Direct-current component suppression method for grid-connected inverter, inverter, and storage medium
By constructing a virtual impedance and introducing a control loop in the grid-connected inverter, the DC component in the grid-connected current is suppressed based on Kirchhoff's laws, thus solving the problem of the DC component in the output current of the grid-connected inverter and achieving effective suppression without increasing hardware costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHENZHEN POWEROAK NEWENER CO LTD
- Filing Date
- 2025-12-25
- Publication Date
- 2026-05-15
AI Technical Summary
The DC component in the output current of a grid-connected inverter affects grid safety and equipment lifespan.
By constructing a virtual impedance and introducing it into the control loop of the grid-connected inverter, the expression of the DC component in the grid-connected current is determined based on Kirchhoff's laws. The virtual impedance is constructed and the modulation wave compensation term is obtained through equivalent transformation. The modulation wave signal is superimposed to suppress the DC component.
It significantly suppresses the DC component in the grid-connected current, improves the current waveform quality, and does not affect the AC fundamental frequency performance. It is also low-cost and requires no additional hardware sensors or compensation circuits.
Smart Images
Figure CN121417699B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of microgrid technology, and in particular to a method for suppressing the DC component of a grid-connected inverter, the inverter, and a storage medium. Background Technology
[0002] Grid-connected inverters are widely used in the field of microgrid technology. A common grid-connected inverter consists of four full-bridge switches and a filter circuit. Its working principle is as follows: the magnitude of the grid-connected current is controlled by a closed loop to generate a modulated wave, which is converted into a high-frequency switching drive signal by a PWM (Pulse Width Modulation) modulator to generate a high-frequency current. This current passes through an LC or LCL filter circuit to filter out harmonic components, and finally outputs high-quality industrial frequency AC power to feed into the grid.
[0003] In theory, grid-connected inverters only output AC power. However, in practice, factors such as zero-point drift of sampling elements, on-state voltage drop and dead-time deviation of power devices, and inconsistent drive signals of switching transistors cause asymmetry in the positive and negative waveforms of the output PWM wave. This results in a zero-point shift of the inverter bridge arm midpoint voltage, ultimately leading to a DC component in the output AC current. The DC component in the output current of a grid-connected inverter can affect grid safety and equipment lifespan. Summary of the Invention
[0004] The embodiments of this application aim to provide a method for suppressing the DC component of a grid-connected inverter, an inverter, and a storage medium, to solve the technical problem of excessive DC component in the grid-connected current in the prior art.
[0005] To address the aforementioned technical problems, the embodiments of this application provide the following technical solutions:
[0006] According to a first aspect of this application, a method for suppressing the DC component of a grid-connected inverter is provided, the method comprising:
[0007] Based on the grid-connected inverter circuit model and Kirchhoff's laws, the expression for the DC component in the grid-connected current is determined.
[0008] Based on the expression for the DC component in the grid-connected current, a virtual impedance that can suppress the DC component in the grid-connected current is constructed.
[0009] The virtual impedance is introduced into the control loop of the grid-connected inverter, and the calculation model of the modulation wave compensation term is obtained through equivalent transformation.
[0010] The original modulated wave signal output by the current loop controller and the modulated wave compensation signal obtained by the calculation model based on the modulated wave compensation term are superimposed to obtain the final modulated wave signal.
[0011] Optionally, determining the expression for the DC component of the grid-connected current based on the grid-connected inverter circuit model and Kirchhoff's laws includes:
[0012] Based on the grid-connected inverter circuit model and Kirchhoff's laws, the expression for the grid-connected current is obtained;
[0013] Based on the expression for the grid-connected current, the expression for the DC component of the grid-connected current is obtained.
[0014] Optionally, the grid-connected inverter includes a DC voltage input source, a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a filter inductor, a filter capacitor, a grid-side inductor, and line impedance. The expression for the grid-connected current is:
[0015]
[0016] in, For grid-connected current, The voltage at the midpoint of the bridge arm. This is the grid voltage. This is the inductance of the filter inductor. This is the capacitance value of the filter capacitor. The inductance of the grid-side inductor. For line impedance, For the Laplace operator.
[0017] Optionally, the expression for the DC component in the grid-connected current is:
[0018]
[0019] in, This refers to the DC component of the grid-connected current. This represents the DC component of the voltage at the midpoint of the bridge arm.
[0020] Optionally, constructing a virtual impedance that can suppress the DC component of the grid-connected current based on the expression for the DC component of the grid-connected current includes:
[0021] Based on the expression for the DC component in the grid-connected current, a virtual impedance is constructed in series with the line impedance and satisfies a preset amplitude-frequency characteristic. The preset amplitude-frequency characteristic includes that the virtual impedance has a high gain at zero frequency and a gain close to zero at the fundamental frequency.
[0022] Optionally, the transfer function of the virtual impedance is:
[0023]
[0024] in, , and All Adjustable parameters.
[0025] Optionally, the calculation model for the modulation wave compensation term is as follows:
[0026]
[0027] in, It is the modulation compensation term. For the gain of the PWM modulation stage, This refers to the DC input voltage amplitude of the inverter. The amplitude of the preset triangular carrier wave.
[0028] According to a second aspect of this application, a grid-connected inverter is provided, the grid-connected inverter including a controller, the controller including: at least one processor and a memory communicatively connected to the at least one processor, the memory storing instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the method described in any of the above.
[0029] Optionally, the grid-connected inverter further includes a DC voltage input source, a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a filter inductor, a filter capacitor, a grid-side inductor, and line impedance.
[0030] According to a third aspect of this application, a computer-readable storage medium is provided, the computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of any of the methods described above.
[0031] The beneficial effects of this application's embodiments are as follows: Unlike existing technologies, this application provides a method for suppressing the DC component of a grid-connected inverter. First, based on the grid-connected inverter circuit model and Kirchhoff's laws, the expression for the DC component in the grid-connected current is determined. Then, based on this expression, a virtual impedance capable of suppressing the DC component is constructed, and this virtual impedance is introduced into the control loop of the grid-connected inverter. An equivalent transformation is then used to obtain a calculation model for the modulation wave compensation term. Finally, the original modulation wave signal output from the current loop controller and the modulation wave compensation signal obtained from the calculation model of the modulation wave compensation term are superimposed to obtain the final modulation wave signal. This method, by introducing a virtual impedance to enhance and suppress the DC component, solves the problem at its source, achieving significant suppression without affecting the AC fundamental frequency performance. Furthermore, this application employs a pure software algorithm, requiring no additional hardware sensors or compensation circuits, resulting in low cost. Attached Figure Description
[0032] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.
[0033] Figure 1 This is a schematic diagram of the grid-connected inverter provided in the embodiments of this application;
[0034] Figure 2 This is a schematic diagram of the controller provided in an embodiment of this application;
[0035] Figure 3 This is a schematic diagram of a conventional grid-connected current control strategy provided in an embodiment of this application;
[0036] Figure 4 This is a flowchart of a DC component suppression method for a grid-connected inverter provided in an embodiment of this application;
[0037] Figure 5 This is the virtual impedance Bode plot provided in the embodiments of this application;
[0038] Figure 6 This is a schematic diagram illustrating the introduction of virtual impedance into the control loop, as provided in an embodiment of this application.
[0039] Figure 7 The embodiments provided in this application are based on Figure 6 A schematic diagram of the control block diagram after equivalent transformation;
[0040] Figure 8 The embodiments provided in this application are based on Figure 6 A schematic diagram illustrating the equivalent transformation process of the control block diagram;
[0041] Figure 9 This is a control effect diagram provided in the embodiments of this application when using a conventional grid-connected current control strategy;
[0042] Figure 10 This is a control effect diagram after adopting the DC component suppression method provided in the embodiments of this application. Detailed Implementation
[0043] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0044] Furthermore, the technical features involved in the various embodiments of this application described below can be combined with each other as long as they do not conflict with each other.
[0045] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.
[0046] Please see Figure 1 , Figure 1 This is a schematic diagram of the grid-connected inverter provided in an embodiment of this application. For example... Figure 1 The grid-connected inverter shown includes an inverter circuit 10 and a controller 20. The inverter circuit 10 includes a DC voltage input source. First switching transistor Second switching transistor Third switching transistor Fourth switching transistor Filter inductor Filter capacitor , grid-side inductor and line impedance In addition, the grid-connected inverter is connected to the power grid. The inverter arm output midpoint voltage is expressed as: .
[0047] The controller 20 is connected to the switching transistors in the inverter circuit 10. The connection is based on the built-in control program that controls the switching transistor. The controller 20 can be turned on and off. In some embodiments, the controller 20 may be a microcontroller unit (MCU) or a digital signal processing (DSP) controller, etc.
[0048] In some embodiments, the grid-connected inverter may further include a grid-connected current sampling unit. This grid-connected current sampling unit is located at the grid inflow side and is used to collect the grid-connected current in real time. .
[0049] Please refer to Figure 2 , Figure 2 An exemplary structure of controller 20 is shown. For example... Figure 2 As shown, the controller 20 includes at least one processor 21 and a memory 22. The memory 22 can be built into the controller 20 or external to the controller 20. The memory 22 can also be a remotely configured memory connected to the controller 20 via a network.
[0050] Memory 22, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules. Memory 22 may include a program storage area and a data storage area, wherein the program storage area may store the operating system and application programs required for at least one function; the data storage area may store data created based on the use of the terminal, etc. Furthermore, memory 22 may include high-speed random access memory and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, memory 22 may optionally include memory remotely located relative to processor 21, and these remote memories can be connected to the terminal via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.
[0051] The processor 21 performs various functions of the terminal and processes data by running or executing software programs and / or modules stored in the memory 22 and calling data stored in the memory 22, thereby performing overall monitoring of the terminal, such as implementing the DC component suppression method of the grid-connected inverter described in any embodiment of this application.
[0052] Processor 21 can be one or more. Figure 2 The example provided is a processor 21. Processor 21 and memory 22 can be connected via a bus or other means. Processor 21 may include a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a controller, a field-programmable gate array (FPGA) device, etc. Processor 21 can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.
[0053] Please refer to Figure 3 , Figure 3 This is a schematic diagram of a conventional grid-connected current control strategy provided in an embodiment of this application. For example... Figure 3 As shown, the grid-connected current reference value Inverter grid-connected current sampling value The difference is then fed into the current loop controller. , to obtain the modulated wave Modulated wave A switching transistor is generated after comparison with a triangular carrier wave. The drive signal generates the midpoint voltage of the bridge arm. Midpoint voltage of bridge arm With the voltage of the filter capacitor The voltage of the filter inductor is obtained by subtraction. Voltage of the filter inductor Divide by the impedance of the filter inductor The current of the filter inductor is obtained. Voltage of the filter capacitor Divide by the impedance of the filter capacitor The current of the filter capacitor is obtained. The current of the filter inductor With the current of the filter capacitor The difference is used to obtain the grid-connected current. .
[0054] Please refer to Figure 4 , Figure 4 This is a flowchart illustrating a DC component suppression method for a grid-connected inverter according to an embodiment of this application. The method is applied to a grid-connected inverter. The grid-connected inverter may include an inverter circuit and a controller, etc. In some embodiments, the grid-connected inverter can... Figure 1 The implementation of the structure is described in detail in the above embodiments and will not be repeated here.
[0055] like Figure 4 As shown, the DC component suppression method of this grid-connected inverter includes:
[0056] Step S401: Based on the grid-connected inverter circuit model and Kirchhoff's laws, determine the expression for the DC component in the grid-connected current.
[0057] based on Figure 1 For the grid-connected inverter in the circuit, based on Kirchhoff's voltage and current laws, the expression for the grid-connected current can be derived as follows:
[0058] (1)
[0059] in, For grid-connected current, The voltage at the midpoint of the bridge arm. This is the grid voltage. This is the inductance of the filter inductor. This is the capacitance value of the filter capacitor. The inductance of the grid-side inductor. For line impedance, For the Laplace operator.
[0060] In theory, the grid-connected current outputs only AC. However, in reality, factors such as zero-point drift of the sampling element, on-state voltage drop and dead-time deviation of power devices, and inconsistent drive signals of the switching transistors cause a shift in the positive and negative waveforms of the output PWM wave, resulting in a DC component in the grid-connected current. In this case, the midpoint voltage of the bridge arm can be... and grid-connected current Decomposed into a superposition of AC and DC components:
[0061] (2)
[0062] (3)
[0063] in, This represents the AC component of the voltage at the midpoint of the bridge arm. The DC component of the voltage at the midpoint of the bridge arm. This refers to the AC component of the grid-connected current. This represents the DC component of the grid-connected current.
[0064] Typically, the power grid can be considered an ideal AC source containing no DC component, i.e. =0. When it is necessary to describe the DC component, that is, let... =0, then in Under the influence of , combining equations (1), (2) and (3), the expression for the DC component in the grid-connected current is:
[0065] (4)
[0066] As can be seen from equation (4), the factors affecting the magnitude of the DC component in the grid-connected current are the DC component of the midpoint voltage of the bridge arm and the line impedance.
[0067] Step S402: Based on the expression of the DC component in the grid-connected current, construct a virtual impedance that can suppress the DC component in the grid-connected current.
[0068] According to the expression (4) for the DC component in the grid-connected current, a feasible solution to suppress the DC component in the grid-connected current is to construct a structure that is compatible with the line impedance. Series virtual impedance At this time, the DC component of the grid-connected current is:
[0069] (5)
[0070] At this point, the expression for the grid-connected current changes from equation (1):
[0071] (6)
[0072] As can be seen from equations (5) and (6), to suppress the DC component in the grid-connected current, the virtual impedance... The construction principle is to maximize its gain at 0Hz while minimizing its impact on signal amplitude and phase at other frequencies.
[0073] Therefore, a virtual impedance is constructed in series with the line impedance and satisfies a preset amplitude-frequency characteristic, which includes a high gain at zero frequency and a gain close to zero at the fundamental frequency. Specifically, based on the preset amplitude-frequency characteristic, the transfer function of the virtual impedance is constructed as follows:
[0074] (7)
[0075] in, , and All Adjustable parameters.
[0076] Please refer to Figure 5 , Figure 5 This is a virtual impedance Bode plot provided in an embodiment of this application. For example... Figure 5 As shown, virtual impedance The gain is relatively large near zero frequency, while the gain and phase are almost zero at other frequencies, especially having almost no effect on the 50Hz fundamental signal. Therefore, it can be called virtual impedance. It is a zero-frequency enhanced virtual impedance.
[0077] Step S403: Introduce the virtual impedance into the control loop of the grid-connected inverter, and obtain the calculation model of the modulation wave compensation term through equivalent transformation.
[0078] The virtual impedance is not directly connected in series with the physical circuit. Instead, it is introduced into the control loop of the grid-connected inverter and, through equivalent transformation, a modulation compensation term is obtained. This compensation term then compensates for the modulation wave to suppress the DC component in the grid-connected current. In other words, a virtual impedance is introduced. The essence is to obtain the modulation wave compensation term.
[0079] Please refer to Figures 6 to 8 , Figure 6 This is a schematic diagram illustrating the introduction of virtual impedance into the control loop, provided in an embodiment of this application. Figure 7 The embodiments provided in this application are based on Figure 6 The diagram is a schematic diagram after the control block diagram has undergone equivalent transformation. Figure 8 The embodiments provided in this application are based on Figure 6 A schematic diagram illustrating the equivalent transformation process of the control block diagram. For example... Figure 7 As shown, the calculation model for the modulation wave compensation term obtained after equivalent transformation is as follows:
[0080] (8)
[0081] in, It is the modulation compensation term. For the gain of the PWM modulation stage, This refers to the DC input voltage amplitude of the inverter. The amplitude of the preset triangular carrier wave.
[0082] Step S404: The original modulated wave signal output by the current loop controller and the modulated wave compensation signal obtained by the calculation model based on the modulated wave compensation term are superimposed to obtain the final modulated wave signal.
[0083] like Figure 7 As shown, the modulation compensation signal is obtained based on the calculation model of the modulation compensation term. Then, the current loop controller The original modulated wave signal output and modulated wave compensation signal The signals are superimposed to form the final modulated wave signal. This achieves the goal of suppressing the DC component in the grid-connected current.
[0084] Please refer to Figure 9 and Figure 10 , Figure 9 This is a control effect diagram provided in the embodiments of this application when using a conventional grid-connected current control strategy. Figure 10 This is a control effect diagram provided in the embodiments of this application after employing the DC component suppression method. The amplitude corresponding to 0Hz is the DC component amplitude. (Comparison) Figure 9 and Figure 10 It can be seen that after adopting the DC component suppression method of this application, the amplitude of the DC component in the grid-connected current is significantly reduced, thus optimizing the waveform quality of the grid-connected current.
[0085] The DC component suppression method for grid-connected inverters provided in this application first determines the expression for the DC component in the grid-connected current based on the grid-connected inverter circuit model and Kirchhoff's laws. Then, based on this expression, a virtual impedance capable of suppressing the DC component in the grid-connected current is constructed, and this virtual impedance is introduced into the control loop of the grid-connected inverter. An equivalent transformation is then performed to obtain a calculation model for the modulation wave compensation term. Finally, the original modulation wave signal output from the current loop controller and the modulation wave compensation signal obtained from the calculation model based on the modulation wave compensation term are superimposed to obtain the final modulation wave signal. This method, by introducing a virtual impedance to enhance and suppress the DC component, addresses the problem at its source, achieving significant suppression without affecting the AC fundamental frequency performance. Furthermore, this application employs a pure software algorithm, requiring no additional hardware sensors or compensation circuits, resulting in low cost.
[0086] This application also provides a non-volatile computer-readable storage medium storing computer-executable instructions that are executed by one or more processors, for example, executing the instructions described above. Figure 4 The method and steps.
[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.
Claims
1. A method for suppressing the DC component of a grid-connected inverter, characterized in that, The method includes: Based on the grid-connected inverter circuit model and Kirchhoff's laws, the expression for the DC component in the grid-connected current is determined. Based on the expression for the DC component in the grid-connected current, a virtual impedance that can suppress the DC component in the grid-connected current is constructed. The virtual impedance is introduced into the control loop of the grid-connected inverter, and the calculation model of the modulation wave compensation term is obtained through equivalent transformation. The original modulated wave signal output by the current loop controller and the modulated wave compensation signal obtained by the calculation model based on the modulated wave compensation term are superimposed to obtain the final modulated wave signal. The construction of a virtual impedance that can suppress the DC component in the grid-connected current, based on the expression for the DC component in the grid-connected current, includes: Based on the expression for the DC component in the grid-connected current, a virtual impedance is constructed in series with the line impedance and satisfies a preset amplitude-frequency characteristic. The preset amplitude-frequency characteristic includes that the virtual impedance has a high gain at zero frequency and a gain close to zero at the fundamental frequency.
2. The method according to claim 1, characterized in that, The expression for the DC component of the grid-connected current, determined based on the grid-connected inverter circuit model and Kirchhoff's laws, includes: Based on the grid-connected inverter circuit model and Kirchhoff's laws, the expression for the grid-connected current is obtained; Based on the expression for the grid-connected current, the expression for the DC component of the grid-connected current is obtained.
3. The method according to claim 2, characterized in that, The grid-connected inverter includes a DC voltage input source, a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a filter inductor, a filter capacitor, a grid-side inductor, and line impedance. The expression for the grid-connected current is: in, For grid-connected current, The voltage at the midpoint of the bridge arm. This is the grid voltage. This is the inductance of the filter inductor. This is the capacitance value of the filter capacitor. The inductance of the grid-side inductor. For line impedance, For the Laplace operator.
4. The method according to claim 3, characterized in that, The expression for the DC component of the grid-connected current is: in, This refers to the DC component of the grid-connected current. This represents the DC component of the voltage at the midpoint of the bridge arm.
5. The method according to claim 4, characterized in that, The transfer function of the virtual impedance is: in, , and All Adjustable parameters.
6. The method according to claim 5, characterized in that, The calculation model for the modulation wave compensation term is as follows: in, It is the modulation compensation term. For the gain of the PWM modulation stage, This refers to the DC input voltage amplitude of the inverter. The amplitude of the preset triangular carrier wave.
7. A grid-connected inverter, characterized in that, The grid-connected inverter includes a controller, the controller comprising: at least one processor and a memory communicatively connected to the at least one processor, the memory storing instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the method according to any one of claims 1 to 6.
8. The grid-connected inverter according to claim 7, characterized in that, The grid-connected inverter also includes a DC voltage input source, a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, a filter inductor, a filter capacitor, a grid-side inductor, and line impedance.
9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, performs the steps of the method as described in any one of claims 1-6.