signal to zero. Experimental results confirm that the proposed scheme has great potential for applications to acquire the accurate motor flux at a low stator frequency. Index Terms--DC offset, measurement disturbance observer (MDO), negative-sequence component due to unbalanced current measurement gains, online-correction method of current measurement errors, positive-sequence component estimation, pure-integration-based flux estimation.

This paper proposes an online compensation strategy for the unwanted disturbance voltage resulting from the zero-current clamping effect for high-frequency-signal-injection-based sensorless control schemes. We derive an analytical model that reveals intrinsic characteristics of the zero clamping effect for high-frequency signal injection. The model in this form is subsequently incorporated into the development of a specialized offline commissioning test to find motor inductances and a voltage distortion factor. From the sensitivity analysis of the effect on magnetic saturation, we confirm that the compensation error due to saturation has little negative impact on the proposed compensation method. The compensation result leads to an accurate position estimate in the zero-current clamping region. The proposed scheme does not rely on a complicated lookup table. Experiments demonstrate the superiority of the proposed method in suppressing the voltage distortions caused by the zero-current clamping effect. Index Terms--Analytical model, offline commissioning test, online compensation strategy for the unwanted disturbance voltage, zero-current clamping effect for high-frequency-signal-injection-based sensorless control.

In an induction machine with deep rotor bars, the rotor parameters change due to skin effect and saturation, and the skin effect is often modeled as a ladder network. For the high-performance drive of an induction machine with deep bars, many sophisticated control strategies and machine models have been discussed. As a control strategy, a complicated airgap flux-oriented control scheme is mostly adopted, because it is not possible to define a unique rotor flux in deep bar model. However, a unique pseudorotor flux can be defined, and it is straightforward to achieve independent control of pseudorotor flux and torque. This control scheme can be applied to any nth multiple ladder network. In this paper, it is described how a deep-bar effect of an induction machine can be negligible by performing the proper field-oriented control. By using the concept of pseudorotor flux, the conventional rotor-flux-oriented control using equivalent rotor parameters is effective for deep-bar and/or double-cage machines. The actual insulated gate bipolar transistor (IGBT) inverter systems with a high-precision torque transducer are implemented and thoroughly tested on a 250-hp induction machine and a 5.5-kW double-cage induction machine to confirm their validity. Index Terms - Deep rotor bars, pseudorotor flux, skin effect.

A new approach to parameter tuning of induction motors in the course of drive commissioning is proposed. Usually, the motors originate from different manufacturers, and so the parameters are not known prior to startup of the drive. The control system of the drive utilizes the parameters obtained by extraneous tests and based on a number of assumptions that are not valid under all operating conditions. Therefore, completion of the tuning of all motors at an industrial site is quite time consuming, and it is a very difficult job, even to skilled engineers. To overcome these problems, the proposed tuning procedure is sensitive to detuning and independent of information on other parameters. The state of detuning is clearly noticeable in the shape of the controller output signal of the drive system. The proposed scheme has the advantage of being general and readily applicable to a wide range of other systems, such as ac/dc boost converters, surface-mounted permanent-magnet synchronous motors, interior permanent-magnet synchronous motors, and so on. Experimental results are offered to validate the feasibility of the proposed tuning algorithm. Index Terms--Controller output signal, drive commissioning, induction motor, parameter tuning.