Half-bridge and full-bridge topology switchable power sub-module and switching method

Abstract

A half-bridge and full-bridge topology switchable power sub-module and switching method. The power sub-module includes a discharge resistor R, a DC-side capacitor C, four power control units, and multiple switches. The four power control units form a bridge circuit. The discharge resistor R and the DC-side capacitor C are connected in parallel with the bridge circuit formed by the four power control units. Each power control unit consists of a fully controlled device and a parallel diode. The first and second power control units are connected in series, and the third and fourth power control units are connected in series. The two series branches formed by the four power control units are connected in parallel. The switches include a switch K2 arranged between the fourth and third power control units, and a switch K3 arranged in parallel on the bypass of the third power control unit. When the switch K2 is open and the switch K3 is closed, it operates in the form of a half-bridge topology. When the switch K2 is closed and the switch K3 is open, it operates in the form of a full-bridge topology, which can avoid the hybrid start of the half-full bridge topology.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible DC power transmission, and particularly relates to a power sub-module with switchable half-bridge and full-bridge topologies and a switching method thereof. Background Art

[0002] Flexible DC power transmission has the characteristics of not relying on grid commutation, not having commutation failures, being able to independently control active and reactive power, having a fast response speed, flexible operation modes, and high controllability. Therefore, it is particularly suitable for fields such as island power supply, new energy grid connection, and asynchronous AC grid interconnection. At the same time, it is also an important technical means to support the power transmission of renewable energy bases, improve the safety and stability of AC grids, and optimize the grid structure. Due to the uneven distribution of energy resources, in order to ensure the balance between power supply and demand, it has become an inevitable trend to develop flexible DC transmission technologies with higher voltage levels and larger capacities.

[0003] Since flexible DC power transmission has applications such as overhead lines and high-voltage voltage transmission, it is necessary to consider the equipment safety guarantee issues when a DC-side fault occurs, as well as the on-line switching of valve groups in the case of series operation of valve groups. One of the current solutions is to adopt the method of connecting full-bridge and half-bridge sub-modules in series, which can not only achieve fault crossing during overhead line DC faults but also realize the on-line switching of valve groups. However, the introduction of full-bridge sub-modules will result in additional power consumption. Even when the full-bridge topology is controlled as a half-bridge topology during operation, there are still necessary device switching and conduction losses. Therefore, even though the application of the full-bridge topology has many advantages, its promotion and application are hindered due to its loss problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a power sub-module with switchable half-bridge and full-bridge topologies and a switching method thereof for the above problems in the existing technology, which can perform on-line switching of valve groups, make full use of the advantages of the full-bridge topology, achieve crossing under the condition of overhead line faults, and can fundamentally reduce the losses of the converter valve during operation.

[0005] To achieve the above purpose, the present invention has the following technical solutions:

[0006] In a first aspect, a power sub-module with switchable half-bridge and full-bridge topologies is provided, including a discharge resistor R, a DC-side capacitor C, four power control units, and multiple switches;

[0007] The four power control units form a bridge circuit. The discharge resistor R and the DC-side capacitor C are connected in parallel with the bridge circuit formed by the four power control units. Each power control unit consists of a fully controlled device and a parallel-connected diode. Among them, the first power control unit is connected in series with the second power control unit, and the third power control unit is connected in series with the fourth power control unit. The two series branches formed by the four power control units are connected in parallel. The switches include a switch K2 arranged between the fourth power control unit and the third power control unit, and a switch K3 arranged in parallel on the bypass of the third power control unit.

[0008] As a preferred solution, when the switch K2 is in the open state and the switch K3 is in the closed state, the power sub-module operates in the form of a half-bridge topology. When the switch K2 is in the closed state and the switch K3 is in the open state, the power sub-module operates in the form of a full-bridge topology.

[0009] As a preferred solution, the switches K2 and K3 are remotely controlled to be opened and closed electrically, or manually controlled to be opened and closed.

[0010] As a preferred solution, a connection wire A is led out between the first power control unit and the second power control unit, and a connection wire B is led out between the third power control unit and the fourth power control unit. A switch K1 is connected between the connection wire A and the connection wire B. The connection wire A and the connection wire B are respectively connected to the connection wire A and the connection wire B of another half-bridge and full-bridge topology switchable power sub-module with the same structure.

[0011] As a preferred solution, the fully controlled device of the power control unit is any one of IGBT, IEGT, and IGCT.

[0012] In a second aspect, a switching method for the half-bridge and full-bridge topology switchable power sub-module is provided, including:

[0013] When starting with non-zero voltage on the DC side of the flexible DC transmission system, control the switch K2 to be in the open state and control the switch K3 to be in the closed state, so that the power sub-module operates in the form of a half-bridge topology.

[0014] In a third aspect, a switching method for the half-bridge and full-bridge topology switchable power sub-module is provided, including:

[0015] In a flexible DC transmission system, the number of full-bridge topology power sub-modules required for zero-voltage start-up and DC fault ride-through is different. When the number of full-bridge power sub-modules required for zero-voltage start-up is more than that required for DC fault ride-through, during the zero-voltage start-up process, control switch K2 is in the closed state and control switch K3 is in the open state. After the start-up is completed, control switch K2 changes from the closed state to the open state, and control switch K3 changes from the open state to the closed state.

[0016] As a preferred solution, after the start-up is completed, the operation of control switch K2 being in the closed state and control switch K3 being in the open state is performed on some of the full-bridge topology power sub-modules.

[0017] As a preferred solution, switch K2 changes from the closed state to the open state at the current zero-crossing point.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] The half-bridge and full-bridge topology switchable power sub-module of the present invention can, by setting switch K2 between the fourth power control unit and the third power control unit and connecting switch K3 in parallel on the bypass of the third power control unit, achieve that when the flexible DC transmission system starts up at non-zero voltage on the DC side, switch K2 is in the open state and switch K3 is in the closed state, and the power sub-module starts to work in the form of a half-bridge topology, thus avoiding the start-up in the hybrid mode of the half-full bridge topology, and the power sub-module has a high charging voltage, good static voltage sharing performance, and less control intervention. When the number of full-bridge power sub-modules required for zero-voltage start-up and DC fault ride-through in the flexible DC transmission system is different, and the number of power sub-modules required for zero-voltage start-up is more than that required for DC fault ride-through, the power sub-module of the present invention can be in the full-bridge topology mode during zero-voltage start-up. After the start-up is completed, the states of switch K2 and switch K3 are changed, control switch K2 changes from the closed state to the open state, and control switch K3 changes from the open state to the closed state, reducing the heat loss during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and those of ordinary skill in the art can obtain other relevant drawings without creative efforts based on these drawings.

[0021] Figure 1 Circuit schematic diagram of the half-bridge and full-bridge topology switchable power sub-module of the embodiment of the present invention;

[0022] Figure 2 Schematic diagram of the connection of the half-bridge and full-bridge topology switchable power sub-module in a single bridge arm of the system in the embodiment of the present invention;

[0023] Figure 3 Schematic diagram of the half-bridge and full-bridge topology switchable power sub-module in the embodiment of the present invention switched to the half-bridge topology;

[0024] Figure 4 Schematic diagram of the half-bridge and full-bridge topology switchable power sub-module in the embodiment of the present invention switched to the full-bridge topology. Detailed implementation manners

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, those of ordinary skill in the art can also obtain other embodiments without creative efforts.

[0026] As Figure 1 shown, an embodiment of the present invention proposes a half-bridge and full-bridge topology switchable power sub-module, which includes a discharge resistor R, a DC-side capacitor C, four power control units, and multiple switches. The four power control units form a bridge circuit. The discharge resistor R and the DC-side capacitor C are connected in parallel with the bridge circuit formed by the four power control units. Each power control unit is composed of a fully controlled device and a parallel diode. The fully controlled device can be any one of IGBT, IEGT, and IGCT. In the embodiment, the first power control unit is composed of IGBT S1 and diode D1, the second power control unit is composed of IGBT S2 and diode D2, the third power control unit is composed of IGBT S3 and diode D3, and the fourth power control unit is composed of IGBT S4 and diode D4. The above first power control unit and the second power control unit are connected in series, the third power control unit and the fourth power control unit are connected in series, and the two series branches formed by the four power control units are connected in parallel. The switching between the half-bridge and full-bridge topologies of the power sub-module is realized through switches, including switch K2 arranged between the fourth power control unit and the third power control unit, and switch K3 arranged in parallel on the bypass of the third power control unit. When switch K2 is in the open state and switch K3 is in the closed state, the power sub-module operates in the form of a half-bridge topology; when switch K2 is in the closed state and switch K3 is in the open state, the power sub-module operates in the form of a full-bridge topology.

[0027] In a possible implementation manner, the switches in the embodiments of the present invention are fast mechanical switches. Switch K2 and switch K3 are remotely controlled to open and close states electrically, or to open and close states manually.

[0028] In a possible implementation, as Figure 2 shown, when the power sub-module of the embodiment of the present invention is connected in the flexible DC transmission system, a wiring A is led out between the first power control unit and the second power control unit, and a wiring B is led out between the third power control unit and the fourth power control unit. A switch K1 is connected between the wiring A and the wiring B. The wiring A and the wiring B are respectively connected to the wiring A and the wiring B of another semi-bridge and full-bridge topology switchable power sub-module with the same structure. When the flexible DC transmission system starts with non-zero voltage on the DC side, the control switch K2 is controlled to be in the open state, and the control switch K3 is controlled to be in the closed state, so that the power sub-module works in the form of a half-bridge topology. The circuit principle of the power sub-module in the form of a half-bridge topology is as Figure 3 shown. This method avoids the start-up in the hybrid mode of the half-full bridge topology, and the power sub-module has a high charging voltage, good static voltage sharing performance, and less control intervention. After the full-bridge topology is switched to a half-bridge, in order to ensure the safety of IGBTS3 and IGBT S4, the drives of the two fully controlled devices will output negative voltages for clamping.

[0029] In a possible implementation, in another embodiment of the switching method of the power sub-module of the present invention, the number of full-bridge topology power sub-modules required for zero-voltage start-up and DC fault crossing in the flexible DC transmission system is different. When the number of full-bridge power sub-modules required for zero-voltage start-up is more than the number of full-bridge topology power sub-modules required for DC fault crossing, during the zero-voltage start-up process, the control switch K2 is in the closed state, the control switch K3 is in the open state. After the start-up is completed, the control switch K2 is switched from the closed state to the open state, and the control switch K3 is switched from the open state to the closed state, so that the power sub-module of the present invention is switched to the full-bridge topology. The circuit principle of the power sub-module in the form of a full-bridge topology is as Figure 4 shown.

[0030] Here, after the start-up is completed, the operation of keeping the control switch K2 in the closed state and the control switch K3 in the open state is performed on some full-bridge topology power sub-modules to reduce the thermal loss during operation.

[0031] Before the zero-voltage start-up, considering that the power sub-module in the flexible DC transmission system is not charged, the switches K2 and K3 can be changed to the expected designed states. At the same time, when the current passes through the zero point, the switch K2 is then controlled to be switched from the closed state to the open state, so as to ensure that the switch K2 does not open with current.

[0032] Compared with the prior art, the half-bridge and full-bridge topology switchable power sub-module in the embodiment of the present invention realizes the flexible conversion of the sub-module topology structure by the state switching of the fast mechanical switch, solves the problem of large long-term input loss of the power sub-module in the full-bridge topology structure in the hybrid operation of the half-bridge and full-bridge topology structures in the prior art, helps to improve the operation reliability of the flexible DC transmission system, improves the energy utilization rate, and broadens the application scenarios of the full-bridge topology structure.

[0033] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A half-bridge and full-bridge topology switchable power sub-module, characterized in that, It includes a discharge resistor R, a DC-side capacitor C, four power control units, and multiple switches; The four power control units form a bridge circuit. The discharge resistor R and the DC-side capacitor C are connected in parallel with the bridge circuit formed by the four power control units. Each power control unit consists of a fully controlled device and a parallel-connected diode. Among them, the first power control unit is connected in series with the second power control unit, the third power control unit is connected in series with the fourth power control unit, and the two series branches formed by the four power control units are connected in parallel. A connection line A is led out between the first power control unit and the second power control unit, and a connection line B is led out between the third power control unit and the fourth power control unit. A switch K1 is connected between the connection line A and the connection line B. The connection line A and the connection line B are respectively connected to the connection line A and the connection line B of another half-bridge and full-bridge topology-switchable power sub-module with the same structure. The switches include a switch K2 arranged between the fourth power control unit and the connection line B, and a switch K3 arranged in parallel on the bypass of the third power control unit.

2. The half-bridge and full-bridge topology switchable power sub-module according to claim 1, wherein When the switch K2 is in the open state and the switch K3 is in the closed state, the power sub-module operates in the form of a half-bridge topology. When the switch K2 is in the closed state and the switch K3 is in the open state, the power sub-module operates in the form of a full-bridge topology.

3. The half-bridge and full-bridge topology-switchable power sub-module according to claim 2, wherein The switches K2 and K3 are remotely controlled to be opened and closed electrically or manually.

4. The half-bridge and full-bridge topology-switchable power sub-module according to claim 1, wherein The fully controlled device of the power control unit is any one of IGBT, IEGT, and IGCT.

5. A switching method for a half-bridge and full-bridge topology switchable power sub-module as described in any one of claims 1-4, characterized in that, It includes: During the non-zero voltage start of the DC side of the flexible DC transmission system, control the switch K2 to be in the open state and control the switch K3 to be in the closed state, so that the power sub-module operates in the form of a half-bridge topology.

6. A switching method for a half-bridge and full-bridge topology switchable power sub-module as described in any one of claims 1-4, characterized in that, It includes: When the number of full-bridge topology power sub-modules required for the zero-voltage start and the DC fault crossing of the flexible DC transmission system is different, and the number of full-bridge power sub-modules required for the zero-voltage start is more than the number of full-bridge topology power sub-modules required for the DC fault crossing, during the zero-voltage start process, control the switch K2 to be in the closed state, control the switch K3 to be in the open state. After the start is completed, control the switch K2 to be converted from the closed state to the open state, and control the switch K3 to be converted from the open state to the closed state.

7. The switching method according to claim 6, characterized in that, After the start is completed, the operation of controlling the switch K2 to be in the closed state and the switch K3 to be in the open state is performed on some full-bridge topology power sub-modules.

8. The switching method according to claim 6, characterized in that, The switch K2 is converted from the closed state to the open state at the current zero-crossing point.

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