Design and Implementation of a Hybrid Output EMI Filter for High-Frequency Common-Mode Voltage Compensation in PWM Inverters

This paper presents a hybrid output electromagnetic interference (EMI) filter for common-mode voltage compensation in pulsewidth-modulation (PWM) inverters. Its structure is composed of a single-leg four-level active filter connected in series with a low-frequency blocking capacitor and a small passive LC filter that which enhances the suppression of the common-mode voltage in the high-frequency range. The series capacitor helps in avoiding the core saturation of the common-mode coupling transformer caused by the low-frequency components of the common-mode voltage. Detection of PWM voltages by high-speed optoisolators is done at the inverter's output to achieve better common-mode voltage detection and compensation characteristics. Analysis and design guidelines for the hybrid filter are also given to facilitate systematic design in the real implementation of the filter. Experimental results with a real drive system clearly illustrate a significant reduction of the common-mode voltage, the leakage current, the shaft voltage, and the bearing current.     

A position-and-velocity sensorless control for brushless DC motorsusing an adaptive sliding mode observer

The sliding mode observer is robust to measurement noises. Since the switching signals of the sliding mode observer contain the induced voltages of the motors, it is possible to obtain the position and velocity of the motors directly from the switching signals. Although the estimated position can be used for locating the position of the rotor, the estimated velocity is heavily contaminated by noises from the switching signals. This direct method nullifies the merit of the sliding mode observer. Thus, the authors also present an adaptive scheme for robust estimation of the velocity of brushless DC motors. Stability of the adaptive scheme is assured, and estimation errors due to parameter deviations are analyzed. A method of parameter adjustment is described     

Time-optimal single-step velocity response control scheme forfield-oriented induction machines considering saturation level

A time-optimal single-step velocity response control scheme of field-oriented induction machines, taking magnetic saturation of rotor flux into account, is implemented based on the analytical solutions of the time-optimal control problem. High velocity response is achieved in spite of field-weakening for low acoustic noise or high-efficiency drives. The equation of the optimal control law is derived, and the look-up table is obtained. The optimal controls scheme is realized by simply adding the look-up table to the flux controller of the variable flux field-oriented control system. Simulation is carried out to verify feasibility of the proposed control algorithm. Problems of the overshoot of the rotor speed and the constraint on rate of change of acceleration or deceleration at the instant of switching from the time-optimal control to the conventional field-oriented control are discussed. The experimental results agree well with the simulation results, and show satisfactory dynamic and steady-state performance on both start-up and acceleration/deceleration     

Slip-Frequency-Type Vector Control Equivalent to Flux-Feedback Vector Control Using Flux Observer

The slip-frequency type vector control and the flux-feedback type vector control arc typical control methods of induction motors. It is shown that the two methods are similar except for a frame of reference. The flux-feedback-type vector control using the rectangular coordinate uses vertical and horizontal components of the rotor flux. The slip-frequency type vector control using the polar coordinate employs absolute value and angle of the rotor flux. Usually, the flux-feedback vector control does not use the rotor flux model but instead, the rotor flux observer for flux estimation. On the other hand, the slip-frequency type control uses the rotor flux model. Therefore the slip-frequency type vector control using the rotor flux observer is proposed. The proposed method is equivalent to the flux-feedback type vector control using the rotor flux observer. Then it is more robust than the conventional slip-frequency type vector control.     

Realization of time-optimal single-step velocity response controlof field-oriented induction machines under the condition ofnonsaturation of flux

A time-optimal single-step velocity response control scheme for field-oriented induction machines was implemented based on the analytical solutions of the time-optimal control problem in the case of nonsaturation of flux. High-velocity response was achieved despite field weakening for low acoustic noise or high-efficiency drives. Optimal control under conditions of startup, acceleration/deceleration, and constant speed control against impact load is considered, and approximate control methods were derived to simplify the control algorithm. The scheme was realized by adding the lookup tables of the optimal control laws to the conventional indirect field-oriented control system. The feasibility of the control scheme was verified by simulations and experiments that show fast and smooth velocity response. Numerical evaluation indicates that the time-optimal control is advantageous, especially when the mechanical response time is comparable with the electrical rotor time constant and when the rated flux is low     

Manipulation of rotor flux for time-optimal single-step velocityresponse of field-oriented induction machines

A single-step time-optimal velocity response control of an induction motor by manipulation of rotor flux is proposed as a control strategy that maintains fast velocity response, even if the flux level is reduced, to attain high efficiency of low acoustic noise drives. This control scheme includes minimization of startup time from standstill and recovery time against impact load. However, the final value of rotor flux is unconstrained, and the proposed control scheme could not be implemented with a field-oriented controller, which accommodates the dynamically changing rotor flux. Introduction of the variable-flux concept causes the induction motor to be nonlinear. Therefore most of the optimal control problems are discussed only numerically. Saturation of the flux has also been treated and the analytical results show that the optimal solution is uniquely defined, being independent of the mechanical load conditions     

Design strategy of an adaptive full-order observer for speed-sensorless induction-motor Drives-tracking performance and stabilization

Design strategy of both feedback gains and adaptation gains for an adaptive full-order observer is a necessary issue to assure the stability and the tracking performance of the speed estimation in the sensorless drives. In this paper, novel design of feedback gains of the observer is proposed to achieve the stability over the whole operation especially in the low-speed region, including the regenerating mode. Stability improvement using the proposed feedback gains is rigorously proven by the method of Lyapunov. For the adaptation proportional-integral (PI) gains, the ramp response characteristic of the speed estimator is proposed as design guidelines. It is revealed that the integral adaptation gain determines the tracking error of the speed estimator during acceleration/deceleration while the sensitivity to current measurement noises depends on the proportional adaptation gain. It is also pointed out that a suitable corner frequency of the adaptation PI gains is required as a design tradeoff to avoid an oscillation. The validity of all theoretical results is verified by simulation and experiment.     

Averaging analysis approach for stability analysis of speed-sensorless induction motor drives with stator resistance estimation

In this paper, the stability property of speed-sensorless induction motor drives with stator resistance estimation is analyzed using the averaging analysis technique. Explicit stability conditions are then derived to clarify analytically when the instability may occur and how the regressor vectors used in the estimation and the integral adaptation gains should be designed to assure stability. The derived stability conditions also reveal that the coupling between the speed and the stator resistance estimation loops is the main cause of instability and that stabilization of each individual estimation loop is necessary but insufficient to guarantee stability. Instead of the conventional regressor vectors that are shown to make the estimation unstable in some regenerative regions, two new regressor vectors are introduced to achieve stability for the whole operating conditions. Moreover, investigation of the persistently exciting (PE) conditions points out theoretically the loss of identifiability of the rotor speed and the stator resistance at no loads and at zero frequency operations. Validity of all the analytical results is verified by simulation and experiment.     

A speed-sensorless IM drive with decoupling control and stabilityanalysis of speed estimation

A new sensorless drive based on a decoupling control and an adaptive full-order observer is developed. A modified decoupling control is introduced and integrated with the adaptive observer to reduce the complexity of the whole system. The speed estimation based on adaptive control theory is analyzed and the necessary and sufficient conditions for stability of the speed estimation are analytically derived. It is indicated that the system can be unstable in the low-speed region with regenerative loads. However, assigning an appropriate feedback gain to the adaptive observer can restore the stability and reduce the unstable region. Sensitivity of the sensorless drive against parameter and measurement errors is also qualitatively discussed. Simulation and experimental results are then given to verify the validity of the theoretical results