Abstract: Construction hoists are indispensable construction equipment in modern high-rise construction. This paper discusses the application of variable frequency drive (VFD) systems in construction hoists, mainly elaborating on the system's control scheme and parameter adjustment. Practical application verifies the effectiveness of the control system, demonstrating its irreplaceable role in ensuring construction schedule and safety, reducing construction costs, and alleviating labor intensity.
1. Introduction
Construction hoists are construction elevators used in buildings, and can also be used as outdoor elevators and hoisting cages on construction sites. They are mainly used in the construction of interior and exterior decoration of high-rise buildings, bridges, chimneys, and other structures. They are one of the essential and important vertical transportation facilities for transporting construction workers, construction materials, tools, and equipment during high-rise construction. The manufacturing technology of domestically produced construction machinery is constantly improving. With the widespread application of frequency converters in hoists, comfort and safety are becoming increasingly sophisticated, laying the foundation for the internationalization of domestically produced construction machinery.
2. Structure of the elevator
2.1 Structure of Construction Hoist
The elevator mainly consists of eight parts: elevator car, door system, weight balance system, traction machine, guiding system, hoistway and guide rails, electric drive system, and electrical control system. These parts work in coordination through the control unit to ensure the stable operation of the elevator.
2.2 Introduction to the Functions of the Construction Hoist Control System
The PLC-controlled elevator system mainly has three operating modes: operator-controlled, operatorless, and fire-fighting. Operator-controlled mode involves specialized personnel controlling the elevator; operatorless mode allows construction workers to control the elevator as needed; and fire-fighting mode requires firefighters to control the elevator exclusively during a building fire, without responding to external calls.
2.3 Workflow of the construction hoist control system
When the elevator detects an external or internal call signal, it immediately compares the calling floor with the current floor to select the destination. For comfort, the elevator uses a frequency converter to regulate speed. The car initially runs at a low speed to ensure smooth operation, then at medium to high speed. When the target floor deceleration point signal is detected, it immediately decelerates, gradually reducing speed from medium to low to bring the car to a smooth stop at the floor level. The doors then open after a few seconds, followed by a delay before closing to allow personnel and goods to enter the car. The elevator then proceeds to the called floor. Throughout this process, the elevator displays the car's current floor position in real time, completing a full call response cycle. The control system also includes fire safety functions.
3. Elevator Control Scheme
The electrical control system is a crucial component of construction hoists, determining the overall performance of the machine. Ordinary hoists use contactors and relays for raising, lowering, and stopping, resulting in limited speed, significant starting and braking shocks, severe damage to the structure and mechanisms, and easy failure of electrical components. Furthermore, their low operating speed negatively impacts both construction speed and the profitability of construction companies. The Puchuan PS500-L integrated construction hoist frequency converter integrates the control logic of ordinary hoists, enabling zero-speed brake release, soft start, and speed adjustment, significantly reducing mechanical shock, extending service life, and improving comfort. Utilizing the PS500-L series frequency converter specifically designed for construction hoists, it features the following characteristics:
• During the upward and downward movement, the frequency converter simultaneously detects the output frequency and output current while controlling the brake. When the brake requirement is met, it outputs a brake signal to achieve dual protection for the safety of equipment and personnel.
• It has a brake feedback input function. When the frequency converter outputs a brake signal but the actual brake does not operate, the frequency converter displays an alarm message, which can more quickly determine the location of the machine fault and improve the efficiency of equipment fault inspection and maintenance.
• By connecting to the limit switch signal, an emergency stop is initiated when the elevator reaches the limit position, ensuring that the equipment stops safely, quickly, and reliably.
4. On-site equipment status
A customer's on-site construction ladder transmission mechanism is a 2-motor worm gear transmission system. The electromagnetic brake three-phase asynchronous motor has the following specifications: 11KW 380V 29A 60HZ 1668RPM. It is configured with an integrated inverter model: PS500-39-030-4, with a rated power of 30KW and a rated output current of 60A.
The scene photos are shown in Figure 1.
Figure 1
Table 1 Parameter Settings
After adopting variable frequency speed control (VFD) for construction hoists, the hoists achieve smooth operation, improve operating efficiency, eliminate starting and braking shocks, reduce electrical maintenance, lower energy consumption, and improve power factor. The significant characteristics of VFD speed control are as follows:
1. High efficiency, with a maximum operating speed up to twice that of traditional elevators;
2. Stepless speed regulation effectively solves the impact on structures and mechanisms, and extends the service life of mechanical structures such as gears, racks, and rollers.
3. The soft-start function of the frequency converter reduces the inrush current to the power grid when the motor starts and alleviates the mutual interference between electrical equipment.
4. Selectable acceleration and deceleration curves ensure passenger comfort and reduce impact during cargo loading; adjustable acceleration and deceleration times and operating frequency ensure accurate leveling of the elevator, reducing the demands on the driver.
5. The use of frequency converters reduces the equipment maintenance costs of elevators, bringing economic benefits to enterprises.
5. Summary
The application of frequency converters reduces the impact on mechanical equipment such as speed reducers and couplings, and also reduces the impact on the power grid, improving work efficiency. Therefore, the frequency conversion of construction ladders is an inevitable direction for future development. Integrated frequency converter systems for construction ladders offer a more professional system solution. This control system boasts comprehensive safety protection functions, convenient installation and maintenance, and one-stop after-sales service, gaining widespread customer recognition.
