Research On Alternating Current Servo System Control Method With Flexibly Connected Load

With the rapid progress of microelectronic technology, power electronic technology of modern control theory, the inevitable trend is that AC transmission servo system replaces DC transmission servo system. Permanent Magnet Synchronous Motor (PMSM) has been widely used in many industrial applications due to its advantages such as small size, light weight, high efficiency and so on. The PMSM speed servo system usually uses double closed-loop control structure with the inner current loop and the outer speed loop. During the speed loop controller designing, the motor rotor-transmission mechanism-load is usually regarded as a rigid body, the load inertia is simply added equivalently to the motor. But in actual servo system, the transmission mechanism is not an ideal rigid body, so the mechanical resonance easily occurs, which makes the current and speed of the system oscillation. In order to avoid mechanical resonance, the speed loop controller must be designed reasonably.Firstly, the research background of PMSM speed-regulation system is introduced. The characteristics and flaws of major PMSM control algorithms are discussed in brief. Then according to the principle of PMSM speed regulation, PMSM vector control program and mathematical model is discussed. The transmission mechanism of servo system is equivalent to a torsion spring, and the entire flexible connection servo system is simplified into a motor-spring-load two-mass system, then the mathematical model of the flexible connection servo system is established through theoretical analysis.Secondly, the pseudo-random sequence as the excitation system, the frequency characteristic identification scheme of speed loop control object is designed, and according to the result of frequency characteristic identification, the resonant frequency of the system is obtained. At the same time, the load inertia and the flexible transmission mechanism stiffness can be obtained. The algorithm is verified by simulation and experimental results.Then, after the system model is simplified, from the reasons of resonance generated, considering the oscillation suppression of load torque, the motor load torque can be estimated by the use of disturbance observer, and the estimation result is compensated to the torque reference. A feedback control algorithm based on load torque observer is designed and proposed. The simulation results verify the effectiveness of the proposed algorithm.At last, according to the application requirements of mechanical resonance online suppressing, the mechanical resonance online suppressing algorithm based on adaptive IIR notch filter is proposed. Using a recursive algorithm, resonant frequency of the system is online estimated, and then the frequency parameters of notch filter are adjusted online. The simulation and experiment results show the effectiveness of this method.