Application of ABB frequency conversion technology in bridge crane

With the development of science and technology, frequency conversion technology has been widely used in industrial production. It has the advantages of wide speed regulation range, high speed regulation accuracy, smooth starting and braking, and can achieve stepless speed regulation. Most of the frequency converter control methods of various brands on the market use flux vector control FVC, while ABB uses a unique direct torque control DTC method. The torque step rise time of the DTC control method is less than 5ms, which is at least half that of the FVC control method, and the dynamic control accuracy is one order of magnitude higher than that of FVC; especially when running at low speed, the power supply quality of the power grid is poor, and the waveform is distorted, DTC can still maintain a high control accuracy.

1. Introduction of ABB AC speed control device

ABB's AC speed control devices are divided into two series: ACC and ACS. ACC and ACS are basically the same in hardware composition and structure, and the difference lies in the control software; ACC is specially designed for cranes. It has a standard lifting application macro that specifically controls the brake, which is used for potential loads. It can make the motor hold the weight at zero speed when the brake is opened, and then accelerate to a given value according to the acceleration and deceleration curve set in the device, solving the problem of hook slippage. ACS is designed for friction loads such as fans, water pumps, and translation mechanisms. In cranes, it is mainly used for translation mechanisms such as walking.

Therefore, in the 75t/20t double-beam crane designed by our company for Hunchun Power Plant, ABB's AC speed control device was selected, of which the main hoist and auxiliary hoist adopt ACC800, and the trolley and carriage travel adopt ACS800.

2. Selection of speed regulating device

1. Selection of inverter capacity

The inverter capacity should be selected based on the principle that the inverter rated current is greater than the motor rated current:

Ib ≥ Id × K1 × K2 / K3

Where: Ib - rated current of the inverter;

Id - rated current of the motor;

K1 - Maximum load factor, which is the ratio of the required maximum torque to the rated torque of the motor;

K2 - Redundancy coefficient, generally K2 = 1.2

K3 - inverter overload capacity coefficient. Different inverter manufacturers have different K3 values. ABB and Yaskawa generally take K3 = 1.5, and Siemens takes K3 = 1.36

2. Selection of brake resistor :

The resistance of the brake resistor should be such that the brake current does not exceed half of the rated current of the inverter:

IB=UD/R≤Ie/2

Thus we get R≥2UD/Ie

Where: R-brake resistor

UD- voltage on the DC side after rectification in the inverter

Ie- inverter rated current

IB-Braking current

Power of brake resistor:

PB≥αBUD2/R

Where: PB- braking resistor power

αB-selection coefficient

UD- The voltage on the DC side after rectification in the inverter

R-brake resistor

The value range of αB is about αB＝0.3~0.5. Because in the crane, the working state of the whole process of hook descending belongs to the regenerative braking state of the motor, which can be considered as a long-time working system, so αB＝1.0 is selected.

3. Selection of brake unit:

The function of the brake unit is to connect the energy consumption circuit when the voltage of the DC circuit exceeds the specified limit, so that the DC circuit releases energy through the brake resistor. The rated current of the brake unit is selected according to twice the current flowing through the brake resistor under the normal DC voltage:

ICM≥2UD/R

3. System introduction of bridge crane

There are two 75t/20t double-beam bridge cranes in the power plant of Hunchun Power Plant. Normally, the two bridge cranes can operate independently. When it is necessary to lift the generator stator or other heavy objects, the two bridge cranes are combined into one. In the driver's cab of any bridge crane, the coordinated operation of the two bridge cranes can be controlled, and the operation of the other bridge crane can also be controlled independently. Therefore, the electronic control system adopts the three-level control scheme of "PLC+frequency conversion speed regulation+MPI network".

The control process of the bridge crane is to transmit the digital signal of the gear position of the linkage station master controller to the PLC. After the PLC calculates and processes it, the PLC analog output module outputs a DC voltage signal (0~10V) to the AC inverter. Through the internal parameter setting of the AC inverter, the corresponding speed is output. The speed of each gear can be set arbitrarily in the PLC.

The electrical systems of the two bridge cranes are the same, mainly consisting of the main lifting mechanism, auxiliary lifting mechanism, trolley running mechanism, carriage running mechanism transmission system, bridge crane operation control system and other parts.

① Lifting mechanism

The main lifting mechanism is driven by a YZPB (F) 250M1-6 37Kw variable frequency motor. The auxiliary lifting mechanism is driven by a YZPB (F) 225M-6 30Kw variable frequency motor. It uses ABB's ACC800-01-0060-3, a built-in brake chopper designed specifically for potential loads; the speed regulation is a closed-loop control with an encoder, and the speed regulation range is 1:10.

Main lifting speed: 0.18~1.8m/min; auxiliary lifting speed: 0.68~6.8m/min. The main controller is divided into four gears, 10%, 30%, 60%, 100% of the rated speed respectively; starting, stopping and speed transition of each gear are smooth and shock-free, which belongs to the gear stepless speed regulation mode.

The operating handles of the main and auxiliary hooks are respectively arranged on the left and right linkage platforms, which can realize the requirements of simultaneous operation of the main and auxiliary hooks and the auxiliary hook cooperating with the main hook to tip or turn over the lifting components.

The circuit diagram of the lifting mechanism is shown in Figure 1:

②Large and small car running mechanism

The trolley running mechanism is driven by two YZPB (F) E132M2-4 6.3Kw variable frequency motors, and the two motors are controlled by a set of inverters; the trolley running mechanism is driven by a YZPB (F) E132M1-4 5.5Kw variable frequency motor. The trolley and trolley running mechanisms are displacement loads, so ABB ACS800-01-0025-3 (trolley) and ACS800-01-0011-3 (trolley) inverters are used for speed regulation. The system adopts open-loop control with a speed regulation range of 1:10.

The running speed of the trolley is 3~30m/min; the running speed of the small trolley is 1.8~18m/min. Like the lifting mechanism, the system uses the master gear switch quantity to process through the PLC, output analog quantity to the AC inverter, and then the AC inverter outputs the corresponding speed. The speed of each gear can be set arbitrarily in the PLC. The master gear of the trolley and the small trolley is divided into five gears, and the speed of each gear is 10%, 30%, 50%, 70%, and 100% of the rated speed; like the lifting mechanism, it also belongs to the gear stepless speed regulation mode. The circuit schematic diagram of the trolley and small trolley operating mechanism is shown in Figure 2:

IV. On-site commissioning of ABB AC speed control device

1. Setting of main parameters of inverter ACC800

①First, select the application macro

ACC provides two application macros: CRANE and M/F CTRL. CRANE macro is an upgrade application macro without master/slave bus function; M/F CTRL is an upgrade application macro with master/slave bus function. This machine selects CRANE macro.

② Setting of basic parameters

Set 99.5~99.9 parameters according to the rated voltage , current , speed, power, etc. on the nameplate of the motor ; you can also use the FUNC function key of the CDP312 control panel to set parameters step by step according to the English prompts of the startup wizard; after the parameters are set, the motor identification operation can be performed. When the motor and the device it drives cannot be separated, the 99.10 parameter should select ID MAGN; when the motor and the device it drives are separated, in order to ensure the best control accuracy, the 99.10 parameter should select STANDARD; according to the characteristics of ACC, the brake response digital input point set by the 10.1 parameter must correspond to the actual wiring. If there is no signal at this input point, the inverter will not be able to start;

③Setting of other parameters

Parameters such as group 13 (analog input), group 14 ( relay output), group 20 (limit value), group 23 (speed control) and group 27 (brake chopper) can be set according to actual needs; the lifting part of this bridge crane adopts the Japanese Watanabe pulse encoder, and the encoder is set by group 50 parameters. The corresponding parameter 98.1 must be set to RTAC-SLOT1 to activate the pulse encoder and make it available. ACC800 has two external control modes: FIELD BUS mode and STAND ALONE mode. This bridge crane adopts external switch control, so parameter 64.1 should be selected TRUE.

2. Setting of main parameters of ACS800 inverter

The trolley running mechanism of the bridge crane adopts ACS800 inverter and open-loop control without encoder. The parameter setting is relatively simple, and the 99.4 parameter is set to DTC control. After setting the group 99 parameters according to the motor nameplate, the motor identification operation can be performed. After the motor identification operation, according to actual needs, set the parameters of group 10 (start/stop/direction), group 11 (given selection), group 13 (analog input), group 14 (relay output), group 20 (limit value), group 21 (start/stop), group 23 (speed control) and group 27 (brake chopper). When the parameter setting is completed, the setting of the inverter parameters of the whole machine is completed.

5. Problems encountered during debugging

During the debugging in the manufacturing plant, due to limited conditions, the speed control device was debugged with the motor only, without the brake. When debugging the main hoist, the given signal was zero, but the motor did not stop. ACC is designed specifically for cranes. After receiving the brake closure confirmation signal, the speed control device also detects the speed signal. When the speed signal is zero, the speed control device stops outputting after a delay. The motor was locked by artificial means. Once released, the motor continued to adjust, and the speed control device never stopped outputting. When checking the device, it was found that when the motor speed was zero, the speed display value of the inverter still had a very small value. After checking the motor, it was found that the connection of the sensor was not fixed well, and the sensor still had signal output due to vibration and other reasons. After fixing it, the above phenomenon disappeared. The same problem was found when debugging the auxiliary hoist. After checking that there was no problem with the motor, it was considered whether there was a problem with the encoder. After replacing it, everything was normal. Therefore, the debugging process without mechanical brake is also necessary. Remind colleagues that you must pay attention to the speed display value of the inverter during on-site debugging. If the speed display value of the inverter is still after the brake is locked, find out the cause immediately and eliminate the fault. Otherwise, the inverter will be in danger of burning out.

Conclusion

The use of ABB frequency conversion technology solves the problems of the old speed control system, such as high failure rate, complex circuits, inability to smoothly adjust speed, and high maintenance. It also simplifies the design work and takes the electrical control performance to a new level. Its reliability and advancement are unmatched by the old speed control system, and it is welcomed by users for its superior performance-price ratio.