Abstract: This article introduces the working principle and application environment of bridge cranes, and elaborates on the crane function modes of Delta VFD-VE series frequency converters. It provides guidance for the application of VFD-VE in the crane industry.
Abstract: The paper introduces the working principle of bridge crane and application environment. And then expounds the platform of VFD - VE series inverter crane function as to provide guidance on VFD - VE application in industry.
Keywords: bridge crane VFD-VE crane function
1 Introduction
A bridge crane is a type of crane that runs on elevated tracks. The bridge of a bridge crane runs longitudinally along tracks laid on both sides of an elevated structure, while the trolley runs laterally along tracks laid on the bridge, forming a rectangular working area. This allows for full utilization of the space beneath the bridge for lifting and transporting materials without obstruction from ground equipment.
Bridge cranes are widely used in indoor and outdoor warehouses, factories, docks, and open-air storage yards. Bridge cranes can be divided into three types: ordinary bridge cranes, simple beam bridge cranes, and metallurgical-specific bridge cranes. This article mainly utilizes Delta VE series and B series frequency converters to drive the bridge crane smoothly.
2- bridge crane
2.1 Process Structure
A typical bridge crane generally consists of a trolley, a bridge traveling mechanism, and a bridge metal structure. The trolley itself is composed of three parts: a hoisting mechanism, a trolley traveling mechanism, and a trolley frame.
The lifting mechanism includes a motor, brake, reducer, drum, and pulley block. The motor drives the drum to rotate via the reducer, causing the wire rope to wind onto or unwind from the drum to lift or lower the load. The trolley frame is the frame that supports and mounts the lifting mechanism and trolley traveling mechanism, and is usually a welded structure.
The driving methods of crane traveling mechanisms can be divided into two main categories: one is centralized drive, which uses a single electric motor to drive a long transmission shaft to drive the two drive wheels on both sides; the other is separate drive, where each drive wheel on both sides is driven by a separate electric motor. Medium and small bridge cranes often adopt a "three-in-one" drive method that combines the brake, reducer, and electric motor into one unit. For large-capacity ordinary bridge cranes, universal couplings are often used in the drive device for ease of installation and adjustment.
Ordinary bridge cranes are mainly electrically driven and are generally operated from the operator's cab, although remote control is also available. Lifting capacity can reach 500 tons, and span can reach 60 meters.
2.2 Driving Demand
As a general-purpose piece of equipment for handling large and heavy items, bridge cranes have special requirements for their drive mechanisms:
1. The crane should have a large starting torque, usually exceeding 150% of the rated torque. If factors such as overload testing are taken into account, it should provide at least 200% of the rated torque during starting and acceleration.
2. Due to the presence of the mechanical brake, in order to ensure a smooth switching between the inverter output torque and the mechanical brake braking torque and to prevent slippage, the control timing of the inverter start signal and the mechanical brake action signal must be controlled.
3 When the hoisting mechanism moves downward or the translation mechanism decelerates rapidly, the motor will be in a regenerative power generation state, and its energy will be fed back to the power source. It is necessary to discuss how to handle this part of the regenerative energy according to different site conditions.
4. When the lifting mechanism grabs a heavy object and leaves or touches the ground, the load changes drastically. The frequency converter should be able to smoothly control this impact load.
3. Variable frequency drive control
3.1 Brake Drive Control
To address the specific requirements of bridge cranes, Delta's VFD-VE series frequency converters are designed with customized drive functions. By monitoring the output current and output frequency in real time through the converter's multi-function terminals, the crane's brake system is controlled, as shown in Figure 1. During startup, if both the output current and output frequency are greater than the set values, the brake is engaged; when the crane stops, if either the output frequency or output current is less than the set value, the brake is disengaged. This method ensures that the frequency converter provides sufficient torque while guaranteeing system safety.
3.2 Lifting Drive Control
The inverter's capacity must be greater than the output required by the load. In the formula: 1.33 is the overload factor; kW is the required motor shaft output power; is the motor efficiency; and is the motor's power factor. The hoisting mechanism requires a starting torque of 1.3–1.6 times its rated torque. Considering the need for a 125% overload, its maximum torque must be 1.6–2 times the rated torque to ensure safe operation. For inverters driving motors of equivalent power, they can provide an overload capacity of up to 60 seconds and 150% of the rated torque; therefore, the overload factor k = 2/1.5 = 1.33.
— Current waveform correction coefficient (1.05-1.1 for PWM modulation)
— Rated output current of the frequency converter, A
—Rated motor current (A) under mains frequency power supply
Typical large-tonnage cranes have two independently driven hoisting mechanisms. Each hoisting mechanism is driven synchronously by two motors, rotating its own wire rope drum, and then lifting the hook through a multi-stage reduction gear block of moving pulleys. The variable frequency speed control transmission scheme of the hoisting mechanism adopts a "one-to-one" scheme with one frequency converter driving one motor. To improve the dynamic characteristics and high torque output capability at low speeds, each motor uses closed-loop speed control with a pulse encoder. The two frequency converters of each hoisting mechanism use a master-slave control scheme with power balance and speed synchronization control functions provided by Zhongke Frequency Converter. These control schemes can achieve precise torque balance distribution between the two motors and speed synchronization of the two hoisting mechanisms.
3.3 Translation Drive Control
The traversing mechanism of a crane is divided into a trolley mechanism and a crane tripping mechanism, both of which generally employ a multi-motor drive scheme. Due to the large rotational inertia of the crane's traversing mechanism, a large starting torque is required to accelerate the motors. Therefore, the motor shaft output power required for the crane's traversing mechanism should consist of the load power and the acceleration power. Since the traversing mechanism uses a common V/F open-loop frequency control method where one frequency converter drives multiple motors, the following formula must be satisfied when selecting the frequency converter capacity:
Where — current waveform correction coefficient (taken as 1.05-1.1 for PWM modulation).
— Rated output current of the frequency converter, A
—Rated current of a single motor under mains frequency power supply, in A
—Number of motors driven by one frequency converter
Because the electronic thermal relay protection function provided by the frequency converter cannot achieve overload protection for a single motor in the general V/F open-loop frequency control mode of "one-to-many" frequency converter, a low-voltage circuit breaker with thermal overload protection function is connected in series in each motor circuit to achieve overload protection for a single motor. The motor fault signal is taken from the auxiliary contact of the low-voltage circuit breaker.
3.4 Delta Inverter Selection
Delta's VE series frequency converters, tailored to the control requirements of this system, offer low price, high quality, noise resistance, durability, and ease of analog control, making them suitable for harsh carbon environments. Their retrofit costs are low. The parameters of the frequency converters used in the overhead crane retrofit are as follows:
(1) One VFD150V43A-2 15kw 20hp 32a 380v 50hz frequency converter is selected for the large vehicle.
(2) The trolley frequency converter is selected as VFD055V43A-2 5.5kw 7.5hp 16a 380v 50hz 1 unit.
(3) One VFD075V43A-2 7.5kw 10hp 22a 380v 50hz frequency converter was selected.
4. Implementation of the electronic control system
4.1 Principle Design of Electrical Control System
The variable frequency speed control system mainly consists of a Delta VE series frequency converter, an ES series PLC, and a dual-handle linkage control console. The PLC collects signals from the hand controller, performs logical judgments through the program, and adjusts the output of the frequency converter based on the judgment results to control the direction, speed, and torque of the drive motor, replacing the original traditional wound-rotor series resistance speed control drive system. The frequency converter brake drive control is shown in Figure 2.
F=20Hz 00-10=0 (Running in VF mode)
01-12=2 (Acceleration time 2s)
01-13=2 (Deceleration time 2s)
02-13=42 (Crane movement)
02-31=3Hz, 02-32=20% (When the output frequency is >3Hz and the output current is >20%, the overhead crane will open the circuit breaker).
02-33=4Hz, 02-34=30% (When the output frequency is <4Hz and the output current is <30%, the overhead crane will shut off the brake).
(2) Parameters of the trolley frequency converter:
F=10Hz 00-10=0 (Running in VF mode)
01-12=5 (Acceleration time 5s)
01-13=5 (Deceleration time 5s)
02-13=42 (Crane movement)
02-31=3Hz, 02-32=20% (When the output frequency is >3Hz and the output current is >20%, the overhead crane will open the circuit breaker).
02-33=4Hz, 02-34=30% (When the output frequency is <4Hz and the output current is <30%, the overhead crane will shut off the brake).
3 key parameters of vehicle inverters:
F=10Hz 00-10=0 (Running in VF mode)
01-12=5 (Acceleration time 5s)
01-13=5 (Deceleration time 5s)
02-13=42 (Crane movement)
02-31=3Hz, 02-32=20% (When the output frequency is >3Hz and the output current is >20%, the overhead crane will open the circuit breaker).
02-33=4Hz, 02-34=30% (When the output frequency is <4Hz and the output current is <30%, the overhead crane will shut off the brake).
5. Conclusion
Bridge cranes powered by Delta VE frequency converters exhibited no hook slippage or speed instability during operation or shutdown. Delta VE frequency converters reduced the failure rate of the original system and improved the flexibility of on-site control. While enhancing system operation quality, they also saved customers operating costs.
