1. Series resonance refers to a circuit where LC circuits are connected in series, and the sum of their impedances is exactly zero. Therefore, the entire circuit is purely resistive, with minimum impedance and maximum current. This can cause overvoltage in power systems, hence it is also called voltage resonance.
2. Parallel resonance refers to a circuit where LC circuits are connected in parallel, and their impedances are equal. Therefore, at resonance, the impedance of the LC circuit is infinite, and a voltage is directly applied across it, resulting in a large current. This is also called current resonance.
In an AC circuit with resistors R, inductors L, and capacitors C, the voltage across the circuit and the current are generally in different phases. If we adjust the parameters of the circuit components (L or C) or the power supply frequency, we can make them in the same phase, and the entire circuit becomes purely resistive. This state is called resonance. In the resonant state, the total impedance of the circuit reaches or nearly reaches its extreme value. The purpose of studying resonance is to understand this objective phenomenon and fully utilize its characteristics in science and applied technology, while also preventing its harmful effects. Depending on the circuit connection, there are two types: series resonance and parallel resonance. In a series circuit composed of a resistor, inductor, and capacitor, when the capacitive reactance XC equals 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 behavior. This phenomenon is called series resonance (also known as voltage resonance). When series resonance occurs, the circuit impedance Z = √(R² + XC - XL²) = R, the total impedance in the circuit is at its minimum, and the current reaches its maximum value. A variable frequency series resonance test device is also called a series resonance test. Principle: Utilizing the principle of series resonance, an excitation transformer is used to excite the series resonant circuit. The output frequency of the variable frequency controller is adjusted to make the circuit inductance L and the test object C resonate in series. The resonant voltage is the voltage applied to the test object.
