UPS inductance and capacitance calculation

qepdcri

UPS inductance and capacitance calculation [Copy link]

 

If the UPS uses a thyristor rectifier, how should the input inductance of the front end be calculated, and how should the output filter capacitor be calculated? Is there a specific formula and derivation?

led2015

Not necessarily correct, you can refer to:

1. Calculation of front-end input inductance

The main function of the front-end input inductor is to smooth the input current, reduce current harmonics, and improve the efficiency of the power supply. The calculation of the inductor is usually related to the input current, switching frequency, and the expected current ripple. However, since the characteristics of the thyristor rectifier are different from those of the switching power supply, the calculation of its current waveform and ripple is more complicated.

Generally speaking, the calculation of inductance can be based on the following considerations:

1. Determine the average and peak input current : This depends on the UPS power rating and input voltage.
2. Determine current ripple requirements : This is usually based on power supply efficiency and electromagnetic compatibility (EMC) requirements.
3. Selecting the switching frequency : Although the SCR itself does not directly control the switching frequency, the UPS system may contain other switching components whose switching frequency will affect the choice of inductor.

A simplified formula for calculating inductance may be based on the relationship between the rate of change of current and time, that is:

[ L = \frac{V_{in} \cdot \Delta t}{\Delta I} ]

in:

• (L) is the inductance (henry)
• (V_{in}) is the input voltage (volts)
• (\Delta t) is the time (seconds) required for the current to change
• (\Delta I) is the change in current (amperes)

But please note that this formula is a very simplified version and more detailed current waveform analysis and system design are required in actual applications.

2. Calculation of output filter capacitor

The main function of the output filter capacitor is to smooth the output voltage and reduce the voltage ripple. The calculation of the filter capacitor is usually based on the load current, output voltage, and the expected voltage ripple.

A commonly used calculation formula for filter capacitance (for filtering after rectification) is:

[ C = \frac{I_{load} \cdot \Delta t}{\Delta V} ]

But more accurate calculations need to consider the charging and discharging process of the capacitor and the dynamic changes of the load. In a UPS system, since the load may change frequently, the selection of filter capacitors needs to be more cautious.

For more complex systems, specialized power supply design software or simulation tools may be required for accurate calculations and analysis.

qepdcri

Is there a more accurate one? I feel this one is not very accurate. Is there a derivation process?