Inverter rope hoist Application technology

Inverter  rope hoist  Application technology
I. Conventional inverter lifting mechanism
1. Structure Introduction
Frequency control technology in a tower hoist the transmission mechanism used in China for nearly 10 years, despite some successful applications experience, and there are a lot of inverter hoisting mechanism is now running the site, but compared to other industries, frequency conversion technology in the application of  rope hoist  tower far not reached the required level, which has cost reasons, there are also technical reasons.
Domestic and foreign programs currently used by a typical, technically speaking, very much the same, except that:
(A) drive different brands, which uses different control loops;
(2) The system is open-loop (no PG) or closed (with PG)
(3) in the form of mechanical structure is not the same: L-type arrangement, п-type arrangement or a font layout, etc.;
(4) is not the same type of gear, such as: cylindrical gear reducer or planetary gear; ratio is fixed or variable speed ratio and so on.
On the drive control technology, the difference was not involved in the control of the above changes in the way, are using an inverter for speed control of a motor typical pattern can also be referred to as conventional inverter hoisting mechanism. In all of these conventional inverter institutions, LIEBHERR EC-H type in the tower hoist mounted on a lifting mechanism frequency characteristics of the most prominent, and it uses 250V motor and matching drive, the configuration variable speed ratio deceleration machines, L-type arrangement. The program has a good lifting speed characteristics, the drawback is the high cost of the system, and general poor parts.
2. Conventional inverter hoisting mechanism design elements
(A) number of motor poles and power check
When the lifting mechanism of the basic parameters (eg: maximum weight, maximum operating speed, etc.) are given, the necessary number of poles of the motor and the power of determination and calculation, the design points are:
a) motor output speed should be less than 3000 rev / min (from the gearbox input stage operating speed restrictions);
b) the system should be less than the maximum operating frequency of 100Hz (the higher the frequency, the greater the power loss of the motor will be damaged constant power characteristics, lifting capacity greatly reduced without practical value);
c) checking the rated motor torque for maximum weight (considering the total transmission ratio, efficiency, magnification, etc.);
d) The rated power of the motor at high speed for checking from the weight (considering the total transmission ratio, efficiency, magnification, etc., if frequency is close to 100Hz, should be considered effective power reduced by 10 to 15%).
When selecting the motor power, according to the above conditions will be able to determine the basic gear reduction ratio and the motor power and the number of poles.
(2) electrical control system design
a) the selection of the inverter
When the system's electric motor is determined, you can proceed with the control system design. The first is the drive selection. Inverter on the market now many brands at home and abroad, the level of control and reliability vary greatly, technically can be roughly divided into the V / F control, vector control and DTC Direct Torque Control of three. Tower hoist for lifting mechanism, it would be best used with a vector control function or is a DTC Direct Torque Control function of the inverter, this inverter more brands, designers can according to their level of familiarity with technology support, other industries such factors as the use of plants to choose from.
Because the frequency of different brands, the same power inverter overload capacity and rated current value is not exactly the same. So, choose the drive capacity, not only depends on the size of the rated power, but also to check the rated operating current is greater than or equal to the rated current of the motor, general rule of thumb is to select the motor power inverter power is greater than 10 to 30 percent.
b) the selection of energy resistance
As electric hoist with inverter system, its design focuses on the state motor is in regenerative braking system reliability, because this system failures often occur when falling in heavy conditions, such as slip hook, overspeed, overvoltage and so on. That decreased weight condition when the inverter system will directly affect the performance of the entire lifting mechanism can operate safely. This requires a clear understanding of the designer feedback inverter drive system working process, in order to be aware of.
Most of the drive chain hoist product description on how to choose the resistance value of the energy and power are not very clear description, and often their recommended standard does not fully meet the requirements of lifting working conditions, while the article discussed in this regard is also rare, so the frequency of lifting control system design, the resistance parameter selection seemed to be somewhat confusing. This article will state motor operates in regenerative braking system when the working mechanism for qualitative analysis, the reader can get through these analyzes further calculation method for resistance parameter.
① resistance value is selected
You can sample the basic parameters given by the drive to determine the basic principle is to consider the DC link voltage (decreased weight conditions will exceed 600VDC) case, the resistor current does not exceed the rated current of the drive.
② resistance power selection
To accurately select the resistance of the power is very important, if the selection is too large, it will increase the system cost, too small will result in unreliable operation. But to reasonably accurate selection of resistance power consumption is a relatively trivial matter, many factors affect the parameters, such as: motor power size, gear reverse efficiency, running down the length of time, the size of negative acceleration, deceleration time and the moment of inertia of the transmission parts, etc. will affect the resistance power of selection. Therefore, we have to first drop from the analysis of system operating conditions in the working process, resulting method for determining the resistance power.
Decline in power is by weight "transmission parts", "motor" (At this point in the power generation state), inverter reverse rectifier circuit and then transmitted to the brake unit "resistor R" on, if the transmission link Reverse the lower the efficiency, resistance smaller power consumption.
Then there are:
"Resistor R" heating power consumption of the transmission path + = heavy decrease the power consumption of the power
Resistance can be further power consumption P expression:
Steady uniform drops in consumption:
Pe = ωm × Me × δ ①
Where: δ is the reverse transmission efficiency
Deceleration peak power:
Pm = Pe + δ × J × (ωm-ωd) / Ta ②
Where: J is the moment of inertia of the transmission system
Combining style and type ① ② are:
When lifting mechanism running at rated power status and high-speed drops, if this deceleration command is given, in the early stages of deceleration, the resistance will reach maximum power consumption;
The deceleration time is too short, it will cause the power consumption in the resistance peak rising;
System, the greater the moment of inertia and the load, the time of deceleration, the higher braking torque will cause the power consumption in the resistance peak increase;
When the mechanical efficiency of the transmission system, the lower the resistance power consumption is also lower.
See, to accurately calculate the resistor consumes power, it is necessary to drive the various components that the moment of inertia, the deceleration start point corresponding end of the speed and working speed, deceleration, and the length of time the system load is size. To determine the exact values   of these parameters in the system design stage there is a certain degree of difficulty, first, in the electric chain hoist is not completed before the product can not be accurately measured or calculated the transmission parts inertia; Second, in actual use , the system will follow the deceleration characteristics and needs of the scene change. So in most cases, neither strictly calculated resistance power. Experience the value of the motor power is generally 40 to 70%, and the reverse gear efficiency is low, you can use a smaller resistance power.
As long as the inverter system to fully understand the working status of the deceleration process, the system can be designed according to the actual performance to correct resistance parameters.
c) the control program to determine
The first is the system uses the open-loop or closed-loop control of the choice, I believe that the general tower hoist lifting mechanism can be used open-loop control mode, those requiring high accuracy speed control only to consider the case closed-loop control. If you want to constitute a closed loop system, there must be PG (encoder), the detection circuit and connecting lines. These links increase the complexity of installation; increase system cost; more importantly, reduce the reliability of the system, because in the closed-loop system, the feedback loop any small mistake may cause the system disorders.
Second is the speed of a given mode selection, the vast majority of the inverter has a variety of speed input methods, such as multi-stage switch input modes and analog given way to many brands of converter also has a bus communication interface. For conventional inverter hoisting mechanism, they use a switch as a speed reference, so different from a PLC or relay logic control. The author believes that the most simple system architecture should be the PLC and inverter communication interface transmission speed and control commands, so that the control cabinet cable minimum.
Second, the dual-frequency  lift hoist
1. Develop dual-frequency necessity lift hoist
So far, the drive tower hoist lift hoist on the application already has nearly 10 years of history, we know from the above analysis, frequency conversion technology tower hoist operation will bring more benefits and relevant national extension departments and industry associations are also organized many seminars inverter technology applications, but the actual amount used is not ideal, the industry only a few powerful OEMs launched frequency lift hoist, which is much can not be compared to other industry applications level. Reason to believe that limiting frequency conversion technology in the industry to promote the main reason is:
Frequency of service after a system failure is difficult, compared with conventional systems, increasing the tower hoist down maintenance time, increased user downtime losses;
Wire rope hoist inverter control system cost than conventional hoisting mechanism, increasing the promotion of difficulty;
Frequency lift hoist is about 60% of the cost of the inverter, the inverter due to the current price is still high, so the total system cost than conventional hoisting mechanism, but with the growing popularity of inverter technology and improve the price of the inverter there is a large decline in space, while the cost of conventional hoisting mechanism basically no longer potential. We believe that in the near future, the cost of conventional lift hoist will be no absolute advantage at all. Therefore, it is imperative industry technology workers how to design a service to reduce the pressure lifting system frequency.
2. Tower hoist lift hoist operating situation analysis
Measure a tower hoist ability to work not only with the hoisting mechanism of the maximum weight of this argument, but more important parameter is the size of the working torque, which is the safe operation of tower hoist an important indicator. It is because of torque limit parameters, tower hoist range is not possible in any work under all  Wire rope hoist  lifting maximum weight, but the actual operation of the construction site from the point of view, the maximum weight  lift hoist  tower work Condition is very small.
Vanda company's 5613 tower hoist, Wire rope hoist tower of the maximum lifting weight 8t, maximum working radius is 56m.
"Light-load area" from the weight of less than 4t, working radius of 56m, operating area of   9847m2;
"Reload zone" from the weight of greater than 4t, working radius of 24m, operating area of   1808m2;
"Full" area from the weight equal to 8t, working radius of 14m, operating area of   615m2;
Its working Dead ( hoist and trolley  minimum working radius) is approximately 3m, an area of   28m2.
After calculate: If 4t weight lifting weight load as the demarcation point, "overloaded zone" area of   operation only "light-load area" operating area of   18%.
And hoist tower at the site for the actual operation of statistics, a computer equipped with hoisting mechanism 8t tower hoist, lifting 4t more real load conditions is very small.
Through the above analysis are:
Tower hoist lifting capacity by half, more than 80% of the working conditions are not affected.
This gives us an idea: if the current by an electric motor and a variable frequency inverter control lift hoist to change the success rate of halving the two motors and two small inverter to co-drive, even if there is a motor or inverter failure, tower hoist in most cases still be working as usual. This greatly reduces the pressure on OEMs service, the user is also very beneficial.
For this particular tower crane Wire rope hoist electric hoist, lift hoist if dual frequency lifting program can:
At light loads, single-motor operation, can achieve energy savings and prolong system life purpose;
There is a drive is damaged, the work can be a single motor, the system will automatically disconnect the faulty circuit, stopping the machine can do maintenance on the system, greatly reducing the tower hoist manufacturer's sales pressure;
There is a failure of a motor, the same can be single-motor work, in most conditions without affecting the Wire rope hoist tower work;
Under heavy load, dual-motor work to perfect hoist tower frequency performance to meet the operational requirements;
The power components become smaller, reducing maintenance costs and difficulty.