Research For Variable Frequency Speed Control System With Small Capacitor

The general variable frequency speed control system always uses electrolytic capacitor with large capacity to keep the bus voltage stability. But due to the characteristic of electrolytic capacitor, it is easy to cause the waveform of AC input current severe distortion. As the result, the power factor of the whole system has been reduced. At the same time due to the short lifetime of the electrolytic capacitor, it directly affects the reliability of the whole system. If the system uses film capacitors with small-capacity, it will be able to avoid the mentioned problems. Therefore, this thesis research the control strategy of variable frequency speed control system based on bus capacitance topology and application solutions. It adopts the permanent magnet synchronous motor(PMSM) as executor and start a detailed study of the analysis and platform design.The thesis first analyzes the mathematical model of PMSM and uses methods of coordinate transformation and feed-forward decoupling to realize independent control of motor current. Then it presents a new control algorithm of new weak flux-weakening Magnetic applicable to small capacitance, based on the field oriented vector control. It also realizes the over-modulation algorithm on the basis of space vector pulse width modulation method. Current loop and speed loop of the small capacitance system have been set up, and the PI parameters have been completed. For single-phase power input features, this thesis gives several methods of single phase locked loop technique and completes the simulation experiments. At the same time, it introduces the start-up methods of PMSM under the initial position of motor rotor.It designs the circuit of the control system, detection and fault protection, communication and storage. The thesis also set up the experimental platform of the frequency control system with a small capacitance, programing software based on TMS320F28335 chip which includes detailed design and program flow chart of initialization module, main loop module, interrupt service module and communication module. Finally it proves that variable frequency speed regulation system with small capacitance combined with the new control strategy has good performance and verifies the correctness of the system design, by building simulation model of the system, finishing a lot of dynamic experiment and debugging the physical experiment platform.