Power factor decomposition of apcups power supply

For a long time, both apcups suppliers and users have been discussing a focus issue in the issue of UPS power factor: users claim to want high power factor UPS, and suppliers also say that the greater the value, the better. Therefore, manufacturers try their best to improve this parameter. Is the power factor of UPS better or smaller?

Apcups power supply has two power factor values: input power factor and output power factor. The input power factor represents the absorption capacity of ups to the active power of the grid and its influence on the power grid; the output power factor represents the adaptability of apcups to nonlinear load. Of course, the higher the input power factor is, the better, while the output power factor of UPS is not necessarily the better.

Let's look at a few concepts first

Apparent power (s): the product of AC voltage and AC current. Its unit is volt ampere, and the nominal capacity of apcups power supply is its apparent power, that is, the product of rated output voltage and rated output current. S = u × I

Apparent power includes two parts: output active power (P) and reactive power (q).

Active power (P): refers to the part of work directly done, in watt (W). For example, make the light on, make the motor run, etc. Because this power becomes heat after doing work, which is converted into heat energy, light energy, mechanical energy and so on, which can be clearly perceived. The relationship between active power and apparent power is: P = s × cos φ = u × I × cos φ

Cos φ is the power factor and angle φ is the phase difference of voltage and current under nonlinear load. Power factor represents the ability of ups to output active power.

Reactive power (q): refers to the part of power stored in the circuit but not directly done work, unit: var. The numerical value is expressed by the formula: q = s × sin φ = u × I × sin φ

Although reactive power is not converted into other forms of energy, it is impossible to work without reactive power for nonlinear loads such as computers.

Most people think that since reactive power does not work, it can of course not. Therefore, it is considered that the power supply with power factor of 1 is the best and can output the maximum power. However, this is not the case.

First of all, in terms of load.

For example, the computer, when the power input, to carry out rectification processing, if you remove the capacitance C at the output end, the output voltage of the rectifier bridge is directly output to the computer, then the power factor of the computer is close to 1, but the output DC voltage is fluctuating wave, which is up and down. Obviously, such voltage can not make the computer work normally, such high power What is the use of the rate factor? In order to make the computer work normally, a large capacitor is added at the output end of the rectifier bridge to filter, so as to input smooth DC voltage uo to the computer. The capacitor filter is like a reservoir. It must store enough electric charge. When the output voltage of the rectifier bridge is low, the charge should be supplemented; when the output voltage of the rectifier bridge is high, the charge should be stored to ensure that the voltage of UO will not have significant fluctuation To output smooth DC voltage. This part of the energy stored in the capacitor is actually reactive power. Some smoothing filter circuits are composed of inductors or capacitors and inductors, but no matter which, the principle is the same. But in the circuit, as long as there is capacitance or inductance, the power factor will not be 1. Therefore, nonlinear loads such as computers need not only active power, but also reactive power to work normally.

Then from the power supply equipment ups.

Apcups power supply is mostly used for computer or other non-linear load such as computer, and seldom used for linear load such as lighting or electric heater. This kind of nonlinear equipment is usually rectified and filtered after directly inputting the mains power. The power factor of these equipments is 0.6 ~ 0.7. According to the basic principle of the circuit, when the load impedance is equal to the power source impedance, the power supply has the highest utilization rate and works in the best state. At this time, the power supply and the load can be matched. In order to match ups with these devices, it is better to have similar or even equal power factor values. Such as the world-famous UPS brand, apcups power supply in the United States has such an output power factor.

Now assume that the output power factor of apcups power supply is 1, then the reactive power is 0. For nonlinear loads such as computers, it is obviously impossible to apply. Such power supply can only carry linear load. At this time, if the current slightly changes, the output voltage will increase dozens of volts, and the overload capacity is very poor. In this case, the power supply can not work at all. In real life, UPS is rarely used for pure linear load.

In fact, there is a corresponding relationship between the output characteristics of the inverter of apcups power supply and the power factor of the load. When the power factor is 1, the apcups power supply can only output 80% of the rated capacity. With the decrease of the power factor, the output energy of ups will correspondingly increase. When the power factor is 0.8, it can output 100% of the rated capacity. That is to say, the smaller the load power factor, the greater the output VA power value. In other words, the stronger the ability to deal with nonlinear load, and the computer is exactly the typical nonlinear load. If the output power factor of UPS computer system is closer, the best matching will be formed. At this time, the active power is fully used and the reactive power is just used