Research on Elevator Energy Feedback based on Active Inverter

Abstract

Aiming at reducing the elevator’s energy consumption, this paper analyses the energy feedback technology, and designs an energy feedback system used for elevator which can return the extra energy to the power grid in the generating state of the motor. The system adopts active inverter technology to achieve energy recycle. In this system, double closed-loop control is used to stabilize the input voltage and realize unity power factor operation. A simulation model is built to demonstrate the performance of the system based on Simulink/Matlab. Introduction Elevator is widely popularized with the development of society. As high-energy equipment, its consumption holds a large proportion of the whole building’s power consumption. The research of saving energy on elevator is pressing in this time of energy shortage. Elevator drives potential energy load. The load consists of the car and the counterweight and has a balance coefficient of nearly 0.5. Thus when the elevator is rising with heavy load or descending with light load, the motor works in the electro-motion state; and on the contrary condition, the motor works in the generating state. Elevators usually use VVVF converter to drive three phase synchronous motor. Due to the unidirectional continuity of the diodes which composed the three-phase pre-rectifier, traditional VVVF elevator controllers cannot transfer the energy to the power grid . The generating process of the motor will produce pump voltage and raise the voltage of the energy storage capacitor. Traditional elevators usually use resistance braking to reduce the voltage on the DC bus. According to research, 25% to 30% of the energy is consumed by the resistor . Energy feedback technology has a vast application prospect. In some foreign countries, many advanced energy feedback devices are designed to use the extra energy and return it to the power grid. But these products have high cost and high demand of the power grid. In China, the elevator energy feedback system hasn’t got good promotion. Thus this paper studies the related technology and designs an elevator energy feedback system which has low cost and simple installation. Design of the Energy Feedback System For recycling the extra energy of the elevator, this paper designs an energy feedback system which is showed in Fig.1. The key of the energy feedback is active inverter . When the motor is working in the generating state, the extra energy can be saved by transforming the DC power into three-phase AC power and returning it to the power grid. The system adopts DSP chip as the central control unit, and is mainly made up by control circuit, inverter circuit and sync circuit. In working condition of the system, the electric energy on the DC bus is returned to the power grid to decrease the voltage on the DC bus, and this process realizes energy regeneration. The system is independent to the elevator controller and few work need to be done to install the equipment. 4th International Conference on Mechatronics, Materials, Chemistry and Computer Engineering (ICMMCCE 2015) © 2015. The authors Published by Atlantis Press 2964 Fig.1 Elevator energy feedback system The three-phase full-bridge inverter is the core of the feedback device, reversing the regenerated power from the DC bus to the power grid . Fig.2 shows the inverter circuit constructed by six IGBTs. As the central switching element of the inverter, IGBT has good electrical performance, like high switching frequency, large drive current, low wastage and so on. IGBT elements are controlled by the PWM signal from the DSP chip.