Direct-current component suppression method for grid-connected inverter, inverter, and storage medium
By establishing a state-space model and using a state observer to estimate the DC component of the grid-connected inverter in real time, the problem of the DC component in the output current of the grid-connected inverter is solved, and the current waveform is optimized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHENZHEN POWEROAK NEWENER CO LTD
- Filing Date
- 2025-11-20
- Publication Date
- 2026-04-24
AI Technical Summary
The DC component in the output current of a grid-connected inverter affects grid safety and equipment lifespan.
A state-space model is established, and the DC component is estimated in real time through a state observer. This DC component is then subtracted from the grid-connected current to obtain the final reference value for closed-loop control.
It effectively suppresses the DC component in the grid-connected current and optimizes the current waveform quality.
Smart Images
Figure CN121173118B_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, this application provides 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] A state-space model is established based on the grid-connected inverter circuit and Kirchhoff's laws.
[0008] By utilizing the slow-varying characteristics of the DC component in the grid-connected current, the DC component is extended into a new state variable in the state-space model, resulting in an extended state-space model.
[0009] Based on the state-space extended model, the DC component is estimated in real time by a state observer to obtain the estimated value of the DC component.
[0010] The result of subtracting the estimated DC component from the original reference value of the grid-connected current is used as the final reference value for the grid-connected current closed-loop control.
[0011] Optionally, the state-space model is:
[0012]
[0013] in, This is the inductance of the filter inductor. The inductance of the grid-side inductor. This is the capacitance value of the filter capacitor. The current in the filter inductor is... The AC component in the grid-connected current. This is the voltage across the filter capacitor. This is the voltage at the midpoint of the inverter bridge arm. This is the grid voltage. This refers to the DC component of the grid-connected current.
[0014] Optionally, the state-space extension model is:
[0015] .
[0016] Optionally, the step of estimating the DC component in real time using a state observer based on the state-space extended model to obtain the estimated DC component value includes:
[0017] The state-space extension model is discretized to obtain a discretized state-space extension model, which includes discretized state extension equations and discretized measurement equations.
[0018] By introducing process noise into the discretized state extension equation and measurement noise into the discretized measurement equation, a state-space extension model in standard difference form is obtained.
[0019] The DC component in the standard difference form of the extended state space model is estimated in real time by using a state observer to obtain the DC component estimate.
[0020] Optionally, both the process noise and the measurement noise conform to a normal distribution.
[0021] Optionally, the state-space extended model in standard difference form is:
[0022]
[0023] in, This is the inductance of the filter inductor. The inductance of the grid-side inductor. This is the capacitance value of the filter capacitor. The current in the filter inductor is... The AC component in the grid-connected current. This is the voltage across the filter capacitor. This is the voltage at the midpoint of the inverter bridge arm. This is the grid voltage. This refers to the DC component of the grid-connected current. For discrete periods, Process noise introduced to model error, For the measurement noise of the current sensor, For measurement variables.
[0024] Optionally, the state observer is a Kalman filter, and the formula for real-time estimation of the DC component in the standard difference form of the state-space extended model using the Kalman filter is as follows:
[0025]
[0026] in, Here is the state transition matrix. To control the input matrix, For the observation matrix, To measure the covariance matrix of the noise, Let be the covariance matrix of the process noise. for Prior state variable estimation, For the state variable to be estimated, which includes a DC component, For Kalman gain, Let be the covariance matrix of the prior error. Let be the covariance matrix of the error. It is a 4-dimensional identity matrix.
[0027] 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.
[0028] 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, and a grid-side inductor.
[0029] 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.
[0030] 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, a state-space model is established based on the grid-connected inverter circuit and Kirchhoff's laws. Then, utilizing the gradual change characteristics of the DC component in the grid-connected current, the DC component is extended into a new state variable in the state-space model, resulting in an extended state-space model. Next, based on the extended state-space model, the DC component is estimated in real-time using a state observer to obtain an estimated value. Finally, the result of subtracting the estimated DC component from the original grid-connected current reference value is used as the final reference value for grid-connected current closed-loop control. This method, by establishing a state-space extended model containing the DC component and using a state observer to estimate the DC component in real-time, and then using the result of subtracting the estimated DC component from the original grid-connected current reference value as the final reference value for grid-connected current closed-loop control, achieves the suppression of the DC component in the grid-connected current. Attached Figure Description
[0031] 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.
[0032] Figure 1 This is a schematic diagram of the grid-connected inverter provided in the embodiments of this application;
[0033] Figure 2 This is a schematic diagram of the controller provided in an embodiment of this application;
[0034] Figure 3 This is a schematic diagram of the original grid-connected current control strategy provided in the embodiments of this application;
[0035] Figure 4 This is a flowchart of a DC component suppression method for a grid-connected inverter provided in an embodiment of this application;
[0036] Figure 5 This is a schematic diagram of the control strategy after adopting the DC component suppression method provided in the embodiments of this application;
[0037] Figure 6 This is a control effect diagram provided in the embodiments of this application when the DC component suppression method is not used;
[0038] Figure 7 This is a control effect diagram provided in the embodiments of this application after adopting the DC component suppression method. Detailed Implementation
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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 and grid-side inductor In addition, the grid-connected inverter is connected to the power grid. The inverter bridge arm output midpoint voltage is expressed as .
[0043] 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.
[0044] In some embodiments, the grid-connected inverter may further include a grid voltage sampling unit and a grid current sampling unit. The grid voltage sampling unit is located on both sides of the grid and is used to collect grid voltage data in real time. The grid-connected current sampling unit is installed at the grid inflow point to collect grid-connected current in real time. .
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] Please refer to Figure 3 , Figure 3 This is a schematic diagram of the original grid-connected current control strategy provided in the embodiments of this application. For example... Figure 3 As shown, the original reference value of the grid-connected current 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 is used to obtain the output midpoint voltage of the inverter bridge arm. Inverter bridge arm output midpoint voltage With the voltage of the filter capacitor The voltage of the filter inductor is obtained by subtraction. Voltage of the filter inductor With filter inductor reactance Divide the two to obtain the current of the filter inductor. The current of the filter inductor With the current of the filter capacitor The difference is used to obtain the grid-connected current. .
[0050] Theoretically, grid-connected current It only outputs AC power, but in reality, due to factors such as zero-point drift of the sampling element, on-state voltage drop and dead-time deviation of the power device, and inconsistent drive signals of the switching transistor, the positive and negative waveforms of the output PWM wave are offset, resulting in grid-connected current. There is a DC component in it. At this time, the grid-connected current can be... Write the form of transaction and DC component superposition:
[0051] (1)
[0052] in, For grid-connected current The communication component in For grid-connected current The DC component in.
[0053] 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.
[0054] like Figure 4 As shown, the DC component suppression method of this grid-connected inverter includes:
[0055] Step S401: Establish a state-space model based on the grid-connected inverter circuit and Kirchhoff's laws.
[0056] According to Kirchhoff's voltage and current laws, the relationships between the variables in a grid-connected inverter circuit are as follows:
[0057] (2)
[0058] in, This is the inductance of the filter inductor. The inductance of the grid-side inductor. This is the capacitance value of the filter capacitor. The current in the filter inductor is... The AC component in the grid-connected current. This is the voltage across the filter capacitor. This is the voltage at the midpoint of the inverter bridge arm. This is the grid voltage.
[0059] In addition, there is grid-connected current in the power grid path. The sampling stage is used to acquire data in real time, including DC components. Grid-connected current Therefore, the following measurement equation can be obtained:
[0060] (3)
[0061] in, for The sampled values, This refers to the DC component of the grid-connected current.
[0062] Furthermore, equations (2) and (3) can be written as follows: Standard state-space equation form:
[0063] (4)
[0064] Step S402: Utilizing the slow-change characteristics of the DC component in the grid-connected current, the DC component is extended into a new state variable in the state-space model to obtain the extended state-space model.
[0065] Typically, the DC component of grid-connected current exhibits a slowly varying characteristic, i.e. Therefore, based on equation (4), the DC component is... Expanding this to new state variables yields the extended state-space model:
[0066] (5)
[0067] Step S403: Based on the state-space extended model, the DC component is estimated in real time through the state observer to obtain the estimated value of the DC component.
[0068] To facilitate the implementation of the method of this application through a mathematical controller, equation (5) needs to be discretized, resulting in the following discretized state-space extended model:
[0069] (6)
[0070] in, It is a discrete period.
[0071] In the modeling process of equation (6), it is assumed that all components are ideal components. Therefore, the obtained model has errors compared with the actual system, resulting in the introduction of process noise. In addition, the current sensor also introduces measurement noise during the measurement of the grid-connected current. Since process noise and measurement noise cannot be measured, it is assumed in this embodiment to conform to a normal distribution, i.e.:
[0072] (7)
[0073] (8)
[0074] in, For process noise and Let be the covariance matrix of its variance. To measure noise and Let its variance be denoted as 'variance'.
[0075] Combining equations (6) to (8), we can obtain the form as follows: The standard difference form of the state-space extended model:
[0076] (9)
[0077] in, For the state variable to be estimated, which includes a DC component, For measurement variables, For input variables, Process noise introduced to model error, The measurement noise is denoted by the current sensor. The coefficient matrix of the state-space extended model in standard difference form is as follows:
[0078]
[0079] in, Here is the state transition matrix. To control the input matrix, This is the observation matrix.
[0080] Based on equation (9), the DC component in the standard difference form of the extended state-space model is estimated in real time using a state observer to obtain the estimated value of the DC component. This state observer includes Kalman filters, Luneburg observers, extended state observers, etc. The estimation method for the DC component is illustrated below using a Kalman filter as an example.
[0081] In one embodiment, the 4-dimensional state variable to be estimated, which contains a DC component, is processed by a Kalman filter. The formula for joint estimation is:
[0082] (10)
[0083] in, for Prior state variable estimation, For Kalman gain, Let be the covariance matrix of the prior error. Let be the covariance matrix of the error. It is a 4-dimensional identity matrix. Here is the state transition matrix. To control the input matrix, For the observation matrix, To measure the covariance matrix of the noise, Let be the covariance matrix of the process noise.
[0084] When calculating the DC component estimate based on equation (10), the parameters in equation (10) are first initialized (for example, , , Then, by obtaining the observed values of the input and measured variables, the estimated 4-dimensional state variables of the inverter can be recursively calculated. The input variables include the inverter bridge arm output midpoint voltage. and grid voltage Inverter bridge arm output midpoint voltage For current loop controller Output The gain KPWM of the PWM modulation stage (where KPWM=1), and the mains voltage. Real-time data acquisition can be achieved through a grid voltage sampling unit. The measured variable is the grid-connected current. It can be collected in real time through the grid-connected current sampling unit.
[0085] Specifically, first according to State variable estimates at time 1 State transition matrix Control input matrix and Input variables at time Calculate Prior state variable estimation at time 1 ; and then according to Covariance matrix of errors at time points State transition matrix Covariance matrix of process noise Calculate Covariance matrix of prior error at time 1 Then, based on the covariance matrix of the prior error... Observation matrix and the covariance matrix of measurement noise Calculate Kalman gain at time step and update Covariance matrix of errors at time points Finally, according to Prior state variable estimation at time 1 , Kalman gain at time step ,exist Time sampling obtained (i.e., grid-connected current) ) and observation matrix Calculate 4-dimensional state variable estimates at time 1 .
[0086] Step S404: The result of subtracting the DC component estimate from the original reference value of the grid-connected current is used as the final reference value for the grid-connected current closed-loop control.
[0087] Please refer to Figure 5 , Figure 5 This is a schematic diagram of the control strategy after employing the DC component suppression method provided in an embodiment of this application. Figure 3 Compared to the original grid-connected current control strategy, Figure 6 The control strategy in is based on Figure 4 Methods for obtaining DC component estimates Then, use the original reference value of the grid-connected current. Subtract the DC component estimate The final result will serve as the final reference value for the grid-connected current closed-loop control. This achieves the suppression of the DC component in the grid-connected current.
[0088] Please refer to Figure 6 and Figure 7 , Figure 6 This is a control effect diagram provided in the embodiments of this application when the DC component suppression method is not used. Figure 7This is a control effect diagram provided in an embodiment of this application after employing a DC component suppression method. The amplitude corresponding to 0Hz is the DC component amplitude. (Comparison) Figure 6 and Figure 7 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.
[0089] The DC component suppression method for grid-connected inverters provided in this application first establishes a state-space model based on the grid-connected inverter circuit and Kirchhoff's laws. Then, utilizing the gradual variation characteristics of the DC component in the grid-connected current, the DC component is extended into a new state variable within the state-space model, resulting in an extended state-space model. Next, based on the extended state-space model, the DC component is estimated in real-time using a state observer to obtain an estimated DC component value. Finally, the result of subtracting the estimated DC component value from the original grid-connected current reference value is used as the final reference value for grid-connected current closed-loop control. This method, by establishing an extended state-space model containing the DC component and using a state observer to estimate the DC component value in real-time, and then using the result of subtracting the estimated DC component value from the original grid-connected current reference value as the final reference value for grid-connected current closed-loop control, achieves the suppression of the DC component in the grid-connected current.
[0090] 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.
[0091] 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: A state-space model is established based on the grid-connected inverter circuit and Kirchhoff's laws. By utilizing the slow-varying characteristics of the DC component in the grid-connected current, the DC component is extended into a new state variable in the state-space model, resulting in an extended state-space model. Based on the state-space extended model, the DC component is estimated in real time by a state observer to obtain the estimated value of the DC component. The result of subtracting the estimated DC component from the original reference value of the grid-connected current is used as the final reference value for the grid-connected current closed-loop control. The state space extension model is as follows: in, This is the inductance of the filter inductor. The inductance of the grid-side inductor. This is the capacitance value of the filter capacitor. The current in the filter inductor is... The AC component in the grid-connected current. This is the voltage across the filter capacitor. This is the voltage at the midpoint of the inverter bridge arm. This is the grid voltage. This refers to the DC component of the grid-connected current.
2. The method according to claim 1, characterized in that, The state-space model is as follows: 。 3. The method according to claim 1 or 2, characterized in that, The step of estimating the DC component in real time using a state observer based on the state-space extended model to obtain the DC component estimate includes: The state-space extension model is discretized to obtain a discretized state-space extension model, which includes discretized state extension equations and discretized measurement equations. By introducing process noise into the discretized state extension equation and measurement noise into the discretized measurement equation, a state-space extension model in standard difference form is obtained. The DC component in the standard difference form of the extended state space model is estimated in real time by using a state observer to obtain the DC component estimate.
4. The method according to claim 3, characterized in that, Both the process noise and the measurement noise conform to a normal distribution.
5. The method according to claim 3, characterized in that, The state-space extension model in the form of standard difference is as follows: in, This is the inductance of the filter inductor. The inductance of the grid-side inductor. This is the capacitance value of the filter capacitor. The current in the filter inductor is... The AC component in the grid-connected current. This is the voltage across the filter capacitor. This is the voltage at the midpoint of the inverter bridge arm. This is the grid voltage. This refers to the DC component of the grid-connected current. For discrete periods, Process noise introduced to model error, For the measurement noise of the current sensor, For measurement variables.
6. The method according to claim 5, characterized in that, The state observer is a Kalman filter, and the formula for real-time estimation of the DC component in the standard difference form of the state-space extended model using the Kalman filter is as follows: in, Here is the state transition matrix. To control the input matrix, For the observation matrix, To measure the covariance matrix of the noise, Let be the covariance matrix of the process noise. for Prior state variable estimation, For the state variable to be estimated, which includes a DC component, For Kalman gain, Let be the covariance matrix of the prior error. Let be the covariance matrix of the error. It is a 4-dimensional identity matrix.
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, and a grid-side inductor.
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.