| Combining with the characteristics and control methods of converter, the mechanical characteristics of variable-frequency speed-adjustable motor are analysed in electric machine theory in the first part of this paper. Various speed-adjusting and operating characteristics can be obtained by using different control methods of converter. In analysis of mechanical characteristics of variable-frequency speed-adjustable motor, the typical curves are divided into two parts, i.e. constant magnetic area and weak magnetic area. According to the derived formulas, typical curves of mechanical characteristics are drawn. These curves can be reference to engineering design of motors. Including torque-speed curve and current-speed curve, the starting characteristic curves are drawn according to result of practical calculation in this paper. In addition, the characteristics during actual starting are also analysed. At present, the variable-frequency adjustable-speed motors are selected as the main driving motors of the machines such as main rolling mill, coiling machine and decoiler used in iron and steel industry. And the requirements to their mechanical load characteristics are rather rigorous. By the design of a low-voltage variable-frequency adjustable-speed motor whose rated power is 1200kilowatt, how to select a rating point and motor parameters to meet the requirements to mechanical load is analysed in this paper. This can offer certain reference to engineering design of low-voltage large-power variable-frequency motor. |
PDF Full Text Request