Filter circuit, filter control device and filter control method
By designing multiple parallel filter branches and dynamically controlled filter branches in the converter, the problem of poor low-frequency harmonic suppression effect of LCL filter topology is solved, and wide-band harmonic filtering effect and resonance prevention are achieved.
Patent Information
- Application Number
- CN202411182915.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-26
- Publication Date
- 2026-03-13
AI Technical Summary
Existing LCL filter topologies have poor suppression of low-frequency harmonics in converters and are prone to resonance of grid-side equipment due to background harmonics in the power grid.
Design a filter circuit and control method. By setting up multiple parallel filter branches, each branch contains different resonant parameter adjustment devices and on/off control devices, and combining the control devices to detect power grid harmonics, the on/off of the filter branches is dynamically controlled to achieve wideband harmonic filtering.
It effectively filters out harmonics in various frequency bands, improves the harmonic filtering effect, avoids the resonant fault of the converter, and realizes wide-band filtering function.
Smart Images
Figure CN121663962A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of circuit technology, and in particular to a filter circuit, a filter control device, and a filter control method. Background Technology
[0002] Reactors and filter capacitors are typically installed between the grid side of the converter and the power grid. The reactors, filter capacitors, and the equivalent leakage inductance of the transformer substation on the grid side form an LCL filter topology. Because the filter capacitors exhibit low impedance to high-frequency harmonics, they can effectively absorb high-frequency harmonics. Therefore, the LCL filter topology can effectively filter out high-frequency harmonics, but its suppression effect on low-frequency harmonics is relatively poor. Summary of the Invention
[0003] In view of this, the embodiments of this specification provide a filtering circuit, a filtering control device, and a filtering control method to effectively filter out harmonics in various frequency bands, have a wide-band filtering function, and improve the harmonic filtering effect in various frequency bands.
[0004] In a first aspect, embodiments of this specification provide a filtering circuit, which includes a first inductor, a first capacitor, and multiple filtering branches; a first end of the first capacitor is used to connect the stator of a generator and the first end of the first inductor, and a second end of the first capacitor is connected to multiple filtering branches; the multiple filtering branches are connected in parallel; the second end of the first inductor is connected to a doubly-fed converter; at least some of the filtering branches include resonant parameter adjustment devices, and the resonant parameter adjustment devices in different filtering branches are different; the filtering branches also include on / off control devices for controlling the on / off state of the filtering branches and the first inductor.
[0005] The aforementioned resonant parameter adjustment devices include resonant peak adjustment devices and / or resonant frequency point adjustment devices.
[0006] If the filter branch includes a resonant parameter adjustment device, the resonant parameter adjustment device in the filter branch includes: a resistor device for reducing the resonant peak value; or a second inductor device for reducing the resonant frequency point; or a second capacitor device for increasing the resonant frequency point.
[0007] The aforementioned filter branches include several of the following: a first branch, which includes a first on / off control device and a resistor; the first on / off control device and the resistor are connected in series; a second branch, which includes a second on / off control device and a second inductor; the second on / off control device and the second inductor are connected in series; a third branch, which includes a third on / off control device and a second capacitor; the third on / off control device and the second capacitor are connected in series; and a fourth branch, which includes a fourth on / off control device.
[0008] The aforementioned first capacitor device includes an AC capacitor.
[0009] Secondly, embodiments of this specification provide a filtering control device, which includes a filtering circuit and a controller; the controller is used to connect to the power grid and detect harmonics of the power grid, and the controller is connected to the filtering circuit and controls the on / off state of the filtering branch in the filtering circuit.
[0010] The aforementioned control device is connected to the on / off control device in each filter branch of the filter circuit, and is used to control the on / off state of the on / off control device.
[0011] Thirdly, this specification provides a filtering control method applied to the aforementioned filtering control device. The method includes: under the operating conditions of the doubly-fed converter, controlling the fourth on / off control device in the filtering circuit to be connected, and disconnecting the first on / off control device, the second on / off control device, and the third on / off control device; determining the first resonant frequency point of the filtering circuit; acquiring the background harmonics of the power grid, and determining whether the doubly-fed converter resonates based on the background harmonics of the power grid and the first resonant frequency point; if the doubly-fed converter resonates, controlling the fourth on / off control device to be disconnected, and controlling the target on / off control device to be connected; wherein, the target on / off control device includes one or more of the first on / off control device, the second on / off control device, and the third on / off control device.
[0012] The steps for determining whether a doubly-fed converter resonates based on the background harmonics of the power grid and the first resonant frequency point include: detecting a specified frequency band harmonic from the background harmonics of the power grid; if the harmonic distortion of the specified frequency band harmonic is greater than a preset harmonic distortion threshold, and the specified frequency band harmonic covers the first resonant frequency point, it is determined that the doubly-fed converter resonates.
[0013] The steps for connecting the control target on / off controller mentioned above include: controlling the second on / off control device to connect.
[0014] Following the steps of controlling the second on / off control device to connect, the method further includes: obtaining the second resonant frequency point of the filter circuit after the second on / off control device is connected; determining whether the doubly-fed converter resonates based on the power grid background harmonics and the second resonant frequency point; and controlling the first on / off control device to connect if the doubly-fed converter resonates.
[0015] After the steps of controlling the second on / off control device and the second on / off control device to be connected, the method further includes: obtaining the third resonant frequency point of the filter circuit when both the first on / off control device and the second on / off control device are connected; determining whether the doubly-fed converter is resonating based on the power grid background harmonics and the third resonant frequency point; if the doubly-fed converter is resonating, controlling the first on / off control device and the second on / off control device to be disconnected, and controlling the third on / off control device to be connected.
[0016] After the above steps of controlling the third on / off control device to connect, the method further includes: obtaining the fourth resonant frequency point of the filter circuit after the third on / off control device is connected; determining whether the doubly-fed converter resonates based on the power grid background harmonics and the fourth resonant frequency point; and controlling the first on / off control device to connect if the doubly-fed converter resonates.
[0017] After the steps described above, if the doubly fed converter resonates, the method further includes: determining that the harmonic distortion of a specified frequency band harmonic in the background harmonics of the power grid is less than or equal to a preset harmonic distortion threshold, controlling the target on / off control device to disconnect, and controlling the fourth on / off control device to connect.
[0018] The above method also includes: detecting the on / off status of the grid-side circuit breaker of the doubly-fed converter under standby conditions; if the grid-side circuit breaker is open, the first on / off control device, the second on / off control device, the third on / off control device and the fourth on / off control device in the control filter circuit are all disconnected.
[0019] The aforementioned filtering circuit, filtering control device, and filtering control method include a first inductor, a first capacitor, and multiple filtering branches; the first end of the first capacitor is used to connect the stator of the generator and the first end of the first inductor, and the second end of the first capacitor is connected to multiple filtering branches; the multiple filtering branches are connected in parallel; the second end of the first inductor is connected to a doubly-fed converter; at least some of the filtering branches include resonant parameter adjustment devices, and the resonant parameter adjustment devices in different filtering branches are different; the filtering branches also include on / off control devices for controlling the on / off state between the filtering branches and the first inductor.
[0020] This filtering circuit has multiple parallel filtering branches, each with a different resonant parameter adjustment device. By controlling the on / off state of the on / off control devices in the filtering branches, different resonant parameter adjustment devices can be connected, thereby filtering out the frequency band harmonics present in the current circuit. By connecting different resonant parameter adjustment devices, harmonics in each frequency band can be effectively filtered out, providing a wide-band filtering function and improving the harmonic filtering effect in each frequency band.
[0021] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description
[0022] To more clearly illustrate the specific embodiments of this application 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 this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0023] Figure 1 This is a schematic diagram showing the connection of the generator, doubly fed converter, and LCL filter topology in related technologies.
[0024] Figure 2 A schematic diagram of a filter circuit provided in an embodiment of this specification;
[0025] Figure 3 This specification provides a schematic diagram of the specific structure and connection of a filter circuit as illustrated in an embodiment.
[0026] Figure 4 A schematic diagram of a filtering control device provided in the embodiments of this specification;
[0027] Figure 5 A detailed connection diagram of the filter control device, generator, and doubly fed converter provided in the embodiments of this specification;
[0028] Figure 6 This is a flowchart of a filtering control method provided in an embodiment of this specification. Detailed Implementation
[0029] To make the objectives, technical solutions, and advantages of the embodiments in this specification clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0030] See Figure 1 The diagram shows the connection of the generator, doubly-fed converter, and LCL filter topology. A filter device is connected to the grid-side inverter circuit of the doubly-fed converter for high and low frequency filtering. The filter device includes a reactor Ls and a filter capacitor C1. The reactor Ls, filter capacitor C1, and the equivalent leakage inductance Lg of the transformer substation constitute the LCL filter topology. This LCL filter topology can effectively filter out high-frequency harmonics, but its suppression effect on low-frequency harmonics is poor, and its filtering bandwidth is narrow.
[0031] In addition, when the doubly fed converter is in standby mode, the equipment on the generator side is not adjusted, but the equipment on the grid side is not adjusted. When the frame circuit breaker Q1 is connected, the equipment on the grid side sends reactive carrier waves, forming a loop with the grid. The background harmonics of the grid can easily cause resonance in the equipment on the grid side.
[0032] Based on the above problems, the filtering circuit, filtering control device and filtering control method provided in the embodiments of this specification can be applied to the filtering of doubly fed converters.
[0033] To facilitate understanding of this embodiment, a filter circuit disclosed in this specification will first be described in detail, such as... Figure 2 As shown, the filter circuit includes a first inductor, a first capacitor, and multiple filter branches.
[0034] The first end of the first capacitor is used to connect the stator of the generator and the first end of the first inductor; the second end of the first capacitor is connected to multiple filter branches; the multiple filter branches are connected in parallel; the second end of the first inductor is connected to the doubly-fed converter. Figure 2 In this example, three filtering branches are used, but the number of filtering branches is not limited in this embodiment.
[0035] At least some filter branches include resonant parameter adjustment devices, and the resonant parameter adjustment devices are different in different filter branches; the resonant parameter adjustment device can be a resonant peak adjustment device, such as a resistor; the resonant parameter adjustment device can also be a resonant frequency point adjustment device, such as an inductor, a capacitor, etc.
[0036] In practical implementation, a resonant parameter adjustment device can be set in each filter branch, or it can be set only in some filter branches. In filter branches without a resonant parameter adjustment device, only wires can be set. In different filter branches with resonant parameter adjustment devices, the type and parameters of the device can be different. For example, a resistor can be set in filter branch 1 and a capacitor can be set in filter branch 2; or, the same type of device can be set with different parameters in different filter branches. For example, a capacitor with capacitance value A can be set in filter branch 3 and a capacitor with capacitance value B can be set in filter branch 4.
[0037] In one embodiment, the aforementioned resonant parameter adjustment device includes a resonant peak adjustment device and / or a resonant frequency adjustment device. Multiple filter branches may simultaneously include both a resonant peak adjustment device and a resonant frequency adjustment device, or they may only include one of either a resonant peak adjustment device or a resonant frequency adjustment device.
[0038] It should be noted that different filter branches can be used to filter out harmonics in different frequency bands. Based on the frequency band of the harmonics in the circuit, the corresponding filter branch is used to filter out the harmonics, thereby achieving wideband harmonic filtering.
[0039] The aforementioned filter branch also includes an on / off control device for controlling the connection and disconnection between the filter branch and the first inductor.
[0040] The on / off control device can be a switch, contactor, circuit breaker, etc. If there is a resonant parameter adjustment device in the filter branch, it is usually connected in series with the corresponding on / off control device.
[0041] For a filter branch, if the on / off control device is connected, the resonant parameter adjustment device in the filter branch is connected to the filter circuit to perform harmonic filtering; if the on / off control device in the filter branch is disconnected, the resonant parameter adjustment device in the filter branch is separated from the filter circuit and no longer performs harmonic filtering.
[0042] During the operation of the filter circuit, the on / off control device in only one filter branch can be controlled, or the on / off control device in multiple filter branches can be controlled. By detecting the background harmonics of the power grid, the current harmonic frequency band is determined, and then the corresponding filter branch is selected for harmonic filtering.
[0043] The aforementioned filtering circuit includes a first inductor, a first capacitor, and multiple filtering branches; the first end of the first capacitor is used to connect the stator of the generator and the first end of the first inductor, and the second end of the first capacitor is connected to multiple filtering branches; the multiple filtering branches are connected in parallel; the second end of the first inductor is connected to a doubly-fed converter; at least some of the filtering branches include resonant parameter adjustment devices, and the resonant parameter adjustment devices in different filtering branches are different; the filtering branches also include on / off control devices for controlling the on / off state between the filtering branches and the first inductor.
[0044] This filtering circuit has multiple parallel filtering branches, each with a different resonant parameter adjustment device. By controlling the on / off state of the on / off control devices in the filtering branches, different resonant parameter adjustment devices can be connected, thereby filtering out the frequency band harmonics present in the current circuit. By connecting different resonant parameter adjustment devices, harmonics in each frequency band can be effectively filtered out, providing a wide-band filtering function and improving the harmonic filtering effect in each frequency band.
[0045] In one specific implementation, if the filter branch includes a resonant parameter adjustment device, the resonant parameter adjustment device in the filter branch includes: a resistor device for reducing the resonant peak value; or a second inductor device for reducing the resonant frequency point; or a second capacitor device for increasing the resonant frequency point.
[0046] Specifically, when a filter branch includes a resonant parameter adjustment device, a filter branch may include only one resonant parameter adjustment device, or only one type of resonant parameter adjustment device. When the resonant parameter adjustment device includes a resistor, the resistor can be set in one filter branch or multiple filter branches; the resistance value of the resistor can be determined by the nth harmonic and nearby harmonics in the current power grid background harmonics. When a filter branch includes a resistor, it may include one resistor or multiple resistors, which can be connected in parallel or series.
[0047] When the resonant parameter adjustment device includes a second inductor, the second inductor can be set in one filter branch or in multiple filter branches. The inductance value of the second inductor can be determined by the nth harmonic and nearby harmonics in the current power grid background harmonics. When a filter branch includes a second inductor, it can include one or multiple second inductors, which can be connected in parallel or series.
[0048] Similarly, when the resonant parameter adjustment device includes a second capacitor, the second capacitor can be set in one filter branch or in multiple filter branches; the capacitance value of the second capacitor can be determined by the nth harmonic and nearby harmonics in the current power grid background harmonics. When a filter branch includes a second capacitor, it can include one or multiple second capacitors, which can be connected in parallel or in series.
[0049] In one specific implementation, refer to Figure 3 The filtering branches include several of the following: a first branch, which includes a first on / off control device S1 and a resistor Rc; the first on / off control device and the resistor are connected in series; a second branch, which includes a second on / off control device S2 and a second inductor Lc; the second on / off control device and the second inductor are connected in series; a third branch, which includes a third on / off control device S3 and a second capacitor C2; the third on / off control device and the second capacitor are connected in series; and a fourth branch, which includes a fourth on / off control device S.
[0050] The first, second, third, and fourth on / off control devices can be switching devices or circuit breakers, etc. The first capacitor C1 mentioned above includes an AC capacitor.
[0051] See Figure 4The diagram shows a filter control device. The filter control device includes a filter circuit and a controller. The controller is used to connect to the power grid and detect the harmonics of the power grid. The controller is connected to the filter circuit and controls the on / off state of the filter branch in the filter circuit.
[0052] The controller may include DSP (Digital Signal Processing) devices, as well as microcontrollers, ARM (Advanced RISC Machines), and other devices.
[0053] Since the controller is connected to the power grid, it can collect signals such as power grid voltage, perform FFT (Fast Fourier Transform) or other frequency analysis on the signals to obtain power grid harmonics; and control the on / off state of the filter branch based on the power grid harmonics.
[0054] Specifically, the aforementioned control device is connected to the on / off control device in each filter branch of the filter circuit, and is used to control the on / off state of the on / off control device. When the on / off control device in a filter branch is connected, the resonant parameter adjustment device in that filter branch is connected to the filter circuit; the control device determines which resonant parameter adjustment device needs to be connected to the filter circuit based on the detected harmonics, and then controls the on / off control device corresponding to that resonant parameter adjustment device to be connected.
[0055] See Figure 5 The diagram shows the detailed connections of the filter control device, generator, and doubly-fed converter. The controller is illustrated using a DSP as an example. One end of the controller connects to each filter branch in the filter circuit, specifically to the on / off control device within that filter branch. The other end of the controller connects to the power grid; alternatively, it can be connected between the frame circuit breaker and the power grid.
[0056] In this circuit, Ls represents the first grid device, also known as the grid-side filter inductor; Lg represents the equivalent leakage inductance of the transformer substation. Each filter branch includes switching devices and damping devices. The first branch is a damping circuit, its function being to reduce the resonant peak value; the second branch is used to lower the resonant frequency point, such as by adding an inductor to the second branch; the third branch is used to raise the resonant frequency point, such as by adding a capacitor to the second branch; the fourth branch is a conventional filter switching circuit, containing only switching devices and not resonant parameter adjustment devices. By controlling the switching of the four filter branches, different filter topologies are formed, which can suppress both high and low frequency harmonics, thus preventing the converter from experiencing resonance faults.
[0057] See Figure 6 The flowchart shown illustrates a filtering control method applied to the aforementioned filtering control device; the method includes the following steps:
[0058] Step S602: Under the operating conditions of the doubly fed converter, the fourth on / off control device in the control filter circuit is connected, and the first on / off control device, the second on / off control device, and the third on / off control device are disconnected.
[0059] refer to Figure 3 When the fourth on / off control device S is connected, and the first on / off control device S1, the second on / off control device S2, and the third on / off control device S3 are disconnected, the filter circuit is a conventional LCL filter topology.
[0060] The first branch consists of S1 and a resistor Rc connected in series; the second branch consists of S2 and a second inductor Lc; the third branch consists of S3 and a second capacitor C2; and the fourth branch consists of a single S. The first, second, and third branches are switched on and off to avoid resonance. The doubly-fed converter has operating and standby modes, each with different control methods.
[0061] Step S604: Determine the first resonant frequency of the filter circuit;
[0062] In one approach, the first resonant frequency can be determined using the following formula:
[0063]
[0064] Where fn is the first resonant frequency, Lg is the equivalent leakage inductance of the transformer, Ls is the inductance of the first inductor device, also known as the grid-side filter inductance, and C1 is the capacitance of the first capacitor device.
[0065] It should be noted that, since the configuration of the doubly fed converter is different for different wind farms, the equivalent leakage inductance of the aforementioned transformer, the first grid device and the first capacitor are usually different, and therefore the resonant frequency point fn is also different for different wind farms.
[0066] Step S606: Collect the background harmonics of the power grid, and determine whether the doubly fed converter resonates based on the background harmonics of the power grid and the first resonant frequency point.
[0067] The grid voltage signal can be acquired through control devices, and frequency analysis, such as FFT analysis, can be performed on the grid voltage signal to obtain the grid background harmonics. Specifically, harmonic distortion of a specified order and nearby harmonics can be detected from the grid background harmonics. This specified order can be represented by n. The specified order n may be different for different wind farms, and different specified orders n have corresponding preset harmonic distortion thresholds. If the harmonic distortion is large, exceeding the corresponding harmonic distortion threshold, and the first resonant frequency point is located in the frequency band of the specified order and nearby harmonics, then it can be determined that the doubly-fed converter has resonated.
[0068] Step S608: If the doubly fed converter resonates, the fourth on / off control device is disconnected, and the target on / off control device is connected; wherein, the target on / off control device includes one or more of the first on / off control device, the second on / off control device, and the third on / off control device.
[0069] For example, if it is necessary to reduce the resonant peak, the first on / off control device S1 is closed to connect the resistor to the filter circuit; if it is necessary to lower the resonant frequency, the second on / off control device S2 is closed to connect the second inductor to the filter circuit; if it is necessary to raise the resonant frequency, the third on / off control device S3 is closed to connect the second capacitor to the filter circuit.
[0070] Alternatively, multiple on / off control devices among the first, second, and third on / off control devices can be closed to connect multiple resonant parameter adjustment devices into the filter circuit, thereby filtering out harmonics more effectively.
[0071] The above-described filtering control method is applied to a filtering control device. Under the operating conditions of the doubly-fed converter, the fourth on / off control device in the filtering circuit is connected, while the first, second, and third on / off control devices are disconnected. The first resonant frequency point of the filtering circuit is determined. The background harmonics of the power grid are collected, and based on the background harmonics of the power grid and the first resonant frequency point, it is determined whether the doubly-fed converter is resonating. If the doubly-fed converter is resonating, the fourth on / off control device is disconnected, and the target on / off control device is connected. The target on / off control device includes one or more of the first, second, and third on / off control devices.
[0072] In this method, multiple parallel filter branches are set in the filter circuit, and different resonant parameter adjustment devices are set in different filter branches. By controlling the on / off control devices in the filter branches, different resonant parameter adjustment devices can be connected, thereby filtering out the frequency band harmonics present in the current circuit. By connecting different resonant parameter adjustment devices, harmonics in each frequency band can be effectively filtered out, which has a wide frequency band filtering function and improves the harmonic filtering effect of each frequency band.
[0073] Furthermore, a specified frequency band harmonic is detected from the background harmonics of the power grid; if the harmonic distortion of the specified frequency band harmonic is greater than a preset harmonic distortion threshold, and the specified frequency band harmonic covers the first resonant frequency point, it is determined that the doubly fed converter has resonated.
[0074] To determine if a doubly-fed converter has resonated, two conditions must be met simultaneously. Condition 1 is that the harmonic distortion of a specified frequency band harmonic is greater than a preset harmonic distortion threshold. Specifically, the total harmonic distortion (THD) of a specified n-order harmonic and its vicinity detected in the grid background harmonics must be greater than the preset harmonic distortion threshold. Condition 2 is that the specified frequency band harmonic covers the first resonant frequency point, which is the resonant frequency point of the aforementioned LCL filter topology. When conditions 1 and 2 are met simultaneously, the doubly-fed converter may resonate, leading to faults such as excessive filter capacitor and filter current.
[0075] Under the premise that the fourth on / off control device S is connected and the first on / off control device S1, the second on / off control device S2 and the third on / off control device S3 are disconnected, when it is determined that the doubly fed converter is in resonance, the fourth on / off control device S is first disconnected and the second on / off control device S2 is connected.
[0076] In this case, the filter circuit uses an L-LC-L type filter topology. Since the filter point changes, the resonant frequency is updated from the aforementioned first resonant frequency to the second resonant frequency. The second resonant frequency can be calculated using the following formula:
[0077]
[0078] f n1 Here, Lg is the equivalent leakage inductance of the transformer, Ls is the inductance of the first inductor (also known as the grid-side filter inductance), Lc is the inductance of the second inductor, and C1 is the capacitance of the first capacitor. Resonance can be avoided by changing the resonant frequency.
[0079] Obtain the second resonant frequency point of the filter circuit after the second on / off control device is connected; based on the background harmonics of the power grid and the second resonant frequency point, determine whether the doubly fed converter resonates; if the doubly fed converter resonates, control the first on / off control device to connect.
[0080] In practical implementation, a specified frequency band harmonic is detected from the background harmonics of the power grid. If the harmonic distortion of the specified frequency band harmonic is greater than the preset harmonic distortion threshold, and the specified frequency band harmonic covers the second resonant frequency point, it is determined that the doubly fed converter is resonating. The resonance of the doubly fed converter may lead to a large THD.
[0081] If the doubly fed converter still resonates after S is opened and S2 is closed, the first on / off control device S1 needs to be closed again.
[0082] By using a parallel connection of a resistor and a second inductor to suppress resonance, both the resonant frequency and the resonant gain are changed, especially the resonant gain is significantly reduced. Furthermore, the second inductor and the resistor shunt the current, with low-frequency harmonic components mainly flowing through the second inductor and high-frequency harmonic components mainly flowing through the resistor, which also reduces the heat loss of the resistor.
[0083] Furthermore, the third resonant frequency point of the filter circuit when both the first and second on / off control devices are connected is obtained; based on the power grid background harmonics and the third resonant frequency point, it is determined whether the doubly-fed converter is resonating; if the doubly-fed converter is resonating, the first and second on / off control devices are disconnected, and the third on / off control device is connected.
[0084] In practical implementation, a specified frequency band harmonic is detected from the background harmonics of the power grid. If the harmonic distortion of the specified frequency band harmonic is greater than the preset harmonic distortion threshold, and the specified frequency band harmonic covers the third resonant frequency point, it is determined that the doubly fed converter is resonating. The resonance of the doubly fed converter may lead to a large THD.
[0085] When the first on / off control device, the second on / off control device, and the fourth on / off control device are all off, only the third on / off control device is controlled to be on, and the second capacitor is connected to the filter circuit. The second capacitor absorbs harmonics, and the resonant frequency point changes, thereby avoiding resonance.
[0086] Furthermore, the fourth resonant frequency point of the filter circuit after the third on / off control device is connected is obtained; based on the background harmonics of the power grid and the fourth resonant frequency point, it is determined whether the doubly fed converter resonates; if the doubly fed converter resonates, the first on / off control device is connected.
[0087] In practical implementation, a specified frequency band harmonic is detected from the background harmonics of the power grid. If the harmonic distortion of the specified frequency band harmonic is greater than the preset harmonic distortion threshold, and the specified frequency band harmonic covers the fourth resonant frequency point, it is determined that the doubly fed converter is resonating. The resonance of the doubly fed converter may lead to a large THD.
[0088] If the doubly-fed converter still resonates after the third on / off control device S3 is closed, the first on / off control device S1 also needs to be closed. Simultaneously closing S1 and S3, and using a resistor and a second capacitor connected in parallel, suppresses the resonance.
[0089] Furthermore, after suppressing resonance by connecting the target on / off control device, it is determined that the harmonic distortion of a specified frequency band harmonic in the background harmonics of the power grid is less than or equal to a preset harmonic distortion threshold. The target on / off control device is then disconnected, and the fourth on / off control device is connected.
[0090] When the harmonic distortion of a specified frequency band harmonic in the power grid background harmonics is less than or equal to a preset harmonic distortion threshold, it can be understood that the resonance risk is low. In this case, the previously connected S1, S2, or S3 can be disconnected, leaving only S connected, and the LCL filter topology can continue to operate. During operation, the doubly-fed converter can be monitored for resonance via control devices. If resonance occurs, the aforementioned target on / off control devices can be continuously controlled to suppress the resonance.
[0091] In other methods, under the standby condition of the doubly-fed converter, the on / off status of the grid-side circuit breaker of the doubly-fed converter is detected; if the grid-side circuit breaker is open, the first on / off control device, the second on / off control device, the third on / off control device and the fourth on / off control device in the control filter circuit are all disconnected.
[0092] The grid-side circuit breaker is as described above. Figure 5 In the case of Q1, when Q2 is disconnected, the grid-side equipment of the doubly fed converter and the stator side of the generator are disconnected from the grid, and no resonance will occur under standby conditions. Therefore, all filter branches in the filter circuit are disconnected.
[0093] When the grid-side circuit breaker Q1 does not disconnect, in standby mode, the generator-side equipment stops modulation, the stator contactor K1 disconnects, the generator's stator-side filter topology is disconnected from the grid, the grid side operates with a single inductor, and there is no risk of resonance.
[0094] In practical implementation, the doubly-fed converter starts up using a soft-start method. The converter is charged via the DC bus; when Q1 is closed, the DC bus continues charging. The converter's generator side is energized, and stator contactor K1 is closed. The fourth branch in the filter circuit is connected, forming an LCL filter topology for filtering. The DSP controller monitors the background harmonics of the power grid, performs FFT analysis, and determines whether the THD exceeds the preset harmonic distortion threshold. If it does, the fourth branch is disconnected, and one or more branches from the first, second, and third branches are connected for harmonic suppression. If the THD does not exceed the preset harmonic distortion threshold, the first, second, and third branches are disconnected, and the fourth branch is connected.
[0095] In the standby mode of the doubly-fed converter, the stator contactor K1 is disconnected, and the filter circuit is disconnected from the power grid. It is then determined whether Q1 is open. If Q1 is open, the grid-side equipment of the doubly-fed converter is disconnected from the power grid, and there is no risk of resonance. If Q1 is closed, the grid-side equipment of the doubly-fed converter operates with a single inductor, and there is no risk of resonance.
[0096] In this embodiment, the filter circuit is installed on the stator side of the generator. When a large harmonic at a certain frequency point of the power grid is detected and exceeds the set threshold, different filter topologies are formed by switching multiple filter branches. This can change the resonant frequency and significantly reduce the resonant peak value. On the one hand, the filter branch can be automatically switched according to the harmonics present in the power grid to achieve high-frequency and low-frequency filtering. On the other hand, it can ensure that no resonance occurs in the standby state.
[0097] The computer program product of a filtering circuit, filtering control device, and filtering control method provided in the embodiments of this specification includes a computer-readable storage medium storing program code. The instructions included in the program code can be used to execute the methods described in the preceding method embodiments. For specific implementation, please refer to the method embodiments, which will not be repeated here.
[0098] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the system and apparatus described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.
[0099] Furthermore, in the description of the embodiments in this specification, unless otherwise expressly 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.
[0100] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.
[0101] In the description of this application, 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 this application and 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 this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.
[0102] Finally, it should be noted that the above embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the technical scope disclosed in this application. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments in this specification, and should all be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.
Claims
1. A filter circuit, characterized in that, The filtering circuit includes a first inductor, a first capacitor, and multiple filtering branches; The first end of the first capacitor is used to connect the stator of the generator and the first end of the first inductor; the second end of the first capacitor is connected to the plurality of filter branches; the plurality of filter branches are connected in parallel; the second end of the first inductor is connected to the doubly-fed converter. At least some of the filter branches include a resonant parameter adjustment device, and the resonant parameter adjustment devices are different in different filter branches; The filtering branch also includes an on / off control device for controlling the connection and disconnection between the filtering branch and the first inductor.
2. The filter circuit according to claim 1, characterized in that, The resonant parameter adjustment device includes a resonant peak adjustment device and / or a resonant frequency point adjustment device.
3. The filter circuit according to claim 1, characterized in that, If the filter branch includes a resonant parameter adjustment device, the resonant parameter adjustment device in the filter branch includes: Resistive devices are used to reduce resonant peak values; Alternatively, a second inductor can be used to lower the resonant frequency. Alternatively, a second capacitor could be used to increase the resonant frequency.
4. The filter circuit according to claim 1, characterized in that, The filtering branch includes several of the following: The first branch includes a first on / off control device and a resistor; the first on / off control device and the resistor are connected in series. The second branch includes a second on / off control device and a second inductor; the second on / off control device and the second inductor are connected in series. The third branch includes a third on / off control device and a second capacitor; the third on / off control device and the second capacitor are connected in series. The fourth branch includes a fourth on / off control device.
5. The filter circuit according to claim 1, characterized in that, The first capacitor includes an AC capacitor.
6. A filtering control device, characterized in that, The filtering control device includes the filtering circuit according to any one of claims 1-5, and further includes a control device; The controller is used to connect to the power grid and detect the harmonics of the power grid. The controller is connected to the filter circuit and controls the on / off state of the filter branch in the filter circuit.
7. The filtering control device according to claim 6, characterized in that, The control device is connected to the on / off control device in each filter branch of the filter circuit and is used to control the on / off state of the on / off control device.
8. A filtering control method, characterized in that, The method is applied to the filter control device according to claim 6 or 7; the method includes: Under the operating conditions of the doubly fed converter, the fourth on / off control device in the control filter circuit is connected, while the first on / off control device, the second on / off control device, and the third on / off control device are disconnected. Determine the first resonant frequency point of the filter circuit; Collect background harmonics of the power grid, and determine whether the doubly-fed converter resonates based on the background harmonics of the power grid and the first resonant frequency point; If the doubly fed converter resonates, the fourth on / off control device is disconnected, and the target on / off control device is connected; wherein the target on / off control device includes one or more of the first on / off control device, the second on / off control device, and the third on / off control device.
9. The method according to claim 8, characterized in that, The step of determining whether the doubly-fed converter resonates based on the background harmonics of the power grid and the first resonant frequency point includes: Detecting a specified frequency band harmonic from the background harmonics of the power grid; If the harmonic distortion of the specified frequency band harmonic is greater than a preset harmonic distortion threshold, and the specified frequency band harmonic covers the first resonant frequency point, it is determined that the doubly fed converter is in resonance.
10. The method according to claim 8, characterized in that, The steps of controlling the target on / off controller to connect include: controlling the second on / off controller to connect.
11. The method according to claim 10, characterized in that, After the step of controlling the connection of the second on / off control device, the method further includes: Obtain the second resonant frequency point of the filter circuit after the second on / off control device is connected; Based on the background harmonics of the power grid and the second resonant frequency point, it is determined whether the doubly fed converter resonates; If the doubly fed converter resonates, the first on / off control device is connected.
12. The method according to claim 11, characterized in that, After the step of controlling the connection between the second on / off control device and the second on / off control device, the method further includes: Obtain the third resonant frequency point of the filter circuit when both the first on / off control device and the second on / off control device are connected; Based on the background harmonics of the power grid and the third resonant frequency point, determine whether the doubly fed converter resonates; If the doubly fed converter resonates, the first and second on / off control devices are disconnected, and the third on / off control device is connected.
13. The method according to claim 12, characterized in that, After the step of controlling the connection of the third on / off control device, the method further includes: Obtain the fourth resonant frequency point of the filter circuit after the third on / off control device is connected; Based on the background harmonics of the power grid and the fourth resonant frequency point, determine whether the doubly fed converter resonates; If the doubly fed converter resonates, the first on / off control device is switched on.
14. The method according to claim 8, characterized in that, If the doubly-fed converter resonates, after controlling the fourth on / off control device to disconnect and the target on / off controller to connect, the method further includes: If the harmonic distortion of a specified frequency band harmonic in the background harmonics of the power grid is less than or equal to a preset harmonic distortion threshold, the target on / off control device is disconnected, and the fourth on / off control device is connected.
15. The method according to claim 8, characterized in that, The method further includes: Under the standby condition of the doubly-fed converter, the on / off status of the grid-side circuit breaker of the doubly-fed converter is detected; If the grid-side circuit breaker is disconnected, the first on / off control device, the second on / off control device, the third on / off control device, and the fourth on / off control device in the filter circuit will all be disconnected.