In textile exhaust dyeing, the control of dyebath pH is a critical factor in order to achieve optimum colour yield and levelness. Conventional controllers have not proved entirely successful in controlling dyebath pH since it is difficult to develop an exact mathematical model for the dyeing process. One method is to apply fuzzy control to the dyeing process. For the fuzzy controller to operate successfully, it is important to understand how the dyeing system responds to given reference pH/time profiles. A dynamic model for the dyeing process has been developed and this allows the fuzzy controller to be fine-tuned by computer simulation. Results of the control system simulation showed very satisfactory tracking performances of the pH profiles. This provides a starting point for further fine-tuning of the system under practical dyeing conditions.
The switch-mode operation of dc to ac inverters produces undesirable harmonics in the voltage and current outputs. Pulse Width Modulation (PWM) schemes based on Selective Harmonic Elimination (SHE) and carrier-based modulation are commonly used to address the harmonic reduction problem, and to provide adjustable inverter output fundamental components. The implementation of each scheme requires introduction of dead-time delays in the power switches of each inverter leg to cater for nonzero switching times of power semiconductors. In this paper we investigate the effect of dead-time distortion on the performance of SHE and sinusoidal PWM techniques for single phase dc to ac inverters with unipolar voltage switching. The modulation schemes are evaluated based on the harmonic distortions in the output currents and voltages, and on the power efficiencies when the inverters are operated at comparable switching frequencies.
Centrifugal pumps driven by induction motors are widely used in industry for liquid transfer and delivery. However, their energy efficiencies may change significantly with operating flow rate, total head and speed. Consequently, many pumping systems delivering variable flow rates operate well below their maximum efficiency. In this paper, a speed control scheme for an induction motor drive for a centrifugal pump is described to ensure that the pump works in its best efficiency region. The motor uses flux vector control to ensure rapid torque and speed response to match the flow rate requirements. The proposed scheme is tested under various operating conditions to validate its performance. Keywords-induction motor; flux vector control; centrifugal pump; efficiency I. INTRODUCTIONPumps operating from electric motors constitute an important share of energy consumption in industrial processes and water supply services. Centrifugal pumps are among the most widely used in these applications, wherein the head or differential pressure produced by the pump is used to impart energy to a liquid, and to overcome frictional losses in the piping system. The pump itself also incurs energy losses at its impeller, casing and bearings. Hence the useful power produced by the pump is only part of the power applied to its shaft from the motor. Pump characteristics are normally described by the head, flow rate, power consumption and efficiency [1][2][3]. For a given shaft speed, the highest operating efficiency of the pump occurs at a specific flow rate. To reduce energy loss, the pump should be operated at efficiencies equal or close to the Best Efficiency Point (BEP). In many applications, however, the mismatch between electrical drive, pump and piping system requirements cause operation well below the optimum efficiency. Apart from producing increased energy losses, operation away from the BEP has been shown to produce cavitation and to reduce the shaft bearing life [4]. Hence there are wide prospects for energy efficiency improvement and reduction in operational costs for such systems. In [5], artificial neural networks are used for increasing energy savings in induction motor drives. However, emphasis is laid on energy efficiency improvement of the motor itself, rather than for the relatively low efficiency pump.
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