1. Series resonance refers to an LC series circuit where the sum of the impedances of the inductor and capacitor is exactly zero. Therefore, the entire circuit is purely resistive, the total circuit impedance is minimized, and the current is maximized. This can cause overvoltage in power systems, so it is also called voltage resonance in power systems.
2. Parallel resonance refers to an LC parallel circuit where the impedances of the inductor and capacitor are equal. Therefore, at resonance, the impedance of the LC combination will be infinite, and the voltage will be directly applied across the LC components, resulting in a large current through the LC components. This is also called current resonance.
In an AC circuit containing resistance R, inductance L, and capacitance C, the phase of the voltage across the circuit is generally different from the phase of the current. By adjusting the parameters of the circuit components (L or C) or the power supply frequency, we can make their phases the same, and the entire circuit becomes purely resistive. This state is called resonance. In the resonant state, the total impedance of the circuit reaches or approximately reaches its extreme value. The purpose of studying resonance is to understand this objective phenomenon and to fully utilize its characteristics in science and applied technology, while also preventing the harm it can cause. Depending on the circuit connection, there are two types: series resonance and parallel resonance. In a series circuit composed of resistance, inductance, and capacitance, when the capacitive reactance XC is equal to the inductive reactance XL, i.e., XC = XL, the voltage U and current I in the circuit are in phase, and the circuit exhibits purely resistive characteristics. This phenomenon is called series resonance (also known as voltage resonance). When series resonance occurs, the circuit impedance Z = √R² + (XC - XL)² = R, the total impedance of the circuit is minimized, and the current reaches its maximum value. The variable-frequency series resonance test device is also called series resonance. Principle: Using the principle of series resonance, an excitation transformer is used to excite the series resonant circuit, and the output frequency of the variable-frequency controller is adjusted to make the circuit inductance L and the test sample C resonate in series. The resonant voltage is the voltage applied to the test sample.
