A single-phase inverter active filtering method and device based on current slope control

Abstract

This disclosure presents an active filtering method and apparatus for a single-phase inverter based on current slope control. The method includes: first, using unipolar pulse width modulation (PWM) technology, converting the DC power supply voltage through an L-type grid-connected single-phase bridge inverter to generate a PWM output voltage. During PWM generation, the relationship between factors affecting the slope change of the output current is analyzed to generate a current slope change law. Then, based on the current slope change law, an active filtering single-phase inverter is used to compensate for voltage changes across the inductor, ensuring control of the current slope during DC-DC conversion. This disclosure optimizes the filter inductor design at the cost of adding an additional bridge circuit, reducing the filter inductance value by 5 to 10 times. This achieves a significant reduction in filter size while maintaining unaffected harmonic suppression.

Description

Technical Field

[0001] This disclosure relates to the field of active filter application technology, and more specifically, to an active filter method and apparatus for a single-phase inverter based on current slope control. Background Technology

[0002] In recent years, with the development of power electronics technology, the size and weight of filters have gradually become a bottleneck in high power density applications. Especially under the requirements of high-frequency operation and compact design, passive filters are often large in size and heavy in weight, making it difficult to meet the power density requirements of modern power electronic converters.

[0003] To address this challenge, existing technologies have proposed four solutions. First, the concept of a two-port active inductor. This technology effectively reduces the energy storage requirements, size, and weight of the inductor by minimizing apparent power handling needs through auxiliary circuitry. However, despite its significant theoretical advantages, the problem caused by high-frequency current harmonics remains unresolved. Second, further applying two-port active inductors to the design of DC bus LC filters in three-phase diode bridge rectifiers achieves significant miniaturization and cost reduction. However, due to the use of a single-phase H-bridge as the basic unit, this scheme requires a large DC bus capacitor when handling subharmonic power, which limits its application in high-efficiency, high-power-density systems. Third, a unified two-port active inductor-capacitor topology eliminates the dependence on large-capacity DC capacitors by integrating active inductor and capacitor functions and modulation strategies in a single circuit. However, this solution also faces the problems of additional losses caused by high-frequency switching and increased system complexity. Fourth, a novel matrix-coupled inductor filter effectively reduces size while maintaining good high-frequency ripple attenuation performance using matrix coupling technology. However, this technology's reliance on custom magnetic cores significantly increases manufacturing costs, posing a challenge for mass production.

[0004] Therefore, how to further improve power density, reduce cost and complexity, while ensuring the stability of high-frequency performance and system efficiency remains a key research challenge.

[0005] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this disclosure is to provide an active filtering method and apparatus for a single-phase inverter based on current slope control, thereby overcoming, at least to some extent, one or more problems caused by the limitations and defects of related technologies.

[0007] According to one aspect of this disclosure, an active filtering method for a single-phase inverter based on current slope control is provided, comprising:

[0008] Using unipolar pulse width modulation technology, the voltage of the DC power supply is converted through an L-type grid-connected single-phase bridge inverter to generate a pulse width modulated output voltage.

[0009] In the process of generating the pulse width modulation wave output voltage, the relationship between the factors affecting the slope change of the output current is analyzed to generate the current slope change law.

[0010] Based on the current slope variation law, an active filter single-phase inverter is used to compensate for the voltage change across the inductor, thereby ensuring control of the current slope during the DC power conversion process.

[0011] In one exemplary embodiment of this disclosure, the voltage of a DC power supply is converted using an L-type grid-connected single-phase bridge inverter, including:

[0012] Based on the standards of the power grid where the inverter is located, a control strategy is generated by setting the conduction state of the power switches in the L-type grid-connected single-phase bridge inverter.

[0013] According to the pre-defined control strategy, the input DC power is converted to output AC power.

[0014] By utilizing unipolar pulse width modulation technology, the high-frequency harmonics generated during the conversion process are suppressed through the filter in the L-type grid-connected single-phase bridge inverter, thereby generating a pulse width modulated output voltage.

[0015] In one exemplary embodiment of this disclosure, a relationship analysis is performed on the factors affecting the slope change of the output current, including:

[0016] Based on Kirchhoff's voltage law, when the upper bridge arm is turned on, the period of the pulse width modulation output voltage is during the positive half-cycle.

[0017] Based on Kirchhoff's voltage law, when the lower bridge arm is turned on, the period of the pulse width modulation output voltage is during the negative half-cycle.

[0018] During the positive half-cycle and the negative half-cycle, the two states of the inductor current in the filter are analyzed to generate the current slope change law.

[0019] In one exemplary embodiment of this disclosure, the current slope variation law includes:

[0020] The current increases linearly, and the slope of the current is directly proportional to the difference between the input DC voltage and the mains voltage, and inversely proportional to the inductance value.

[0021] The current decreases linearly, and the slope of the current is directly proportional to the negative value of the grid voltage and inversely proportional to the inductance value.

[0022] In one exemplary embodiment of this disclosure, an active-filter single-phase inverter includes:

[0023] By replacing the L-type filter in the L-type grid-connected single-phase bridge inverter with an active filter in series, an active filter single-phase inverter is generated.

[0024] The trigger signal of the active filter is shared with the trigger signal of the single-phase bridge inverter;

[0025] The power supply for the active filter is provided through a voltage divider circuit.

[0026] In one exemplary embodiment of this disclosure, compensation for voltage changes across the inductor includes:

[0027] During the positive half-cycle of generating the pulse width modulation output voltage, the active inductor of the active filter is charged through a voltage source and a compensation voltage, based on the linear increase of current.

[0028] During the positive half-cycle of generating the pulse width modulation output voltage, based on the linear decrease of current, the active inductor of the active filter is discharged through a voltage source and a compensation voltage.

[0029] Based on the charging and discharging behavior of the active inductor during the positive half-cycle, compensation is provided to the voltage across the inductor to ensure control of the current slope during the generation of the sinusoidal pulse width modulation output voltage.

[0030] In one exemplary embodiment of this disclosure, compensation for voltage changes across the inductor includes:

[0031] During the negative half-cycle of generating the pulse width modulation output voltage, the active inductor of the active filter is charged through a voltage source and a compensation voltage, based on the linear increase of current.

[0032] During the negative half-cycle of generating the pulse width modulation output voltage, based on the linear decrease of current, the active inductor of the active filter is discharged through a voltage source and a compensation voltage.

[0033] Based on the charging and discharging behavior of the active inductor during the negative half-cycle, compensation is provided to the voltage across the inductor to ensure control of the current slope during the generation of the negative sinusoidal pulse width modulation output voltage.

[0034] In one aspect of this disclosure, an active filter for a single-phase inverter based on current slope control is provided, comprising:

[0035] The single-phase bridge inverter module is used to convert the voltage of the DC power supply through an L-type grid-connected single-phase bridge inverter using unipolar pulse width modulation technology to generate a pulse width modulated output voltage.

[0036] The current slope analysis module is used to generate the current slope change law by analyzing the relationship between the factors affecting the slope change of the output current during the process of generating the pulse width modulation wave output voltage.

[0037] An active-filter single-phase inverter module is used to control the current slope during the DC power conversion process by compensating for voltage changes across the inductor based on the current slope variation law.

[0038] An exemplary embodiment of this disclosure provides an active filtering method for a single-phase inverter based on current slope control. First, using unipolar sinusoidal pulse width modulation (PWM) technology, an L-type grid-connected single-phase bridge inverter converts the DC power supply voltage to generate a PWM output voltage. During PWM generation, the relationship between factors affecting the slope change of the output current is analyzed to generate a current slope change law. Then, based on the current slope change law, an active filtering single-phase inverter compensates for voltage changes across the inductor, ensuring control of the current slope during DC-DC conversion. This embodiment optimizes the filter inductor design at the cost of adding an additional bridge circuit, reducing the filter inductance value by 5 to 10 times. This achieves a significant reduction in filter size while maintaining unaffected harmonic suppression.

[0039] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0040] The above and other features and advantages of this disclosure will become more apparent from the detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0041] Figure 1 A flowchart of an active filtering method for a single-phase inverter based on current slope control according to an exemplary embodiment of the present disclosure is shown.

[0042] Figure 2 A schematic diagram of an L-type grid-connected single-phase bridge inverter topology is shown, illustrating an active filtering method for a single-phase inverter based on current slope control according to an exemplary embodiment of the present disclosure.

[0043] Figure 3A schematic diagram of a single-pole sinusoidal pulse width modulation waveform of an active filtering method for a single-phase inverter based on current slope control according to an exemplary embodiment of the present disclosure is shown.

[0044] Figure 4 An equivalent schematic diagram of a passive L-type filter topology for a single-phase inverter active filtering method based on current slope control according to an exemplary embodiment of the present disclosure is shown.

[0045] Figure 5 A schematic diagram of the current waveform of a single-phase inverter active filter method based on current slope control according to an exemplary embodiment of the present disclosure is shown when the inductance value is L.

[0046] Figure 6 An exemplary embodiment of the present disclosure illustrates an active filtering method for a single-phase inverter based on current slope control, with an inductance value of... A schematic diagram of the current waveform at that time;

[0047] Figure 7 An equivalent schematic diagram of a series active filter topology for a single-phase inverter based on current slope control according to an exemplary embodiment of the present disclosure is shown.

[0048] Figure 8 A schematic diagram of the current waveform after applying a compensation voltage is shown in an exemplary embodiment of the present disclosure for a single-phase inverter active filtering method based on current slope control.

[0049] Figure 9 A schematic diagram of an active-filter single-phase inverter topology is shown, illustrating an active-filter method for a single-phase inverter based on current slope control according to an exemplary embodiment of the present disclosure.

[0050] Figure 10 A first schematic diagram of the operating current path of an active-filter single-phase inverter according to an exemplary embodiment of the present disclosure is shown;

[0051] Figure 11 A second schematic diagram of the operating current path of an active-filter single-phase inverter according to an exemplary embodiment of the present disclosure is shown;

[0052] Figure 12 A third schematic diagram of the operating current path of an active-filter single-phase inverter according to an exemplary embodiment of the present disclosure is shown;

[0053] Figure 13 A fourth schematic diagram of the operating current path of an active-filter single-phase inverter according to an exemplary embodiment of the present disclosure is shown;

[0054] Figure 14A schematic diagram of the simulated current waveform of a series active filter with L = 0.2mH is shown in an exemplary embodiment according to the present disclosure;

[0055] Figure 15 A schematic block diagram of an active filter device for a single-phase inverter based on current slope control is shown according to an exemplary embodiment of the present disclosure. Detailed Implementation

[0056] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0057] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details described, or other methods, components, materials, apparatuses, steps, etc., can be employed. In other instances, well-known structures, methods, apparatuses, implementations, materials, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0058] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software, or in one or more software-hardened modules, or in different network and / or processor devices and / or microcontroller devices.

[0059] In this example embodiment, an active filtering method for a single-phase inverter based on current slope control is first provided; refer to Figure 1 As shown, this active filtering method for a single-phase inverter based on current slope control may include the following steps:

[0060] Step S110: Using unipolar sinusoidal pulse width modulation technology, the voltage of the DC power supply is converted through an L-type grid-connected single-phase bridge inverter to generate a pulse width modulated output voltage.

[0061] Step S120: In the process of generating the pulse width modulation wave, the relationship between the factors affecting the slope change of the output current is analyzed to generate the current slope change law.

[0062] Step S130: Based on the current slope change law, an active filter single-phase inverter is used to compensate for the voltage change across the inductor, thereby ensuring control of the current slope during the DC-DC conversion process.

[0063] An exemplary embodiment of this disclosure provides an active filter control method for a single-phase inverter based on current slope control. First, using unipolar sinusoidal pulse width modulation (PWM) technology, an L-type grid-connected single-phase bridge inverter converts the DC power supply voltage to generate a PWM output voltage. During PWM generation, the relationship between factors affecting the slope change of the output current is analyzed to generate a current slope change law. Then, based on the current slope change law, an active filter single-phase inverter compensates for voltage changes across the inductor, ensuring control of the current slope during DC-DC conversion. This embodiment optimizes the filter inductor design at the cost of adding an additional bridge circuit, reducing the filter inductance value by 5 to 10 times. This achieves a significant reduction in filter size while maintaining unaffected harmonic suppression.

[0064] The active filtering method for a single-phase inverter based on current slope control in this example embodiment will be further described below.

[0065] In template configuration step S110, unipolar pulse width modulation technology can be used to convert the voltage of the DC power supply through an L-type grid-connected single-phase bridge inverter to generate a pulse width modulated output voltage.

[0066] In this example embodiment, the L-type grid-connected single-phase bridge inverter is an inverter topology used to convert direct current (DC) power (typically the output of solar panels or battery storage systems) into alternating current (AC) that matches the power grid. With this type of inverter, DC power can be converted into AC power that meets the grid frequency and voltage requirements. In this process, L-type filters are typically used to smooth the output AC current, reducing harmonics and current ripple.

[0067] like Figures 2-3 As shown, the L-type grid-connected single-phase bridge inverter first modulates the input DC voltage, using PWM (Pulse Width Modulation) technology to generate an AC waveform. In this specific example, this step is achieved by switching the switching transistors (...) in the bridge inverter. Figure 2 This is achieved using S1, S2, S3, and S4 in the converter. This requires setting a control strategy to modulate the on / off state of these switches (e.g., insulated-gate bipolar transistors or metal-oxide-semiconductor field-effect transistors) so that the inverter's output voltage approximates a sinusoidal waveform.

[0068] During modulation, the inverter generates an SPWM (Sinusoidal Pulse Width Modulation) signal by rapidly switching transistors. This signal has a frequency much higher than the grid frequency, typically between several kilohertz and tens of kilohertz, ensuring that the inverter's output is a near-sinusoidal signal. However, the inverter's output signal often contains high-frequency harmonics, therefore an L-type filter (composed of an inductor and a capacitor) is needed to smooth the signal. The inductor L limits the rate of change of current (i.e., reduces current ripple), while the capacitor C filters out high-frequency components, resulting in an AC output that more closely approximates an ideal sine wave.

[0069] Finally, after modulation and filtering, the pulse width modulated output voltage of the inverter (it is necessary to ensure that the amplitude and phase of the inverter output voltage are synchronized with the grid) matches the grid voltage and frequency, thus completing the grid connection.

[0070] In the template configuration step S120, during the generation of the pulse width modulation wave, the relationship analysis of the factors affecting the slope change of the output current can be performed to generate the current slope change law.

[0071] During the PHC (positive half-cycle) in this example embodiment, the upper arm is on ( Figure 2 In S1), the change in inductor current can be described by Kirchhoff's Voltage Law (KVL) in two states:

[0072] When switches S1 and S4 are turned on, the slope of the inductor current With the input DC voltage V dc , The grid voltage V during switching g And it is related to the inductance value L:

[0073]

[0074] As shown in equation (1), in the linear increase of current, the current slope is directly proportional to the difference between the input DC voltage and the grid voltage during switching, and inversely proportional to the inductance value. When the switching frequency is much greater than the grid frequency, the grid voltage is considered constant.

[0075] When switches S2 and S3 are turned on, the slope of the inductor current Only related to the grid voltage V during switching g Related to the inductance value L:

[0076]

[0077] As shown in equation (2), the current decreases linearly, and the current slope is directly proportional to the negative value of the grid voltage and inversely proportional to the inductance value. When the switching frequency is much greater than the grid frequency, the grid voltage is considered constant.

[0078] Similarly, during the NHC (negative half-cycle) in this example embodiment, the lower arm conducts ( Figure 2 In S2), the change in inductor current can also be described by Kirchhoff's voltage law (KVL) in the two states mentioned above.

[0079] Therefore, the law governing the change in current slope can be analyzed as follows: Figures 4-6 As shown, the current slope of the inductor current (i.e., current ripple) is caused by the input DC voltage V dc , The grid voltage V during switching g And it is determined by the inductance value L. So if the size of the inductor is reduced by a factor of n (that is, the filter inductance value is reduced by a factor of n), the current slope will also increase by a factor of n, thereby introducing a large number of harmonics.

[0080] In template configuration step S130, based on the current slope change law, an active filter single-phase inverter can be used to compensate for the voltage change across the inductor, thereby ensuring control of the current slope during DC-DC conversion.

[0081] In this example embodiment, the goal is to address the issue of the current slope variation in S120, that is, to minimize the inductor current ripple while maintaining a small inductance value. A feasible approach is to modify or compensate the voltage across the inductor. For example... Figures 7-8 As shown, when the filter inductance value L decreases to its original value... At this time, it is necessary to ensure that the voltage across the inductor also needs to be reduced to a minimum. and This ensures that the current slope after reducing the inductance value is consistent with the original current slope.

[0082] To achieve this goal, such as Figure 9 As shown, by introducing a series active filter to compensate for the voltage across the inductor, the original large L-shaped filter is replaced with a smaller active filter. Unlike traditional passive filters (such as filters composed of inductors, capacitors, and resistors), active filters can provide gain or compensation, thereby actively adjusting the frequency response of a signal. They are often used to suppress noise at specific frequencies, filter out unwanted signals, or improve signal quality.

[0083] However, its drawback is also obvious: it requires an external power supply to enable the active components to regulate current and voltage. Therefore, in a specific example, to simplify the drive circuit, the active filter is powered by a voltage divider circuit, and its trigger signal is shared with the trigger signal of the single-phase bridge inverter.

[0084] In this example embodiment, the operating principle of the L-type single-phase bridge inverter with series active filter can be described using the following two half-cycles.

[0085] Positive half-cycle (PHC), such as Figures 10-11 As shown, S1 and S5 remain on, while S4, S8 and S3, S7 are turned on and off in a complementary manner to generate a positive SPWM output voltage.

[0086] This includes two operating modes:

[0087] Mode 1: S1 and S5 are on, S4 and S8 are on. Active inductor. Charging is achieved through a voltage source and a compensation voltage, with current flowing through switches S1 and S4, and diodes D5 and D8 (the freewheeling diodes of switches S5 and S8, respectively). The inductor current increases linearly, and the compensation voltage provided by the active filter is... The variation law of the current slope can be described as follows:

[0088] Mode 2: S1 and S5 are on, S3 and S7 are on. Active inductor. Discharge is achieved through a voltage source and a compensation voltage, with current flowing through switches S1 and S7, and diodes D3 and D5 (the freewheeling diodes of switches S3 and S5, respectively). The inductor current decreases linearly, and the compensation voltage provided by the active filter is... The variation law of the current slope can be described as follows:

[0089] Negative half-cycle (NHC), such as Figures 12-13 As shown, S2 and S6 remain on, while S3, S7 and S4, S8 are turned on and off in a complementary manner, generating a negative SPWM output voltage. The two operating modes included are the same as the two operating modes of the positive half-cycle.

[0090] Throughout the process, the current direction of the active filter is opposite to that of the main circuit, and the current slope of the active inductor is consistent with that of the traditional passive inductor filter (L-type filter).

[0091] In a specific example, to verify the performance of the proposed topology, a single-phase bridge inverter system was simulated in MATLAB / SIMULINK simulation software. The simulation compared the performance of the L-type single-phase bridge inverter with a series active filter with that of a conventional L-type single-phase bridge inverter.

[0092] In a passive L-type filter topology, when the filter inductor is set to 1.2mH, the current waveform quality is high, the ripple is minimal, and the total harmonic distortion (THD) is 5.36%. However, under the same operating conditions, reducing the filter inductor value in the passive L-type filter topology to 0.2mH significantly increases the current ripple, causing the THD to rise sharply to 31.0%. In contrast, the proposed series active filter topology achieves comparable performance using only a 0.2mH filter inductor, which is 1 / 6 of the inductor value in the passive L-type filter topology, with the THD increasing only slightly to 5.45%. Figure 14 As shown.

[0093] Simulation results show that despite a significant reduction in filter inductance, the proposed series active filter topology still effectively suppresses harmonics, demonstrating excellent harmonic suppression capability and validating the effectiveness of the design. This characteristic not only significantly reduces the filter's size and cost but also achieves an optimal balance between performance and cost-effectiveness.

[0094] It should be noted that although the steps of the method in this disclosure are described in a specific order in the accompanying drawings, this does not require or imply that the steps must be performed in that specific order, or that all the steps shown must be performed to achieve the desired result. Additional or alternative steps may be omitted, multiple steps may be combined into one step, and / or a step may be broken down into multiple steps.

[0095] Furthermore, in this example embodiment, an active filter device for a single-phase inverter based on current slope control is also provided. (Refer to...) Figure 15 As shown, the single-phase inverter active filter device 400 based on current slope control may include: a single-phase bridge inverter module 410, a current slope analysis module 420, and an active filter single-phase inverter module 430. Wherein:

[0096] The single-phase bridge inverter module 410 is used to convert the voltage of the DC power supply through an L-type grid-connected single-phase bridge inverter using unipolar pulse width modulation technology to generate a pulse width modulated output voltage.

[0097] The current slope analysis module 420 is used to generate the current slope change law by analyzing the relationship between the factors affecting the slope change of the output current during the generation of the pulse width modulation wave.

[0098] The active filter single-phase inverter module 430 is used to control the current slope during the DC-DC conversion process by compensating for the voltage change across the inductor based on the current slope change law.

[0099] The specific details of each of the above-mentioned active filter modules for single-phase inverters based on current slope control have been described in detail in the corresponding active filter method for single-phase inverters based on current slope control, so they will not be repeated here.

[0100] It should be noted that although several modules or units of a single-phase inverter active filter device 400 based on current slope control have been mentioned in the detailed description above, this division is not mandatory. In fact, according to embodiments of this disclosure, the features and functions of two or more modules or units described above can be embodied in one module or unit. Conversely, the features and functions of one module or unit described above can be further divided and embodied by multiple modules or units.

[0101] Furthermore, the above figures are merely illustrative of the processes included in the method according to exemplary embodiments of the present invention, and are not intended to be limiting. It is readily understood that the processes shown in the above figures do not indicate or limit the temporal order of these processes. Additionally, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0102] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

[0103] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. An active filter control method for a single-phase inverter based on current slope control, characterized in that, include: Using unipolar pulse width modulation technology, the voltage of the DC power supply is converted through an L-type grid-connected single-phase bridge main inverter to generate a pulse width modulated output voltage. During the generation of the pulse width modulation output voltage, the factors affecting the output current slope change are analyzed based on Kirchhoff's voltage law to obtain the current slope change law; the current slope change law includes: a linear increase law of current, where the current slope is directly proportional to the difference between the DC power supply voltage and the grid voltage and inversely proportional to the inductance value; and a linear decrease law of current, where the current slope is directly proportional to the negative value of the grid voltage and inversely proportional to the inductance value. An active filter, including an H-bridge, is connected in series at the output of an L-type grid-connected single-phase bridge main inverter. According to the current slope change law, the active filter compensates for the voltage change across the inductor to stabilize the current slope. The trigger signals of the H-bridge switching transistors of the active filter are synchronously shared with the trigger signals of the switching transistors of the main inverter, and the active filter is powered by a voltage divider circuit.

2. The method according to claim 1, characterized in that, The voltage of the DC power supply is converted using an L-type grid-connected single-phase bridge main inverter, including: The control strategy for the switching transistors in the main inverter is set based on the power grid standard. The input DC power is converted to AC power according to the control strategy described above; The high-frequency harmonics in the conversion process are suppressed by using unipolar pulse width modulation technology to generate a pulse width modulated output voltage.

3. The method according to claim 1, characterized in that, Analyze the factors that cause changes in the output current slope, including: Based on Kirchhoff's voltage law, the output voltage of the pulse width modulation wave is divided into positive half-cycle and negative half-cycle. During the positive and negative half-cycles, the changes in the inductor current are analyzed to obtain the current slope variation law.

4. The method according to claim 1, characterized in that, Compensation for voltage variations across the inductor is achieved through an active filter, including: During the positive half-cycle of the pulse width modulation output voltage, the inductor of the active filter is charged based on the linear increase of current and discharged based on the linear decrease of current. Based on the charging and discharging of the inductor during the positive half-cycle, the voltage across the inductor is compensated, and the current slope is stabilized.

5. The method according to claim 1, characterized in that, Compensation for voltage variations across the inductor is achieved through an active filter, including: During the negative half-cycle of the pulse width modulation output voltage, the inductor of the active filter is charged based on the linear increase of current and discharged based on the linear decrease of current. Based on the charging and discharging of the inductor during the negative half-cycle, the voltage across the inductor is compensated, and the current slope is stabilized.

6. An active filter control device for a single-phase inverter based on current slope control, characterized in that, include: The L-type grid-connected single-phase bridge main inverter module is used to convert the voltage of the DC power supply through the L-type grid-connected single-phase bridge main inverter using unipolar pulse width modulation technology, and generate pulse width modulated wave output voltage. The current slope analysis module is used to analyze the factors affecting the change of the output current slope based on Kirchhoff's voltage law during the generation of the pulse width modulation output voltage, and to obtain the current slope change law. The current slope change law includes: a linear increase law of current, in which the current slope is directly proportional to the difference between the DC power supply voltage and the grid voltage and inversely proportional to the inductance value; and a linear decrease law of current, in which the current slope is directly proportional to the negative value of the grid voltage and inversely proportional to the inductance value. An active filter compensation module is used to connect an active filter, including an H-bridge, in series at the output terminal of an L-type grid-connected single-phase bridge main inverter. According to the current slope change law, the active filter compensates for the voltage change across the inductor to stabilize the current slope. The trigger signals of the H-bridge switching transistors of the active filter are synchronously shared with the trigger signals of the switching transistors of the main inverter, and the active filter is powered by a voltage divider circuit.

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