An energy dissipation device

Abstract

The application discloses an energy releasing device, comprising: each energy releasing module is connected with an alternating current bus, the alternating current bus is connected with an alternating current system through a transformer, and the energy releasing modules are connected in a star or angular connection mode; when the voltage peak value of any one of the alternating current buses is greater than the rated peak value of the alternating current bus by a first preset multiple, each energy releasing module is connected with the alternating current bus to consume the energy of the alternating current bus; and when the voltage peak value of each alternating current bus is less than or equal to the rated peak value of the alternating current bus by a second preset multiple, each energy releasing module is disconnected from the alternating current bus, so that the voltage of the alternating current bus is suppressed when the overvoltage of the alternating current bus occurs.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission technology, and more specifically to an energy dissipation device. Background Technology

[0002] The increasing installed capacity of new energy sources in Northwest my country has led to a "weak AC" characteristic in the region's AC power grid. A significant amount of new energy power cannot be absorbed locally and needs to be transmitted to high-load areas in the east via ultra-high voltage (UHVDC) transmission technology. UHVDC converters require substantial reactive power, typically compensated for by on-site filter stations within the converter station. Commutation failure is one cause of overvoltage in the sending-end grid of conventional UHVDC transmission. During this process, the surplus reactive power from the filter station introduces substantial transient overvoltage into the sending-end AC system, and this overvoltage increases with power surplus and line equivalent reactance. AC system faults causing additional reactive power transmission from new energy power plants can also lead to overvoltage in the later stages of fault recovery. Furthermore, overvoltage in the sending-end AC system is influenced by a combination of factors, including commutation failure and DC single / double pole blocking, all of which can contribute to overvoltage in the sending-end AC grid to varying degrees. These problems lead to overvoltages that severely restrict the safe and stable operation of the sending-end AC system, especially for weak AC systems where overvoltage is more pronounced. Extensive research has been conducted on suppressing overvoltages in sending-end AC systems, and three main approaches have been identified: Approach 1: Active optimization control and optimized reactive power compensation control at the sending end. This method mitigates overvoltage at the control source through optimized control. Optimizing control parameters can effectively increase the system response speed and control the reactive power compensation amount, thereby keeping the overvoltage at a low level. Coordination between the sending and receiving ends and reactive power compensation can effectively reduce overvoltage in the sending-end AC system. However, this method has high control requirements and may require coordination and communication between the sending and receiving ends, potentially reducing system reliability. Furthermore, uniform parameter tuning for different renewable energy plant scenarios presents significant challenges. Approach 2: Increasing the system short-circuit ratio. Compared to power surplus, this method suppresses overvoltage by increasing the system short-circuit ratio. While increasing the short-circuit ratio and reducing the system line impedance can suppress system overvoltage, this is generally achieved through reactive power compensation methods such as series capacitors on the lines. This can generate harmonics, reducing power quality, and can also cause system oscillations. Furthermore, modifying the line corridor or adding reactive power regulation devices requires significant material investment for upgrading existing UHVDC transmission systems. Method three: Passive energy consumption. This involves introducing energy consumption devices to eliminate power surplus during faults, effectively reducing overvoltage. Its effectiveness is limited by the type of energy consumption device and its corresponding control switching method. Summary of the Invention

[0003] Therefore, the technical problem to be solved by the present invention is to overcome the shortcomings of the existing AC system overvoltage suppression methods, which are prone to system oscillation and have high requirements for control methods, thereby providing an energy discharge device.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides an energy dissipation device, comprising: multiple energy dissipation modules, wherein each energy dissipation module is connected to a phase AC bus, the AC bus is connected to an AC system via a transformer, and the energy dissipation modules are connected in a star or delta configuration; when the peak voltage of any phase AC bus exceeds a first preset multiple of the rated peak voltage of the AC bus, each energy dissipation module is connected to the AC bus to consume surplus energy in the AC system and suppress overvoltage in the AC system; when the peak voltage of each phase AC bus is less than or equal to a second preset multiple of the rated peak voltage of the AC bus, each energy dissipation module is disconnected from the AC bus; the first preset multiple is greater than the second preset multiple, and the second preset multiple is a value greater than 1.

[0006] In one embodiment, each energy dissipation module includes a bypass switch and multiple energy dissipation sub-units connected in series. The energy dissipation sub-units are connected in series and then connected to a phase AC bus via the bypass switch. When the peak value of any phase AC bus voltage is greater than the rated peak value of the AC bus voltage by a first preset multiple, each bypass switch is in a closed state. When the peak value of each phase AC bus voltage is less than or equal to the rated peak value of the AC bus voltage by a second preset multiple, the bypass switch of each energy dissipation module is in an open state.

[0007] In one embodiment, when there is a limit to the number of energy dissipation subunits in each energy dissipation module, the energy dissipation modules are connected in a star configuration.

[0008] In one embodiment, the rated peak value of the AC bus voltage of the first preset multiple is less than the preset voltage threshold of the AC system.

[0009] In one embodiment, the number of energy dissipation subunits is determined by the rated power of the AC system, the AC system power factor, the rated peak value of the AC bus voltage, and the volt-ampere characteristic curve of the energy dissipation subunits.

[0010] In one embodiment, the number of energy-draining subunits is calculated using the following formula:

[0011]

[0012]

[0013] In the formula, N is the number of energy leakage subunits, and U peakThe rated peak value of the AC bus voltage is given, γ is the preset AC system power factor, P is the rated power of the AC system, and I is the rated power of the AC system. e Let λU be the current value at the operating point of the current-voltage characteristic curve of the energy dissipation subunit. peak Here, f(x) represents the preset voltage threshold and is the current-voltage characteristic curve of the energy dissipation subunit.

[0014] In one embodiment, the energy-dissipating subunit is a surge arrester.

[0015] In one embodiment, the bypass switch is a power electronic switch.

[0016] The technical solution of this invention has the following advantages:

[0017] 1. The energy dissipation device provided by this invention has each energy dissipation module connected to a phase AC bus, which is connected to the AC system via a transformer. The energy dissipation modules are connected in a star or delta configuration. When the peak voltage of any phase AC bus exceeds the rated peak voltage of the AC bus by a first preset multiple, each energy dissipation module is connected to the AC bus to dissipate the AC bus energy. When the peak voltage of each phase AC bus is less than or equal to the rated peak voltage of the AC bus by a second preset multiple, each energy dissipation module is disconnected from the AC bus. Therefore, by switching the energy dissipation modules on and off, the voltage of the AC bus can be suppressed when the AC bus is overvoltaged, avoiding the drawbacks of AC system overvoltage suppression methods that easily lead to system oscillation and have high requirements for control methods.

[0018] 2. The energy dissipation device provided by the present invention adopts the switching control of a controllable surge arrester, thereby achieving the suppression of AC bus overvoltage caused by faults, and maintaining the reliability of the switching as much as possible to ensure the overvoltage suppression effect.

[0019] 3. The energy dissipation device provided by the present invention determines the number of energy dissipation subunits based on the rated power of the AC system, the power coefficient of the AC system, the rated peak value of the AC bus voltage, and the volt-ampere characteristic curve of the energy dissipation subunit, thereby realizing the reasonable setting of the number of energy dissipation subunits and avoiding excessive energy consumption of the energy dissipation module. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figures 1(a) and 1(b) are both composition diagrams of a specific example of the energy dissipation device provided in the embodiments of the present invention;

[0022] Figures 2(a) and 2(b) are composition diagrams of another specific example of the energy dissipation device provided in the embodiments of the present invention;

[0023] Figures 3-5 All of these are simulation waveforms provided in the embodiments of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0028] Example

[0029] This invention provides an energy dissipation device for applications requiring suppression of overvoltage in AC systems, as shown in Figures 1(a) and 1(b), comprising: multiple energy dissipation modules 1.

[0030] As shown in Figures 1(a) and 1(b), each energy dissipation module in this embodiment of the invention is connected to a phase AC bus, which is connected to the AC system through a transformer, and the energy dissipation modules are connected in a star or delta configuration.

[0031] In this embodiment of the invention, when the peak value of any phase AC bus voltage is greater than the rated peak value of the AC bus voltage by a first preset multiple, each energy dissipation module is connected to the AC bus to consume the surplus energy in the AC system and suppress the overvoltage of the AC system; when the peak value of each phase AC bus voltage is less than or equal to the rated peak value of the AC bus voltage by a second preset multiple, each energy dissipation module is disconnected from the AC bus.

[0032] In this embodiment of the invention, the rated peak value of the AC bus voltage at the first preset multiple is less than the preset voltage threshold of the AC system, i.e., the first preset multiple α is greater than the second preset multiple β, and the second preset multiple β is a value greater than 1, i.e., α>β>1. The first preset multiple α is not infinitely large, but is set according to the overvoltage requirements of the AC bus of each AC system. For example, for a 35kV AC bus, some systems require suppressing the overvoltage at the 35kV bus port to within 1.3 pu (1.3 pu is the preset voltage threshold), while others require suppressing the overvoltage at the 35kV bus port to within 1.2 pu (1.2 pu is the preset voltage threshold). For safety reasons, the overvoltage of the 35kV bus can be uniformly suppressed to within 1.2 pu, thereby ensuring the reliable operation of various types of renewable energy power plants. It should be noted that the specific setting value of the first preset multiple α is set according to the actual situation and is not limited here.

[0033] In this embodiment of the invention, the difference between the first preset multiple α and the second preset multiple β needs to be relatively large. This is to ensure that the energy dissipation module has sufficient time to consume the surplus energy in the AC system, and to prevent malfunctions caused by a small difference between the first preset multiple α and the second preset multiple β when the AC bus voltage is unstable.

[0034] In one specific embodiment, as shown in Figures 2(a) and 2(b), each energy dissipation module includes a bypass switch 11 and multiple energy dissipation sub-units 12 connected in series.

[0035] As shown in Figures 2(a) and 2(b), the energy dissipation subunits of this embodiment are connected in series and then connected to a single-phase AC bus via a bypass switch.

[0036] In this embodiment of the invention, when the peak value of any phase AC bus voltage is greater than the rated peak value of the AC bus voltage by a first preset multiple, each bypass switch is in a closed state; when the peak value of each phase AC bus voltage is less than or equal to the rated peak value of the AC bus voltage by a second preset multiple, the bypass switch of each energy dissipation module is in an open state.

[0037] The energy dissipation subunit in this embodiment of the invention can be a surge arrester, but it can be any other device capable of consuming energy. The bypass switch can be a power electronic switch, which can be controlled by the controller of the AC system. The controller determines whether the peak value of the AC bus voltage is greater than a first preset multiple of the rated peak value of the AC bus voltage, or determines whether the peak value of the AC bus voltage is less than or equal to a second preset multiple of the rated peak value of the AC bus voltage. When the peak value of the AC bus voltage is greater than the first preset multiple of the rated peak value of the AC bus voltage, the controller controls each power electronic switch to close. When the peak value of the AC bus voltage is less than or equal to the second preset multiple of the rated peak value of the AC bus voltage, the controller controls each power electronic switch to open or close. In addition, the bypass switch can be any other controllable switch, which is not limited here.

[0038] In one specific embodiment of the present invention, the energy dissipation modules can generally be connected in either a delta connection or a star connection. The main difference is that in the case of a delta connection, more energy dissipation sub-units are required due to the line voltage, which leads to an increase in the total energy consumption of the energy dissipation modules. In addition, when there is a limit to the number of energy dissipation sub-units in each energy dissipation module, the energy dissipation modules are connected in a star connection.

[0039] In one specific embodiment, the number of energy dissipation subunits is determined by the rated power of the AC system, the AC system power factor, the rated peak value of the AC bus voltage, and the volt-ampere characteristic curve of the energy dissipation subunits.

[0040] Specifically, the number N of energy-discharging subunits is calculated using the following equation (1):

[0041]

[0042] In the formula, N is the number of energy leakage subunits, and U peak The rated peak value of the AC bus voltage is given, γ is the preset AC system power factor, P is the rated power of the AC system, and I is the rated power of the AC system. e Let λU be the current value at the operating point of the current-voltage characteristic curve of the energy dissipation subunit. peak Here, f(x) represents the preset voltage threshold and is the current-voltage characteristic curve of the energy dissipation subunit.

[0043] Specifically, for an AC system with a rated power of P, the energy required by the energy dissipation module can be determined based on its preset AC system power coefficient γ (power surplus coefficient) (obtained by multiplying γ by P). The energy consumed by the energy dissipation module can be expressed as... It should be equal to γP, therefore, when the rated power is determined to be P, the preset AC system power factor γ, and the rated peak value of the AC bus voltage U, peak Then, the current value I at the operating point of the current-voltage characteristic curve of the energy dissipation subunit can be determined. e And based on the current-voltage characteristic curve of the energy leakage subunit. The number of energy dissipation subunits can then be determined.

[0044] In this embodiment of the invention, the preset AC system power factor γ can be selected based on simulation and can be appropriately adjusted based on the simulation results; no restrictions are imposed here. It should be noted that the above principles are for parameter selection in a star connection; for a delta connection, the selection can be slightly adjusted after conversion based on the relationship between line voltage and phase voltage.

[0045] The parameter design process of this invention embodiment is as follows: Figure 3 As shown, taking the energy dissipation subunit as an example of a surge arrester, it is composed of... Figure 3 It can be seen that, firstly, based on the overvoltage requirements of the AC bus of each AC system, the overvoltage suppression level is determined (the preset voltage threshold is determined). According to the surge arrester model and surge arrester loss, the connection method between the energy dissipation modules is determined. According to the rated peak value of the AC bus voltage and the preset voltage threshold, the first preset multiple and the second preset multiple are determined. According to formula (1), the number of surge arresters is determined. Then, it is determined whether the AC bus overvoltage can be suppressed after all surge arresters are connected to the AC bus. When it cannot be suppressed, the step of determining the connection method between the energy dissipation modules is returned until the AC bus overvoltage can be suppressed after all surge arresters are connected to the AC bus.

[0046] To further illustrate its application effect, a case study is presented, using a surge arrester as an example, in conjunction with the control application of a new energy power station. Based on the aforementioned method and relevant engineering parameters, with a short-circuit ratio (SCR) of 2.2 and a rated power of 1000MW, a delta connection scheme with N=7.6 surge arresters and a star connection scheme with N=4 surge arresters are designed.

[0047] The simulation waveform for a single-phase metallic fault lasting 0.15s without a controllable surge arrester is as follows. Figure 3 As shown, by Figure 3 It can be seen that the system overvoltage reaches 1.31 pu, which fails to meet the specified voltage suppression standard, and power electronic equipment may be damaged or disconnected from the grid as a result. However, simulation results using the delta connection method show that the overvoltage level of the 35kV bus is significantly reduced and maintained at 1.2 pu. Figure 4 As shown, the surge arrester consumes 100MW of energy and has a peak current of 50kA. Simulation results under the same star connection method show that the overvoltage of the 35kV bus can also be maintained below 1.2pu using the star connection method. In comparison, the delta connection requires more surge arrester plates and consumes more energy than the star connection, such as... Figure 5 As shown, the surge arrester consumes 58MW of energy and has a peak current of 45kA.

[0048] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An energy dissipation device, characterized in that, include: Multiple energy dissipation modules, among which, Each energy dissipation module is connected to a single-phase AC bus, which is connected to the AC system via a transformer. The energy dissipation modules are connected in a star or delta configuration. When the peak value of any phase AC bus voltage exceeds the rated peak value of the AC bus voltage by a first preset multiple, each energy discharge module is connected to the AC bus to consume the surplus energy in the AC system and suppress the AC system overvoltage. When the peak value of the AC bus voltage of each phase is less than or equal to the rated peak value of the AC bus voltage of the second preset multiple, each energy dissipation module is disconnected from the AC bus. The first preset multiple is greater than the second preset multiple, and the second preset multiple is a value greater than 1; Each energy dissipation module includes a bypass switch and multiple energy dissipation sub-units connected in series. The energy dissipation sub-units are connected in series and then connected to one phase AC bus via the bypass switch. When the peak value of any phase AC bus voltage is greater than the rated peak value of the AC bus voltage by a first preset multiple, each bypass switch is in the closed state. When the peak value of each phase AC bus voltage is less than or equal to the rated peak value of the AC bus voltage by a second preset multiple, the bypass switch of each energy dissipation module is in the open state. The number of energy-dissipating subunits is determined by the rated power of the AC system, the AC system power factor, the rated peak value of the AC bus voltage, and the volt-ampere characteristic curve of the energy-dissipating subunit. The number of energy-dissipating subunits is calculated using the following formula: In the formula, N The number of energy-discharging subunits, U peak This is the rated peak value of the AC bus voltage. γ To preset the AC system power factor, P The rated power of the AC system, I e The value of the current at the operating point of the current-voltage characteristic curve of the energy dissipation subunit is given. λU peak For the preset voltage threshold, f ( x ( ) represents the current-voltage characteristic curve of the energy-dissipating subunit.

2. The energy dissipation device according to claim 1, characterized in that, When there is a limit to the number of energy dissipation subunits in each energy dissipation module, the energy dissipation modules are connected in a star configuration.

3. The energy dissipation device according to claim 1, characterized in that, The rated peak value of the AC bus voltage of the first preset multiple is less than the preset voltage threshold of the AC system.

4. The energy dissipation device according to claim 1, characterized in that, The energy-dissipating subunit is a surge arrester.

5. The energy dissipation device according to claim 1, characterized in that, The bypass switch is a power electronic switch.

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