A negative sequence current suppression system and method based on network configuration transformer

Abstract

The application discloses a negative sequence current suppression system and method based on a network configuration transformer, and relates to the technical field of grid-connected transformers. A negative sequence current feedback module comprises: a first filter unit which filters three-phase output currents to obtain negative sequence component instantaneous values; an amplification unit which amplifies the negative sequence component instantaneous values to obtain amplified negative sequence component instantaneous values; and a difference unit which performs difference calculation on a first voltage reference value and the amplified negative sequence component instantaneous values to obtain a second voltage reference value. A negative sequence voltage feedforward control module comprises: a second filter unit which filters three-phase system voltages to obtain three-phase negative sequence components; and a summation unit which performs summation calculation on the second voltage reference value and the three-phase negative sequence components to obtain a third voltage reference value. The application reduces negative sequence components in transformer output currents and improves the stability of transformer and power system operation.

Description

Technical Field

[0001] This invention relates to the field of grid-connected converter technology, and in particular to a negative sequence current suppression system and method based on a network-constructed converter. Background Technology

[0002] Currently, most grid-connected converters in practical applications adopt a network tracking (grid-following) control strategy. The basic principle is to use a phase-locked loop (PLL) to track the system voltage phase at the grid connection point of the converter, and to use a decoupled current tracking control strategy to control the active and reactive currents injected into or flowing out of the grid, effectively creating a three-phase current source.

[0003] On the one hand, the grid-connected control strategy decouples the active and reactive power output of the grid-connected converter from the operating state of the power grid, which is detrimental to the frequency stability and voltage stability of the power system.

[0004] On the other hand, the strong coupling between the output of the phase-locked loop and the power grid reduces the anti-interference stability of the grid-connected converter when connected to a weak system. With the continuous increase in the total capacity of power electronic devices, especially the installed capacity of new energy sources, the impact of grid-connected converters on power system stability is becoming increasingly apparent.

[0005] To address the issues of grid-connected converters, network-structured converters (FSCs) have been proposed. FSCs do not require phase-locked loops (PLLs) and can achieve self-synchronization with the power grid. Furthermore, their output characteristics can be equivalent to a three-phase voltage source, allowing them to operate normally in both islanded and grid-connected modes, which is beneficial for frequency and voltage support in power systems. They have already seen initial applications in practical engineering. However, currently, FSCs suffer from a high negative-sequence component in their output current.

[0006] The reasons are as follows: 1) Due to the control accuracy of pulse width modulation (PWM) drive and the asymmetry of component parameters, the three-phase system voltage and three-phase output current of the grid-connected converter may have a slight asymmetry when operating normally, that is, there is a small amount of negative sequence component in the three-phase system voltage and three-phase output current; 2) When an asymmetric fault occurs in the power system, the system voltage at the output of the grid-connected converter is severely asymmetric. Since the grid-connected converter can only output positive sequence voltage, there is a large negative sequence component in its output current. Under some operating conditions, this can lead to overcurrent in the grid-connected converter, which has an adverse effect on the stable operation of the converter and the power system. Summary of the Invention

[0007] The purpose of this invention is to provide a negative sequence current suppression system and method based on a network-based converter, so as to reduce the negative sequence component of the converter output current and improve the stability of the converter and power system operation.

[0008] To achieve the above objectives, embodiments of the present invention provide the following solutions:

[0009] A negative sequence current suppression system based on a network-based converter, the negative sequence current suppression system based on a network-based converter includes a grid-connected converter network control system, a negative sequence current feedback module and a negative sequence voltage feedforward control module;

[0010] The grid-connected converter and the grid-type control system output three-phase output current;

[0011] The negative sequence current feedback module includes:

[0012] The first filtering unit is used to filter the three-phase output current to obtain the instantaneous value of the negative sequence component; the instantaneous value of the negative sequence component includes the instantaneous value of the negative sequence component of any one phase of the three-phase output current.

[0013] An amplification unit, connected to the first filtering unit, is used to amplify the instantaneous value of the negative-order component to obtain the amplified instantaneous value of the negative-order component.

[0014] A difference unit, connected to the amplification unit, is used to calculate the difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component to obtain the difference value; the difference value is the second voltage reference value.

[0015] The negative sequence voltage feedforward control module includes:

[0016] The second filtering unit is used to filter the three-phase system voltage at the grid connection point of the grid-connected converter to obtain the three-phase negative sequence components; the three-phase negative sequence components include any one phase negative sequence component of the three-phase system voltage.

[0017] The summation unit, connected to the second filtering unit, is used to sum the first voltage reference value and the three-phase negative sequence components to obtain a sum value; the sum value is the third voltage reference value.

[0018] Optionally, the negative sequence voltage feedforward control module further includes:

[0019] The determination unit, connected to the second filtering unit, is used to determine the effective value of the line voltage of the three-phase negative sequence component and the magnitude of the preset threshold.

[0020] If the effective value of the line voltage of the three-phase negative sequence component is less than or equal to the preset threshold, then the second voltage reference value is output.

[0021] If the effective value of the line voltage of the three-phase negative sequence component is greater than the preset threshold, then the third voltage reference value is output.

[0022] Optionally, the first filtering unit includes:

[0023] The first Park transformation submodule is used to perform Park transformation on the three-phase output current to obtain the transformed three-phase output current;

[0024] The first filter, connected to the first Park transformation submodule, is used to filter the transformed three-phase output current to obtain the filtered three-phase output current.

[0025] The first Park inverse transform submodule is connected to the first filter and is used to perform Park transform on the filtered three-phase output current again to obtain the instantaneous value of the negative sequence component.

[0026] Optionally, the second filtering unit includes:

[0027] The second Park transformation submodule is used to perform Park transformation on the three-phase system voltage to obtain the transformed three-phase system voltage.

[0028] The second filter, connected to the second Park transformation submodule, is used to filter the transformed three-phase system voltage to obtain the filtered three-phase system voltage.

[0029] The second Park inverse transform submodule is connected to the second filter and is used to perform Park transform on the filtered three-phase system voltage again to obtain the three-phase negative sequence components.

[0030] Optionally, the formula for calculating the effective value of the line voltage of the three-phase negative sequence component is as follows:

[0031]

[0032] Among them, u neg u represents the effective value of the line voltage of the three-phase negative sequence component. a_neg u represents the instantaneous value of the negative sequence component of phase a. b_neg u represents the instantaneous value of the negative sequence component of phase b. c_neg This represents the instantaneous value of the negative sequence component of phase c.

[0033] To achieve the above objectives, embodiments of the present invention also provide the following solutions:

[0034] A method for suppressing negative-sequence current based on a network-based constructive converter, comprising the aforementioned negative-sequence current suppression system based on a network-based constructive converter, including:

[0035] The three-phase output current is acquired and filtered to obtain the instantaneous value of the negative sequence component; the grid-connected converter grid-type control system outputs the three-phase output current; the instantaneous value of the negative sequence component includes the instantaneous value of the negative sequence component of any one phase of the three-phase output current;

[0036] The instantaneous value of the negative-order component is amplified to obtain the amplified instantaneous value of the negative-order component.

[0037] The difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component is calculated to obtain the difference; the difference is the second voltage reference value.

[0038] The three-phase system voltage is acquired and filtered to obtain the three-phase negative sequence components; the three-phase negative sequence components include the instantaneous value of any one phase negative sequence component in the three-phase system voltage.

[0039] The first voltage reference value is summed with the three-phase negative sequence components to obtain a sum value; the sum value is the third voltage reference value.

[0040] Optionally, the negative sequence current suppression method based on network-based structural converters further includes:

[0041] Determine the effective value of the line voltage of the three-phase negative sequence component and the magnitude of the preset threshold.

[0042] If the effective value of the line voltage of the three-phase negative sequence component is less than or equal to the preset threshold, then the second voltage reference value is output.

[0043] If the effective value of the line voltage of the three-phase negative sequence component is greater than the preset threshold, then the third voltage reference value is output.

[0044] Optionally, the step of filtering the three-phase output current to obtain the instantaneous value of the negative sequence component specifically includes:

[0045] The three-phase output current is subjected to Park transformation to obtain the transformed three-phase output current;

[0046] The transformed three-phase output current is filtered to obtain the filtered three-phase output current.

[0047] The filtered three-phase output current is subjected to Park inverse transform to obtain the instantaneous value of the negative sequence component.

[0048] Optionally, the filtering of the three-phase system voltage to obtain the three-phase negative sequence components specifically includes:

[0049] The three-phase system voltage is subjected to Park transformation to obtain the transformed three-phase system voltage;

[0050] The transformed three-phase system voltage is filtered to obtain the filtered three-phase system voltage.

[0051] The filtered three-phase system voltage is subjected to Park inverse transform to obtain the three-phase negative sequence components.

[0052] Optionally, the formula for calculating the effective value of the line voltage of the three-phase negative sequence component is as follows:

[0053]

[0054] Among them, u neg u represents the effective value of the line voltage of the three-phase negative sequence component. a_neg u represents the instantaneous value of the negative sequence component of phase a. b_neg u represents the instantaneous value of the negative sequence component of phase b. c_neg This represents the instantaneous value of the negative sequence component of phase c.

[0055] In this embodiment of the invention, the negative sequence current suppression system based on the network-structured converter adds a negative sequence current feedback module and a negative sequence voltage feedforward control module to the grid-connected converter network-structured control system.

[0056] The negative sequence current feedback module includes: a first filtering unit, an amplification unit, and a difference unit.

[0057] The first filtering unit filters the three-phase output current to obtain the instantaneous value of the negative sequence component. The amplification unit amplifies the instantaneous value of the negative sequence component to obtain the amplified instantaneous value of the negative sequence component. The difference unit calculates the difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component to obtain the difference value; the difference value is the second voltage reference value. The negative sequence current feedback module can suppress the generation of negative sequence current under normal operating conditions caused by factors such as the PWM drive control accuracy of the grid-connected converter and the asymmetry of the three-phase component parameters of the power system, thereby reducing the negative sequence component of the grid-connected converter output.

[0058] The negative sequence voltage feedforward control module includes: a second filtering unit and a summing unit.

[0059] The second filtering unit filters the three-phase system voltage to obtain the three-phase negative sequence components. The summing unit sums the first voltage reference value with the three-phase negative sequence components to obtain the sum value; this sum value is the third voltage reference value. Based on the negative sequence current feedback module, the negative sequence voltage feedforward control module ensures that the output voltage of the grid-connected converter contains a negative sequence component identical to the three-phase system voltage. This prevents negative sequence current from flowing into or out of the grid-connected converter, further reducing the negative sequence current output by the grid-connected converter when an asymmetrical fault occurs in the power system, thus improving the stability of both the grid-connected converter and the power system operation. Attached Figure Description

[0060] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0061] Figure 1 A schematic diagram of the negative sequence current suppression system based on a network-based structural converter provided in an embodiment of the present invention;

[0062] Figure 2 A waveform diagram of the three-phase output current provided in an embodiment of the present invention;

[0063] Figure 3 A waveform diagram of the second voltage reference value provided in an embodiment of the present invention;

[0064] Figure 4 A waveform diagram of a three-phase system voltage provided in an embodiment of the present invention;

[0065] Figure 5 A schematic diagram of the waveform of the current output by the grid-connected converter grid-type control system provided in an embodiment of the present invention;

[0066] Figure 6 This is a waveform diagram of the current output by the negative sequence current feedback module provided in an embodiment of the present invention.

[0067] Figure 7 A waveform diagram of the negative sequence voltage feedforward control module provided in an embodiment of the present invention;

[0068] Figure 8 This is a schematic diagram of the structure of the first filtering unit provided in an embodiment of the present invention;

[0069] Figure 9 This is a flowchart illustrating the negative sequence current suppression method based on a network-based structural converter provided in an embodiment of the present invention.

[0070] Symbol explanation:

[0071] The system consists of a negative sequence current suppression system-1 based on a network-based converter, a negative sequence current feedback module-11, a first filter unit-111, an amplification unit-112, a negative sequence voltage feedforward control module-12, a second filter unit-121, a decision unit-122, and a grid-based control system for the grid-connected converter-2. Detailed Implementation

[0072] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0073] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0074] With the accelerated construction of new power systems, the trend of high proportion of new energy sources and high proportion of power electronic equipment in power systems is becoming increasingly apparent. Photovoltaic power generation, wind power generation, and other new energy units are all connected to the grid through power electronic converters, and electrochemical energy storage, flywheel energy storage, and other equipment in the power system are also connected to the grid through power electronic converters.

[0075] The negative sequence current suppression system of a network-built converter directly generates the phase and amplitude of the converter's output voltage based on the set active and reactive power, equivalent to a controllable three-phase voltage source, similar to a synchronous generator. Network-built converters do not rely on grid frequency / phase measurements for frequency / phase synchronization, offering more flexible frequency and voltage regulation in weak grids, which is beneficial for the stable operation of the power system. In power systems with a high proportion of renewable energy, the system strength decreases due to the reduction in synchronous generators. In this case, a network-built control method is more suitable for the converter, thereby enhancing the system's frequency and voltage stability. Network-built converters achieve system synchronization based on the active power of the equipment, independent of grid phase. Therefore, they can operate normally in both islanded and grid-connected modes.

[0076] Figure 1 An exemplary structure of the negative sequence current suppression system based on the aforementioned network-based constructivist converter is shown. It includes at least: a negative sequence current feedback module 11, a first filter unit 111, an amplification unit 112, a difference unit, a negative sequence voltage feedforward control module 12, a second filter unit 121, and a summing unit. Each module is described in detail below.

[0077] The negative sequence current suppression system 1 based on the network-structured converter adds a negative sequence current feedback module 11 and a negative sequence voltage feedforward control module 12 to the grid-connected converter network-structured control system 2.

[0078] The grid-connected converter and grid-connected control system output three-phase output current;

[0079] The negative sequence current feedback module 11 includes at least: a first filter unit 111, an amplification unit 112, and a difference unit.

[0080] The first filtering unit 111 is used to filter the three-phase output current to obtain the instantaneous value of the negative sequence component; the instantaneous value of the negative sequence component includes the instantaneous value of the negative sequence component of any one phase of the three-phase output current.

[0081] In one example, the first filter unit 111 is used to extract the three-phase output current i of the converter. abc_out The instantaneous value of the negative sequence component (instantaneous value of the negative sequence current component). For the three-phase output current (e.g., phase a, phase b, and phase c) of the grid-connected converter grid-type control system, please refer to [link to relevant documentation]. Figure 2 The vertical axis represents the magnitude of the three-phase output current, and the horizontal axis represents time. The three curves correspond one-to-one with the three-phase output current.

[0082] Amplification unit 112 is connected to first filtering unit 111. Amplification unit 112 is used to amplify the instantaneous value of negative sequence component to obtain amplified instantaneous value of negative sequence component.

[0083] In one example, the amplification unit 112 can specifically be an amplifier.

[0084] The difference unit is connected to the amplification unit 112. The difference unit is used to calculate the difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component to obtain the difference value; the difference value is the second voltage reference value u. abc_ref1 .

[0085] Please refer to the second voltage reference value. Figure 3 The horizontal axis represents time, and the vertical axis represents voltage value.

[0086] In one example, if the reactance of any one phase (e.g., phase a) of a power transmission line is slightly greater than that of the other two phases (e.g., phases b and c), meaning the three-phase parameters of the transmission line are mismatched, although the converter's output voltage is three-phase symmetrical, the output current still exhibits a slight asymmetry. After incorporating negative-sequence current feedback, the converter's output voltage becomes slightly asymmetrical, offsetting the effects of transmission line parameter asymmetry or other factors causing output current asymmetry, thereby reducing the content of negative-sequence current in the power system.

[0087] First voltage reference value u abc_ref Subtracting the amplified instantaneous value of the negative sequence component (e.g., phase a) from the first voltage reference value (e.g., phase a) yields the second voltage reference value (e.g., phase a). Detailed calculations for the second voltage reference values ​​of phases b and c are provided above and will not be repeated here. The difference calculation between the first voltage reference value and the amplified instantaneous value of the negative sequence component is unitless and only a numerical calculation.

[0088] First voltage reference value u abc_ref Includes the a-phase output voltage reference value u a_ref1 b-phase output voltage reference value ub_ref1 and the reference value of the c-phase output voltage u c_ref1 .

[0089] The negative sequence voltage feedforward control module 12 includes at least: a second filtering unit 121 and a summing unit.

[0090] The second filtering unit 121 is used to filter the three-phase system voltage at the grid connection point of the grid-connected converter to obtain the three-phase negative sequence components; the three-phase negative sequence components include the negative sequence component of any one phase of the three-phase system voltage.

[0091] In one example, the second filter unit 121 is used to filter the three-phase system voltage u. abc_sys After filtering, the three-phase negative sequence component u is obtained. abc_neg For the grid-connected converter and grid-connected control system 2, please refer to the output three-phase system voltage (e.g., phase a, phase b, and phase c). Figure 4 The horizontal axis represents time, and the vertical axis represents the three-phase system voltage. The three curves correspond one-to-one with the three-phase system voltage.

[0092] The summing unit is connected to the second filter unit 121. The summing unit is used to convert the first voltage reference value u abc_ref0 With the three-phase negative sequence component u abc_neg Perform a summation calculation to obtain the sum value; the sum value is the third voltage reference value u. abc_ref2 .

[0093] In one example, the summation unit is used to sum the first voltage reference value u abc_ref0 Any one phase (e.g., phase a) and the three-phase negative sequence component u abc_neg The corresponding phase (e.g., phase a) is summed to obtain the sum value; the sum value is the corresponding third voltage reference value u. abc_ref2 (e.g., phase a).

[0094] Please see Figure 5 When an asymmetrical short-circuit fault occurs in the power system, the three-phase output current i of the grid-connected converter grid-type control system 2... abc_out There may be a large negative sequence component, which could cause overcurrent and damage the equipment. In this case, if only the negative sequence current feedback module 11 is used, although the magnitude of the negative sequence current is significantly suppressed, please refer to [the relevant documentation / reference]. Figure 6 However, it is still quite noticeable. With the addition of the negative sequence voltage feedforward control module 12, the three-phase output current i abc_out The negative order components are reduced to almost zero; see [link to relevant documentation]. Figure 7 .

[0095] In summary, the first filtering unit 111 filters the three-phase output current to obtain the instantaneous value of the negative sequence component. The amplification unit 112 amplifies the instantaneous value of the negative sequence component to obtain the amplified instantaneous value of the negative sequence component. The difference unit calculates the difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component to obtain the difference; the difference is the second voltage reference value. The negative sequence current feedback module 11 can suppress the generation of negative sequence current under normal operating conditions caused by factors such as the PWM drive control accuracy of the grid-connected converter and the asymmetry of the three-phase component parameters of the power system, thereby reducing the negative sequence component of the grid-connected converter output. Please refer to [link to relevant documentation]. Figure 6 .

[0096] The second filtering unit 121 filters the three-phase system voltage to obtain the three-phase negative sequence components. The summation unit sums the first voltage reference value with the three-phase negative sequence components to obtain the sum value; the sum value is the third voltage reference value. Based on the negative sequence current feedback module 11, the negative sequence voltage feedforward control module 12 ensures that the output voltage of the grid-connected converter contains a negative sequence component identical to the three-phase system voltage, thereby preventing negative sequence current from flowing into or out of the grid-connected converter. This further reduces the negative sequence current output by the grid-connected converter when an asymmetrical fault occurs in the power system, improving the stability of the grid-connected converter and the power system operation. Please refer to [link to relevant documentation]. Figure 7 .

[0097] In other embodiments of the present invention, the negative sequence voltage feedforward control module 12 further includes a determination unit 122.

[0098] The determination unit 122 is connected to the second filter unit 121. The determination unit 122 is used to determine the effective value of the line voltage of the three-phase negative sequence component and the magnitude of the preset threshold.

[0099] If the effective value of the line voltage of the three-phase negative sequence component is less than or equal to the preset threshold, then the second voltage reference value is output.

[0100] If the effective value of the line voltage of the three-phase negative sequence component is greater than the preset threshold, then the third voltage reference value is output.

[0101] In one example, those skilled in the art can flexibly design preset thresholds, such as a preset threshold of 3% of the rated value of the three-phase output voltage, a preset threshold of 5% of the rated value of the three-phase output voltage, a preset threshold of 8% of the rated value of the three-phase output voltage, etc., which will not be elaborated here.

[0102] In other embodiments of the present invention, the first filtering unit 111 includes at least: a first Park transform submodule, a first filter, and a first Park inverse transform submodule.

[0103] The first Park transformation submodule is used to perform Park transformation on the three-phase output current to obtain the transformed three-phase output current.

[0104] The first filter is connected to the first Park transformation submodule. The first filter is used to filter the transformed three-phase output current to obtain the filtered three-phase output current.

[0105] The first Park inverse transform submodule is connected to the first filter. The first Park inverse transform submodule is used to perform Park inverse transform on the filtered three-phase output current to obtain the instantaneous value of the negative sequence component.

[0106] In one example, the first filter can be specifically divided into a band-stop filter and a low-pass filter. The frequency threshold of the band-stop filter is 100Hz, and the frequency range of the low-pass filter is 250 to 1000Hz.

[0107] Please see Figure 8 After the three-phase output current is input to the first Park transform submodule, it undergoes the first Park transform to obtain the transformed three-phase output current. The transformed three-phase output current undergoes the first filtering through a 100Hz band-stop filter, and then the second filtering through a 250-1000Hz low-pass filter to obtain the filtered three-phase output current. The filtered three-phase output current then undergoes the second Park transform through the first Park inverse transform submodule to obtain the instantaneous value of the negative sequence component.

[0108] In another example, the instantaneous values ​​of the three-phase output voltage are transformed by Park using the negative value of the phase angle of the positive-sequence three-phase output voltage of the power system, -θ (-120 degrees). The resulting voltage signals on the d-axis and q-axis are then filtered by a 100Hz band-stop filter and another low-pass filter. Finally, the negative-sequence components of the three phases are transformed by Park using -θ.

[0109] In other embodiments of the present invention, the second filtering unit 121 includes at least: a second Park transform submodule, a second filter, and a second Park inverse transform submodule.

[0110] The second Park transformation submodule is used to perform Park transformation on the three-phase system voltage to obtain the transformed three-phase system voltage.

[0111] The second filter is connected to the second Park transformation submodule. The second filter is used to filter the transformed three-phase system voltage to obtain the filtered three-phase system voltage.

[0112] The second Park inverse transform submodule is connected to the second filter. The second Park inverse transform submodule is used to perform Park inverse transform on the filtered three-phase system voltage to obtain the three-phase negative sequence components.

[0113] In one example, a detailed description of the second filter unit 121 is provided in the first filter unit 111 above, and will not be repeated here.

[0114] In other embodiments of the present invention, the formula for calculating the effective value of the line voltage of the three-phase negative sequence component is as follows:

[0115]

[0116] Among them, u neg u represents the effective value of the line voltage of the three-phase negative sequence component. a_neg u represents the instantaneous value of the negative sequence component of phase a. b_neg u represents the instantaneous value of the negative sequence component of phase b. c_neg This represents the instantaneous value of the negative sequence component of phase c.

[0117] To achieve the above objectives, embodiments of the present invention also provide the following solutions:

[0118] Please see Figure 9 A method for suppressing negative-sequence current based on a network-based structural converter, and a negative-sequence current suppression system based on a network-based structural converter, comprising:

[0119] Step 1: Obtain the three-phase output current and filter it to obtain the instantaneous value of the negative sequence component. The grid-connected converter outputs the three-phase output current in the grid-connected control system; the instantaneous value of the negative sequence component includes the instantaneous value of the negative sequence component of any one phase of the three-phase output current.

[0120] Step 1 can be performed by the aforementioned first filtering unit 111. For a detailed description of the first filtering unit 111, please refer to the previous text, which will not be repeated here.

[0121] Step 2: Amplify the instantaneous value of the negative-order component to obtain the amplified instantaneous value of the negative-order component.

[0122] Step 2 can be performed by the aforementioned amplification unit 112. For a detailed description of the amplification unit 112, please refer to the previous text, and it will not be repeated here.

[0123] Step 3: Calculate the difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component. This difference is the second voltage reference value.

[0124] Step 3 can be performed by the aforementioned difference unit. For a detailed description of the difference unit, please refer to the previous text, which will not be repeated here.

[0125] Step 4: Obtain the three-phase system voltage and filter the three-phase system voltage at the grid connection point of the grid-connected converter to obtain the three-phase negative sequence components. The three-phase negative sequence components include the instantaneous value of the negative sequence component of any one phase of the three-phase system voltage.

[0126] Step 4 can be performed by the aforementioned second filtering unit 121. For a detailed description of the second filtering unit 121, please refer to the previous text, and it will not be repeated here.

[0127] Step 5: Summate the first voltage reference value with the three-phase negative sequence components to obtain the sum. The sum is the third voltage reference value.

[0128] Step 5 can be performed by the aforementioned summation unit. For a detailed description of the summation unit, please refer to the previous text, which will not be repeated here.

[0129] In other embodiments of the present invention, the negative sequence current suppression method based on network-based structural converters further includes:

[0130] Step 6: Determine the effective value of the line voltage of the three-phase negative sequence component and the magnitude of the preset threshold.

[0131] If the effective value of the line voltage of the three-phase negative sequence component is less than or equal to the preset threshold, then the second voltage reference value is output.

[0132] If the effective value of the line voltage of the three-phase negative sequence component is greater than the preset threshold, then the third voltage reference value is output.

[0133] Step 6 can be executed by the aforementioned determination unit 122. For a detailed description of determination unit 122, please refer to the previous text, and it will not be repeated here.

[0134] In other embodiments of the present invention, filtering the three-phase output current to obtain the instantaneous value of the negative sequence component specifically includes:

[0135] Step 11: Perform Park transformation on the three-phase output current to obtain the transformed three-phase output current.

[0136] Step 11 can be executed by the aforementioned first Park transformation submodule. For a detailed description of the first Park transformation submodule, please refer to the previous text, which will not be repeated here.

[0137] Step 12: Filter the transformed three-phase output current to obtain the filtered three-phase output current.

[0138] Step 12 can be performed by the first filter mentioned above. For a detailed description of the first filter, please refer to the previous text, which will not be repeated here.

[0139] Step 13: Perform Park inverse transform on the filtered three-phase output current to obtain the instantaneous value of the negative sequence component.

[0140] Step 13 can be executed by the aforementioned first Park inverse transformation submodule. For a detailed description of the first Park inverse transformation submodule, please refer to the previous text, which will not be repeated here.

[0141] In other embodiments of the present invention, filtering the three-phase system voltage to obtain the three-phase negative sequence components specifically includes:

[0142] Step 41: Perform Park transformation on the three-phase system voltage to obtain the transformed three-phase system voltage.

[0143] Step 41: This can be executed by the aforementioned second Park transformation submodule. For a detailed description of the second Park transformation submodule, please refer to the previous text, which will not be repeated here.

[0144] Step 42: Filter the transformed three-phase system voltage to obtain the filtered three-phase system voltage.

[0145] Step 42 can be performed by the aforementioned second filter. For a detailed description of the second filter, please refer to the previous text, which will not be repeated here.

[0146] Step 43: Perform Park inverse transform on the filtered three-phase system voltage to obtain the three-phase negative sequence components.

[0147] Step 43 can be executed by the aforementioned second Park inverse transformation submodule. For a detailed description of the second Park inverse transformation submodule, please refer to the previous text, which will not be repeated here.

[0148] In other embodiments of the present invention, the formula for calculating the effective value of the line voltage of the three-phase negative sequence component is as follows:

[0149]

[0150] Among them, u neg u represents the effective value of the line voltage of the three-phase negative sequence component. a_neg u represents the instantaneous value of the negative sequence component of phase a. b_neg u represents the instantaneous value of the negative sequence component of phase b. c_neg This represents the instantaneous value of the negative sequence component of phase c.

[0151] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0152] This document uses specific examples to illustrate the principles and implementation methods of the embodiments of the present invention. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of the embodiments of the present invention. At the same time, for those skilled in the art, there will be changes in specific implementation methods and application scope based on the ideas of the embodiments of the present invention. In summary, the content of this specification should not be construed as a limitation on the embodiments of the present invention.

Claims

1. A negative sequence current suppression system based on a network-based structural converter, characterized in that, The negative sequence current suppression system based on the network-structured converter includes a grid-connected converter network-structured control system, a negative sequence current feedback module, and a negative sequence voltage feedforward control module. The grid-connected converter grid-type control system is used to output three-phase output current; The negative sequence current feedback module includes: The first filtering unit is used to filter the three-phase output current to obtain the instantaneous value of the negative sequence component; the instantaneous value of the negative sequence component includes the instantaneous value of the negative sequence component of any one phase of the three-phase output current. An amplification unit, connected to the first filtering unit, is used to amplify the instantaneous value of the negative-order component to obtain the amplified instantaneous value of the negative-order component. A difference unit, connected to the amplification unit, is used to calculate the difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component to obtain the difference value; the difference value is the second voltage reference value. The negative sequence voltage feedforward control module includes: The second filtering unit is used to filter the three-phase system voltage at the grid connection point of the grid-connected converter to obtain the three-phase negative sequence components; the three-phase negative sequence components include any one phase negative sequence component of the three-phase system voltage; the formula for calculating the effective value of the line voltage of the three-phase negative sequence components is: ； Among them, u neg u represents the effective value of the line voltage of the three-phase negative sequence component. a_neg u represents the instantaneous value of the negative sequence component of phase a. b_neg u represents the instantaneous value of the negative sequence component of phase b. c_neg This represents the instantaneous value of the negative sequence component of phase c; The summation unit, connected to the second filtering unit, is used to sum the first voltage reference value and the three-phase negative sequence components to obtain a sum value; the sum value is the third voltage reference value.

2. The negative sequence current suppression system based on a network-based structural converter according to claim 1, characterized in that, The negative sequence voltage feedforward control module also includes: The determination unit, connected to the second filtering unit, is used to determine the effective value of the line voltage of the three-phase negative sequence component and the magnitude of the preset threshold. If the effective value of the line voltage of the three-phase negative sequence component is less than or equal to the preset threshold, then the second voltage reference value is output. If the effective value of the line voltage of the three-phase negative sequence component is greater than the preset threshold, then the third voltage reference value is output.

3. The negative sequence current suppression system based on a network-based structural converter according to claim 1, characterized in that, The first filtering unit includes: The first Park transformation submodule is used to perform Park transformation on the three-phase output current to obtain the transformed three-phase output current; The first filter, connected to the first Park transformation submodule, is used to filter the transformed three-phase output current to obtain the filtered three-phase output current. The first Park inverse transform submodule is connected to the first filter and is used to perform Park inverse transform on the filtered three-phase output current to obtain the instantaneous value of the negative sequence component.

4. The negative sequence current suppression system based on a network-based structural converter according to claim 1, characterized in that, The second filtering unit includes: The second Park transformation submodule is used to perform Park transformation on the three-phase system voltage to obtain the transformed three-phase system voltage. The second filter, connected to the second Park transformation submodule, is used to filter the transformed three-phase system voltage to obtain the filtered three-phase system voltage. The second Park inverse transform submodule is connected to the second filter and is used to perform Park inverse transform on the filtered three-phase system voltage to obtain the three-phase negative sequence components.

5. A method for suppressing negative sequence current based on a network-based structural converter, characterized in that, The negative sequence current suppression system based on a network-based constructivist converter according to any one of claims 1-4 includes: The three-phase output current is acquired and filtered to obtain the instantaneous value of the negative sequence component; the grid-connected converter grid-type control system outputs the three-phase output current; the instantaneous value of the negative sequence component includes the instantaneous value of the negative sequence component of any one phase of the three-phase output current; The instantaneous value of the negative-order component is amplified to obtain the amplified instantaneous value of the negative-order component. The difference between the first voltage reference value and the amplified instantaneous value of the negative sequence component is calculated to obtain the difference; the difference is used as the second voltage reference value. The three-phase system voltage at the grid connection point of the grid-connected converter is obtained, and the three-phase system voltage is filtered to obtain the three-phase negative sequence components; the three-phase negative sequence components include the instantaneous value of any one phase negative sequence component in the three-phase system voltage; the effective value of the line voltage of the three-phase negative sequence components is calculated using the following formula: ； Among them, u neg u represents the effective value of the line voltage of the three-phase negative sequence component. a_neg u represents the instantaneous value of the negative sequence component of phase a. b_neg u represents the instantaneous value of the negative sequence component of phase b. c_neg This represents the instantaneous value of the negative sequence component of phase c; The first voltage reference value is summed with the three-phase negative sequence components to obtain a sum value; the sum value is the third voltage reference value.

6. The negative sequence current suppression method based on a network-based structural converter according to claim 5, characterized in that, The negative sequence current suppression method based on network-based structural converters further includes: Determine the effective value of the line voltage of the three-phase negative sequence component and the magnitude of the preset threshold. If the effective value of the line voltage of the three-phase negative sequence component is less than or equal to the preset threshold, then the second voltage reference value is output. If the effective value of the line voltage of the three-phase negative sequence component is greater than the preset threshold, then the third voltage reference value is output.

7. The negative sequence current suppression method based on a network-based structural converter according to claim 5, characterized in that, The filtering of the three-phase output current to obtain the instantaneous value of the negative sequence component specifically includes: The three-phase output current is subjected to Park transformation to obtain the transformed three-phase output current; The transformed three-phase output current is filtered to obtain the filtered three-phase output current. The filtered three-phase output current is subjected to Park inverse transform to obtain the instantaneous value of the negative sequence component.

8. The negative sequence current suppression method based on a network-based structural converter according to claim 5, characterized in that, Filtering the three-phase system voltage to obtain the three-phase negative sequence components specifically includes: The three-phase system voltage is subjected to Park transformation to obtain the transformed three-phase system voltage; The transformed three-phase system voltage is filtered to obtain the filtered three-phase system voltage. The filtered three-phase system voltage is subjected to Park inverse transform to obtain the three-phase negative sequence components.

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