Bridge cranes are indispensable equipment for my country's national economic development and are important lifting equipment in large-scale manufacturing workshops. The control of bridge cranes requires high standards for stable, safe, and reliable operation.
This article mainly introduces the successful application of HiPu Monte HD30 series frequency converters and HDRU series energy feedback units in a 20-ton bridge crane, as well as the successful energy-saving solution achieved through four-quadrant frequency conversion technology.
1. Characteristics of Bridge Crane Systems
A bridge crane is a lifting device that spans across workshops, warehouses, and material yards to lift and transport materials. Because its two ends are supported by tall concrete pillars or metal supports, resembling a bridge, it is distinguished from other lifting equipment and is therefore called a bridge crane.
Bridge cranes run longitudinally along tracks laid on elevated structures on both sides, making full use of the space beneath the bridge to lift materials without being obstructed by ground equipment. They are the most widely used and numerous type of lifting machinery.
A bridge crane generally consists of a lifting trolley, a bridge traveling mechanism (main trolley), and a bridge metal structure.
The crane trolley consists of three parts: the hoisting mechanism, the trolley traveling mechanism, and the trolley frame. The hoisting mechanism includes a motor, brake, reducer, drum, and pulley block. The motor drives the drum to rotate through the reducer, causing the wire rope to wind onto or unwind from the drum to lift or lower heavy objects. The trolley frame is the frame that supports and mounts the hoisting mechanism and trolley traveling mechanism, and is usually a welded structure.
The main trolley runs on the elevated track, driven by two motors on both sides of the bridge frame for longitudinal movement; the auxiliary trolley moves on the bridge arm, driven by a single motor for lateral movement; the lifting mechanism is mounted on the auxiliary trolley and driven by a single motor for vertical movement. The three sets of motors can be controlled from the control room to switch directions and accelerate/decelerate.
The driving methods of the traveling mechanism of a bridge crane 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. The bridge cranes on site are all 20-ton cranes, and they all use separate drive. The power configuration is shown in Table 1.
Table 1 Power Configuration Relationship of Bridge Cranes
Location | motor power | Load characteristics | Braking method |
The left drive motor of the large vehicle | 5.5kW | Normal load | Deceleration braking + electromagnetic brake |
Right-side drive motor of the large vehicle | 5.5kW | Normal load | Deceleration braking + electromagnetic brake |
The trolley running mechanism drive motor | 4kW | Normal load | Deceleration braking + electromagnetic brake |
Trolley lifting drive motor | 22kW | Large inertia load | Deceleration braking + electromagnetic brake |
The control room transmits analog speed signals to the PLC system via control handles; after processing by the PLC system, the signals are output to the frequency converter; the frequency converter drives the motor to run according to the operating commands and frequency parameters of the PLC system; at the same time, the PLC system controls the opening and closing of the electromagnetic brake to complete the power control.
2 Application Solutions
2.1 System Configuration
There are a total of four AC motors on site: two 5.5kW trolley drive motors, one 4kW trolley drive motor, and one 22kW hoisting motor.
The trolley is driven by a motor that runs on an elevated track, characterized by its large span and long travel distance. To ensure that it does not tilt during long-distance operation, an 18kW frequency converter (HD30-4T018G, V/f control mode) is selected to drive two 5.5kW motors. Excluding the effects of motor slippage and pressure between the drive wheels and the track, the two motors operate at essentially the same speed.
The trolley travel drive motor drives the trolley to run on the bridge arm. The track span is small, so a 5.5kW frequency converter (HD30-4T5P5G, V/f control mode) is selected to drive a 4kW AC motor.
The trolley lifting motor is the most critical motor in the entire system, responsible for lifting a 20-ton workpiece. A 37kW frequency converter (HD30-4T037G, vector control) is selected to drive a 22kW lifting motor.
The matching relationship between motors and frequency converters is shown in Table 2.
Table 2 Matching Relationship between Motor and Frequency Converter
direction | motor | quantity | drive | Control method | Accessories |
cart | 5.5kW | 2 | HD30-4T018G | V/f | \ |
small car | 4kW | 1 | HD30-4T5P5G | V/f | \ |
promote | 22kW | 1 | HD30-4T037G | PG-free vector control | HDRU-4T075 |
The entire control system of the bridge crane consists of a control room control panel, a PLC control system, a frequency converter drive system, a motor system, and a braking system. The PLC coordinates and processes the input and output commands of the control system. The motion direction and speed signals output from the control room control panel are processed by the PLC to control the corresponding frequency converters. Simultaneously, the frequency converters feed back operating signals to the PLC. The PLC judges the frequency converter operating signals and output frequency, and controls the electromagnetic brake to release the holding brake. The corresponding motor then outputs power. The entire system control is shown in Figure 1.
2.3 Control signal wiring
The trolley and trolley drive frequency converters operate in V/f control mode. The PLC control system provides commands for running direction, analog speed, and fault reset, while the frequency converters provide feedback signals to the PLC regarding the frequency converter's operating status.
The wiring diagram is shown in Figure 2 , and the parameter settings are shown in Table 3 .
The lifting inverter drives a high-inertia load motor, requiring very high lifting torque. The load is at its maximum the instant the brake is released, while the motor is still at zero speed. The HD30 uses PG- free vector control, and its starting torque can reach 180% of the rated torque at 0.5Hz , which can meet the requirements of lifting conditions and ensure that the lifting system does not slip.
When the hoist lowers the workpiece (load), the AC motor becomes a generator under the drag of the workpiece, causing the DC bus voltage to rise. Conventional frequency converter systems use braking units and braking resistors to dissipate the excess voltage on the DC bus to ensure the normal operation of the frequency converter. However, here we choose the Hipumont HDRU-4T075 energy feedback unit. The energy feedback unit not only saves on the cost of braking units and braking resistors, but more importantly, it can invert the excess electricity on the DC bus into industrial frequency AC power and feed it back into the grid, thereby achieving energy savings.
The wiring diagram of the booster inverter (including HDRU ) is shown in Figure 3 , and the parameter settings are shown in Table 4 .
2.4 Parameter Settings
Table 3 Parameter Settings for the Inverter Drives of Large and Small Vehicles
Parameter number | Setting value | Select Definition | Parameter number | Setting value | Select Definition |
F00.10 | 3 | The frequency setting channel is an analog input. | F15.00 | 2 | DI1 is selected as forward rotation. |
F00.11 | 1 | Command setting channel selection is terminal run command | F15.01 | 3 | DI2 is selected as inverted |
F00.17 | 1 | Running direction selection is reversed. | F15.04 | 46 | DI5 is selected as reset |
F02.13 | 1 | The shutdown method is set to deceleration shutdown. | F15.18 | 2 | DO1 is selected as the inverter is running. |
F03.01 | 20 | Acceleration time | F16.01 | 2 | The analog A1 input function is for frequency setting channels. |
F03.02 | 20 | deceleration time |
Parameter number | Setting value | Select Definition | Parameter number | Setting value | Select Definition |
F00.01 | 2 | Open-loop vector operation | F08.04 | 715 | Motor rated speed |
F01.10 | 3 | The frequency setting channel is an analog input. | F08.07 | 0.210 | Stator resistance |
F01.11 | 1 | The command specifies the channel for terminal control. | F08.08 | 0.207 | Rotor resistance |
F01.17 | 1 | Reverse the direction of operation | F08.09 | 1.4 | Leakage |
F02.02 | 2.00 | The starting frequency is 2Hz | F08.10 | 21.1 | Mutual induction |
F02.03 | 0.30 | The start-up frequency is maintained for 0.3 seconds. | F08.11 | 30.7 | No-load excitation current |
F02.13 | 1 | Free stop | F15.00 | 2 | Forward |
F08.00 | 22.0 | Motor rated power | F15.01 | 3 | Reversal |
F08.01 | 380 | Motor rated voltage | F15.04 | 46 | Fault Reset |
F08.02 | 46.9 | Motor rated current | F15.19 | 2 | Inverter in operation |
F08.03 | 50.0 | Motor rated frequency | F16.01 | 2 | The analog A1 input function is a frequency setting channel. |
2.5 Debugging Steps
Debugging of large vehicle drive frequency converter
The large trolley uses one frequency converter to power two motors. During commissioning, the maximum operating frequency, acceleration/deceleration time, and frequency command channel must be set first. Then, a jog test should be performed on each motor individually to confirm the correct wiring sequence. This is to prevent malfunctions caused by the two motors operating in opposite directions.
Car drive frequency converter debugging
The main tasks of trolley commissioning are to set the maximum operating frequency of the motor, acceleration and deceleration time, and frequency setpoint channel. During the test run, it is also important to check whether the direction indicated by the control lever matches the direction of motor operation; otherwise, the direction of operation of the frequency converter needs to be set.
Improve drive inverter debugging
The boost drive inverter uses vector control, so the motor parameters in the inverter need to be set according to the motor nameplate parameters first. Then, no-load self-tuning is required to achieve superior vector control. On-site testing shows that no-load self-tuning is significantly more effective than stationary self-tuning.
The energy feedback unit is easy to install. Connect the input (+) and (-) terminals to the inverter's DC bus (+) and (-) respectively, and connect the output terminals L1, L2, and L3 to the mains power grid. Set the feedback voltage to 670V, and leave other parameters at factory defaults. When the load is increased and decreased, the energy feedback unit inverts the excess voltage on the DC bus into mains AC power to feed back to the grid, maintaining the inverter's DC bus voltage within a safe range of 670V.
2.6 Actual Results
The entire solution features streamlined wiring and easy control. During trial operation, when lifting a 15-ton steel component, the lifting torque was sufficient, and the performance was stable, especially at high speeds. When lowering the steel component, the energy feedback unit provided an average feedback current of around 30A, resulting in significant energy savings. Furthermore, the horizontal movement was smooth, and the acceleration and deceleration performance during motion was excellent.
No overcurrent or overvoltage faults occurred during the entire commissioning process, and the machine's performance was fully recognized by the customer and the crane equipment supplier. In particular, the introduction of the energy feedback unit transformed the energy originally consumed in the braking resistor into AC power feedback to the power grid, reducing the crane's energy consumption and earning high praise from the customer.
3. Conclusion
The adoption of variable frequency control technology for motor control in bridge cranes improves system control performance, enhances control accuracy, and increases safety. The integration of a frequency converter and energy feedback unit in the lifting direction achieves industry-leading four-quadrant frequency conversion technology, which has significant implications for energy conservation in lifting equipment.
