Application of common DC bus frequency conversion

2022-06-13
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Application of common DC bus frequency conversion speed regulation system in polyester staple line

1. Introduction

polyester staple device is a main device in the west area of polyester Department of Shanghai Petrochemical Co., Ltd., with a total of six production lines and a design single line output of 15000 tons/year. The electric drive of the front spinning adopts the semiverter frequency converter and permanent magnet synchronous motor of AEG company in Germany, and the rear spinning adopts the long shaft drive of DC motor. The spinning device is a large-scale production device designed and manufactured by ourselves in the early 1980s. Although it has created certain economic and social benefits in the early stage of completion, due to the limitations of historical conditions, there are some congenital deficiencies. The product types and unit consumption can not meet the ministerial standards and can not meet the needs of the market. Therefore, it is transformed in the position of the original line 1 A 30000 T/a polyester staple production line (hereinafter referred to as the new production line) has been introduced. The electrical transmission adopts German Siemens 6SE70 Series frequency converter, permanent magnet synchronous motor (front spinning) and asynchronous motor (rear spinning). This paper discusses the application of shared DC bus multi inverter speed regulation system in spinning line

2. Development overview of variable frequency speed regulation system of synthetic fiber spinning machine

the development of variable frequency speed regulation system of synthetic fiber spinning machine can be roughly divided into three stages:

(1) large frequency converter speed regulation is driven by a high-power frequency converter to drive multiple permanent magnet synchronous motors. Motors can be started one by one or in groups. The utility model has the advantages of simple system and convenient control, and can ensure the synchronous operation of multiple motors. The disadvantage is that the capacity of frequency converter must be very large; Short circuit fault of single motor may cause frequency conversion trip and stop the whole spinning machine

(2) multiple small frequency converters drive, and each motor is driven by a small frequency converter. Compared with large frequency converter drive, the advantages are: a) one frequency converter drives one motor, which can realize soft start, and the capacity of frequency converter is basically the same as that of motor; b) When a motor fails, the corresponding frequency converter stops working, which will not affect the normal operation of the whole spinning machine. Disadvantages are: a) additional adjustment links are required for general setting and general startup; b) The output frequencies of several frequency converters will be discrete. In order to achieve speed synchronization, a serial communication interface needs to be added

(3) multiple small inverters with common DC power supply are used for driving. In addition to maintaining the characteristics of small frequency converter driving, it is more important to realize regenerative power generation braking and prevent shutdown faults caused by instantaneous low voltage (including instantaneous power loss)

3. Basic requirements of polyester staple fiber spinning device for electrical control system and analysis of the original driving system

(1) basic requirements of polyester staple fiber spinning device for electrical control system

the requirements of spinning machine for electrical transmission are "four high" and "one low"

● four highs: namely, high synchronization (the motor speed of different spinning positions of a spinning machine shall be consistent in transverse speed and synchronous in longitudinal proportion); High accuracy (stable speed, accuracy up to 0.1% ~ 0.01%); High speed or very high speed (under the condition of no speed-up gearbox, the motor speed is up to 8000 ~ 9000r/min); High reliability (ensure safe and continuous operation for 8000 hours a year at least)

● one less: less maintenance or no maintenance, no need to look after. After adopting the speed regulation system composed of high-precision frequency converter and permanent magnet synchronous motor, high synchronization, high precision, high speed and less maintenance can be realized, but high reliability can not be achieved, which affects the stable, long and excellent production of spinning device. Taking 30000 T/a staple production line as an example, its daily output is 100 tons of staple fiber. If the external power is instantaneously low voltage (or instantaneously powered off), the metering pump frequency converter will be out of service and the motor will be stopped, which will increase the polyester melt pressure and force the melt booster pump of the polyester unit to stop, thus affecting the normal production of the polyester unit

(2) advantages and disadvantages of the original electric drive system

the frequency converter of the original 15000 T/a short silk direct spinning device belongs to the first generation of frequency converter, that is, one frequency converter drives multiple permanent magnet synchronous motors. This kind of frequency converter technically adopts a common commutation link and has a commutation circuit of auxiliary charging device. A) advantage: it is reliable even when the DC voltage is low. b) . when several times of the rated current (up to 3 times) in a short time, the current can also be exchanged reliably. c) . when the frequency converter changes from no-load state to load state, it can quickly suppress the limit value of starting current. However, there are still the following deficiencies in the operation of the frequency conversion device: a) since multiple motors share one frequency converter, the short wire device cannot realize soft start, so when selecting, we should not only consider the direct start at the highest frequency, but also consider that when several motors are running at high speed, a spinning position will continue to be put into operation after troubleshooting, so the capacity of the frequency converter has to be too large. b) The failure and shutdown rate of spinning machine is high. However, because the frequency converter can not bear the instantaneous low voltage (including instantaneous power loss), and due to lightning, cable grounding fault and switch switching operation, the instantaneous low voltage phenomenon will occur, resulting in the shutdown of the frequency converter, resulting in the shutdown of the whole spinning machine, resulting in huge losses. c) . regenerative power generation braking cannot be realized. DC drive is adopted for post spinning, so the maintenance of motor is very troublesome, and the adjustment of draft ratio is also very difficult

4. Analysis of the characteristics of the variable frequency speed regulation system of the front spinning device (the group powered by ups and with the smallest small △ vs value is the high-precision inverter permanent magnet synchronous motor open-loop synchronous drive system)

Figure 1 the variable frequency speed regulation system of the front spinning part of the new production line

the variable frequency speed regulation system of the front spinning part of the new production line is shown in Figure 1. The variable frequency speed regulation system of the front spinning device is mainly composed of UPS power supply and small inverter permanent magnet synchronous motor open-loop synchronous drive system. The main improvement of the front spinning device is that the power supply system adopts UPS (Siemens system 4233330kva) power supply

under normal conditions, the power is supplied by the municipal power supply. If the power is lost instantaneously or the voltage is low, the electronic switch will automatically switch to the battery power supply to ensure that the inverter is not affected. In order to ensure the spinning accuracy, the front spinning does not adopt the control mode of one inverter with one motor, but two large inverters provide variable frequency AC power supply to 32 metering pump motors (permanent magnet synchronous motor) respectively. The device is controlled by distributed digital process control system (DCS) and microprocessor network system. The open-loop control is composed of PLC and serial communication interface between the two inverters to ensure that the output frequency of the two inverters is the same, that is, to ensure the absolute synchronization of the motor speed of 32 metering pumps. Compared with the original production line, although the one-time investment is large, it can ensure that the metering pump can work normally under instantaneous low voltage (including instantaneous power loss) and improve economic benefits. In the front spinning speed regulation system, all inverters of 32 metering pump motors, 7-roll wire guide roller motors and feed wheel motors are connected to the common DC bus

5. Characteristic analysis of frequency conversion speed regulation system of post-processing device

the frequency conversion speed regulation system of post spinning device is shown in Figure 2. In the post-treatment device, the traction of drafting, tension heat setting, wire folding and crimping adopts the common DC multi inverter variable frequency speed regulation system with the wide use of PP material in the automotive interior, and its inverter is connected to the same DC bus. The motor adopts high-power asynchronous motor. The common DC bus is powered by 1 and 2 rectifier devices. The superposition of two sets of rectifiers can not only expand the capacity, but also reduce ripple and harmonic and stabilize the DC voltage. Compared with the original production line, it has the following advantages:

Figure 2 frequency conversion speed regulation system of rear spinning device

(1) using common DC bus, it can adaptively adjust the braking torque of the towed motor under different drafting ratio. For example, for a set drafting ratio, the speeds of the first, second and third drafting machines are N1, N2 and N3 respectively. Due to the tension of the wire, when there is no braking function, the first drafting roller will be dragged by the rear drafting roller. Now, after the frequency conversion speed regulation of common DC bus is adopted, once the value of N1 exceeds the set value, the motor will enter the regenerative power generation braking state. On the one hand, the towed motor becomes a generator, and the electric energy generated is rectified by the freewheeling diode into DC and fed back to the DC bus. The motor not only does not need to absorb energy from the electricity, but also can supply the braking energy to other inverters, which can stabilize the DC bus voltage. Due to the large capacity of the motor (for example, the motor generated by the second traction machine is of high quality, and the motor is 400KW), the electric energy saving is also considerable. On the other hand, the towed motor is in the braking state. As long as the corresponding frequency ratio is set, the speed ratio can be controlled to ensure the draft ratio control accuracy

(2) the post-treatment draft tension heat setting combined unit of polyester staple is a key process in the production of polyester staple fiber, which is mainly responsible for drawing and setting the precursor according to a certain draft ratio. For the post spinning drive of the polyester staple device, a high-power DC motor drives a mechanical long side shaft, and then drives each drafting roller, tension heat setting roller, etc. Although the DC motor has good performance in speed regulation range, speed regulation accuracy and dynamic response, the most fatal problem of DC drive is that the maintenance of DC motor is very troublesome and has high requirements for the environment. In addition, with long side shaft transmission, if the production variety is to be changed, the adjustment of drafting ratio is difficult, and the accuracy can not meet the requirements, which is bound to affect the product quality, variety modification and the development of high value-added products. The new production line adopts AC frequency conversion speed regulation, and each drafting roller has independent frequency conversion transmission. It is easy to adjust the drafting ratio required by the process by changing the frequency of each frequency converter. From the analysis of the production situation after putting into operation, the variety of polyester staple fiber produced has increased (of which the sales volume of 1.33 dtex bright sewing thread accounts for more than 1/2 of the national sales volume), the quality has been improved, the unit consumption has decreased, the parking faults have been greatly reduced, and the economic benefits are remarkable

the speed regulation scheme of sharing DC bus and multiple inverters is also adopted for wire stacker and crimper, but the power is small and will not be discussed. The cutter is an independent frequency converter, which has the same principle as the general frequency conversion speed regulation, and will not be carried out here

6. Conclusion

(1) as mentioned above, the frequency conversion speed regulation technology of shared DC bus is reliable. Although the one-time investment is high, it can reduce the shutdown for 2 ~ 3 times a year. Calculated according to a 30000 T/a production line, it can reduce the pet discharge by 8 ~ 12 tons, and avoid the fiber quality fluctuation caused by parking (one-time shutdown will affect the quality stability of 144 ~ 216 tons of fiber), In this way, the reconstruction cost can be recovered in a few years

(2) due to the common DC bus frequency conversion speed regulation technology, the overall production conditions are in a stable state, which brings great convenience to change product specifications and adjust process parameters. Short transition time, less waste silk and accurate process adjustment

(3) from the actual operation of the new production line, the common DC multi inverter speed regulation system has prominent advantages in the production of polyester staple fiber, which represents the development direction of spinning machine drive. However, in the post spinning part, the influence of power loss on the frequency converter cannot be completely eliminated. For example, once the frequency converter is out of service, a section of polyester fiber (about 100m) being drawn will be scrapped. The improved method can use two independent AC power supplies, which are respectively rectified by the rectifier and then sent to the common DC bus (diode isolation is required). Once one power supply is lost, there is still another AC power supply to support it, so it is not necessary北京耳鸣腰酸可以吃五子衍宗丸吗
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