Research On Control System Of External Rotor Motor For Centrifugal Fan

Permanent magnet synchronous machine(PMSM)has many advantages,such as small size,high power density,simple structure and fast dynamic response,all those advantages make PMSM become more and more important in this industrial society.Control strategies without sensors,which do not need any mechanical sensors,save both the space and cost of the system.Furthermore,when the machine works in some harsh environments,Control strategies without sensors has higher reliability.In this paper,the practical application environment and operating requirements of the external rotor motor for centrifugal fan are studied,a set of control strategies are carried out to make the system efficient and reliable.First of all,based on researching the mathematical model of PMSM in two-phase stationary coordinate system,a sliding mode observer(SMO)is designed.Aiming at the matter of chatting due to the mechanism of the variable structure,saturation function is used to replace sign function,to weaken the chatting,the mode called prospective sliding mode,and phase locked loop(PLL)is constructed to smooth the chatting composition of estimation process for rotor position,all those improvement measures make the torque and speed of PMSM smooth.Secondly,considering the various situations that external rotor motor for centrifugal fan may encounter during the static start-up process,based on analyzing the electromagnetic torque function and mechanical function of PMSM in acceleration process,the principle of self-stabilization between torque and power-angle for PMSM is used to guarantee the reliability and stability of both I/F control stage and state transition process.Aiming at the matter that,external rotor motor for centrifugal fan without sensors cannot start reliably in rotating conditions,two zero-vectors are applied to inverter to make three phase stator windings of the machine have a short-circuit.Through analyzing the angle variation of the currents in ?? coordinates,the rotational direction and speed of the machine are derived.Furthermore,through analyzing the transient state process of the currents in dq coordinates,the rotor position of the machine is estimated.At last,the control strategies mentioned above is evaluated on the experimental platform,which TMS320F28027 provided by TI is used as the master of the whole control system,and a fan is used as the load of PMSM,whose rated power is 550W.The experimental results show that,reliable start of PMSM in complex conditions can be achieved,whatever the machine is in static or rotating condition,and the performance in the high-speed can meet the requirement perfectly.