There are two parts to measure the performance of UPS: one part is the adaptability to the utility grid and load; the other part is the technical performance of the UPS. These performances include:
②Input index 2 Input voltage, current and frequency range, phase number
③Input power factor, input current harmonics)
① Output voltage, output frequency, output voltage stability
③Load power factor
④Current crest factor
⑤Dynamic voltage transient range
⑥ Transient response time
⑦ Load imbalance
⑩Bypass switch switching time
The above technical indicators are clearly stipulated in the standard.
①Capacity: The primary indicator of UPS, which can be divided into input capacity and output capacity. The capacity given in general indicators refers to output capacity, which is the product of output voltage and output current rating. The unit of capacity is generally volt-ampere ( V·A) indicates that this is because the load nature of the UPS varies from device to device, so it has to be expressed by apparent power. One thing to note here is that in order to make the UPS work more reliable, it is best not to use the full capacity , To leave a certain margin.
②Input voltage range: The input voltage can indicate what kind of power supply system the UPS adapts to, and should indicate whether the input AC voltage is single-phase or three-phase, and whether the value of the input voltage is 220 V, 110 V or 380 V, etc. The input voltage range refers to how much the UPS adapts to changes in the mains voltage. For example, if it is marked with ±15%, it means that there is a range of +15% to -15% on the basis of the rated voltage.
③Input frequency: It is used to indicate the frequency of the input AC power supply and the allowable variation range, such as 50 Hz ± 2.5 Hz.
④Input current: refers to the effective value of AC phase current (single-phase) or line current (three-phase) when UPS guarantees the rated output power and battery charging power, that is, the rated input current. The value given by the input current can be It is easy to calculate the wire diameter and equipment capacity of the AC input distribution line.
⑤ Output voltage: such as 220 V, 380 V, etc., and some also give the number of output phases at the same time. Users can choose UPS according to the voltage level and power supply system required by their own equipment
⑥ Output frequency: If the frequency of the mains power grid is 50 Hz, the user must pay attention to its output frequency is compatible with the frequency of the mains power grid when choosing a UPS. The online UPS is in a synchronization lock state, and its output frequency drift can reach: ±2Hz; and When the mains fails and the output frequency is determined by the internal vibration, the general drift is ±(0.5~1)Hz.
⑦Output voltage waveform: When purchasing UPS, you can choose UPS according to your own use, not necessarily non-sine wave output products, such as the computer host square wave, trapezoidal wave and sine wave, but square wave UPS The circuit is simple and low in price. When marking the output voltage waveform, it is generally necessary to indicate the range of total harmonic distortion. For example, if THDi<3% is indicated, it means that the total wave distortion is less than <3%.
⑧Power factor: For nonlinear circuits, although the input voltage is a sine wave, the current may be a non-sine wave, so the distortion of the current must be considered for the nonlinear circuit.
In the formula, PF (PowerFasto) is the power factor: P is the active power: S is the apparent power.
In a nonlinear circuit, the ratio of the effective value of the fundamental current to the effective value of the non-sinusoidal current is defined as the distortion factor, that is, the current distortion factor Kd (distortion) is
In the formula, I1, I2,…, In are the effective values of 1.2, .., n-th spectral wave currents respectively. If it is assumed that the phase difference between the fundamental current and voltage is φ, the power factor PF can be expressed as
In other words, the power factor of a nonlinear circuit is the product of the distortion factor and the displacement factor (cosφ).
The power factor of UPS is divided into input power factor and rated load power factor. The input power factor refers to the ratio of the active power that the UPS requires from the grid and the apparent power that the grid provides to the UPS when the inverter (online) of the UPS is working instead of the bypass. It can reflect the effective utilization of the grid energy by the UPS At the same time, it also implies the pollution degree of UPS to the power grid. Obviously, the higher the input power factor of the UPS, the better.
The rated load power factor of the UPS means that when the UPS is used as an AC power source, the ratio of the reactive power required by the connected load from the UPS to the UPS output volt-ampere must meet the index requirements, otherwise it will cause the voltage of the UPS without an output transformer to rise. In severe cases, the UPS can be burned. In addition, the low rated load power factor means that the load requires a large proportion of reactive power from the UPS, and the UPS must be derated for use.
Generally, UPSs with several kilovolt-amperes require a rated load power factor greater than 0.8. Of course, the larger the value, the better. The higher the rated load power factor, the higher the utilization rate of the UPS. Too low rated load power factor is extremely detrimental to the use of UPS. But generally the rated load power factor is fixed, which requires UPS designers to design a UPS with a high rated load power factor.
⑨Overload capacity: UPS overload capacity refers to the amount of UPS output exceeding the rated output and the time it can be maintained. For example, the Merlin Gerin Maxipae3.5kV·A UPS can be overloaded by 20% and its duration is 10min.
⑩Static stability of output voltage: It is a commonly used index in stable power supply, but it is a vague concept. Therefore, when various manufacturers use this index, its meaning is not completely the same. The so-called concept ambiguity firstly refers to the phenomenon that the greater the stable value, the worse the stability according to the definition of the voltage stability concept itself. Secondly, it is not clear whether the voltage stability focuses on the power grid characteristics or the load regulation rate. But most think it is a voltage stability index focusing on load regulation, that is, the relative change in output voltage when the load current changes from 100% of the rated value to 0 under any input voltage within the rated input voltage range.
⑪Dynamic stability of output voltage: The dynamic stability of output voltage refers to the instantaneous maximum relative change of output voltage when the load current makes a 100% step.
⑫Efficiency: The efficiency of AC output stable power supply is defined as
Efficiency = (output active power/source active power) × 100%
If the UPS efficiency is not high, it means that the UPS generates a large amount of heat, which will waste electrical energy and cause excessive electricity bills. On the other hand, it will also cause the ambient temperature to rise, and cooling equipment has to be configured. When the UPS itself heats up severely, it will also cause accelerated aging of the components used, shorten the life span, and increase the failure rate.
In addition to the above performance indicators, some manufacturers also provide data or instructions on noise, whether there is a communication interface, whether there is a three-remote function, whether it can be paralleled, and the mean time between failures.