Current impact test of film capacitor

With the rapid development of power electronics technology, metallized capacitors are used in a wide range of applications, such as various inverters, UPS and SVG power supplies, solar and wind power generation systems, energy storage in new energy fields such as hybrid and pure electric vehicles. Capacitor and absorption protection capacitors are all made of thin film metallization structure, and high specific energy pulse capacitors are also beginning to develop toward metallization.

Power electronic capacitors are usually used in non-power frequency applications. Their peak current resistance and surge current resistance are key technical parameters. Since current withstand capability is the weakest link of metallized film capacitors, products with this index must have current withstand capability. Test assessment. The high-power electronic switch is used to form the capacitor charging and discharging circuit. By adjusting the charging voltage or the discharge circuit parameters to quantitatively control the discharge current, current decay circumference and current voltage change rate, the test method is quick, simple and practical, and is a design verification of the film capacitor. An effective means of quality control.

The severity of the current impact test is mainly determined by the following parameters:

1. A large discharge current value whose peak size depends on the charging voltage and the impedance of the discharge loop.

2. Current change rate (di/d1) is mainly determined by the inductance L of the discharge circuit. The smaller the inductance L, the higher the current change rate.

3. The decay frequency f of the discharge current depends on the measured capacitance C and the loop inductance L.

4. The number of discharge current cycles is determined by the resistance R of the discharge circuit. Under the same current peak and rate of change, the number of cycles is large and the severity is high.

So we perform current surge tests on these parameters:

1. Set the charging voltage value U, the voltage value determines the peak value of the discharge current, I = U / R.

2. Setting the charging time The charging time is determined according to the capacitor capacity C of the capacitor under test, the internal resistance r of the charging power source, and the required voltage U.

3. The charging switch s is controlled by an adjustable time relay, S is closed, and the adjustable DC power supply E is charged to the test capacitor C.

4. Charging time is up, S is turned on, charging is finished, the control circuit sends a pulse to the thyristor SCR, SCR is turned on. Capacitor C starts to discharge.

5. Due to the resistance and inductance of the discharge loop, the discharge process is oscillating attenuation. After several weeks of oscillating end, the current is zero and the thyristor SCR is turned off. The period of several cycles from the start of oscillation to the end is generally much less than 1 s.

6. After the discharge is completed, the charging switch is closed and charging begins again, and the above test is repeated.