CN111865076A - DC step-down circuit applied to power supply of relay protection devices in substations - Google Patents

Abstract

The invention provides a DC step-down circuit applied to the power supply of a relay protection device in a substation, comprising a three-coil coupled inductor, a capacitor, two power switch tubes, a diode and a load resistor; a power switch tube and the three The coil coupling inductor, the load resistor, and the power supply are connected in series, and the other power switch tube and the capacitor are connected in series with the diode and the load resistor in parallel. The invention has simple circuit structure, many degrees of freedom of conversion gain and wide range, and can flexibly convert 220V DC voltage into 48V, 24V, 12V, 5V and other voltage values required by the relay protection device, and realize flexible application of the power converter.

Description

DC step-down circuit applied to power supply of relay protection devices in substations

technical field

The invention provides a direct current step-down circuit applied to the energy supply of a relay protection device in a substation, and belongs to the technical field of power electronic converters.

Background technique

The secondary protection device inside the substation is very important for the reliable operation of the primary power equipment, which reduces the failure rate of the primary equipment and reduces the damage degree of the primary equipment. The power supply of the relay protection device in the station is DC voltage 48V, 24V, 12V and 5V, which are all converted from 220V DC voltage. The existing step-down technology has a narrow gain conversion range and few degrees of freedom, and cannot realize the modular application of the power supply of all relay protection devices in the station. Therefore, how to seek a wide-range, high-degree-of-freedom DC step-down replacement module technology has become a research topic. hot spot.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a DC step-down circuit applied to the power supply of the relay protection device in the substation to solve the above problems.

The DC step-down circuit applied to the power supply of the relay protection device in the substation according to the present invention comprises a three-coil coupled inductor, a capacitor, two power switch tubes, a diode and a load resistor; a power switch tube is connected to all The three-coil coupled inductor, load resistor, and power supply are connected in series, and another power switch tube and capacitor are connected in series with the diode and the load resistor in parallel.

Preferably, it includes a first coupled inductor N1, a second coupled inductor N2, a third coupled inductor NA, a diode DM1, a second power switch M2, a third power switch MA, a clamping capacitor CA and an output load R; wherein, The drain of the second power switch M2 is connected to the positive pole of the power supply Vin, the source of the second power switch M2 is connected to one end of the second coupling inductor N2, the other end of the second coupling inductor N2 is connected to one end of the third coupling inductor NA, and the clamping capacitor CA One end is connected, the other end of the third coupling inductor NA is connected to one end of the first coupling inductor N1, the anode of the diode DM1 is connected, the other end of the first coupling inductor N1 is connected to one end of the load R, and the drain of the third power switch tube MA is connected to the other end of the clamping capacitor CA. One end is connected, and the source of the third power switch tube MA is connected to the negative electrode of the power supply Vin, the cathode of the diode DM1, and the other end of the load R.

Preferably, the gain expression is:

Among them, D is the on-duty ratio of the power switch tube, N=N2/N1, NA=NA/N1.

The working process of the DC step-down circuit is divided into seven switch modes, which are switch mode 1 to switch mode 7 respectively.

Preferably, in switching mode 1, the second power switch tube M2 is turned on, and the excitation inductor LM is charged linearly.

Preferably, in switching mode 2, due to the existence of the leakage inductance LKi, the third power switch MA is turned on at zero current, the diode DM1 is turned on, the leakage inductance LKA and the clamp capacitor CA resonate, and the current IA decreases; the leakage inductance LK2 and the clamp The resonance of the bit capacitor CA causes the current I2 to rise; at the same time, the voltage VL applies a voltage to the leakage inductance LK1 and the second coupled inductor N2 through the diode DM1, and the current I1 falls slower than the current IA; when the leakage inductance LKA and the leakage inductance LK1 currents are equal , Mode 2 ends.

Preferably, when the switching mode 3 starts, the diode DM1 is turned off at zero current; LK1 and LKA transmit energy to the coil 1, the leakage inductance LK2 and the clamping capacitor CA resonate, the current flowing into the low-voltage side rises, and the third power switch tube MA The current drops; when the current of the third power switch tube MA is zero, mode 3 ends.

Preferably, in switching mode 4, when the current of the third power switch tube MA is zero and the current IM2 decreases, the current IMA reverses through the diode DMA; the resonance continues, the current flows through the diode DM2 and the diode DMA, and the second power switch tube M2 and The third power switch tube MA and the phase-shifted full bridge ZVZCS are turned off; when DM2 is turned off at time t4, the resonance ends when ZCS is turned off.

Preferably, in switching mode 5, when the diode DM2 is turned off, the diode DM1 is turned on, and the leakage inductance LK1 transfers energy to the coil 2; the leakage inductance LKA and the clamping capacitor CA resonate, the current IDMA decreases, and at the same time, the current IDM1 increases. When the current ILM is current, the current IDMA is zero, and mode 5 ends.

Preferably, the switching mode 6 mode starts, the diode DMA zero-current switch is turned off, and the excitation inductor LM is linearly charged by the load.

Preferably, when the second power switch M2 is turned on due to the zero-current switch of the leakage inductance LK2, the switching mode 7 starts; when the current IDM1 decreases, the current ILK2 and the current ILKA rise linearly; when the current IDM1 is zero, all the The leakage inductance current reaches the current ILM/(N+1), and at the end of the mode, the diode DM1 zero-current switch is turned off.

Compared with the prior art, the beneficial effects of the present invention are:

Compared with the prior art, the present invention has the advantages of simple circuit structure, many degrees of freedom of conversion gain and wide range, and can flexibly convert 220V DC voltage into voltage values such as 48V, 24V, 12V, and 5V required by the relay protection device, and realize power supply. Converter flexible application.

Description of drawings

Figure 1 shows a DC step-down technology applied to the power supply of the relay protection device in the substation;

Fig. 2 is a modal diagram of a DC step-down technology applied to the energy supply of the relay protection device in the substation;

FIG. 3 is an equivalent circuit diagram of switching mode 1 of a DC step-down technology applied to power supply of relay protection devices in substations;

FIG. 4 is an equivalent circuit diagram of switching mode 2 of a DC step-down technology applied to power supply of relay protection devices in substations;

FIG. 5 is an equivalent circuit diagram of switching mode 3 of a DC step-down technology applied to power supply of relay protection devices in substations;

FIG. 6 is an equivalent circuit diagram of switching mode 4 of a DC step-down technology applied to the power supply of the relay protection device in the substation;

FIG. 7 is an equivalent circuit diagram of switching mode 5 of a DC step-down technology applied to the power supply of the relay protection device in the substation;

FIG. 8 is an equivalent circuit diagram of switching mode 6 of a DC step-down technology applied to power supply of relay protection devices in substations;

FIG. 9 is an equivalent circuit diagram of switching mode 7 of a DC step-down technology applied to power supply of relay protection devices in substations;

Detailed ways

Example 1

As shown in the figure, the present invention is further described below with reference to the accompanying drawings: a DC step-down circuit applied to the power supply of the relay protection device in the substation according to the present invention includes a three-coil coupled inductor, a capacitor, two power A switch tube, a diode and a load resistor; a power switch tube is connected in series with the three-coil coupling inductor, load resistor and power supply, and the other power switch tube is connected in series with the capacitor and the diode and the load resistor in parallel.

Specifically, it includes a first coupled inductor N1, a second coupled inductor N2, a third coupled inductor NA, a diode DM1, a second power switch M2, a third power switch MA, a clamping capacitor CA and an output load R; wherein, The drain of the second power switch M2 is connected to the positive pole of the power supply Vin, the source of the second power switch M2 is connected to one end of the second coupling inductor N2, the other end of the second coupling inductor N2 is connected to one end of the third coupling inductor NA, and the clamping capacitor CA One end is connected, the other end of the third coupling inductor NA is connected to one end of the first coupling inductor N1, the anode of the diode DM1 is connected, the other end of the first coupling inductor N1 is connected to one end of the load R, and the drain of the third power switch tube MA is connected to the other end of the clamping capacitor CA. One end is connected, and the source of the third power switch tube MA is connected to the negative electrode of the power supply Vin, the cathode of the diode DM1, and the other end of the load R.

Among them, Vin is the input power supply, the first coupled inductor N1, the second coupled inductor N2, the third coupled inductor NA, the diode DM1, the second power switch M2, the third power switch MA, the clamping capacitor CA and the output load R , LM and LKi are the excitation inductance and equivalent leakage inductance of the coupled inductor.

The working process is divided into 7 switching modes, namely switching mode 1 to switching mode 7, the specific description is as follows:

Switching mode 1 corresponds to [t0, t1] in Figure 2: the equivalent circuit is shown in Figure 3, M2 is turned on, and the excitation inductor is charged linearly.

Switching mode 2, corresponding to [t1, t2] in Figure 2: the equivalent circuit is shown in Figure 4, at t1, due to the existence of leakage inductance, MA zero current conducts, DM1 conducts, LKA and CA resonate, The current IA drops. Additionally, LK2 and CA resonate causing I2 to rise. At the same time, VL applies voltage to LK1 and N2 through DM1, and the falling speed of I1 is slower than that of IA. Mode 2 ends when the LKA and LK1 currents are equal.

Switching mode 3, corresponding to [t2, t3] in Figure 2: The equivalent circuit is shown in Figure 5. At the beginning of the mode, DM1 is turned off at zero current. LK1 and LKA phase coil 1 transmit energy, LK2 and CA resonate, the current flowing into the low-voltage side increases, and the MA current decreases. Mode 3 ends when the MA current is zero.

Switching mode 4, corresponding to [t3, t4] in Figure 2: the equivalent circuit is shown in Figure 6, at time t3, the MA current is zero, and when IM2 drops, IMA reverses through DMA. The resonance continues, current flows through DM2 and DMA, and M2 and MA ZVZCS is turned off. The resonance ends when DM2 turns off ZCS at time t4.

Switching mode 5, corresponding to [t4, t5] in Figure 2: the equivalent circuit is shown in Figure 7, at time t5, DM2 is turned off, DM1 is turned on, and LK1 transfers energy to coil 2. LKA and CA resonate, IDMA falls, and at the same time, IDM1 rises, when ILM is reached, IDMA is zero, and mode 5 ends.

Switching mode 6, corresponding to [t5, t6] in Figure 2: The equivalent circuit is shown in Figure 8, the mode starts, the DMA ZCS is turned off, and the LM is charged linearly by the load.

Switch mode 7, corresponding to [t6, t7] in Figure 2: the equivalent circuit is shown in Figure 9, when M2 is turned on because of LK2 ZCS, this mode starts. When IDM1 falls, ILK2 and ILKA rise linearly. When IDM1 is zero, all leakage inductance currents reach ILM/(N+1). At the end of the mode, DM1 ZCS turns off.

From the above analysis, the gain expression can be obtained as:

Among them, D is the conduction duty ratio of the power switch tube N=N2/N1, NA=NA/N1.

Claims (10)

1. A direct current voltage reduction circuit applied to the energy supply of a relay protection device of a transformer substation is characterized by comprising a three-coil coupling inductor, a capacitor, two power switch tubes, a diode and a load resistor; one power switch tube is connected with the three-coil coupling inductor, the load resistor and the power supply in series, and the other power switch tube is connected with the capacitor in series and then connected with the diode and the load resistor in parallel.

2. The direct-current voltage reduction circuit applied to the power supply of the substation relay protection device is characterized by comprising a first coupling inductor N1, a second coupling inductor N2, a third coupling inductor NA, a diode DM1, a second power switch tube M2, a third power switch tube MA, a clamping capacitor CA and an output load R; the drain of the second power switch tube M2 is connected with the positive electrode of the power source Vin, the source of the second power switch tube M2 is connected with one end of a second coupling inductor N2, the other end of the second coupling inductor N2 is connected with one end of a third coupling inductor NA and one end of a clamping capacitor CA, the other end of the third coupling inductor NA is connected with one end of a first coupling inductor N1 and the anode of a diode DM1, the other end of the first coupling inductor N1 is connected with one end of a load R, the drain of the third power switch tube MA is connected with the other end of the clamping capacitor CA, and the source of the third power switch tube MA is connected with the negative electrode of the power source Vin, the cathode of the diode DM1 and the.

3. The direct-current voltage reduction circuit applied to the power supply of the relay protection device of the substation according to claim 1, wherein the gain expression is as follows:

d is the conduction duty ratio of the power switch tube, N is N2/N1, and NA is NA/N1.

The working process of the direct current voltage reduction circuit is divided into 7 switching modes, namely a switching mode 1 to a switching mode 7.

4. The direct-current voltage reduction circuit applied to power supply of the substation relay protection device according to claim 1, wherein the second power switch tube M2 is turned on in switching mode 1, and the excitation inductor LM is charged linearly.

5. The direct-current voltage reduction circuit applied to the power supply of the substation relay protection device is characterized in that in the switching mode 2, due to the existence of the leakage inductance LKi, the third power switch tube MA is conducted at zero current, the diode DM1 is conducted, the leakage inductance LKA and the clamping capacitor CA resonate, and the current IA is reduced; the leakage inductance LK2 and the clamp capacitor CA resonate to cause the current I2 to rise; meanwhile, the voltage VL applies a voltage to the leakage inductance LK1 and the second coupling inductance N2 through the diode DM1, and the current I1 falls at a slower speed than the current IA; mode 2 ends when the leakage inductance LKA and leakage inductance LK1 currents are equal.

6. The direct-current voltage reduction circuit applied to the power supply of the substation relay protection device is characterized in that the switch mode 3 is started in a mode, and the diode DM1 is turned off at zero current; LK1 and LKA transmit energy to the coil 1, leakage inductance LK2 and clamping capacitor CA resonate, current flowing into a low-voltage side rises, and current of a third power switch tube MA falls; when the MA current of the third power switch tube is zero, mode 3 ends.

7. The direct-current voltage reduction circuit applied to the power supply of the substation relay protection device in claim 1, wherein in the switching mode 4, when the MA current of the third power switching tube is zero and the IM2 decreases, the IMA current is reversed through a diode DMA; the resonance continues, the current flows through the diode DM2 and the diode DMA, the second power switch tube M2, the third power switch tube MA and the phase-shifted full bridge ZVZCS are switched off; resonance ends when the ZCS is turned off at time t4 when DM 2.

8. The direct-current voltage reduction circuit applied to the power supply of the substation relay protection device is characterized in that when the diode DM2 is turned off in the switching mode 5, the diode DM1 is turned on, and the leakage inductance LK1 transfers energy to the coil 2; leakage inductance LKA resonates with clamp capacitor CA and current IDMA decreases while current IDM1 increases, and when current ILM is reached, current IDMA is zero and mode 5 ends.

9. The direct-current voltage reduction circuit applied to the power supply of the substation relay protection device is characterized in that the switch mode 6 is started, the diode DMA zero-current switch is turned off, and the excitation inductor LM is linearly charged by a load.

10. The direct-current voltage reduction circuit applied to the power supply of the substation relay protection device in claim 1, wherein when a second power switch tube M2 is switched on due to zero current of a leakage inductance LK2, a switching mode 7 is started; when the current IDM1 falls, the current ILK2 and the current ILKA rise linearly, when the current IDM1 is zero, all leakage currents reach the current ILM/(N +1), and at the end of the mode, the zero-current switch of the diode DM1 is turned off.

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