| With the increasing deterioration of the environment and continuous depletion of fossil energy,energy saving and emission reduction need to be further strengthened.Therefore,to solve such problems,the frequency converters are widely used due to their high efficiency.Meanwhile,the requirements for the frequency converters are becoming stricter.On the one hand,the harmonic problems caused by the increasing nonlinearity of the electrical equipment have become more and more serious in the world,then relevant regulations have been put on the electrical equipment,particularly for the high power factor which has become a critical indicator of the converters.On the other hand,in the wide-ranging applications of the frequency converters,users are also inclined to pursue electrical products with higher quality.In addition,there are progressively more occasions for converters driving motors through long cables,which makes the design of converters more difficult.Therefore,this paper not only studies the common drive systems but also optimizes the frequency converters for long cable drive.Firstly,this paper introduces the structure of high-power-factor converters with long cables.The three-phase power factor correction(PFC)circuit and motor driver are the main components of a high-power-factor converter,which both belong to voltage-type devices.Therefore,the relationship between the PFC and motor driver has been established when analyzing the principal and theory of the converters,including the control targets and mathematical models.Based on the similar principles of both main parts of converters,a large number of unified control strategies can be obtained to simplify the design of the frequency converters driving motors.Then,in order to achieve a better performance of the frequency converters,it is necessary tooptimize control strategies.Taking the three-phase PFC as an example,while analyzing theshortcomings of the traditional PI control with fixed parameters from small signal models andinvestigating the limitations of PI control on harmonic suppression from internal model principle,segmented parallel repetitive control has been proposed,which has the advantages of bothsegmented PI and repetitive control so that to achieve the performance of high power factor in abroad range of load condition.However,the segmented parallel repetitive control contains manycontrol parameters,thus the solution and optimization of control parameters based on the geneticalgorithm are proposed to speed up the design of the control system.Besides,the starting processof the converters is different from the normal working state,so it is necessary to design a suitablestart-up strategy and the corresponding hardware.This paper has optimized the three-step startup method and the pre-charge strategy to ensure the stable starting process of the motor and the three-phase PFC respectively.After the discussion of control strategies applied to the converters,the hardware design of high-power-factor converters with long cables has been introduced briefly.Finally,the analysis of the long-cable drive system has been stressed.Aiming at the problems of over-voltage and CM current when the converters are connected to motors with long cables,a new filter has been proposed in this paper,including the weak damping RLC filter served as DM filter and the CM transformer served as CM filter.The validity and feasibility of the proposed design and optimization in this paper have been verified through simulations and experiments,and the results have been compared with other converters’ designs,showing the improvements of converters’ performance after adopting the proposed design and optimization. |
