Complete steps of high-frequency online (double-conversion VFI type) UPS power grid adaptability test
First, the test basis
GB/T 7260.3-2024 (equivalent to IEC 62040-3:2021) covers eight power grid adaptability projects, namely, input steady-state power grid tolerance, voltage sag/sag, frequency offset, harmonic distortion, three-phase imbalance, instantaneous power failure, commercial power recovery and reverse feed protection; The test object is high-frequency dual-conversion on-line UPS (always inverter output, power grid disturbance does not interrupt load power supply).
Second, the pre-test preparation stage (steps 1 ~ 4)
1. Test system construction
1) Main equipment: programmable power grid simulator (voltage regulation, frequency modulation, harmonic superposition and simulated sag/interruption), programmable AC/DC electronic load, high-precision power analyzer, oscilloscope above 100MHz, data recorder and thermometer;
2) Wiring specification:
Power grid simulator output → UPS mains input (L/N/PE is reliably grounded, and three phases need balanced wiring);
UPS output → electronic load;
The pow analyzer simultaneously collect that voltage/current/harmonic of the input side and the output side; The oscilloscope is connected with the output voltage probe to capture the transient waveform;
The battery pack is connected to the UPS DC terminal according to the rated configuration, and fully charged and allowed to stand;
3) Safety configuration: UPS is closed to maintain bypass idle opening, EPO emergency stop, input and output circuit breakers, overcurrent protection threshold is set, and on-site insulation protection is provided.
2. Pre-heating of prototype and calibration of reference working condition
1) The power grid simulator is equipped with rated commercial power (220V/50Hz single phase; 380V/50Hz three-phase);
2) The 2)UPS is powered on and enters the normal inverter mode, running stably for 30min with 0% no load, 50% half load and 100% full load respectively, and the temperature rise of the whole machine is stable;
3) Record reference data: input PF, input THDi, output voltage accuracy, output THDu, inverter synchronization state and battery critical switching voltage as comparison reference.
3. Division of test conditions
All power grid disturbance items need to be tested repeatedly in three groups of working conditions: no-load, 50% and 100% rated resistive load; Three-phase UPS additionally increases unbalanced load conditions of single-phase full load and two-phase full load.
4. Data recording specification
Save each group of disturbances: steady-state power data, oscilloscope transient waveform, UPS alarm log, switching sequence and battery action record; The whole video/waveform shall be kept for future reference.
Third, sub-project standard test operation steps
Item 1: Test of input steady-state voltage adaptation range (voltage stabilization adaptability of basic power grid)
Objective: To verify that UPS does not cut the battery and its output is stable under wide voltage fluctuation.
The power grid simulator has a fixed rating of 50Hz and slowly and continuously adjusts the input voltage;
Downregulation voltage: decrease from 220V to the lower limit specification (conventional 160V, industrial width 110V) at a uniform speed, and stay for 3 minutes every 10V;
Step-up voltage: rise from 220V to the upper limit specification (conventional 275V, industrial 300V) at a uniform speed, and stay for 3 minutes every 10V;
Key observations:
Whether to trigger battery inverter switching;
Output voltage deviation ≤ 1%, THDU ≤ 3%;
The rectifier has no overcurrent, alarm and shutdown;
Record the critical low-voltage and over-voltage alarm thresholds of battery switching; Restore the rated commercial power for 3min before proceeding to the next project.
Item 2: Test of input steady-state frequency adaptation range (adapting to generator/weak current network)
The input voltage is rated at 220V, and the frequency is adjusted slowly;
Low frequency band: 50Hz→47Hz (broadband model to 40Hz), staying for 2 min every 1Hz;
High frequency band: 50Hz→63Hz (broadband model to 70Hz), staying for 2 min every 1Hz;
Judgement criteria:
Synchronous tracking of inverter, no out-of-step and bypass jump;
Output frequency error ≤±0.1Hz；;
No surge of input current, no harmonic amplification and no battery disconnection.
Item 3: Voltage Sag (Sudden Drop) Tolerance Test of Power Grid (Most Common Power Grid Faults)
Short-term low voltage caused by lightning strike, short circuit and high-power motor start-up in simulated power grid.
Benchmark: rated commercial power, full load inverter stability of UPS for 5min；;
The power grid simulator is set with step disturbance (jump is completed within 20ms) and divided into multiple groups of gradients:
The temporary dip depth is 1: 70% UN (pressure drop is 30%) and lasts for 10s；;
The temporary descent depth is 2: 50% UN for 5s;
The temporary descent depth is 3: 35% UN, lasting for 0.5s；;
Operation process:
① Steady-state operation for 5min；;
② One-key trigger voltage drops temporarily, and the whole oscilloscope captures the output waveform;
(3) automatically restore the rated voltage after the disturbance, and observe for 5min；;
Qualification criteria: the load has no power interruption, the output transient fluctuation is ≤ 3%, and there is no misoperation of battery cutting and no protection shutdown.
Item 4: Voltage Surge (Surge) Tolerance Test of Power Grid
Simulate the high voltage impact of load rejection and generator voltage regulation fault in power grid.
Step up the voltage to 130% Un for 5s; 120% Un lasts for 10s；;
Disturbance quickly recovered, and output overshoot and rectifier input current were recorded;
Requirements: Stop the machine without overvoltage protection, and the output voltage stabilization accuracy meets the specifications.
Project 5: Short-time interruption (power failure/flashover) switching test of power grid (core power grid adaptability)
Verify that the mains supply is lost, seamlessly cut the battery and restore the mains supply.
Step A: Switching from commercial power to battery inversion
The rated commercial power is fully loaded and stable;
The power grid simulator instantly cuts off the input (0ms interrupt);
Oscilloscope captures output voltage gap and switching time;
Standard: high-frequency on-line switching time < 10μ s, output without breakpoint and drop.
Step b: Automatic switching back of mains supply recovery
Keep the battery inverter running for 5min；;
Restore the rated mains input;
Observe inverter synchronization, rectification soft start, charging input and output without disturbance;
Record the transient voltage fluctuation of failback, without alarm and impact on the load.
Project 6: Harmonic Adaptability Test of Power Grid (Anti-Distortion Power Grid)
Simulate nonlinear pollution power grids such as steel mills, frequency converters and charging piles.
The power grid simulator superimposes the specified harmonics (3/5/7/9 times, THDi=10%/15%/20% third gear) on the rated fundamental wave;
Each harmonic condition is operated for 10min； at no load, half load and full load;
Test content:
Harmonic suppression ability of UPS input side;
Output waveform distortion THDu change;
Rectifier, power device temperature rise, whether there is harmonic overcurrent alarm;
Requirements: THDu output is ≤3% in the whole process, without protection tripping.
Item 7: unbalanced adaptability test of three-phase power grid (three-phase UPS only)
Simulated single-phase disconnection and single-phase high-power load lead to three-phase voltage imbalance.
Working condition 1: Two-phase rated, and the voltage of one phase is reduced to 70% Un for 10min；;
Working condition 2: one phase is fully loaded and the other two phases are unloaded and unbalanced;
Monitoring: three-phase output voltage imbalance, neutral current, module current sharing, and no phase protection misoperation.
Item 8: Frequency Sudden Disturbance Test (Sudden Loading and Unloading of Generator)
After the benchmark 50Hz is stable, it jumps to 47Hz/63Hz in 20ms, and then jumps back after 5s;
Observe the tracking speed, output frequency fluctuation and bypass tripping of PLL.
Item 9: Reverse Feed Protection Test (Power Grid Power Loss and Inverter Backflow Prevention)
UPS battery runs in reverse, simulating the short circuit on the grid side before artificially restoring the mains input;
Check that no reverse high voltage/large current is fed into the power grid at the UPS input terminal to prevent electric shock during maintenance;
Automatic recovery of synchronous rectification after disturbance elimination.
Fourth, finishing and judging steps after the test
After the completion of all disturbance projects, restore the rated commercial power, run at no-load for 30min, and check whether the whole machine has hidden faults, fever and abnormal noise;
Arrange all waveforms, power data and alarm records, and judge item by item according to product specifications and GB/T 7260.3 indicators:
All working conditions are output without interruption, shutdown and error-free protection;
Steady-state voltage/frequency accuracy, harmonics and transient fluctuations meet the limits;
The switching timing conforms to the zero interruption characteristic of on-line UPS;
Issue a power grid adaptability test report with screenshot of disturbance waveform, data table and judgment conclusion;
