| According to the periodically variable running load of the motors working in the oil pumping machines,a novel energy saving control principle of intermittent power supply is put forward in this paper.The integrated energy saving control method is studied combined with voltage regulation and reactive power compensation techniques,which is of great significance to the energy saving,emission reduction and the efficient use of energy source for oil extraction industry.A rapid soft re-switching approach of power supply for induction motors and its control strategy are put forward here in order to avoid the inrush current at the time of re-switching in the course of the intermittent power supply control.The transient mathematical models are established for thyristor-motor system to describe rapid soft re-switching course comprehensively.The main influnce factor of rapid soft re-switching course is studied by means of analytical method and the practicable calculating method of series of firing angles is obtained finally.The concrete research work includes the following aspects:1) Aiming at the alternating transient between two-phase and three-phase switching-on of rapid soft re-switching of the induction motors,the reduced order mathematical models for asymmetrical transient and symmetrical transient are established respectively.For the analytical research of asymmetrical transient model,the problem of extracting three-order eigenvalue is solved by using the Cardannao formula method.Futhermore,the transient stator current of initial two-phase switching-on can be expressed in time domain.By means of the analytical method in space vector complex coordinate for the symmetrical mathematical model,the analytical expression of transient stator current is got when the third phase switching on.The asymmetrical transient model can also be expressed with space vector, which is associated with the symmetrical transient to realize the connecting of the alternating course between two-phase and three-phase switching-on.2) The control parameters such as firing angles of rapid soft re-switching control are studied to reveal the control rules and analyze the influnce factors.The basic relationship between the the first half-wave peak value of transient current and the initial firing angles is found by means of analytical method.The practical method is put forward to determine the initial two-phase and the third phase firing angles with the limiting value and the space vector varying track of transient current.And then the subsequent series of firing angles with the even step are calculated by using the speed at the time of re-switching.The suppressive effect to the inrush current is verified with simulation and experiment of rapid soft re-switching control,by which the influence of different speed to rapid soft re-switching course is analyzed besides.3) To analyze the power loss for typical periodically variable running load and deeply study the energy-saving principle and control mode of the intermittent power supply approach. Futhermore,the novel integrated energy-saving control technique is developed on base of the intermittent power supply approach.In the course of studying the energy saving approach of the voltage regulation optimization in association with the intermittent power supply,a new loss calculation method of asynchronous motor is put forward under the condition of periodically changing load,which can be used to calculate the torque and optimal voltage with the measured data.The traditional energy saving approaches of wye-delta transform and reactive power compensation are restructured and made it to associate with the intermittent supply control to form the integrated energy-saving control technique,by which the comprehensive energy saving rate is improved greatly.
|
PDF Full Text Request