Theoretical Basis and Application Features of Vector Control and Direct Torque Control Systems
CHEN Bo-shi (Shanghai University, Shanghai 200072, China)
Both vector control system (VC) and direct torque control system (DTC) are widely used ac adjustable speed systems with high performances. Their theoretical basis derives from the multivariable nonlinear mathematical model of electric motors. The dynamic model of induction motors in the 2-phase coordinates can be described by 5th-order state-variable equations. The difference between VC and DTC lies only in that VC system selects ω-Ψr-is equations, but DTC selects ω-Ψr-is. Besides, the general control structure of the two systems are identical, and hence as a high-performance ASD system VC and DTC are essentially the same. But the concrete control methods of them are different, so they possess different charac-teristics, different merits and defects. Besides the popularly used high-performance variable speed systems, they are laid with particular emphasis on different application area. Along with the technical progress, the products of these 2 systems are advancing in the direction of overcoming their defects. The way of scientific research should be to learn from each oth-er's strong points and to make up the deficiencies.