Part 8: PV side secondary system and power prediction and dispatching SOP of photovoltaic power station
This article corresponds to the panoramic topology diagram of the photovoltaic power plant [Module 8: Secondary System and Power Forecasting and Scheduling], which serves as the center for site-wide monitoring and command and dispatching, covering photovoltaic SCADA monitoring background, dual-machine hot standby switching, database management, photovoltaic power prediction system (short-term/ultra-short-term), AGC automatic power generation control, AVC automatic voltage control, PR energy efficiency ratio calculation, microcomputer relay protection setting review, GPS/Beidou full-station time synchronization, and telecontrol RTU Four-remote testing and comprehensive site-wide cross-system troubleshooting SOP.
1. Photovoltaic SCADA monitoring background, database and dual-machine hot standby maintenance SOP
The SCADA system realizes centralized monitoring and remote control of data from the entire station's photovoltaic arrays, inverters, box-type transformers, high-voltage cabinets and weather stations.
(1) SCADA main/standby server dual-machine hot standby switching test SOP
Main/standby server running status check: Check the SCADA main server (Master) and backup server (Slave) running status, confirm that the dual-machine heartbeat cable (Heartbeat Cable) is connected normally, and the database real-time redundant mirror synchronization is without delay.
Dual-machine hot standby automatic switching test SOP (executed every six months):
When the power station is running smoothly, the network cable of the main server is manually unplugged or the power supply of the main server is cut off (simulating a sudden host failure). The standby server must automatically take over control of the entire site within < 1.0s. The SCADA monitoring screen must not freeze or crash, the data must not be lost, and the AGC/AVC strategy being executed must not be interrupted.
(2) Time series database management and performance optimization
Database disk space check: Check local time series database (such as InfluxDB, TDengine or MySQL) disk partition space. Disk remaining space must be > 30%.
Data archiving and backup: Second-level sampling data of the entire site must be saved locally for ≥ 90 days; minute-level historical data and alarm logs must be saved for ≥ 3 years. Database index reconstruction and cold data offline backup must be performed every quarter.
2. Photovoltaic power prediction system (NWP) and AGC/AVC power control SOP
(1) Photovoltaic power prediction system (short-term/ultra-short-term) algorithm calibration
The photovoltaic power prediction system predicts the future output power of the power station based on numerical weather prediction (NWP) data and measured data from weather stations.
NWP weather forecast data reception: Check that the NWP data reception channel is normal and receive the latest irradiance, cloud cover, temperature and wind speed forecast data on time every day.
Forecast accuracy calculation and model calibration:
Evaluation indicator: monthly calculation of power prediction accuracy. The accuracy of short-term power prediction (072h) must be ≥ 85.0%; the accuracy of ultra-short-term power prediction (04h) must be ≥ 90.0% (the accuracy rate meets the standard to avoid power grid dispatch assessment fines).
Model calibration: When the prediction accuracy for three consecutive days is <80%, the photovoltaic array photoelectric conversion attenuation coefficient and the meteorological inversion model must be recalibrated.
(2) AGC/AVC power control and whole-station PR energy efficiency ratio calculation
AGC (automatic power generation control) active power derating and power limit response:
When receiving the AGC power limit instruction issued by the grid dispatcher (for example, the dispatcher requires the power station to limit the power output by 50%), SCADA/EMS must complete the instruction decomposition and issue it to each inverter within < 1.0s. The tracking accuracy of the actual output power of the whole station to the AGC instruction must be ≥ 99.0%.
AVC (automatic voltage control) reactive power regulation:
According to the grid-side node voltage fluctuation, the inverter output reactive power (lead/lag) is automatically controlled to control the 35kV bus voltage deviation within ± 2.5% of the rated voltage range.
Whole-site PR (Performance Ratio) energy efficiency ratio calculation:
Calculate the PR energy efficiency ratio of the entire site every month: PR = (Actual output grid power kWh) / [Nominal installed capacity kWp × (Actual cumulative irradiance kWh/m² / 1 kW/m²)] × 100%. Qualification standard: PR of the entire site must be ≥ 82.0%.
3. Relay protection device, full station time synchronization and telecontrol RTU "four remote" maintenance SOP
(1) Microcomputer relay protection device and anti-backflow system
Review of the relay protection setting list: Check the microcomputer protection devices (overcurrent, quick-break, zero-sequence overvoltage, differential protection) on the high-voltage switch cabinet and the main control room protection screen. Derive the device setting value and check it word for word with the latest setting notice from the power grid dispatching department. The current/voltage setting value error must be 0.0% (absolutely consistent).
Anti-backflow protection device test: In power stations where reverse transmission is prohibited, the anti-backflow protection device is tested. When it is detected that the reverse power reaches the set threshold (such as 10 kW), the anti-backflow device must send a derating or shutdown command to the SCADA and inverter within < 200ms.
(2) Precise clock synchronization of the whole station (NTP / IEEE 1588 PTP)
Check that the satellite time synchronization receiver (GPS/Beidou dual-mode time synchronization source) in the main control room receives normally. The clock error of all servers, inverter control boards, weather stations and relay protection devices in the entire site must be ≤ 1.0 ms to ensure that the timestamps of the sequence of events record (SOE) are completely consistent when an accident occurs.
(3) Telecontrol RTU and dispatch gateway "four remote" test SOP
Communicate with the power grid dispatching main station through the IEC 60870-5-104 protocol, and conduct regular "four remote" function checks:
Telemetry (YC): Check the total active/reactive power of the entire station, 35kV bus voltage, and string current analog quantities, with an error ≤ ± 0.5%;
Remote signaling (YX): Test switch circuit breaker opening and closing status, fault alarm signal, displacement response time < 100ms;
Remote control (YK): Test and dispatch remote control of the main circuit breaker opening and closing function, and the locking logic is safe and correct;
Remote adjustment (YT): Test dispatch remotely issues the active/reactive power settings of the inverter.
4. Typical cross-system troubleshooting and recovery SOP (code-level diagnosis) of the entire photovoltaic power station
(1) Comprehensive fault one: The insulation resistance of the whole station is too low (Riso Low). SOP for troubleshooting of string cascading
Step 1: Environment investigation. Check meteorological data in SCADA interface. If heavy rain and snowfall cause the matrix humidity to be >90% RH, and the insulation recovers after the rain has cleared and the humidity drops, it is determined to be caused by high humidity and condensation. If the humidity is normal but the insulation is low, go to step 2.
Step 2: Separate the inverter side and square array side. Disconnect the DC side input circuit breaker of the inverter. Use a 1000V insulated megger to measure the impedance of the inverter DC input to ground and the photovoltaic array DC bus impedance to ground. If the impedance on the inverter side is low, repair the inverter DC input filter circuit; if the impedance on the array side is low, go to step 3.
Step 3: String plugging and unplugging test (locating the faulty string). Unplug all DC string MC4 plugs under the inverter or combiner box. Use a multimeter/micrometer to test the insulation resistance of each string to ground (positive pole to ground, negative pole to ground). Locks out faulty strings with insulation resistance < 2.0 MΩ (e.g. PV String 08).
Step 4: Check along the line and repair the insulation. On-site inspection along the PV String 08 line ➔ Check whether the MC4 plug is soaked in the bracket water tank, the cable is worn by the sharp edge of the metal bracket to expose copper, or water has entered the junction box ➔ Replace the MC4 terminal/bandage and repair the damaged cable ➔ Retest the string insulation resistance > 10.0 MΩ ➔ Restore closing.
(2) Comprehensive fault two: Overvoltage/undervoltage/overfrequency/off-grid trip recovery SOP on the grid side of the inverter
Step 1: Call up the power quality analyzer waveform to confirm the true voltage and frequency of the power grid at the time of tripping.
Step 2: Check the protection action delay. If the grid-side voltage exceeds 1.1 Un (overvoltage) or is lower than 0.85 Un (undervoltage), confirm that the inverter trips accurately according to the protection delay.
Step 3: After the grid voltage/frequency returns to the normal range, perform a fault reset on the SCADA interface and resume grid-connected power generation according to the logic of "boost transformer ➔ AC circuit breaker ➔ DC side switch ➔ inverter standby ➔ power start".
(3) Comprehensive fault three: PV string zero current/low current (deviation > 10%) cascade troubleshooting SOP
Step 1: The SCADA background compares the current of each string under the same inverter. Locate abnormal strings whose operating current is 0 A or significantly more than 10% lower than other strings.
Step 2: Use a DC clamp meter to re-measure the string current on site. If the current measured by the clamp meter is normal, it is determined that the combiner box/inverter Hall sampling module is damaged and the sampling board must be replaced.
Step 3: If the measured current is indeed 0 A, test the string open circuit voltage Voc. If Voc is 0 V, check whether the DC fast fuse (Fuse) is blown or the MC4 plug is tripped and disconnected; if Voc is lower than 1/3 or 1/2, check whether the bypass diode in the component junction box is broken down and short-circuited or the component has severe hot spots/cracks, and replace the faulty component or diode.
Photovoltaic power station PV side secondary system and power prediction dispatch equipment level inspection and operation and maintenance sign-in form
Power station name: _______________________________ Inspection date: ____ month ____ day, 2026
Inspection area: Main control room secondary system and SCADA backend Inspection person in charge: ____________________
Field equipment inspection and test data recording
2. Registration of inspection defects and dispatch of work to eliminate defects
3. Inspection sign-in and review signature
Inspection Engineer (Signature): _______________ Supervision Engineer (Signature): _______________
Review (signature) of the shift leader: _______________ Sign-in and filing time: ____ hour on ____ month ____ day 2026