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High power frequency converters for industrial and power plant drives
MECNATRONICS
PERGAMON
Mechatronics 8 (1998) 1-11
High power frequency converters for industrial and power plant drives L. Bojtor*, E. Pa/d Ganz Ansaldo Electric Ltd, Department of Power Electronics, H-1024 Budapest, LOv6hgtz u. 39, Hungary
Received 5 February 1997; revised 26 September 1997; accepted 3 October 1997
Abstract
The paper introduces a modern static frequency converter family developed for high power synchronous drives and static starter of gas turboset applications. The main circuit configuration and the technical data of a static starter equipment are described. The control strategies and the architecture of the microcomputer control system are discussed in detail. The field experiences are also presented. © 1998 Published by Elsevier Science Ltd
1. Introduction
Ganz Ansaldo Electric Ltd has developed a modern and economic static frequency converter (SFC) family during the 1990s which mainly targets the heavy and energy industry applications particularly high power variable speed synchronous drives and static starters for gas turbosets. The main characteristics of the new SFC family is the flexibility in size and functions. The modular power part of the equipment makes it possible to fit the size to the required rated power. The p r o g r a m m a b l e control system is easily adaptable to the process control environment and the requested operating modes. The first two SFC equipment from the family were installed for synchronous m o t o r drives (motor power: 3.2 MVA) of exhaustor fans in D u n a Steel Works (Hungary) in 1992. The third SFC equipment was supplied for static starter application (rated power: 1.8 MW) in a gas turboset unit (generator power: 156 MVA) of Kelenf61d Power Plant (Budapest, Hungary). The installation was completed in 1995. This paper presents the configuration and the main characteristics of the high power
* Corresponding author 0957~4158/98 $19.00 ~) 1998 Published by Elsevier Science Ltd. All rights reserved PII: S0957-4158(97)00040 8
"~
L. B*~/tm', L'. Pa~?l, Mechalromc.~ ~' ~' 1998) l 11
frequency converter family and introduces the SFC equipment installed in KelenfOld Power Plant.
2. Static starter for gas turbosets
Gas turbine systems are applied extensively in energy supplies to cover peak load requirements. The gas turboset must be accelerated by a starting device to the speed necessary to ignite the gas turbine. The most favourable and economical starting device is the static frequency converter SFC (see Fig. 1). On the line side the SFC is supplied from the power plant medium voltage AC mains through a circuit breaker and a power transformer. On the machine side the SFC is connected to the generator stator through a three phase disconnecting switch. The SFC runs up the gas turboset by feeding the generator as a synchronous m o t o r up to the speed where the gas turbine takes over the acceleration of the gas turboset. At the end of the start-up controlled by SFC the equipment is switched off and isolated from the generator. The main advantages of the static starter equipment are the following: • Comparing with the starter machine the static solution ensures shorter length of shaft, smaller place request, lower vibration. • One starter is able to start more turbosets. • Cross connection of two static starter results in redundancy. • Several operating modes are provided to help the maintenance of the gas turbines. • Minimal maintenance is required for SFC. • Built-in diagnostic tools support quick trouble-shooting.
LSC
L~
MSC
SM
? @
f-f-f,
CONTROL UNIT & INTERFACES
[~E~OTE'OONTRO~] Fig, l. The main circuil o f the SF:(" for slatic starter application.
EXC
L. Bojtor, E. Pa&l/Mechatronics 8 (1998) 1 11
2.1. Main data of the presented SFC
Rated power Breakaway torque Rated torque Power supply Frequency range Output voltage EMC complies to
1.8 MW 31.5 kNm 15.5 kNm 6.3 kV 0-36 Hz 0-1.3 kV (0-36 Hz) IEC 801
2.2. Main data of the generator
Rated power Rated power factor Stator voltage Rated frequency Rated speed Subtransient reactance
156.5 MVA 0.8 15.75 kV 50 Hz 3000 rpm 0.182 p.u.
3. The main circuit of the static frequency converter
The SFC is a static frequency converter with intermediate DC link (see Fig. 1). It contains a feeding transformer, a line side converter (LSC), a machine side converter (MSC) and a smoothing reactor. The LSC is a three phase, line commutated thyristor rectifier fed from the 6.3 kV grid through the circuit breaker and the power transformer. The MSC is a three phase, load commutated thyristor inverter. Its three phase output supplies the generator through the isolator during the starting process. The load commutation of the MSC is made possible by the induced stator voltage of the overexcited synchronous machine operating at a leading power factor. The LSC and the MSC are separated by the smoothing reactor in the intermediate DC circuit. The most favourable characteristics of the SFC is that the MSC and the LSC are identical with each other, supplementary components are not required for commutation. It results in a simple and highly reliable configuration of the main circuit. The LSC operates at mains frequency as a conventional converter. The MSC works in self controlled mode of operation, so the frequency of this converter is slaved to the machine speed. The MSC firing pulses are triggered to a directly measured (e.g. shaft position, stator voltage) or a derived (e.g. flux) machine signal. The synchronous machine with self controlled converter is equivalent to a DC motor in which the mechanical commutator has been replaced by an electronic converter, with obvious advantages. The SFC increases the speed of the turboset
4
l,. Bojtor, L. Pa~l/Mevllalronic.s,~' ;1998) 1 1l
Fig. 2. SFC for gas turboset (Kelenf61d: 1.8 MW).
similarly up to the limit corresponding to the maximum DC voltage available from LSC. Further increase in speed is obtained by reducing the excitation current to give field weakening region of operation. The wave form of the stator voltage is near sinusoidal whereas the stator current and the line side input current have trapezoid fl~rm. The LSC generates harmonics on the mains which has to be reduced below the allowed maximum value of total harmonic distortion (THD). In the presented prqiect the T H D ' s maximum value is 5 %, however in some cases higher value is also acceptable since the starting process is a very short period, only a few minutes. The T H D value is reducible applying higher short circuit power on the grid or twelve pulses configuration of the LSC system.
3. I. Feeding tran,ffbrnler It is a three phase dry type cast resin, natural air cooled transformer equipped with thermistors for overload protection. Rated/peak power Rated secondary voltage Rated primary voltage
2000/2550 kVA 1300 V 6300 V
L. Bojtor, E. Padtl/Mechatronics8 (1998) 1 ll 3.2. Line side and machine side converters (LSC, M S C )
Rated DC/AC current Rated DC/AC voltage
1375/1125 A 1310/1300 V
The power converters are three phase, fully controlled, forced air cooled thyristor bridges with one thyristor in each arm. The applied modern disc type thyristors have large diameter, high value of fit, reverse voltage and du/dt. The SFC's converters (LSC, MSC) are built in modular system (see Fig. 3). One
Fig. 3. Twelvethyristormodulein one cubicle.
6
L. Bojlor, E. PadlMechalronic.s,S' ( 199~f; 1 11
module contains the thyristor and its heatsink, RC snubber, pulse transformer and fuse. The twelve modules are identical and can be replaced easily. During the start-up process the switching o1" line side circuit breaker and machine side isolator can result in overvoltages. The LSC is protected against over voltages both on AC and DC side. The MSC is backed only on AC side. The protection include RC combination and varistor elements. 3.3. S m o o l h i n , q r e a c t o r
The smoothing reactor of the SFC (see Fig. 4) separates the line side and the machine side voltage system and reduces the current fluctuation significantly which is
Fig. 4. Smoothing reactor built-in cubicle.
L. Bojtor, E. Padl/Mechatronics 8 (1998) 1 11
7
fairly characteristic of the current fed inverts. The presented SFC has a dry type cast resin, natural air cooled reactor built in cubicle. The smoothing reactor has an iron chore with air gap and it is equipped with thermistor for overload protection. Rated/peak current Rated inductance
1100/1600 A 3.2 mH
4. The control unit of the static frequency converter
The control unit (see Fig. 5) consists of a microcomputer completed with converter and plant interfaces and power supplies. The converter and plant interfaces include pulse amplifiers to the thyristors, analog transducers and relay circuits to plant control unit and to the static exciter, flux interface and voltage protection. The flux interface produces the subtransient flux of the synchronous machine derived from stator current and voltage. The voltage protection detects overvoltage occurrence in the machine and gives immediate command to the excitation system to discharge the field. The
LSC
L~
MSC
MMI
~
GS
PLANT CONTROL
Fig. 5. Control unit of the SFC.
l_. Bojlor, E. Paal/Mechalronic.~',~ (1998) I I1
power supply for the microcomputer and the interlaces is fed from both AC and DC auxiliary input voltage coupled inside in order to ensure improved redundancy. The microcomputer of the SFC is built up on the Ganz PCS industrial process control system and placed in a single EURO rack. The PCS offers a distributed intelligent master slave multi-processor structure based on a high density backplane. The robust industrial construction and the extensive hardware error checking ensure high immunity in industrial traction and power plant environment. The CPU and the converter control slave cards are based on the Intel 80196 microcontroller making possible considerable code compatibility. The slave cards for converter control are identical with each other and configurable for different converter types and trigger signals. The slave cards communicate with the CPU through mail box memories. The optically isolated digital input circuits are on-line tested contemporary with the normal operation. The optically isolated digital outputs are accessible only by redundant commands those have to be checked back prior to the execution. The analog inputs, outputs has 12 bit resolution and the inputs are equipped with sample hold circuits sampled in the same instant in order to help vector calculation. The microcomputer has built in real time clock for diagnostic purposes and LED display for detailed status and error signalling. The microcomputer has a dedicated serial channel for the PC-hosted MMI man machine interlace. Other communication channels with standard interfaces and protocols are available for connection to plant control or supervision remote computer.
5. Control and diagnostics The main control loop of the adjustable speed SFC drive is the speed controller (see Fig. 6). The subordinated current controller with firing control makes the LSC a current source with limitation from the feeding mains. The voltage controller with the subordinated excitation current controller regulates the field of the synchronous machine. The excitation current controller with the converter control is usually part of the static exciter. The SFC commands the exciter through the excitation current reference. The voltage reference is a function of the speed according to the field weakening characteristics. In order to provide quick voltage control, feedback and feed-forward structure has been applied together. The feedback loop has PI characteristic with speed compensation. The feedback signal is the vector amplitude of the subtransient voltage derived from the subtransient flux and the speed. The production of the flux and the voltage subtransient component gives the best filtering of the strongly distorted stator voltage without any time constant. The feed-forward control calculates the excitation current reference as function of the DC current and the flux reference of the machine. The MSC load commutated reverter has to be controlled in order to obtain the maximum power factor and the optimum torque. The constant margin angle control with adequate setting provides maximum power factor with safe overload capability in the whole operating range. The constant margin angle control requires continuous
L. Bojtor, E. Pa6l/Mechatronics 8 (1998) 1 11 LDc
LSC
MSC
GS
fp
IDC
U"
U" START-STOP SEQUENCE AND CONTROL
,
~ Lc-R9 9 9-M-P-U-T-E-R-C-O-HT-R-OL- _ .
loc
, CONVERTER & PLANT INTERFAC PLANT CONTROL
Fig. 6. Control structure of the SFC.
compensation of the firing angle as a function of the DC current and the actual flux in the machine. The feed-forward control of the excitation and the firing angle compensation of the MSC is based on the steady state calculation of the SFC [4]. The applied calculations consider the machine parameters and the margin angle but result in transparent relations for any flux characteristics, that is particularly favourable respecting the wide field weakening range. The introduced SFC offers the synchronization of the self controlled MSC to the shaft position applying an encoder or to the subtransient flux derived by the flux interface. The shaft position synchronization is recommended if durable low speed operation or start with strong breakaway is required. Otherwise the flux synchronization is more favourable since the encoder mounted on the shaft is dispensable improving the system reliability.
I0
L. Bq/tor, E. Pa6l/Mechatronic,s 8 ~1998) I l l
5.1. Error detection and prolecliotts
Besides the control functions the SFC has been equipped with the following extensive error detection and protections to prevent failure or damaging of the equipment: • • • •
overcurrent, overload and overtemperature protections, stall, overspeed and overvoltage protection, failure detection for power supplies, fans, fuses and control unit, feedback, reference and synchronizing signal monitoring.
5.2. Man machine inteJjuce
The break-off for commissioning and trouble-shooting is significantly reducible using the PC-hosted high level MM! man machine interface and diagnostic integrated environment. The MMI provides all the relevant functions such as symbolic access to variables, built-in oscilloscope, eight channel data recorder with graphical displaying, event logging, data storage and printing for archive. The SFC is accessible by the MMI either directly or through a modem-phone link as a remote diagnostic terminal.
6. Field experiences
The transient and the steady state behaviour of the presented SFC has been investigated extensively m test-room and power plant environment. The characteristic start-up process has been recorded with the aid of the built in diagnostic tools (see Fig. 7). In the first period of the start-up the SFC accelerates then leaves coasting down the gas turboset for cranking. Following the cranking the turbine is ignited. When the flame is stabilised in the combustion chamber of the turbine the SFC accelerates again. Exceeding the rated speed the SFC switches off automatically since the turbine has sufficient torque to take over the acceleration of the turboset up to the synchronous speed.
7. Conclusions
The paper has introduced el new verter (SFC) family developed by turbosets. The system configuration detail. Start-up process recorded on
microcomputer controlled static frequency conGanz Ansaldo particularly for start-up of gas and the control structure have been discussed in the field has been presented.
L. Bojtor, E. Pahl/Mechatronics 8 (1998) 1 11 Speed
25OO
1400
I . . . . . . . Voltage
I
:
..................
1200
20OO /
,". . . . . .
',
•
'°i
r: I
•
800
t
6OO
IO00
40O 5OO
2OO I
I
b
I
I
I
I
t
I
1
2
3
4
5
6
7
8
9
I
t
I
I
I
I
0
t
10 11 12 13 14 15 16 17
Time [min]
1600
I
I
~
,
DC current I
....... E xc current
~ 5oo .
[ 450
1200
35O ~
1000
3O0
800
250 =u .......... ,,,~a,
40O 200
-~,,~,,v-. . . . .
150 '~ 100 tU
.-~
i ;.7.. 1
0
0
1 2
3 4
0
5 6 7 8 9 10 11 12 13 14 15 16 17 Time [minl
Fig. 7. Start-up process.
References
1. Richter, W., Microprocessor control of the inverter fed synchronous motor. Process Automation, 1981. 2. Meyer, A., Schweickardt, H. and Strozzi, P., The converter-fed synchronous motor as a variable-speed drive system. Brown Boveri Review 4-5, 1982. 3. Schmidt, I. and Bojtor, L., Microprocessor controlled converter-fed synchronous motor without shaft position sensor. Proceedings of the Conference on Power Electronics and Motion Control. Budapest, 1990. 4. Bojtor, L. and Schmidt, I., Microprocessor controlled converter-fed synchronous motor using subtransient flux model. Electric Machines and Power Systems 20. Hemisphere Publishing Co., New York, 1992. 5. Bojtor, L. and Schmidt, I., Simulation of controlled converter-fed synchronous motors. Proceedings q/" the European Conference on Power Electronics and Application. Florence, 1991. 6. Bojtor, L., Csizmazia, J., Gill, I., Paoli, E., Stadler, G. and Szil~gyi, P., A static starter for large gas turbines. Proceedings of the European Conference on Power Electronics and Application. Sevilla, 1995.
PERGAMON
Mechatronics 8 (1998) 1-11
High power frequency converters for industrial and power plant drives L. Bojtor*, E. Pa/d Ganz Ansaldo Electric Ltd, Department of Power Electronics, H-1024 Budapest, LOv6hgtz u. 39, Hungary
Received 5 February 1997; revised 26 September 1997; accepted 3 October 1997
Abstract
The paper introduces a modern static frequency converter family developed for high power synchronous drives and static starter of gas turboset applications. The main circuit configuration and the technical data of a static starter equipment are described. The control strategies and the architecture of the microcomputer control system are discussed in detail. The field experiences are also presented. © 1998 Published by Elsevier Science Ltd
1. Introduction
Ganz Ansaldo Electric Ltd has developed a modern and economic static frequency converter (SFC) family during the 1990s which mainly targets the heavy and energy industry applications particularly high power variable speed synchronous drives and static starters for gas turbosets. The main characteristics of the new SFC family is the flexibility in size and functions. The modular power part of the equipment makes it possible to fit the size to the required rated power. The p r o g r a m m a b l e control system is easily adaptable to the process control environment and the requested operating modes. The first two SFC equipment from the family were installed for synchronous m o t o r drives (motor power: 3.2 MVA) of exhaustor fans in D u n a Steel Works (Hungary) in 1992. The third SFC equipment was supplied for static starter application (rated power: 1.8 MW) in a gas turboset unit (generator power: 156 MVA) of Kelenf61d Power Plant (Budapest, Hungary). The installation was completed in 1995. This paper presents the configuration and the main characteristics of the high power
* Corresponding author 0957~4158/98 $19.00 ~) 1998 Published by Elsevier Science Ltd. All rights reserved PII: S0957-4158(97)00040 8
"~
L. B*~/tm', L'. Pa~?l, Mechalromc.~ ~' ~' 1998) l 11
frequency converter family and introduces the SFC equipment installed in KelenfOld Power Plant.
2. Static starter for gas turbosets
Gas turbine systems are applied extensively in energy supplies to cover peak load requirements. The gas turboset must be accelerated by a starting device to the speed necessary to ignite the gas turbine. The most favourable and economical starting device is the static frequency converter SFC (see Fig. 1). On the line side the SFC is supplied from the power plant medium voltage AC mains through a circuit breaker and a power transformer. On the machine side the SFC is connected to the generator stator through a three phase disconnecting switch. The SFC runs up the gas turboset by feeding the generator as a synchronous m o t o r up to the speed where the gas turbine takes over the acceleration of the gas turboset. At the end of the start-up controlled by SFC the equipment is switched off and isolated from the generator. The main advantages of the static starter equipment are the following: • Comparing with the starter machine the static solution ensures shorter length of shaft, smaller place request, lower vibration. • One starter is able to start more turbosets. • Cross connection of two static starter results in redundancy. • Several operating modes are provided to help the maintenance of the gas turbines. • Minimal maintenance is required for SFC. • Built-in diagnostic tools support quick trouble-shooting.
LSC
L~
MSC
SM
? @
f-f-f,
CONTROL UNIT & INTERFACES
[~E~OTE'OONTRO~] Fig, l. The main circuil o f the SF:(" for slatic starter application.
EXC
L. Bojtor, E. Pa&l/Mechatronics 8 (1998) 1 11
2.1. Main data of the presented SFC
Rated power Breakaway torque Rated torque Power supply Frequency range Output voltage EMC complies to
1.8 MW 31.5 kNm 15.5 kNm 6.3 kV 0-36 Hz 0-1.3 kV (0-36 Hz) IEC 801
2.2. Main data of the generator
Rated power Rated power factor Stator voltage Rated frequency Rated speed Subtransient reactance
156.5 MVA 0.8 15.75 kV 50 Hz 3000 rpm 0.182 p.u.
3. The main circuit of the static frequency converter
The SFC is a static frequency converter with intermediate DC link (see Fig. 1). It contains a feeding transformer, a line side converter (LSC), a machine side converter (MSC) and a smoothing reactor. The LSC is a three phase, line commutated thyristor rectifier fed from the 6.3 kV grid through the circuit breaker and the power transformer. The MSC is a three phase, load commutated thyristor inverter. Its three phase output supplies the generator through the isolator during the starting process. The load commutation of the MSC is made possible by the induced stator voltage of the overexcited synchronous machine operating at a leading power factor. The LSC and the MSC are separated by the smoothing reactor in the intermediate DC circuit. The most favourable characteristics of the SFC is that the MSC and the LSC are identical with each other, supplementary components are not required for commutation. It results in a simple and highly reliable configuration of the main circuit. The LSC operates at mains frequency as a conventional converter. The MSC works in self controlled mode of operation, so the frequency of this converter is slaved to the machine speed. The MSC firing pulses are triggered to a directly measured (e.g. shaft position, stator voltage) or a derived (e.g. flux) machine signal. The synchronous machine with self controlled converter is equivalent to a DC motor in which the mechanical commutator has been replaced by an electronic converter, with obvious advantages. The SFC increases the speed of the turboset
4
l,. Bojtor, L. Pa~l/Mevllalronic.s,~' ;1998) 1 1l
Fig. 2. SFC for gas turboset (Kelenf61d: 1.8 MW).
similarly up to the limit corresponding to the maximum DC voltage available from LSC. Further increase in speed is obtained by reducing the excitation current to give field weakening region of operation. The wave form of the stator voltage is near sinusoidal whereas the stator current and the line side input current have trapezoid fl~rm. The LSC generates harmonics on the mains which has to be reduced below the allowed maximum value of total harmonic distortion (THD). In the presented prqiect the T H D ' s maximum value is 5 %, however in some cases higher value is also acceptable since the starting process is a very short period, only a few minutes. The T H D value is reducible applying higher short circuit power on the grid or twelve pulses configuration of the LSC system.
3. I. Feeding tran,ffbrnler It is a three phase dry type cast resin, natural air cooled transformer equipped with thermistors for overload protection. Rated/peak power Rated secondary voltage Rated primary voltage
2000/2550 kVA 1300 V 6300 V
L. Bojtor, E. Padtl/Mechatronics8 (1998) 1 ll 3.2. Line side and machine side converters (LSC, M S C )
Rated DC/AC current Rated DC/AC voltage
1375/1125 A 1310/1300 V
The power converters are three phase, fully controlled, forced air cooled thyristor bridges with one thyristor in each arm. The applied modern disc type thyristors have large diameter, high value of fit, reverse voltage and du/dt. The SFC's converters (LSC, MSC) are built in modular system (see Fig. 3). One
Fig. 3. Twelvethyristormodulein one cubicle.
6
L. Bojlor, E. PadlMechalronic.s,S' ( 199~f; 1 11
module contains the thyristor and its heatsink, RC snubber, pulse transformer and fuse. The twelve modules are identical and can be replaced easily. During the start-up process the switching o1" line side circuit breaker and machine side isolator can result in overvoltages. The LSC is protected against over voltages both on AC and DC side. The MSC is backed only on AC side. The protection include RC combination and varistor elements. 3.3. S m o o l h i n , q r e a c t o r
The smoothing reactor of the SFC (see Fig. 4) separates the line side and the machine side voltage system and reduces the current fluctuation significantly which is
Fig. 4. Smoothing reactor built-in cubicle.
L. Bojtor, E. Padl/Mechatronics 8 (1998) 1 11
7
fairly characteristic of the current fed inverts. The presented SFC has a dry type cast resin, natural air cooled reactor built in cubicle. The smoothing reactor has an iron chore with air gap and it is equipped with thermistor for overload protection. Rated/peak current Rated inductance
1100/1600 A 3.2 mH
4. The control unit of the static frequency converter
The control unit (see Fig. 5) consists of a microcomputer completed with converter and plant interfaces and power supplies. The converter and plant interfaces include pulse amplifiers to the thyristors, analog transducers and relay circuits to plant control unit and to the static exciter, flux interface and voltage protection. The flux interface produces the subtransient flux of the synchronous machine derived from stator current and voltage. The voltage protection detects overvoltage occurrence in the machine and gives immediate command to the excitation system to discharge the field. The
LSC
L~
MSC
MMI
~
GS
PLANT CONTROL
Fig. 5. Control unit of the SFC.
l_. Bojlor, E. Paal/Mechalronic.~',~ (1998) I I1
power supply for the microcomputer and the interlaces is fed from both AC and DC auxiliary input voltage coupled inside in order to ensure improved redundancy. The microcomputer of the SFC is built up on the Ganz PCS industrial process control system and placed in a single EURO rack. The PCS offers a distributed intelligent master slave multi-processor structure based on a high density backplane. The robust industrial construction and the extensive hardware error checking ensure high immunity in industrial traction and power plant environment. The CPU and the converter control slave cards are based on the Intel 80196 microcontroller making possible considerable code compatibility. The slave cards for converter control are identical with each other and configurable for different converter types and trigger signals. The slave cards communicate with the CPU through mail box memories. The optically isolated digital input circuits are on-line tested contemporary with the normal operation. The optically isolated digital outputs are accessible only by redundant commands those have to be checked back prior to the execution. The analog inputs, outputs has 12 bit resolution and the inputs are equipped with sample hold circuits sampled in the same instant in order to help vector calculation. The microcomputer has built in real time clock for diagnostic purposes and LED display for detailed status and error signalling. The microcomputer has a dedicated serial channel for the PC-hosted MMI man machine interlace. Other communication channels with standard interfaces and protocols are available for connection to plant control or supervision remote computer.
5. Control and diagnostics The main control loop of the adjustable speed SFC drive is the speed controller (see Fig. 6). The subordinated current controller with firing control makes the LSC a current source with limitation from the feeding mains. The voltage controller with the subordinated excitation current controller regulates the field of the synchronous machine. The excitation current controller with the converter control is usually part of the static exciter. The SFC commands the exciter through the excitation current reference. The voltage reference is a function of the speed according to the field weakening characteristics. In order to provide quick voltage control, feedback and feed-forward structure has been applied together. The feedback loop has PI characteristic with speed compensation. The feedback signal is the vector amplitude of the subtransient voltage derived from the subtransient flux and the speed. The production of the flux and the voltage subtransient component gives the best filtering of the strongly distorted stator voltage without any time constant. The feed-forward control calculates the excitation current reference as function of the DC current and the flux reference of the machine. The MSC load commutated reverter has to be controlled in order to obtain the maximum power factor and the optimum torque. The constant margin angle control with adequate setting provides maximum power factor with safe overload capability in the whole operating range. The constant margin angle control requires continuous
L. Bojtor, E. Pa6l/Mechatronics 8 (1998) 1 11 LDc
LSC
MSC
GS
fp
IDC
U"
U" START-STOP SEQUENCE AND CONTROL
,
~ Lc-R9 9 9-M-P-U-T-E-R-C-O-HT-R-OL- _ .
loc
, CONVERTER & PLANT INTERFAC PLANT CONTROL
Fig. 6. Control structure of the SFC.
compensation of the firing angle as a function of the DC current and the actual flux in the machine. The feed-forward control of the excitation and the firing angle compensation of the MSC is based on the steady state calculation of the SFC [4]. The applied calculations consider the machine parameters and the margin angle but result in transparent relations for any flux characteristics, that is particularly favourable respecting the wide field weakening range. The introduced SFC offers the synchronization of the self controlled MSC to the shaft position applying an encoder or to the subtransient flux derived by the flux interface. The shaft position synchronization is recommended if durable low speed operation or start with strong breakaway is required. Otherwise the flux synchronization is more favourable since the encoder mounted on the shaft is dispensable improving the system reliability.
I0
L. Bq/tor, E. Pa6l/Mechatronic,s 8 ~1998) I l l
5.1. Error detection and prolecliotts
Besides the control functions the SFC has been equipped with the following extensive error detection and protections to prevent failure or damaging of the equipment: • • • •
overcurrent, overload and overtemperature protections, stall, overspeed and overvoltage protection, failure detection for power supplies, fans, fuses and control unit, feedback, reference and synchronizing signal monitoring.
5.2. Man machine inteJjuce
The break-off for commissioning and trouble-shooting is significantly reducible using the PC-hosted high level MM! man machine interface and diagnostic integrated environment. The MMI provides all the relevant functions such as symbolic access to variables, built-in oscilloscope, eight channel data recorder with graphical displaying, event logging, data storage and printing for archive. The SFC is accessible by the MMI either directly or through a modem-phone link as a remote diagnostic terminal.
6. Field experiences
The transient and the steady state behaviour of the presented SFC has been investigated extensively m test-room and power plant environment. The characteristic start-up process has been recorded with the aid of the built in diagnostic tools (see Fig. 7). In the first period of the start-up the SFC accelerates then leaves coasting down the gas turboset for cranking. Following the cranking the turbine is ignited. When the flame is stabilised in the combustion chamber of the turbine the SFC accelerates again. Exceeding the rated speed the SFC switches off automatically since the turbine has sufficient torque to take over the acceleration of the turboset up to the synchronous speed.
7. Conclusions
The paper has introduced el new verter (SFC) family developed by turbosets. The system configuration detail. Start-up process recorded on
microcomputer controlled static frequency conGanz Ansaldo particularly for start-up of gas and the control structure have been discussed in the field has been presented.
L. Bojtor, E. Pahl/Mechatronics 8 (1998) 1 11 Speed
25OO
1400
I . . . . . . . Voltage
I
:
..................
1200
20OO /
,". . . . . .
',
•
'°i
r: I
•
800
t
6OO
IO00
40O 5OO
2OO I
I
b
I
I
I
I
t
I
1
2
3
4
5
6
7
8
9
I
t
I
I
I
I
0
t
10 11 12 13 14 15 16 17
Time [min]
1600
I
I
~
,
DC current I
....... E xc current
~ 5oo .
[ 450
1200
35O ~
1000
3O0
800
250 =u .......... ,,,~a,
40O 200
-~,,~,,v-. . . . .
150 '~ 100 tU
.-~
i ;.7.. 1
0
0
1 2
3 4
0
5 6 7 8 9 10 11 12 13 14 15 16 17 Time [minl
Fig. 7. Start-up process.
References
1. Richter, W., Microprocessor control of the inverter fed synchronous motor. Process Automation, 1981. 2. Meyer, A., Schweickardt, H. and Strozzi, P., The converter-fed synchronous motor as a variable-speed drive system. Brown Boveri Review 4-5, 1982. 3. Schmidt, I. and Bojtor, L., Microprocessor controlled converter-fed synchronous motor without shaft position sensor. Proceedings of the Conference on Power Electronics and Motion Control. Budapest, 1990. 4. Bojtor, L. and Schmidt, I., Microprocessor controlled converter-fed synchronous motor using subtransient flux model. Electric Machines and Power Systems 20. Hemisphere Publishing Co., New York, 1992. 5. Bojtor, L. and Schmidt, I., Simulation of controlled converter-fed synchronous motors. Proceedings q/" the European Conference on Power Electronics and Application. Florence, 1991. 6. Bojtor, L., Csizmazia, J., Gill, I., Paoli, E., Stadler, G. and Szil~gyi, P., A static starter for large gas turbines. Proceedings of the European Conference on Power Electronics and Application. Sevilla, 1995.