Method and device for suppressing direct current component of output current of network construction type equipment

Abstract

The invention provides a method and a device for suppressing a direct current component of an output current of network construction type equipment. The method comprises the following steps: acquiring a three-phase current value of a grid-connected point of the network construction type equipment; decomposing the three-phase current value into dq-axis current components based on coordinate transformation; extracting a dq-axis current component of 50Hz from the dq-axis current components; taking the condition that the 50Hz dq-axis current component is equal to 0 as a control target of a current control model, and obtaining a dq-axis modulation voltage increment required for realizing the control target based on the current control model; and injecting the dq-axis modulation voltage increment into a voltage modulation link of the network construction type equipment to form suppression control on the direct current component of the output current. According to the method provided by the invention, the direct-current component can be quickly suppressed, so that the overcurrent capability of the equipment is released, and the equipment can be used for supporting the system voltage to the greatest extent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power equipment optimization, and in particular to a method and device for suppressing direct current component of output current of network-constructing equipment. BACKGROUND

[0002] At present, the energy transformation speed is accelerated, and the new energy proportion of the power system is gradually increased. In the power electronic power system mainly composed of new energy, the proportion of synchronous machines is low, and the system presents low inertia and weak damping characteristics, which brings great challenges to the operation of the power grid. Network-constructing equipment develops in this background and has a wide application prospect in building new power systems.

[0003] The network-constructing equipment is essentially a voltage source, can actively construct voltage frequency, provide inertia support for the system, and is beneficial to improve the stability of the system, and is an effective means to improve the active support capability of new energy. The network-constructing equipment has overcurrent capability higher than the rated current on the primary equipment within a certain time, and adopts the rotor motion equation and automatic voltage regulation equation of the generator in the secondary control to form the generator characteristics within the overcurrent capability range.

[0004] At present, the primary structure of the network-constructing equipment is usually composed of energy storage or power generation equipment on the DC side, a converter, and filter equipment on the AC side. The general control structure is as shown in Figure 1 First, the power calculation module is input into the control loop of the network-constructing equipment as a feedback quantity, and outputs the basic amplitude and phase angle of the internal potential. Since the network-constructing equipment uses power electronic devices, the current limit requirement is high, and therefore a current limit link is added. The common current limit link is to use a virtual impedance to output the limit amplitude and phase angle of the internal potential, or to use a current inner loop to limit the current. Through the superposition of the basic internal potential and the limit internal potential, the final internal potential is generated, and through the coordinate transformation module, the three-phase modulation voltage can be obtained. Finally, through the PWM modulation module, the switching signal can be output to control the switching module of the converter, so as to output the ideal voltage source signal.

[0005] When the network-constructing equipment uses the current control framework, the characteristics of the voltage source can be realized within the overcurrent multiple range, but once the overcurrent occurs, the pure voltage source characteristics of the network-constructing equipment will degenerate into the characteristics determined by the voltage source and the current limit control link. Therefore, it is hoped that the overcurrent capability of the equipment can respond to the changes of the system voltage to the greatest extent.

[0006] In the application scene with low resistance and inductance (such as high-voltage direct hanging application scene), when the network-constructing equipment adjusts the output voltage to support the system, there will be a large direct current decay component in the current, and the decay time will last for a long time, which will seriously affect the support capability of the network-constructing equipment. Therefore, it is necessary to add a control link for suppressing the direct current component on the basis of the general network-constructing equipment control strategy framework. SUMMARY

[0007] In view of the above, the present application provides a method and device for suppressing DC component of output current of grid-forming equipment to solve at least one of the above-mentioned problems.

[0008] To achieve the above-mentioned purpose, the present application adopts the following scheme:

[0009] According to a first aspect of the present application, a method for suppressing DC component of output current of grid-forming equipment is provided, the method comprising: obtaining three-phase current values of a grid-connection point of the grid-forming equipment; decomposing the three-phase current values into dq-axis current components based on coordinate transformation; extracting 50Hz dq-axis current components from the dq-axis current components; taking the 50Hz dq-axis current components equal to 0 as a control target of a current control model, obtaining dq-axis modulation voltage increments required for achieving the control target based on the current control model; injecting the dq-axis modulation voltage increments into a voltage modulation link of the grid-forming equipment, forming suppression control on the DC component of the output current.

[0010] As an embodiment of the present application, the method for extracting 50Hz dq-axis current components from the dq-axis current components comprises: performing high-pass or band-pass filtering processing on the dq-axis current components to extract the 50Hz dq-axis current components.

[0011] As an embodiment of the present application, the method for performing band-pass filtering processing on the dq-axis current components comprises: performing filtering processing on the dq-axis current components by using a second-order band-pass filter, the function of the second-order band-pass filter being:

[0012]

[0013] wherein s is a complex frequency variable in Laplace transform.

[0014] As an embodiment of the present application, the method further comprises: establishing a mathematical model of the grid-forming equipment in an abc coordinate system based on physical structure and electrical connection of the grid-forming equipment; converting the mathematical model in the abc coordinate system into a mathematical model in a dq0 synchronous rotating coordinate system through abc-dq0 coordinate transformation; referring to a control model of the grid-forming equipment, and constructing the current control model based on the mathematical model in the dq0 synchronous rotating coordinate system.

[0015] As an embodiment of this application, the method described above for obtaining the dq-axis modulation voltage increment required to achieve the control objective based on the current control model includes: comparing the extracted 50Hz d-axis current component with the d-axis current reference value to obtain the d-axis current deviation; comparing the extracted 50Hz q-axis current component with the q-axis current reference value to obtain the q-axis current deviation; inputting the d-axis current deviation and the q-axis current deviation into the PI controller respectively, and combining them with the decoupling term to calculate the dq-axis modulation voltage increment.

[0016] As an embodiment of this application, the method described above, which injects the dq-axis modulation voltage increment into the voltage modulation stage of the network device, includes: superimposing the dq-axis modulation voltage increment with the internal potential base component output by the main control loop and the internal potential limiting component output by the current limiting module to generate a final reference internal potential for subsequent PWM modulation and driving of the converter switching module.

[0017] According to a second aspect of this application, an apparatus for suppressing the DC component of the output current of a grid-connected device is provided. The apparatus includes: a current acquisition unit for acquiring the three-phase current value at the grid connection point of the grid-connected device; a current decomposition unit for decomposing the three-phase current value into dq-axis current components based on coordinate transformation; a component extraction unit for extracting a 50Hz dq-axis current component from the dq-axis current components; a modulation voltage acquisition unit for obtaining the dq-axis modulation voltage increment required to achieve the control target based on the current control model, using the 50Hz dq-axis current component being equal to 0 as the control target of the current control model; and a suppression control unit for injecting the dq-axis modulation voltage increment into the voltage modulation stage of the grid-connected device to form suppression control of the DC component of the output current.

[0018] As an embodiment of this application, the component extraction unit is specifically used to: perform high-pass or band-pass filtering on the dq-axis current component to extract the 50Hz dq-axis current component.

[0019] As an embodiment of this application, the component extraction unit performs bandpass filtering on the dq-axis current component by: filtering the dq-axis current component using a second-order bandpass filter, wherein the function of the second-order bandpass filter is:

[0020]

[0021] Where s is the complex frequency variable in the Laplace transform.

[0022] As an embodiment of this application, the above-mentioned apparatus further includes: a mathematical model construction unit, used to establish a mathematical model of the network-type device in the abc coordinate system based on the physical structure and electrical connection of the network-type device; a model coordinate transformation unit, used to convert the mathematical model in the abc coordinate system into a mathematical model in the dq0 synchronous rotating coordinate system through an abc-dq0 coordinate transformation; and a current control model construction unit, used to construct the current control model based on the control model of the network-type device and the mathematical model in the dq0 synchronous rotating coordinate system.

[0023] As an embodiment of this application, the above-mentioned modulation voltage acquisition unit includes: a first comparison module, used to compare the extracted 50Hz d-axis current component with the d-axis current reference value to obtain the d-axis current deviation; a second comparison module, used to compare the extracted 50Hz q-axis current component with the q-axis current reference value to obtain the q-axis current deviation; and an incremental voltage acquisition module, used to input the d-axis current deviation and the q-axis current deviation into a PI controller respectively, and calculate the dq-axis modulation voltage increment by combining a decoupling term.

[0024] As an embodiment of this application, the above-mentioned suppression control unit injects the dq-axis modulation voltage increment into the voltage modulation stage of the network device by superimposing the dq-axis modulation voltage increment with the internal potential base component output by the main control loop and the internal potential limiting component output by the current limiting module to generate a final reference internal potential for subsequent PWM modulation and driving of the converter switching module.

[0025] According to a third aspect of this application, an electronic device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the method described above.

[0026] According to a fourth aspect of this application, a computer-readable storage medium is provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the above-described method.

[0027] According to a fifth aspect of this application, a computer program product is provided, comprising a computer program / instructions that, when executed by a processor, implement the steps of the above-described method.

[0028] The method and apparatus for suppressing the DC component of the output current of grid-connected equipment proposed in this application can effectively optimize the response characteristics of grid-connected equipment under grid voltage fluctuations (especially system faults) through an additional DC component suppression strategy. In low impedance-to-inductance ratio applications, conventional control strategies can lead to a slowly decaying DC component in the current, which can occupy and limit the overcurrent capacity of the grid-connected equipment. The method proposed in this application can quickly suppress this DC component, thereby releasing the overcurrent capacity of the equipment and enabling it to be used to support the system voltage to the greatest extent. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0030] Figure 1 It is a generalized control structure diagram for network-type equipment;

[0031] Figure 2 This is a flowchart illustrating a method for suppressing the DC component of the output current of a network-type device according to an embodiment of this application;

[0032] Figure 3 This is a frequency response characteristic diagram of the bandpass filter provided in the embodiments of this application;

[0033] Figure 4 This is a flowchart illustrating the current control model construction process provided in the embodiments of this application;

[0034] Figure 5 This is a basic structural diagram of a network-type device provided in an embodiment of this application;

[0035] Figure 6 This is a schematic diagram of the process for obtaining the dq-axis modulation voltage increment provided in an embodiment of this application;

[0036] Figure 7 This is a control block diagram of a network-type device that considers additional control strategies to suppress DC components, as provided in the embodiments of this application.

[0037] Figure 8 This is a per-unit voltage diagram of the grid connection point of the grid-type equipment provided in the embodiments of this application;

[0038] Figure 9 This is a diagram of the reactive power output of a network-type device provided in an embodiment of this application;

[0039] Figure 10This is the output current diagram of the network-type device provided in the embodiments of this application;

[0040] Figure 11 This is a schematic diagram of a device for suppressing the DC component of the output current of a network-type device provided in an embodiment of this application;

[0041] Figure 12 This is a schematic diagram of a device for suppressing the DC component of the output current of a network-type device according to another embodiment of this application;

[0042] Figure 13 This is a schematic diagram of the modulation voltage acquisition unit provided in an embodiment of this application;

[0043] Figure 14 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the embodiments of this application will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments and descriptions of this application are used to explain this application, but are not intended to limit this application.

[0045] In applications with low impedance (such as high-voltage direct connection), network-type equipment exhibits a significant DC attenuation component in the current when adjusting the output voltage to support the system. This attenuation lasts for a considerable period, severely impacting the support capability of the network-type equipment. Therefore, it is necessary to add a control mechanism to suppress the DC component to the general network-type equipment control strategy framework. This application provides a method and apparatus for suppressing the DC component of the output current of a network-type equipment based on the aforementioned objective.

[0046] like Figure 2 The diagram shown is a flowchart illustrating a method for suppressing the DC component of the output current of a network-type device according to an embodiment of this application. The method includes the following steps:

[0047] Step S201: Obtain the three-phase current value at the grid connection point of the grid-connected equipment.

[0048] In this step, the three-phase AC current at the connection point between the grid-connected equipment and the grid (i.e., the grid connection point) can be measured and acquired in real time using current sensors. These real-time current values ​​are the basis for all subsequent calculations and controls, and accurate measurement is a prerequisite for ensuring the effectiveness of the entire suppression strategy.

[0049] To ensure the accuracy of the three-phase current values ​​acquired at the grid connection point of the grid-connected equipment, this embodiment employs several methods. Firstly, high-precision, high-bandwidth current sensors can be selected. Secondly, signal conditioning and acquisition circuits can be optimized. Thirdly, compensation and correction algorithms, such as temperature compensation, nonlinearity correction, and three-phase imbalance correction, can be provided at the software level. By comprehensively utilizing these hardware selection, circuit design, periodic calibration, and software compensation methods, the accuracy of the three-phase current measurement at the grid connection point can be maximized, providing reliable data input for subsequent coordinate transformation, DC component extraction, and suppression control.

[0050] Step S202: Decompose the three-phase current values ​​into dq-axis current components based on coordinate transformation.

[0051] For ease of control and analysis, the measured current values ​​in the three-phase stationary coordinate system (abc coordinate system) need to be transformed into a coordinate system (dq0 coordinate system) that rotates synchronously with the grid voltage. This step is achieved using the standard abc-dq0 coordinate transformation, and its transformation matrix is ​​shown in equation (1):

[0052]

[0053] After transformation, the three-phase AC current is decomposed into d-axis current components (id) and q-axis current components (iq). Under steady-state conditions, these two components are DC quantities, which directly reflect the magnitude of active and reactive currents.

[0054] Step S203: Extract the 50Hz dq-axis current component from the dq-axis current component.

[0055] The dq0 coordinate system (synchronous rotating coordinate system) is a reference coordinate system that rotates synchronously with the fundamental angular frequency of the power grid (50Hz, i.e., ω=2πf).

[0056] When a normal 50Hz three-phase alternating current from a power grid is transformed into the synchronously rotating dq0 coordinate system using the abc-dq0 transformation, the relative motion between the reference frame and the signal itself is zero because they rotate at the same speed. Therefore, a physical quantity that appears as a 50Hz sine wave in the stationary coordinate system becomes a DC quantity in the dq0 coordinate system. Conversely, if a DC component (i.e., a 0Hz signal) is superimposed on the original three-phase current (abc coordinate system), when this DC signal is transformed into the dq0 coordinate system rotating at a high speed of 50Hz, from the perspective of rotation, the stationary DC component appears as an alternating current rotating in the opposite direction at 50Hz. Simply put, this is a concept of relative motion: a person rotating at 50Hz (dq0 coordinate system) looking at another object rotating in the same direction at 50Hz (fundamental alternating current) will perceive the other as stationary (DC). A person rotating at 50Hz (dq0 coordinate system) looking at a completely stationary object (DC component) will perceive the object as rotating in the opposite direction at 50Hz (50Hz AC component). Therefore, in order to suppress the DC attenuation component that appears in the ABC three-phase current, the control system needs to accurately identify and eliminate the 50Hz AC component in the transformed dq0 coordinate system.

[0057] For the reasons mentioned above, it is necessary to extract the 50Hz dq axis current component separately in this step.

[0058] Step S204: Taking the 50Hz dq-axis current component being equal to 0 as the control target of the current control model, the dq-axis modulation voltage increment required to achieve the control target is obtained based on the current control model.

[0059] The goal of this step is to counteract the effect of the generated DC current component by actively injecting a compensation voltage. The 50Hz dq-axis current component extracted in step S203 is used as the input to the control model, and its control target is set to 0. This means that the controller will focus on eliminating this 50Hz component, thereby indirectly eliminating the DC component in the original three-phase current.

[0060] The current control model in this step is based on the mathematical model of the networked device in the dq0 coordinate system, and references the current inner-loop control concept of the networked device. This current control model describes the dynamic relationship between the device's output voltage and output current.

[0061] Step S205: Inject the dq axis modulation voltage increment into the voltage modulation stage of the network-type device to form suppression control of the DC component of the output current.

[0062] Specifically, the calculated dq-axis modulation voltage increments are injected into the main control loop of the grid-connected device. These two increments are superimposed with the internal potential components generated by the original main loop (such as the power control loop, virtual impedance current limiting loop, etc.) to form the final reference internal potential signal. This synthesized signal is then subjected to coordinate inverse transformation and PWM modulation to ultimately control the inverter switching action. As a result, the output voltage of the grid-connected device includes a component that suppresses the DC component, achieving closed-loop suppression control of the DC component of the output current.

[0063] As described above, the method for suppressing the DC component of the output current of grid-connected equipment proposed in this application, through an additional DC component suppression strategy, can effectively optimize the response characteristics of grid-connected equipment under grid voltage fluctuations (especially system faults). In low impedance-to-inductance ratio applications, conventional control strategies can lead to a slowly decaying DC component in the current, which consumes and limits the overcurrent capacity of the grid-connected equipment. The method proposed in this application can quickly suppress this DC component, thereby releasing the overcurrent capacity of the equipment and enabling it to be used to support the system voltage to the greatest extent possible.

[0064] In one embodiment of this application, the step S203 above, in which the 50Hz dq-axis current component is extracted from the dq-axis current component, may specifically include: performing high-pass or band-pass filtering on the dq-axis current component to extract the 50Hz dq-axis current component.

[0065] As mentioned earlier, the DC component of the three-phase current (abc coordinate system) will appear as a 50Hz AC component on the dq axis after synchronous rotating coordinate transformation. Therefore, the goal of this step is to separate this 50Hz AC signal from the predominantly DC dq axis current.

[0066] In this embodiment, a high-pass filter or a band-pass filter can be used to achieve this goal. A high-pass filter can filter out the DC fundamental component of the dq axis, allowing the 50Hz AC component to pass. A band-pass filter can more precisely allow signals within a very narrow frequency band around 50Hz to pass, filtering out not only the DC component but also interference from other high-frequency harmonics.

[0067] While fourth-order and sixth-order bandpass filters offer advantages such as reduced transition band and faster attenuation, they increase the difficulty of stability control. However, the fundamental frequency of the dq-axis current output by a network-type device is a DC component, and its harmonics are mostly high-frequency components; therefore, the requirements for the transition band and attenuation characteristics of the filter are not high. Therefore, preferably, this embodiment uses a second-order bandpass filter to filter the aforementioned dq-axis current components.

[0068] The transfer function of the second-order bandpass filter in this embodiment is shown in equation (2) below:

[0069]

[0070] In the above formula, s is the complex frequency variable in the Laplace transform, ω0 is the center angular frequency of the filter, and Q is the quality factor of the filter.

[0071] In this embodiment, the design parameters are ω0 = 2πf0 = 314.159, bandwidth BW = 2πf = 37.6991Hz, and quality factor. The bandpass filter function is obtained as shown in equation (3), and its frequency response characteristics are as follows: Figure 3 As shown.

[0072]

[0073] from Figure 3 It can be seen that the filter has an amplitude of 0dB at 50Hz, and the gain drops to -3dB at 47Hz and 53Hz. The amplitude decreases in other frequency bands, which meets the pre-design requirements.

[0074] In another embodiment of this application, the above method further includes a process for constructing a current control model, such as... Figure 4 As shown, the construction process of this current control model includes the following steps:

[0075] Step S401: Based on the physical structure and electrical connection of the network-type device, establish a mathematical model of the network-type device in the abc coordinate system.

[0076] First, we analyze the physical structure and electrical connections of grid-type equipment. The structure of grid-type equipment is almost identical to that of traditional grid-type equipment, the difference being that its DC-side capacitors often use supercapacitors or energy storage components. For example... Figure 5 The diagram shown is a basic structural diagram of a network-type device provided in an embodiment of this application.

[0077] Network-type equipment uses a cascaded H-bridge structure and can be connected in either delta or star configurations. Figure 5 The diagram illustrates a star connection, with each H-bridge module having a supercapacitor of C. dc The voltage is u dc Each phase has N modules connected in series, and the total DC bus voltage is U. dc =N×u dc The inductance value of the connected reactor is L. f The resistance is R f The system voltage is u. a_grid u b_grid u c_grid The grid-connected current is i a_grid i b_grid i c_grid The grid-connected voltage is u a_svg u b_svgu c_svg Its mathematical model in the abc coordinate system can be shown in equation (4) below:

[0078]

[0079] This provides a mathematical model of a grid-type equipment in a three-phase (abc) stationary coordinate system. This model is a set of descriptions of u _abc_svg i _abc_grid and u _abc_grid The differential equation relating them.

[0080] Step S402: Transform the mathematical model in the abc coordinate system into a mathematical model in the dq0 synchronous rotating coordinate system through the abc-dq0 coordinate transformation.

[0081] In a three-phase AC system (abc coordinate system), the variables are AC quantities that change with time, making direct control very complex. By introducing the dq0 synchronous rotating coordinate transformation, the power frequency AC quantity can be transformed into a DC quantity, thereby greatly simplifying the controller design. In this step, the mathematical model of the network-type equipment under dq0 can be obtained through the abc-dq0 coordinate transformation, as shown in the following equation (5):

[0082]

[0083] In the formula, the grid-connected voltage is u. d_grid u q_grid The grid-connected current is i d_svg i q_svg The device output voltage is u d_svg u q_svg .

[0084] After transformation, a mathematical model of the network-type device in the dq0 coordinate system is obtained. In this model, all voltages and currents (such as u) are represented. d_grid u q_grid i d_svg i q_svg All of these become relative direct currents, and there is a coupling term (L) between the d-axis and the q-axis. f ω0i q_svg and L f ω0i d_svg ).

[0085] Step S403: Referring to the control model of the grid-type device and based on the mathematical model under the synchronous rotating coordinate system of dq0, construct the current control model.

[0086] In this step, based on the mathematical model of the grid-type device and with reference to the control model of the grid-type device, the current control model of the grid-type device can be obtained, as shown in equation (6) below:

[0087]

[0088] In the formula: U dc U is the total DC bus voltage. dc_ref For DC voltage reference, Q ac Q is the reactive power output of the grid. ac_ref i is the reference value for reactive power. d_svg For the d-axis current output by the network-type device, i d_ref For the d-axis current reference, i q_svg For the q-axis current output by the network-type device, i q_ref For the d-axis current reference, k p_dc and k i_dc These are the proportional and integral coefficients of the DC voltage controller, respectively, k p_V and k i_V These are the proportional and integral coefficients of the AC voltage controller, respectively, k p_I and k i_I These are the proportional coefficient and integral coefficient of the inner loop current controller, respectively.

[0089] This step ultimately yields a clear, decoupled current control model. This model clarifies the complete control logic from the power / voltage reference to the final output voltage and the required PI controller parameters, which forms the basis for achieving stable operation of grid-connected equipment and additional DC suppression functionality.

[0090] In another embodiment of this application, such as Figure 6 As shown, in step S204 above, the control target of the current control model is that the 50Hz dq-axis current component is equal to 0. Based on the current control model, the dq-axis modulation voltage increment required to achieve the control target includes:

[0091] Step S601: Compare the extracted 50Hz d-axis current component with the d-axis current reference value to obtain the d-axis current deviation.

[0092] Step S602: Compare the extracted 50Hz q-axis current component with the q-axis current reference value to obtain the q-axis current deviation.

[0093] Step S603: Input the d-axis current deviation and the q-axis current deviation into the PI controller respectively, and calculate the dq-axis modulation voltage increment by combining the decoupling term.

[0094] In this embodiment, the target value is set to zero for the filtered dq-axis 50Hz component. Based on the current control model obtained above, an additional control model for the grid-type equipment that suppresses DC components can be obtained, as shown in equation (7). Its control block diagram is as follows.Figure 7 As shown.

[0095]

[0096] The ultimate goal of this application is to completely eliminate the DC component in the original three-phase current. This DC component is represented as a 50Hz AC component in the dq coordinate system. Therefore, ideally, the amplitude of the 50Hz component in the dq-axis current should be zero. Based on the above goal, the reference values ​​of the inner loops of the d-axis and q-axis currents ( Figure 7 in i d_ref and i q_ref The setting is 0. This means that it is expected that the 50Hz current component will disappear through control.

[0097] The 50Hz d-axis current component (i.e., i) extracted through the bandpass filter d_svg The d-axis current deviation is obtained by comparing it with the d-axis current reference value (0). Similarly, the extracted 50Hz q-axis current component (i.e., i... q_svg The q-axis current deviation is obtained by comparing it with the q-axis current reference value (0).

[0098] Then, the current deviations along the d-axis and q-axis obtained in the previous step are fed into two independent PI (proportional-integral) controllers. For example... Figure 7 As shown, these two PI controllers have the same proportional coefficient k. p_I and integral coefficient k i_I .

[0099] In the dq rotating coordinate system, there is a coupling effect between the d-axis and the q-axis (as shown in equation (5)). f ω0i q_svg and L f ω0i d_svg (As shown in the item). To achieve precise independent control, decoupling is necessary. This means that when calculating the d-axis output voltage, the coupling effect of the q-axis current (-L) needs to be subtracted. f ω0i' q_svg Similarly, when calculating the q-axis output voltage, the effect of the d-axis current (+L) must be taken into account. f ω0i' d_svg ).

[0100] The PI controller performs proportional and integral calculations on the input deviation, and then, combined with the decoupling term, calculates the dq-axis modulation voltage increment required to eliminate the 50Hz current deviation. Figure 7 The ΔE shown d 'and ΔE q '.

[0101] In another embodiment of this application, the step S105 above, in which the dq-axis modulation voltage increment is injected into the voltage modulation stage of the network-type device to suppress and control the DC component of the output current, may further include:

[0102] The dq-axis modulation voltage increment is superimposed with the basic component of the internal potential output by the main control loop and the limiting component of the internal potential output by the current limiting module to generate the final reference internal potential, which is used for subsequent PWM modulation and driving of the converter switching module.

[0103] Network-type devices themselves have a main control loop (such as...) Figure 1 As shown in the diagram, it calculates a basic internal potential reference signal based on the system's power, voltage, and other requirements. This signal determines the voltage and frequency that the device should output under normal steady-state conditions.

[0104] To protect power electronic devices, grid-connected equipment also includes a current limiting element (such as...). Figure 1 (As shown). When the current is about to exceed the safe range, the module outputs a limiting internal potential component to adjust the final output voltage, thereby confining the current within the safe threshold.

[0105] The DC suppression module outputs a modulation voltage increment, which is a correction voltage specifically generated to cancel out the 50Hz current component (i.e., the original DC component).

[0106] The three components—the base component, the limiting component, and the calculated dq-axis modulation voltage increment—are vector-superimposed. This synthesis process can be understood as follows: on top of the base voltage required for normal operation of the equipment, the necessary protective limiting voltage is superimposed, and finally, a fine-tuning voltage for eliminating the DC component is superimposed. The final synthesized signal is the final reference internal potential that contains all control objectives.

[0107] This final reference internal potential is transformed into a three-phase (abc) reference voltage signal through a reverse dq0-abc coordinate transformation. This three-phase signal is then fed into a PWM (Pulse Width Modulation) module to generate high-frequency switching drive signals. These switching signals ultimately drive the H-bridge module in the converter to precisely turn on and off, thereby outputting the desired ideal voltage waveform with DC components eliminated on the AC side of the grid-connected equipment.

[0108] Therefore, this step seamlessly integrates the calculation results (modulation voltage increment) of the DC component suppression strategy into the existing, complex multi-objective control framework of the network-type equipment. By superimposing signals, precise suppression of the DC component of the output current is achieved without interfering with the main functions of the equipment (such as voltage frequency support and overcurrent protection).

[0109] Taking a grid-connected device with a capacity of 20Mvar and a connection point voltage of 16kV as an example, such as Figure 8 , Figure 9 , Figure 10 The figure shows a comparison of the voltage step response characteristics of conventional grid-type equipment in a low impedance-inductance ratio system after adopting the aforementioned DC component suppression strategy. It can be seen that the addition of the DC component suppression strategy effectively reduces the DC component of the output current during the voltage change process, while not changing the steady-state value of the grid-type equipment output, i.e., its support for the system voltage, which proves the effectiveness of this application.

[0110] As described above, the method for suppressing the DC component of the output current of grid-connected equipment provided in this application, through an additional DC component suppression strategy, can effectively optimize the response characteristics of grid-connected equipment under grid voltage fluctuations (especially system faults). In low impedance-to-inductance ratio applications, conventional control strategies can lead to a slowly decaying DC component in the current, which consumes and limits the overcurrent capacity of the grid-connected equipment. The method proposed in this application can quickly suppress this DC component, thereby releasing the overcurrent capacity of the equipment and enabling it to be used to support the system voltage to the greatest extent.

[0111] like Figure 11 The diagram shown is a schematic representation of a device for suppressing the DC component of the output current of a grid-type device according to a specific embodiment. The device includes: a current acquisition unit 1110, a current decomposition unit 1120, a component extraction unit 1130, a modulation voltage acquisition unit 1140, and a suppression control unit 1150, which are connected sequentially.

[0112] The current acquisition unit 1110 is used to acquire the three-phase current value at the grid connection point of the grid-connected equipment.

[0113] The current decomposition unit 1120 is used to decompose the three-phase current values ​​into dq-axis current components based on coordinate transformation.

[0114] The component extraction unit 1130 is used to extract the 50Hz dq-axis current component from the dq-axis current component.

[0115] The modulation voltage acquisition unit 1140 is used to obtain the dq axis modulation voltage increment required to achieve the control target based on the current control model, with the 50Hz dq axis current component being equal to 0.

[0116] The suppression control unit 1150 is used to inject the dq axis modulation voltage increment into the voltage modulation stage of the grid-type device to form suppression control of the DC component of the output current.

[0117] In one embodiment of this application, the component extraction unit 1030 is specifically used to: perform high-pass or band-pass filtering on the dq-axis current component to extract the 50Hz dq-axis current component.

[0118] In one embodiment of this application, the component extraction unit 1030 performs bandpass filtering on the dq-axis current component by: filtering the dq-axis current component using a second-order bandpass filter, wherein the function of the second-order bandpass filter is:

[0119]

[0120] Where s is the complex frequency variable in the Laplace transform.

[0121] In one embodiment of this application, such as Figure 12 As shown, the above-mentioned device also includes:

[0122] The mathematical model building unit 1160 is used to establish a mathematical model of the network-type device in the abc coordinate system based on the physical structure and electrical connection of the network-type device.

[0123] The model coordinate transformation unit 1170 is used to transform the mathematical model in the abc coordinate system into the mathematical model in the dq0 synchronous rotating coordinate system through the abc-dq0 coordinate transformation.

[0124] The current control model construction unit 1180 is used to refer to the control model of the grid-connected equipment and construct the current control model based on the mathematical model in the dq0 synchronous rotating coordinate system.

[0125] In one embodiment of this application, such as Figure 13 As shown, the modulation voltage acquisition unit 1140 includes:

[0126] The first comparison module 1141 is used to compare the extracted 50Hz d-axis current component with the d-axis current reference value to obtain the d-axis current deviation.

[0127] The second comparison module 1142 is used to compare the extracted 50Hz q-axis current component with the q-axis current reference value to obtain the q-axis current deviation.

[0128] The incremental voltage acquisition module 1143 is used to input the d-axis current deviation and the q-axis current deviation into the PI controller respectively, and calculate the dq-axis modulation voltage increment by combining the decoupling term.

[0129] In one embodiment of this application, the suppression control unit 1050 injects the dq-axis modulation voltage increment into the voltage modulation stage of the network device by superimposing the dq-axis modulation voltage increment with the internal potential base component output by the main control loop and the internal potential limiting component output by the current limiting module to generate a final reference internal potential for subsequent PWM modulation and driving of the converter switching module.

[0130] As described above, the device for suppressing the DC component of the output current of grid-connected equipment provided in this application can effectively optimize the response characteristics of grid-connected equipment under grid voltage fluctuations (especially system faults) through an additional DC component suppression strategy. In low impedance-to-inductance ratio applications, conventional control strategies can lead to a slowly decaying DC component in the current, which can occupy and limit the overcurrent capacity of the grid-connected equipment. The method proposed in this application can quickly suppress this DC component, thereby releasing the overcurrent capacity of the equipment and enabling it to be used to support the system voltage to the greatest extent.

[0131] Figure 14 This is a schematic diagram of the electronic device provided in the embodiments of this application. Figure 14 The illustrated electronic device is a general-purpose data processing apparatus, comprising a general-purpose computer hardware architecture, including at least a processor 801 and a memory 802. The processor 801 and memory 802 are connected via a bus 803. The memory 802 is adapted to store one or more instructions or programs executable by the processor 801. These instructions or programs are executed by the processor 801 to implement the steps in the method for suppressing the DC component of the output current of a network-type device described above.

[0132] The processor 801 described above can be a standalone microprocessor or a collection of one or more microprocessors. Thus, the processor 801 executes commands stored in the memory 802, thereby performing the method flow described in the embodiments of this application to process data and control other devices. The bus 803 connects the aforementioned components together, and also connects these components to the display controller 804, the display device, and the input / output (I / O) device 805. The input / output (I / O) device 805 can be a mouse, keyboard, modem, network interface, touch input device, motion-sensing input device, printer, and other devices known in the art. Typically, the input / output (I / O) device 805 is connected to the system via an input / output (I / O) controller 806.

[0133] The memory 802 can store software components, such as an operating system, a communication module, an interaction module, and application programs. Each of the modules and application programs described above corresponds to a set of executable program instructions that perform one or more functions and the methods described in the embodiments of the invention.

[0134] This application also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the method for suppressing the DC component of the output current of a network-type device.

[0135] This application also provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the steps of the method for suppressing the DC component of the output current of a network-type device.

[0136] The method and apparatus for suppressing the DC component of the output current of grid-connected equipment proposed in this application can effectively optimize the response characteristics of grid-connected equipment under grid voltage fluctuations (especially system faults) through an additional DC component suppression strategy. In low impedance-to-inductance ratio applications, conventional control strategies can lead to a slowly decaying DC component in the current, which can occupy and limit the overcurrent capacity of the grid-connected equipment. The method proposed in this application can quickly suppress this DC component, thereby releasing the overcurrent capacity of the equipment and enabling it to be used to support the system voltage to the greatest extent.

[0137] Preferred embodiments of this application have been described above with reference to the accompanying drawings. Many features and advantages of these embodiments are apparent from this detailed description, and therefore the claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. Furthermore, since many modifications and alterations will readily occur to those skilled in the art, the embodiments of this application are not intended to be limited to the precise structures and operations illustrated and described, but rather to encompass all suitable modifications and equivalents falling within their scope.

[0138] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0139] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart...Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0140] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0141] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0142] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for suppressing the DC component of the output current of a network-type device, characterized in that, The method includes: Obtain the three-phase current value at the grid connection point of the grid-connected equipment; Based on coordinate transformation, the three-phase current values ​​are decomposed into dq-axis current components; Extract the 50Hz dq-axis current component from the dq-axis current components; Taking the 50Hz dq-axis current component being equal to 0 as the control objective of the current control model, the dq-axis modulation voltage increment required to achieve the control objective is obtained based on the current control model. The dq-axis modulation voltage increment is injected into the voltage modulation stage of the network-type device to suppress the DC component of the output current.

2. The method for suppressing the DC component of the output current of a network-type device as described in claim 1, characterized in that, The extraction of the 50Hz dq-axis current component from the dq-axis current component includes: The dq-axis current component is subjected to high-pass or band-pass filtering to extract the 50Hz dq-axis current component.

3. The method for suppressing the DC component of the output current of a network-type device as described in claim 1, characterized in that, Bandpass filtering of the dq-axis current components includes: The dq-axis current components are filtered using a second-order bandpass filter. The function of the second-order bandpass filter is: Where s is the complex frequency variable in the Laplace transform.

4. The method for suppressing the DC component of the output current of a network-type device as described in claim 1, characterized in that, The method further includes: Based on the physical structure and electrical connections of the network-type device, a mathematical model of the network-type device in the abc coordinate system is established. The mathematical model in the abc coordinate system is transformed into a mathematical model in the dq0 synchronous rotating coordinate system through the abc-dq0 coordinate transformation. Referring to the control model of the grid-type equipment and based on the mathematical model under the dq0 synchronous rotating coordinate system, the current control model is constructed.

5. The method for suppressing the DC component of the output current of a network-type device as described in claim 1, characterized in that, The dq-axis modulation voltage increment required to achieve the control objective based on the current control model includes: The extracted 50Hz d-axis current component is compared with the d-axis current reference value to obtain the d-axis current deviation. The extracted 50Hz q-axis current component is compared with the q-axis current reference value to obtain the q-axis current deviation; The d-axis current deviation and the q-axis current deviation are respectively input into the PI controller, and the dq-axis modulation voltage increment is calculated by combining the decoupling term.

6. The method for suppressing the DC component of the output current of a network-type device as described in claim 1, characterized in that, The voltage modulation step of injecting the dq-axis modulated voltage increment into the network-type device includes: The dq-axis modulation voltage increment is superimposed with the basic component of the internal potential output by the main control loop and the limiting component of the internal potential output by the current limiting module to generate the final reference internal potential, which is used for subsequent PWM modulation and driving of the converter switching module.

7. A device for suppressing the DC component of the output current of a network-type device, characterized in that, The device includes: The current acquisition unit is used to acquire the three-phase current value at the grid connection point of grid-connected equipment; A current decomposition unit is used to decompose the three-phase current values ​​into dq-axis current components based on coordinate transformation. A component extraction unit is used to extract a 50Hz dq-axis current component from the dq-axis current components. The modulation voltage acquisition unit is used to take the 50Hz dq-axis current component being equal to 0 as the control target of the current control model, and to obtain the dq-axis modulation voltage increment required to achieve the control target based on the current control model. The suppression control unit is used to inject the dq axis modulation voltage increment into the voltage modulation stage of the network-type device to form suppression control of the DC component of the output current.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

10. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method according to any one of claims 1 to 6.

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