- Optical power prediction system
The main function of the optical power prediction system is to analyze the weather forecast data of the area where the photovoltaic power station is located and the data collected by the environmental detector in the station, and send the generated data file to the local power grid dispatching department through the non real-time switch. The power grid dispatching department receives the data files, puts them into storage and analyzes them to obtain the daily power generation load forecast of the power station, so as to facilitate the centralized control of the whole new energy power station in the region.
（1） Structure and working principle of optical power prediction system
The optical power prediction system generally exists in the form of screen in the power station. A host and a display are placed in the monitoring background to facilitate the inspection and maintenance of the operation and maintenance personnel in the station. The equipment contained in the screen generally includes firewall, reverse isolator, network server and switch. Usually, each manufacturer has its own product network structure diagram. The photovoltaic power prediction system is based on the global mesoscale model numerical weather prediction data, combined with the micro site selection of photovoltaic power stations and the parameterization scheme according to different regional characteristics. After the modernization of large-scale parallel distributed computer clusters, the high-precision medium and small-scale numerical weather prediction is obtained as the basis of solar irradiation prediction. The whole system shall have high-precision numerical weather forecast, photoelectric signal numerical purification, networked real-time communication, general power information data interface and other functional modules .
The working process of optical power prediction system is mainly divided into the following steps:
(1) The external network server of the system downloads the weather forecast data of the area of the power station from the server of the public meteorological department designated by the system through the Internet, and then transmits it to the internal network server through the reverse isolator.
(2) The main function of the intranet server is to receive the data required for prediction in the power station and the data collected by the environmental detector, store them in the database of the server, and then the program in the intranet server takes the teaching data from the database. According to the corresponding values and the calculation model of the prediction system, the prediction data file required by the dispatching department is generated. Chang Bei’s data file PDV format is generated and transmitted to the power grid dispatching department through 102 protocol (or FTP form). The documents generated by the prediction system include short-term documents, ultra short-term documents and meteorological documents.
(3) The background host display can display the curves and data of dispatching requirements generated by the prediction system, and display them relatively intuitively to the on-site operation and maintenance personnel to facilitate operation and maintenance management.
（2） Function of optical power prediction system
- Improve the stability of power grid and increase the photoelectric capacity of power grid
The load output of photovoltaic power generation has the characteristics of intermittence, randomness and fluctuation, which brings a series of problems to the safe operation of public power grid. If there is no accurate load forecasting, the power grid dispatching department can only take the traditional means of switching off and limiting power to control the power grid load balance.
With the increase of the proportion of photovoltaic power supply in the power structure of power grid, photovoltaic power prediction system becomes particularly important. Only the more accurate the photovoltaic power prediction is, the smaller the impact of photovoltaic grid connection on the safe operation of the power grid, which can effectively help the power grid dispatching department make the dispatching plan of various power sources.
- Improve the efficiency of dispatching plan, reduce power limitation loss and improve power generation efficiency
The more accurate the optical power prediction is, the power grid dispatching department will be able to optimize the power grid dispatching plan, reduce the power output restrictions on photovoltaic power plants as much as possible, and greatly improve the power grid’s ability to absorb photovoltaic power. The reduction of power rationing loss is also equivalent to improving the power generation efficiency and the return on investment of photovoltaic power stations.
（3） Operation and maintenance of optical power prediction system
The optical power prediction system shall comply with the following operation regulations:
(1) The switching on and off of optical power prediction system shall be carried out in strict accordance with the dispatching requirements, and it is not allowed to switch on and off without authorization.
(2) The maintenance of optical power prediction system shall be submitted to the dispatcher on time according to the requirements of relevant maintenance regulations, and the maintenance can be carried out only after the dispatcher approves it.
(3) When the optical power prediction system works on site, safety measures shall be taken as required to ensure the normal operation of the system.
The patrol inspection of optical power prediction system should pay attention to the following requirements:
(1) The power indicator of the device is on.
(2) The optical power prediction server operates normally without abnormal signal.
(3) The display screen shall transmit other information correctly.
(4) The operation indicator of network security isolation device has no other abnormalities.
(5) The operation indicator of Ethernet switch is normal without other abnormal information.
(6) The abnormal conditions of the outgoing line of the device shall be checked step by step to eliminate the abnormal conditions. If they cannot be discharged, they shall be reported to the dispatcher and the leader in charge in time and contacted for treatment.
- AGC power control system
（1） Overview of automatic power control
Automatic power control (AGC) is that the inverter of grid connected photovoltaic power station tracks the instructions issued by power dispatching within the specified output adjustment range, and adjusts the power generation output in real time according to a certain adjustment rate to meet the requirements of power system frequency and tie line power control.
Overview of common AGC control strategies:
(1) When the current active power plan value received by AGC host is less than the current output of photovoltaic power station, the control of reducing the total active power output shall be implemented, and the active power distribution shall be carried out reasonably according to the mode of equal margin or equal proportion by comprehensively considering the operation state and current active power output of each inverter.
(2) When the current active power plan value received by AGC host is greater than the current output of photovoltaic power station, the control of increasing the total active power output shall be implemented, which can comprehensively consider the operation state and the predicted value of active power output of each inverter, and reasonably distribute the active power according to the methods of equal margin or equal proportion.
(3) AGC host has the ability to limit the change rate of active output of photovoltaic power station, and has the ability to adjust the rate setting for 1min and 10min, so as to prevent the impact of large power change fluctuation on the power grid.
(4) When the high-voltage side of the booster station adopts multi section bus, the AGC host has the ability to receive the total active power setting command of the outgoing line connected by different buses.
（2） AGC system operation and maintenance specification
- AGC operation and exit rules
After the commissioning of AGC system is successfully put into operation, the operation personnel of the power station shall not exit the operation except under special circumstances (such as failure), and the necessary operation and exit shall be carried out according to the order of the bottom power grid dispatching department.
(1) The AGC control mode of the unit shall be determined by the provincial dispatching shift dispatcher according to the system conditions.
(2) The AGC function of the unit can be switched on or off normally, and the shift supervisor can order the operation after obtaining the consent of the provincial dispatching on duty dispatcher.
(3) When the unit is abnormal or its AGC function cannot operate normally, the operator on duty shall immediately report to the shift chief operator and withdraw the AGC function according to the on-site operation regulations after obtaining the consent. The shift chief operator shall report to the provincial dispatching dispatcher on duty at the same time and make records.
(4) Before putting AGC into operation for the first time after overhaul or automatic system maintenance of the unit, the control signal channel must be checked and confirmed to be intact. When the signal is unblocked, the AGC control system shall not be pulled out.
(5) When the equipment out of service maintenance affects the normal operation of the AGC function of the unit, the shift supervisor shall apply to the provincial dispatching department for approval.
- AGC startup and shutdown steps
(1) ACC input.
1) AGC load regulation section: the lower limit is 0mw and the upper limit is the actual grid connected capacity.
2) Setting of load change rate: when AGC is put into operation, the required load change rate shall not be less than 2% of the rated load per minute. The AGC regulation rate is finally determined according to the relevant performance test data of AGC. It is forbidden for operators to change the AGC regulation rate at will.
3) AGC can be put into operation only after receiving the dispatching command or obtaining the consent of the dispatcher. At the same time, after checking that ACC meets the input conditions, click the “AGC” button on the DCS “unit coordinated control” screen to put AGC into operation and check that “ACC” has been put into operation. At this time, the AGC control mode of the unit has been put into operation normally, and the load command changes with the dispatching command.
(2) AGC exits.
1) AGC can be exited only after receiving the dispatching order or obtaining the consent of the dispatcher
2) Click the “ACC” button on the DCS “unit coordinated control” screen to exit AGC, and check that “AGC” has exited. The unit changes to CCS control mode, at this time, the unit AGC control has exited, and the unit load is set according to the oral command of the dispatcher.
- Precautions for AGC operation
(1) Pay attention to the change of AGC load command, load rate and unit regulation. If the weather changes greatly and the manual intervention regulation still cannot be maintained, contact the maintenance personnel in time for inspection and treatment.
(2) When the AGC command continues to increase, the cooling device of power generation equipment shall be adjusted in time to prevent overheating for a long time during load rise.
(3) When the AGC command of the unit stays at the upper limit, lower limit or other load values of the load limit value for a long time, contact the dispatcher in time to confirm whether the ACC command is normal; If the AGC load command interval at the provincial dispatching end is normal, the maintenance personnel shall check and deal with it immediately.
(4) The shift supervisor should understand the periodic change trend and general law of the unit load. The operators should pay close attention to the change of ACC load command, and timely start and stop the pulverizing system under the condition of large load change, so as to ensure the normal regulation of AGC.
(5) When the unit load approaches the upper limit of AGC regulation, the operator needs to strengthen monitoring. In case of abnormal operating parameters, exit AGC control mode in time and make necessary adjustments. The operating parameters of the unit are strictly prohibited to exceed the limit for a long time.
(6) When the performance of main and auxiliary equipment cannot meet the load rate, the AGC shall be released in time and reported to the shift supervisor, who shall communicate with the dispatcher in time.
(7) When the unit load is unable to adjust the AGC command load due to weather, equipment defects and other reasons, the shift supervisor shall communicate with the dispatcher in time.
(8) When ACC exits for some reason during the operation of the unit and the operation adjustment or inspection is normal, pay attention to contact the provincial dispatching and put AGC into operation in time to ensure that the operation rate of ACC meets the assessment requirements of provincial dispatching.