Series distributed direct current energy consumption device and offshore wind power flexible direct current system

Abstract

The invention discloses a series distributed direct current energy consumption device and an offshore wind power flexible direct current system, according to the series distributed direct current energy consumption device provided by the invention, a main loop switch module and an energy consumption valve module are arranged between a submarine cable port and an overhead line port, and the main loop switch module and the energy consumption valve module are connected in parallel; a plurality of energy-consuming valve units are connected in series in the energy-consuming valve module, and each energy-consuming valve unit comprises an energy-consuming resistor and a switch element used for controlling the energy-consuming resistor to be switched on or switched off; the control module is used for controlling on-off of switch elements in the main loop switch module and the energy consumption valve module. When the overhead line breaks down, the device controls the main loop switch module to be switched off through the control module, so that direct current flows through a loop where the energy consumption valve module is located, then the total energy consumed by the energy consumption loop is controlled by controlling the switching number of energy consumption resistors of all the energy consumption valve units, and balance of surplus power of a system is achieved.

Description

Technical Field

[0001] The present application relates to the field of offshore wind power technology, and in particular to a series distributed direct current energy consumption device and an offshore wind power system. Background Art

[0002] With its high utilization rate and abundant resource reserves, offshore wind power is rapidly becoming one of the key areas for the development of new energy sources at present and in the future. As the scale of offshore wind power continues to expand and the transmission distance increases, intensive and centralized unified development and utilization will be the main way to utilize offshore wind power in the future. At present, offshore wind power is generally sent to onshore converter stations via submarine DC cables, and then the DC is converted into AC through converters and connected to the coastal power grid. However, with the rapid growth of the scale of offshore wind power development, this offshore wind power nearshore grid connection method is no longer suitable for future ultra-large-scale offshore wind power development scenarios. In order to further compress the transmission corridor, reduce the transmission cost, and avoid increasing the short-circuit current of the nearshore power grid, offshore wind power will be directly sent to the load center via a hybrid DC line of submarine cables and overhead lines, which will become one of the main ways to develop ultra-large-scale offshore wind power in the future.

[0003] In existing offshore wind power flexible direct current transmission projects, generally only direct current submarine cables are used for power transmission, and parallel direct current energy consumption devices are used to achieve fault voltage regulation. The specific principle is: after a fault occurs in the receiving power grid, the direct current voltage increases, and the parallel direct current energy consumption device is started to consume surplus power and maintain the direct current voltage. However, this device is not suitable for offshore wind power flexible direct current systems that are a mixture of submarine cables and overhead lines, resulting in the technical problem of low reliability in existing offshore wind power flexible direct current systems that are a mixture of submarine cables and overhead lines. Summary of the invention

[0004] The present application provides a series-connected distributed DC energy consumption device and an offshore wind power flexible DC system, which are used to solve the technical problem of low reliability of the existing offshore wind power flexible DC system that is a mixture of submarine cables and overhead lines.

[0005] In order to solve the above technical problems, the first aspect of the present application provides a series-connected distributed DC energy consumption device, including: a submarine cable port, an overhead line port, a main circuit switch module, an energy consumption valve module and a control module;

[0006] The main circuit switch module and the energy consumption valve module are arranged between the submarine cable port and the overhead line port, and the main circuit switch module and the energy consumption valve module are connected in parallel;

[0007] The energy-consuming valve module is connected in series with a plurality of energy-consuming valve units, each of which comprises an energy-consuming resistor and a switch element for controlling the energy-consuming resistor to be switched in or out;

[0008] The control module is used to control the on and off of the switch elements in the main circuit switch module and the energy consumption valve module.

[0009] Preferably, the main circuit switch module specifically comprises: a main circuit mechanical switch and a power electronic switch connected in series in sequence.

[0010] Preferably, the power electronic switch is specifically a switch array composed of a plurality of SM sub-modules.

[0011] Preferably, the SM submodule is specifically: a full-bridge submodule.

[0012] Preferably, the energy-consuming valve unit specifically comprises: a first diode, a first switch tube, a dynamic voltage-sharing resistor, an energy storage capacitor, a second diode, a second switch tube and an energy-consuming resistor;

[0013] The cathode of the first diode is connected to the first port of the energy-consuming valve unit, and the anode is connected to the second port of the energy-consuming valve unit;

[0014] The first switch tube is connected in parallel with the first diode, and an anode of the first switch tube is connected to a first port of the energy-consuming valve unit, and a cathode of the first switch tube is connected to a second port of the energy-consuming valve unit;

[0015] The dynamic voltage-equalizing resistor is connected in parallel with the second diode, and one end of the dynamic voltage-equalizing resistor is connected to the anode of the second diode and the first port of the energy-consuming valve unit, and the other end of the dynamic voltage-equalizing resistor is connected in series with the cathode of the second diode and the energy storage capacitor, and then connected to the second port of the energy-consuming valve unit, to form an RCD buffer circuit;

[0016] The energy dissipation resistor and the second switch tube are connected in series to form an energy dissipation resistor loop, and the energy dissipation resistor loop is connected in parallel with the RCD buffer loop.

[0017] Preferably, the energy-consuming valve unit further includes: an energy-consuming valve bypass switch;

[0018] The energy-consuming valve bypass switch is used to control the input or output of the energy-consuming valve unit.

[0019] The second aspect of the present application provides an offshore wind power flexible direct current system, comprising: an offshore converter station, a terminal conversion station and an onshore converter station, wherein the terminal conversion station is provided with a series-connected distributed direct current energy consumption device as described in the first aspect of the present application;

[0020] The offshore converter station is connected to the submarine cable port in the series distributed DC energy consumption device via a submarine cable;

[0021] The onshore converter station is connected to an overhead line port in the series-connected distributed DC energy consumption device through an overhead line.

[0022] Preferably, the offshore converter station is specifically a half-bridge MMC converter station.

[0023] Preferably, the onshore converter station is specifically a full half-bridge hybrid MMC converter station.

[0024] Preferably, the proportion of full-bridge sub-modules in the full-half-bridge hybrid MMC converter station is greater than 50%.

[0025] It can be seen from the above technical solutions that this application has the following advantages:

[0026] The present application provides a series distributed DC energy consumption device applicable to an offshore wind power flexible DC system of a submarine cable-overhead line hybrid line, comprising: a submarine cable port, an overhead line port, a main circuit switch module, an energy consumption valve module and a control module; the main circuit switch module and the energy consumption valve module are arranged between the submarine cable port and the overhead line port, and the main circuit switch module and the energy consumption valve module are connected in parallel; a plurality of energy consumption valve units are connected in series in the energy consumption valve module, and each energy consumption valve unit comprises an energy consumption resistor and a switch element for controlling the energy consumption resistor to be put in or cut out; the control module is used to control the on and off of the switch elements in the main circuit switch module and the energy consumption valve module. When an overhead line fails, the voltage at the overhead line port of the series-connected distributed DC energy-consuming device is controlled to zero according to the fixed DC voltage control commonly used in the onshore converter station. Considering the voltage drop of the overhead line, the DC voltage at the port of the onshore converter station is negative. At this time, the device controls the main circuit switch module to disconnect through the control module, so that the DC current flows through the circuit where the energy-consuming valve module is located, and then controls the number of energy-consuming resistors of each energy-consuming valve unit to be switched on and off, thereby controlling the total energy consumed by the energy-consuming circuit and achieving system surplus power balance.

[0027] The proposed solution solves the fault ride-through and surplus power balance problems of the DC system of the submarine cable-overhead line hybrid line. The offshore converter station can adopt a half-bridge topology, which reduces the investment cost and construction difficulty of the offshore converter station. By controlling the input and output of distributed energy-consuming resistors, the surplus power can be accurately consumed with small power fluctuations. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0029] Figure 1 A schematic diagram of the architecture of an offshore wind power flexible direct current system including a submarine cable-overhead line hybrid line provided for this application.

[0030] Figure 2A schematic structural diagram of an embodiment of a series-connected distributed DC energy consumption device provided in the present application.

[0031] Figure 3 This is a schematic diagram of the circuit structure of the SM submodule in the series distributed DC energy consumption device provided in this application.

[0032] Figure 4 A schematic diagram of the circuit structure of the energy-consuming valve unit in the series-connected distributed DC energy-consuming device provided in the present application.

[0033] Figure 5 A schematic diagram of the control logic flow of a series distributed DC energy consumption device and an offshore wind power flexible DC system provided in this application. DETAILED DESCRIPTION

[0034] In view of the problems existing in the existing technology, it has been found through research that since the existing offshore wind power flexible direct current transmission projects generally only use direct current submarine cables, there is no need to consider the problem of direct current fault ride-through. However, the fault rate of overhead lines is high and direct current faults cannot be ignored. After a fault occurs in the overhead line, in addition to clearing the direct current fault, the system also needs to consume the system surplus power to avoid the direct current voltage being too high to trigger the system protection and cause shutdown, or even endanger the safety of the equipment. Therefore, it is necessary to install energy-consuming devices in the system. However, the offshore wind power flexible direct current system of the submarine cable-overhead line hybrid direct current line needs to consider the problem of direct current fault ride-through. However, based on the full half-bridge hybrid direct current line, the DC fault ride-through problem is not solved. When clearing a DC fault, the MMC needs to reduce the DC voltage to zero or negative voltage, which conflicts with the need to maintain a stable DC voltage when the parallel DC energy consumption device is working. Therefore, the parallel DC energy consumption device is not compatible with the submarine cable-overhead line hybrid line flexible DC system, and cannot effectively consume surplus power for the submarine cable-overhead line hybrid line system, resulting in the current technical status quo of low reliability of the existing offshore wind power flexible DC system that is a hybrid of submarine cables and overhead lines. Therefore, seeking a surplus power consumption solution that is compatible with the submarine cable-overhead line hybrid line system has become one of the key research goals of technical personnel in this field.

[0035] The present application provides a series-connected distributed DC energy consumption device and an offshore wind power flexible DC system, which are used to solve the technical problem of low reliability of the existing offshore wind power flexible DC system that is a mixture of submarine cables and overhead lines.

[0036] In order to make the purpose, features, and advantages of the invention of this application more obvious and easy to understand, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the embodiments described below are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0037] First, a detailed description of an offshore wind power flexible direct current system embodiment including a submarine cable-overhead line hybrid line provided by the present application is as follows:

[0038] This embodiment proposes a submarine cable-overhead line hybrid line offshore wind power flexible direct current system based on the series connection of distributed direct current energy consumption devices. Figure 1 As shown, the submarine cable-overhead line hybrid offshore wind power flexible direct current system includes an offshore converter station, a submarine cable, a terminal conversion station, an overhead line, and an onshore converter station. The offshore converter station adopts a half-bridge MMC, and the onshore converter station adopts a full half-bridge hybrid MMC. The full-bridge ratio needs to be greater than 50%, and generally 60% is used.

[0039] Figure 1 The terminal conversion station in the embodiment is a node where the submarine cable and the overhead line are connected. The station is provided with a series distributed DC energy consumption device as provided in the present application. The device structure is as follows: Figure 2 As shown, it includes: a submarine cable port, an overhead line port, a main circuit switch module, an energy consumption valve module and a control module (not shown in the figure);

[0040] The main circuit switch module and the energy consumption valve module are arranged between the submarine cable port and the overhead line port, and the main circuit switch module and the energy consumption valve module are connected in parallel;

[0041] More specifically, the main circuit switch module specifically includes: a main circuit mechanical switch and a power electronic switch array connected in series in sequence.

[0042] More specifically, the power electronic switch is a switch array composed of a plurality of SM submodules. The SM submodule preferably adopts a full-bridge submodule, wherein a feasible topology is as follows: Figure 3 As shown in FIG. 1 , the topology is: a full-bridge module composed of a power device, an anti-parallel diode and a capacitor. When the power device is in the on state, the capacitor voltage is zero. When the power device is in the off state, the DC current charges the capacitor and the capacitor voltage rises.

[0043] It should be noted that the power electronic switch array is used to control the on-off of current. Since the current carrying capacity of the IGBT device is limited, a single SM cannot bear the rated DC current. Therefore, the power electronic switch array of this embodiment can shunt the current by connecting multiple SMs in parallel to improve the current carrying capacity of the main circuit.

[0044] The energy-consuming valve module is connected in series with a plurality of energy-consuming valve units, each of which comprises an energy-consuming resistor and a switch element for controlling the energy-consuming resistor to be switched in or out;

[0045] The control module is used to control the on and off of the switch elements in the main circuit switch module and the energy consumption valve module.

[0046] More specifically, if Figure 4 As shown, the energy consumption valve unit specifically includes: a first diode D1, a first switch tube T1, a dynamic voltage balancing resistor R d , energy storage capacitor C, second diode D2, second switch tube T2 and energy dissipation resistor R ch ;

[0047] The cathode of the first diode D1 is connected to the first port of the energy-consuming valve unit, and the anode is connected to the second port of the energy-consuming valve unit;

[0048] The first switch tube is connected in parallel with the first diode D1, and an anode of the first switch tube D1 is connected to a first port of the energy-consuming valve unit, and a cathode of the first switch tube D1 is connected to a second port of the energy-consuming valve unit;

[0049] The dynamic voltage balancing resistor R d The second diode D2 is connected in parallel, and the dynamic voltage balancing resistor R d One end of the second diode D2 and the anode of the second diode D2 and the first port of the energy consumption valve unit, the dynamic voltage balancing resistor R d The other end is connected in series with the cathode of the second diode D2 and the energy storage capacitor C, and then connected to the second port of the energy consumption valve unit to form an RCD buffer loop;

[0050] The energy dissipation resistor R ch The second switch tube T2 is connected in series to form an energy-consuming resistance loop, and the energy-consuming resistance loop is connected in parallel with the RCD buffer loop.

[0051] It should be noted that a single energy-consuming valve consists of a capacitor C and a dynamic voltage-equalizing resistor R d , diode D2, energy dissipation resistor R ch , integrated gate commutated thyristors (IGCT) T1 and T2, anti-parallel diode D1, bypass switch K, R d Connected in parallel with D2 and then in series with capacitor C to form an RCD snubber circuit. ch Together with T2, it forms an energy-consuming circuit. The RCD buffer circuit and the energy-consuming circuit are then connected in parallel with T1, D1 and K. When T1 is turned on, the capacitor voltage is zero. When T1 is turned off, the current charges the capacitor through the RCD buffer circuit. The capacitor voltage can be controlled by controlling the on and off of T1. When the capacitor voltage is maintained at the rated voltage, turn on T2 to connect the energy-consuming resistor to consume the surplus power of the system. Turn off T2 to cut out the energy-consuming resistor. By controlling the on and off of T2, the surplus power of the system can be accurately consumed. The anti-parallel diode D1 is used to reverse the DC current when the offshore converter station is started. The bypass switch K is activated when the voltage of the energy-consuming valve is too high to protect the device from overvoltage damage.

[0052] The energy-consuming valve unit mentioned in this embodiment is not only Figure 5 This topology structure shown in the figure can be used to control the energy dissipation resistor R ch Energy-consuming circuit topologies with input and output functions can be used as alternative implementations.

[0053] More specifically, the energy-consuming valve unit further includes: an energy-consuming valve bypass switch K;

[0054] The energy-consuming valve bypass switch K is used to control the input or output of the energy-consuming valve unit. If the energy-consuming valve fails, the bypass switch will be closed, and the switch will be open under normal operating conditions.

[0055] It should be noted that if Figure 5 As shown in the figure, when the system is in steady-state operation, the offshore converter station adopts VF control to provide a stable AC voltage for the wind turbine to be connected to the grid. The onshore converter station adopts fixed DC voltage control to maintain the rated DC voltage U dc The main circuit mechanical switch and the main circuit power electronic switch array of the series distributed DC energy consumption device are both in the on state, providing a path for the DC current. The bypass switch K of the energy consumption valve in the energy consumption circuit remains in the off state, and the T1 switch is in the on state, which can provide a path for the rated current. Moreover, because the DC current rises very quickly after a DC line fault occurs, if the T1 tube remains in the on state, the increased DC current can be transferred to the energy consumption circuit T1, and there is no delay in turning on T1. The T2 switch is in the off state, and the energy consumption resistor is bypassed.

[0056] When an overhead line fails, the offshore converter station still uses VF control to maintain stable AC voltage. The onshore converter station still uses fixed DC voltage control, and the control target is to control the voltage at the overhead line port of the series-connected distributed DC energy-consuming device to zero. Considering the voltage drop of the overhead line, the DC voltage at the onshore converter station port is negative at this time. The main circuit mechanical switch and the main circuit power electronic switch of the series-connected distributed energy-consuming device are both closed, and the DC current flows through the energy-consuming circuit. The energy-consuming valve controls the voltage at both ends of the energy-consuming valve by controlling the conduction and closing of the T1 switch tube. The control target is the rated voltage U C , and satisfies 2*N*U C =U dc , where N is the number of energy-consuming valves in a single series distributed energy-consuming device, U dc is the rated voltage of the DC system.

[0057] In order to balance the system surplus power, the distributed energy consumption devices are connected in series to obtain the power P sent by the offshore converter station. w When the energy consumption valve T2 switch tube is turned on, the energy consumed by the energy consumption valve is P ch =U C 2 / R chTherefore, by controlling the switch tubes of each energy-consuming valve T2, the total energy consumed by the energy-consuming circuit can be controlled, and P w =n ch *P ch , where n ch is the number of energy-consuming valves whose T2 switch tube is in the on state.

[0058] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0059] Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0060] As described above, 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A series-connected distributed DC energy consumption device, characterized in that: include: Submarine cable port, overhead line port, main circuit switch module, energy consumption valve module and control module; The main circuit switch module and the energy consumption valve module are arranged between the submarine cable port and the overhead line port, and the main circuit switch module and the energy consumption valve module are connected in parallel; The energy-consuming valve module is connected in series with a plurality of energy-consuming valve units, each of which comprises an energy-consuming resistor and a switch element for controlling the energy-consuming resistor to be switched in or out; The control module is used to control the on and off of the switch elements in the main circuit switch module and the energy consumption valve module.

2. A series-connected distributed DC energy consumption device according to claim 1, characterized in that: The main circuit switch module specifically includes: a main circuit mechanical switch and a power electronic switch connected in series.

3. A series-connected distributed DC energy consumption device according to claim 2, characterized in that: The power electronic switch is specifically a switch array composed of a plurality of SM sub-modules.

4. A series-connected distributed DC energy consumption device according to claim 3, characterized in that: The SM submodule is specifically: a full-bridge submodule.

5. A series-connected distributed DC energy consumption device according to claim 1, characterized in that: The energy consumption valve unit specifically includes: a first diode, a first switch tube, a dynamic voltage balancing resistor, an energy storage capacitor, a second diode, a second switch tube and an energy consumption resistor; The cathode of the first diode is connected to the first port of the energy-consuming valve unit, and the anode is connected to the second port of the energy-consuming valve unit; The first switch tube is connected in parallel with the first diode, and an anode of the first switch tube is connected to a first port of the energy-consuming valve unit, and a cathode of the first switch tube is connected to a second port of the energy-consuming valve unit; The dynamic voltage-equalizing resistor is connected in parallel with the second diode, and one end of the dynamic voltage-equalizing resistor is connected to the anode of the second diode and the first port of the energy-consuming valve unit, and the other end of the dynamic voltage-equalizing resistor is connected in series with the cathode of the second diode and the energy storage capacitor, and then connected to the second port of the energy-consuming valve unit, to form an RCD buffer circuit; The energy dissipation resistor and the second switch tube are connected in series to form an energy dissipation resistor loop, and the energy dissipation resistor loop is connected in parallel with the RCD buffer loop.

6. A series-connected distributed DC energy consumption device according to claim 1, characterized in that: The energy-consuming valve unit further includes: an energy-consuming valve bypass switch; The energy-consuming valve bypass switch is used to control the input or output of the energy-consuming valve unit.

7. An offshore wind power flexible direct current system, characterized in that: include: An offshore converter station, a terminal conversion station and an onshore converter station, wherein the terminal conversion station is provided with a series-connected distributed DC energy consumption device according to any one of claims 1 to 6; The offshore converter station is connected to the submarine cable port in the series distributed DC energy consumption device via a submarine cable; The onshore converter station is connected to an overhead line port in the series-connected distributed DC energy consumption device through an overhead line.

8. The offshore wind power flexible direct current system according to claim 7, characterized in that: The offshore converter station is specifically a half-bridge MMC converter station.

9. The offshore wind power flexible direct current system according to claim 7, characterized in that: The onshore converter station is specifically a full half-bridge hybrid MMC converter station.

10. An offshore wind power flexible direct current system according to claim 9, characterized in that: The proportion of full-bridge submodules in the full-half-bridge hybrid MMC converter station is greater than 50%.

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