To judge the anti-interference ability of high-frequency on-line UPS, the core focuses on three core dimensions: input anti-interference (anti-power grid disturbance), output anti-interference (output purity) and electromagnetic compatibility (EMC), combined with the comprehensive judgment of standard certification, performance parameters, measured data and circuit design, and taking into account the topological characteristics of high-frequency machines (no power frequency transformer, anti-interference depends more on circuit and component design). The following judgment methods can be grounded, from professional detection to intuitive selection.
First, look at the official standard certification: the most basic compliance basis.
The core compliance standard of anti-interference ability is electromagnetic compatibility (EMC) certification, and there are clear mandatory standards in different regions/industries. Certification directly reflects whether the product design meets the basic requirements of anti-interference. High-frequency UPS needs to focus on EMI (electromagnetic radiation/conducted emission, which does not interfere with other equipment by itself) and EMS (electromagnetic sensitivity, which resists external interference by itself) certification:
General industrial standards: GB/T 17626 (equivalent to IEC 61000) and EN 61000 (European Union), in which EMS is the core for judging anti-interference, and it needs to cover key items such as electrostatic discharge (ESD), electrical fast transient (EFT), Surge and radio frequency radiation/conduction;
Industry-specific standards:
Communication industry: YD/T 1095 (mandatory standard for communication UPS, with higher requirements for power grid surge and pulse interference);
Power industry: DL/T 724 (power system UPS, with strict requirements for anti-harmonic and surge capacity);
Medical/military: YY 0505, GJB 151B (higher electromagnetic shielding and anti-interference requirements);
Certification marks: EU CE-EMC, China CQC-EMC, and US FCC Part 15. It is necessary to confirm that the certification covers the "high-frequency online UPS" machine, not parts.
Selection key: under the same power section, the higher the EMS test level covered by certification, the stronger the anti-interference ability (for example, electrostatic discharge contact test 8 kV/air ±15kV, surge line-line 2kV/line-ground 4kV is an industrial high level).
Second, check the core performance parameters: quantify the hard index of anti-interference ability
Extract the key parameters from the product manual/specification, and directly quantify the input anti-disturbance ability (anti-grid interference) and output purity (no interference from its own output, so as to avoid interference to the load) of UPS. High-frequency UPS should focus on the following parameters, and the better the parameters, the stronger the anti-disturbance ability:
(1) Input side: anti-grid interference/disturbance capability (see "wide adaptability+anti-disturbance" for the core)
There is no power frequency transformer at the input side of high-frequency online UPS, and it relies on PFC circuit, rectifier bridge and surge suppression circuit for anti-interference. The key parameters are as follows:
Input voltage range: the wider the range, the stronger the anti-interference ability of grid voltage fluctuation (industrial high-frequency machine: AC 120~280V, wide-range machine: AC 90~300V, even 80 ~ 320 V);
Input frequency range: conventional 50/60hz 5%, wide range 10%, suitable for power grid frequency fluctuation;
Input power factor (PF): The high-frequency machine comes standard with active PFC, with PF≥0.95 (the closer to 1, the better). Active PFC can not only improve energy efficiency, but also suppress input harmonics, reduce the interference of grid harmonics to UPS and reduce the harmonic pollution of UPS to the grid.
Surge suppression capability: the input surge tolerance values indicated in the manual (such as line-to-line 2kV and line-to-ground 4kV, which conform to IEC 61000-4-5), and whether surge suppression devices such as MOV (varistor), GDT (gas discharge tube) and TVS (transient suppression diode) are built in;
Anti-harmonic interference: The input total harmonic distortion (THDI) is ≤ 5% (the smaller the better), which means that UPS can effectively suppress the interference of grid harmonics, and at the same time, it does not inject harmonics into the grid.
Total Harmonic Distortion (THDv) of output voltage: THDv≤3% under linear load, and ≤5% under nonlinear load is an industrial high grade (the smaller the better, the linear load of conventional machine ≤5%). THDv directly reflects the purity of output voltage, and the lower the distortion, the smaller the electromagnetic interference to the load;
Voltage stabilization accuracy of output voltage: conventional 1% (high accuracy 0.5%), far better than 2% of power frequency machine. The higher the voltage stabilization accuracy, the stronger the anti-interference ability of power grid/load fluctuation;
Output filtering ability: output filtering frequency band marked in the manual (such as suppressing radio frequency interference from 10kHz~30MHz), and whether LC filtering and EMI filtering circuits are built in (the design of filtering circuit of high-frequency machine is the key to anti-interference, without shielding of power frequency transformer, and high-frequency interference is suppressed entirely by filtering circuit);
Dynamic response characteristics: when the load suddenly changes from 0% to 100%, the recovery time of output voltage is less than 5 ms (the shorter the better), and the voltage drop is less than 5%, which reflects the ability of UPS to resist the interference of sudden load change and avoids the distortion of output voltage caused by load fluctuation.
(3) Other key parameters
Isolation: The high-frequency machine has no power frequency transformer, and it depends on whether it has built-in high-frequency isolation transformer or optocoupler/magnetocoupler isolation circuit. The input-output isolation ≥2kV can effectively suppress the ground loop interference of the power grid;
Common mode rejection ratio (CMRR): ≥ 60dB (the higher the better), to suppress the influence of input common mode interference (the most common interference form in power grid) on the output.
Third, analyze the internal circuit design: judge the hardware support of anti-interference from the root.
The anti-interference ability of high-frequency online UPS is essentially determined by the circuit topology and component selection, without the inherent characteristics of power frequency transformer, which makes it more dependent on the combined design of "active circuit+passive device", which can be judged by product disassembly/design data. The core points are as follows:
Input side protection circuit: whether there is a three-stage surge suppression circuit (first-stage MOV+GDT, second-stage TVS, third-stage inductive filtering) instead of a simple single-stage MOV, and the three-stage protection can absorb power grid surge and pulse group interference more effectively;
EMI filter circuit: Whether there is an independent EMI filter (including differential mode inductance, common mode choke and safety capacitor) on the input/output side, the higher the order of the filter (secondary/tertiary EMI), the stronger the anti-radiation/conducted interference ability;
Active PFC circuit: whether it is totem-pole active PFC (better than conventional Boost PFC), totem-pole PFC has stronger harmonic suppression ability, lower input THDi and better anti-harmonic interference of power grid;
Inverter topology: whether it is full-bridge inverter+SPWM/SVPWM modulation, the higher the modulation frequency (20~50kHz for high-frequency machines), the smaller the ripple and distortion of the output voltage with LC filter circuit, and whether there are dead-time compensation and harmonic compensation algorithms;
Grounding and shielding design: whether there are independent grounding copper bars in the machine, whether there are metal shielding covers for high-frequency components (such as capacitors and inductors), and whether the chassis is all-metal sealed structure (reducing electromagnetic radiation and improving its anti-radio interference ability);
Component selection: whether to use industrial/vehicle code-grade components (such as capacitors made in Japan/Taiwan, inductors shielded, and chips with high anti-interference level) instead of civilian-grade components, the temperature resistance, voltage resistance and anti-interference characteristics of components directly determine the actual anti-interference ability of UPS.
Fourth, do field/laboratory measurement: the most accurate practical ability verification
If there are high requirements for UPS anti-interference ability (such as precision instruments, military industry and communication room), it needs to be verified by measured data, which is divided into laboratory professional test and simple field test, covering EMS anti-interference test and output purity test:
(a) laboratory professional testing (according to IEC 61000/GB/T 17626 standard)
Entrust a third-party laboratory to do eight EMS tests, focusing on verifying the core anti-interference items. During the test, UPS should continue to work normally, and the output should be uninterrupted and out of tolerance:
Electrostatic discharge (ESD): contact discharge is ±8kV, air discharge is ±15kV (industrial grade), the UPS shell, operation panel and terminal are tested, and there is no crash or output fluctuation;
Electrical fast transient (EFT): the power line is ±4kV, the signal line is ±2kV, the input and output lines are tested, the UPS is not reset, and the output voltage is stable;
