High-frequency on-line UPS is a dual-conversion topology, and the core verification of power grid adaptability includes eight items: steady-state voltage/frequency tolerance, voltage sag/surge, short-time interruption, power grid harmonics, three-phase imbalance, bypass synchronous compatibility, generator adaptation and power grid fault switching protection. The whole process is divided into five stages: test preparation → pretreatment → item-by-item test → ultimate durability test → data judgment and closing.
First, the test preparation (safety+equipment+wiring)
1. List of test equipment
Programmable power grid simulation source (voltage regulation, frequency modulation, harmonic superposition, sag/interruption, simulation of three-phase imbalance)
High-precision power analyzer (input/output voltage, current, THD, power factor, harmonics 2 ~ 50 times)
High-speed storage oscilloscope (≥100MHz, capturing switching transient waveform and conversion time)
Programmable electronic load (resistive/nonlinear, 25%/50%/75%/100% rated load adjustable)
Temperature inspection instrument, battery monitor, three-phase unbalanced load unit
Safety isolating switch and grounding protection device
2. System wiring specification (high frequency online double conversion)
Main loop: programmable grid source → UPS main input; Bypass independent grid source (analog bypass mains); UPS output → electronic load; The battery pack is fully charged and connected to the UPS DC bus.
Monitoring wiring
Power analyzer 1: Connect the input side of UPS in series, and measure the power quality of power grid side.
Power analyzer 2: connected to the output side of UPS to measure the quality of on-load power supply.
Oscilloscope dual channels: one input voltage and one output voltage, and synchronously collect transient waveforms.
Safety confirmation: reliable grounding, insulation inspection and correct battery polarity, and the disconnect switch is convenient for emergency stop.
3. Environment and benchmark conditions
Environment: temperature 25 5℃, humidity 30% ~ 75%, no strong electromagnetic interference.
Reference power grid: rated voltage Un (single-phase 220V/three-phase 380V), rated frequency fn=50Hz, THD < 1%, and three-phase balance < 0.5%.
Load condition: each test is repeated under 25%, 50% and 100% rated resistive load respectively; Non-linear load (crest coefficient 3:1) plus one set.
Second, the sample pretreatment (unified initial state)
Connect the reference mains, UPS works in normal double conversion mode, and preheat for 30min without load until the temperature of the whole machine is stable.
The battery is fully charged to the floating charge voltage, and the initial voltage and internal resistance of the battery are recorded; Turn off the UPS special protection threshold (return to factory default).
Step loading: no load →25%→50%→75%→100% full load, and each gear runs for 15min. Make sure that the output voltage is stable, the waveform is normal, and there is no alarm or protection misoperation.
Collect reference data: input PF, input THDi, output voltage accuracy, output THD, inverter and bypass phase difference as comparison reference.
III. Formal Test Steps for Power Grid Adaptability of Sub-projects (Core Process)
Project 1: Steady-state input voltage adaptability test (long-term high and low voltage tolerance of power grid)
Objective: To verify that UPS runs continuously and stably in the nominal wide voltage range, without cutting the battery and stopping without protection.
Keep the reference frequency at 50Hz, and fix the load in the third gear of 25%/50%/100%;
The programmable source adjusts the input voltage in steps;
Low pressure range: Un-20%, Un-15%, Un-10% and Un-5%.
High pressure range: Un+5%, Un+10%, Un+15%, Un+20%.
Each gear voltage runs stably for 30min, and records continuously:
UPS operation mode (maintain double conversion, do not turn the battery)
Steady-state accuracy of output voltage, output THD, rectified input current and temperature rise of power devices.
The boundary limit point is lengthened to 2h for full load durability; Slowly adjust back to the rated voltage and observe that there is no abnormal fluctuation.
Judgment: the whole output voltage is within the nominal tolerance, and there is no overvoltage/undervoltage protection tripping and frequent charging and discharging.
Item 2: Steady-state input frequency adaptability test (grid/generator frequency drift tolerance)
The input voltage is fixed Un, and the load is divided into three grades; The frequency is adjusted in steps of 0.5Hz;
Standard tracking interval: 49.0～51.0Hz (47 ~ 53 Hz for wide-range models), and each frequency point is stable for 15min；;
Exceeding the tracking bandwidth: slowly pull it to 46Hz and 54Hz, and observe the UPS action: if it exceeds the range, the battery should be smoothly switched off for inverter without output voltage drop;
Frequency callback to the tracking interval, automatic switching back to the mains mode, no disturbance.
Records: frequency tracking phase-locked time, output transient fluctuation, bypass synchronization ability.
Item 3: Voltage sag/surge (voltage sag/surge immunity test, the most critical dynamic item)
Simulating power grid short circuit, motor starting and lightning boosting, which are triggered in two phases: zero crossing and peak point:
3.1 Voltage sag (sag)
50% and 100% full load; Reference Un 50Hz；;
Graded drop amplitude and duration (typical grade of national standard):
0% Un (complete power failure): 5ms/10ms/20ms/100ms.
40% Un, 60% Un, 85% Un: lasting 20ms/100ms/500ms.
The programmable source instantly drops the specified amplitude, and the oscilloscope captures the input and output waveforms synchronously;
Measurement indicators: the maximum drop depth of output voltage, recovery time, whether to cut the battery or not, and whether there is load power failure or not.
3.2 voltage surge (surge boost)
The order jumped to 115% Un and 130% Un for 20ms/100ms；;
Observe the voltage stabilizing ability of rectifier, and the output has no overshoot and does not trigger overvoltage protection.
Judgment: the output interruption time in the sag process is less than 1 ms, the voltage fluctuation is within the allowable load range, and there is no shutdown.
Item 4: Short-time voltage interruption test (complete power-off adaptation)
The analog commercial power completely disappears: the input voltage is 0V, lasting 5 ms/20 ms/100 ms/500 ms;
Observe the whole process of UPS mains → battery inverter switching;
Conversion time (high frequency online theory 0ms, measured output drop amplitude)
During the interruption, the output waveform is continuous without distortion.
Instantaneous power supply recovery: battery → power supply switching back, no surge and no load disturbance.
Item 5: Power Grid Harmonic Adaptability Test (Distorted Power Grid Compatibility)
Simulate harmonic pollution of power grid caused by industrial inverter and rectifier load.
Reference Un/50Hz, load 100%; Programmable source superposition harmonic:
Odd harmonics: 3rd, 5th, 7th, 9th and 11th order, THDu=5%, 8% and 10%.
Continuous operation for 30min, monitoring:
UPS input current distortion, DC bus ripple
Whether the output voltage THD is deteriorated, whether there is abnormal sound, and the temperature rise of the heat dissipation device.
After superposition of higher harmonics, UPS shall not accidentally trigger the input harmonic protection and frequently cut the battery.
Item 6: Three-phase input imbalance adaptability (three-phase high-frequency online UPS must be tested)
Only three-phase high-frequency UPS is used to simulate single-phase high-power load and off-line phase bias:
Three-phase reference balanced input, full load operation;
There are two unbalanced working conditions:
Unbalanced amplitude: one phase is reduced to 70% Un, and the other two phases are Un for 1h;
Single-phase disconnection: one-phase input is disconnected intermittently, and the cycle is 1min;
Record the DC bus voltage difference, rectified current of each phase, and three-phase unbalance of output, and there will be no false tripping of phase-missing protection and three-phase deviation of output exceeding the standard.
Item 7: Synchronization of Bypass Power Supply and Compatibility Test of Power Grid
High-frequency online fault/overload cuts the bypass, which needs to be compatible with the main power grid:
There are two independent programmable sources for the main input and the bypass input, and the phase difference (5, 10 and 15) and frequency difference (±0.5Hz；) are made.
Manually trigger inverter → bypass switching and overload automatic switching;
Oscilloscope observes switching transient output voltage sag and phase impact;
When the bypass is powered alone, verify that the bypass has wide voltage/frequency tolerance and the bypass belt runs stably with full load.
Item 8: Generator Compatibility Simulation Test (weak current network adaptation)
The generator voltage and frequency fluctuate greatly and the harmonics are different, which simulates the output characteristics of diesel generator;
Set the power grid source: voltage fluctuation 10%, frequency fluctuation 2 Hz, THDU = 8%;
UPS runs continuously for 4 hours with full load;
Monitoring: rectification does not oscillate, battery is not cut repeatedly, low-frequency howling does not occur, and the bus bar does not fluctuate greatly.
Item 9: Verification of Power Grid Fault Linkage Protection
Input overvoltage, undervoltage, overclocking, underfrequency, lack of phase, inversion and harmonic overrun are simulated one by one;
