A single thyristor capacitor switching circuit

Abstract

The present invention discloses a single thyristor capacitor switching circuit, which belongs to the technical field of reactive power compensation equipment. It includes a first diode, a second diode, a third diode, a fourth diode, a first capacitor, a second capacitor, a third capacitor, a thyristor, a reactor, and a pulse transformer; the cathode of the first diode is connected to the A phase of three-phase electricity through the first capacitor, and the anode of the first diode is connected to the B phase of three-phase electricity through the second capacitor; the cathode of the second diode is connected to the C phase of three-phase electricity through the third capacitor, and the anode of the second diode is connected to the anode of the first diode and the anode of the reactor; the cathode of the third diode is connected to the cathode of the first diode, the anode of the third diode is connected to the anode of the fourth diode and the anode of the thyristor, and the cathode of the thyristor is connected to the cathode of the reactor. It has the advantages of low cost, good energy-saving effect, simple control, and no oscillation overcurrent phenomenon.

Description

Technical Field

[0001] The invention relates to a single thyristor capacitor switching circuit, belonging to the technical field of reactive power compensation equipment. Background Art

[0002] Power capacitors are essential electrical equipment for reactive power compensation, energy conservation, and loss reduction. However, with the increasing intelligence and automation of production equipment, reactive power compensation equipment needs to be adjusted quickly. Therefore, power capacitors need to be switched on and off more and more frequently. In many factories, capacitors are switched on and off multiple times within a minute. However, the switching of capacitors inevitably generates large inrush currents and sometimes even operational overvoltages, which not only cause significant damage to the capacitors themselves, but also cause voltage fluctuations or oscillations in the power supply system. Therefore, how to limit the inrush current of power capacitors has always been a research focus of reactive power compensation technology.

[0003] The existing technology adopts two solutions. One is the thyristor switching switch, which uses thyristors to achieve zero-point switching, which can effectively reduce inrush current, but the thyristor switching switch is very expensive; the other is the current limiting reactor. The use of reactors to limit current has a long history, but if the reactor's inductance is small, the inrush current suppression capability is insufficient. If the inductance is large, it will cause transient oscillations during opening and closing, further damaging the capacitor. The overall current limiting effect is general, and the inrush current suppression capability can only reach about 5 times the rated current. Therefore, developing a capacitor switching circuit with low cost, good inrush current suppression capability and good reliability will be of great benefit to improving the switching frequency and compensation effect of power capacitors. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a single thyristor capacitor switching circuit, which solves the problems of the existing switching circuits, such as high cost, poor energy saving effect and inrush current suppression capability to be improved.

[0005] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0006] A single thyristor capacitor switching circuit includes a first diode, a second diode, a third diode, a fourth diode, a first capacitor, a second capacitor, a third capacitor, a thyristor, a reactor, and a pulse transformer;

[0007] The cathode of the first diode is connected to the phase A of the three-phase electricity through the first capacitor, and the anode of the first diode is connected to the phase B of the three-phase electricity through the second capacitor;

[0008] The cathode of the second diode is connected to the C phase of the three-phase power through the third capacitor, and the anode of the second diode is connected to the anode of the first diode and the anode of the reactor;

[0009] The cathode of the third diode is connected to the cathode of the first diode, the anode of the third diode is connected to the anode of the fourth diode and the anode of the thyristor, and the cathode of the thyristor is connected to the cathode of the reactor;

[0010] The cathode of the fourth diode is connected to the cathode of the second diode;

[0011] The secondary side of the pulse transformer is connected between the negative electrode and the trigger electrode of the thyristor, and the primary side of the pulse transformer is connected to the output end of the external switching control circuit.

[0012] As a preferred example, the first capacitor, the second capacitor, and the third capacitor are three capacitors with the same specifications.

[0013] The beneficial effects of the present invention are:

[0014] (1) Low cost. This circuit uses a single thyristor element to realize the switching control of three-phase power capacitors. Its cost is several times lower than that of the existing switching switches with multiple thyristor structures, thus greatly reducing the cost of the thyristor capacitor switching circuit;

[0015] (2) Good energy-saving effect. This circuit only uses one thyristor, and the rest are diodes. The forward voltage drop of the diode is significantly smaller than that of the thyristor, which reduces the power loss of the switching circuit and achieves energy-saving effect.

[0016] (3) Simple control. The thyristor switching in the prior art requires calculation of the current and voltage zero-crossing points of each thyristor, which places high demands on the sampling calculation of the control circuit. This circuit only needs to control one thyristor and does not need to consider the coordination of the zero-crossing moments of multiple thyristors. Therefore, its control circuit is very simple and can be implemented with a simple analog circuit. This not only improves the reliability of the system but also further reduces costs.

[0017] (4) No oscillating overcurrent phenomenon. Although the existing thyristor switching switch can achieve zero-crossing switching, it is not completely accurate. Therefore, there is still oscillation in the switching process. After adding a current-limiting reactor, it may be more serious. However, the reactor of this circuit is connected in series in the thyristor loop. Due to the unidirectional conductive characteristics of the thyristor, the power of the inductive element and the capacitive element cannot be converted, which essentially eliminates the oscillation condition.

[0018] (5) This circuit uses a clever combination of diodes and a unidirectional thyristor element to achieve the switching control of three-phase three-group power capacitors. The existing technology requires at least two bidirectional thyristors or four unidirectional thyristors to achieve this. Compared with the existing technology, this circuit is a groundbreaking innovation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1Schematic diagram of the circuit structure of the present invention.

[0020] In the figure: a first diode 1, a second diode 2, a third diode 3, a fourth diode 4, a first capacitor 5, a second capacitor 6, a third capacitor 7, a thyristor 8, a reactor 9, and a pulse transformer 10. DETAILED DESCRIPTION

[0021] In order to make the technical means, creative features, objectives and effects of the present invention easier to understand, the present invention is further explained below with reference to specific illustrations.

[0022] like Figure 1 As shown, a single thyristor capacitor switching circuit includes a first diode 1, a second diode 2, a third diode 3, a fourth diode 4, a first capacitor 5, a second capacitor 6, a third capacitor 7, a thyristor 8, a reactor 9, and a pulse transformer 10;

[0023] The cathode of the first diode 1 is connected to the phase A of the three-phase electricity through the first capacitor 5, and the anode of the first diode 1 is connected to the phase B of the three-phase electricity through the second capacitor 6;

[0024] The cathode of the second diode 2 is connected to the C phase of the three-phase power through the third capacitor 7, and the anode of the second diode 2 is connected to the anode of the first diode 1 and the anode of the reactor 9;

[0025] The cathode of the third diode 3 is connected to the cathode of the first diode 1 , the anode of the third diode 3 is connected to the anode of the fourth diode 4 and the anode of the thyristor 8 , and the cathode of the thyristor 8 is connected to the cathode of the reactor 9 ;

[0026] The cathode of the fourth diode 4 is connected to the cathode of the second diode 2;

[0027] The secondary side of the pulse transformer 10 is connected between the negative electrode and the trigger electrode of the thyristor 8, and the primary side of the pulse transformer 10 is connected to the output terminal of the external switching control circuit.

[0028] The first capacitor 5 , the second capacitor 6 , and the third capacitor 7 are three capacitors with the same specifications.

[0029] Working principle:

[0030] When the thyristor 8 is not conducting, only 1 / 2 of the diodes are conducting in the circuit, which is equivalent to half-wave rectification for the capacitors. The three capacitors can only be charged but not discharged, so the current is zero, which is equivalent to no capacitor input. When the thyristor 8 is triggered and turned on, since the voltage drop of the thyristor 8 and the diode is very small, it is equivalent to short-circuiting the low-voltage side of the three-phase capacitor bank. The three-phase capacitor is equivalent to a three-phase star-connected access system, realizing the generation of reactive current. Since the current flowing through the four diodes and the thyristor 8 is a fluctuating half-wave DC component, when the current of the thyristor 8 crosses zero, the trigger is removed. After the pulse is sent, the thyristor 8 will no longer be turned on after the next half-wave, thus realizing the exit of the three-phase capacitor; when the capacitor needs to be put into operation, a trigger pulse can be directly added. Since the reactor 9 does not need to consider the oscillation overcurrent, its inductive reactance can be made very large, so the inrush current is very small, and it is not necessary to consider the voltage zero point input, thereby greatly simplifying the control circuit. This circuit uses a thyristor 8 element to realize the switching control of the three-phase power capacitor. Its cost is several times lower than that of the existing switching switch with multiple thyristors 8 structures, thereby greatly reducing the cost of the thyristor 8 capacitor switching circuit

[0031] It has the following advantages:

[0032] (1) Low cost. This circuit uses a single thyristor 8 element to realize the switching control of three-phase power capacitors. Its cost is several times lower than that of the existing switching switch with multiple thyristor 8 structures, thus greatly reducing the cost of the thyristor 8 capacitor switching circuit;

[0033] (2) Good energy-saving effect. This circuit only uses one thyristor 8, and the rest are diodes. The forward conduction voltage drop of the diode is significantly smaller than that of the thyristor 8, which reduces the power loss of the switching circuit and achieves energy-saving effect.

[0034] (3) Simple control. The prior art thyristor 8 switching operation requires calculation of the current and voltage zero-crossing points of each thyristor 8, which places high demands on the sampling calculation of the control circuit. The present circuit only needs to control one thyristor 8 and does not need to consider the coordination of the zero-crossing moments of multiple thyristors 8. Therefore, its control circuit is very simple and can be implemented with a simple analog circuit. This not only improves the reliability of the system but also further reduces costs.

[0035] (4) No oscillating overcurrent phenomenon. Although the existing thyristor 8 switching switch can achieve zero-crossing switching, it is not completely accurate. Therefore, there is still oscillation in the switching process. After adding the current-limiting reactor 9, it may be more serious. However, the reactor 9 of this circuit is connected in series in the thyristor 8 circuit. Due to the unidirectional conductive characteristics of the thyristor 8, the power of the inductive element and the capacitive element cannot be converted, which essentially eliminates the oscillation condition.

[0036] (5) This circuit uses a clever combination of diodes and a unidirectional thyristor 8 element to achieve the switching control of three-phase three-group power capacitors. The existing technology requires at least two bidirectional thyristors 8 or four unidirectional thyristors 8 to achieve this. Compared with the existing technology, this circuit is a groundbreaking innovation.

[0037] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art will appreciate that the present invention is not limited to the foregoing embodiments and that various modifications and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such modifications and improvements are intended to fall within the scope of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A single thyristor capacitor switching circuit, characterized in that: It comprises a first diode (1), a second diode (2), a third diode (3), a fourth diode (4), a first capacitor (5), a second capacitor (6), a third capacitor (7), a thyristor (8), a reactor (9), and a pulse transformer (10); The cathode of the first diode (1) is connected to the A phase of the three-phase electricity through the first capacitor (5), and the anode of the first diode (1) is connected to the B phase of the three-phase electricity through the second capacitor (6); The cathode of the second diode (2) is connected to the C phase of the three-phase electricity through the third capacitor (7), and the anode of the second diode (2) is connected to the anode of the first diode (1) and the anode of the reactor (9); The cathode of the third diode (3) is connected to the cathode of the first diode (1), the anode of the third diode (3) is connected to the anode of the fourth diode (4) and the anode of the thyristor (8), and the cathode of the thyristor (8) is connected to the cathode of the reactor (9); The cathode of the fourth diode (4) is connected to the cathode of the second diode (2); The secondary side of the pulse transformer (10) is connected between the negative electrode and the trigger electrode of the thyristor (8), and the primary side of the pulse transformer (10) is connected to the output end of the external switching control circuit.

2. A single thyristor capacitor switching circuit according to claim 1, characterized in that: The first capacitor (5), the second capacitor (6) and the third capacitor (7) are three capacitors with the same specifications.

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