CN213879668U

CN213879668U - Reactive current transformer

Info

Publication number: CN213879668U
Application number: CN202022101199.0U
Authority: CN
Inventors: 吴强国; 赵明; 张明军; 陈奇; 陈岁超
Original assignee: Guangzhou Zhiguang Electric Technology Co ltd; Guangzhou Zhiguang Electric Co Ltd
Current assignee: Guangzhou Zhiguang Electric Technology Co ltd; Guangzhou Zhiguang Electric Co Ltd
Priority date: 2020-09-22
Filing date: 2020-09-22
Publication date: 2021-08-03
Anticipated expiration: 2030-09-22

Abstract

The present application discloses a reactive power converter. The single-phase shunt in the reactive power converter includes a grid-connected switch, a soft-start circuit, a filter circuit and a switch circuit; the first end of the grid-connected switch can be connected to the corresponding phase power of the grid, and the second end is connected to the first end of the filter circuit The grid-connected switch is connected in parallel with the soft-start circuit; the soft-start circuit includes a series-connected soft-start resistor and a soft-start switch, and is connected to the corresponding phase of the grid through the soft-start switch, and the second end of the filter circuit and the switch circuit are connected through the soft-start switch. The third ends of the filter circuits of each single-phase branch are connected together, and the second ends of the switch circuits of each single-phase branch are connected together; the filter circuit is provided with a filter capacitor switch in series with the filter capacitor. The soft-start switch can power off the main circuit during maintenance to improve safety, and the filter capacitor switch can be disconnected during soft-start to isolate the filter device and ensure that the bus capacitor can be charged to a high enough voltage.

Description

Reactive current transformer

Technical Field

The application relates to the technical field of power electronics, in particular to a reactive converter.

Background

SVGs (Static Var generators, Active Power filters) and APFs (Active Power filters) and other reactive converters need to be soft started when in use due to the fact that the bus capacitor is large, and the converter is put into normal use after the bus capacitor is charged. One way is to use a soft start resistor and connect it in parallel with the grid-connected switch of the reactive current transformer, and to use the reactive current transformer normally by closing the grid-connected switch to short-circuit the soft start resistor. However, it can be seen that when the reactive power converter is in normal use, the soft start resistor is still connected in series in the circuit, so that the internal main loop cannot be completely powered off when the reactive power converter is overhauled, and the overhauling safety is poor.

It should be noted that the statements herein merely provide background information related to the present application and may not necessarily constitute prior art.

SUMMERY OF THE UTILITY MODEL

In view of the above, the present application is proposed in order to provide a reactive converter that overcomes or at least partially solves the above mentioned problems.

According to an aspect of the present application, there is provided a reactive power converter, including a single-phase shunt circuit corresponding to each phase electricity, the single-phase shunt circuit including a grid-connected switch, a soft start circuit, a filter circuit, and a switching circuit;

the first end of the grid-connected switch can be connected with corresponding phase power of a power grid, and the second end of the grid-connected switch is connected with the first end of the filter circuit; the grid-connected switch is connected with the soft start circuit in parallel;

the soft start circuit comprises a soft start resistor and a soft start switch which are connected in series, is connected with corresponding phase power of a power grid through the soft start switch, and is connected with the second end of the filter circuit and the first end of the switch circuit through the soft start resistor;

the third ends of the filter circuits of the single-phase shunts are connected together, and the second ends of the switch circuits of the single-phase shunts are connected together;

and a filter capacitor switch connected with the filter capacitor in series is arranged in the filter circuit.

Optionally, in a soft start stage of the reactive power converter, the grid-connected switch is turned off, the soft start switch is turned on, and the filter capacitor switch is turned off, so that a current charges a bus capacitor in the switch circuit through the soft start resistor.

Optionally, when the reactive power converter is overhauled, the grid-connected switch and the soft start switch are both turned off, so that a main loop of the reactive power converter is not electrified.

Optionally, the reactive converter is adapted to connect a three-phase ac power grid, the number of single-phase shunts being three.

Optionally, the filter circuit is an LC filter circuit.

Optionally, a second end of the grid-connected switch is connected to a first end of a filter inductor in the LC filter circuit and a first end of the filter capacitor switch;

the second end of the filter inductor is connected with the first end of the switch circuit, and the second end of the filter capacitor switch is connected with the first end of the filter inductor;

the second terminals of the filter capacitors in the single-phase branches are connected in common.

Optionally, the switching circuit is a bridge rectifier circuit based on a first switching device, a second switching device, a third switching device, a fourth switching device and a bus capacitor,

the first conducting end of the third switching device and the second conducting end of the fourth switching device are connected to form a first end of the switching circuit;

the second conducting end of the third switching device, the second conducting end of the first switching device and the first end of the bus capacitor are connected together;

the first conduction end of the second switching device, the first conduction end of the fourth switching device and the second end of the bus capacitor are connected together;

the first conducting end of the first switching device and the second conducting end of the second switching device are connected to form a second end of the switching circuit.

Optionally, each switching device is an insulated gate bipolar transistor IGBT.

According to the reactive power converter, the soft start switch connected with the soft start resistor in series is added, the soft start resistor is not directly connected with the grid-connected switch in parallel any more, so that the soft start switching is realized by the grid-connected switch, the soft start resistor can be conveniently disconnected from the circuit through the soft start switch, the reactive power converter is convenient to overhaul when in fault, and the safety is improved. The filter circuit is provided with the filter capacitor switch connected with the filter capacitor in series, and the filter capacitor switch can be disconnected to realize the isolation of the filter device on the alternating current side, so that the bus capacitor can be charged to a sufficiently high voltage. Compared with the mode of using a diode and a soft start resistor, the soft start device does not participate in the normal operation process of the reactive power converter, rapid aging and loss of the soft start device are avoided, the charging voltage is higher, the impact current of a bus after grid connection is reduced, and the reliability of equipment is enhanced.

The foregoing description is only an overview of the technical solutions of the present application, and the present application can be implemented according to the content of the description in order to make the technical means of the present application more clearly understood, and the following detailed description of the present application is given in order to make the above and other objects, features, and advantages of the present application more clearly understandable.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the application. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:

fig. 1 shows a schematic diagram of a reactive converter circuit topology according to an embodiment of the present application;

fig. 2 shows a schematic diagram of a reactive converter circuit according to an embodiment of the present application.

Detailed Description

Exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

The mode of directly connecting the soft start resistor and the grid-connected switch in parallel is simple, devices are saved, and the maintenance is not facilitated. In another reactive current converter soft start mode, a diode and a resistor are selected as soft start devices, but the soft start devices and the reactive current converter run synchronously for a long time in the mode, so that the loss is large, the aging is fast, and the reliability is low.

To this, this application has proposed the scheme of chooseing for use switch and resistance, and the soft start circuit that obtains is parallelly connected with reactive current transformer's the switch that is incorporated into the power networks for soft start resistance can conveniently break off from the circuit, makes things convenient for the equipment maintenance. In addition, a filter capacitor switch connected with the filter capacitor in series is arranged in a filter circuit of the reactive power converter, so that an alternating-current side filter device can be isolated during soft start, and the bus capacitor can be charged to a sufficiently high voltage.

Fig. 1 shows a schematic diagram of a reactive power converter circuit topology according to an embodiment of the present application, and as shown in fig. 1, the reactive power converter includes single-phase shunts respectively corresponding to phases, and each single-phase shunt includes a grid-connected switch, a soft start circuit, a filter circuit and a switch circuit; the first end of the grid-connected switch can be connected with the corresponding phase power of the power grid, and the second end of the grid-connected switch is connected with the first end of the filter circuit; the grid-connected switch is connected with the soft start circuit in parallel; the soft start circuit comprises a soft start resistor and a soft start switch which are connected in series, is connected with the corresponding phase power of the power grid through the soft start switch, and is connected with the second end of the filter circuit and the first end of the switch circuit through the soft start resistor; the third ends of the filter circuits of the single-phase shunts are connected together, and the second ends of the switch circuits of the single-phase shunts are connected together; the filter circuit is provided with a filter capacitor switch connected with the filter capacitor in series.

The switching devices in the switching circuit operate to generate harmonics, and therefore the reactive power converter is usually provided with a filter circuit.

In the soft start stage of the reactive power converter, the grid-connected switch is disconnected, the soft start switch is closed, and the filter capacitor switch is disconnected, so that the current charges the bus capacitor in the switch circuit through the soft start resistor. Therefore, the problem that the bus capacitor cannot be charged to a sufficiently high voltage due to voltage division of the filter capacitor can be avoided.

Before the reactive power converter is overhauled, the grid-connected switch and the soft start switch are both disconnected, so that a main circuit of the reactive power converter is uncharged. This improves the safety of the overhaul.

This is explained below with reference to a specific circuit example. Fig. 2 shows a schematic diagram of a reactive converter circuit according to an embodiment of the present application. As shown in fig. 2, the reactive power converter 200 includes grid-connected switches K7 (corresponding to a phase), K8 (corresponding to B phase), and K9 (corresponding to C phase) corresponding to three-phase power of a power grid, and a soft start circuit 210 corresponding to three-phase power of the power grid, specifically, a soft start resistor R1 and a soft start switch K1 correspond to a phase, a soft start resistor R2 and a soft start switch K3 correspond to B phase, and a soft start resistor R3 and a soft start switch K5 correspond to C phase.

Taking fig. 2 as an example, the filter circuit 230 is an LC filter circuit, and may be an LCL filter circuit in other embodiments.

In the embodiment of the present application, a filter capacitor switch connected in series with a filter capacitor is disposed in a filter circuit, and taking fig. 2 as an example, the filter circuit 230 corresponding to a includes a filter inductor L1, a filter capacitor switch K2, and a filter capacitor C2; the filter circuit 230 corresponding to B comprises a filter inductor L2, a filter capacitor switch K4 and a filter capacitor C4; the filter circuit 230 corresponding to C includes a filter inductor L3, a filter capacitor switch K6, and a filter capacitor C6.

During the soft start phase, K1, K3 and K5 are closed, K2, K4 and K6 are opened, and K7, K8 and K9 are opened. At this time, the soft start resistor in the soft start circuit 210 is connected to the circuit, the filter capacitor of the filter circuit 230 is cut off, and the current charges the bus capacitors C1, C3 and C5 through the soft start resistor.

In some embodiments, the switching circuit is an insulated Gate Bipolar transistor (igbt) based bridge rectifier circuit.

Taking fig. 2 as an example, the reactive power converter includes a switching circuit 220 corresponding to three-phase power, and includes 12 IGBT transistors Q1 to Q12, and 3 bus capacitors C1, C3, and C5.

Specifically, the switch circuit corresponding to a includes Q1, Q2, Q3, and Q4, and a bus capacitor C1; the switch circuit corresponding to B comprises Q5, Q6, Q7 and Q8, and a bus capacitor C3; the switching circuit corresponding to C includes Q9, Q10, Q11, and Q12, and a bus capacitor C5.

As can be seen from fig. 2, C1 charges through the following two paths:

route 1: phase A → K1 → R1 → Q3 → C1 → Q2 → Q5 → C3 → Q8 → R2 → K3 → phase B;

route 2: phase A → K1 → R1 → Q3 → C1 → Q2 → Q9 → C5 → Q12 → R3 → K5 → phase C.

C3 charges through the following two paths:

route 3: phase B → K3 → R2 → Q7 → C3 → Q6 → Q1 → C1 → Q4 → R1 → K1 → phase a;

path 4: phase B → K3 → R2 → Q7 → C3 → Q6 → Q9 → C5 → Q12 → R3 → K5 → phase C.

C5 charges through the following two paths:

path 5: phase C → K5 → R3 → Q11 → C1 → Q10 → Q5 → C3 → Q8 → R2 → K3 → phase B;

path 6: phase C → K5 → R3 → Q11 → C1 → Q10 → Q1 → C1 → Q4 → R1 → K1 → phase A.

When the charge meets the required voltage, K1, K3 and K5 are opened and K2, K4 and K6 are closed. And closing K7, K8 and K9 when the reactive power converter operates normally. Therefore, the isolation of the alternating current side filter device can be realized, the problem that the soft start resistor and the alternating current side filter impedance cannot be reasonably matched is solved, and the fact that the bus capacitor can be charged to higher voltage (can reach 1.414 times of the voltage of a power grid) is ensured, so that the phenomenon that the bus capacitor impact current is too large due to too large bus capacitor pressure difference during grid connection is avoided, and the use requirement is met. That is, the filter switches K2, K4, and K6 are used in the soft start phase to optimize impedance matching.

The soft start switches K1, K3 and K5 are used for controlling connection and disconnection of the soft start resistor, the filter capacitor switches K2, K4 and K6 are used for isolating the filter devices on the alternating current side, the grid-connected switches K7, K8 and K9 are used for controlling the main circuit, and the switches K1-K9 can be selected from various switches.

The soft start switches K1, K3 and K5 and the soft start switches K1, K3 and K5 can be kept off when the reactive power converter 200 is overhauled, so that the main circuit in the reactive power converter is uncharged, and the overhauling safety is improved.

The application provides a reactive current transformer has increased the soft start switch who establishes ties with soft start resistance, and soft start resistance no longer directly is parallelly connected with the switch that is incorporated into the power networks, makes the switching of soft start not only rely on the switch that is incorporated into the power networks to realize like this, and soft start resistance can conveniently break off from the circuit through soft start switch, and the maintenance when the reactive current transformer trouble of being convenient for has improved the security. The filter circuit is provided with the filter capacitor switch connected with the filter capacitor in series, and the filter capacitor switch can be disconnected to realize the isolation of the filter device on the alternating current side, so that the bus capacitor can be charged to a sufficiently high voltage. Compared with the mode of using a diode and a soft start resistor, the soft start device does not participate in the normal operation process of the reactive power converter, rapid aging and loss of the soft start device are avoided, the charging voltage is higher, the impact current of a bus after grid connection is reduced, and the reliability of equipment is enhanced.

While the foregoing is directed to embodiments of the present application, other modifications and variations of the present application may be devised by those skilled in the art in light of the above teachings. It should be understood by those skilled in the art that the foregoing detailed description is for the purpose of better explaining the present application, and the scope of protection of the present application shall be subject to the scope of protection of the claims.

Claims

1. A reactive power converter, characterized in that the reactive power converter comprises a single-phase shunt corresponding to each phase of electricity respectively, and the single-phase shunt comprises a grid-connected switch, a soft-start circuit, a filter circuits and switching circuits;

The first end of the grid-connected switch can be connected to the corresponding phase of the power grid, and the second end is connected to the first end of the filter circuit; the grid-connected switch is connected in parallel with the soft-start circuit;

The soft-start circuit includes a series-connected soft-start resistor and a soft-start switch, the soft-start switch is connected to the corresponding phase of the power grid, and the soft-start resistor is connected to the second end of the filter circuit and the switch circuit through the soft-start switch. The first end of the connection;

The third ends of the filter circuits of each single-phase branch are connected together, and the second ends of the switch circuits of each single-phase branch are connected together;

The filter circuit is provided with a filter capacitor switch connected in series with the filter capacitor.

2. The reactive power converter according to claim 1, characterized in that,

In the soft-start stage of the reactive power converter, the grid-connected switch is turned off, the soft-start switch is turned on, and the filter capacitor switch is turned off, so that the current flows through the soft-start resistor for the switching circuit charging the bus capacitors.

3. The reactive power converter according to claim 1, wherein,

When the reactive power converter is overhauled, the grid connection switch and the soft-start switch are both disconnected, so that the main circuit of the reactive power converter is not charged.

4 . The reactive power converter according to claim 1 , wherein the reactive power converter is suitable for connecting to a three-phase AC power grid, and the number of the single-phase shunts is three. 5 .

5. The reactive power converter according to claim 1, wherein the filter circuit is an LC filter circuit.

6 . The reactive power converter according to claim 5 , wherein the second end of the grid-connected switch is connected to the first end of the filter inductor in the LC filter circuit and the first end of the filter capacitor switch. 7 . one end connection;

The second end of the filter inductor is connected to the first end of the switch circuit, and the second end of the filter capacitor switch is connected to the first end of the filter inductor;

The second ends of the filter capacitors in each single-phase branch are connected in common.

7 . The reactive power converter according to claim 1 , wherein the switching circuit is a bridge type based on the first switching device, the second switching device, the third switching device, the fourth switching device and the bus capacitance. 8 . rectifier circuit,

The first conducting end of the third switching device and the second conducting end of the fourth switching device are connected to form the first end of the switching circuit;

the second conducting end of the third switching device, the second conducting end of the first switching device and the first end of the bus capacitor are connected in common;

The first conducting end of the second switching device, the first conducting end of the fourth switching device and the second end of the bus capacitor are connected in common;

The first conducting end of the first switching device and the second conducting end of the second switching device are connected to form the second end of the switching circuit.

8 . The reactive power converter according to claim 7 , wherein each switching device is an insulated gate bipolar transistor (IGBT). 9 .