Elevator System Based on PLCComposed by the order of relay control system is a realization of the first elevator control method. However, to enter the nineties, with the development of science and technology and the widespread application of computer technology, the safety of elevators, reliability of the increasingly high demand on the relay control weaknesses are becoming evident. Elevator control system relays the failure rate high, greatly reduces the reliability and safety of elevators, and escalators stopped often to take with the staff about the inconvenience and fear. And the event rather than taking the lift or squat at the end of the lift will not only cause damage to mechanical components, but also personal accident may occur. Programmable Logic Controller (PLC) is the first order logic control in accordance with the needs of developed specifically for industrial environment applications to operate the electronic digital computing device. Given its advantages, at present, the relay control the lift has been gradually replaced by PLC control. At the same time, AC variable frequency motor speed control technology, the way the lift drag speed has been a gradual transition from DC to AC frequency converter. Thus, PLC control technology increases VVVF Elevator modern technology has become a hot industry.1. PLC elevator control advantages (1) used in elevator control PLC, with software for automatic control of lift operation, reliability greatly increased. (2) layer was removed and a majority of the relay, the control system structure is simple, to simplify the external circuit. (3) PLC can be a variety of complex control system, easy to add or change control functions. (4) PLC can be automated fault detection and alarm display to improve the operation of security and ease of maintenance. (5) for the group control the allocation and management, and improve the efficiency of elevator operation. (6) do not need to change the control scheme changes when the hardware connection. 2. VVVF elevator control characteristics With the power electronics, microelectronics and computer technology to control the rapid development of technology, communication technology VVVF also a very rapid rate. AC variable frequency motor speed control technology is the power to improve the process in order to improve product quality and improving the environment and promoting technological progress as a primary means. Frequency of its excellent performance and the speed brake from a smooth performance, high efficiency, high power factor and power-saving effect of a broad scope of application and many other advantages of being at home and abroad recognized as the most promising approach speed Exchange characteristics of VVVF Elevator (1)low energy consumption (2) low load circuit, the required emergency power supply device of small In the acceleration stage, the required start-up current of less than 2.5 times the rated current. Peak starting current and time is short. Since the starting current is drastically reduced, so power consumption and power supply cable diameter can be reduced a lot. Required for emergency power supply devices are also relatively small size. (3) high reliability and long service life. (4) good comfort Elevator operation is best to follow the speed curve of a given operation. Their characteristics can be adapted to human feelings, and to ensure that noise operation, smooth brake Ping layer and high precision (5) Stable noise-free (6) In the car, the engine room and adjacent areas to ensure that noise. Because their systems use a high clock frequency. Always produce a true sine wave power supply current yet. Motor torque ripple does not appear. Therefore, to eliminate vibration and noise.3. Elevator control technology The so-called elevator control technology refers to the elevator drive system and electrical control system of automatic control. 70 as the 20th century in Chinas elevator was marked by the exchange of two-speed elevator. Its speed is used to change the elevator traction motor of the very few, two or multi-level approach to the number of windings, very few of them as high-speed winding of the winding, a very few number of windings as the low-speed winding. Windings for high-speed elevator-speed start-up and running, low-speed windings for braking and the maintenance of elevators. The early 80s, VVVF inverter controlled variable lift system available. It uses AC motor drives, are able to reach the level of DC motor, control the speed of the current has reached 6 m / sec. Its small size, light weight, high efficiency, energy saving, including the past almost all the advantages of the lift. Is the latest elevator drive system. Operation in vertical lift, there is also the starting point of the terminus station. For more than three-story elevator buildings, the starting point of the terminal stations and stops between the