The Development Of Measuring System For Motor's Operating Based On Virtual Instrumentation Technology

For the purpose of monitoring AC motors' operating states in variable speed drive and providing powerful measuring tools for prompting their energy conversion ratios, reduce their harmonic losses and improve their power factors, it is necessary to acquire parameters of motors' operating states synchronously and consecutively, which include 3-phase voltages and currents of variable speed drive' outputs. It also needs to save, analyze and redisplay these signals. But traditional measuring instruments can't satisfy these requirements already. Digital oscilloscopes have little storage, few channels and weak analytical ability. The virtual instrumentation technology, which is a combination of computer science and instrumentation technology, can solve problems above and satisfy the requirements for motors' measuring. Aiming at induction machines and their control systems, this dissertation researches the issue on measuring motors' operating states based on virtual instrumentation technology, and tries to solve the current problem of measuring the efficiencies of inverters.Based on the theories of measuring voltages and currents, this dissertation discusses the system scheme, hardware and software. According to measuring requirements of induction machines, hardware and software of the measuring system are designed. An effective scheme with strong functions is chosen and implemented, which is proven to reach the desired goal by experiments.The main structure of the signal processing circuit and data acquiring circuit, selection of components, design of analog inputs, A/D sampling method, data transmitting and data reading methods are argued in detail in this dissertation. The input and output interfaces, power supply modules, PLL, control circuit are also discussed. At last, according to the device's technical requirements, the hardware circuit is chosen and designed, which accords with desired technical targets.The software is also designed, which includes the driver and user application. The driver of the data acquiring card in Windows 2000 and its communication with LabVIEW are designed in this dissertation. The main program and the structure of each function module are analyzed. The user application is of comprehensive function, easy operation and stable performance.The measuring system passes two experiments: measuring inverter's efficiency and current waveforms in vector controlled induction machine drive. It is proven that the system scheme is complete and the design of the hardware and software is right. This measuring system has good dynamic response, real-time display and intelligence, which can reveal the current waveforms in vector controlled induction machine drive synchronously and exactly. It also can measure inverters' efficiencies.The development of this measuring system puts forward a new solution for application of the virtual instrumentation technology in monitoring motors' operating states and measuring inverters' efficiencies, and achieves a success.