Research For Dual-PWM Direct Drive Elevator Control System

At present, almost all the domestic inverter of elevator adopts uncontrollable rectifier in the network side. This control method is simple but it has the disadvantage of low power factor, high current harmonics and the regenerative braking power of motor can not be flown into the grid but consumed by the unloading circuit. The rectifier side and inverter side of Dual-PWM converter are symmetrical that the power can flow bi-directionally. Unity power factor can be achieved by controlling the phase of current of grid side, which can suppress current harmonics and realize the four quadrant running of motor.In the first part of the thesis, the research background and current development of Variable-frequency Regulating Speed Technology of Motor is presented first and several topological structures of PWM rectifier and the significance of dissertation are analyzed.PWM rectifier is the key to the whole control system. the mathematical model,dq model and the voltage equation based on dq model of the three-phase voltage source PWM rectifier are presented first in part two. By use of PMSM mathematical model, the stator flux equation and electromagnetic torque equation are established.Control strategies of the PWM rectifier are analyzed in part three, the control system adopts double loop control mode which consists of outer voltage loop and inner current loop. According to the voltage source PWM rectifier has the characteristics of nonlinear and multivariable coupling, the inner current loop adopts the nonlinear control method based on Lyapunov function, which improves stability in wide-range. Motor speed regulation adopts double closed-loop control method,and the inner current loop adopts the nonlinear control method based on Lyapunov function as well.The hardware and software design of the control system are introduced in part four, The main circuit, driving circuits, protection circuits, sampling circuits are presented. The software part is mainly some program based the TI’s TMS320F28335DSP, such as program about PWM, eQEP, AD converting, serial port communication and so on. due to time consuming with the large quantity of control code of dual PWM variable frequency speed regulation, some of mathematical function is improved. To square root and sine and cosine functions, the look-up table method is generally used. But the look-up table method can not take both the accuracy and time into account. The sine and cosine program based on the Taylor series expansion is designed and the procedure of square root adopts Newton iterative method, which reduces the expense of the CPU greatly with high accuracy.Finally, the experimental platform of dual PWM variable frequency speed is developed and it is proved by the experiment. The experimental curve is also given. The experimental results are consistent with the theoretical analysis which verify the correctness of the design of system scheme.