Series parallel resonance problems? What is the difference and characteristics of series resonance a

In this circuit, it is impossible to have parallel resonance and series resonance at the same time;

1) If there is parallel resonance, then at most there is only one pure resistor left at the AB end, then it cannot form a series resonance with C1;

2) When parallel resonance occurs, the C1 capacitive reactance at this frequency must be very small, so that the excitation source can maintain parallel resonance;

Then, when the resonant frequency is shifted to a low level, the parallel circuit of L and C2 will show inductance, so that it will form a series resonance with C1;

Frequency starts from zero, start:

C1 open, L short. C2 is short-circuited and does not work.

The frequency is slowly increasing:

C1 capacitive.

l Inductive resistance. Gradually, it manifests itself.

At lower frequencies, the L-inductive reactance is small, while the C2 capacitive reactance is large.

So, l, c2 are connected in parallel, totalImpedanceIt's inductance.

So, they are connected in parallel, which is equivalent to an inductor.

The frequency continues to increase slowly:

The capacitive resistance of C1 slowly decreases.

l The inductive reactance presented in parallel with C2 gradually increases.

When the two are equal, it happensSeries resonance

The frequency continues to increase slowly:

The capacitive reactance of C1 continues to decrease.

However, C1 is connected in series, and the smaller the impedance, it can be ignored and considered a short circuit.

l In parallel with C2, it cannot be ignored.

theirsReactance, when equal, parallel resonance occurs with a total reactance ofInfinity

Therefore, the series resonance occurs first, and the entire circuit is equivalent to a short circuit.

After parallel resonance occurs, the entire circuit, which is equivalent to an open circuit.

Don't forget.

At low frequency, the capacitive reactance (electric acceptance) of C2 is significantly greater than (less than) the inductive reactance (electric acceptance) of L, and the inductive reactance of L and C2 in parallel is inductive, and it will resonate in series with C1, and continue to increase the frequency, and the capacitive reactance of C2 and the inductive reactance of L are equal, and parallel resonance occurs. Shari Potter's analysis is good and points out my mistakes, which I hereby explain.

Series resonance: A circuit property.

The variable frequency series resonance test device, also known as series resonance, is composed of a variable frequency power supply, an excitation transformer, a reactor and a capacitance voltage divider. The capacitor of the tested product and the reactor form a series resonant connection mode; The voltage divider is connected in parallel on the test piece, which is used to measure the resonant voltage on the test product and is used as an overvoltage protection signal; The frequency modulation power output is coupled to the series resonant circuit through the excitation transformer to provide the excitation power of series resonance.

In a circuit where the inductor and capacitor are connected in parallel, when the size of the capacitor is exactly the same phase as the voltage and current in the circuit, that is, all the power supply energy is consumed by resistance and becomes a resistance circuit, it is called parallel resonance. Parallel resonance is a complete compensation, and the power supply does not need to provide reactive power, only the active power required by the resistor.

At resonance, the total current of the circuit is the smallest, while the current of the branch is often greater than the total current of the circuit, therefore, parallel resonance is also known as current resonance. When parallel resonance occurs, a large current flows through the inductor and capacitive elements, which can cause the fuse of the circuit to blow or burn the electrical equipment. However, it is often used in radio engineering to select signals and eliminate interference.

In the resistor, capacitance and inductance series circuit, the phenomenon of power supply, voltage and current in phase is called series resonance, which is characterized by: the circuit is pure resistivity, the power supply, voltage and current are in phase, the reactance x is equal to 0, and the impedance z is equal to the resistance r. The resonant voltage is superimposed with the original voltage, and the parallel resonance:

In the resistor, capacitance, inductor parallel circuit, the phenomenon that the voltage and total current at the end of the circuit are in phase is called parallel resonance, which is characterized by: parallel resonance is a complete compensation, the power supply does not need to provide reactive power, only provides the active power required by the resistor, when resonating, the total current of the circuit is the smallest, and the branch current is often greater than the total current in the circuit, therefore, parallel resonance is also called current resonance.

In a series circuit of resistance, inductance and capacitance, the terminal voltage of the circuit and the total current of the circuit are in phase, which is called series resonance. The characteristics of series resonance are: the circuit is pure resistive, the terminal voltage and the total current are in phase, the impedance is the smallest, the current is the largest, and the inductance and capacitance may produce a high voltage many times greater than the power supply voltage, so series resonance is also called voltage resonance.

In power engineering, due to the series resonance, there will be overvoltage and high current, which will damage the electrical equipment, so it is necessary to avoid series resonance. In a circuit where an inductance coil and a capacitor are connected in parallel, the terminal voltage of the parallel circuit and the total current of the circuit are in phase, which is called parallel resonance. The total impedance of the parallel resonant circuit is the largest, so the total current of the circuit becomes the smallest, but for each branch, its current may be much larger than the total current, so current resonance is also called current resonance.

Parallel resonance does not produce resonant overvoltages that endanger the safety of the equipment, but each branch generates an overcurrent.

Series resonance and parallel resonance are both circuit properties, and the main differences are as follows:

First, the voltage that needs to be borne is different

The thyristor of the series inverter needs to withstand a low voltage, and when the power supply is supplied by a 380V grid, a 1200V thyristor is sufficient, but the entire current of the load circuit, including the active and reactive components, needs to flow through the thyristor. The loss of pulse of the inverter thyristor will only stop the oscillation and will not cause the inverter to subvert.

The voltage required by the thyristor of the parallel inverter is high, and its value increases rapidly as the power factor angle increases. However, the load itself constitutes an oscillating current loop, and only the active current flows through the inverter thyristor, and when the inverter thyristor occasionally loses the trigger pulse, it can still maintain oscillation, and the work is relatively stable.

Second, the working frequency is different

The working frequency of the series inverter must be lower than the natural oscillation frequency of the load circuit, that is, a suitable t time should be ensured, otherwise the commutation will fail due to the straight through of the upper and lower side arms of the inverter.

The operating frequency of the parallel inverter must be slightly higher than the natural oscillation frequency of the load circuit to ensure that there is a suitable backvoltage time t, otherwise it will lead to the failure of the transmutation between the thyristors; However, if it is too high, the reverse voltage of the thyristor during commutation will be too high, which is not allowed.

Third, the input and output are different

The input voltage of the series inverter is constant, the output voltage is a rectangular wave, the output current is similar to a sine wave, and the commutation is carried out after the current on the thyristor crosses zero, so the current is always ahead of the voltage corner.

The input current of the parallel inverter is constant, the output voltage is similar to a sine wave, the output current is a rectangular wave, the commutation is carried out before the voltage crosses zero on the resonant capacitor, and the load current is always ahead of the voltage corner. This means that both operate under capacitive load.

1. The impedance is different. Parallel resonance has a maximum impedance. Series resonance has a minimum impedance.

2. The voltage and current are different. Parallel resonance has the highest voltage for the current source. Series resonance has a maximum current for a voltage source.

3. The current and voltage of capacitors and inductors are different. Parallel resonant inductor capacitors have a maximum current (QLI). The series resonant capacitor has the highest voltage qvi) on the inductor