Technologie de contrôle de variation de fréquence dans ventilateur aspirant de générateur de 300MW
2009-12-27 21:54:23
Résumé : cette page introduit la modification du ventilateur aspirant et le nouveau design de contrôle à fréquence variable du système DCS Siemens nommé TELEPERM ME, reporte son application dans la centrale de Yangguang, conduit la révision du projet et établi les suggestions d’amélioration.
Mots clés : pression du fourneau, technologie de fréquence variable, DCS.

 Variable frequency speed adjusting devices can optimize the motor operation state, improve the motor efficiency and realize the energy saving purpose. With the rapid development of the electronic devices and control technology in recent years, the price goes down. The reliability has been enhanced and the capacity has not been limited because of modularization design, so the medium voltage heavy power VFD starts widely to apply to the fan market.

Two 2000kW/6kV VFDs made by Beijing Leader & Harvest Electrical Technologies Company are installed respectively on two ID fans in the furnace 1# rebuilding project of Shanxi Yangguang Power Generation Company. The controller are made up of high speed singlechip, HMI and PLC. Singlechip realizes the PWM controlling. HMI supplies friendly windows monitoring and operation interface, and in the mean time, it realizes the networking control and long distance monitoring. PLC is used for logic processing of the signal in the cabinet, flexible communicating with field interface and satisfying the user special needs. The VFD uses Siemens S7-200 PLC, which has good interfacing ability with DCS. According to the operation characteristics of ID fan and the exact requirement of the VFD control, we design the following scheme of interfacing and controlling between VFD system and DCS system.

1. Design of interfacing and controlling between VFD system and DCS system

The total signals between DCS and VFD is 22 point. Digital signal 18 point, analog signal 4 point. VFD digital signals in each ID fan includes: ①ready state; ②running state; ③stop state; ④light fault alarm; ⑤heavy fault alarm; ⑥medium voltage allowable; ⑦cell bypass; ⑧start; ⑨stop. VFD analog signals in each ID fan includes: speed adjusting instruction and speed feedback signal.

The variable frequency control scheme is realized by defining above points in DCS logic configuration.

2.Adding following to DCS control

To realize the purpose of VFD start/stop and speed adjusting, add following to the DCS display and control:

(1)DCS starts and stops VFD for the remote start/stop VFD function.

(2)DCS controls VFD to adjust ID fan speed for auto/mannual function.

(3)DCS display adds 3 alarm pionts: VFD light fault, VFD heavy fault, VFD bypass.

3.Operation mode and control logic

3.1 VFD operation mode on ID fan

In general, ID fan starts in variable frequency operation mode. Considering possible VFD faults, ID fan also has mode of “one unit variable frequency one unit direct on line” and mode of “ 2 units direct on line”.

There are local control and remote control for VFD mode. In local control, DCS speed output command signal traces the VFD feedback speed signal. The remote control is invalid for VFD in this period.

DCS controls VFD in auto and mannual two method. In mannual method, operator changes the speed control menu to control the VFD speed, and to realize the adjustment of subpressure.

3.2 Conditions of starting VFD on ID fan

Starting has three conditions: ①the medium voltage part of ID fan A and B have been started well; ②for VFDs of ID fan A and B, the start signal from PLC is on ; ③the VFD set speed output value of ID fan A and B are less than 30%.

 The VFD starting preconditions are that the medium voltage switch of ID fan motor must be on and start feedback is 1. Original start conditons of ID fan is still playing roles in the entire logic. That is to say, original start conditions for fan is preserved for ID fan VFD starting. In addition, considering actual condition of VFD site status, we add VFD ready signal and ID fan variable frequency ready signal as another start requirement.

In commissioning of VFD remote start, VFD set speed may be a high value. If operator starts VFD at this high speed, there must be disturbence to furnace. So we add a limitation for command <30% in start process.

3.3 Self-regulation of VFD’s speed adjusting

(1)Digital signals of ID fan A&B speed atuo function

When the static blade of ID fan turns into the auto state, A&B VFD’s speed auto function will be locked. When the furnace subpressure signal goes wrong, sensor fault signal sends and VFD exits auto function. When the furnace subpressure low setting touches off, VFD locks speed increasing fuction after 3s. When the furnace subpressure high setting touches off, VFD locks speed decreasing fuction after 3s.

(2)Analog signals of ID fan A&B speed atuo function

Variable frequency adjusting and ID fan static blade adjusting has the same adjusting object, so, the original difference loop can be directly used into the variable frequency control. For specific needs of variable frequency control, we add the balance loop. Considering speed to keep balance of the two side output, we add the gain loop independently to the single and double fan variable frequency method. The original difference loop has already included forward feedback part of the total wind flow, so, new variable frequency control does not need to add it. In situation of one VFD trips off and not recoveries to variable frequency state, the current balance loop in the old damper needs be displaced by position feedback balance loop, at the same time, another unit ID fan VFD needs be gradualy adjusted to large output, then, the self-regulation of ID fan is put into.

3.4 Ralated VFD trip protection

(1)Single side ID fan VFD trips protection should jointly trips the corresponding FD fan in another side.

(2)After two sides ID fan VFDs trip protection action, the corresponding medium voltage breaker of ID fan A & B jointly trip. MFT trip loop in old furnace protection PLC controller keeps unchanged for this reason.

(3)VFD heavy fault joint triping ID fan fuction is added to the trip loop of the old ID fan. It makes sure that VFD can jointly trip the ID fan in variable frequency operation. It is locked in direct online operation.

ID fan control flow is showed in figure No.1.

4.ID fan parameter automatic setting and related debuging

(1)Start ID fan A , B and VFDs, tune dampers to 100% position, set the furnace subpressure value -50 Pa.

(2)Open the rotating blade (FD fan dampers) to the 10% position after FD fan A and B starting, set the lowest speed 225 r/min in VFD of ID fan A and B, change the VFD into auto operation, then do the setting disturbing test by changing the setting 20% and record the VFD automatic changes.

(3)For pressure adjusting characteristics: set the integral time to 4 min, proportion coefficient to 0.3, then gradually change the proportion coefficient, tune the parameters by the critical proportioning method. When adjusted oscillation appears, according to this method, begin the first setting. There is a basic parameters: P=0.025，Ti=100s.

 (4)Do the opening position increasing test at every 10% of A and B FD fan rotating blade, observe the changing of the furnace subpressure, record the difference value and disappearing time, then do the he opening position decreasing test, do the disturbing tests using the A and B FD fan rotating blade.

(5)Change one FD fan opening to 30%, observe the speed changing and subpressure response time, continue the disturbing tests for the A and B FD fan rotating blade. Do the opening position increasing test at every 10% of A and B FD fan rotating blade, observe the changing of the furnace subpressure, record the difference value, disappearing time, the VFD command output and the actual speed, then do the opening position decreasing test, check the proportional gain of single fan and double fans operation.

(6)Simulate the action conditions of MFT, open the FD fan A and B blades to 50%, observe the furnace subpressure changing. Do a real action test for the related interlocks of ID fan VFD in case of VFD is switched to auto after finishing the auto state tests.

 (7)Cut the single side FD fan in the test process to simulate whether VFD auto control can realize the satisfied control effect of the subpressure in this situation.

(8)The safe operation of the boiler is very important for the power supplying to the entire plant. So, the switch function between direct online and variable frequency is necessary to assure the boiler safe operation. If one unit ID fan is in fault and does not recovery in short time, the automation control need to be changed to opening control. Therefore, this situation need to be tested. Stop one unit ID fan VFD, make full power output of another unit ID fan VFD, do the disturbing test in old ID fan auto control state (static blade), adjust and modify some parameter through testing.

PID parameters of ID fan VFD is optimized through above tests. The variable frequecny operation makes subpressure regulation more stable and reliable, better adjusting performance, and provides the spare space for the operation safety. When old static blade damper adjusting runs in mode of one unit direct online one variable frequency state, the PID parameters of the old static blade damper adjusting is modified too. When one unit VFD breaks and the system needs to work direct online, the system still can use the static blade damper to control the subpressure.

5.Benefits of applying VFD

(1)After retrofiting project, motor realizes the soft start. It reduces the peak current and peak current time, deliminates the impact on the grid and load, avoids damage to the motor insulation by operation overvoltage and prolongs the life of motor and fan.

(2)Saves large amount of energy and satisfies the peak load regulation need.

Dampers are full open, which reduces the wasting energy on the damper and realizes the uniformity of speed adjusting.

(3)Saves large amount of maintance cost. Cut down the speed in light load, reduce the abrasion and vibration of mechanical parts, prolongs the fan heavy repair period.

(4)Benefits for safe operation of the motor and fan. High control precision, high anti-jamming ability, low harmonic, perfect protection and calm starting from zero speed.

6.Conclusion

(1)Field comparison tests between variable frequency adjustment and static blade damper adjustment shows: VFR method can satisfy the output need of generator unit. Its performance is stable and reliable, the self-regulation quality has been improved clearly, especially for the response time. The big executive inherent dead zone shortcoming of SDR method is basicly eliminated.

(2)The operation effeciency is highly heightened. SDR method is about 55% while VFR method is 75%-80% in different generator unit loads.

(3)The fan runs economically with excellent adjusting performance and remarkable energy saving effect in VFR method. The damper is full open and the energy consumption on damper is saved.

References:

[1] Jincheng Du. Electrical variable frequency speed adjusting design technology[M].Beijing: China electric power publishing house,2002.

[2] Lingge Xie. Auto control Principle[M].Xian: China water electric power publishing house,1985.

Source:Electric Power Paper,2006.1.total 74th vol.