Research On Control System Of BLDCM For The Logging With All-digital RDC

Oil well logging ultrasound transducers are usually operated in high temperatureand humid environments. Such harsh working conditions are not conducive to thestability of the system hardware. Besides, the transducer has a high accuracyrequirement for the position signal. Desired to replace the original hardware decoding,while increasing the conversion accuracy of software decoding, after checking largeamounts of relevant information, a new type of all-digital RDC BLDC motor controlsystem has been designed in this paper.Firstly, combined with the needs of logging condition, track-type axis angleconversion was selected as the resolver conversion method in this paper, while phasesensitive demodulation method was used in conjunction. According to the requirementsof control system, a model of track-type axis angle conversion method was established.The rules and correspondences between parameters and performance in system hadbeen found.Secondly, by comparing the common errors in resolver, a function errorelimination solution by using second-order generalized integrator had been proposed inthis paper. Through modeling and analysis of the second-order generalized integrator,the correspondences between parameters, angular position signal error and conversionrapidity were clear up. After the simulation of the BLDC motor control system, thefeasibility of axis angle conversion solution depend on software had been verified.Considering the conversion accuracy, rapidity and applicability, the second-ordergeneralized integrator coefficients were determined.Thirdly, the experimental platform of BLDC motor control system has beenintroduced, including the core control circuit and its peripheral signal conditioningcircuit, current sampling and other units. On this basis, the control algorithm wasillustrated. Through the cooperation of hardware and software, the resolver excitationsignal was produced. A series of full functions such as motor soft start, all-digital RDC,communication with the host computer, and logging trigger pulse output were achieved.At last, the BLDC motor control system was tested. The experimental resultsshowed that the scheme of all-digital RDC with function error elimination can achieve abetter angle position signal. The whole device fully realized the requirements of loggingultrasonic transducer.