Simulation Research On AC-DC-AC Variable-Frequency System

As a fan, pumps, compressors, machine tools and other equipment of the force, motors has been widely used in industrial, commercial, utilities and household appliances and other fields. Induction Motors is the broadest applications and requirement in all kind of motors. Therefore, improving the efficiency of motor to save energy has great significance.With power electronic technology, computer technology, automatic control technology is developing rapidly, AC variable-frequency system technology has been developing rapidly. Significant energy efficiency and precision and broad scope of speed control, perfect protection and easy to implement automatic communications, all which have win the many users acceptance. In the safe and reliable operation, installation, maintenance, AC variable-frequency system also brought great convenience to users. However, converter consists of harmonic currents in supply-side .These harmonic currents will have a negative impact on power quality. And in its output side of the inverter, the high order harmonics will bring to motors and cause such as fever intensified, torque pulsation and noise and may even cause damage to motor. In addition, the harmonics also have the serious disturbance to the communication and electronic equipments, affecting around the normal operation of equipment. Therefore, studying the harmonics in the variable-frequency system has the significance to reliability and efficiency.In order to analyze the inverter influences on the motor, simulation models of AC-DC-AC variable-frequency system are built by using the Matlab simulation tool. The harmonics influence on AC motor torque, insulation, and the efficiency of motor are studied in this thesis. And influences of the voltage modulation, carrier frequency and delay time of inverter circuit are discussed.Nearly 10 years, in various of power quality problems, voltage sags which cause voltage sensitive equipment fails to function properly in the first place. For voltage sags, adjustable speed drive is a typical sensitivity load. In this thesis, the definition causes, etc. of voltage sags are described and the response of four different types of AC-DC-AC variable-frequency system are analyzed for voltage sags. Finally, the different types of converter endure curves are depicted.