Modular Sub-module Topology of a DC Energy Discharging Device and Its Control Method

Abstract

Modular sub-module topology of a DC energy dissipation device and its control method. The modular sub-module includes an upper module and a lower module connected in series. The upper and lower modules have the same electrical structure and share a bypass switch. The control method is to independently trigger the turn-on and turn-off of the first turn-off switch device and the second turn-off switch device respectively, or to select to simultaneously trigger the turn-on and turn-off of the first turn-off switch device and the second turn-off switch device. Integrating two sub-modules with the same structure into a sub-module structure with higher integration will be beneficial to reducing the number of sub-modules in series and also reducing the requirement for the structural space of the sub-module. When a fault occurs in the receiving-end system, the turn-off semiconductor switch in the energy dissipation loop of the sub-module will receive a conduction signal, and precisely control the DC energy dissipation device to quickly consume the excess electrical energy on the line, avoiding the voltage increase caused by the accumulation of electrical energy, thereby maintaining the stability of the system.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a modular sub-module topology of a DC energy discharging device and a control method thereof. Background Art

[0002] New energy is the future development direction of energy, especially the development and application of large-scale offshore wind energy. A DC energy discharging device is often required in the DC voltage power grid connected by a new energy grid-connected converter, so that in the case of a fault on the AC side at the inverter side, the excess electric energy transmitted on this line can be consumed within a few seconds. The system judges the fault type on the AC side and decides whether to re-energize the inverter-side converter.

[0003] In the currently designed energy discharging device using distributed resistors, the sub-module is a single-module structure, and a bypass switch, a freewheeling diode, an energy storage capacitor, a turn-off semiconductor switch, and a dissipating resistor with a single configuration are adopted. In order to simplify the control and structure simultaneously and reduce the input of optical fibers, two sub-modules can be integrated into a subsystem module. This will make the integration degree of the sub-module structure higher, the overall volume smaller, and the number of optical receiving and transmitting fibers halved. Summary of the Invention

[0004] In order to solve the technical problems in the background art, the present invention provides a modular sub-module topology of a DC energy discharging device and a control method thereof. This module integrates two sub-modules with the same structure into a sub-module structure with a higher integration degree, which is beneficial to reducing the number of series-connected sub-modules and also reducing the requirement for the structural space of the sub-module.

[0005] In order to achieve the above object, the present invention is implemented by adopting the following technical solutions:

[0006] A modular sub-module topology of a DC energy discharging device, the modular sub-module includes an upper module and a lower module connected in series up and down. The upper module and the lower module have the same electrical structure and share a bypass switch (92).

[0007] The upper module includes a first energy storage capacitor (31) and a first discharging resistor (51); it further includes a first turn-off switch device (41). The first turn-off switch device (41) is connected in series with the first discharging resistor (51) and then connected in parallel with the first energy storage capacitor (31);

[0008] Further, the upper module further includes two series-connected diodes: a first diode (21) and a second diode (22). The negative poles of the two series-connected diodes are connected to the positive pole of the first energy storage capacitor (31), and the positive poles are connected to the negative pole of the first energy storage capacitor (31). The midpoint of the two series-connected diodes is the positive pole access point X1 of the modular sub-module.

[0009] Further, a first anti-parallel diode (23) is also connected in parallel across both ends of the first turn-off switch device (41) of the upper module; a second anti-parallel diode (24) is also connected in parallel across both ends of the first discharge resistor (51).

[0010] Further, a third turn-off switch device (43) is also connected in parallel across both ends of the second diode (22).

[0011] The lower module includes a second energy storage capacitor (32) and a second discharge resistor (52); it further includes a second turn-off switch device (42), and the second turn-off switch device (42) is connected in series with the second discharge resistor (52) and then connected in parallel with the second energy storage capacitor (32).

[0012] The lower module further includes two series-connected diodes: a third diode (25) and a fourth diode (26). After the two diodes are connected in series, the negative electrode is connected to the positive electrode of the second energy storage capacitor (32), and the positive electrode is connected to the negative electrode of the second energy storage capacitor (32). The midpoint of the series connection of the two diodes is the negative electrode access point X2 of the modular sub-module.

[0013] Further, a third anti-parallel diode (28) is also connected in parallel across both ends of the second turn-off switch device (42) of the lower module; a fourth anti-parallel diode (27) is also connected in parallel across both ends of the second discharge resistor (52).

[0014] Further, a fourth turn-off switch device (44) is also connected in parallel across both ends of the third diode (25).

[0015] Further, the first turn-off switch device (41) to the fourth turn-off switch device (44) are one of IGBT, MOSFET, and thyristor.

[0016] A control method for the modular sub-module topology of a DC energy dissipation device. The control mode of the modular sub-module adopts discrete control or synchronous control, that is, the first turn-off switch device (41) and the second turn-off switch device (42) are separately and independently triggered to turn on and off, or the first turn-off switch device (41) and the second turn-off switch device (42) are selected to be triggered to turn on and off simultaneously.

[0017] Further, the control mode of the modular sub-module adopts separately and independently triggering the first turn-off switch device (41), the second turn-off switch device (42), the third turn-off switch device (43), and the fourth turn-off switch device (44) to turn on and off, or selecting to simultaneously trigger the first turn-off switch device (41) and the second turn-off switch device (42) or the third turn-off switch device (43) and the fourth turn-off switch device (44) to turn on and off.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1) The present invention integrates two sub-modules with the same structure into a sub-module structure with higher integration, which is beneficial to reducing the number of series-connected sub-modules and also reducing the requirement for the structural space of the sub-modules.

[0020] 2) When a fault occurs in the receiving-end system, the turn-off semiconductor switch in the energy-consuming circuit of the sub-module will receive a conduction signal, precisely control the DC energy-dissipating device to quickly consume the excess electric energy on the line, avoid the voltage increase caused by the accumulation of electric energy, and thus maintain the stability of the system.

[0021] 3) Add two turn-off semiconductor switches (the third and fourth turn-off switching devices) at the sub-module ports. The conventional topology can only switch the energy-dissipating resistor and cannot cut off the capacitor. This topology provides the possibility of quickly switching the sub-module during operation. It realizes the complete control of the energy-dissipating sub-module and can completely control the voltage and current of the energy-dissipating branch. For example, in the initial stage of an AC fault in the receiving-end system, the DC energy-dissipating device is quickly controlled to consume the excess electric energy on the line. This control method uses the turn-off semiconductor switch at the port to actively control the removal / insertion of the sub-module, thereby controlling the electric energy consumed by the DC energy-dissipating device. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the multi-sub-module series topology structure diagram of the DC energy-dissipating device;

[0023] Figure 2 is the electrical diagram of Embodiment 1 of the modular sub-module topology of a DC energy-dissipating device of the present invention;

[0024] Figure 3 is the electrical diagram of Embodiment 2 of the modular sub-module topology of a DC energy-dissipating device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The following provides a detailed description of the specific embodiments provided by the present invention in conjunction with the accompanying drawings.

[0026] As Figure 1 shown, an embodiment of the DC energy-dissipating device composed of the various sub-modules mentioned in the present invention connected in series with each other. In the field of DC power transmission, when an AC fault occurs in the receiving-end system and the line transmission power cannot flow into the receiving-end system, with the accumulation of energy, the DC-side line voltage will rise sharply. This will bring risks of power system outage or equipment damage. In this case, the DC energy-dissipating device installed in the receiving-end system will consume the excess electric energy in a short time to ensure that the DC voltage is within a reasonable range. When the AC-side fault in the receiving-end system is cleared, the system can resume normal operation again and achieve AC fault ride-through. Figure 1It is also shown that in the DC energy dissipation device (12), the control system (82) communicates with each sub-module (62) through an optical fiber (72). The optical fiber (72) sends the voltage and current of the sub-module and the states of each turn-off semiconductor switch to the control system, and the control system will process this information. When a fault occurs in the receiving-end system, the control system will send the control signal for turning on the turn-off semiconductor switch to the sub-module through the optical fiber (72).

[0027] As Figure 2 shown, the modular sub-module topology of a DC energy dissipation device according to the present invention, the modular sub-module (62) includes an upper module and a lower module connected in series, and the upper and lower modules have the same electrical structure and share a bypass switch (92).

[0028] The upper module includes a first energy storage capacitor (31) and a first discharge resistor (51); it also includes a first turn-off switch device (41), and the first turn-off switch device (41) is connected in series with the first discharge resistor (51) and then connected in parallel with the first energy storage capacitor (31);

[0029] The upper module also includes two diodes connected in series: a first diode (21) and a second diode (22). After the two diodes are connected in series, the negative pole is connected to the positive pole of the first energy storage capacitor (31), and the positive pole is connected to the negative pole of the first energy storage capacitor (31). The middle point of the two diodes connected in series is the positive pole access point X1 of the modular sub-module (62).

[0030] A first anti-parallel diode (23) is also connected in parallel at both ends of the first turn-off switch device (41) of the upper module; a second anti-parallel diode (24) is also connected in parallel at both ends of the first discharge resistor (51).

[0031] A third turn-off switch device (43) is also connected in parallel at both ends of the second diode (22).

[0032] The lower module includes a second energy storage capacitor (32) and a second discharge resistor (52); it also includes a second turn-off switch device (42), and the second turn-off switch device (42) is connected in series with the second discharge resistor (52) and then connected in parallel with the second energy storage capacitor (32).

[0033] The lower module also includes two diodes connected in series: a third diode (25) and a fourth diode (26). After the two diodes are connected in series, the negative pole is connected to the positive pole of the second energy storage capacitor (32), and the positive pole is connected to the negative pole of the second energy storage capacitor (32). The middle point of the two diodes connected in series is the negative pole access point X2 of the modular sub-module (62).

[0034] A third anti-parallel diode (28) is also connected in parallel across both ends of the second turn-off switch device (42) of the lower module; a fourth anti-parallel diode (27) is also connected in parallel across both ends of the second discharge resistor (52).

[0035] A fourth turn-off switch device (44) is also connected in parallel across both ends of the third diode (25).

[0036] The first turn-off switch device (41) to the fourth turn-off switch device (44) are one of IGBT, MOSFET, and thyristor.

[0037] The principle of the present invention is as follows:

[0038] 1) Figure 2 The modular sub-module (62) of the first embodiment includes a first diode (21), a second diode (22), a third diode (25), a fourth diode (26), a first energy storage capacitor (31), and a second energy storage capacitor (32) to form a parallel energy storage circuit. The first turn-off switch device (41), the second turn-off switch device (42), the first discharge resistor (51), and the second discharge resistor (52) are connected in series to form a power consumption circuit. The components in the power consumption circuit are respectively connected in anti-parallel with the first anti-parallel diode (23), the second anti-parallel diode (24), the third anti-parallel diode (27), and the fourth anti-parallel diode (28). The number of sub-modules contained in the DC energy dissipation device is reduced, so the number of optical fibers used in the control system is reduced, greatly reducing the economic cost.

[0039] The sub-module (62) can achieve current controllability through the first turn-off switch device (41) and the second turn-off switch device (42), thereby realizing energy conversion, and controlling each semiconductor power switch element by a common method in MMC technology. When the turn-off semiconductor switch is turned on, the corresponding series-connected power consumption resistor converts the current energy into heat energy. When the turn-off semiconductor switch is turned off, no current will pass through the corresponding series-connected power consumption resistor. The diodes connected in anti-parallel with the power consumption circuit can provide freewheeling and protection for key devices. When a fault occurs in the internal components of the sub-module (62), the control system closes the bypass switch (92) to bypass the faulty sub-module and ensure the stable operation of the DC energy dissipation device.

[0040] To increase flexibility, the control mode of the sub-module (62) can adopt discrete control or synchronous control, that is, the first turn-off switch device (41) or the second turn-off switch device (42) can be independently triggered to turn on and off, or the first turn-off switch device (41) and the second turn-off switch device (42) can be selected to be triggered to turn on and off simultaneously.

[0041] 2) Figure 3The modular sub-module (64) of the second embodiment is shown. Compared with the sub-module (62), the third turn-off switch device (43) and the fourth turn-off switch device (44) are added to the sub-module (64). When the HVDC transmission system operates normally, the DC energy discharging device (12) installed in the receiving-end system operates in a non-energy-discharging state. At this time, the first discharging resistor (51) and the second discharging resistor (52) of each sub-module (64) are not connected, and the voltages of the first energy storage capacitor (31) and the second energy storage capacitor (32) are stable.

[0042] When a fault occurs on the AC side of the receiving-end system, resulting in excess electrical energy on the line, the control system (82) of the DC energy discharging device (12) will selectively cut off some of the sub-modules (64) through the third turn-off switch device (43) and the fourth turn-off switch device (44) at the port, and then quickly absorb the energy on the DC line through the energy storage capacitor to accelerate the response speed of the energy discharging circuit. Then, the first turn-off switch device (41) and the second turn-off switch device (42) of the energy-consuming circuit of the remaining sub-modules (64) are turned on. Since the third turn-off switch device (43) and the fourth turn-off switch device (44) are configured at the port of a sub-module, when using this control method, the first discharging resistor (51) or the second discharging resistor (52) to be cut off / inserted can be selected more flexibly, so as to achieve a more flexible and accurate control effect.

[0043] For the second embodiment, the first turn-off switch device (41), the second turn-off switch device (42), the third turn-off switch device (43), and the fourth turn-off switch device (44) can be independently triggered to turn on and off, or the first turn-off switch device (41), the second turn-off switch device (42) or the third turn-off switch device (43), the fourth turn-off switch device (44) can be selected to be triggered to turn on and off simultaneously.

[0044] The above embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation manners and specific operation processes are given, but the protection scope of the present invention is not limited to the above embodiments. The methods used in the above embodiments are all conventional methods unless otherwise specified.

Claims

1. A modular sub-module topology of a DC energy discharging device, characterized in that, The modular sub-module includes an upper module and a lower module connected in series. The electrical structures of the upper module and the lower module are the same, and they share a bypass switch (92). The upper module includes a first energy storage capacitor (31) and a first discharge resistor (51); it also includes a first turn-off switch device (41). The first turn-off switch device (41) and the first discharge resistor (51) are connected in series and then connected in parallel with the first energy storage capacitor (31); it also includes two series-connected diodes: a first diode (21) and a second diode (22). After the two diodes are connected in series, the negative electrode is connected to the positive electrode of the first energy storage capacitor (31), and the positive electrode is connected to the negative electrode of the first energy storage capacitor (31). The midpoint of the two series-connected diodes is the positive electrode access point X1 of the modular sub-module. A third turn-off switch device (43) is also connected in parallel across the two ends of the second diode (22). The lower module includes a second energy storage capacitor (32) and a second discharge resistor (52); it also includes a second turn-off switch device (42). The second turn-off switch device (42) and the second discharge resistor (52) are connected in series and then connected in parallel with the second energy storage capacitor (32); it also includes two series-connected diodes: a third diode (25) and a fourth diode (26). After the two diodes are connected in series, the negative electrode is connected to the positive electrode of the second energy storage capacitor (32), and the positive electrode is connected to the negative electrode of the second energy storage capacitor (32). The midpoint of the two series-connected diodes is the negative electrode access point X2 of the modular sub-module. A fourth turn-off switch device (44) is also connected in parallel across the two ends of the third diode (25). When a fault occurs on the AC side of the receiving-end system, resulting in an excess of electrical energy on the line, the control system (82) of the DC energy dissipation device (12) will selectively cut off some of the sub-modules (64) through the third turn-off switch device (43) and the fourth turn-off switch device (44) at the port, and then quickly absorb the energy on the DC line through the energy storage capacitor to accelerate the response speed of the energy dissipation loop. Then, the first turn-off switch device (41) and the second turn-off switch device (42) of the energy dissipation loop of the remaining sub-modules (64) are turned on.

2. The modular sub-module topology of a DC energy discharging device according to claim 1, characterized in that, A first anti-parallel diode (23) is also connected in parallel across the two ends of the first turn-off switch device (41) of the upper module; a second anti-parallel diode (24) is also connected in parallel across the two ends of the first discharge resistor (51).

3. The modular sub-module topology of a DC energy dissipation device according to claim 1, characterized in that, A third anti-parallel diode (28) is also connected in parallel across the two ends of the second turn-off switch device (42) of the lower module; a fourth anti-parallel diode (27) is also connected in parallel across the two ends of the second discharge resistor (52).

4. The modular sub-module topology of a DC energy-dissipating device according to claim 1, wherein The first turn-off switch device (41) to the fourth turn-off switch device (44) are one of IGBT, MOSFET, and thyristor.

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