The vector inverter technology is based on the DQ axis theory. Its basic idea is to decompose the current of the motor into D axis current and Q axis current. The D axis current is the excitation current and the Q axis current is the torque current. This could separate control the excitation current and torque current of the AC motor, so that the AC motor has similar control characteristics as the DC motor. It is an ideal control theory designed for the AC motor, which greatly improves the control characteristics of the AC motor. However, this control theory is not only applied to AC asynchronous motors, DC variable frequency motors (BLDC, that is permanent magnet synchronous motors) also use this control theory extensively. Here we’ll share some applications of vector inverters in the use of escalators.
Under the premise of not having other negative effects on the normal use of the escalator, the concept of vector frequency conversion speed regulation is introduced. That is, according to the signal generated by the sensor, the escalator runs at the original speed (50Hz) when someone is riding; when there is no one, the escalator decelerates to a low speed or stops running.
The system requires the frequency inverter to start and run smoothly, with good acceleration performance, large starting torque, and strong overload capacity. At the same time, it should have the ability to automatically switch the control system to industrial frequency operation when the inverter speed regulation system fails， to ensure the normal implementation of the escalator’s transportation function .
For passenger escalators, the peak usage period generally occurs in the afternoon and evening, and the usage rate in the rest of the period is low, which has considerable energy-saving space. According to the above transformation principles, considering the investment cost and automation level, the following frequency conversion drive schemes could be used:
1. Adopt frequency converter to drive the main machine of elevator, the frequency converter adopts multi-speed control mode, and set the main frequency (low speed), multi-speed frequency 1 (high speed) two operating frequencies;
2. Install an infrared sensor switch at the beginning and the end of the elevator. When passengers pass the elevator, the infrared sensor switch is triggered and sends a switch signal to the frequency inverter;
3. When there is passenger flow, the infrared sensor switch is triggered, and the inverter immediately accelerates to multi-speed frequency 2 and makes the elevator run at high speed;
4. When the elevator is running at high speed, the built-in timer of the inverter starts timing. If no passengers pass the elevator during the timing period, the inverter will automatically switch to multi-speed frequency 1 after the timing ends, and run at low speed;
5. If a passenger re-triggers the infrared sensor switch during the timer timing, the timer will re-timing;
6. For the elevator up and down, the peripheral control adopts switch interlock to ensure the normal operation of the escalator system;
7. In order to consume the excess energy generated during the down or braking process, a braking resistor must be installed on the frequency converter.
The structure of all Lingshida’s products adopts independent cooling air duct design, and some inverters adopt fully sealed design, which avoids direct contact between PCB boards and components and harsh environments, effectively prolonging the lifetime. Lingshida’s high-performance vector inverters’ electrical components are all made of industrial grade materials. The production process strictly implements the quality management system and adopts the entire process to control all links in the supply chain. A standardized factory building of 6000 square meters, with three intelligent production lines, and a dedicated laboratory equipped with a full set of test lines, simulates various harsh environments and is close to actual combat needs.
Post time: Nov-10-2021