A variable voltage DC energy dissipation device and its control method

Abstract

The present invention provides a variable-voltage DC energy dissipation device and its control method. The device does not need to be provided with a water-cooling system for heat dissipation. It is connected in parallel between the positive and negative poles of a high-voltage DC line. By adding a voltage conversion device between the centralized energy dissipation resistor and the switching device, the voltage across the energy dissipation resistor is reduced, the use of high-voltage wall bushings is reduced, the overall cost of the equipment is reduced while achieving the purpose of energy dissipation, and the problem of poor economy caused by high-voltage wall bushings in the energy dissipation device is solved; the energy dissipation resistor is directly connected in series with the secondary side of the transformer, with a simple structure and high reliability; the on-off of the switching device in the bridge arm can be effectively used to realize the connection and disconnection of the energy dissipation resistor. The energy dissipation device structure proposed by the present invention has the characteristics of low cost and high reliability.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible direct current power transmission protection, and in particular relates to a transformer-type direct current energy consumption device and a control method thereof. Background Art

[0002] Today, fossil energy is gradually depleting. Due to the increasingly severe environmental problems caused by traditional fossil energy, the proportion of renewable energy in the total power generation will continue to increase. Wind power generation is a relatively mature and highly potential power generation method in the current new energy power generation technology. After decades of development, offshore wind power generation has become an important part of renewable energy. With the continuous improvement of modern science and technology, offshore wind power generation will shift to the deep sea area, and the number of offshore wind turbines will further increase.

[0003] Flexible DC transmission technology based on voltage source converter has the advantages of flexible control and no need for commutation. It is a transmission technology that is extremely suitable for offshore wind power grid connection. In the flexible DC transmission system based on offshore wind power, energy consumption devices are crucial equipment. When a fault occurs at the receiving end of the system, the output power of the wind farm cannot be sent out, which will cause the voltage of the DC side transmission line to rise. At present, most offshore wind power DC transmission projects use MMC (Modular Multilevel Converter) topology. Although this type of converter structure has certain redundancy characteristics, the internal IGBT and other switching devices have limited voltage resistance. The DC voltage rise level caused by the fault at the receiving end far exceeds its normal operating range, which can easily cause various equipment in the system to fail permanently due to overvoltage.

[0004] With the continuous improvement of my country's economic construction, offshore wind power DC transmission projects will be developed on a large scale, and the requirements for their stability will become increasingly stringent. In particular, how to ensure the stability of wind farms and main power grids under fault conditions and improve the fault ride-through capability of offshore wind power generation systems are technical issues that need to be urgently addressed and important research directions.

[0005] DC energy dissipation devices mostly use centralized energy dissipation resistors or distributed energy dissipation resistors to dissipate energy. Centralized energy dissipation resistors can be separated from other components in the circuit through high-voltage wall bushings. During operation, no independent water cooling system is required for heat dissipation. The cost of high-voltage wall bushings increases with the increase of voltage levels. Distributed energy dissipation resistors are arranged in each submodule of the energy dissipation device. During the actual installation process, it is impossible to separate the energy dissipation resistors from other components in the circuit. Therefore, during operation, an independent water cooling system needs to be installed to dissipate heat so that the heat emitted by the energy dissipation resistors can be discharged in time to avoid failure of other components in the circuit due to overheating. The price is slightly expensive. Summary of the invention

[0006] The object of the present invention is to solve the problems in the prior art, and a variable-voltage DC energy-consuming device and its control method are proposed.

[0007] The present invention is realized by the following technical solutions. The present invention proposes a variable-voltage DC energy-consuming device, and the energy-consuming device includes four groups of switch bridge arms and a centralized energy-consuming module; the four groups of switch bridge arms are respectively the upper bridge arm A1, the upper bridge arm B1, the lower bridge arm B2, and the lower bridge arm A2; each group of switch bridge arms is composed of several groups of switch modules; the centralized energy-consuming module includes a transformer connected in series and a centralized energy-consuming resistor connected in series with the secondary side of the transformer.

[0008] Further, the circuit structure of each switch module is the same, including a switching tube Q1 and a varistor MOV1. The collector and emitter of the switching tube Q1 are connected in parallel with both ends of the varistor MOV1 to form a group of switch modules.

[0009] Further, the switch modules of each group between the upper and lower bridge arms are connected through the collector and emitter of the switching tube Q1; from top to bottom and from left to right, the upper and lower bridge arms are arranged as the upper bridge arm A1, the upper bridge arm B1, the lower bridge arm B2, and the lower bridge arm A2 in sequence.

[0010] Further, the centralized energy-consuming module includes a transformer T1 and an energy-consuming resistor R1; one end of the primary side of the transformer T1 is connected to the emitters of the switching tubes Q1 at the tail ends of the switch modules of the two groups of bridge arms A1 and B1, and the heads of the bridge arms A1 and B1 are connected to the positive pole of the DC bus through the collectors of the switching tubes Q1 in the first switch module in the bridge arms; the other end of the primary side of the transformer T1 is connected to the collectors of the switching tubes Q1 of the first switch modules at the heads of the other two groups of bridge arms A2 and B2, and the tails of the bridge arms A2 and B2 are connected to the negative pole of the DC bus through the emitters of the switching tubes Q1 of the last group of switch modules at the tails.

[0011] Further, both ends of the secondary side of the transformer T1 are respectively connected to both ends of the energy-consuming resistor and are arranged outdoors through high-voltage wall bushings to facilitate the release of heat generated during the energy-consuming process.

[0012] Further, the switching tube Q1 is a power semiconductor switching device, the base of the switching tube is the control end, the collector of the switching tube is the input end, and the emitter of the switching tube is the output end.

[0013] Further, each group of switch bridge arms includes 2 groups of switch modules.

[0014] The present invention also proposes a control method for a variable-voltage DC energy-consuming device, and the specific control method is as follows:

[0015] The upper bridge arm A1 and the lower bridge arm A2 are divided into one group of bridge arms, and the upper bridge arm B1 and the lower bridge arm B2 are divided into another group of bridge arms. Each group of bridge arms controls the on and off of the switching tubes by the same switching signal.

[0016] When the DC bus voltage rises, a PWM signal with a certain frequency is applied to the switching tubes in the upper bridge arm A1 and the lower bridge arm A2 to control the on-off of the switching tubes, and the upper bridge arm B1 and the lower bridge arm B2 always remain off; or a PWM signal with a certain frequency is applied to the switching tubes in the upper bridge arm B1 and the lower bridge arm B2 to control the on-off of the switching tubes, and the upper bridge arm A1 and the lower bridge arm A2 always remain off;

[0017] To generate a positive current or a reverse current in the primary side of the transformer; an induced voltage is generated in the secondary side of the transformer, and the energy-consuming resistor dissipates energy; the PWM signal applied to the switching tubes is adjusted according to the voltage across the DC bus. When the current of the energy-consuming resistor is greater than the set value, the duty cycle of the PWM signal is reduced. When the current of the energy-consuming resistor is less than the set value, the duty cycle of the PWM signal is increased to achieve the adjustment of the dissipated power.

[0018] The present invention also proposes a control method for a voltage-transforming type DC energy-consuming device, and the specific control method is as follows:

[0019] The upper bridge arm A1 and the lower bridge arm A2 are divided into a group of bridge arms, and the upper bridge arm B1 and the lower bridge arm B2 are divided into another group of bridge arms. Each group of bridge arms controls the on-off of the switching tubes by the same switching signal;

[0020] When the DC bus voltage rises, a PWM signal with a certain frequency is applied to the switching tubes in the upper bridge arm A1 and the lower bridge arm A2, and at the same time, a PWM signal opposite to it is applied to the switching tubes in the upper bridge arm B1 and the lower bridge arm B2, so as to generate a positive and negative alternating current with a certain frequency in the primary side of the transformer. At the same time, an induced voltage is generated in the secondary side, and the energy-consuming resistor dissipates energy; when the current of the energy-consuming resistor is greater than the set value, the duty cycle of the PWM signal is reduced. When the current of the energy-consuming resistor is less than the set value, the duty cycle of the PWM signal is increased to achieve the adjustment of the dissipated power.

[0021] The present invention has at least the following advantages: The present invention proposes a centralized energy-consuming device, which does not require a water cooling system for heat dissipation. It is connected in parallel between the positive and negative poles of the high-voltage DC line. By adding a voltage-transforming device between the centralized energy-consuming resistor and the switching device, the voltage across the energy-consuming resistor is reduced, and the use of high-voltage wall bushings is reduced, achieving the purpose of energy dissipation while reducing the overall cost of the equipment, and solving the problem of poor economy caused by high-voltage wall bushings in the energy-consuming device; adopting the direct series connection mode of the energy-consuming resistor and the secondary side of the transformer, the structure is simple and the reliability is high; cooperating with the on-off of the switching device in the bridge arm can effectively realize the switching on and off of the energy-consuming resistor. The energy-consuming device structure proposed by the present invention has the characteristics of low cost and high reliability. Brief Description of the Drawings

[0022] Figure 1 It is the topological structure diagram of the energy-consuming device;

[0023] Figure 2 It is the structure diagram of a single - group energy - consuming bridge arm;

[0024] Figure 3 It is the structure diagram of a single - group switch module.

[0025] The names of the labels in the figure: 1. Upper bridge arm A1; 2. Upper bridge arm B1; 3. Switch module; 4. Lower bridge arm B2; 5. Lower bridge arm A2; 6. Positive pole of DC bus; 7. Negative pole of DC bus; 8. Transformer; 9. Outer wall of building; 10. High - voltage wall - piercing bushing; 11. Dissipative resistor; 12. Switching transistor Q1; 13. Metal oxide varistor MOV1. Specific implementation manners

[0026] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described with reference to 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, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0027] The present invention proposes a centralized energy - consuming device, which does not need to set up a water - cooling system for heat dissipation. It is connected in parallel between the positive and negative poles of a high - voltage DC line. By adding a voltage - transforming device between the centralized energy - consuming resistor and the switching device, the voltage across the energy - consuming resistor is reduced, the use of high - voltage wall - piercing bushings is reduced, the overall cost of the equipment is reduced while achieving the purpose of energy dissipation, and the problem of poor economy caused by high - voltage wall - piercing bushings in the energy - consuming device is solved; the energy - consuming resistor is directly connected in series with the secondary side of the transformer, with a simple structure and high reliability; the on - off of the switching device in the bridge arm can effectively realize the switching on and off of the energy - consuming resistor. The energy - consuming device structure proposed by the present invention has the characteristics of low cost and high reliability.

[0028] Combined with Figures 1 - 3 , the present invention proposes a voltage - transforming DC energy - consuming device. The circuit structure topology diagram of this device is as Figure 1 shown. This device is arranged on the DC line. The energy - consuming device includes four groups of switch bridge arms and a centralized energy - consuming module; the four groups of switch bridge arms are respectively the upper bridge arm A1, the upper bridge arm B1, the lower bridge arm B2, and the lower bridge arm A2; each group of switch bridge arms is composed of several groups of switch modules ( Figure 1 the part within the dotted line box in

[0029] is a group of switch modules); the centralized energy - consuming module includes a transformer connected in series and a centralized energy - consuming resistor connected in series with the secondary side of the transformer. Each switch module has the same circuit structure, including a switching transistor Q1 and a metal oxide varistor MOV1. The collector and emitter of the switching transistor Q1 are connected in parallel with both ends of the metal oxide varistor MOV1 to form a group of switch modules.

[0030] The switch modules of each group between the upper and lower bridge arms are connected through the collector and emitter of the switching transistor Q1; from top to bottom and from left to right, the upper and lower bridge arms are arranged in sequence as upper bridge arm A1, upper bridge arm B1, lower bridge arm B2, and lower bridge arm A2. Each group of switch bridge arms includes 2 groups of switch modules.

[0031] The centralized energy dissipation module includes a transformer T1 and an energy dissipation resistor R1; one end of the primary side of the transformer T1 is connected to the emitter of the switching transistor Q1 of the tail-end switch modules of the two groups of bridge arms A1 and B1, and the heads of the bridge arms A1 and B1 are connected to the positive pole of the DC bus through the collector of the switching transistor Q1 in the first switch module in the bridge arm; the other end of the primary side of the transformer T1 is connected to the collector of the switching transistor Q1 of the first switch module at the head of the other two groups of bridge arms A2 and B2, and the tails of the bridge arms A2 and B2 are connected to the negative pole of the DC bus through the emitter of the switching transistor Q1 of the last group of switch modules at the tail end.

[0032] Both ends of the secondary side of the transformer T1 are respectively connected to both ends of the energy dissipation resistor, and are arranged outdoors through a high-voltage wall bushing to facilitate the release of heat generated during the energy dissipation process.

[0033] The switching transistor Q1 is a power semiconductor switching device, the base of the switching transistor is the control end, the collector of the switching transistor is the input end, and the emitter of the switching transistor is the output end.

[0034] The present invention also proposes a control method for a variable-voltage DC energy dissipation device. The specific control method is as follows:

[0035] The upper bridge arm A1 and the lower bridge arm A2 are divided into one group of bridge arms, and the upper bridge arm B1 and the lower bridge arm B2 are divided into another group of bridge arms. Each group of bridge arms controls the on and off of the switching transistor by the same switching signal;

[0036] When the DC bus voltage rises, a PWM signal with a certain frequency is applied to the switching transistors in the upper bridge arm A1 and the lower bridge arm A2 to control the on and off of the switching transistors, and the upper bridge arm B1 and the lower bridge arm B2 are always kept off; or a PWM signal with a certain frequency is applied to the switching transistors in the upper bridge arm B1 and the lower bridge arm B2 to control the on and off of the switching transistors, and the upper bridge arm A1 and the lower bridge arm A2 are always kept off;

[0037] A forward current or a reverse current is generated in the primary side of the transformer; an induced voltage is generated in the secondary side of the transformer, and the energy dissipation resistor dissipates energy; the PWM signal applied to the switching transistor is adjusted according to the voltage across the DC bus. When the current of the energy dissipation resistor is greater than the set value, the duty ratio of the PWM signal is reduced. When the current of the energy dissipation resistor is less than the set value, the duty ratio of the PWM signal is increased to achieve the adjustment of the dissipated power.

[0038] The present invention also proposes a control method for a variable-voltage DC energy dissipation device. The specific control method is as follows:

[0039] The upper arm A1 and the lower arm A2 are grouped as one set of arms, and the upper arm B1 and the lower arm B2 are grouped as another set of arms. Each set of arms controls the on and off of the switching tubes with the same switching signal.

[0040] When the DC bus voltage rises, a PWM signal with a certain frequency is applied to the switching tubes in the upper arm A1 and the lower arm A2, and at the same time, a PWM signal opposite to it is applied to the switching tubes in the upper arm B1 and the lower arm B2, so as to generate a positive and negative alternating current with a certain frequency in the primary side of the transformer. At the same time, an induced voltage is generated in the secondary side, and the energy dissipation resistor dissipates the energy. When the current of the energy dissipation resistor is greater than the set value, the duty cycle of the PWM signal is reduced. When the current of the energy dissipation resistor is less than the set value, the duty cycle of the PWM signal is increased to realize the regulation of the dissipation power.

[0041] The present invention proposes an energy dissipation device and its control method for energy dissipation after transformer voltage transformation, including a switching bridge arm, a transformer, and an energy dissipation resistor connected in parallel at the DC line end. The present invention inherits the advantage of the centralized energy dissipation device that there is no need to install an independent heat dissipation system separately, and by adding a transformer between the energy dissipation resistor and the switching bridge arm, the voltage level at both ends of the energy dissipation resistor is reduced, the use of high-voltage wall bushings in the actual application process is reduced, and the overall cost is reduced.

[0042] The above has introduced in detail a voltage-transforming DC energy dissipation device and its control method proposed by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A variable voltage DC energy consumption device, characterized in that, The energy-consuming device includes four groups of switch bridge arms and a centralized energy-consuming module; the four groups of switch bridge arms are the upper bridge arm A1, the upper bridge arm B1, the lower bridge arm B2, and the lower bridge arm A2 respectively; each group of switch bridge arms consists of several groups of switch modules; the centralized energy-consuming module includes a transformer T1 and a centralized energy-consuming resistor R1 connected in series with the secondary side of the transformer; The circuit structure of each switch module is the same, including a switching transistor Q1 and a varistor MOV1. The collector and emitter of the switching transistor Q1 are connected in parallel with both ends of the varistor MOV1 to form a group of switch modules; The switch modules of each group between the upper and lower bridge arms are connected through the collector and emitter of the switching transistor Q1; from top to bottom and from left to right, the upper and lower bridge arms are arranged as the upper bridge arm A1, the upper bridge arm B1, the lower bridge arm B2, and the lower bridge arm A2 in sequence; One end of the primary side of the transformer T1 is connected to the emitters of the switching transistors Q1 at the tail ends of the switch modules of the two groups of bridge arms A1 and B1. The heads of the bridge arms A1 and B1 are connected to the positive pole of the DC bus through the collectors of the switching transistors Q1 in the first switch module in the bridge arms; the other end of the primary side of the transformer T1 is connected to the collectors of the switching transistors Q1 at the heads of the first switch modules of the other two groups of bridge arms A2 and B2. The tails of the bridge arms A2 and B2 are connected to the negative pole of the DC bus through the emitters of the switching transistors Q1 in the last group of switch modules at the tails; 2. The device according to claim 1, characterized in that Both ends of the secondary side of the transformer T1 are respectively connected to both ends of the energy-consuming resistor and are arranged outdoors through high-voltage wall bushings to facilitate the release of heat generated during the energy-consuming process.

3. The device according to claim 2, characterized in that, The switching transistor Q1 is a power semiconductor switching device. The base of the switching transistor is the control end, the collector of the switching transistor is the input end, and the emitter of the switching transistor is the output end.

4. The device according to claim 3, characterized in that Each group of switch bridge arms includes 2 groups of switch modules.

5. A control method for a variable-voltage DC energy-consuming device according to any one of claims 1-4, characterized in that, The specific control method is as follows: The upper bridge arm A1 and the lower bridge arm A2 are divided into one group of bridge arms, and the upper bridge arm B1 and the lower bridge arm B2 are divided into another group of bridge arms. Each group of bridge arms controls the conduction and cut-off of the switching transistors with the same switching signal; When the DC bus voltage rises, a PWM signal with a certain frequency is applied to the switching transistors in the upper bridge arm A1 and the lower bridge arm A2 to control the on and off of the switching transistors, and the upper bridge arm B1 and the lower bridge arm B2 always remain off; or a PWM signal with a certain frequency is applied to the switching transistors in the upper bridge arm B1 and the lower bridge arm B2 to control the on and off of the switching transistors, and the upper bridge arm A1 and the lower bridge arm A2 always remain off; To generate a positive current or a reverse current in the primary side of the transformer; an induced voltage is generated in the secondary side of the transformer, and the energy-consuming resistor dissipates energy; the PWM signal applied to the switching transistors is adjusted according to the voltage across the DC bus. When the current in the energy-consuming resistor is greater than the set value, the duty cycle of the PWM signal is reduced. When the current in the energy-consuming resistor is less than the set value, the duty cycle of the PWM signal is increased to achieve the adjustment of the dissipated power.

6. A control method for a variable voltage DC energy dissipation device as described in any one of claims 1-4, characterized in that, The specific control method is as follows: The upper bridge arm A1 and the lower bridge arm A2 are divided into one group of bridge arms, and the upper bridge arm B1 and the lower bridge arm B2 are divided into another group of bridge arms. Each group of bridge arms controls the conduction and cut-off of the switching transistors with the same switching signal; When the DC bus voltage rises, a PWM signal with a certain frequency is applied to the switching tubes in the upper bridge arm A1 and the lower bridge arm A2, and at the same time, a PWM signal opposite to it is applied to the switching tubes in the upper bridge arm B1 and the lower bridge arm B2, so as to generate a positive and negative alternating current with a certain frequency on the primary side of the transformer. At the same time, an induced voltage is generated on the secondary side, and the energy-consuming resistor dissipates energy. When the current of the energy-consuming resistor is greater than the set value, the duty cycle of the PWM signal is reduced. When the current of the energy-consuming resistor is less than the set value, the duty cycle of the PWM signal is increased to realize the regulation of the dissipation power.

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