Part 3: Equipment-level inspection and operation and maintenance SOP of PV side inverter (DC/AC) system of photovoltaic power station
This article corresponds to the panoramic topology diagram of the photovoltaic power plant [Module 3: Photovoltaic inverter system], as the core of DC/AC energy conversion, covering the appearance of string inverters and centralized inverter cabins, dust-proof purging, AC and DC incoming circuit breakers and terminal temperature rise, IGBT Power module and thermal grease overcoating, DC support capacitor (DC-Link), filter inductor, sampling accuracy calibration, actual measurement of anti-islanding protection (Anti-Islanding) and low/high voltage ride through (LVRT/HVRT) protection logic.
1. Inverter appearance protection, dustproof ventilation and AC/DC switch maintenance SOP
The photovoltaic inverter is responsible for inverting the DC power generated by the components into low-voltage AC power. It contains high-frequency switching power electronic devices and control cards, and is extremely sensitive to ambient temperature, humidity and dust accumulation.
(1) Cabin/cabinet environment and sealing and anti-condensation control
Cabin temperature and humidity control: Check the temperature and humidity sensor in the inverter cabin/cabinet. The ambient temperature must be controlled between 0 ℃ ~ 40 ℃; the relative humidity must be < 70% RH. The anti-condensation heater must start automatically when the humidity is ≥ 75% RH. Check that the EPDM sealing strips on the cabinet are not aging and falling off, and that the rainproof eaves and drainage channels are clear.
Protection level inspection: Check the cabinet door locking mechanism. The protection level must meet IP54/IP65 standards and there should be no severe vibration or abnormal noise.
(2) Dust filter cleaning and cabin water-free purging SOP
Removing and washing the primary dust filter: Remove the primary filter from the air inlet of the inverter, clean it with an industrial vacuum cleaner or rinse it with neutral detergent. It must be completely dried (moisture content 0%) and then reinstalled.
SOP for dry purging without water in the cabin (implemented for annual power outage and overhaul):
Apply for a power outage, check the power and connect the ground wire. Use a compressed air pump with a high-efficiency water removal filter (the air pressure is strictly controlled at 0.20 ~ 0.30 MPa), equipped with an insulated nozzle hose, and blow out the gaps between the circuit board and the radiator in the order of "top to bottom, from inside to outside". It is strictly prohibited to use a wet cloth with water or an air gun that has not removed water to directly blow the circuit board.
(3) Fastening of AC and DC side circuit breakers and infrared temperature measurement
DC side molded case circuit breaker (DC Breaker): Disassemble the arc extinguishing cover and check that the grid plate has no ablation and deformation; check that the magnetic blowing coil is well insulated and has no burnt smell; test that the shunt release is sensitive.
AC side frame circuit breaker (AC Breaker): Check the energy storage time of the electric energy storage mechanism < 10s; measure the three-phase closing aberration must be < 1.0 ms.
Infrared temperature measurement and tightening torque standards:
After the inverter runs at full power for 30 minutes, use an infrared thermal imaging camera to scan the AC/DC circuit breaker terminals. The operating temperature must be < 65.0 ℃, and the temperature difference between phases/poles ΔT ≤ 5.0 ℃.
Heating treatment SOP: If the terminal temperature > 75.0 ℃ or the temperature difference ΔT ≥ 15.0 ℃, the power must be cut off to disassemble the copper bar, polish the oxide layer with 1000-grit sandpaper and apply 0.1 mm anti-oxidation conductive paste, and then tighten the bolts according to the following table:
2. Equipment-level maintenance SOP for IGBT power modules, DC-Link capacitors and filter inductors
The IGBT module is the core AC-DC conversion semiconductor component inside the inverter that changes the direction and frequency of current.
(1) IGBT power module and thermal grease overcoating SOP
IGBT junction temperature monitoring: Read the IGBT junction temperature of each phase through the inverter’s local screen or SCADA. The junction temperature must be < 85.0 ℃ at full load operation; when the junction temperature reaches 95.0 ℃, the power will be automatically derated by 50%; when the junction temperature reaches 105.0 ℃, an over-temperature trip will be triggered. Check that the driver board triggering fiber is not bent or blocked, and that the driver board indicator light is normal.
Thermal grease recoating SOP (performed every 3 years or when the junction temperature rises > 10.0°C from the initial level):
Step 1: Cut off the power, check the power, and use a special discharge rod to release the residual charge of the DC bus (make sure the DC bus voltage is < 10.0 V).
Step 2: Remove the IGBT module connection cable, and use isopropyl alcohol and a lint-free cloth to completely wipe off the old silicone grease on the bottom plate.
Step 3: Use a scraper or screen printing to evenly apply a layer of new thermal conductive silicone grease (thermal conductivity > 3.0 W/m·K, thickness controlled at 50 ~ 100 μm).
Step 4: Reinstall the module, tighten the bolts twice in a diagonal cross sequence (torque: 3.0 ~ 5.0 N·m), and rewire and receive power.
(2) DC bus support capacitors (DC-Link Capacitors) maintenance
Appearance and leakage inspection: Check that the film/electrolytic capacitor shell has no bulges, leakage, and explosion-proof valve rupture.
Capacity and ESR test: After full discharge after a power outage, use an LCR meter to measure the capacitance capacity. When the capacity attenuates > 10% from the nominal value or the equivalent series resistance (ESR) increases > 50% from the initial value, the entire capacitor must be replaced.
Bus voltage ripple coefficient: Under full power discharge, the DC bus voltage ripple coefficient γ measured using an oscilloscope (AC coupling mode) must be < 1.0%.
(3) Maintenance of DC/AC filter inductor and LC filter
Insulation and temperature rise test: Use a 1000V megger to measure the insulation resistance of the inductor winding to ground. It must be ≥ 100 MΩ; the operating temperature of the inductor must be < 90.0 ℃.
Noise check: Under full load operation, the measured noise at a distance of 1 meter from the cabinet must be < 75 dB. If there is abnormal high-frequency magnetic shock and abnormal sound, the power must be cut off and the core bolts must be retightened (M12 torque: 70 N·m).
3. Secondary control loop, sampling accuracy, phase locking and grid adaptive protection logic measured SOP
(1) Sampling accuracy and zero point calibration
Sampling accuracy verification: Use a power quality analyzer to measure the inverter AC/DC voltage and current, and compare it with the monitoring screen. The voltage sampling error must be ≤ ± 0.5%, and the current sampling error must be ≤ ± 0.5%.
Zero point calibration: If the monitor displays a small current in the standby state (current 0 A), "Hall sensor zero offset automatic calibration" must be performed in the control background.
(2) Measured SOP of phase-locked loop (PLL) and anti-islanding (Anti-Islanding)
Phase-locked loop tracking: When the grid-side frequency fluctuates within the range of 45.0 ~ 55.0 Hz, the phase-locked loop must accurately lock the phase within < 20 ms, with a phase tracking error of < 1°.
Measured SOP for anti-islanding protection:
When the large power grid loses power, the inverter must automatically disconnect the grid-connected switch and stop inversion within ≤ 2.0s to prevent power supply to unplanned islands.
Actual measurement steps: In the grid-connected discharge (50% power) state, manually open the grid-side analog circuit breaker. Oscilloscope monitoring shows that the inverter must cut off the AC current output and report a grid-side power loss alarm within < 200 ms.
(3) Low/high voltage ride through (LVRT/HVRT) and wind turbine maintenance
Low/high voltage ride-through: When the grid-side voltage drops to 20% of the rated voltage, the inverter must ensure that it does not go off-grid within 0.625s and inject dynamic reactive current; when the voltage rises to 130%, it must ensure that it does not go off-grid for 0.50s.
Cooling fan array: Check the Wind Pressure Switch function. When a fan fails and stops spinning, the inverter must report a fan failure within <3s and derate the power by 30%. Fans must be replaced in groups after 20,000 operating hours.
Photovoltaic power station PV side inverter (DC/AC) system equipment level inspection and operation and maintenance sign-in form
Power station name: _______________________________ Inspection date: ____ month ____ day, 2026
Inspection area: Inverter cabin/string inverter area Inspection person in charge: ____________________
Field equipment inspection and test data recording
2. Inspection defect registration and defect elimination dispatch
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