The hottest Weichuang AC60 frequency converter and

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Weichuang AC60 frequency converter and Siemens S7

this paper introduces the RS-485 communication control and data format between Siemens s series PLC and Weichuang frequency converter, and analyzes in detail the advantages of communication control speed regulation system compared with general analog control speed regulation system. An application example and the idea of PLC program design are given

I. Introduction

in the paper industry, a synchronous production line initially adopted the following control mode: synchronous controller (such as ctkt governor) + slip motor → synchronous controller (such as delta) + frequency converter. Until now, most commonly used PLC + d/a module + variable frequency drive is the most common. When using d/a expansion module to control the frequency of the frequency converter, it is better than the synchronous controller, but PVC pipes with a diameter of 1m are also vulnerable to the fluctuation of analog signals and the inconsistent attenuation of analog signals caused by inconsistent distances, which reduces the working stability and reliability of the whole system. From an economic point of view, when multiple inverters need to be controlled, the cost will be greatly increased if d/a expansion module is used. We explain it with a six point system, so at least one 4-channel 4d/a module and one 2-channel 2d/a module are required to form the system. The price of only two modules is about 2500 yuan. Using s series PLC, not only the d/a module, but also the communication module is omitted (Mitsubishi FX series PLC requires a 485bd communication module, with a price of 200 yuan), because the programming port port0 (port1) of S is an RS-485 communication interface after setting parameters, and we can save a lot of input points of PLC host by combining input points. Taking a 6-point synchronous paper machine system as an example, only one s cpu224 host + 6 frequency converters can achieve all the functions of the paper machine, such as main speed rise/fall, proportion adjustment between points, tension, crawling, etc. Compared with the traditional PLC host +d/a module mode, it saves at least 3000 yuan. The more synchronous points, the greater the price difference and the more economical

II. System configuration (described by the 6-point synchronous system)

the synchronous control system of this paper machine adopts a Siemens s-cpu224 PLC and 6 frequency converters to drive the first press, the second press, the first cylinder, the second cylinder, the third cylinder, and the paper cutting (roll)

after the transformation, the following functions can be achieved: main lifting/main lowering, emergency stop, elimination of proportional memory, and there are proportional micro lifting/micro lowering, tension, and crawling at each point respectively

III. key points of program design

the focus of this system is the design and compilation of programs. First of all, we must understand the working principle of the paper machine synchronization system in detail, so we should pay attention to the following points when writing the program:

1. Speed chain function for the paper machine, when the whole production line operates normally, because the mechanical transmission ratio between each point is different, and the diameter of the drying cylinder is different, under the guarantee of a certain line speed, the motor speed at each point is bound to be different, That is, the frequency output by the frequency converter is different. In other words, there is a certain proportional relationship b between the speeds of two adjacent motors. We assume that the main speed is n, and the speed of 1 # - 6 # frequency converter is N1, N2, N3. The virus not only seriously affects our lives, N4, N5, N6. Namely:




n4=n3*b4= n1*b2*b3*b4

n5=n4*b5= n1*b2*b3*b4*b5

n6=n5*b6= n1*b2*b3*b4*b5*b6

it is not difficult to see from the above relationship that synchronization is carried out.During speed regulation, no matter which point the proportional coefficient is adjusted, it will not affect the synchronous relationship between other parts. Therefore, a subroutine module of speed chain is written according to the above principles. Make the program clear and concise

2. The following function can also be seen according to the above relationship. When pressing the "tight" button at any point, the following points will follow automatically. The previous point remains unchanged. When the "tension" button is released, the original synchronous linear speed will be restored. That is, the function of "not following in front of the heel" is mainly used to press this button and add Hz frequency under the existing synchronous line speed when the paper in a certain link is loose and slowly sagging

3. Each point of crawling function has (Hz). It is mainly used during maintenance

4. The memory and memory elimination function automatically remembers after each adjustment, and there is no need to adjust it again at the next boot, which is very convenient. If the whole system is disordered, the memory can also be eliminated, that is, the speed of each point runs under the main speed n

5. If the emergency stop function is abnormal, press the red mushroom head button to lock itself, and then the system pauses to close the output. After the abnormality is removed, release the mushroom head button, and the system will run at the linear speed just before the shutdown

6. Preparation of communication program

ac60 series inverter adopts the international standard Modbus protocol, and the communication format is RTU (remote terminal unit) mode. The communication data format is as follows:

composition of bytes: including start bit, 8 data bits, check bit and stop bit

start bit bit1bit2bit3bit4bit5bit6bit7bit8 no parity check odd check stop bit

protocol format explanation:

start bit, that is, the frame header starts with a transmission time pause interval of at least 3.5 bytes Transmit a frame of data in sequence until the end

Bit1 slave address the frequency converter is the slave, and the local address of the frequency converter is the slave address of PLC communication. The command code sent by the host is the parameter setting of the frequency converter (h-67)

bit2 command code, and the corresponding operations are carried out on the slave, such as 03h reading slave parameters, 06h writing slave parameters, and 08h loop self-test

bit3/bit4 data address high/low is the slave data address

bit5/bit6 data address high/low is the content of the slave data address

bit5/bit6 CRC check low/high

adopt Siemens SPLC programming as follows:

1, CRC check subroutine programming first set the programming port port0 (port1) through smb30 (smb130), that is, the content of even check (E, 8, 1) and the value of baud rate. Initialize the PLC. And write CRC verification subroutine. The programming port at this time cannot be monitored. Subroutines use multiple local variables to facilitate the invocation of other subroutines

in the Siemens sten programming environment (as shown in Figure 1)

CRC verification and communication protocol parameter prt0 port setting

set the following parameters of the frequency converter:

h-66=0//the frequency converter is set as the slave station

h-67=1//the communication address of the frequency converter is 1

h-69=3//the communication baud rate is 9.6K

h-68=1//(E, 8, 1)//Communication data parity

e-01=2//the operation of the frequency converter adopts 333 decoration engineering communication mode

e-02=6//the given frequency setting of the frequency converter adopts communication mode

2. The speed chain subroutine designs the subroutine according to the proportional relationship we mentioned above. The maximum resolution of the frequency converter, i.e. 0.01Hz, can be achieved by using floating-point operation processing and adjusting the proportional coefficient

3. The RS transmission format subroutine sends a frame of data every 30ms and sends it repeatedly. Practice has proved that the effect is very good

4. For others, pay attention to the amplitude limit of the rise and fall value (resolution) in unit time. The rise and fall speed of the master and the rise and fall speed of the slave must be divided into two timers

5. As shown in the above figure, the combination mode is adopted at the input points, which saves a lot of input points and effectively reduces the cost

VII. Conclusion

using PLC to communicate with frequency converters, it is easy to realize synchronous and proportional linkage operation between multiple frequency converters. The system has the characteristics of low cost, high signal accuracy (up to the highest resolution of the frequency converter), long transmission distance and strong anti-interference. We have made dozens of control systems in this way, and the users have responded very well. It has the characteristics of simple wiring, high control accuracy and low cost. It is especially suitable for the synchronization and proportional linkage of multiple frequency converters in addition to cost, as well as the occasions that require high frequency accuracy of frequency converters. (end)

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