What is the difference between a series resonant circuit and a parallel resonant circuit

Difference 1: The load resonance mode is different.

The load resonance mode of series resonance and parallel resonance can be divided into two types: series inverter and parallel inverter, the difference between these two types is their technical characteristics** The circuit is different, the series inverter is connected in series with L, R and C, and the parallel inverter is connected in parallel with L, R and C.

These two types of load circuits also exhibit different impedance rates to the power supply. The series inverter has a low impedance, and the parallel inverter has a high impedance. When the series inverter is low impedance, it requires a voltage source to be powered, which results in a large filter capacitor being connected to the rectified and filtered DC power end.

When the inverter fails, the inrush current will increase, resulting in protection difficulties. When the shunt inverter has a high impedance, it is required to be powered by a current source, so it is necessary to connect a large reactor in series at the end of the DC power supply. However, in this way, when the inverter fails, it is easier to protect, because the current is limited by the large reactance, and the impact is not large.

Difference 2: The input mode and power supply mode are different.

The input of the series inverter is constant voltage and constant voltage source power supply, and the input of parallel inverter is constant current and constant current source power supply.

When the input voltage of the series inverter is constant: the output current is close to the sine wave, the output voltage is a rectangular wave, and the current is always one corner ahead of the voltage, because the current on the thyristor crosses zero and then commutation.

When the input current of the parallel inverter is constant, the output current is a rectangular wave, the output voltage is close to the sine wave, and the load current will always be ahead of the voltage corner, because the voltage on the resonant capacitor is commutated before the zero crossing. Both operate under capacitive load.

The series inverter supplies power to Hengyuan. When commutating, it is necessary to ensure that it is turned off first and then turned on to avoid short circuit caused by the power supply due to the on-ion of the thyristor of the upper and lower side arms of the inverter. That is, there needs to be a period of time (t) for all thyristors and other power electronics to remain turned off.

In this case, the induced potential generated from the DC terminal to the lead inductance of the device is collectively referred to as stray inductance, which may damage the device, so it is necessary to select a suitable surge voltage absorption circuit for the device. In order to prevent the thyristor from being affected by the high voltage on the converter capacitor and to ensure the continuity of the load current, fast diodes must be connected in parallel at both ends of the thyristor during the shutdown state.

The parallel inverter supplies power to the constant current. During commutation, the thyristors on and down the inverter must be switched on and off first. That is, it is necessary to ensure that all thyristors are in a conductive state during commutation.

In order to ensure that a large induced potential is generated on the filter reactance LD, the current must be continuous. Since the LD is large enough, even if the inverter arm is straight-through, it will not cause a short circuit in the DC power supply. However, if the commutation time is too long, the efficiency of the system will be reduced, so it is necessary to shorten ty, that is, reduce the lk value.

In series resonant circuits, the impedance of resonance is ideally equal to 0; In parallel resonant circuits, the impedance of the resonant is equal to infinity when ideal.

1.Circuit impedance.

z is smallest, and is a pure resistance, and z = r.

2.The current i in the circuit reaches a maximum value and is the same as the supply voltage.

Series resonance occurs in the circuit.

The current is called the resonant current, which is denoted by io, when the supply voltage is constant:

The current of the RLC series circuit can be judged by whether the current in the series circuit has reached the maximum.

The voltages on are equal in magnitude and in opposite directions, canceling each other out.

Therefore, series resonance is also called voltage resonance, and the equivalent impedance of the inductor and capacitor at the time of resonance is 0, which is equivalent to a short circuit.

4.The voltage on the resistor is equal to the supply voltage, reaching a maximum value.

5.Power. Active power: The power emitted by the power supply and the power consumed by the circuit resistor, and the power is the largest.

Reactive power. In resonance, the circuit does not absorb reactive power from the outside. However, the inductance and capacitance inside the circuit periodically exchange magnetic field energy with electric field energy.

Series resonance means that the sum of the impedances of the two LC series in the loop is just 0, so the whole loop is purely resistive, the impedance of the whole loop is the smallest, and the current will be the largest. The characteristics of series resonance: the circuit impedance is the smallest, Z=R, when the voltage is constant, the current is the maximum, and the voltage at both ends of the capacitor or inductor is Q times of the power supply voltage.

First of all, I despise the upstairs, which is the content of circuit theory, and the university physics does not talk about parallel resonant circuits: when the applied frequency is equal to its resonant frequency, the impedance of the circuit is purely resistive, and there is a maximum value; When it is less than that, it is inductive, and when it is larger, it is not very demanding, but the characteristics are just the opposite of parallel connection.

Series resonance: A circuit property.

The inductive reactance and capacitive reactance in the RLC series circuit have the effect of canceling each other, that is, L-1 C=0, at this time, the reactance in the series circuit is 0, and the current and voltage are in the same phase, which is called series resonance.

The inductive reactance and capacitive reactance in the parallel circuit of the RLC have the effect of canceling each other, that is, 1 L-C=0, the reactance in the parallel circuit is 0, and the current and voltage are in the same phase, which is called parallel resonance.

Differences:1The current rms of series resonance reaches the maximum, and the voltage rms of parallel resonance reaches the maximum, 2High voltages may occur at the L and C ends of the series resonant, and overcurrents can occur at the L and C ends of the parallel resonances.

3.The series resonant reactance voltage is 0, and the parallel resonant reactance current is 0

Parallel resonance: In the resistor, capacitance, inductance parallel circuit, the circuit terminal voltage and total current are in phase phenomenon, called parallel resonance, its characteristics are: parallel resonance is a complete compensation, the power supply does not need to provide reactive power, only provide the active power required by the resistor, resonance, 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.

The characteristics of series resonance are: the circuit is pure resistive, the power supply, voltage and current are in the same phase, the reactance x is equal to 0, and the impedance z is equal to the resistance r.

Series resonance is current resonance, which generally plays the role of current amplification. For example, the old radio amplifies the weak current signal through series resonance. Parallel resonance is the act of voltage amplification.

02 The impedance of the series resonant circuit Z(JW)=R+J(WL-1 WC), when the reactance of the series circuit is zero, the resonance occurs. Series resonance has the function of controlling and adjusting the amplitude of current and voltage during resonance in a circuit.

04 The impedance of the parallel resonant circuit Y(JW)=G+J(WC-1 WL), when the input current I is in phase with the voltage U, the resonance occurs.