I. Background The primary frequency modulation function of the generator set is an essential function of grid-connected generators. It has been neglected in the past due to the digital transformation of the speed control system of the generator set. In recent years, with the gradual improvement of the frequency stability requirements of cross-regional interconnected power grids, perfecting and standardizing the primary frequency modulation function of the online units has been re-emphasized by all parties, and has gradually become an important work in the “coordination of machine networks†after the reform. Developed in major regional power grids. In 2005, China Southern Power Grid also started to implement unified deployment of the power grids of the five provinces and districts under its jurisdiction, and improved and invested in the primary frequency modulation function of the units as soon as possible. The basic work effectively supports the frequency stability of the power grid and ensures that the new assessment standards (CPS) T are comparable. Good AGC (automatic power generation control) performance.
Yunnan Power Grid, as the sending end of the South China Power Grid, has its own operating characteristics. Due to the weak link with the South Network, frequent frequent frequency fluctuations in the control area caused by the tripping of the tie-line often occur, and the high-cycle problems of the power grid are more prominent. Under the premise of coordinated operation of safety and stability control devices and improved generator set OPC (Overspeed Protection Control) function, if the frequency adjustment function of each grid-connected unit can be improved and put into use, the fast frequency response of the speed control system can partially suppress the generation of The frequency fluctuations caused by power imbalances are helpful for the rapid recovery of accidents. In addition, ensuring the correct investment of a sufficient number of grid-connected generators with one frequency tuning function is conducive to the further improvement of the AGC performance (CPS standard assessment results) in the control area of ​​Yunnan Power Grid under the existing TBC (tie line frequency deviation control) control method.
The installed capacity of Yunnan Power Grid is 1230OMW, of which 525MWW for thermal power units, 705OMW for hydropower units, and hydropower generating units account for a relatively large proportion and are rather special among the provincial power grids in China. The quick start and stop methods of hydropower units and better regulation performance bring a lot of benefits to the grid dispatch operation (including the stability control strategy and AGC control). However, due to the unique “anti-regulation phenomenon†and long time constant of the hydroelectric generator set's speed control system, the normal input of the primary frequency modulation function of the hydropower generating unit has been adversely affected. In addition, the AGC function design and the frequency modulation function of the speed control system in the current large-scale hydropower plant computer monitoring system do not match each other, so that the normal input of the primary frequency modulation function of the hydropower unit is completed, both on the unit side and on the grid side (making related technical specifications) There are many issues worth exploring and studying.
2. Unit-side work In July 2005, the Yunnan Power Grid Dispatching Center promulgated the “Regulations on the Regulation of Primary Frequency Regulation of Yunnan Power Generation Units (Trial)â€. According to the requirements of the "Regulations", each of the on-grid power plants conducted a complete modification of the relevant control functions with respect to the characteristics of its own unit, conducted a dynamic test, and conducted a one-time FM function according to the test results and the relevant technical provisions in the "Regulations". acceptance. The main technical specifications of the “Regulations†are as follows: (1) Manual speed dead zone: ±0.033Hz; (2) Adjustment ratio (inconstant): Inequality of thermal power unit 4%~5%, coefficient of variation of hydropower unit 3 %~4%; (3) Response time: less than 3s; (4) Adjustment speed and stabilization time: stabilization time should be less than lmin; (5) Response amplitude: ±6% MCR for thermal power of 30OMW and above (maximum continuous operation) Load); below, ±8% MCR; no limit for hydropower units.
2.1 Situation of Thermal Power Units 2.1.1 Program Planning Thermal power units of 100 MW or above in Yunnan Power Grid are equipped with DEH (digital electro-hydraulic speed control) system. According to the requirements of the “Regulations†and the “Acceptance Program†in the appendix, the primary frequency modulation function of the thermal power unit Must be based on the DEH side, mainly considering the rapid response requirements of the frequency response of the unit. At the same time, the comprehensive valve position command under the valve control mode, the power command under the power control mode, and the strategy of controlling the output feedforward and superimposing the frequency modulation amount are considered on the DEH side. Guarantee rapidity requirements. The primary tuning function of the CCS (coordinated control system) is auxiliary frequency tuning. The main consideration is to make necessary adjustments to the CCS integrated valve position instruction when the unit CCS (mainly a coordinated control method based on the boiler following method) is used. On the one hand, it is ensured that the input of CCS will not affect the normal function of the unit's primary frequency regulation function; on the other hand, through the coordinated control function of the CCS side, the amount of fuel entering the unit unit is changed to ensure the continuity of the frequency modulation effect (without changes in steam parameters). And fluctuations). In the aspect of function input, the methods of switching between the CCS main control screen and the DEH operation screen were unified in the past, and the function input signal was remotely transmitted to the dispatch center for remote monitoring through the RTU (Remote Terminal Unit) as a remote signaling signal. Once the operator presses the input button, the control system will automatically determine the frequency modulation mode (DEH FM or DEH/CCS integrated FM) according to the current operation mode of the unit.
2.1.2 Implementation and results Take the example of Guotou Qujing Power Plant No. 3 (30OMW). The DEH and DCS (Distributed Control System) are the Westinghouse OVATION system. Briefly introduce the dynamic test results (see Figure 1).
As can be seen from the curves, the unit is capable of responding quickly to changes in the frequency deviation of the system in all three control modes. The response speed is fast (less than 15), the steady-state response amplitude meets the setting of the adjustment coefficient (5%) and the dynamic adjustment stability. Less than lmin technical requirements, FM performance is good. It is particularly worth mentioning that when the unit is under coordinated control mode, that is, CCSBF (boiler follows CCS), the frequency response of the unit is affected by both the feedforward on the DEH side and the power command on the CCS side. The boiler command is based on The unit command changes ahead of time for fuel quantity compensation, making the unit's active output response speed faster, the response steady-state accuracy is higher (better than the valve control mode), while the pre-machine pressure fluctuation in the FM dynamic process is smaller (better than the DEH power control The method), while meeting the grid frequency support role, also ensures the safe and stable operation of the unit.
2.2 Situation of the motor group 2.2.1 Analysis of the status quo and special situation The completion of the hydropower unit's scheme and dynamic test has not yet begun. However, the previous stage has been designed and demonstrated through the acquisition and investigation. At present, the larger hydropower units in the Yunnan Power Grid are mostly Francis type units with a stand-alone capacity of 200~25OMW. The typical frequency response curve of this type of unit speed control system is shown in Figure 2. It can be seen from the curve in Fig. 2 that for the effect of the "anti-regulation" of the Francis turbine unit, the response has the characteristics of a non-minimum phase system, and the initial phase of the response shows a significant reverse regulation, and the duration is longer. For a frequency modulation, this effect may affect the normal FM function of the system. In addition, due to the limitation of the principle process, the speed regulation system of the hydro-generator set makes the inherent rotational speed dead-zone larger and the time constant longer, which is not conducive to the unit's rapid response to system frequency deviation.
The AGC function in the computer monitoring system of the hydropower plant may also be inconsistent with the FM function of the speed control system. Huaneng Manwan Power Plant AGC function and speed control system interface functions shown in Figure 3, once the frequency difference occurs, the governor is the first to reflect (microcomputer governor relatively short host operation cycle is relatively short), according to the adjustment requirements to change the unit active power output Afterwards, the power-closed-loop controllers of the various units in the monitoring system detected a deviation between the unit command (AGC/LOCal: dispatching/local) and the actual power generated after the FM, resulting in an instruction output that is opposite to the FM operation, and the speed The interface pulse of the device changes the active power output of the unit in the opposite direction, causing it to return to the previous AGC setting value. Therefore, it is necessary to ensure that the primary frequency modulation function of the hydropower unit monitors the interface pulse of the system governor, and changes the active power output of the unit in the opposite direction so that it can return to the previous AGC setting value. Therefore, to ensure the correct input of the primary frequency modulation function of the hydropower unit (without affecting the original AGC function), the monitoring system must be properly adjusted to match the governor action.
2.2.2 Suggested implementation plan To address the above issues, it is recommended that the existing hydropower unit control plan be modified.
(1) Governor side: In the existing control mode, in addition to the original Permanent Droop coefficient, a transient correction coefficient (TransientDroop) coefficient correction loop is added (see Fig. 4) in order to use the temporary Principle of state adjustment in response to the beginning of the dynamic phase, increasing the coefficient of adjustment, slowing the guide vane opening speed, thereby to some extent ease the negative effects of "negative phenomenon", the transient adjustment loop is not in the steady state Plays a role, so it does not affect the static rate of the unit (according to the permanent state adjustment coefficient). The above process simulation results are shown in Figure 5.
(2) The whole plant computer monitoring system side: In the existing monitoring system AGC function design, there is a frequency tuning mode, but only the units that have been put into the AGC participate in the command distribution, and the requirement that the on-grid generator set must have a frequency tuning function cannot be met. In the AGC frequency modulation mode (normal FM/emergency FM), the load command correction algorithm is not reasonable (using the actual power plus frequency correction term, there is a process of successive accumulation), and it does not match the governor side FM function, so Not working properly after putting in. For this reason, consider the scheme shown in the dashed line in FIG. 3 to perform the frequency difference correction on the active-closed-loop controller set value end of each unit on the AGC side, and the correction amount is matched with the governor side, thus avoiding the input of the AGC and once There are contradictions in the frequency modulation function. At the same time, the AGC side and the governor side maintain the same FM operation and do not cancel each other out.
2.3 Water and Thermal Power Generation Units Coordinate One Frequency Modulation Action The primary frequency regulation function of the power grid is mainly aimed at the frequency fluctuation caused by the short-cycle load changes and the rapid and stable recovery of the grid frequency under the accident conditions. Therefore, it is required that the FM operation respond quickly and have a certain degree of response and continuity. Sex. From the analysis of the response characteristics of the hydro-thermal power unit and the test results from the previous two sections, the two have their own characteristics. The time constant of the speed control system of the thermal power unit is small, and the response speed is fast, generally less than 2 seconds, ie, it produces a correct response, but The amplitude and continuity of the response are affected by the pre-machine steam parameters. The response speed of the hydropower unit is slow. At the same time, the influence of the “anti-regulation effect†may adversely affect the overall frequency response of the system, but the hydropower unit responds as soon as it starts responding. Larger amplitude, higher precision, longer duration. Considering comprehensively, in order to better play the role played by the primary FM function in the Yunnan Power Grid to stabilize the system frequency, the FM operation of the hydro-thermal power unit must be resolved. Specifically propose the following two measures.
(1) Due to the characteristics of the hydropower generating unit's speed control system and the effect of the reverse regulation, if the frequency of the short-cycle fluctuations of the follow-up system is frequently adjusted, on the one hand it is possible to offset the normal frequency response of the thermal power unit; on the other hand, it also jeopardizes the speed controller itself. For this reason, it is recommended to use the idea of ​​sub-control by ACE (area control deviation) similar to the AGC strategy. The hydro-thermal power units are each set with their own manual speed dead zone, and it is determined through experiments that the frequently-adjusted frequency difference section is reasonably avoided, and the thermal power unit adopts Smaller manual speed dead zone in order to cope with short-cycle load fluctuations; hydropower unit uses a larger manual speed dead zone setting, while avoiding frequent actions, and the system has a large frequency accident (such as liaison line tripping or large unit accident Such as splitting, etc.), hydropower generating units have the advantages of large response and good continuity, which is conducive to the rapid and stable recovery of the system frequency. Both sides complement each other and coordinate their actions.
(2) On the basis of complementing the transient adjustment function of hydropower units, properly reduce the set of permanent state adjustment coefficient of the hydropower unit (smaller than that of the thermal power unit), speed up the response speed and response range of the hydropower unit, and maximize its regulation performance. The advantages.
III. Conclusion In order to meet the higher requirements for improving the system's frequency stability in connection with inter-regional power grid interconnection and capacity expansion of the power grid, Yunnan Power Grid started to compile the “Regulations for the Regulation of Primary Frequency Modulation of Yunnan Power Generation Units (Trial)†from 2005, and Based on this, the perfection and standardization of the primary frequency modulation function of the main generator set in the network was carried out.
On the side of thermal power units, they have extensively learned from the successful experiences of East China, North China, and Guangdong Power Grid, and formulated detailed and feasible implementation plans based on their actual high standards. Through the program modification and dynamic test adjustment, most of the thermal power units in the network have been equipped with a frequency modulation. Functional input conditions.
The work of the hydropower unit side started late due to the maintenance plan arrangement, but the preliminary technical preparation work has been carried out adequately. Through technical investigation, investment collection, and discussions with experts, a detailed and feasible plan has been formulated according to the characteristics of the hydropower unit itself. Wait for the implementation.
Focusing on the large proportion of hydropower generating units in Yunnan Power Grid, a study was conducted on how to coordinate the frequency modulation of hydro-thermal power units. A solution was initially developed and the system was tested for practical feasibility.
Yunnan Power Grid, as the sending end of the South China Power Grid, has its own operating characteristics. Due to the weak link with the South Network, frequent frequent frequency fluctuations in the control area caused by the tripping of the tie-line often occur, and the high-cycle problems of the power grid are more prominent. Under the premise of coordinated operation of safety and stability control devices and improved generator set OPC (Overspeed Protection Control) function, if the frequency adjustment function of each grid-connected unit can be improved and put into use, the fast frequency response of the speed control system can partially suppress the generation of The frequency fluctuations caused by power imbalances are helpful for the rapid recovery of accidents. In addition, ensuring the correct investment of a sufficient number of grid-connected generators with one frequency tuning function is conducive to the further improvement of the AGC performance (CPS standard assessment results) in the control area of ​​Yunnan Power Grid under the existing TBC (tie line frequency deviation control) control method.
The installed capacity of Yunnan Power Grid is 1230OMW, of which 525MWW for thermal power units, 705OMW for hydropower units, and hydropower generating units account for a relatively large proportion and are rather special among the provincial power grids in China. The quick start and stop methods of hydropower units and better regulation performance bring a lot of benefits to the grid dispatch operation (including the stability control strategy and AGC control). However, due to the unique “anti-regulation phenomenon†and long time constant of the hydroelectric generator set's speed control system, the normal input of the primary frequency modulation function of the hydropower generating unit has been adversely affected. In addition, the AGC function design and the frequency modulation function of the speed control system in the current large-scale hydropower plant computer monitoring system do not match each other, so that the normal input of the primary frequency modulation function of the hydropower unit is completed, both on the unit side and on the grid side (making related technical specifications) There are many issues worth exploring and studying.
2. Unit-side work In July 2005, the Yunnan Power Grid Dispatching Center promulgated the “Regulations on the Regulation of Primary Frequency Regulation of Yunnan Power Generation Units (Trial)â€. According to the requirements of the "Regulations", each of the on-grid power plants conducted a complete modification of the relevant control functions with respect to the characteristics of its own unit, conducted a dynamic test, and conducted a one-time FM function according to the test results and the relevant technical provisions in the "Regulations". acceptance. The main technical specifications of the “Regulations†are as follows: (1) Manual speed dead zone: ±0.033Hz; (2) Adjustment ratio (inconstant): Inequality of thermal power unit 4%~5%, coefficient of variation of hydropower unit 3 %~4%; (3) Response time: less than 3s; (4) Adjustment speed and stabilization time: stabilization time should be less than lmin; (5) Response amplitude: ±6% MCR for thermal power of 30OMW and above (maximum continuous operation) Load); below, ±8% MCR; no limit for hydropower units.
2.1 Situation of Thermal Power Units 2.1.1 Program Planning Thermal power units of 100 MW or above in Yunnan Power Grid are equipped with DEH (digital electro-hydraulic speed control) system. According to the requirements of the “Regulations†and the “Acceptance Program†in the appendix, the primary frequency modulation function of the thermal power unit Must be based on the DEH side, mainly considering the rapid response requirements of the frequency response of the unit. At the same time, the comprehensive valve position command under the valve control mode, the power command under the power control mode, and the strategy of controlling the output feedforward and superimposing the frequency modulation amount are considered on the DEH side. Guarantee rapidity requirements. The primary tuning function of the CCS (coordinated control system) is auxiliary frequency tuning. The main consideration is to make necessary adjustments to the CCS integrated valve position instruction when the unit CCS (mainly a coordinated control method based on the boiler following method) is used. On the one hand, it is ensured that the input of CCS will not affect the normal function of the unit's primary frequency regulation function; on the other hand, through the coordinated control function of the CCS side, the amount of fuel entering the unit unit is changed to ensure the continuity of the frequency modulation effect (without changes in steam parameters). And fluctuations). In the aspect of function input, the methods of switching between the CCS main control screen and the DEH operation screen were unified in the past, and the function input signal was remotely transmitted to the dispatch center for remote monitoring through the RTU (Remote Terminal Unit) as a remote signaling signal. Once the operator presses the input button, the control system will automatically determine the frequency modulation mode (DEH FM or DEH/CCS integrated FM) according to the current operation mode of the unit.
2.1.2 Implementation and results Take the example of Guotou Qujing Power Plant No. 3 (30OMW). The DEH and DCS (Distributed Control System) are the Westinghouse OVATION system. Briefly introduce the dynamic test results (see Figure 1).
As can be seen from the curves, the unit is capable of responding quickly to changes in the frequency deviation of the system in all three control modes. The response speed is fast (less than 15), the steady-state response amplitude meets the setting of the adjustment coefficient (5%) and the dynamic adjustment stability. Less than lmin technical requirements, FM performance is good. It is particularly worth mentioning that when the unit is under coordinated control mode, that is, CCSBF (boiler follows CCS), the frequency response of the unit is affected by both the feedforward on the DEH side and the power command on the CCS side. The boiler command is based on The unit command changes ahead of time for fuel quantity compensation, making the unit's active output response speed faster, the response steady-state accuracy is higher (better than the valve control mode), while the pre-machine pressure fluctuation in the FM dynamic process is smaller (better than the DEH power control The method), while meeting the grid frequency support role, also ensures the safe and stable operation of the unit.
2.2 Situation of the motor group 2.2.1 Analysis of the status quo and special situation The completion of the hydropower unit's scheme and dynamic test has not yet begun. However, the previous stage has been designed and demonstrated through the acquisition and investigation. At present, the larger hydropower units in the Yunnan Power Grid are mostly Francis type units with a stand-alone capacity of 200~25OMW. The typical frequency response curve of this type of unit speed control system is shown in Figure 2. It can be seen from the curve in Fig. 2 that for the effect of the "anti-regulation" of the Francis turbine unit, the response has the characteristics of a non-minimum phase system, and the initial phase of the response shows a significant reverse regulation, and the duration is longer. For a frequency modulation, this effect may affect the normal FM function of the system. In addition, due to the limitation of the principle process, the speed regulation system of the hydro-generator set makes the inherent rotational speed dead-zone larger and the time constant longer, which is not conducive to the unit's rapid response to system frequency deviation.
The AGC function in the computer monitoring system of the hydropower plant may also be inconsistent with the FM function of the speed control system. Huaneng Manwan Power Plant AGC function and speed control system interface functions shown in Figure 3, once the frequency difference occurs, the governor is the first to reflect (microcomputer governor relatively short host operation cycle is relatively short), according to the adjustment requirements to change the unit active power output Afterwards, the power-closed-loop controllers of the various units in the monitoring system detected a deviation between the unit command (AGC/LOCal: dispatching/local) and the actual power generated after the FM, resulting in an instruction output that is opposite to the FM operation, and the speed The interface pulse of the device changes the active power output of the unit in the opposite direction, causing it to return to the previous AGC setting value. Therefore, it is necessary to ensure that the primary frequency modulation function of the hydropower unit monitors the interface pulse of the system governor, and changes the active power output of the unit in the opposite direction so that it can return to the previous AGC setting value. Therefore, to ensure the correct input of the primary frequency modulation function of the hydropower unit (without affecting the original AGC function), the monitoring system must be properly adjusted to match the governor action.
2.2.2 Suggested implementation plan To address the above issues, it is recommended that the existing hydropower unit control plan be modified.
(1) Governor side: In the existing control mode, in addition to the original Permanent Droop coefficient, a transient correction coefficient (TransientDroop) coefficient correction loop is added (see Fig. 4) in order to use the temporary Principle of state adjustment in response to the beginning of the dynamic phase, increasing the coefficient of adjustment, slowing the guide vane opening speed, thereby to some extent ease the negative effects of "negative phenomenon", the transient adjustment loop is not in the steady state Plays a role, so it does not affect the static rate of the unit (according to the permanent state adjustment coefficient). The above process simulation results are shown in Figure 5.
(2) The whole plant computer monitoring system side: In the existing monitoring system AGC function design, there is a frequency tuning mode, but only the units that have been put into the AGC participate in the command distribution, and the requirement that the on-grid generator set must have a frequency tuning function cannot be met. In the AGC frequency modulation mode (normal FM/emergency FM), the load command correction algorithm is not reasonable (using the actual power plus frequency correction term, there is a process of successive accumulation), and it does not match the governor side FM function, so Not working properly after putting in. For this reason, consider the scheme shown in the dashed line in FIG. 3 to perform the frequency difference correction on the active-closed-loop controller set value end of each unit on the AGC side, and the correction amount is matched with the governor side, thus avoiding the input of the AGC and once There are contradictions in the frequency modulation function. At the same time, the AGC side and the governor side maintain the same FM operation and do not cancel each other out.
2.3 Water and Thermal Power Generation Units Coordinate One Frequency Modulation Action The primary frequency regulation function of the power grid is mainly aimed at the frequency fluctuation caused by the short-cycle load changes and the rapid and stable recovery of the grid frequency under the accident conditions. Therefore, it is required that the FM operation respond quickly and have a certain degree of response and continuity. Sex. From the analysis of the response characteristics of the hydro-thermal power unit and the test results from the previous two sections, the two have their own characteristics. The time constant of the speed control system of the thermal power unit is small, and the response speed is fast, generally less than 2 seconds, ie, it produces a correct response, but The amplitude and continuity of the response are affected by the pre-machine steam parameters. The response speed of the hydropower unit is slow. At the same time, the influence of the “anti-regulation effect†may adversely affect the overall frequency response of the system, but the hydropower unit responds as soon as it starts responding. Larger amplitude, higher precision, longer duration. Considering comprehensively, in order to better play the role played by the primary FM function in the Yunnan Power Grid to stabilize the system frequency, the FM operation of the hydro-thermal power unit must be resolved. Specifically propose the following two measures.
(1) Due to the characteristics of the hydropower generating unit's speed control system and the effect of the reverse regulation, if the frequency of the short-cycle fluctuations of the follow-up system is frequently adjusted, on the one hand it is possible to offset the normal frequency response of the thermal power unit; on the other hand, it also jeopardizes the speed controller itself. For this reason, it is recommended to use the idea of ​​sub-control by ACE (area control deviation) similar to the AGC strategy. The hydro-thermal power units are each set with their own manual speed dead zone, and it is determined through experiments that the frequently-adjusted frequency difference section is reasonably avoided, and the thermal power unit adopts Smaller manual speed dead zone in order to cope with short-cycle load fluctuations; hydropower unit uses a larger manual speed dead zone setting, while avoiding frequent actions, and the system has a large frequency accident (such as liaison line tripping or large unit accident Such as splitting, etc.), hydropower generating units have the advantages of large response and good continuity, which is conducive to the rapid and stable recovery of the system frequency. Both sides complement each other and coordinate their actions.
(2) On the basis of complementing the transient adjustment function of hydropower units, properly reduce the set of permanent state adjustment coefficient of the hydropower unit (smaller than that of the thermal power unit), speed up the response speed and response range of the hydropower unit, and maximize its regulation performance. The advantages.
III. Conclusion In order to meet the higher requirements for improving the system's frequency stability in connection with inter-regional power grid interconnection and capacity expansion of the power grid, Yunnan Power Grid started to compile the “Regulations for the Regulation of Primary Frequency Modulation of Yunnan Power Generation Units (Trial)†from 2005, and Based on this, the perfection and standardization of the primary frequency modulation function of the main generator set in the network was carried out.
On the side of thermal power units, they have extensively learned from the successful experiences of East China, North China, and Guangdong Power Grid, and formulated detailed and feasible implementation plans based on their actual high standards. Through the program modification and dynamic test adjustment, most of the thermal power units in the network have been equipped with a frequency modulation. Functional input conditions.
The work of the hydropower unit side started late due to the maintenance plan arrangement, but the preliminary technical preparation work has been carried out adequately. Through technical investigation, investment collection, and discussions with experts, a detailed and feasible plan has been formulated according to the characteristics of the hydropower unit itself. Wait for the implementation.
Focusing on the large proportion of hydropower generating units in Yunnan Power Grid, a study was conducted on how to coordinate the frequency modulation of hydro-thermal power units. A solution was initially developed and the system was tested for practical feasibility.
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