Single-phase full-wave controllable rectifier circuit Single-phase bridge half-controlled rectifier circuit

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Single-phase full-wave controllable rectifier circuit, single-phase bridge half-controlled rectifier circuit

1. Single-phase full-wave controllable rectifier circuit

Single Phase Full Wave Controlled Rectifier, also known as single-phase dual half-wave controlled rectifier circuit.

Figure 1 Single-phase full-wave controllable rectifier circuit and waveform

Single-phase full-wave and single-phase fully controlled bridges are basically the same when viewed from the DC output end or the AC input end. Transformers do not have problems with DC magnetization. The difference between single-phase full-wave and single-phase fully-controlled bridges is that the transformer structure in single-phase full-wave is more complex and consumes more materials. The single-phase full-wave circuit uses only 2 thyristors, which is 2 fewer than the single-phase fully controlled bridge. Correspondingly, the gate drive circuit also has 2 fewer gate drive circuits; however, the maximum voltage that the thyristors can withstand is twice that of the single-phase fully controlled bridge. The single-phase full-wave conductive circuit contains only one thyristor, which is one less than the single-phase bridge, so the tube voltage drop is also one less. Therefore, the single-phase full-wave circuit is beneficial to applications in low output voltage situations 1. Circuit structure

In a single-phase fully controlled bridge, there are two thyristors in each conductive loop, and one thyristor can be replaced by a diode, thereby simplifying the entire circuit. This becomes a single-phase bridge half-controlled rectifier circuit (VDR is not considered for now). The circuit diagram of a single-phase fully controlled bridge rectifier circuit with a resistive load is shown in 2. Four inter-transistor transistors form a rectifier bridge, in which vTl and vT4 form a pair of bridge arms, vT 2 and vT3 form another pair of bridge arms, vTl The two thyristors vT3 and VT3 are connected to a common cathode, the two thyristors VT2 and VT 4 are connected to a common anode, the secondary voltage ratio of the transformer is connected to points a and b, u2=1.414U2sin(wt) 2. Semi-controlled resistive load The circuit operates the same as the fully controlled circuit with a resistive load. The working process is as follows: a) During the positive half cycle of u2, u2 supplies power to the load via VT1 and VD4. b) When u2 crosses zero and becomes negative, the current no longer flows through the secondary winding of the transformer due to the inductance, but continues to flow through VT1 and VD2. c) VT3 is triggered at the negative half-cycle firing angle a of u2, VT3 is turned on, and u2 supplies power to the load via VT3 and VD2. d) When u2 crosses zero and becomes positive, VD4 is turned on and VD2 is turned off. VT3 and VD4 continue to flow, and ud is zero again. 3. The function of freewheeling diode 1) To avoid possible out-of-control phenomena. 2) If there is no freewheeling diode, when a suddenly increases to 180 or the trigger pulse is lost, it will happen that one thyristor continues to conduct and the two diodes conduct in turn, which makes ud a sinusoidal half wave, and its average value Remaining constant is called out of control. 3) When there is a freewheeling diode VDR, the freewheeling process is completed by the VDR to avoid out-of-control phenomena. 4) During the freewheeling period, there is only one tube voltage drop in the conductive circuit, which is beneficial to reducing losses. 4. Another connection method of single-phase bridge half-controlled rectifier circuit

Figure 2. Single-phase bridge semi-controlled rectifier circuit with freewheeling diode and resistive-inductive load circuit and waveform

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Figure 4. Circuit and waveform of single-phase fully controlled bridge with resistive load. Figure 5. Another connection method of single-phase bridge half-controlled rectifier circuit is equivalent to replacing VT3 and VT4 in the above figure with diodes VD3 and VD4. This can save the freewheeling diode VDR, and the freewheeling diode is realized by VD3 and VD4. 2. Resistive-inductive load (assuming WL>R) 1. Circuit structure The single-phase fully controlled bridge circuit with resistive-inductive load is shown in Figure 3-7(a). Due to the induced potential of the inductor, the output voltage waveform appears negative. The output current is nearly straight, and the current in the intertransistor and the secondary side of the transformer is a rectangular wave. Figure 3 Single-phase bridge type fully controlled rectifier circuit [resistive inductive load]

2. Working principle and working waveform

(1) In the interval of u2 positive half wave

When wt=oa: The inter-product tubes vT 1 and vT4 are under positive pressure, but there is no trigger pulse and are in the off state. Assuming that the circuit is working in a stable state, the inductance releases energy in the o-a interval, and the thyristors vT2 and vT4 remain on.

When wt=a and later: trigger the thyristors vTl and vT4 at wt=a to turn on, and the current flows along a—>vT1->L->

The secondary winding a>a of R->VT4-b-Tr flows, and at this time there is output voltage and current on the load. The power supply voltage is applied to the thyristors vT2 and vT3 in reverse direction, causing them to withstand the back pressure and be in the off state.

(2) In the negative half-wave interval of u2'

When wt=180 degrees: the power supply voltage naturally crosses zero, the induced potential causes the thyristors vTl and vT4 to continue to conduct waves, and the inter-transistor vT2 and vT3 bear positive pressure. Because the element triggers the pulse, vTz and v are in the off state. .

At the time of wt=180+a and later: trigger the inter-product tube vT2 and VT3 at wt=180+a to conduct, and the current flows along b—VT3—L—R—VT2—a—Tr The secondary winding a>b flows, and the power supply voltage is applied to the load in the direction of the positive half cycle. There is output voltage and current on the load. At this time, the power supply voltage is reversely added to vTl and vT4, causing it to withstand the back pressure and change is in shutdown state. Thyristors vT2 and VT3 are turned on until the inter-transistors vT1 and vT4 are triggered again at wt=360+a in the next cycle.

3. In order to expand the phase shift range and increase the output voltage, a freewheeling diode can also be installed at both ends of the load.

4. The circuit is shown in Figure 4(a). After connecting the freewheeling diode vD, when the power supply voltage drops to zero, the load current freewheels through the freewheeling diode vD, so that the DC output end of the circuit only has a voltage drop of about 1v, forcing the current of the inter-transistor to be smaller than the sustaining current. And shut down. The operating waveform within one cycle is shown in Figure 4(b).