An Active Filter Based on Capacitive Inductance Bidirectional Controllable and Its Analysis Method

Abstract

This invention belongs to the field of active filter technology and provides an active filter based on bidirectional controllable capacitance and its analysis method. The active filter includes an equivalent inductance module and an equivalent capacitance module. The equivalent inductance module includes a first inductor, a first controllable switch, and a first capacitor. One end of the inductor is connected to the positive input terminal, and the other end is connected to the first controllable switch and the first capacitor, which are connected in parallel. The equivalent capacitance module includes a second inductor, a second controllable switch, a second capacitor, and a diode. One end of the second inductor is connected to one end of the first controllable switch, the first capacitor, and the second capacitor, and to the positive output terminal. The other end of the second inductor is connected in series with the second controllable switch and the diode. The cathode of the diode is connected to the other end of the second capacitor, the negative input terminal, and the negative output terminal. This invention utilizes a minimal number of controllable switching devices to control the filtering effect.

Description

Technical Field

[0001] This invention belongs to the field of active filter technology, specifically relating to an active filter based on capacitive bidirectional controllable and its analysis method. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In recent years, with the large-scale development and widespread application of power electronics technology, electrical energy has been utilized more fully. However, the nonlinearity inherent in power electronic devices also causes voltage and current distortion in the power grid. The increasing number and rated capacity of these highly nonlinear devices have exacerbated the problem of harmonic pollution in the power system, making it a public nuisance affecting power quality and significantly impacting the safe and economical operation of the power system. On the other hand, power suppliers and their power system equipment, as well as users and their electrical appliances, have increasingly higher requirements for power quality. This contradiction has led to greater attention being paid to the problem of harmonic pollution.

[0004] Therefore, whether from the perspective of ensuring the safe, stable, and economical operation of the power system, or from the perspective of ensuring the safety and normal operation of users' electrical equipment, it is urgent to effectively control harmonics, limit them to within permissible ranges, restore a safe and clean electrical environment to the power grid, and create a new type of power system.

[0005] Currently, suppressing or reducing harmonics in power systems is mainly considered from two aspects:

[0006] Firstly, addressing the source of harmonics—the devices themselves—by actively mitigating harmonic sources can effectively limit harmonic generation. This involves incorporating harmonic suppression mechanisms into the initial design of these devices to reduce harmonic injection. However, due to the complexity of modern power systems and the rapid development of power electronics and semiconductors, it is difficult to completely eliminate grid harmonics.

[0007] Secondly, there is passive harmonic mitigation, which involves effectively filtering and compensating for harmonics in the system. There are two main types of passive harmonic mitigation measures:

[0008] Currently, traditional passive filters are widely used. These filters utilize the resonant characteristics of inductors and capacitors to create low-impedance branches in the impedance shunt circuit, thereby reducing harmonic currents flowing to the power grid and compensating for reactive power. They offer advantages such as simple structure, low initial investment, low operating costs, and convenient maintenance. However, due to structural and operational limitations, they suffer from the following insurmountable drawbacks in application:

[0009] (1) It can only filter out harmonics of a specific order. The resonant frequency depends on the component parameters, therefore a single-tuned filter can only eliminate harmonics of a specific order. Installing multiple passive filter branches will increase the cost and size of the entire filtering device;

[0010] (2) Filter parameters affect filtering performance. Due to tuning offset and residual resistance, the ideal condition of zero impedance is impossible, and impedance uncertainty will greatly affect the filtering effect. Drift of LC parameters will also cause changes in filtering characteristics, making filtering performance unstable;

[0011] (3) Wave characteristics depend on grid parameters. The impedance and harmonic frequencies of the grid change constantly with the operating conditions and modes of the power system, which greatly affects the filtering effect of the passive filter;

[0012] (4) Series and parallel resonance will occur with the system impedance. For special harmonics, or when the system impedance and frequency change, "harmonic amplification" may occur due to parallel resonance with the power supply impedance, which may cause the circuit to fail to work properly.

[0013] With the continuous development of power electronics technology and the advancement of control technology, active power filtering technology has seen significant advancements. Active power filters detect harmonic currents (voltages) in the power grid system and generate opposing compensating currents (voltages) to counteract them in transmission lines. Active filters offer many advantages: their filtering performance is unaffected by system impedance; they do not resonate in series or parallel with system impedance, and changes in system structure do not affect their filtering effect; they are theoretically superior to passive filters, allowing for the suppression of all harmonics with a single device; and they achieve dynamic harmonic suppression, rapidly responding to changes in the frequency and magnitude of harmonics.

[0014] However, the active filters currently used in the market and in academic research are complex in structure, large in size, and use many switching device modules, which makes them expensive, costly, and difficult to apply in high-capacity applications. Summary of the Invention

[0015] To address the aforementioned problems, this invention proposes an active filter based on capacitive inductance bidirectional controllable and its analysis method. This invention overcomes the drawback of fixed parameters in passive filters and utilizes the fewest controllable switching devices to control the filtering effect. It can dynamically change the filtering characteristics of the circuit according to requirements and can be widely applied in communication and power conversion applications that extract useful signals and filter out interference information.

[0016] According to some embodiments, the present invention adopts the following technical solution:

[0017] In the first aspect, the present invention provides an active filter based on capacitive bidirectional controllable inductance.

[0018] An active filter based on bidirectional controllable capacitance includes: an equivalent inductance module and an equivalent capacitance module.

[0019] The equivalent inductance module includes a first inductor, a first controllable switch, and a first capacitor. One end of the inductor is connected to the positive input terminal, and the other end is connected to the first controllable switch and the first capacitor. The first controllable switch and the first capacitor are connected in parallel.

[0020] The equivalent capacitor module includes a second inductor, a second controllable switch, a second capacitor, and a diode. One end of the second inductor is connected to one end of the first controllable switch, the first capacitor, the second capacitor, and the positive output terminal, respectively. The other end of the second inductor is connected in series with the second controllable switch and the diode. The negative terminal of the diode is connected to the other end of the second capacitor, the negative input terminal, and the negative output terminal, respectively.

[0021] Furthermore, the waveform input at the positive input terminal is passed through the active filter to obtain a standard sine wave, wherein the waveform includes: a square wave, a non-standard sine wave containing harmonics, a triangular wave, or a sawtooth wave.

[0022] Furthermore, the positive and negative input terminals are connected to a high-frequency square wave circuit, which includes a DC voltage source, a voltage regulator circuit, and a full-bridge inverter circuit. The voltage regulator circuit is connected in parallel with the full-bridge inverter circuit.

[0023] Furthermore, the active filter includes a first operating mode, a second operating mode, a third operating mode, a fourth operating mode, and a fifth operating mode in one conversion cycle.

[0024] Furthermore, the first working mode is:

[0025] The first switching mode is completed within a first preset time and a second preset time. At the first preset time, the instantaneous voltage across the second capacitor crosses zero, the first controllable switch is in the conducting state, and the instantaneous current through the first inductor flows in the positive direction. After that, the instantaneous voltage across the second capacitor is always positive, and the diode is ready to conduct. The current direction is defined as the positive direction of the current flowing from the input terminal to the output terminal.

[0026] Furthermore, the second working mode is:

[0027] The second switching mode is completed within the second and third preset times. At the second preset time, the first controllable switch is turned off, the instantaneous voltage across the second capacitor is always positive, and the diode is ready to conduct. This mode lasts for three circuit operation stages. In the first stage, the instantaneous current through the first inductor flows in the forward direction. During this process, the instantaneous current through the first inductor flows through the first capacitor to form a path. In the second stage, the instantaneous current through the first inductor flows in the reverse direction after crossing zero. The instantaneous voltage across the first capacitor reaches its maximum when the instantaneous current through the first inductor crosses zero, and then begins to decay until it decays to zero. In the third stage, the instantaneous current through the first inductor will pass through the body diode in the first controllable switch to form a freewheeling current.

[0028] Furthermore, the third working mode is:

[0029] The third switching mode is completed within the third and fourth preset times. At the third preset time, the second controllable switch is turned on, and the instantaneous current through the first inductor remains negative. This process will continue for three circuit operation stages. In the first stage, the instantaneous voltage across the second capacitor is positive, and the second controllable switch will achieve zero-current switching technology. The second inductor, the first controllable switch, and the diode form a path. In the second stage, the instantaneous voltage across the second capacitor increases in the reverse direction after crossing zero. The instantaneous current through the second inductor reaches its maximum when the instantaneous voltage across the second capacitor crosses zero, and then begins to decay until it decays to zero. When the instantaneous current through the second inductor is zero, the diode is turned off and loses the conduction condition. In the third stage, the branch of the second inductor, the first controllable switch, and the diode is disconnected.

[0030] Furthermore, the fourth working mode is:

[0031] The fourth switching mode is completed within the fourth and fifth preset times. The second controllable switch remains in the on state. At the fourth preset time, the first controllable switch begins to conduct, and the instantaneous voltage across the second capacitor is always negative. The diode does not have the conditions to conduct. This process will continue for two circuit operation stages. In the first stage, because the instantaneous current through the first inductor flows in the negative direction, zero-voltage switching technology can be achieved when the first controllable switch is on. In the second stage, the instantaneous current through the first inductor flows in the positive direction after crossing zero until the second controllable switch is turned off.

[0032] Furthermore, the fifth working mode is:

[0033] The fifth switching mode is completed within the fifth and sixth preset times. The first controllable switch remains on. At the fifth preset time, the second controllable switch is off. The instantaneous current through the first inductor remains positive. The instantaneous voltage across the second capacitor is always negative. The diode does not have the conditions to conduct.

[0034] Secondly, this invention provides an analysis method based on a capacitively bidirectionally controllable active filter.

[0035] An analysis method for an active filter based on capacitive inductance bidirectional controllable, employing the active filter based on capacitive inductance bidirectional controllable described in the first aspect, includes:

[0036] The equivalent series inductance value L of the equivalent inductance module eq for:

[0037]

[0038] The capacitance value C of the equivalent parallel capacitance module eq for:

[0039]

[0040] Where α is the phase shift angle of the first controllable switch S1, and its value ranges from [π / 2, π]; L S C is the inductance value of the first inductor. LS Let α be the capacitance value of the first capacitor; as α increases, the equivalent series inductance L... eq Continuously increases; β is the phase shift angle of the second controllable switch S2, with a value range of [π / 2, π]; f is the switching frequency; C P L is the capacitance value of the second capacitor. CP Let C be the inductance value of the second inductor; as β increases, the equivalent parallel capacitance C... eq It keeps growing.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] (1) This invention proposes an active filter based on capacitive inductance bidirectional controllable. This active filter can be widely used in communication and power conversion applications to extract useful signals and filter out interference information. Essentially, this topology is a low-pass filter. This topology has only one stage structure, is simple in structure, uses few components, and overcomes the disadvantage of fixed parameters of passive filters.

[0043] (2) The active filter based on bidirectional controllable capacitance proposed in this invention broadens the working range of the original filter circuit and can be applied to a variety of working conditions. It can dynamically change the filtering characteristics of the circuit according to the requirements. This topology can be widely applied to various working environments such as unclear original circuit characteristics and easy-to-change load.

[0044] (3) The active filter based on bidirectional controllable capacitance proposed in this invention uses the fewest controllable switching devices. Compared with active power filter (APF), this new topology uses fewer devices and has a lower production cost. That is, the dynamic values ​​of the filter inductor and filter capacitor can be adjusted bidirectionally by using one controllable switch, thereby controlling the filtering effect of the active filter.

[0045] (4) This invention proposes a working principle and control method for a capacitively inductively bidirectionally controllable active filter. The five operating modes of this topology are analyzed in detail. Overall, the control strategy is relatively simple and can eliminate the influence of factors such as device component parameters. Furthermore, both controllable switches in this topology can implement soft-switching technology, greatly reducing switching losses and improving power conversion efficiency.

[0046] (5) This invention provides an external equivalent analysis method for a two-port circuit based on a capacitive bidirectional controllable active filter, and gives a calculation method for equivalent capacitance and equivalent inductance. The equivalent inductance and equivalent capacitance are related to the switching frequency f, the parameters of the circuit energy storage device, and the phase shift angle α / β. Attached Figure Description

[0047] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0048] Figure 1 This is a topology diagram of an active filter based on capacitive bidirectional controllable active filter as shown in this invention;

[0049] Figure 2 This is a schematic diagram illustrating an important application scenario of the active filter based on capacitive bidirectional controllable capacitance, as shown in this invention.

[0050] Figure 3 This is a diagram of the high-frequency square wave active filter topology shown in this invention;

[0051] Figure 4 This is a key waveform diagram of the active filter based on capacitive bidirectional controllable active filter shown in this invention;

[0052] Figure 5 This is the operating mode 1 of the active filter based on capacitive bidirectional controllable shown in this invention;

[0053] Figure 6 This is the operating mode 2 of the active filter based on capacitive bidirectional controllable shown in this invention;

[0054] Figure 7 This is the operating mode 3 of the active filter based on capacitive bidirectional controllable shown in this invention;

[0055] Figure 8 This is the operating mode 4 of the active filter based on capacitive bidirectional controllable shown in this invention;

[0056] Figure 9 This is the operating mode 5 of the active filter based on capacitive bidirectional controllable shown in this invention;

[0057] Figure 10 This is a schematic diagram illustrating the parametric relationships of an active filter based on capacitive bidirectional controllable capacitance, as shown in this invention. Detailed Implementation

[0058] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0059] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0060] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0061] In this invention, terms such as "connected" and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0062] Example 1

[0063] This embodiment provides an active filter based on capacitive bidirectional controllable inductance.

[0064] An active filter based on bidirectional controllable capacitance includes: an equivalent inductance module and an equivalent capacitance module.

[0065] The equivalent inductance module includes a first inductor, a first controllable switch, and a first capacitor. One end of the inductor is connected to the positive input terminal, and the other end is connected to the first controllable switch and the first capacitor. The first controllable switch and the first capacitor are connected in parallel.

[0066] The equivalent capacitor module includes a second inductor, a second controllable switch, a second capacitor, and a diode. One end of the second inductor is connected to one end of the first controllable switch, the first capacitor, the second capacitor, and the positive output terminal, respectively. The other end of the second inductor is connected in series with the second controllable switch and the diode. The negative terminal of the diode is connected to the other end of the second capacitor, the negative input terminal, and the negative output terminal, respectively.

[0067] The specific solution for this embodiment can be implemented by referring to the following content:

[0068] like Figure 1 As shown, the topology of the capacitively bidirectionally controllable active filter in this embodiment includes:

[0069] 1. Equivalent inductance L eq Module: This module includes inductor L S Controllable switch S1, capacitor C LS ;

[0070] 2. Equivalent capacitance C eq Module: This module includes capacitor C P Controllable switch S2, inductor L CP Diode D1.

[0071] This topology can be externally equivalent to a two-port device.

[0072] like Figure 2 This is the main application scenario for the active filter in this embodiment. This two-port active filter topology can transform the input waveform, such as a square wave, a non-standard sine wave containing harmonics, a triangular wave, or a sawtooth wave, to obtain a standard sine wave of the same frequency or with low harmonic content at the output.

[0073] Example 2

[0074] This embodiment provides an application example of an active filter.

[0075] Figure 3 This is a high-frequency square wave active filter topology. A DC voltage source VDC, passing through capacitor C... IN Voltage regulation and filtering are achieved through a full-bridge inverter circuit composed of switching transistors T1, T2, T3, and T4 to obtain a high-frequency square wave. After the high-frequency square wave is converted into electrical energy by an active filter, a standard sine wave with stable output and low harmonic content can be obtained at the load RL.

[0076] The following section mainly analyzes the working principle of the active filter topology in Embodiment 1 and Embodiment 2.

[0077] Key waveforms of the capacitively bidirectionally controllable active filter topology are as follows: Figure 4 As shown.

[0078] iLS For input terminal or through inductor L S The instantaneous current; switch S1 represents the drive signal for switching transistor S1; v CLS For capacitor C LS The instantaneous voltage across the two ends; α is the phase shift angle of the drive signal for switch S1, used as a control signal and current i LS Phase difference at the zero-crossing point. CP For capacitor C P The instantaneous voltage across the terminals; S2 represents the drive signal for switch S2; i LCP To pass through inductor L CP The instantaneous current; β is the phase shift angle of the drive signal for switch S2, which serves as the control signal and voltage v. CP Phase difference at zero crossing point; diode D1 represents the diode conduction signal.

[0079] A capacitively inductively bidirectionally controllable active filter has five operating modes within one conversion cycle. These five modes are primarily based on the operating states of the switching transistors, and each mode may contain several operating states of different topologies. Before proceeding with the modal analysis, three basic assumptions are made for simplification:

[0080] (1) Inductor L in the active filter S L CP Capacitor C LS C P Without considering its additional losses;

[0081] (2) Switches S1 and S2 and diode D1 are all ideal devices;

[0082] (3) For ease of analysis, the input current i LS and voltage v CP It is approximately an alternating sine wave;

[0083] like Figure 5 As shown, Mode 1: [t0-t1]. At time t0, the capacitor voltage v CP At the zero-crossing point, S1 is in the conducting state, and the inductor current i LS Forward flow (the current direction is defined as from the input terminal to the output terminal); thereafter, the capacitor voltage v CP The value is always positive, and diode D1 is ready to conduct.

[0084] like Figure 6 As shown, mode 2: [t1-t2]. At time t1, switch S1 is off, and the capacitor voltage v... CP The diode D1 remains positive, thus meeting the conduction condition. This mode lasts for three circuit operation phases. The first is the inductor current i... LS The process of forward flow, in which iLS From capacitor C LS A path is formed; secondly, the inductor current i LS After crossing zero, the current flows in the reverse direction, and the capacitor voltage v CLS In the inductor current i LS The inductor current reaches its maximum at zero crossing, then begins to decay until it reaches zero; finally, the inductor current i... LS It will pass through the body diode D in the switching transistor S1 S1 A continuous flow is formed.

[0085] like Figure 7 As shown, mode 3: [t2-t3], at time t2, switch S2 is turned on, and the inductor current i LS Maintaining a negative flow, this process will continue in three stages. First, the capacitor voltage v... CP In the positive direction process, S2 will achieve zero-current switching technology (ZCS), and the inductor L CP Switch S1 and diode D1 form a circuit; then the capacitor voltage v CP After crossing zero, the voltage increases in the reverse direction, through inductor L. CP current i LCP At capacitor voltage v CP It reaches its maximum at zero crossing, then begins to decay until it reaches zero, at which point the inductor current i... LCP When the voltage is zero, diode D1 is turned off, losing its conduction condition; finally, inductor L... CP The current in this branch is cut off by switch S1 and diode D1.

[0086] like Figure 8 As shown, in mode 4 [t3-t4], S2 remains on. At time t3, switch S1 begins to conduct, and the capacitor voltage v CP Since the current is always negative, diode D1 does not meet the conditions for conduction, and this process will continue in two stages. First, because the inductor current i LS When the inductor flows in the negative direction, zero-voltage switching (ZVS) can be achieved when the switching transistor is turned on; then the inductor current i LS After crossing zero, it flows in the forward direction until switch S2 is closed.

[0087] like Figure 9 As shown, in mode 5 [t4-t5], S1 remains on, at time t4, switch S2 is off, and the inductor current i LS Maintaining forward flow, capacitor voltage v CP Since the value is always negative, diode D1 does not meet the conditions for conduction.

[0088] This embodiment proposes the working principle and control method of a capacitively inductively bidirectionally controllable active filter. The five operating modes of this topology are analyzed in detail. Overall, the control strategy is relatively simple and can eliminate the influence of factors such as device component parameters. Furthermore, both controllable switches in this topology can implement soft-switching technology, greatly reducing switching losses and improving power conversion efficiency.

[0089] Example 3

[0090] This embodiment provides an analysis method based on a capacitively bidirectionally controllable active filter.

[0091] This embodiment is based on the control method of a capacitively bidirectionally controllable active filter, and the related equivalent effect diagram is shown below. Figure 10 As shown.

[0092] An analysis method for an active filter based on capacitive inductance bidirectional controllable, using the active filter based on capacitive inductance bidirectional controllable described in Example 1, includes: the active filter based on capacitive inductance bidirectional controllable includes 4 energy storage elements and 3 switching devices, of which 2 are controllable switching transistors.

[0093] The analytical method includes:

[0094] The controllable switch S1 is used to control the capacitor C. LS The time during which the controllable switch S1 and capacitor C participate in the power conversion. LS and inductor L S The equivalent inductance L that constitutes the active controllable filter is... eq The equivalent of Figure 10 The expression is as follows:

[0095]

[0096] Where α is the phase shift angle of the controllable switch S1, with a value ranging from [π / 2, π]; f is the switching frequency; L S C is the inductance value. LS Let α be the capacitance value. As α increases, the external equivalent inductance L... eq It continues to increase. The minimum value is:

[0097]

[0098] The maximum value is:

[0099] L eq(max) =L S

[0100] The controllable switch S2 is used to control the inductor L CP The time during which the controllable switch S2, diode D1, and capacitor C participate in the power conversion.P and inductor L CP The equivalent capacitance C of the transformation of the active controllable filter is... eq The equivalent of Figure 10 The expression is as follows:

[0101]

[0102] Where β is the phase shift angle of the controllable switch S2, with a value ranging from [π / 2, π]; f is the switching frequency; C P L is the capacitance value. CP Let be the inductance value. As β increases, the external equivalent capacitance C... eq It continues to increase. The minimum value is:

[0103]

[0104] The maximum value is:

[0105] C eq(max) =C P

[0106] This embodiment provides an external equivalent analysis method for a capacitive bidirectional controllable active filter as a two-port circuit, and gives the calculation method of equivalent capacitance and equivalent inductance. The equivalent inductance and equivalent capacitance are related to the switching frequency f, the parameters of the circuit energy storage device, and the phase shift angle α / β.

[0107] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An active filter based on capacitive inductance bidirectional controllable, characterized in that, include: Equivalent inductance module and equivalent capacitance module, The equivalent inductance module includes a first inductor, a first controllable switch, and a first capacitor. One end of the inductor is connected to the positive input terminal, and the other end is connected to the first controllable switch and the first capacitor. The first controllable switch and the first capacitor are connected in parallel. The equivalent capacitance module includes a second inductor, a second controllable switch, a second capacitor, and a diode. One end of the second inductor is connected to one end of the first controllable switch, the first capacitor, the second capacitor, and the positive output terminal, respectively. The other end of the second inductor is connected in series with the second controllable switch and the diode. The negative terminal of the diode is connected to the other end of the second capacitor, the negative input terminal, and the negative output terminal, respectively. The active filter includes a first operating mode, a second operating mode, a third operating mode, a fourth operating mode, and a fifth operating mode in one conversion cycle; The first working mode is: The first switching mode is completed within a first preset time and a second preset time. At the first preset time, the instantaneous voltage across the second capacitor crosses zero, the first controllable switch is in the conducting state, and the instantaneous current through the first inductor flows in the positive direction. After that, the instantaneous voltage across the second capacitor is always positive, and the diode is ready to conduct. The current direction is defined as the positive direction of the current flowing from the input terminal to the output terminal. The second working mode is: The second switching mode is completed within the second preset time and the third preset time. At the second preset time, the first controllable switch is turned off, the instantaneous voltage across the second capacitor is always positive, and the diode is ready to conduct. This mode lasts for three circuit operation stages. In the first stage, the instantaneous current through the first inductor flows in the positive direction. During this process, the instantaneous current through the first inductor flows through the first capacitor to form a path. In the second stage, the instantaneous current through the first inductor flows in the reverse direction after crossing zero. The instantaneous voltage across the first capacitor reaches its maximum when the instantaneous current through the first inductor crosses zero, and then begins to decay until it decays to zero. In the third stage, the instantaneous current through the first inductor will pass through the body diode in the first controllable switch to form a freewheeling current. The third working mode is: The third switching mode is completed within the third preset time and the fourth preset time. At the third preset time, the second controllable switch is turned on, and the instantaneous current through the first inductor remains negative. This process will continue for three circuit operation stages. In the first stage, the instantaneous voltage across the second capacitor is positive, and the second controllable switch will realize zero-current switching technology. The second inductor, the first controllable switch, and the diode form a path. In the second stage, the instantaneous voltage across the second capacitor increases in the reverse direction after crossing zero. The instantaneous current through the second inductor reaches its maximum when the instantaneous voltage across the second capacitor crosses zero, and then begins to decay until it decays to zero. When the instantaneous current through the second inductor is zero, the diode turns off and loses its conduction condition. In the third stage, the current in the branch of the second inductor, the first controllable switch, and the diode is cut off. The fourth working mode is: The fourth switching mode is completed within the fourth and fifth preset times. The second controllable switch remains in the on state. At the fourth preset time, the first controllable switch begins to conduct, and the instantaneous voltage across the second capacitor is always negative. The diode does not have the conditions to conduct. This process will continue for two circuit operation stages. In the first stage, because the instantaneous current through the first inductor flows in the negative direction, zero-voltage switching technology can be achieved when the first controllable switch is on. In the second stage, the instantaneous current through the first inductor flows in the positive direction after crossing zero until the second controllable switch is turned off. The fifth working mode is: The fifth switching mode is completed within the fifth and sixth preset times. The first controllable switch remains on. At the fifth preset time, the second controllable switch is off. The instantaneous current through the first inductor remains positive. The instantaneous voltage across the second capacitor is always negative. The diode does not have the conditions to conduct.

2. The active filter based on capacitive bidirectional controllable capacitance according to claim 1, characterized in that, The waveform input at the positive input terminal is passed through the active filter to obtain a standard sine wave, wherein the waveform includes: square wave, non-standard sine wave containing harmonics, triangle wave or sawtooth wave.

3. The active filter based on capacitive bidirectional controllable capacitance according to claim 1, characterized in that, The positive and negative input terminals are connected to a high-frequency square wave circuit, which includes a DC voltage source, a voltage regulator circuit, and a full-bridge inverter circuit. The voltage regulator circuit is connected in parallel with the full-bridge inverter circuit.

4. An analysis method for an active filter based on capacitive bidirectional controllable filter, characterized in that, The active filter based on capacitive bidirectional controllable filter according to any one of claims 1-3 includes: The equivalent series inductance value L of the equivalent inductance module eq for: The capacitance value C of the equivalent parallel capacitance module eq for: Where α is the phase shift angle of the first controllable switch, and its value ranges from [π / 2, π]; L S C is the inductance value of the first inductor. LS Let α be the capacitance value of the first capacitor; as α increases, the equivalent series inductance L... eq It continuously increases; β is the phase shift angle of the second controllable switch, and its value ranges from [π / 2, π]. f C is the switching frequency; P L is the capacitance value of the second capacitor. CP Let C be the inductance value of the second inductor; as β increases, the equivalent parallel capacitance C... eq It keeps growing.

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