Buffer circuit for silicon controlled rectifier inversion protection

Abstract

The utility model discloses a buffer circuit used for silicon controlled rectifier inversion protection. The buffer circuit comprises a diode, a first resistor, a second resistor and a capacitor. The negative electrode of the diode is connected with the first resistor in series and is connected with the second resistor in parallel to form a circuit which is connected with the capacitor in series to form a buffer circuit; in the buffer circuit, the anode of a diode and the output end of a capacitor are respectively connected with two ends of a silicon controlled rectifier, so that the buffer circuit is connected with the silicon controlled rectifier in parallel. By adopting the buffer circuit for silicon controlled rectifier inversion protection, the discharge current can be reduced, the DI / DT of the silicon controlled rectifier can be limited, and the silicon controlled rectifier can be well protected.

Description

Technical Field

[0001] The utility model relates to a buffer circuit for thyristor inversion protection, which belongs to the field of thyristor design. Background Art

[0002] The thyristor can be regarded as a high-power electrical component composed of three PN junctions. When the thyristor is in the blocking state, because the layers are very close to each other, the junction surface of the middle junction is equivalent to a capacitor C. When a forward voltage is applied between the anode and cathode of the thyristor, the two external junctions J1 and J3 are forward biased and the middle junction J2 is reverse biased, and a charging current will flow through the capacitor C. If the rate of this current rises too fast, the thyristor will be turned on without gate triggering, causing the thyristor to be mis-conducted and damaged.

[0003] When the thyristor is turned on by the gate trigger, the area near the gate is turned on immediately, and then quickly expands to the entire effective area. If the current rise rate DI / DT is very large at the moment the thyristor is turned on, and the current has not had time to expand to the entire area of ​​the thyristor's internal junction, local overheating will occur near the gate, causing partial burning and short circuit of the thyristor.

[0004] In order to limit very high DI / DT values, it is necessary to use an air-core inductor in series with the thyristor in the circuit according to the allowable DI / DT parameters of the thyristor design, and use the characteristic that the inductor current cannot change suddenly to suppress the DI / DT value in the circuit when the thyristor is turned on, so that it is lower than the allowable value of the thyristor.

[0005] In order to limit the rate of rise of the anode voltage applied to the thyristor, the prior art connects a non-inductive capacitor in parallel at both ends of the thyristor, and uses the characteristic that the voltage at both ends of the capacitor cannot change suddenly to suppress the DV / DT when the thyristor is disconnected. However, in actual use, it is found that only the capacitor cannot play a good role in protecting the thyristor, and the thyristor is still frequently damaged. Utility Model Content

[0006] The purpose of the utility model is to overcome the deficiencies of the prior art and provide a buffer circuit for thyristor inverter protection.

[0007] A technical solution to achieve the above object is: a buffer circuit for thyristor inverter protection, characterized by: comprising a diode, a first resistor, a second resistor and a capacitor;

[0008] The cathode of the diode is connected in series with the first resistor, and the two are connected in parallel with the second resistor. The circuit formed is connected in series with the capacitor to form a buffer circuit; in the buffer circuit, the anode of the diode and the output end of the capacitor are respectively connected to the two ends of the thyristor, so that the buffer circuit is connected in parallel with the thyristor.

[0009] Furthermore, the resistance of the second resistor is greater than the resistance of the first resistor.

[0010] Furthermore, the resistance of the first resistor is 2-6Ω, the power is 1400W, and the withstand voltage is 6000VDC.

[0011] Furthermore, the resistance of the second resistor is 30-100Ω, the power is 1400W, and the withstand voltage is 6000VDC.

[0012] Furthermore, the first resistor and the second resistor are water-cooled resistors.

[0013] Furthermore, the capacitor is a non-inductive capacitor with a capacity of 1.0 to 3.0 μf and a withstand voltage of 3000 VDC.

[0014] Furthermore, the diode is a fast recovery diode.

[0015] The buffer circuit for thyristor inverter protection of the utility model can reduce the discharge current, limit the DI / DT of the thyristor, and have a better protection effect on the thyristor. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The utility model is a circuit structure schematic diagram of a buffer circuit for thyristor inverter protection. DETAILED DESCRIPTION

[0017] In order to better understand the technical solution of the utility model, the following is a detailed description through specific embodiments:

[0018] The utility model discloses a buffer circuit for thyristor inverter protection, which comprises a diode, a first resistor, a second resistor and a capacitor.

[0019] The cathode of the diode is connected in series with the first resistor, and the two are connected in parallel with the second resistor. The circuit formed is connected in series with the capacitor to form a buffer circuit; in the buffer circuit, the anode of the diode and the output end of the capacitor are respectively connected to the two ends of the thyristor, so that the buffer circuit is connected in parallel with the thyristor.

[0020] A non-inductive capacitor with a capacity of 1.0-3.0μf and a withstand voltage of 3000VDC is connected in parallel at both ends of the thyristor. The characteristic that the voltage at both ends of the capacitor will not change suddenly is used to reduce the impact high voltage of the SCR from conduction to disconnection, which plays a protective role on the SCR. However, for the protection circuit with only capacitors, there will be a situation where the capacitor is overcharged. Test test: For the three-phase full-bridge rectifier circuit with an incoming line voltage of 575AC, the test found that the voltage at both ends of the capacitor reached about 1600VDC. This voltage will not only damage the capacitor itself, but also increase the discharge current during the SCR discharge process. Excessive discharge current will also cause damage to the SCR, reducing the protection effect of the SCR.

[0021] In order to reduce the impact current during the charging and discharging process of the capacitor, a first resistor with a small resistance is connected in series on the line of a single capacitor. The first resistor is a water-cooled non-inductive resistor with a resistance value of 2 to 6Ω, a power of 1400W, and a withstand voltage of 6000VDC. Because there is always leakage inductance in the circuit, the first resistor connected in series with the capacitor can act as a damping agent to prevent the oscillation of the R, L, and C circuits during the transition process and reduce the charging voltage at both ends of the capacitor. The test found that it not only reduces the impact current during the charging and discharging process of the capacitor, but also reduces the voltage at both ends of the capacitor. For a three-phase full-bridge rectifier circuit with an incoming line voltage of 575AC, the voltage at both ends of the capacitor can be reduced from about 1600VDC to about 1100VDC. At the same time, the test also found that after the capacitor is connected in series with a resistor, the SCR protection effect is better, but only this resistor is still large in the SCR discharge current. In order to better achieve the protection effect of the SCR and improve the protection of the capacitor at the same time, the SCR discharge current must be further reduced.

[0022] By utilizing the unidirectional conduction characteristics of the diode, the current path is blocked during the capacitor discharge process, allowing the discharge current to discharge along the high-impedance circuit, reducing the discharge current, and protecting both the thyristor and the capacitor. A second resistor is connected in parallel in the circuit to reduce the discharge current during the capacitor discharge process and quickly consume energy to protect the thyristor. For example: the capacitor voltage is 1100VDC, the resistance of R2 is 50Ω, and its discharge current is only 1100 / 50=22A. The protection circuit resistor is improved from a high-power aluminum shell resistor to a water-cooled resistor. Without increasing the installation space, a higher-power resistor can be selected to achieve better resistor heat dissipation and reduce the temperature rise of the working environment.

[0023] The capacitor is a non-inductive capacitor with a capacity of 1.0-3.0 μf and a withstand voltage of 3000 VDC; the first resistor is a water-cooled non-inductive resistor with a resistance value of 2-6 Ω, a power of 1400 W, and a withstand voltage of 6000 VDC; the second resistor is a water-cooled non-inductive resistor with a resistance value of 30-100 Ω, a power of 1400 W, and a withstand voltage of 6000 VDC, and the diode adopts a fast recovery diode.

[0024] See also Figure 1 , which is a circuit diagram of buffer circuits connected in parallel at both ends of the thyristor, wherein the first buffer circuit includes a first buffer circuit diode D1, a first buffer circuit first resistor R1, a first buffer circuit second resistor R2 and a first buffer circuit capacitor C1; the second buffer circuit includes a second buffer circuit diode D2, a first buffer circuit first resistor R3, a first buffer circuit second resistor R4 and a first buffer circuit capacitor C2.

[0025] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A buffer circuit for thyristor inverter protection, characterized in that: comprising a diode, a first resistor, a second resistor and a capacitor; The cathode of the diode is connected in series with the first resistor, and the two are connected in parallel with the second resistor. The circuit formed is connected in series with the capacitor to form a buffer circuit; in the buffer circuit, the anode of the diode and the output end of the capacitor are respectively connected to the two ends of the thyristor, so that the buffer circuit is connected in parallel with the thyristor.

2. A buffer circuit for thyristor inverter protection according to claim 1, characterized in that: The resistance value of the second resistor is greater than the resistance value of the first resistor.

3. A buffer circuit for thyristor inverter protection according to claim 2, characterized in that: The resistance of the first resistor is 2-6Ω, the power is 1400W, and the withstand voltage is 6000VDC.

4. A buffer circuit for thyristor inverter protection according to claim 2, characterized in that: The resistance of the second resistor is 30-100Ω, the power is 1400W, and the withstand voltage is 6000VDC.

5. The buffer circuit for thyristor inverter protection according to claim 2, characterized in that: The first resistor and the second resistor are water-cooled resistors.

6. The buffer circuit for thyristor inverter protection according to claim 1, characterized in that: The capacitor is a non-inductive capacitor with a capacity of 1.0 to 3.0 μf and a withstand voltage of 3000 VDC.

7. The buffer circuit for thyristor inverter protection according to claim 1, characterized in that: The diode is a fast recovery diode.

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