Research on elevator drive device with super capacitor for energy storage

To keep the switch frequency constant and reduce the fluctuation of flux linkage and torque in traditional elevator drive direct torque control (DTC) system, a method of SVM-DTC based on reference flux linkage is used. Switching table and hysteresis controller in traditional DTC is replaced by flux linkage estimator and SVPWM modulation module. For the problems of complex control and harmonic interference when elevator's regenerative braking energy feed back to the grid, a method of storing renewable energy by super capacitor is proposed in this paper. Because the power changes in a large range in the process of charging and discharging, the super capacitor is accessed to the DC bus by a bi-directional DC/DC converter. The converter can achieve the function of limiting the inductor current and maintaining the DC bus voltage constant. A small signal model is established in the paper. The control strategy of double-loop control, outer voltage loop and inner current loop, can effectively control the super capacitor's charging and discharging process. Simulation results show that the method can not only solve the problems when energy feedback to the grid, realize the purpose of elevator drive's energy saving, but also effectively reduce the fluctuation of flux linkage and torque, and improve the control performance of motor.